JP2016218399A - Fixing device and image forming apparatus using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optimum nip width, without reducing productivity and to maintain stable fixation performance.SOLUTION: A fixing device includes a heating source 24, a fixing roller 15 which is configured by forming an elastic layer 17b on the outer peripheral surface of a core metal 17a, fixing roller rotation speed detection means 21 which detects the rotation speed of the fixing roller 15, a pressure roller 17 which comes into press-contact with the elastic layer 17b of the fixing roller 15, to form a nip part N, and moving means 18 which performs movement so that the pressure roller 17 is brought into contact with and separated from the fixing roller 15. In the fixing device, the fixing roller 15 is rotated according to the pressure roller 17. Further, the fixing device includes nip width adjustment means 22A which adjusts the increase and decrease of the width of the nip part N, according to the rotation speed of the fixing roller 15, in paper passing operation.SELECTED DRAWING: Figure 2

Description

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

2. Description of the Related Art Conventionally, image forming apparatuses such as electrophotographic copying machines and printers are provided with a fixing device that heats and melts a toner image transferred onto a sheet and fixes it on the sheet.
Examples of the fixing device include a belt fixing type that heats and melts the toner image on the paper by the heat of the fixing belt, and a roller fixing type that heats and melts the toner image on the paper by the heat of the fixing roller. It has been.

For example, the configuration of the fixing device of the belt fixing system described above is as follows.
That is, this type of fixing device includes a pressure roller that presses against the fixing roller via a fixing belt stretched around a fixing roller, a heating roller, and the like to form a nip portion, and the pressure roller is fixed to the fixing roller. A moving mechanism for moving in the direction of contact and separation is provided.
Then, when the paper is sandwiched and sent out through the fixing belt through a nip formed between the fixing roller and the pressure roller, the toner image on the paper is heated and melted by the heat of the fixing belt, and pressure is applied. The toner image is fixed on the paper.
In such a fixing device, the width of the nip portion (hereinafter referred to as the nip width) is appropriately controlled in order to obtain an optimum amount of heat to the toner image on the paper passing through the nip portion to obtain a stable fixing performance. It is important to do.

There is a configuration disclosed in Patent Document 1 as a fixing device of the belt fixing system.
The fixing device disclosed in Patent Document 1 has a configuration in which a pressure roller is brought into contact with and separated from the fixing roller. In this configuration, when the pressure roller contacts the fixing roller, the position of the pressure roller when the temperature change rate of the pressure roller exceeds the reference value is determined. It is detected as the contact start position at which contact with the layer has started.

  Then, the amount of movement of the pressure roller from the contact start position where the optimum nip width is obtained is calculated according to the type of paper, and the pressure roller is moved toward the fixing roller by the calculated amount of movement. Also, based on the core temperature of the fixing roller, it is determined whether it is in a transient state or an equilibrium state, and when it is determined as a thermal transient state, the amount of movement of the pressure roller is set according to the expanding fixing roller. Adjust to form the required nip width.

However, in the fixing device described in Patent Document 1 described above, the following problems remain unsolved.
That is, in the operation of continuously conveying and fixing the paper (continuous paper passing), the position of the pressure roller is moved from the position in contact with the fixing roller to a position separated from the position in order to obtain an optimal amount of movement of the pressure roller. After that, the contact start position must be obtained. For this reason, a decrease in productivity cannot be avoided, and furthermore, this technique cannot be applied to a configuration in which the fixing roller is rotated by the pressure roller.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a fixing device that can obtain an optimal nip width without reducing productivity and can maintain stable fixing performance.

  In order to solve the above-described problems, the present invention provides a heating source, a fixing roller having an elastic layer formed on the outer peripheral surface, a rotational speed detection means for detecting the rotational speed of the fixing roller, and the elasticity of the fixing roller. A fixing device comprising: a pressure roller that presses against a layer to form a nip portion; and a moving means that moves the pressure roller so as to contact and separate from the fixing roller, and the fixing roller rotates according to the pressure roller. In this embodiment, a nip width adjusting means is provided for adjusting the width of the nip portion in accordance with the number of rotations of the fixing roller during a sheet passing operation.

  According to the present invention, an optimum nip width can be obtained without reducing productivity, and stable fixing performance can be maintained.

