JP2013127544A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a paper crease from occurring even when a fixing roller and a pressure roller are deteriorated due to continuous use of an image forming device.SOLUTION: An image forming device 100 has a fixing roller 31 and a pressure roller 32 and is configured such that at least one of the fixing roller 31 and the pressure roller 32 is crown-shaped in which outer diameters at both ends are larger than the outer diameter at a central part in an axial direction, and the image forming device 100 is provided with a temperature adjustment part 40 for adjusting at least one of the temperatures of the fixing roller 31 and the pressure roller 32 so that the temperatures at both ends become higher than the temperature at the central part in the axial direction and a control part 90 for controlling the temperatures adjustment part 40 so that a temperature difference between the central part and both ends in the axial direction of at least one of the fixing roller 31 and the pressure roller 32 becomes large according to the increase in a value of parameter regarding the use history of at least one of the fixing roller 31 and the pressure roller 32.

Description

  The present invention relates to an image forming apparatus.

  2. Description of the Related Art Conventionally, an electrophotographic image forming apparatus is provided with a fixing unit that performs heat-fixing processing on recording paper, and at least one of a fixing roller and a pressure roller constituting the fixing unit has both ends in the axial direction. The outer diameter of the portion is a crown shape that is larger than the outer diameter of the central portion (see, for example, Patent Document 1).

  By forming at least one of the fixing roller and the pressure roller of the fixing unit in a crown shape, the recording paper conveyance speed at both ends of the nip part of both rollers is made higher than the recording paper conveyance speed at the center part of the nip part. Speed is increased, and the tension on the recording paper is generated on both sides in the width direction to suppress the generation of paper wrinkles.

JP 2010-102109 A

  However, in the conventional image forming apparatus as described above, at least one of the fixing roller and the pressure roller is configured by providing an elastic layer on the outer periphery of the cored bar, and this elastic layer is used in the image forming apparatus. It may deteriorate over time and shrink due to use.

  Specifically, as shown in FIG. 8, the elastic layers of the fixing roller and the pressure roller have a crown shape in which the outer diameters at both ends are larger than the outer diameters at the central part. FIG. 8 is a view showing the outer diameter of the pressure roller from one end to the other end in the axial direction of the pressure roller. Since the pressure roller has such a shape, both ends of the pressure roller are strongly pressed in the heat fixing process, and when the pressure roller is continuously used, both ends of the elastic layer are shown as indicated by arrows a in FIG. The part deteriorates and shrinks. As shown in FIG. 9, the difference between the outer diameter of both ends of the elastic layer and the outer diameter of the central portion (hereinafter referred to as the crown amount) is the number of times that image formation has been performed on the recording paper (hereinafter referred to as the crown amount) The number of prints) decreases as the number increases. When the crown amount decreases, it becomes impossible to secure a difference in outer diameter between the central region and the end region of the pressure roller, and paper wrinkles are likely to occur on the recording paper.

FIG. 10 is a graph plotting the number of prints in which paper wrinkles are generated on recording papers having different paper widths when the recording paper is a thin paper having a basis weight of 40 g / m ² . From FIG. 10, it can be seen that the larger the width of the recording paper, the more paper wrinkles occur with a smaller number of prints. From this, it is considered that the recording paper having a larger paper width causes paper wrinkles due to a slight decrease in the crown amount.

  Accordingly, an object of the present invention is to provide an image forming apparatus that does not cause paper wrinkles even when the fixing roller and the pressure roller deteriorate due to continuous use of the image forming apparatus.

In order to solve the above problems, according to one aspect of the present invention,
A fixing roller having a first heater, and a pressure roller that nips recording paper between the fixing roller and performs heat fixing processing, and at least one of the fixing roller and the pressure roller is a shaft In the image forming apparatus having a crown shape in which the outer diameter of both ends is larger than the outer diameter of the center in the direction,
A temperature adjusting unit that adjusts the temperature of at least one of the fixing roller and the pressure roller so that the temperature at both ends is higher than the temperature at the center in the axial direction;
The temperature difference between the central portion and both end portions in the axial direction of at least one of the fixing roller and the pressure roller increases as the parameter value regarding the use history of at least one of the fixing roller and the pressure roller increases. A control unit for controlling the temperature adjustment unit.

