JP2018120070A - Image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the rise of temperature of a fixation unit and the occurrence of a difference in temperature levels, and enable a satisfactory fixation process free of picture quality degradation to be performed.SOLUTION: The present invention comprises: a heating rotor (e.g., a heating belt 101), to which a paper 106 with an image formed on the basis of image data transferred thereto is conveyed, for causing the transferred image to be fixed by heating; a pressuring rotor (e.g., a pressure roller 104) for pressing the paper against the heating rotor; and a fixation control unit 200 for setting the pressure with which the pressuring rotor is pressed against the heating rotor to a first pressure for a period in which the paper passes between the pressuring roller and the heating roller, and setting the pressure with which the pressuring rotor is pressed against the heating rotor to a second pressure weaker than a prescribed pressure or a state where the pressuring rotor and the heating rotor are separated for a period in which the paper does not pass between the pressuring roller and the heating roller.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an image forming apparatus that transfers an image formed based on image data onto a sheet and then fixes the image on the sheet.

  In an image forming apparatus such as a copying machine, a facsimile machine, a printer, or a multifunction machine, a latent image is formed on a photoconductor based on image data obtained by reading a document, and the latent image is developed with a developer, and then formed on a sheet. The transferred paper is passed through a heated fixing roller or fixing belt to fix the image on the paper.

  Fixing portions such as a fixing roller and a fixing belt are always heated at a constant temperature by a heater or the like during fixing. However, when a normal temperature sheet is passed, heat is taken away by the sheet, the surface temperature of the fixing unit is lowered, and temperature unevenness occurs in the fixing unit. This temperature unevenness is solved by heating with a heater as time passes. However, when the sheet is continuously passed by printing at a high speed or the like, the temperature unevenness of the fixing unit is not solved. The next page of paper arrives. As a result, the paper in contact with the low-temperature part of the fixing unit is partially insufficiently fixed and has a low gloss, resulting in a gloss level difference in the image fixed in the sub-scanning direction, and the print quality is deteriorated.

  In Patent Document 1, in order to eliminate a temperature step in the paper feeding direction (sub-scanning direction) that occurs in the roller of the fixing unit due to the passage of paper, a member for heating or cooling the roller is arranged to heat the roller. Techniques for performing operations and cooling operations are described.

JP 2010-14759 A

  As described in Patent Document 1, the temperature step in the sub-scanning direction generated on the roller can be eliminated by directly heating or cooling the roller as the fixing member. However, even if the temperature difference of the temperature of the roller that performs the fixing operation is eliminated, in reality, other members such as a pressure roller that presses the sheet against the fixing member (roller) are also arranged in the fixing unit and are continuously provided. When the sheet is passed through, the temperature of these members such as the pressure roller also rises, which is a factor that deteriorates the print quality.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus that can prevent a temperature rise of a fixing unit and a temperature step.

  The image forming apparatus of the present invention has a heating rotator that transports a sheet on which an image formed based on image data is transferred and fixes the transferred image by heating, and a pressure rotation that presses the sheet against the heating rotator. The pressure that presses the pressure rotator against the heating rotator during the period in which the body and the paper pass between the pressure rotator and the heating rotator is the first pressure, and the paper is heated and rotated with the pressure rotator. Fixing in a state in which the pressure for pressing the pressure rotator against the heating rotator is a second pressure that is weaker than a predetermined pressure or the pressure rotator and the heating rotator are separated from each other during a period of no passage between the body and the body. And a control unit.

  According to the present invention, it is possible to prevent the occurrence of a steep temperature change portion of the fixing unit, and it is possible to prevent a member such as a pressure rotator from becoming high temperature, thereby improving the print quality.

1 is a configuration diagram illustrating an example of a fixing unit of an image forming apparatus according to an exemplary embodiment of the present invention. 6 is a flowchart illustrating an example of a fixing nip width control process linked to a sheet feeding operation according to an embodiment of the present invention. It is explanatory drawing which shows the nip width by one embodiment of this invention. It is operation | movement explanatory drawing which shows the example of the control state of the nip width by one embodiment of this invention. It is a characteristic view which shows the temperature change example of the pressure roller by the example of 1 embodiment of this invention. It is a characteristic view showing an example of surface temperature change (fixing nip outlet temperature) of a heating belt according to an embodiment of the present invention. It is a characteristic view which shows the example of surface temperature change of the pressure roller by the example of 1 embodiment of this invention. It is a characteristic view showing an example of surface temperature change (fixing nip inlet temperature) of a heating belt according to an embodiment of the present invention.

