JPH08220920A - Fixing device - Google Patents

Abstract

PURPOSE: To solve the deterioration of an oil quantity controlling performance caused by the effect that an oil applying roller always comes in press contact with a heating roller and a cleaning roller, especially, various failures caused by the excess supply of oil in a fixing device which is constituted so that the cleaning roller may be rotated with the oil applying roller in order to efficiently remove a foreign matter stuck the oil applying roller which is rotated with the heating roller. CONSTITUTION: In this fixing device provided with the heating roller 1 and the pressure roller 2 which are rotated in press contact with each other through the outer peripheral surfaces, the oil applying roller 5 which is rotated in contact with the outer peripheral surface of the heating roller 1 so as to apply the oil to the heating roller 1, the cleaning roller 6 which is rotated in press contact with the outer peripheral surface of the oil applying roller 5, the device is provided with a pressure reducing mechanism 7 capable of switching the press contact force of the oil applying roller 5 to the heating roller 1, or the cleaning roller 6 in at least two stages.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a fixing device used in an image forming apparatus having an electrophotographic image forming section such as a copying machine, a printer, a facsimile machine, etc. In a fusing device that heat-fuses and fixes the foreign matter adhering to the oil roller that supplies oil to the heating roller that constitutes the fusing device, the foreign matter adheres to the heating roller in reverse, resulting in toner stains on the recording paper and image quality. The present invention relates to a fixing device that can solve problems such as deterioration. More specifically, by preventing the controllability of the oil supply amount from being deteriorated due to the oil applying roller being pressed by the heating roller and the cleaning roller, the fixing property of the heating roller is not deteriorated. The present invention relates to a fixing device capable of preventing excessive supply of oil from a coating roller to a heating roller.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine, a printer, a facsimile machine, etc., which is equipped with an electrophotographic image forming section, optical image information such as reflected light from a document is preliminarily uniformly charged on a photoreceptor. The electrostatic latent image obtained by irradiation,
Toner is supplied from a developing device to form a visible image, the toner image is transferred onto a recording paper, and then the paper is passed through a fixing device for thermal fixing. This fixing device has a heating roller having a heater inside and a pressure roller that is in pressure contact with the outer peripheral surface of the heating roller, and heats the transferred recording paper passing between both rollers while applying pressure, The toner image is being fixed.

In the above-mentioned conventional fixing device, in order to prevent the adhesion of toner to the heating roller and the occurrence of offset (decrease in fixing ability) due to the adhesion, high-viscosity silicone oil is applied to the outer peripheral surface of the heating roller. The oil film is formed by pressing the impregnated oil application means or the oil application means for applying a small amount of oil that oozes out from the oil tank provided in the roller through the felt. Since the coating means is in constant contact with the heating roller, foreign matter such as toner and paper dust that adheres to the peripheral surface of the heating roller is transferred to the oil coating means side, which only lowers the ability to uniformly apply oil. However, the foreign substances gradually accumulated on the oil application means side flow backward to the heating roller side,
Finally, there is a problem that it adheres to the recording paper and causes deterioration of image quality (Japanese Patent Laid-Open No. 61-109084, 62-5).
284, 1-120171, 3-114064).

That is, FIG. 9 is an explanatory view of the configuration of a conventional fixing device, in which a recording paper P having unfixed toner T is conveyed from an image forming portion located on the right side of the drawing, and a heating roller 1 is provided.
01 and the pressure roller 102 enter the nip portion, the toner T on the recording paper P is fixed on the paper and discharged to a paper discharge unit (not shown) located on the left side of the fixing device. Normal,
The recording paper P holding the toner T is melted by the heat of the fixing roller 101 and fused to the recording paper. However, when the releasability of the surface of the heating roller 011 is poor, a part of the toner adheres to the surface of the heating roller 101, causing a slight offset. The toner accumulated by the small amount of offset becomes a lump of toner with time and adheres to the surface of the heating roller, which not only lowers the fixing property of the heating roller, but also accelerates deterioration. As a countermeasure for this, it is possible to prevent the offset by pressing the oil applying roller 105 filled with silicone oil into the heating roller 101 to constantly supply the silicone oil to the heating roller 101 to enhance the mold release property. It is being appreciated. This method is excellent in terms of space saving and ease of maintenance.