  Preferably, the parameter relating to the use history is a rotation number, a rotation time, or a print number of the fixing roller or the pressure roller.

  Preferably, the temperature adjusting unit includes a second heater that heats both ends of at least one of the fixing roller and the pressure roller in the axial direction.

  Preferably, the temperature adjustment unit includes a cooling unit that cools a central part in at least one of the fixing roller and the pressure roller in the axial direction.

  According to the present invention, even when the fixing roller and the pressure roller deteriorate due to continuous use of the image forming apparatus, it is possible to prevent the generation of paper wrinkles.

1 is a schematic view showing an image forming apparatus according to the present invention. FIG. 2 is a schematic diagram illustrating a temperature adjustment unit and a fixing roller of the image forming apparatus in FIG. 1. It is a block diagram which shows control systems, such as a temperature adjustment part. FIG. 6 is a diagram illustrating an example of a set temperature of a fixing roller according to the number of prints. It is a figure which shows an example of the temperature correction amount according to the use log | history of a pressure roller. It is the schematic explaining the modification of a temperature adjustment part. It is the schematic explaining the other modification of a temperature adjustment part. It is a figure which shows the outer diameter from the one end part to the other end part in the axial direction of a pressure roller. It is a figure explaining a crown amount decreasing according to the number of prints. FIG. 10 is a diagram for explaining that the number of prints in which paper wrinkles are generated differs according to the paper width of the recording paper.

  EMBODIMENT OF THE INVENTION Below, the form for implementing this invention is demonstrated using drawing. However, although various technically preferable limitations for implementing the present invention are given to the embodiments described below, the scope of the invention is not limited to the following embodiments and illustrated examples.

FIG. 1 is a schematic configuration diagram of an image forming apparatus 100 according to the present invention.
The image forming apparatus 100 is a tandem color image forming apparatus, and performs color image formation by four sets of image forming units.

  The document placed on the document table is scanned and exposed by the optical system of the scanning exposure device of the image reading device 70 and read by the line image sensor, and the photoelectrically converted image information signal is received by an image processing unit (not shown). After analog processing, A / D conversion, shading correction, image compression processing, and the like are performed, they are input to the optical writing unit of the image forming unit.

  The paper transport system 8 includes a plurality of trays 291, a plurality of paper feed units 21, a plurality of transport rollers 13, registration rollers 22, and the like. The tray 291 accommodates recording paper S of a determined size, and operates the paper feeding unit 21 of the tray 291 determined according to an instruction from the control unit 90 to supply the recording paper S. The transport roller 13 transports the recording paper S sent out from the tray 291 by the paper feeding unit 21 to the registration roller 22. The registration roller 22 adjusts the timing at which the recording paper S is supplied to the secondary transfer roller 9.

  Around the transfer belt 6, there are provided four sets of image forming portions 10Y, 10M, 10C, and 10K including colored toner image forming portions of yellow Y, magenta M, cyan C, and black K. In each of the image forming units 10Y, 10M, 10C, and 10K, Y, M, C, and K toner images are formed and transferred onto the transfer belt 6 in a superimposed manner. The transferred toner image is collectively transferred onto the recording paper S whose timing is adjusted by the registration roller 22.

  The four sets of image forming units 10Y, 10M, 10C, and 10K will be described. In each of the image forming units 10Y, 10M, 10C, and 10K, the same constituent members are denoted by the same reference numerals, and the reference numerals Y, M, C, and K representing the respective colors are appended to the reference numerals. In addition, when there is no need for distinction, the symbols Y, M, C, and K are used without description.

  The photosensitive drum 1 as an image forming body is an image carrier having a photoconductive layer formed on the surface thereof, and is configured to be rotatable in the direction of the arrow in FIG. 1 by a driving device (not shown). The charger 2 uniformly charges the surface of the photosensitive drum 1 and charges the surface of the photosensitive drum 1 uniformly. The exposure device 3 includes a beam emission source such as a laser diode, and the charged surface of the photosensitive drum 1 is irradiated with beam light so that the charge of the irradiated portion disappears, and image data of each color is stored on the photosensitive drum 1. An electrostatic latent image corresponding to the above is formed. The developing unit 4 accommodates toner of any one of Y, M, C, and K, supplies toner corresponding to the image data of Y, M, C, and K to the photosensitive drum 1, and the surface of the photosensitive drum 1 Then, toner images of each color are formed. The drum cleaner 5 cleans the surface of the photosensitive drum 1 and removes toner remaining on the surface of the photosensitive drum 1.