[1. Configuration of fixing unit of image forming apparatus]
Hereinafter, an embodiment of the present invention (hereinafter referred to as “this example”) will be described with reference to the accompanying drawings.
FIG. 1 shows a configuration example of the fixing unit 100 of the image forming apparatus of this example.
The fixing unit 100 includes a heating belt 101, a heating roller 102, a fixing roller 103, a pressure roller 104, and a heat removal roller 105.
The heating belt 101 is a heating rotator that is stretched between the heating roller 102 and the fixing roller 103 and travels (rotates) in conjunction with the rotation of the fixing roller 103 by a driving source (not shown) of the fixing roller 103, for example. . The heating roller 102 includes, for example, a heater therein and heats the heating belt 101 that passes through the surface of the heating roller 102. Heating of the heating belt 101 by the heating roller 102 is controlled by the heating driving unit 202.

A portion where the fixing roller 103 and the pressure roller 104 face each other is a fixing nip 107 that performs a fixing operation of the paper. When the paper 106 passes through the fixing nip 107, the paper 106 is heated by the heat of the heating belt 101. The image formed on the paper 106 is fixed. The timing at which the paper 106 passes through the fixing nip 107 is set by the paper feed driving unit 204.
The heating belt 101 runs in conjunction with the rotation of the fixing roller 103. The rotation speed (cycle) of the fixing roller 103 is controlled by the rotation driving unit 201.

  The pressure roller 104 is a pressure rotator that rotates in conjunction with the running of the heating belt 101, and includes a pressing mechanism 104 a that applies pressure to the fixing roller 103 side to contact the heating belt 101. The pressure P1 at which the pressure roller 104 contacts the heating belt 101 applied to the fixing roller 103 can be set variably. This pressure P1 is controlled by the pressurization drive unit 205. In the state where the pressure P1 is the weakest, the pressure roller 104 and the heating belt 101 are in a separated state.

The heat removal roller 105 is disposed at a position in contact with the heating belt 101. In the heat removal roller 105, the pressure P2 that comes into contact with the heating belt 101 is variably set by the heat removal drive unit 203. The heat removal roller 105 is formed of a material such as rubber, for example. When the heat removal roller 105 comes into contact with the heating belt 101, the heat removal roller 105 absorbs the heat of the heating belt 101 at the contacted position and cools the heating belt 101. Acts like In the weakest state, the heat removal roller 105 and the heating belt 101 are separated from each other even when the pressure P2 with which the heat removal roller 105 comes into contact is weakest. In the state where the heat removal roller 105 and the heating belt 101 are separated from each other, the heating belt 101 is not cooled.
The heat removal roller 105 rotates in conjunction with the running of the heating belt 101 when contacting the heating belt 101. Or you may provide the drive source which rotates the heat removal roller 105 itself.

The rotation operation of the fixing roller 103 by the rotation drive unit 201, the heating operation by the heating drive unit 202, the heat removal operation by the heat removal drive unit 203, the paper feed operation by the paper feed drive unit 204, and the pressure drive unit 205 The pressurizing operation is executed under the control of the fixing control unit 200, respectively.
Needless to say, an image formed based on the image data is transferred to the sheet 106 conveyed to the fixing nip 107 of the fixing unit 100 by a transfer unit (not shown).

[2. Flow of fixing process]
Next, the flow of the fixing operation executed by the fixing unit 100 under the control of the fixing control unit 200 will be described.
FIG. 2 is a flowchart showing the flow of control processing performed by the fixing control unit 200 of this example.
First, when the fixing control unit 200 starts the fixing operation, the belt cycle in which the heating belt 101 rotates and the cycle in which the paper 106 is supplied to the fixing nip 107 (paper feeding interval) are asynchronously matched. Control. As the asynchronous control by the fixing control unit 200, it is possible to simply perform control so that the belt rotation cycle does not coincide with the paper feed interval (paper feed cycle). The fixing control unit 200 may perform timing control so that the vicinity of the generation point does not come into contact with the leading end portion of the supplied paper 106.
In the initial state, the fixing control unit 200 sets the pressure P1 to the weakest state and separates the pressure roller 104 and the heating belt 101 from each other. Then, the pressure P2 is made strong and the heat removal roller 105 and the heating belt 101 are brought into contact with each other.

