JP2004020716A - Fixing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device which can automatically adjust a nip width according to a conveyance speed of sheets of paper and can meet a plurality of the conveyance speeds by one kind of pressure roller. <P>SOLUTION: The fixing device has a displacing mechanism 40 for displacing the pressure roller 2 in a direction where the roller attaches and detaches to and from a hot roller, an electromagnetic clutch 3 for actuating the displacing mechanism 40, and a control section for controlling the driving voltage of the electromagnetic clutch 3 according to the conveyance speed of the sheets of paper. The fixing device is adapted to adjust the nip width produced by pressurized contact of the hot roller 1 and the pressure roller 2 across the displacing mechanism 40 by controlling the driving voltage of the electromagnetic clutch 3 so as to make the nip width greater as the conveyance speed of the sheets of paper is higher and to make the nip width smaller as the conveyance speed of the sheets of paper is lower. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a fixing device in a laser printer or the like, and more particularly, to adjustment of a nip width caused by press contact between a hot roller and a pressure roller.
[0002]
[Prior art]
In a fixing device of a laser printer or a copying machine, a hot roller and a pressure roller that presses against the hot roller are provided, and a sheet carrying unfixed toner is passed between the rollers and heated by the hot roller. The toner is fixed on the paper by applying pressure with a pressure roller while the toner is being pressed. JP-A-6-250559, JP-A-11-231700 and JP-A-2-136273 describe such a fixing device. The fixing device described in JP-A-6-250559 varies the rotation speed of a pressure roller in accordance with the width and material of a sheet, and the fixing device described in JP-A-11-231700 employs a fixing device. When the rotation speed of the pressure roller falls below a certain value, the pressure roller is directly driven to rotate at a predetermined rotation speed. The fixing device described in Japanese Utility Model Laid-Open Publication No. 2-136273 drives a pressure roller separately from a hot roller, and changes the rotation speed of the hot roller in two stages.
[0003]
[Problems to be solved by the invention]
By the way, in the fixing device as described above, the nip width generated due to the pressure contact between the hot roller and the pressure roller needs to be adjusted to an optimum value according to the paper transport speed. This will be described with reference to FIG. In FIG. 10, R1 is a hot roller having a built-in heater therein, R2 is a pressure roller that presses against the hot roller R1, and S is a sheet that is nipped and conveyed by both rollers R1 and R2. As the rollers R1 and R2 rotate in the directions A and B, respectively, the sheet S is transported in the direction C. At this time, the unfixed toner carried on the sheet S is fixed on the sheet S by being heated by the hot roller R1 and pressed by the pressing roller R2.
[0004]
Here, since the pressure roller R2 is formed of a rubber roller having a rubber layer on the surface, when the pressure roller R2 is pressed against the hot roller R1 at a predetermined pressure, the pressure roller R2 is slightly depressed and the hot roller R1 is pressed. Contact with The length W1 of the contact portion in the paper transport direction is a two-p width. When the sheet S is conveyed at a high speed, the contact time between the sheet S and the hot roller R1 is short. If the nip width is small, sufficient heat is not transmitted to the sheet S from the hot roller R1 and a fixing failure occurs. It is necessary to increase the nip width W1 as shown in FIG. On the other hand, when the sheet S is conveyed at a low speed, the contact time between the sheet S and the hot roller R1 is long, so if the nip width is large, heat is excessively transmitted from the hot roller R1 to the sheet S, causing color deformation and the like. Therefore, it is necessary to reduce the nip width W2 as shown in FIG. For this reason, it is required to adjust the nip width according to the transport speed of the sheet S.
[0005]
For this reason, for example, in the case of a laser printer, in a printer for high-speed printing, in order to increase the nip width, a rubber having relatively low hardness is used as the rubber of the pressure roller R2, and low-speed printing is performed. In a printer for printing, a relatively hard rubber is used as the rubber of the pressure roller R2 in order to reduce the nip width. However, in this case, there is a problem that it is necessary to prepare several types of pressure rollers having different rubber hardnesses according to the printing speed, and the production cost is high. Conventionally, no effective countermeasures have been taken against such a problem, and the prior art described in each of the above-mentioned publications is also a technology relating to the control of the rotational speed of the roller. Does not suggest.