  The primary transfer roller 7 faces the photosensitive drum 1 via the transfer belt 6, and transfers the toner image on the photosensitive drum 1 to the transfer belt 6.

  The transfer belt 6 is an endless belt and is stretched by a driving roller 61 and a plurality of tension rollers 62. The transfer belt 6 is configured to be rotatable in the direction of the arrow in FIG. The secondary transfer roller 9 faces the tension roller 62 through the transfer belt 6 and transfers the toner image transferred onto the transfer belt 6 onto the recording paper S supplied from the paper transport system 8. The recording sheet S on which the toner image is transferred is conveyed to the fixing unit 30.

  The fixing unit 30 applies heat and pressure to the recording paper S to which the toner image has been transferred by the fixing roller 31 and the pressure roller 32 to perform heat fixing processing, thereby fixing the image on the recording paper S. The recording sheet S on which the image is fixed is conveyed to the paper discharge unit 50 through the fixing paper discharge roller 33 of the fixing unit 30 and is discharged from the paper discharge unit 50 to the outside of the apparatus.

  Further, the image forming apparatus 100 includes a sheet reversing unit 24, and the recording sheet S subjected to the heat fixing process is conveyed from the fixing discharge roller 33 to the sheet reversing unit 24, and is discharged with the front and back reversed. Image formation can be performed on both sides of the recording paper S.

  The size and number of recording sheets S when performing image formation can be set from the operation display unit 80 installed at the top of the main body of the image forming apparatus 100.

  The control unit 90 controls each unit of the image forming apparatus 100. The control unit 90 includes a CPU (Central Processing Unit), a RAM (Random Access Memory), and a ROM (Read Only Memory) (not shown), and performs various operations according to various processing programs for the image forming apparatus 100.

  Hereinafter, the configuration of the fixing unit 30 and its periphery will be described in detail with reference to FIGS. 1 and 2. FIG. 2 is a schematic configuration diagram illustrating the fixing roller 31 and the temperature adjustment unit 40.

The fixing unit 30 includes the fixing roller 31 and the pressure roller 32 as described above.
The fixing roller 31 is formed by forming an elastic layer made of silicone rubber or the like and a release layer made of a fluororesin tube or the like on the surface of a metal core made of metal having high thermal conductivity. A heater (first heater) 34 such as a halogen lamp is provided. The heater 34 extends in the axial direction of the fixing roller 31 and heats the entire surface of the fixing roller 31 to a predetermined temperature. Further, the fixing roller 31 is configured to be rotatable in the direction of the arrow in FIG. 1 by a driving device (not shown).

The pressure roller 32 is configured by coating a metal core having high thermal conductivity with an elastic layer made of silicone rubber or the like, and a release layer is further formed on the surface thereof. The pressure roller 32 is disposed to face the fixing roller 31. Further, the pressure roller 32 is configured to be rotatable in the direction of the arrow in FIG. 1 by a driving device (not shown).
In addition, the elastic layer of the pressure roller 32 has a crown shape in which the outer diameter at both axial ends is larger than the outer diameter at the central portion in the axial direction, thereby suppressing the occurrence of paper wrinkles.
Since the elastic layer of the pressure roller 32 is thermally expanded by being heated, the outer diameter of the pressure roller 32 is larger during use than at room temperature. The amount of thermal expansion changes depending on the temperature, and the amount of thermal expansion becomes larger at higher temperatures. The crown shape of the pressure roller is designed to be optimal during use.
However, since the elastic layer has a crown shape, both ends of the pressure roller 32 are strongly pressed against the fixing roller 31 during the heat fixing process. For this reason, both ends of the elastic layer of the pressure roller 32 are likely to deteriorate, and when the pressure roller 32 is used for a long period of time, both ends in the axial direction of the elastic layer of the pressure roller 32 deteriorate and the outer diameter is reduced. The crown amount decreases (see FIG. 8). The crown amount changes and deviates from the optimum value, and paper wrinkles are likely to occur. The reason why the outer diameter of the elastic layer shrinks due to the use of the pressure roller 32 is that the elastic layer is deteriorated due to strong pressure contact and the elastic force is lowered, the volatile component is released from the end face of the elastic layer, etc. Guessed.