After controlling the timing to be asynchronous in this way, the fixing control unit 200 determines whether or not the leading edge of the conveyed paper 106 is in a state of approaching the fixing nip 107 (Step S11). If it is determined that the fixing nip 107 is not approached (NO in step S11), the fixing control unit 200 waits until the leading edge of the sheet 106 approaches.
When it is determined that the leading edge of the paper 106 has approached the fixing nip 107 (YES in step S11), the fixing control unit 200 sends a command to the pressure driving unit 205 to increase the pressure P1 by the pressure roller 104. Pressurization is started and the pressure P1 is set to a set first pressure value (a nip width n1 described later is in a maximum state) (step S12). As described above, the sheet 106 passes through the fixing nip 107 between the heating belt 101 and the pressure roller 104 in a state where the pressure P1 is set to the first pressure value.

Next, the fixing control unit 200 determines whether or not it is time for the trailing edge of the paper 106 to move away from the fixing nip 107 (step S13). Here, when it is determined that it is not the timing when the trailing edge of the sheet 106 is separated from the fixing nip 107 (NO in Step S13), the fixing control unit 200 waits until the trailing edge of the sheet 106 is separated.
When it is determined that it is time to move the trailing edge of the sheet 106 away from the fixing nip 107 (YES in step S13), the fixing control unit 200 sends a command to the pressure driving unit 205, and the pressure P1 applied by the pressure roller 104. Is started (step S14). In the process of decreasing the pressure P1, the pressure P1 is decreased from the first pressure value to the second pressure value (a nip width n1 described later is in a minimum state).
Thereafter, the fixing control unit 200 returns to the determination in step S11.

Further, in parallel with the control processing described so far, the fixing controller 200 starts the heating belt of the heat removal roller 105 at a timing when a predetermined time has elapsed since the start of the pressing by the pressing roller 104 in Step S12. The contact with the terminal 101 is finished, and a separated state is set (step S21).
Further, the fixing control unit 200 starts the contact of the heat removal roller 105 with the heating belt 101 at a timing after a certain time has elapsed after the pressurization by the pressure roller 104 is finished in Step S14, and the heat removal. (Step S22).

  For a certain period of time in steps S21 and S22, the position at which the heating belt 101 contacts the heat removal roller 105 from the position (point x in FIG. 3 to be described later) in contact with the pressure roller 104 (point y in FIG. 3 to be described later). It is time to travel (move) to.

[3. Explanation of state in which processing of this example is performed]
Next, a change in temperature of each part in the fixing unit 100 when the control shown in the flowchart of FIG. 2 is performed will be described.
First, the nip width will be described with reference to FIG.
As shown in FIG. 3, the nip width n <b> 1, which is the width at which the pressure roller 104 contacts the heating belt 101, varies depending on the pressure P <b> 1 when the pressure roller 104 contacts the heating belt 101. That is, the nip width n1 is increased when the contact pressure P1 is strong, and the nip width n1 is 0 when the pressure roller 104 is separated from the heating belt 101.

As shown in FIG. 3, the nip width n <b> 2, which is the width at which the heat removal roller 105 contacts the heating belt 101, changes due to the pressure P <b> 2 when the heat removal roller 105 contacts the heating belt 101. That is, when the contact pressure P2 is strong, the nip width n2 becomes large, and when the heat removal roller 105 is separated from the heating belt 101, the nip width n2 becomes zero.
In this example, as described with reference to the flowchart of FIG. 2, the fixing control unit 200 controls the fixing operation, so that the nip widths n1 and n2 change in conjunction with the feeding of the paper 106, and the heating belt. The temperature of 101 is in an appropriate state.

The timing for controlling the nip width n1 of the pressure roller 104 and the timing for controlling the nip width n2 of the heat removal roller 105 are set to shifted timings in consideration of the time for which the heating belt 101 moves.
Specifically, as shown in FIG. 3, the center of the position where the heating belt 101 contacts the pressure roller 104 (the center of the nip width n1) is x, and the center of the position where the heating belt 101 contacts the heat removal roller 105. When (y) (the center of the nip width n2) is y, the fixing control unit 200 sets the control timing to be shifted by the time required for the heating belt 101 to travel (move) from the position x to the position y.