1 is a side view illustrating a schematic configuration of a tandem color laser printer as an example of an image forming apparatus. FIG. FIG. 3 is an enlarged side view showing details of the fixing device according to the first embodiment of the present invention. 5 is a graph showing the relationship between the number of rotations of the fixing roller and the outer diameter of the fixing roller. It is a graph which shows the cam surface distance from the rotating shaft center of a cam. FIG. 6 is an explanatory diagram illustrating a state in which the rotation speed of the fixing roller is detected by a fixing roller rotation speed detection sensor. 6 is a graph showing the relationship between the core temperature of the fixing roller and the outer diameter of the fixing roller in the fixing device according to the second embodiment of the present invention. It is a graph which shows the cam surface distance from the rotating shaft center of a cam. 6 is a graph showing an example of transition of a core metal temperature of a fixing roller in a fixing device according to a second embodiment. 4 is a graph showing an enlargement of a core metal temperature of a fixing roller during paper passing. 6 is a graph showing an example of a temperature transition of a cored bar of a fixing roller in a fixing device according to a second embodiment.

  Hereinafter, a fixing device according to a first embodiment of the present invention and an image forming apparatus using the same will be described with reference to the drawings. In the present embodiment, a belt fixing type fixing device will be described as an example, and a tandem color laser printer will be described as an example of an image forming apparatus.

FIG. 1 is a side view showing a schematic configuration of the above-described tandem color laser printer.
The color laser printer 100 includes image forming units 1a, 1b, 1c, and 1d for four colors of Y (yellow), M (magenta), C (cyan), and K (black). These image forming units 1a, 1b, 1c, and 1d are of a tandem type in which the transfer belt 10 is sequentially arranged along the traveling direction (the direction of arrow B in the figure).

  The image forming units 1a, 1b, 1c, and 1d include photosensitive members 2a to 2d, drum chargers 3a to 3d, exposure devices 4a to 4d, developing devices 5a to 5d, transfer devices 6a to 6d, and cleaning devices 7a to 7d, respectively. I have.

  The photoconductors 2a to 2d are formed in a drum shape and are rotated in the direction of arrow A in the drawing. The drum chargers 3a to 3d uniformly charge the photoconductors 2a to 2d that are rotated. The exposure devices 4a to 4d scan the surfaces of the photoreceptors 2a to 2d charged by the drum chargers 3a to 3d with laser beams to form electrostatic latent images based on the image data.

  The developing devices 5a to 5d develop the electrostatic latent images formed on the photoreceptors 2a to 2d by the exposure devices 4a to 4d with toner. The transfer units 6a to 6d transfer the toner images formed on the photoreceptors 2a to 2d to the transfer belt 10 by the development of the developing units 5a to 5d. The cleaning devices 7a to 7d clean the surfaces of the photoreceptors 2a to 2d.

The operation of the color laser printer 100 having the above-described configuration is as follows.
The toner images of four colors Y, M, C, and K formed by the image forming units 1a, 1b, 1c, and 1d are transferred onto the transfer belt 10 in a superimposed manner. A toner image is formed.
The toner image formed on the transfer belt 10 reaches the paper transfer unit 9 and is simultaneously conveyed in the direction of arrow H by the action of a high voltage applied to the paper transfer unit 9 to transfer the transfer belt 10 and the paper transfer The image is transferred onto the recording medium P that passes between the container 9 and the recording medium P. Further, untransferred toner on the transfer belt 10 is collected by a belt cleaning device 12. The toner image transferred onto the recording medium (hereinafter referred to as “paper”) P is fixed on the paper P by the fixing device 11.

Next, details of the fixing device 11 will be described with reference to FIG. FIG. 2 is an enlarged side view showing details of the fixing device 11 according to the first embodiment.
This fixing device 11 is of a belt fixing type using a fixing belt 13. The fixing device 11 includes, in addition to the fixing belt 13, a heating roller 14, a fixing roller 15, a pressure roller 17, a pressure roller moving mechanism 18, a fixing belt temperature sensor 19, a pressure roller temperature sensor 20, and a fixing roller rotation number detection. A sensor 21 and a control unit 22 are provided.
The fixing roller rotational speed detection sensor 21 is a fixing roller rotational speed detection means for detecting the rotational speed of the fixing roller 15.