[0006]
The present invention solves the above-mentioned problems, and an object of the present invention is to automatically adjust the nip width in accordance with the paper conveyance speed, thereby enabling a single type of pressure roller to be used. It is an object of the present invention to provide a fixing device capable of coping with the conveyance speed of the fixing device. Another object of the present invention is to provide a fixing device capable of automatically adjusting the nip width according to the thickness of a sheet and capable of coping with a plurality of types of sheets with one type of pressure roller. It is in.
[0007]
[Means for Solving the Problems]
The fixing device according to the present invention includes a displacement mechanism that displaces the pressure roller in a direction to contact and separate from the hot roller, an electromagnetic drive unit that operates the displacement mechanism, and an electromagnetic drive unit that operates in accordance with a sheet conveying speed. A control unit for controlling the drive voltage. By controlling the drive voltage of the electromagnetic drive means, the nip width is adjusted via a displacement mechanism, and the nip width increases as the paper transport speed increases, and the nip width decreases as the paper transport speed decreases. I try to be smaller.
[0008]
In this way, the nip width is automatically adjusted by the electromagnetic driving means and the displacement mechanism according to the paper transport speed and is set to an optimum state. It is not necessary to prepare pressure rollers having different rubber hardnesses, and it is possible to cope with models of various transport speeds by preparing only one type of pressure roller. As a result, manufacturing costs can be reduced.
[0009]
The present invention can also be applied to the adjustment of the nip width for a plurality of types of paper having different thicknesses. In this case, the fixing device according to the present invention includes a displacement mechanism that displaces the pressure roller in a direction to contact and separate from the hot roller, an electromagnetic drive unit that operates the displacement mechanism, and an electromagnetic drive unit that operates according to the type of paper. A control unit for controlling the drive voltage of the means. Then, by controlling the driving voltage of the electromagnetic driving means, the nip width generated by the pressure contact between the hot roller and the pressure roller is adjusted via the displacement mechanism, and the nip width increases as the paper becomes thicker, and as the paper becomes thinner. The nip width is reduced.
[0010]
By doing so, the nip width is automatically adjusted by the electromagnetic driving means and the displacement mechanism according to the thickness of the paper, so that the nip width can be set to an optimal value suitable for the type of paper. In particular, the generation of wrinkles when using thick paper can be effectively prevented.
[0011]
In the present invention, it is preferable to provide a pair of electromagnetic drive units on the left and right sides in the axial direction of the pressure roller, and to provide a displacement mechanism for adjusting the nip width at both ends of the pressure roller for each electromagnetic drive unit. According to this, since the nip width is adjusted at both ends of the pressure roller, the left and right balance is obtained as compared with a case where the nip width is adjusted only on one side of the pressure roller, and the adjustment can be performed with high accuracy. .
[0012]
Further, in the present invention, one electromagnetic drive means is provided at an intermediate position in the axial direction of the pressure roller, and a displacement mechanism which operates using the electromagnetic drive means as a common drive source is provided. May be used to adjust the nip width. According to this, there is an advantage that the cost can be reduced because only one electromagnetic driving means is required, in addition to the high accuracy of the adjustment by the right and left balance.
[0013]
As the electromagnetic driving means in the present invention, an electromagnetic clutch driven by a PWM-controlled pulse is used, and by controlling ON / OFF timing of the pulse, the nip width is adjusted by changing the stroke of the plunger of the electromagnetic clutch. Is preferred. According to this, a commercially available electromagnetic clutch can be used as it is, and the drive voltage of the electromagnetic clutch can be easily and accurately controlled by the PWM control, so that the nip width can be finely adjusted easily.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
1 to 3 show an example of a fixing device 100 built in a laser printer. FIG. 1 is a top view, FIG. 2 is an enlarged view of a main part of FIG. 1, and FIG. 3 is a right side view of FIG. . In the figure, reference numeral 1 denotes a hot roller, in which a heater (not shown) for heating is incorporated, and shaft portions 1 a at both ends are supported by side frames 8. Reference numeral 2 denotes a pressure roller which is in pressure contact with the hot roller 1, and is provided at a position facing the lower side of the hot roller 1, and shaft portions 2a at both ends are connected to a rotating member 6 described later. The hot roller 1 is formed by coating a surface of a metal tube with a resin having good releasability, and the pressure roller 2 is formed of a rubber roller having a surface of a metal tube provided with a rubber layer such as silicon rubber. . Reference numeral 3 denotes an electromagnetic clutch which constitutes an electromagnetic driving means of the present invention. As shown in FIG. 40 are provided. The electromagnetic clutch 3 includes a main body 3a, an armature 3b operated by an electromagnet (not shown) built in the main body 3a, and a plunger 3c connected to the armature 3b. The plunger 3c is inserted into the main body 3a and is capable of moving forward and backward in the axial direction. The armature 3b is connected to one end of the plunger 3c. Are provided. The tip 3f of the plunger 3c comes into contact with the rotating member 4.