FIG. 4 shows a state in which the nip widths n1 and n2 change in conjunction with the supply of the paper 106 to the fixing unit 100 based on the control of the fixing control unit 200.
The vertical axis in FIG. 4 indicates the values of the nip widths n1 and n2, and the horizontal axis indicates time. FIG. 4 shows changes in the nip widths n1 and n2 for each cycle ta when the paper 106 is fed. The characteristic R1 (solid line) is the nip width n1 between the pressure roller 104 and the heating belt 101, and the characteristic R2 (broken line) is the nip width n2 between the heat removal roller 105 and the heating belt 101. As described with reference to the flowchart of FIG. 2, one cycle ta in which the paper 106 is fed is set so as not to coincide with one cycle in which the heating belt 101 rotates.

  When the nip widths n1 and n2 on the vertical axis are the smallest values, the pressure roller 104 or the heat removal roller 105 is separated from the heating belt 101. The separated state is an example. When the nip widths n1 and n2 are the smallest values (when the pressure P1 or P2 is the weakest), the pressure roller 104 or the heat removal roller 105 is in contact with the heating belt 101. May be maintained.

A characteristic R1 indicating a change in the nip width n1 between the pressure roller 104 and the heating belt 101 occurs during periods t1, t2, t3, and t4 in different states during one cycle ta.
During the period t1, the nip width n1 increases almost linearly from the separated state (or the minimum nip width n1) to the maximum value. This period t1 is set immediately before the sheet 106 passes through the fixing nip 107.
During the period t2, the nip width n1 is maintained in the maximum state. This period t2 is set while the sheet 106 passes through the fixing nip 107.
During the period t3, the nip width n1 decreases almost linearly until the nip width n1 is away from the maximum value (or the minimum nip width n1). This period t3 is set immediately after the sheet 106 passes through the fixing nip 107.
The period t4 is a state where the pressure roller 104 is separated from the heating belt 101 (or a state where the nip width n1 is the smallest).

  This period t1 to t4 is repeated for each cycle in which the paper 106 is supplied. The period t2 in which the nip width n1 is maintained at the maximum varies depending on the size of the paper 106. The period t1 in which the nip width n1 increases and the period t3 in which the nip width n1 decreases are, for example, the same length of time. Further, the period t4 in which the state where the nip width n1 is separated changes according to one cycle ta in which the sheet 106 is fed.

The characteristic R2 indicating the change in the nip width n2 between the heat removal roller 105 and the heating belt 101 occurs during periods t11, t12, t13, and t14 in different states during one cycle ta.
In the period t11, the state where the nip width n2 is separated (or the minimum nip width n2) is maintained.
During the period t12, the nip width n2 increases almost linearly from the separated state (or the minimum nip width n2) to the maximum value.
During the period t13, the nip width n2 is maintained in the maximum state. This period t2 is set while the sheet 106 passes through the fixing nip 107.
During the period t14, the nip width n2 decreases almost linearly until the nip width n2 is away from the maximum value (or the minimum nip width n2).

  This period t11 to t14 is repeated for each cycle in which the paper 106 is supplied. Note that the period t12 in which the nip width n2 increases and the period t14 in which the nip width n2 decreases are set to the same length of time, for example. Furthermore, the periods t1 and t3 in which the nip width n1 on the pressure roller 104 side increases or decreases and the periods t12 and t14 in which the nip width n2 on the heat removal roller 105 side increases or decreases are set to the same length of time. May be.

  However, the change characteristic R1 of the nip width n1 and the change characteristic R2 of the nip width n2 described so far are set at a shifted timing. Specifically, when the running position changes so that the heating belt 101 that has passed the point x (FIG. 3) passes the point y (FIG. 3) during the period t4 when the nip width n1 is the minimum. A period t13 in which the nip width n2 is maximized is set at a timing shifted by the time required for the movement from the point x to the point y.

  FIG. 5 shows the temperature characteristic T1 of the pressure roller 104 when the control is performed by changing the nip width n1 for bringing the pressure roller 104 into contact with the heating belt 101 in conjunction with the conveyance of the paper 106 (case in this example). FIG. 6 is a diagram comparing temperature characteristics T2 (comparative example) of the pressure roller 104 when the nip width n1 is always constant.