However, as described above, the oil applying roller 10
Even if 5 is used, it is difficult to completely prevent the offset, and a slight amount of offset remains on the heating roller 101. As a result, the oil applying roller 105 also serves as a cleaning roller. As the oil applying roller 105 is used, the oil applying roller 105 becomes dirty, the amount of oil applied decreases, and the cleaning roller (not shown in FIG.
Re-transfer of the toner mass adhering to the cleaning roller (which directly contacts the heating roller) to the heating roller 101 occurs,
Causes image stains.

From such a point, as shown in FIG. 9, the cleaning roller 10 with respect to the oil applying roller 105.
It is performed that 6 is pressed and rotated together. In this fixing device, the cleaning roller 106 removes foreign matter such as toner adhering to the oil application roller 105. Reference numeral 103 is a heater, 104 is a thermistor for temperature detection, 108 is a separation claw, 109, 1
10 is a paper ejection guide, 111 is a separation claw spring, 112
Is a paper discharge roller, 113 is an inlet guide, and 114 is an oil supply unit.

However, in such a fixing device, since the oil application roller 105 is constantly in pressure contact with both the heating roller 101 and the cleaning roller 106, the surface oil amount of the oil supply roller can be properly controlled. I don't know. In particular, when the fixing device is left standing for a long time, a large amount of oil adheres to the other member that comes into contact with the oil application roller.
This large amount of oil adheres to the recording paper when the recording paper passes and causes oil stains. Further, this oil causes slipping between the pressure roller 102 and the oil applying roller which rotate in pressure contact with the heating roller, and damages the roller surface. Further, a large amount of oil that has adhered to the cleaning roller causes deterioration of the cleaning performance of the cleaning roller, and eventually leads to deterioration of image quality.

On the other hand, in order to solve the problem caused by the oil applying roller 105 being pressed by the adjacent rollers 101 and 106, the oil applying roller is separated from the heating roller 101 and the cleaning roller 106 or comes into contact therewith. With such a configuration, heat conduction from the heating roller 101, which is a heat source, is not performed and the oil viscosity changes, which accelerates the deterioration of the heating roller 101 or when the oil application roller is re-contacted by pressure. Since the heat is taken away by the application roller, the fixing property of the recording paper deteriorates.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has a structure in which an oil applying roller is made to rotate with a cleaning roller in order to efficiently remove foreign matters adhering to the oil applying roller which is rotated with the heating roller. In the fixing device described above, the oil amount controllability is lowered due to the oil application roller being constantly in pressure contact with the heating roller and the cleaning roller, and in particular, various types of oil are generated due to excessive supply of oil. It is an object of the present invention to provide a fixing device capable of solving the above problems.

[0010]

In order to achieve the above object, the invention according to claim 1 is such that a heating roller and a pressure roller which rotate while being in pressure contact with each other on the outer peripheral surface, and a heating roller which rotates while contacting the outer peripheral surface of the heating roller. In a fixing device including an oil application roller for applying oil to the roller and a cleaning roller that rotates while being in pressure contact with the outer peripheral surface of the oil application roller, the oil application roller for the heating roller or the cleaning roller is It is characterized in that a pressure reducing mechanism capable of switching the pressure contact force in at least two stages is provided.

According to a second aspect of the present invention, eccentric drive transmission rollers for receiving the rotational drive force from the heating roller and driving the cleaning roller are provided at both axial ends of the oil application roller. Is configured to switch the pressure contact force of the oil application roller with respect to the heating roller. According to a third aspect of the present invention, a pressure contact state detection device for detecting a state in which the oil application roller is in pressure contact with the heating roller is provided, and oil is supplied to a position where the pressure contact force of the oil application roller is minimized at the end of the fixing operation. It is characterized in that control is performed so as to stop the roller.

According to a fourth aspect of the present invention, the drive transmission roller is connected to the shaft of the oil application roller via a one-way clutch, and a heating roller drive source capable of forward and reverse rotation is used to heat the roller after the fixing operation is completed. The reverse rotation torque is not transmitted to the oil application roller when the roller is reversely rotated by a certain amount. According to a fifth aspect of the present invention, a recording paper passage detecting means for detecting that the recording paper has passed through the pressure contact portion between the heating roller and the pressure roller is provided, and the oil applying roller of the oil applying roller is provided except when the recording paper is passing. It is characterized in that the pressure reducing mechanism is operated so that the pressure contact force is minimized. According to a sixth aspect of the present invention, there is provided rotation speed detection means for detecting the rotation speed of the pressure roller, and when the rotational deviation from the rotation speed of the heating roller exceeds a certain value, the oil application roller is provided. The pressure reducing mechanism is controlled so that the pressure reducing mechanism is operated so as to minimize the pressure contact force.