[0015]
The rotating member 4 has a substantially triangular shape, and is rotatably supported on the bracket 9 by a shaft 12. Reference numeral 5 denotes an arm member that reciprocates in conjunction with the rotation of the rotation member 4, and one end of the arm member 5 is engaged with an engagement hole 10 of the rotation member 4, and While being connected, the other end of the arm member 5 is engaged with the engagement hole 16 of the swing member 6 and is connected to the swing member 6. The swing member 6 is supported on the side frame 8 by a shaft 13, and has a concave portion 6a formed on the upper end side as shown in FIG. A bearing member 14 is fitted in the concave portion 6a, and a shaft 2b protruding from the shaft portion 2a of the pressure roller 2 is supported by the bearing member 14. Reference numeral 15 denotes a ring fitted to the shaft 2b. A projecting piece 6b is formed at the lower end side of the swinging member 6, and a coil, which is an elastic member, is provided between the projecting piece 6b and one of the cut-and-raised pieces 11a, 11b of the base frame 11. A spring 7 is suspended. A displacement mechanism 40 is configured by the above-described rotating member 4, arm member 5, swinging member 6, and coil spring 7.
[0016]
1 to 3 show a state where the electromagnetic clutch 3 is not excited. In this state, the armature 3b of the electromagnetic clutch 3 receives the urging force in the left direction in FIG. 1 by the spring 3d and is separated from the main body 3a. As shown in FIG. 3, the swing member 6 swings about the shaft 13 in the counterclockwise direction M1 due to the pulling force of the spring 7, whereby the arm member engaged with the swing member 6 is engaged. 5 is drawn in the Z1 direction. As a result, the turning member 4 engaged with the arm member 5 receives the turning force in the Y1 direction in FIG. 2 and contacts the tip 3f of the plunger 3c of the electromagnetic clutch 3. At this time, as described above, as a result of the swing member 6 swinging in the counterclockwise direction M1 about the shaft 13, the bearing member 14 supported by the swing member 6 in FIG. The shaft 2b of the pressure roller 2 supported by the bearing member 14 is also lifted in the N1 direction integrally with the bearing member 14. Therefore, the pressure roller 2 comes into contact with the hot roller 1 with a strong pressing force due to the elastic force of the spring 7, and the nip width w1 also increases. The above operation is common to the left and right electromagnetic clutches 3 and the displacement mechanism 40. In FIG. 3, A and B indicate the rotation directions of the hot roller 1 and the pressure roller 2, respectively, and C indicates the transport direction of the sheet S passing between the hot roller 1 and the pressure roller 2. . The paper S carrying the unfixed toner is pressed by the pressure roller 2 while being heated by the hot roller 1 when passing between the rollers 1 and 2, and the toner is fixed on the paper S.
[0017]
Next, when the electromagnetic clutch 3 is excited, as shown in FIG. 4, the armature 3b of the electromagnetic clutch 3 is attracted to the body 3a against the urging force of the spring 3d, and the plunger 3c is also displaced in the X2 direction. I do. At this time, the displacement amount of the armature 3b, that is, the stroke of the plunger 3c changes according to the magnitude of the drive voltage applied to the electromagnetic clutch 3. If the drive voltage is large, the current flowing through the electromagnetic clutch 3 increases and a large torque is generated, so that the stroke increases. On the other hand, if the driving voltage is small, the generated torque is small, so that the stroke is also small. Therefore, by controlling the drive voltage of the electromagnetic clutch 3, the stroke of the plunger 3c can be varied. The method of controlling the drive voltage will be described later.
[0018]
When the plunger 3c is displaced in the X2 direction, the rotating member 4 that is in contact with the distal end 3f of the plunger 3c is pushed by the distal end 3f, and the rotating member 4 rotates about the shaft 12 in the Y2 direction. When the rotation member 4 rotates in the Y2 direction, the arm member 5 engaged with the rotation member 4 is pulled in the Z2 direction, thereby engaging with the arm member 5 as shown in FIG. The swinging member 6 swings in the clockwise direction M2 against the elastic force of the spring 7. Therefore, the bearing member 14 supported by the swing member 6 is lowered in the N2 direction, and the shaft 2b of the pressure roller 2 supported by the bearing member 14 is also lowered in the N2 direction integrally with the bearing member 14. As a result, the pressing force of the pressing roller 2 against the hot roller 1 becomes weak, and the nip width w2 also decreases. The above operation is common to the left and right electromagnetic clutches 3 and the displacement mechanism 40. In FIG. 5, the same parts as those in FIG. 3 are denoted by the same reference numerals.