In FIG. 5, the vertical axis represents temperature, and the horizontal axis represents time. FIG. 5 shows the temperature change characteristic when the fixing operation of a certain number of sheets 106 is continuously performed.
As shown in FIG. 5, the temperature characteristic T2 when the nip width n1 is always constant gradually increases as the number of processed sheets increases.
On the other hand, it can be seen that the temperature characteristic T1 in which the nip width n1 is changed in conjunction with the sheet feeding as in this example maintains a relatively low temperature even when the number of processed sheets increases.
Therefore, the fixing unit 100 of this example can prevent the pressure roller 104 from becoming high temperature even when the fixing operation of the paper 106 is continuously performed. It is possible to effectively prevent a decrease in print quality that occurs.

Next, changes in the temperature of the heating belt 101 and the pressure roller 104 in conjunction with the fixing operation for each sheet when fixing the paper 106 will be described.
First, a change in the surface temperature of the heating belt 101 as viewed at the sheet exit of the fixing nip 107 will be described with reference to FIG. In FIG. 6, the vertical axis indicates the surface temperature of the heating belt 101 at the paper exit of the fixing nip 107, and the horizontal axis indicates time.
A period t21 shown in FIG. 6 is a period in which the heating belt 101 is in contact with the sheet 106 (corresponding to a period t2 in FIG. 4), and a period t22 is a period in which the heating belt 101 is not in contact with the sheet 106 (in FIG. 4). Corresponding to periods t1, t3, and t4). 7 and 8 described later, the periods t21 and t22 indicate the same state.

FIG. 6 shows temperature characteristics V11, V12, and V13 under three different conditions.
The temperature characteristic V11 is an example in which the heating belt 101 is in a relatively high temperature, and the pressure P1 for bringing the pressure roller 104 into contact with the heating belt 101 is controlled to be constant (that is, the width of the fixing nip 107 is constant). .
The temperature characteristic V12 is an example in which the heating belt 101 is in a relatively low temperature state, and the pressure P1 for bringing the pressure roller 104 into contact with the heating belt 101 is controlled to be constant (that is, the width of the fixing nip 107 is constant).
The temperature characteristic V13 is an example in which the heating belt 101 is in a relatively low temperature state and the pressure P1 for bringing the pressure roller 104 into contact with the heating belt 101 is changed by the control according to the flowchart of FIG. This temperature characteristic V13 corresponds to an example in which the processing in this example is executed. Temperature characteristics V11 and V12 are comparative examples in which the pressure P1 is constant.

As can be seen by comparing the temperature characteristics V11, V12, and V13 shown in FIG. 6, in the period t21 in contact with the paper 106, the heat of the heating belt 101 moves to the paper 106 side in any example. The outlet temperature is a relatively low and almost constant temperature.
On the other hand, in the period t22 when the sheet 106 is not in contact, in the case of the temperature characteristics V11 and V12, the sheet outlet temperature of the fixing nip 107 reaches a certain value corresponding to the temperature of the pressure roller 104 at each time point. To rise.
Here, the temperature characteristic V13 in which the contact pressure P1 of the pressure roller 104 at the fixing nip 107 is variably set as in this example corresponds to a change in the width of the fixing nip 107 corresponding to the contact pressure P1 of the pressure roller 104. Then, after the temperature has increased to a certain value, it decreases again after a certain period of time. The constant value of the rising temperature at this time depends on the temperature of the pressure roller 104 itself at that time.

FIG. 7 shows changes in the surface temperature of the pressure roller 104. In FIG. 7, the vertical axis indicates the surface temperature of the pressure roller 104 at the paper exit of the fixing nip 107, and the horizontal axis indicates time.
FIG. 7 shows an example of a temperature characteristic R11 in which the contact pressure P1 of the pressure roller 104 is constant and a temperature characteristic R12 in which the contact pressure of the pressure roller 104 is changed.
The surface temperature of the pressure roller 104 in the period t21 in contact with the paper 106 is maintained at a relatively low temperature according to the temperature of the pressure roller 104 regardless of the temperature characteristics R11 and R12. The temperature characteristic R12 obtained by changing the contact pressure P1 is slightly lower.

On the other hand, the surface temperature of the pressure roller 104 during the period t22 when it is not in contact with the paper 106 increases to a high temperature when the contact pressure P1 of the pressure roller 104 is constant at the constant temperature characteristic R11. In the temperature characteristic R12 in which the contact pressure P1 of 104 is changed, the temperature rise is suppressed in conjunction with the change of the contact pressure P1 with the heating belt 101.
As can be seen from FIG. 7, the temperature rise of the pressure roller 104 can be suppressed by changing the contact pressure P <b> 1 of the pressure roller 104.