[0013]

According to the invention of claim 1, the oil application roller comprises:
Since the pressure reducing force capable of switching the pressure contact force between the heating roller and the cleaning member is changed, it is possible to prevent the oil from excessively flowing out from the oil applying roller, and the fixing property is not deteriorated.

According to the second aspect of the present invention, since the drive transmission member for transmitting the driving force from the heating roller to the coating roller is an eccentric roller, each pressure contact force from the oil coating roller to the heating roller and the cleaning roller is switched. As a result, it is possible to switch the pressure contact force of the oil application roller with a simple configuration.
Excessive oil outflow can be prevented and an appropriate amount of oil can be applied.

According to the third aspect of the present invention, since the pressure contact force of the oil application roller is controlled to be the minimum when the fixing operation is stopped, the oil outflow amount when the operation is stopped can be minimized. .

According to the fourth aspect of the present invention, the positional relationship between the eccentric drive transmission member and the oil supply roller changes every time the fixing operation is stopped, so that it is possible to prevent the situation where the surface of the oil application roller is only partially deteriorated. .

According to the fifth aspect of the present invention, the pressure contact force can be minimized except when the recording paper is passing through the fixing device, and excessive outflow of oil from the oil application roller can be prevented.

According to the sixth aspect of the invention, the pressure roller slips against the fixing roller and cannot be driven to rotate due to excessive outflow of oil from the oil applying roller, resulting in paper jam or heating roller. Can be prevented from being damaged.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a front view showing the configuration of an embodiment of a fixing device of the present invention, and FIG. 2 is a plan view of a pressure reducing mechanism.
This fixing device includes a heating roller 1 having a heater 3 inside.
A pressure roller 2 in pressure contact with the heating roller 1, a thermistor 4 for detecting the surface temperature of the heating roller 1, an oil application roller 5 in pressure contact with the surface of the heating roller 1 and rotated by frictional force, and oil application The cleaning roller 6 that rotates by being pressed against the surface of the roller 5, the depressurizing mechanism 7 that varies the pressure applied to the heating roller 1 and the oil applying roller 5 to the cleaning roller 6, and the recording paper attached to the surface of the heating roller 1. A separation claw 8 for peeling, a biasing spring 8a thereof, a guide 9 for guiding the recording paper P holding the unfixed toner T on the entrance side, an exit guide 10, and a paper discharge roller 1.
Has 1 etc. The cleaning roller 6 is pressed against the oil applying roller 5 by a spring 6a. The decompression mechanism 7 is connected to the shaft 5a of the oil applying roller 5, and the shaft is
It is configured to urge in a pressurizing direction and a non-pressurizing direction.

The heating roller 1 is, for example, an aluminum journal portion whose surface is treated with a fluororesin, and PFA, PTFA or the like is used as the fluororesin. As the oil applying roller 5, a roller whose surface layer is made of a fluororesin such as PFA or PTFA, or a silicone rubber-based elastic body is used, and it is difficult for toner to adhere thereto and silicon oil is easily supplied. The cleaning roller 6 is made of, for example, a metal roller with fluororubber 10 to 100 μm on the surface.
It is a coated roller. Oil supply roller 7
Has a surface made of PTFA resin and has an oil tank inside. A fine hole is formed in the surface PTFE, and a minute amount of silicone oil oozes out from this hole to apply the silicone oil to the surface of the oil applying roller 5.