[0019]
As described above, by varying the stroke of the plunger 3c by controlling the drive voltage of the electromagnetic clutch 3, the nip width generated by the pressure contact between the hot roller 1 and the pressure roller 2 is adjusted via the displacement mechanism 40. Can be. Therefore, as long as the fixing device 100 in which the nip width when the electromagnetic clutch 3 is not excited is set to w1 (maximum value) is prepared, the fixing device 100 is incorporated into laser printers having various printing speeds, and the respective printing is performed. By controlling the drive voltage of the electromagnetic clutch 3 so that a nip width commensurate with the speed is obtained, the fixing device 100 can be shared.
[0020]
FIG. 6 is an electric block diagram of the laser printer 30 on which the fixing device 100 is mounted. Here, only the blocks related to the present invention are shown. Reference numeral 31 denotes a control unit mainly including a CPU, and reference numeral 32 denotes a memory including a ROM and a RAM. The control unit 31 and the memory 32 are incorporated in an ASIC (Application Specific Integrated Circuit) 33. I have. Reference numeral 34 denotes a setting unit for performing various settings relating to printing, and 35 denotes a motor drive unit that drives a motor 36 for rotating rollers and the like. Reference numeral 37 denotes a clutch control unit for driving the pair of left and right electromagnetic clutches 3 shown in FIG. 1. The clutch control unit 37 controls the ON / OFF timing of the pulse to change the output voltage. (Pulse Width Modulation) circuit.
[0021]
As shown in FIG. 7, the printing speeds V1, V2, V3, and the corresponding driving voltages P1, P2, P3,... Of the electromagnetic clutch 3 are stored in the memory 32 in advance as a table. In the factory, after the above-described fixing device 100 is incorporated in the laser printer 30, the printing speed of the model is set in the setting unit 34, and the product is shipped. After the laser printer 30 has passed to the user, when printing is performed by the printer, the control unit 31 reads out the electromagnetic clutch voltage corresponding to the printing speed from the table in FIG. The clutch controller 37 is controlled based on the value.
[0022]
Specifically, the drive voltages P1, P2, P3,... In the table of FIG. 7 are data of ON / OFF timing (duty) of the pulse to be PWM-modulated, and the control unit 31 outputs the drive output from the clutch drive unit 37. The voltage is controlled by the ON / OFF timing. As a result, a drive voltage corresponding to the printing speed of the printer is output from the clutch drive unit 37, and each of the electromagnetic clutches 3 is driven by this voltage. When the electromagnetic clutch 3 is driven, the displacement mechanism 40 operates as described above, the contact pressure of the pressure roller 2 with respect to the hot roller 1 changes, and the nip width is adjusted. Here, the nip width is automatically set to an optimum value by previously selecting the ON / OFF timing, that is, the drive voltage of the electromagnetic clutch 3 to a value that can obtain a nip width corresponding to the printing speed of the printer. Can be adjusted.
[0023]
That is, in a printer that performs high-speed printing, adjustment is performed so that the nip width W1 is increased as shown in FIG. 3, and sufficient heat is transmitted from the hot roller 1 to the sheet S, so that a fixing failure occurs. Can be avoided. On the other hand, in a printer having a low printing speed, adjustment is performed so that the nip width W2 is reduced as shown in FIG. There is no risk of occurrence.
[0024]
In this manner, in the above-described embodiment, the nip width is automatically adjusted according to the paper transport speed and is set to the optimum state. It is not necessary to prepare a pressure roller, and the manufacturing cost can be reduced by using a common fixing device 100 incorporated in the laser printer 30. Also, since a pair of the electromagnetic clutch 3 and the displacement mechanism 40 are provided on the left and right sides and the nip width is adjusted at both ends of the pressure roller 2, the nip width is adjusted on one side of the pressure roller 2. The balance between the left and right is maintained, and the adjustment can be performed with high precision. Further, a commercially available electromagnetic clutch can be used as it is as the electromagnetic driving means, and the driving voltage of the electromagnetic clutch 3 is controlled by PWM control, so that the nip width can be easily and accurately controlled.