In the case of this example, the heat removal roller 105 further performs the heat removal operation of the heating belt 101, so that the temperature increase of the heating belt 101 can be further suppressed.
FIG. 8 shows a state where the surface temperature of the heating belt 101 can be suppressed by the heat removal operation by the heat removal roller 105. FIG. 8 shows a change in the surface temperature of the heating belt 101 as seen at the sheet entrance of the fixing nip 107. In FIG. 8, the vertical axis indicates the surface temperature of the heating belt 101 at the paper inlet of the fixing nip 107, and the horizontal axis indicates time.

  A temperature characteristic V21 illustrated in FIG. 8 indicates a temperature change of the heating belt 101 when the contact pressure P2 of the heat removal roller 105 is changed while the contact pressure P1 of the pressure roller 104 is changed. A temperature characteristic V22 shown in FIG. 8 shows a temperature change of the heating belt 101 when the contact pressure P2 of the heat removal roller 105 is kept constant while changing the contact pressure P1 of the pressure roller 104. The temperature characteristic V21 corresponds to the characteristic when the process of the flowchart of FIG. 2 is executed.

As can be seen by comparing the two temperature characteristics V21 and V22 shown in FIG. 8, in the temperature characteristic V21 when the contact pressure P2 of the heat removal roller 105 is changed, the heat removal operation by the heat removal roller 105 is performed. The temperature of the heating belt 101 is prevented from rising. That is, in the temperature characteristic V21 in the example of FIG. 8, the temperature of the heating belt 101 is maintained substantially constant during the period t22 when it is not in contact with the paper 106.
On the other hand, in the temperature characteristic V22 when the contact pressure P2 of the heat removal roller 105 is not changed, the temperature change due to the change of the contact pressure P1 of the pressure roller 104 remains in the period t22 when it does not contact the paper 106. It is in a state.
In the example of FIG. 8, the temperature difference (so-called temperature step) between the period t21 and the period t22 in the two temperature characteristics V21 and V22 is substantially the same. For example, the fixing operation is continuously performed for a long time. When it is performed, the temperature difference in the temperature characteristic V22 where the heat removal operation is not performed has a temperature difference higher than the temperature difference in the temperature characteristic V21 where the heat removal operation is performed. As described above with reference to FIG. 5, the temperature rise can be prevented when the fixing unit 100 of this example performs the fixing operation continuously for a long time.

Therefore, even when the fixing operation of the paper 106 is continuously performed for a long time, the fixing unit 100 of this example can prevent the temperature rise during the period t22 when it is not in contact with the paper 106, as shown in FIG. The state where the temperature step is small is maintained.
In the case of this example, during the fixing operation, the belt cycle in which the heating belt 101 rotates and the cycle in which the paper 106 is supplied to the fixing nip 107 are controlled so as not to coincide with each other. This section changes every time the paper 106 is fixed, and the same portion of the heating belt 101 can be appropriately prevented from gradually becoming hot. Therefore, even if the fixing unit 100 of this example repeatedly performs the fixing operation of the paper 106, it is possible to effectively prevent a temperature step from occurring in the heating belt 101, and a specific portion of the heating belt 101 becomes high temperature. This can also be prevented, and it is possible to effectively eliminate the cause of the decrease in print quality during the fixing operation.

[4. Modified example]
In the embodiment described so far, both the pressure P1 for bringing the pressure roller 104 into contact with the heating belt 101 and the pressure P2 for bringing the heat removal roller 105 into contact with the heating belt 101 are used to supply the paper 106. Although it is changed in conjunction with each other, only one of them may be changed in association with paper feeding.

For example, only the nip width n1 is changed by the pressure P1 at which the pressure roller 104 is brought into contact with the heating belt 101, and the nip width n2 is set at a constant value at the pressure P2 at which the heat removal roller 105 is brought into contact with the heating belt 101. Good. Here, the constant value of the nip width n2 includes a case where the state where the heat removal roller 105 is not brought into contact with the heating belt 101 is maintained.
Or conversely, the nip width n2 may be controlled to vary with the pressure P2 at which the heat removal roller 105 contacts the heating belt 101, and the nip width n1 between the pressure roller 104 and the heating belt 101 may be constant.