  A temperature adjustment unit 40 is provided in the vicinity of the fixing unit 30. The temperature adjustment unit 40 is configured to be able to adjust the temperature of the pressure roller 32 so that the temperature at both axial ends is higher than the temperature at the axial center of the pressure roller 32.

The temperature adjustment unit 40 includes a first temperature detection sensor 41 provided in the vicinity of the axial center portion of the fixing roller 31, a second temperature detection sensor 42 provided in the vicinity of one end portion of the fixing roller 31 in the axial direction, An end heater (second heater) 43 that heats both axial ends of the fixing roller 31 is provided. The end heaters 43 are built in the fixing roller 31 and are respectively disposed at both ends of the fixing roller 31 in the axial direction. The first temperature detection sensor 41 detects the surface temperature of the central portion of the fixing roller 31 in the axial direction, and the second temperature detection sensor 42 detects the surface temperature of the end portion of the fixing roller 31 in the axial direction. As the first temperature detection sensor 41 and the second temperature detection sensor 42, for example, a non-contact type sensor such as an infrared detection sensor or a contact type sensor such as a thermistor can be used.
The end heater 43 may be built in the pressure roller 32 and configured to heat both ends of the pressure roller 32 in the axial direction. In addition, the first temperature detection sensor 41 and the second temperature detection sensor 42 are provided in the vicinity of the axial center portion and the axial end portion of the pressure roller 32, respectively, and detect the temperature of the pressure roller 32. Also good.
Further, the heater 34 incorporated in the fixing roller 31 may be configured to be temperature-controllable in the axial direction, and may also serve as a temperature adjustment unit.

  With this configuration, the temperature adjustment unit 40 can make the temperature at both ends relatively higher than the temperature at the center in the axial direction of the fixing roller 31, and By increasing the temperature, the temperature at both ends in the axial direction of the pressure roller 32 facing the fixing roller 31 can be made higher than the temperature at the central portion in the axial direction. Therefore, the center and both ends of the elastic layer of the pressure roller 32 are individually thermally expanded by adjusting the temperature of the center and both ends in the width direction of the pressure roller 32 by the temperature adjusting unit 40. The crown amount of the pressure roller 32 can be adjusted.

  The temperature adjustment unit 40 configured in this way is controlled by the control unit 90 as shown in FIG. That is, the control unit 90 controls the end heater 43 based on the detection results by the first temperature detection sensor 41 and the second temperature detection sensor 42, and according to the increase in the parameter value regarding the usage history of the pressure roller 32, The temperature adjusting unit 40 is controlled so that the temperature difference between the axial center portion of the pressure roller 32 and both axial end portions becomes large. In other words, the control unit 90 controls the temperature adjustment unit 40 so that the crown amount of the pressure roller 32 becomes constant as the parameter value related to the usage history of the pressure roller 32 increases.

  Here, parameters relating to the usage history of the pressure roller 32 include the number of prints, the number of rotations / rotation time of the fixing roller 31 and the pressure roller 32, the usage time (rotation time) of the photosensitive drum 1, and the use of the developing unit 4. Time (rotation time) etc. are mentioned. If these values are measured, the usage amount of the fixing roller 31 and the pressure roller 32 can be estimated from the magnitude of the values, and the degree of deterioration of the elastic layer of each roller can also be estimated. Note that these parameters may be measured by the control unit 90 or may be measured by a predetermined measurement unit. These parameters may be input by the user. In addition, the usage history parameters are not limited to the above examples as long as the usage amounts of the fixing roller 31 and the pressure roller 32 can be estimated.