[0025]
In the above embodiment, the case where the nip width is adjusted according to the transport speed is described as an example. However, the present invention can also be applied to the case where the nip width is adjusted according to a plurality of types of paper having different thicknesses. . The configuration and operation of the fixing device 100 in this case are the same as those described with reference to FIGS. The electric block diagram when the fixing device 100 is incorporated in the laser printer 30 is also the same as that in FIG. However, the table shown in FIG. 8 is stored in the memory 32 instead of the table of FIG. 8, the sheet types S1, S2, S3,... And the corresponding drive voltages Q1, Q2, Q3,. As the paper types S1, S2, S3,..., For example, types such as plain paper, OHP paper, postcard, envelope, and the like are set. The drive voltages Q1, Q2, Q3,..., Like the drive voltages P1, P2, P3,.
[0026]
When printing is performed by the laser printer 30, a media sensor (not shown) determines the type of paper set in the printer, and based on the determination result, the control unit 31 determines from the table of FIG. Is read, and the clutch controller 37 is controlled based on this value. As a result, a drive voltage corresponding to the type of paper is output from the clutch drive unit 37, and each electromagnetic clutch 3 is driven by this voltage, and the contact pressure of the pressure roller 2 with respect to the hot roller 1 via the displacement mechanism 40. Changes, and the nip width is adjusted. The nip width is automatically adjusted to an optimum value by previously selecting the ON / OFF timing, that is, the drive voltage of the electromagnetic clutch 3 to a value that can obtain a nip width suitable for the type of paper. can do.
[0027]
That is, in the case of a thick paper such as a postcard, if the nip width is small, heat is not sufficiently transmitted to the paper and a fixing failure occurs, so that the nip width w1 is increased as shown in FIG. I do. Also, by increasing the nip width, wrinkles generated on thick paper can be eliminated. On the other hand, in the case of thin paper such as plain paper, if the nip width is large, heat is excessively transmitted from the hot roller 1 to the paper S, causing color deformation and the like. Make it smaller.
[0028]
FIG. 9 is a top view showing another embodiment of the fixing device 100 according to the present invention. 9, the same parts as those in FIG. 1 are denoted by the same reference numerals. In FIG. 1, one pair of electromagnetic clutches 3 is provided on the left and right. In FIG. 9, however, one electromagnetic clutch 3 is provided at an intermediate position of the pressing roller 2 in the axial direction. The nip width is adjusted at both ends of the pressure roller 2 by the displacement mechanism 40 using the electromagnetic clutch 3 as a common drive source. In this case, the rotating member 4 is shared by the left and right displacement mechanisms 40, and the arm member 50 includes a base 51 connected to the rotating member 4 and a branch 52 branched from the base 51. A substantially T-shaped member is used, and the tip side of each branch 52 is connected to the left and right swing members 6.
[0029]
According to the embodiment of FIG. 9, in addition to the advantage that the adjustment can be performed with good balance between the left and right sides of the pressure roller 2 as in the embodiment of FIG. 1, the advantage that the cost can be reduced because only one electromagnetic clutch 3 is required. is there.
[0030]
The present invention is not limited to only the above-described embodiment, and may adopt various other modes. For example, in the above-described embodiment, an example in which the electromagnetic clutch 3 is used as the electromagnetic driving means has been described, but an electromagnetic solenoid may be used instead of the electromagnetic clutch 3.
[0031]
7 and 8, the case where the nip width is adjusted according to the printing speed and the case where the nip width is adjusted according to the type of paper (thickness) are described separately. An optimum nip width depending on the combination with the type may be set in advance in the table, and the nip width may be adjusted from both the printing speed and the paper type.
[0032]
Furthermore, in the above embodiment, the case where the present invention is applied to a laser printer is described as an example. However, the present invention can be applied not only to a laser printer but also to a copying machine, a facsimile, and the like.
[0033]
【The invention's effect】
According to the present invention, the nip width is automatically adjusted in accordance with the paper transport speed, so that one type of pressure roller can handle a plurality of transport speeds, and a common fixing device can be used. Thus, the manufacturing cost can be reduced.
[0034]
Further, by applying the present invention to the adjustment of the nip width for a plurality of types of paper, an optimal nip width according to the paper can be obtained, and wrinkles generated on thick paper can be effectively eliminated.