Further, as a process for variably setting the nip widths n1 and n2, when the pressures P1 and P2 are minimum, the pressure roller 104 or the heat removal roller 105 is separated from the heating belt 101, but the pressures P1 and P2 are minimum. Even in this case, the nip widths n1 and n2 may be prevented from becoming zero due to contact with the heating belt 101 side.
Further, the time required for the nip widths n1 and n2 to change (corresponding to the periods t1, t3, t12, and t14 in FIG. 4) is set to the same time in the above-described embodiment. The time required for the appropriate nip width n1 or n2 to change individually on the pressure roller 104 side and the heat removal roller 105 side may be set.

  Further, the process of variably setting the nip width n1 of the pressure roller 104 and the process of variably setting the nip width n2 of the heat removal roller 105 are appropriately performed according to the operation of the fixing unit 100 at that time. Also good. For example, when the number of sheets 106 on which the fixing operation is performed is small, the fixing control unit 200 does not change the nip widths n1 and n2, and the fixing operation of the sheets 106 is performed continuously for a certain period of time. When the temperature of the pressure roller 104 is assumed to be high, the fixing control unit 200 may perform control to variably set the nip widths n1 and n2. Alternatively, the temperature of the heating belt 101 or the pressure roller 104 is measured by a sensor, and when the measured temperature of the belt or the like exceeds a predetermined threshold or when a temperature step greater than the threshold is detected, the nip width n1, Either one or both of n2 may be varied.

  In this example, as the temperature adjustment body of the heating belt 101, both the heating operation and the heat removal operation are performed as a configuration including the heating roller 102 and the heat removal roller 105, but either one of the temperature adjustment bodies is provided. It is good also as a structure provided only with. For example, the heat removal roller 105 may be omitted, and only the temperature adjustment by the heating operation by the heating roller 102 at the portion where the temperature of the heating belt 101 is lowered may be performed.

  Further, in the fixing unit 100 of this example, the belt cycle in which the heating belt 101 rotates and the cycle in which the paper 106 is supplied to the fixing nip 107 do not coincide with each other, but the control processing when driving the heating belt 101 is performed. In order to simplify the process, it is possible not to perform control so that the respective periods do not coincide with each other.

The apparatus configuration shown in FIG. 1 shows an example, and the apparatus to which the present invention is applied is not limited to the configuration shown in FIG.
For example, in the configuration illustrated in FIG. 1, the fixing unit 100 includes the heating belt 101 that is a heating rotator stretched over the fixing roller 103, but the fixing roller 103 itself functions as a heating rotator. The heating belt 101 may be omitted.

  DESCRIPTION OF SYMBOLS 100 ... Fixing part, 101 ... Heating belt, 102 ... Heating roller, 103 ... Fixing roller, 104 ... Pressure roller, 104a ... Pressing mechanism, 105 ... Heat removal roller, 106 ... Paper, 107 ... Fixing nip, 200 ... Fixing control , 201: Rotation drive unit, 202 ... Heating drive unit, 203 ... Heat removal drive unit, 204 ... Paper feed drive unit, 205 ... Pressure drive unit

Claims (5)

A sheet of paper on which an image formed based on image data is transferred, and a heating rotator for fixing the transferred image by heating;
A pressure rotator for pressing the paper against the heating rotator;
During the period in which the paper passes between the pressurizing rotator and the heating rotator, the pressure that presses the pressurizing rotator against the heating rotator is a first pressure, and the paper is the pressurizing rotation. A pressure that presses the pressure rotator against the heating rotator during a period that does not pass between the body and the heating rotator, or a second pressure that is weaker than the first pressure or the pressure rotator and the pressure rotator. An image forming apparatus comprising: a fixing control unit configured to separate the heating rotator. 2. The image forming apparatus according to claim 1, wherein the fixing control unit performs an asynchronous control so that a cycle in which the sheet is supplied and a rotation cycle of the heating rotator do not coincide with each other. A temperature adjusting body for heating or cooling the heating rotating body;
The fixing control unit controls heating or cooling operation of the heating rotating body by the temperature adjusting body in conjunction with a change in the first pressure, the second pressure, or the separated state. The image forming apparatus described in 1. The fixing controller is configured to press the pressure rotator against the heating rotator with the second pressure from a state where the pressure rotator is pressed against the heating rotator with the first pressure. The image forming apparatus according to claim 3, wherein the time required for the change between the pressure rotating body and the heating rotating body to be separated is controlled. The temperature adjusting body is constituted by a roller that contacts a part of the heating rotator, and the rotation of the roller is driven by a drive source different from a drive source that drives the heating rotator. The image forming apparatus according to 3.

Images