  When the number of prints is used as a parameter related to the usage history of the pressure roller 32, the control unit 90 performs, for example, temperature control at the central portion in the axial direction of the pressure roller 32 and temperature control at both ends in the axial direction in FIG. Do as shown. That is, as the number of prints increases, the control unit 90 increases the temperature at both ends of the fixing roller 31 by the end heater 43, and sets the temperature at both ends in the axial direction of the pressure roller 32 that contacts the fixing roller 31. Raise. If it does so, the temperature difference of a center part and both ends will become large in the axial direction of the pressure roller 32, and the thermal expansion coefficient of the both ends of the pressure roller 32 will become larger than the thermal expansion coefficient of a center part. As a result, even if the elastic layers at both ends deteriorate due to the use of the pressure roller 32 and the outer diameter shrinks, the outer diameter is reduced by heating so that the temperature at both ends of the pressure roller 32 increases as the number of prints increases. Therefore, the amount of shrinkage of the elastic layer due to deterioration is offset, and the crown amount of the pressure roller 32 during the heat fixing process can be kept constant.

  Further, the degree of deterioration of the elastic layer of the pressure roller 32 varies depending not only on the number of prints but also on the paper size and paper type (basis weight) of the recording paper S on which image formation has been performed. For example, when the recording paper S to be image-formed is a thin paper, the pressure applied by the pressure roller 32 is set low because the pressure applied by the pressure roller 32 required for performing the heat fixing process is low. . That is, when the recording paper S on which image formation has been performed is a thin paper, the degree of deterioration of the pressure roller 32 is small, and the reduction amount of the crown amount is also small.

For this reason, it is preferable that the control unit 90 sets a coefficient corresponding to the paper size of the recording paper S, and uses the first count number obtained by multiplying the number of prints by the coefficient as a parameter. Furthermore, it is more preferable that the control unit 90 sets a coefficient corresponding to the paper type of the recording paper S and uses the second count number obtained by multiplying the obtained first count number by the coefficient as a parameter. .
Note that the control unit 90 may use a count number obtained by multiplying the number of prints by a coefficient corresponding to the paper type as a parameter.

Here, an example of the first count number and the second count number is shown in Table 1 below. The example shown in Table 1 shows an example of the number of counts when image formation is performed a total of four times. The first image formation is 100 sheets of A4 size plain paper, and the second image formation is A3 size. In this example, 50 sheets of thin paper, 200 sheets of A3 size plain paper for the third image formation, and 50 sheets of A4 size thick paper for the fourth image formation are shown. In Table 1, the basis weight of 60 g / ^{m 2} or less of the paper and thin paper, the paper in a range of basis weight 61~162g / ^{m 2} and plain paper, wherein a basis weight 163 g / ^{m 2} or more sheets as thick doing.

  As shown in Table 1, a paper size coefficient corresponding to each paper size is set, and a numerical value obtained by multiplying the number of prints by the paper size coefficient is used as the first count number. Also, a paper type coefficient corresponding to each paper type is set, and a numerical value obtained by multiplying the first count number by the paper type coefficient is used as the second count number. The control unit 90 uses a numerical value obtained by summing up the first count number of each time of image formation or a numerical value obtained by summing up the second count number of each time of image formation as a parameter relating to the usage history of the pressure roller 32. The paper size coefficient and the paper type coefficient shown in Table 1 are examples, and are not limited to these.

Further, as shown in FIG. 5 as an example, the control unit 90 determines the temperature correction amount of the end heater 43 according to the calculated first count number or second count number. The temperature correction amount indicates the amount of temperature increase at both axial end portions with respect to the temperature at the axial central portion of the pressure roller 32.
Note that the temperature correction amount shown in FIG. 5 is an example, and is appropriately set and changed according to the physical properties of the elastic layer of the pressure roller 32 and the usage environment of the pressure roller 32.

  Further, the ease of occurrence of paper wrinkles differs depending on the type of recording paper S that is the target of image formation. For example, when the recording paper S is a thick paper, even if the pressure roller 32 having a reduced crown amount is used, paper wrinkles are hardly generated. When the recording paper S is a thin paper, the pressure roller having a reduced crown amount. When 32 is used, paper wrinkles are likely to occur. Therefore, the control unit 90 reduces the adjustment amount of the crown amount when the recording paper S is a thick paper, and increases the adjustment amount of the crown amount when the recording paper S is a thin paper. The temperature correction amount may be changed according to the type of recording paper S to be changed.