[Brief description of the drawings]
FIG. 1 is a top view illustrating an example of a fixing device according to the present invention.
FIG. 2 is an enlarged view of a main part of FIG.
FIG. 3 is a right side view of FIG. 1;
FIG. 4 is an enlarged view of a main part for explaining nip width adjustment in the fixing device.
FIG. 5 is a right side view of FIG.
FIG. 6 is an electric block diagram of a laser printer equipped with a fixing device.
FIG. 7 is a diagram showing a table in a memory.
FIG. 8 is a diagram showing another example of the table in the memory.
FIG. 9 is a top view showing another embodiment of the fixing device according to the present invention.
FIG. 10 is a diagram illustrating adjustment of a nip width.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Hot roller 2 Pressure roller 3 Electromagnetic clutch 3c Plunger 4 Rotating member 5 Arm member 6 Swinging member 7 Coil spring 30 Laser printer 31 Control unit 32 Memory 37 Clutch control unit 40 Displacement mechanism 100 Fixing device w1, w2 Nip width

Claims (6)

It has a hot roller and a pressure roller that is in pressure contact with the hot roller. The sheet carrying unfixed toner is passed between the rollers, and is heated by the hot roller and pressed by the pressure roller while being heated. In a fixing device of a laser printer configured to fix toner,
An electromagnetic clutch provided on the left and right in the axial direction of the pressure roller,
A pair of displacement mechanisms that operate in conjunction with the plungers of each of the electromagnetic clutches and displace the pressure roller in a direction to contact and separate from the hot roller;
A clutch drive unit that drives the electromagnetic clutch with a PWM-controlled pulse;
A control unit that controls ON / OFF timing of a pulse output from the clutch driving unit in accordance with a printing speed;
By controlling the ON / OFF timing by the control unit, the stroke of the plunger of the electromagnetic clutch is changed to adjust the nip width generated by the pressure contact between the hot roller and the pressure roller via the displacement mechanism, thereby performing printing. The fixing device according to claim 1, wherein the nip width increases as the speed increases, and the nip width decreases as the printing speed decreases. It has a hot roller and a pressure roller that is in pressure contact with the hot roller. The sheet carrying unfixed toner is passed between the rollers, and is heated by the hot roller and pressed by the pressure roller while being heated. In a fixing device for fixing toner,
A displacement mechanism for displacing the pressure roller in a direction to contact and separate from the hot roller,
Electromagnetic driving means for operating the displacement mechanism,
A control unit that controls a drive voltage of the electromagnetic drive unit according to a sheet conveyance speed,
By controlling the drive voltage by the control unit, the nip width generated by pressing the hot roller and the pressure roller through the displacement mechanism is adjusted, and the nip width increases as the paper transport speed increases. A fixing device configured to reduce the nip width as the sheet conveying speed decreases. It has a hot roller and a pressure roller that is in pressure contact with the hot roller. The sheet carrying unfixed toner is passed between the rollers, and is heated by the hot roller and pressed by the pressure roller while being heated. In a fixing device for fixing toner,
A displacement mechanism for displacing the pressure roller in a direction to contact and separate from the hot roller,
Electromagnetic driving means for operating the displacement mechanism,
A control unit that controls the drive voltage of the electromagnetic drive unit according to the type of paper,
By controlling the driving voltage by the control unit, the nip width generated by the pressure contact between the hot roller and the pressure roller is adjusted via the displacement mechanism, and the nip width increases as the paper becomes thicker, and the paper becomes thinner. The nip width is reduced as the nip width decreases. The fixing device according to claim 2 or 3,
The electromagnetic drive means is provided in a pair on the left and right sides in the axial direction of the pressure roller, and each electromagnetic drive means is provided with a displacement mechanism for adjusting a nip width at both ends of the pressure roller. Fixing device. The fixing device according to claim 2 or 3,
One electromagnetic drive means is provided at an intermediate position in the axial direction of the pressure roller, and a displacement mechanism that operates using the electromagnetic drive means as a common drive source adjusts the nip width at both ends of the pressure roller. A fixing device, which is provided. The fixing device according to claim 2, wherein
The electromagnetic driving means includes an electromagnetic clutch driven by a PWM-controlled pulse,
The fixing device according to claim 1, wherein the nip width is adjusted by controlling the ON / OFF timing of the pulse to change the stroke of the plunger of the electromagnetic clutch.

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