  The fixing belt 13 is stretched and supported by the heating roller 14 and the fixing roller 15. The fixing belt 13 is an endless belt having a multilayer structure in which an elastic layer and a release layer are sequentially laminated on a base layer made of a resin material. The elastic layer of the fixing belt 13 is formed of an elastic material such as fluorine rubber, silicone rubber, or foamable silicone rubber. The release layer is made of PFA (tetrafluoroethylene barfluoroalkyl vinyl ether copolymer resin), polyimide, polyetherimide, PES (polyether sulfide), or the like. In addition, by providing a release layer on the surface layer of the fixing belt 13, releasability (peelability) with respect to the toner image T is secured.

The heating roller 14 is a thin cylindrical body made of a metal material, and a heater 24 (heating source) is disposed inside the cylindrical body. The heater 24 is a halogen heater or a carbon heater, and both ends thereof are fixed to a side plate (not shown) of the fixing device 11.
The heating roller 14 is rotatably attached to the side plate of the fixing device 11 at both end shafts via bearings. The heater 24 generates heat when electric power whose output is controlled is supplied from the power supply unit (AC power supply) of the color laser printer 100. The heating roller 14 is heated by the radiant heat from the heater 24, and heat is applied to the toner image T on the paper P from the surface of the fixing belt 13 heated by the heat conduction from the heating roller 14.
The surface temperature of the fixing belt 13 is detected by a fixing belt temperature sensor 19 such as a thermopile disposed opposite to the surface of the fixing belt 13, and the surface temperature of the fixing belt 13 is constant at a desired control temperature (fixing temperature). Thus, the output of the heater 24 is controlled.

The fixing roller 15 has an elastic layer formed on the outer peripheral surface of the cored bar 15a.
Specifically, an elastic layer 15b made of fluorine rubber, silicone rubber, foamable silicone rubber or the like is formed on a cored bar 15a made of stainless steel (for example, SUS304, SUS420).
The fixing roller 15 has shafts at both ends rotatably attached to side plates of the fixing device 11 via bearings. In the present embodiment, the fixing roller 15 rotates according to the pressure roller 17. As a result, the fixing belt 13 is driven and travels in the direction of arrow D in the figure. The fixing roller 15 may be rotationally driven by a fixing roller driving unit (not shown).

  The pressure roller 17 has substantially the same configuration as that of the fixing roller 15, and an elastic layer such as fluorine rubber, silicone rubber, and foamable silicone rubber on a cored bar 17 a made of stainless steel (for example, SUS304, SUS420). A roller member 17b is formed.

  In the fixing device 11 having the above-described configuration, the pressure roller 17 is pressed against the fixing roller 15 via the fixing belt 13 to form a nip portion N (see FIG. 2). In the fixing device 11, the elastic layer 15 b of the fixing roller 15 is made thicker than the elastic layer 17 b of the pressure roller 17 in order to form the nip portion N. As an example, the elastic layer 17b of the pressure roller 17 is 2 mm, while the elastic layer 15b of the fixing roller 15 is 15 mm.

The pressure roller moving mechanism 18 is a moving means for moving the pressure roller 17 so as to contact and separate from the fixing roller 15.
The pressure roller moving mechanism 18 includes a swing arm 18a, and both end bearings of the pressure roller 17 are supported by the swing arm 18a in a rotatable state. The swing arm 18a is swingable around a swing shaft 18b provided at one end thereof. Further, a bearing 18c is fixed to the other end side of the swing arm 18a, and a cam 18d is provided at a position in contact with the bearing 18c below in the figure.

  This cam 18d is driven by a motor (not shown) such as a stepping motor capable of controlling the cam rotation angle. Further, the cam 18d is provided with a shielding plate 18e, and the cam position detection means 18f can grasp the reference position of the cam 18d by detecting the position of the shielding plate 18e.

  The cam 18d is always kept in contact with the bearing 18c by the tension of the swing arm spring 18g connected to the swing arm 18a. When the cam 18d rotates in the direction of arrow E in the figure by driving the motor, the bearing 18c moves in the direction of arrow F in the figure. As a result, the pressure roller 17 supported by the swing arm 18a moves in the direction of arrow G in the drawing, that is, in the direction approaching the fixing roller 15. On the other hand, when the cam 18d rotates in the direction of arrow E 'in the figure by driving the motor, the bearing 18c moves in the direction of arrow F' in the figure. As a result, the pressure roller 17 supported by the swing arm 18 a moves in the direction of the arrow G ′ in the drawing, that is, in the direction away from the fixing roller 15.