  As described above, according to the present embodiment, as the parameter value related to the usage history of the pressure roller 32 increases, the pressure at the axial end portions becomes higher than the temperature at the axial central portion of the pressure roller 32. Since the temperature of the roller 32 is adjusted, the outer diameters at both ends of the pressure roller 32 can be increased by thermal expansion according to the amount of the pressure roller 32 used. Therefore, even if the elastic layer of the pressure roller 32 deteriorates and shrinks due to use, the crown amount can be reduced by heating both ends in the axial direction of the pressure roller 32 to a temperature higher than the central portion in the axial direction to expand the elastic layer. The heat fixing process can be performed without changing the state before the pressure roller 32 deteriorates. Therefore, even if the pressure roller 32 deteriorates after being used for a long time, the heat fixing process can be performed without causing paper wrinkles.

  Moreover, since the parameter regarding the usage history of the pressure roller 32 is the rotation number, rotation time, or number of prints of the fixing roller 31 or the pressure roller 32, the amount of use and the degree of deterioration of the pressure roller 32 can be accurately and easily determined. Can be detected.

  Further, since the temperature adjustment unit 40 includes end heaters 43 that heat both ends of the fixing roller 31 in the axial direction, the temperature of the both ends in the axial direction of the pressure roller 32 can be set to a central portion in the axial direction with a simple structure. The temperature can be higher.

  In the above-described embodiment, the temperature adjustment unit 40 includes the first temperature detection sensor 41, the second temperature detection sensor 42, the end heater 43, and the like. Not necessary. In other words, the temperature adjusting unit has any configuration as long as it can heat the pressure roller 32 so that the temperature at both axial ends of the pressure roller 32 is relatively higher than the temperature at the central portion in the axial direction. May be.

Here, with reference to FIG.6 and FIG.7, each modification of the temperature adjustment part 40 is demonstrated.
Since configurations other than those described below are substantially the same as those of the image forming apparatus 100 of the above-described embodiment, the same configurations are denoted by the same reference numerals, and detailed descriptions thereof are omitted.

<Modification 1>
FIG. 6 is a schematic configuration diagram illustrating the temperature adjustment unit 40a and the fixing roller 31a according to the first modification.

  As shown in FIG. 6, the temperature adjustment unit 40 a according to Modification 1 does not include the second temperature detection sensor 42 and the end heater 43, but includes a cooling unit 44 and an abnormality detection sensor 45 instead. Yes. The fixing roller 31 a further includes a heater 35 of the same type as the heater 34 in addition to the heater 34.

The cooling unit 44 is a cooling fan provided to face the central portion in the axial direction of the fixing roller 31 and is configured to cool the central portion in the axial direction of the fixing roller 31. As a result, the temperature at both axial ends of the fixing roller 31 can be made relatively higher than the temperature at the axial central portion.
The cooling unit 44 may not be a cooling fan, and may be configured to cool the central portion in the axial direction of the fixing roller 31 by using, for example, a Peltier element or the like. .
The cooling unit 44 may be provided to face the central portion in the axial direction of the pressure roller 32, and may be configured to cool the central portion in the axial direction of the pressure roller 32.

  The abnormality detection sensor 45 is a sensor provided in a conventional image forming apparatus, and is provided to detect an excessive temperature rise in the fixing unit. Therefore, even if the second temperature detection sensor 42 that detects the temperature of the end portion of the fixing roller 31 is not provided as in the above-described embodiment, the shaft of the fixing roller 31 is provided by the conventionally provided abnormality detection sensor 45. The temperature adjustment unit 40a can be controlled based on the temperature information by detecting the temperature at both ends in the direction.

<Modification 2>
FIG. 7 is a schematic configuration diagram illustrating the temperature adjustment unit 40b, the fixing roller 31b, and the pressure roller 32 according to the second modification.

  As shown in FIG. 7, the temperature adjustment unit 40 b according to Modification 2 does not include the end heater 43, but includes a heating roller (second heater) 46 instead.