In the first embodiment of the present invention, the oil application roller 5 is constructed so that the pressure contacting the heating roller 1 and the cleaning roller 6 can be adjusted by the depressurizing mechanism 7 to achieve the above-mentioned object. ing. The depressurizing mechanism 7 has a pressurizing solenoid 20 as a drive source and an operating mechanism 21 operated by the pressurizing solenoid 20. The pressurizing solenoid 20 has its main body fixed to the fixing device side, and the pin 22 is attached to the rod 22 protruding in the arrow direction.
One end of the substantially L-shaped connecting member 23 is pivotally supported by 2a,
Since the pin 24 fixed to the fixing device is loosely fitted in a proper position near the other end of the connecting member 23, the other end 23a of the connecting member 23 can rotate in the arrow direction. The other end portion 23a of the connecting member is a portion for coming into contact with and pressing the actuating mechanism 21, or for releasing the pressing. Connecting member 2
3 is constantly urged by a spring 25 in a direction in which the rod 22 is projected.

When the solenoid 20 is turned on and the rod 22 is retracted, the connecting member 23 rotates counterclockwise around the pin 24, and conversely, the solenoid causes the rod 22 to move O.
When the FF is performed and the rod 22 is projected by the force of the spring 25, the connecting member 23 rotates about the pin 24 in the clockwise direction. The operating mechanism 21 includes a stay 31 as a long plate whose upper end edge is rotatably supported by a shaft 30 fixed to the fixing device side, and a plate shape fixed to the lower end edges of the stay 31 at the lower ends of the longitudinal direction. Elastic bodies 32, brackets 33 fixed to the tip ends of the elastic bodies 32, and bearings 34 fixed to the brackets 33. The bearings 34 project from both axial ends of the oil application roller 5. The shaft 5a is rotatably supported. Reference numerals 35 and 36 denote stays 3.
It is a stopper for stopping the rotation of 1. The oil application roller 5 is driven to rotate when the heating roller 1 is rotated via the gears 41 and 40 by the rotation of the drive motor 42 as shown in FIG. Further, the cleaning roller 6 that is in contact with the oil applying roller 5 also rotates.

The operation of the oil applying roller pressure reducing mechanism 7 is as follows. That is, when the pressure solenoid 20 is turned off, the force of the spring 25 causes the connecting member 23 to center around the pin 24.
Rotates in the clockwise direction in FIG. Then, the stay 31 which has been urged to the solid line position in FIG. 1 by the connecting member 23 is rotated counterclockwise around the shaft 30 and retracted to the dotted line position in FIG. As a result of the solenoid 20 being in the ON state, when the stay 31 is in the pressing position shown by the solid line, the spring force of the elastic body 32 causes the oil application roller 5 to move.
Are in pressure contact with the pressure roller 1 and the cleaning roller 6, respectively, and the pressing force is regulated by the stopper 36.
When the stay 31 moves to the depressurized position shown by the dotted line, the pressing force is adjusted to decrease. The stopper 35 limits the pressure reduction by restricting the rotation amount of the stay 31 in the pressure reduction direction.

When the solenoid 20 is turned on while the stay 31 is at the position indicated by the dotted line, the connecting member 2 located at the position indicated by the dotted line
Since 3 rotates to the solid line position, the stay 31 rotates about the shaft 30 in the clockwise direction in FIG. 1 and rotates until it comes into contact with the stopper 36. Therefore, the force of the elastic body 32 causes the oil application roller 5 to shift to a pressed state.

3, 4, and 5 are a front view and a perspective view showing another embodiment of the pressure reducing mechanism of the present invention. The oil application roller 5 is in contact with the outer peripheral surface of the heating roller 1 in contact with the pressure roller 2 and is rotating. The heating roller 1 has a gear 40 integrated at one axial end of the heating roller 1 and a motor 42.
The output gear 41 of FIG.
The motor 42 is configured to be rotatable in the forward and reverse directions. An eccentric cam (eccentric drive transmission roller) 45 is connected to each shaft 5a protruding from both axial ends of the oil applying roller 5 via a one-way clutch 46. The eccentric cam 45 is
The outer peripheral surface is made of high resistance material such as heat resistant rubber,
The transmission of the driving force from the heating roller 1 to the oil application roller 5 is realized by the eccentric cam 45 contacting the outer peripheral surface of the heating roller 1 on its outer peripheral surface and rotating together. The cleaning roller 6 also receives a driving force from the outer peripheral surface of the eccentric cam 45.