  In order to heat and melt the toner image T on the paper P and stably fix the toner image T on the paper P, the width of the nip portion N (nip width) that is the portion that sandwiches the paper P between the fixing roller 15 and the pressure roller 17. ) Is appropriately set according to the type of paper P to be used, and an optimal amount of heat must be applied to the toner image T.

  The nip width can be adjusted by controlling the position of the pressure roller 17 with respect to the fixing roller 15 by moving the pressure roller 17 in the direction of contacting and separating from the fixing roller 15 using the pressure roller moving mechanism 18 described above. . However, the outer diameter of the fixing roller 15 increases as the elastic layer 15b of the fixing roller 15 expands as the temperature rises. As a result, even if the position of the pressure roller 17 with respect to the fixing roller 15 is set to a predetermined position, the nip width varies, and as a result, the fixing property may vary.

  Therefore, in the fixing device 11 according to the present embodiment, the outer diameter displacement amount of the fixing roller 15 is calculated from the rotation number of the fixing roller detected by the fixing roller rotation number detection sensor 21. Based on the outer diameter displacement amount of the fixing roller 15, the amount by which the pressure roller moving mechanism 18 moves the pressure roller 17 to the fixing roller 15 side is controlled. As a result, an optimum nip width can be obtained.

  2 is connected to the input side of the control unit 22 shown in FIG. 2, and the pressure roller moving mechanism 18 and the heater 24 of the heating roller 14 are connected to the output side. The following functions are realized by executing the required programs.

(1) A function of increasing / decreasing the width of the nip portion N based on the number of rotations of the fixing roller 15 during the sheet passing operation. This function is referred to as “nip width adjusting means 22A”.
In the present embodiment, the outer diameter displacement amount of the fixing roller 15 is calculated based on the rotation number of the fixing roller 15 detected by the fixing roller rotation number detection sensor 21. Then, the width of the nip portion N is adjusted to increase or decrease by moving the pressure roller 17 by the pressure roller moving mechanism 18 in the direction of contact with and separating from the fixing roller 15.

  A more specific description will be given with reference to FIGS. 3 and 4 in addition to FIG. FIG. 3 is a graph showing the relationship between the rotation speed of the fixing roller and the outer diameter of the fixing roller, and FIG. 4 is a graph showing the cam surface distance from the rotation axis center of the cam 18d. In FIG. 3, the vertical axis represents the outer diameter of the fixing roller, and the horizontal axis represents the rotation speed of the fixing roller. In FIG. 4, the vertical axis indicates the cam distance, and the horizontal axis indicates the rotation angle.

  When the outer diameter of the fixing roller 15 that rotates (follows) in accordance with the pressure roller 17 is small, the rotation speed of the fixing roller 15 is high, and the elastic layer 15b of the fixing roller 15 expands due to a temperature rise and the outer diameter of the fixing roller 15 is increased. When is large, the rotation speed of the fixing roller 15 is low. Although the specific rotation speed varies depending on the thickness and elastic modulus of the elastic layer 15b of the fixing roller 15, it can be easily determined experimentally.

As shown in FIG. 4, the cam surface height is determined according to the rotation angle of the cam 18d.
From the above two graphs, for example, when the fixing roller rotational speed detection sensor 21 detects that the rotational speed of the fixing roller 15 has decreased by a certain rotational speed, the outer diameter of the fixing roller 15 according to the decreased rotational speed. It can be seen that has expanded. Further, it can be seen how much the pressure roller 17 should be moved in the G ′ direction away from the fixing roller 15 in accordance with the increase in the outer diameter.
Since how much the height of the cam surface is displaced from the current position is uniquely determined according to the amount of movement, how much the cam 18d is rotated in the direction E to obtain the amount of displacement of the cam surface height. I know if it ’s good. When the cam 18d is rotated by a motor (not shown) by the rotation angle, the pressure roller moving mechanism 18 moves the pressure roller 17 in the G ′ direction by a predetermined amount.

  Even when the fixing roller rotation speed increases by a certain rotation speed, the amount of movement of the pressure roller 17 in the G direction and the rotation angle of the cam 18d corresponding to the amount of movement are obtained in the same manner as described above. Moves the pressure roller 17 in the G direction by a predetermined amount. In addition, when changing the movement amount of the pressure roller 17, since it is performed in said procedure, it is not necessary to return the pressure roller 17 to a reference position. Therefore, the pressure roller 17 can be directly moved from the position before the movement to the position after the movement.