The heating roller 46 is provided in contact with the outer peripheral surface of the pressure roller 32 at both axial ends of the pressure roller 32. The heating roller 46 rotates following the rotational drive of the pressure roller 32 and heats both ends of the pressure roller 32. Thereby, the temperature of the axial direction both ends of the pressure roller 32 can be made higher than the temperature of an axial direction center part.
The heating roller 46 may be provided in contact with both axial ends of the fixing roller 31a.

  In the above embodiment and the modification, the fixing unit is a roller fixing method, but may be a belt fixing method.

  Further, in the above-described embodiment and modification, it has been described that the elastic layer of the pressure roller has a crown shape, but only the elastic layer of the fixing roller may have a crown shape, or the elasticity of the fixing roller. Both the layer and the elastic layer of the pressure roller may have a crown shape. When the elastic layer of the fixing roller has a crown shape, the temperature adjusting unit is configured to be able to adjust the temperature of the fixing roller, and the control unit is configured to adjust the temperature adjusting unit according to an increase in the parameter value related to the usage history of the fixing roller. To control.

  Moreover, in the said embodiment and modification, although temperature control shall be performed in two steps of the axial direction center part and axial direction both ends of a pressure roller, the heating member and / or pressure roller which heat a pressure roller A plurality of cooling members for cooling the pressure roller may be provided in the axial direction, and the pressure roller may be temperature-controlled in multiple stages in the axial direction by controlling the plurality of heating members and / or cooling members.

  In the embodiment and the modification, the temperature of the fixing roller or the pressure roller is detected by the temperature detection sensor, and various heating members are controlled based on the detection result. It is good also as what detects the electric current to flow and controls a heating member etc. based on the detection result.

  Moreover, in the said embodiment, the temperature adjustment part is provided with the 2nd temperature detection sensor and the edge part heater, and in the said modification 1, the temperature adjustment part is provided with the cooling fan and the abnormality detection sensor, The said modification In 2, although the temperature adjustment part shall be provided with the heating roller, the temperature adjustment part may be provided with all of these, and may be provided with combining any of these.

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charging device 3 Exposure device 4 Developing part 5 Drum cleaner 6 Transfer belt 7 Primary transfer roller 8 Paper transfer system 9 Secondary transfer roller 10 Image forming part 13 Transport roller 21 Paper feed part 22 Registration roller 24 Paper reversing part 30 Fixing section 31, 31a, 31b Fixing roller 32, 32b Pressure roller 33 Fixing discharge roller 34 Heater (first heater)
35 Heater 40, 40a, 40b Temperature adjustment unit 41 First temperature detection sensor 42 Second temperature detection sensor 43 End heater (second heater)
44 Cooling unit 45 Abnormality detection sensor 46 Heating roller (second heater)
50 Paper discharge unit 61 Driving roller 62 Tension roller 70 Image reading device 80 Operation display unit 90 Control unit 100 Image forming device 291 Tray S Recording paper

Claims (4)

A fixing roller having a first heater, and a pressure roller that nips recording paper between the fixing roller and performs heat fixing processing, and at least one of the fixing roller and the pressure roller is a shaft In the image forming apparatus having a crown shape in which the outer diameter of both ends is larger than the outer diameter of the center in the direction,
A temperature adjusting unit that adjusts the temperature of at least one of the fixing roller and the pressure roller so that the temperature at both ends is higher than the temperature at the center in the axial direction;
The temperature difference between the central portion and both end portions in the axial direction of at least one of the fixing roller and the pressure roller increases as the parameter value regarding the use history of at least one of the fixing roller and the pressure roller increases. An image forming apparatus comprising: a control unit that controls the temperature adjustment unit.   The image forming apparatus according to claim 1, wherein the parameter relating to the use history is a rotation number, a rotation time, or a print number of the fixing roller or the pressure roller.   3. The image forming apparatus according to claim 1, wherein the temperature adjustment unit includes a second heater that heats both ends of at least one of the fixing roller and the pressure roller in the axial direction.   4. The image formation according to claim 1, wherein the temperature adjustment unit includes a cooling unit that cools a central part in the axial direction of at least one of the fixing roller and the pressure roller. 5. apparatus.

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