FIG. 3 shows the shaft 5 of the outer peripheral surface of the eccentric cam 45.
FIG. 4 shows the maximum pressure state in which the surface closest to a is in contact with the heating roller surface, and FIG. 4 shows the minimum eccentric cam outer surface in the farthest distance from the shaft 5a in contact with the heating roller outer surface. The reduced pressure state is shown. When the eccentric cam 45 is at the angle shown in FIG. 3, the oil application roller 5 is in sufficient contact with the heating roller 1 and the cleaning roller 6 to supply oil. Further, when the eccentric cam 45 is at the angle shown in FIG. 4, the oil application roller 5 is weakened in contact with both rollers 5, 6.

The eccentric cam 45 is connected to the shaft 5a via the one-way clutch 46 so that only the same portion of the oil applying roller 5 is continuously kept in pressure contact with the heating roller and the cleaning roller with a high pressing force when the copying operation is stopped. This is to prevent the oil from flowing out from the contact portion to accelerate the reduction of the oil in the coating roller, and prevent the roller surface from being soiled because cleaning cannot be done in time. That is,
The motor 42 is capable of normal and reverse rotation, and when the copying operation is stopped, the motor 42 is controlled so as to rotate in the reverse direction for a predetermined time. At this time, the heating roller 1, the eccentric cam 45, and the cleaning roller 6 rotate in the reverse direction. The coating roller does not rotate in the reverse direction because the driving force is cut off by the one-way clutch 46.
Therefore, by keeping the oil applying roller in a depressurized state during reverse rotation while the copying is stopped, the positional relationship between the eccentric cam 45 and the surface of the oil applying roller is changed, and only one place of the oil applying roller 5 is strongly pressed. The above problem can be solved.

Further, the marking portion 4 is provided so that the eccentric position can be detected at a proper position on the end surface of the eccentric cam 45 (in this example, a position closest to the outer peripheral surface where the distance from the shaft 5a is the shortest = depressurized position).
7 are provided. A reflection type photo interrupter (cam position detecting means) 48 is arranged at a position where it can face the marking section 47. By detecting the marking section 47 by this reflection type photo interrupter 48, after the copying is completed, the oil is depressurized as shown in FIG. It is possible to control the reverse rotation drive of the motor 42 (reverse rotation when the copy is stopped) so that the angle of the coating roller 5 reaches. In other words, it is possible to prevent one place from continuing contact by performing reverse rotation for a certain period of time while the oil application roller 5 is in a depressurized state. The marking portion 47 and the cam position detecting means 48 constitute a pressure contact state detecting device.

Reference numeral 50 in FIGS. 1 and 5 designates the pressure roller 2.
Is a rotation number detecting means (reflection type photo sensor) for detecting the number of rotations of the pressure roller 2, and detects a marker group 51 formed at a predetermined interval along the circumferential direction on the outer peripheral surface of one end of the pressure roller 2 in the axial direction. Thus, the rotation speed is detected. The control unit operates the pressure reducing mechanism so that the pressure contact force of the oil application roller is minimized when the rotational deviation between the pressure roller and the heating roller exceeds a certain value. Therefore, it is possible to prevent the paper jam and the damage of the pressure roller due to the slip.

Further, reference numeral 52 is a paper detection means (recording paper passage detection means) which faces the recording paper P entering through the opening 9a formed in the guide 9, and detects the entrance of the front end of the paper and the passage of the rear end thereof. Detect. Based on the detection result, the control unit determines whether or not the recording paper is passed, and operates the pressure reducing mechanism so that the pressure contact force of the oil application roller is minimized except when the recording paper is passed. It is possible to prevent wasteful oil outflow and extend the life of the oil supply roller.

FIG. 6 is a block diagram showing the control system of the fixing device of the present invention, which is a microcomputer (CPU, R).
OM, RAM, I / O ports, etc.) and an operation panel 61, and the control unit 60 includes the rotation detecting means 5
0, the paper detection means 52, the cam position detection means 48 and the like, and the drive motor 42 and the roller pressure solenoid 20 based on the data obtained based on the detection signals.
Control each. A control signal for controlling each control target is stored in a storage unit such as a ROM. The control unit 60 also receives an input signal from an operation key 62 such as a copy key and displays various messages on the display 63.