  In addition, the fixing device 11 according to the present embodiment is set so as to calculate the adjustment amount of the nip width based on the number of rotations between sheets when the sheet P is not in the nip portion N during the sheet passing operation. When the paper P enters the nip portion N, the pressure applied to the fixing roller 15 and the pressure roller 17 increases by the thickness of the paper P, and when the pressure varies, the compression amount of the elastic layer 15b of the fixing roller 15 varies. The rotational speed of the fixing roller 15 varies. That is, the rotation speed of the fixing roller 15 varies depending on the thickness of the paper P. Since various thicknesses of paper are mixedly fed to the fixing device 11, the adjustment amount of the nip width is calculated based on the number of rotations of the fixing roller 15 during the interval between the sheets, which does not vary depending on the thickness of the paper P. Is done.

  Further, during continuous printing, the fixing device 11 according to the present embodiment adjusts the nip width by rotating the cam 18d when there is no paper P in the nip portion N. If the cam 18d rotates and the nip width is adjusted when there is paper in the nip portion N, the fixing property may fluctuate within one page. Therefore, when the paper P is in the nip portion N, the nip width is adjusted. Absent.

  The temperature of the fixing roller 15 at the time of starting the sheet passing operation varies widely from a cold state in which the fixing roller 15 is sufficiently cooled to a hot state immediately after the end of the previous sheet passing operation. Accordingly, the expansion amount of the elastic layer 15b of the fixing roller 15 is not constant. Therefore, the fixing device 11 according to the present embodiment determines the amount of movement of the pressure roller 17 based on the number of rotations of the fixing roller 15 before the sheet passing operation before the sheet P enters the nip portion N. When the paper P enters the nip portion N, the paper can be passed with an optimum nip width.

Next, a configuration for detecting the rotation speed of the fixing roller will be described with reference to FIG. FIG. 5 is an explanatory diagram showing how the fixing roller rotation speed detection sensor 21 detects the rotation speed of the fixing roller.
On the side of the fixing roller 15, the fixing roller rotation number detection sensor 21 described above is arranged to detect the rotation number of the fixing roller 15.
In the present embodiment, the fixing roller rotation number detection sensor 21 is an optical sensor including a light emitting element and a light receiving element, for example. The fixing roller rotation number detection sensor 21 detects passing through a pattern 15c that absorbs light formed on the surface of the fixing roller 15 at certain intervals. Accordingly, the rotation number of the fixing roller 15 can be calculated by the control unit 22 from the period of change in the amount of light obtained by the light receiving element.

  The light absorbing pattern 15 c formed on the fixing roller 15 may be inside the fixing roller 15 or on the side surface of the fixing roller. Further, the fixing roller rotation number detection sensor 21 is a hall sensor, and the pattern formed on the fixing roller 15 is a magnetic pattern at a certain interval, so that the control unit 22 detects the fixing roller 15 from the fluctuation cycle of the hall sensor output. It is possible to calculate the rotation speed. With this configuration, it is possible to provide a fixing device that is less affected by erroneous sensor detection due to toner powder or paper powder than when an optical sensor is used.

  Next, a fixing device according to the second embodiment will be described with reference to FIGS. In addition, about the thing equivalent to what was demonstrated in embodiment mentioned above, the code | symbol same as them is attached | subjected and those description is abbreviate | omitted.

  The fixing device 11 according to the second embodiment is provided with a fixing roller temperature detection sensor 21A (see FIG. 2) in place of the fixing roller rotation number detection sensor 21, thereby adjusting the core metal temperature of the fixing roller 15. Detected. The control unit 22 shown in the present embodiment realizes the following functions by executing a required program.

(2) A function of increasing / decreasing the width of the nip portion N based on the core metal temperature of the fixing roller 15 during the sheet passing operation. This function is referred to as “nip width adjusting means 22B”.
In the present embodiment, the outer diameter displacement amount of the fixing roller 15 is calculated based on the temperature (core temperature) of the fixing roller 15 detected by the fixing roller temperature detection sensor 21A. Then, the width of the nip portion N is adjusted to increase or decrease by moving the pressure roller 17 by the pressure roller moving mechanism 18 in the direction of contact with and separating from the fixing roller 15. Further, the adjustment amount of the nip width is calculated based on the core metal temperature at the time when the sheet P is not in the nip portion N during the sheet passing operation.