Next, the operation of the oil applying roller will be described with reference to FIGS. FIG. 7 shows the operation of the embodiment shown in FIGS. When the copy key 62 is turned on, the drive motor 42 of the fixing device is turned on to start driving. When the paper detection unit 52 detects the entry of the recording paper, the control unit turns on the pressure solenoid 20 (steps 1 to 4). When the driving of the fixing device is stopped, the connecting member 23 is in the depressurized position shown by the dotted line because the solenoid 20 is off, so the operating mechanism 21 is also in the depressurized state, and the oil application roller 5 is the pressure roller 1 and the cleaning roller 6 Although it is in a depressurized state, the connecting member 23 can be moved to the pressurizing state shown by the solid line by turning on the pressurizing solenoid 20, and as a result, the oil applying roller 5 is in the pressurizing state. .

Subsequently, in step 5, it is determined whether or not the pressure roller 2 is slipping between the pressure roller 2 and the heating roller 1 while the recording paper is being fixed. That is, the presence / absence of the slip is detected by the rotation detecting means 50, and the control unit 60 makes a determination based on the rotation speed of the pressure roller. If the slip is large, the oil amount is large. After making a determination, the solenoid 20 is turned off and the pressure is reduced (steps 6 to 9). Even when it is determined that the recording sheet has passed through the fixing device based on the trailing edge passage signal from the sheet detection unit 52 and the transport speed, the solenoid 20 is also provided.
Is turned off to reduce the pressure applied by the oil application roller to the heating roller 1 and the cleaning roller 6. As a result, the pressure applied when the paper is not passed is always reduced, and the excessive supply of oil is prevented.

FIG. 8 shows the operation of the embodiment shown in FIGS. 3, 4 and 5. When the copy key 62 is turned on, the drive motor 42 of the fixing device is turned on to start driving. In the embodiments shown in FIGS. 3, 4 and 5, pressurization and depressurization alternate when the coating roller 5 rotates, but the above-mentioned inconvenience occurs when the position where the coating roller comes into contact with the counterpart roller is always constant during pressurization. Therefore, when the copying is stopped, the angle of the cam 45 is detected, the motor is turned off when it is in the pressure reducing position, the motor is reversely rotated when it is not in the pressure reducing state, and when it is detected that the cam angle is in the pressure reducing position. The motor is stopped (steps 11-14).

[0035]

As described above, according to the first aspect of the present invention, the heating roller 1 and the pressure roller 2 which rotate while being pressed against each other on the outer peripheral surface, and the heating roller which rotates while contacting the outer peripheral surface of the heating roller. In a fixing device provided with an oil applying roller 5 for applying oil to the roller and a cleaning roller 6 which is pressed against an outer peripheral surface of the oil applying roller to rotate, a pressure contact force of the oil applying roller with respect to a heating roller or a cleaning roller. Since the pressure reducing mechanism 7 capable of switching at least two stages is provided, it is possible to prevent the oil from unnecessarily flowing out, prevent oil stains on the recording paper, deterioration of the heating roller, and extend the life of the oil applying roller. It can be postponed.

According to a second aspect of the present invention, an eccentric drive transmission roller (eccentric cam) which receives the rotational driving force from the heating roller at both axial ends of the oil application roller and drives the cleaning roller. ) 45, the pressure contact force of the oil application roller with respect to the heating roller is switched, so that the pressure contact force of the oil application roller can be switched with a simple configuration. Also,
Since the driving force is not transmitted on the surface of the oil applying roller, deterioration of the oil applying roller can be prevented.

According to the third aspect of the present invention, a pressure contact state detecting device (45, 48) for detecting the state where the oil application roller is in pressure contact with the heating roller is provided, and the pressure contact force of the oil application roller at the end of the fixing operation. Since the control is performed so that the oil supply roller is stopped at the position where the pressure is minimized, the pressure contact force can be switched accurately.

According to a fourth aspect of the present invention, the drive transmission roller 45 is connected to the shaft of the oil application roller via a one-way clutch, and a heating roller drive source capable of normal and reverse rotation is used to complete the fixing operation. Since the heating roller is configured to reversely rotate by a certain amount, the positional relationship between the drive transmission roller 45 and the oil applying roller 5 (the portion where the oil applying roller contacts the heating roller and the cleaning roller) is made different when the fixing device is stopped. Therefore, it is possible to prevent only a part of the oil application roller from deteriorating.