FIG. 6 is a graph showing the relationship between the core temperature of the fixing roller and the outer diameter of the fixing roller in the fixing device according to the second embodiment, and FIG. 7 is a graph showing the cam surface distance from the center of the rotation axis of the cam. .
As shown in FIG. 6, since the expansion rate of the fixing roller 15 is determined by the material, the linear expansion coefficient of the elastic layer 15b is determined, so that the outer diameter of the fixing roller 15 can be determined according to the temperature in consideration of the expansion amount of the elastic layer 15b. Further, as shown in FIG. 7, the cam surface height is determined according to the rotation angle of the cam 18d.

  As shown in FIG. 6, when the fixing roller temperature detection sensor 21A detects that the fixing roller mandrel 15a has increased by a certain temperature, the outer diameter of the fixing roller 15 increases (expands) according to the temperature increase. You can see what happened. Then, it can be seen how much the pressure roller 17 should be moved in the G ′ direction away from the fixing roller 15 according to the increased outer diameter.

Since how much the height of the cam surface is displaced from the current position is determined in accordance with the amount of movement described above, the cam 18d is rotated in the direction E to obtain the amount of height displacement of the cam surface. I know what to do. Then, the cam 18d is rotated by a motor (not shown) by the rotation angle, so that the pressure roller moving mechanism 18 moves the pressure roller 17 in the G ′ direction by a predetermined amount.
Even when the fixing roller core 15a is lowered by a certain temperature, the amount of movement of the pressure roller 17 in the G direction and the rotation angle of the cam 18d corresponding to the amount of movement can be obtained in the same manner as described above. 18 moves the pressure roller 17 by a predetermined amount in the G direction.

In addition, when changing the movement amount of the pressure roller 17, since it is performed in said procedure, it is not necessary to return the pressure roller 17 to a reference position. Therefore, the pressure roller 17 can be directly moved from the position before the movement to the position after the movement.
Further, during continuous printing, the fixing device 11 according to the present embodiment adjusts the nip width by rotating the cam 18d when there is no paper P in the nip portion N. If the cam 18d rotates and the nip width is adjusted when the paper P is in the nip portion N, the fixing property may fluctuate within one page. Therefore, when the paper P is in the nip portion N, the nip width is adjusted. Not performed. Further, in the fixing device 11 according to the present embodiment, the temperature detection timing of the fixing roller core 15a during the sheet passing operation is set when there is no sheet in the nip portion N.

FIG. 8 is a graph showing an example of the transition of the cored bar temperature of the fixing roller in the fixing device according to the second embodiment, and FIG. 9 is a graph showing the cored bar temperature of the fixing roller during paper passing in an enlarged manner. .
The heater 24 is turned on and off so that the surface temperature of the fixing belt 13 is maintained at the control temperature. During this time, the core metal 15a of the fixing roller 15 continues to rise gradually. Thereafter, when a predetermined warm-up time elapses, paper feeding is started.
The temperature of the core 15a of the fixing roller 15 gradually increases as shown in FIG. 8 until the paper is passed, but the temperature rises and falls as shown in FIG. 9 when the paper is passed. This is because when the paper P passes through the nip portion N, the paper P absorbs the heat of the fixing belt 13 and the temperature of the fixing roller 15 in contact with the fixing belt 13 also decreases. For this reason, the temperature of the cored bar 15a of the fixing roller 15 decreases to T1, but since there is no heat absorbed between the sheets where the sheet P is not in the nip portion N, the temperature increases to T2.
From the above, the detection timing of the fixing roller temperature detection sensor 21 is set at the time when the paper P passes through the nip portion N in order to stabilize the fixing property within one page and stabilize the fixing property for each page. ing. When the paper is passed again after the paper is passed, the temperature of the cored bar 15a of the fixing roller 15 is not necessarily the same.

FIG. 10 is a graph showing an example of the temperature transition of the cored bar of the fixing roller in the fixing device according to the second embodiment. In FIG. 10, the vertical axis indicates the core metal temperature of the fixing roller, and the horizontal axis indicates time.
When the first sheet is passed, the temperature of the core 15a of the fixing roller 15 is T3, and the amount of movement of the pressure roller 17 according to the temperature T3 is determined. Although the temperature rises due to the paper passing, the amount of movement of the pressure roller 17 is controlled between the papers in accordance with the temperature rise, and the paper is passed while keeping the nip width constant.