According to a fifth aspect of the present invention, recording paper passage detection means for detecting that the recording paper has passed through the pressure contact portion between the heating roller and the pressure roller is provided, and the oil is used except when the recording paper is passing. Since the pressure reducing mechanism is operated so as to minimize the pressure contact force of the coating roller, it is possible to prevent wasteful oil outflow and extend the life of the oil supply roller.

According to a sixth aspect of the present invention, there is provided rotation speed detection means for detecting the rotation speed of the pressure roller, and when the rotation deviation from the rotation speed of the heating roller exceeds a certain value, Since the pressure reducing mechanism is controlled to operate so that the pressure contact force of the oil application roller is minimized, it is possible to detect the pressure roller due to oil and prevent damage to the heating roller due to slip.

[Brief description of drawings]

FIG. 1 is a front view of a fixing device according to an embodiment of the present invention.

FIG. 2 is a plan view of the pressure reducing mechanism of FIG.

FIG. 3 is an operation explanatory view of a pressure reducing mechanism according to another embodiment of the present invention.

FIG. 4 is an operation explanatory view of the pressure reducing mechanism of the embodiment of FIG.

5 is a perspective view showing the configuration of the embodiment shown in FIGS. 3 and 4. FIG.

FIG. 6 is a block diagram showing a control system according to an embodiment of the present invention.

FIG. 7 is a flowchart showing a control procedure of the embodiment of FIG.

FIG. 8 is a flowchart showing a control procedure of the embodiment shown in FIGS. 3, 4 and 5.

FIG. 9 is a structural explanatory view of a conventional example.

[Explanation of symbols]

1 heating roller, 2 pressure roller, 3 heater, 4 thermistor, 5 oil application roller, 6 cleaning roller, 7 pressure reducing mechanism, 8 separation claw, 9 guide, 10
Guides, 11 paper discharge rollers, 20 pressure solenoids, 2
1 Actuating Mechanism, 22 Rod, 23 Connecting Member, 24
Pins, 25 springs, 30 shafts, 31 stays, 32 elastic bodies, 33 brackets, 34 bearings, 35, 36 stoppers, 40, 41 gears, 45 eccentric cams, 46 clutches, 47 marking parts, 50 rotation speed detection means (reflection type Photo sensor), 51 marker group, 52 paper detection means, 60 control unit, 61 working panel, 63 display.

Claims (6)

[Claims] 1. A heating roller and a pressure roller that rotate while being pressed against each other on their outer peripheral surfaces, an oil applying roller that rotates by contacting the outer peripheral surface of the heating roller and applies oil to the heating roller, and an oil applying roller. And a cleaning roller that rotates in pressure contact with the outer peripheral surface of the oil roller, and a depressurizing mechanism that can switch the pressure contact force of the oil application roller to the heating roller or the cleaning roller in at least two stages. A fixing device characterized by being provided. 2. An eccentric drive transmission roller that receives the rotational drive force from the heating roller and drives the cleaning roller is provided at both axial ends of the oil application roller. The fixing device according to claim 1, wherein the fixing device is configured to switch the pressure contact force with respect to the heating roller. 3. A pressure contact state detecting device for detecting a state where the oil application roller is in pressure contact with the heating roller is provided, and the oil supply roller is stopped at a position where the pressure contact force of the oil application roller is minimized at the end of the fixing operation. The fixing device according to claim 1, wherein the fixing device is controlled so as to perform the fixing operation. 4. The drive transmission roller is connected to the shaft of the oil application roller via a one-way clutch, and a heating roller drive source capable of forward and reverse rotation is used to reverse the heating roller by a predetermined amount after the fixing operation is completed. The fixing device according to claim 2 or 3, wherein the reverse rotation torque is configured not to be transmitted to the oil application roller when the fixing device is rotated. 5. A recording paper passage detection means for detecting that the recording paper has passed through the pressure contact portion between the heating roller and the pressure roller is provided, and the pressure contact force of the oil application roller is provided except when the recording paper is passing. The pressure reducing mechanism is configured to operate so as to minimize the pressure.
Or the fixing device described in 4. 6. A pressure detecting means for detecting the number of revolutions of the pressure roller is provided, and when the rotational deviation from the number of revolutions of the heating roller exceeds a certain value, the pressure contact force of the oil application roller is reached. The control is performed such that the pressure reducing mechanism is operated so that the pressure is minimized.
Alternatively, the fixing device according to item 5.