  Thereafter, when the sheet passing is completed and the standby is started, the temperature set for the fixing belt 13 during standby is lower than that during the sheet passing, so that the temperature of the core 15a of the fixing roller 15 decreases. When the paper is passed again, the temperature T4 of the core 15a of the fixing roller 15 depends on the length of the standby time, and thus does not necessarily satisfy T3 = T4. Therefore, by determining the movement amount of the pressure roller 17 at the start of paper passing based on the core temperature T4 before the paper passing operation, it is possible to pass the paper with the optimum nip width.

The present invention is not limited to the embodiment described above, and the following modifications can be made.
For example, in each of the above-described embodiments, the belt fixing type fixing device 11 has been described as an example. However, the present invention is not limited to this and can be effectively applied to other types of fixing devices such as a roller fixing type. It is. In the above embodiment, the example in which the present invention is applied to the tandem color laser printer 100 has been described. However, the present invention can be effectively applied to any image forming apparatus including a fixing device.

2a to 2d Photoconductors 4a to 4d Exposure device 9 Paper transfer device 10 Transfer belt 12 Belt cleaning device 14 Heating roller 15 Fixing roller 15a Core metal 15b Elastic layer 17 Pressure roller 17a Core metal 17b Elastic layer 18 Moving means (Pressure roller) Moving mechanism)
18a oscillating arm 18b oscillating shaft 18d cam 18e shielding plate 21 fixing roller rotation number detection sensor 21A fixing roller temperature detection sensor 22A, 22B nip width adjusting means 100 color laser printer N nip part P paper T toner image T4 core metal temperature

JP 2012-42755 A

Claims (10)

A heating source;
A fixing roller formed by forming an elastic layer on the outer peripheral surface of the core metal;
Fixing roller rotation number detecting means for detecting the rotation number of the fixing roller;
A pressure roller that presses against an elastic layer of the fixing roller to form a nip portion;
A fixing device that moves the pressure roller so as to contact and separate from the fixing roller, and the fixing roller rotates according to the pressure roller.
A fixing device comprising a nip width adjusting means for increasing or decreasing the width of the nip portion in accordance with the number of rotations of the fixing roller during a sheet passing operation. A heating source;
A fixing roller formed by forming an elastic layer on the outer peripheral surface of the core metal;
Fixing roller temperature detecting means for detecting a core metal temperature of the fixing roller;
A pressure roller that presses against an elastic layer of the fixing roller to form a nip portion;
A fixing device that moves the pressure roller so as to contact and separate from the fixing roller, and the fixing roller rotates according to the pressure roller.
A fixing device comprising: a nip width adjusting means for increasing or decreasing the width of the nip portion according to a core metal temperature of the fixing roller during a sheet passing operation.   The fixing device according to claim 1, wherein the nip width adjusting unit calculates an outer diameter displacement amount of the fixing roller based on a rotation number of the fixing roller.   The fixing device according to claim 2, wherein the nip width adjusting unit calculates an outer diameter displacement amount of the fixing roller based on a core metal temperature of the fixing roller.   The fixing device according to claim 1, wherein the nip width adjusting unit determines the amount of movement of the pressure roller at the start of paper passing based on the number of rotations of the fixing roller before the paper passing operation.   5. The fixing device according to claim 2, wherein the nip width adjusting unit determines the amount of movement of the pressure roller at the start of paper passing based on a core metal temperature of the fixing roller before the paper passing operation. .   The nip width adjusting means calculates the adjustment amount of the nip width based on the number of rotations of the fixing roller when there is no paper in the nip portion during the paper passing operation. 5. The fixing device according to 5.   5. The nip width adjusting unit calculates an adjustment amount of the nip width based on a core metal temperature of a fixing roller when there is no sheet in the nip portion during a sheet passing operation. Or the fixing device according to 6;   The nip width adjusting means moves the pressure roller directly from the position before the movement to the position after the movement when the width of the nip portion is adjusted by moving the pressure roller to the fixing roller side by a predetermined amount. The fixing device according to claim 1, wherein: An image forming apparatus using the fixing device according to claim 1.