JPH09190105A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the surface of a fixing roller from being locally worn by a thermistor which is arranged in contact with the fixing roller so as to prolong the life of a fixing device. SOLUTION: The fixing device 50 is constituted so that a pressure roller 52 is brought into press-contact with the fixing roller 51 having a heater 53 inside. The thermistor 56 is arranged in contact with the surface of the fixing roller 51, and the temperature of the roller 51 is controlled based on the detected temperature. A motor 60 capable of switching a speed is connected to the roller 51, and the rotational speed of the roller 51 is switched to a normal mode and a low-speed mode by a controller 59. A non-paper passing state where a sheet material is not pass between the rollers 51 and 52 is detected by a sensor; and the roller 51 is switched to the low-speed mode through the controller 59 and the motor 60 in the case of the non-paper passing condition, so that the wear on the surface of the roller 51 caused by the thermistor 56 is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus in which a sheet material conveying speed in a fixing device is changed according to the presence or absence of a sheet material.

[0002]

2. Description of the Related Art A heat roller type fixing device is known as a fixing device used in an image forming apparatus such as a copying machine or a laser beam printer.

The main component of this device is a fixing roller having a heater inside and a pressure roller which is pressed against the fixing roller to form a fixing nip portion between the fixing roller and the fixing roller. At the time of fixing, the sheet material carrying the unfixed toner image is heated and pressed while being nipped and conveyed in the fixing nip portion, whereby the toner image is melted and fixed. In this fixing device, in order to maintain the fixing temperature at a predetermined temperature,
A thermistor is arranged in contact with the surface of the fixing roller.
The temperature of the fixing roller is measured by a thermistor, and ON / OFF control is performed based on the measured temperature to keep the temperature of the fixing roller at a predetermined fixing temperature.

As another fixing device, there is a fixing film type fixing device.

This device is mainly composed of a fixing film, a heating member and a pressure roller which sandwich the fixing film from the inside and the outside thereof, respectively. That is,
A plate-shaped heating member is arranged inside the endless heat-resistant fixing film, and the fixing film is pressed against the heating member by a pressure roller from the outside. At the time of fixing, the pressure roller is rotated to orbit the fixing film with the heating member. Then, while the sheet material carrying the unfixed toner image is nipped and conveyed between the surface of the pressure roller and the outer surface of the fixing film, the toner image is fixed on the surface of the sheet material by the heating member in contact with the inner surface of the fixing film. .

[0006]

However, according to the above-mentioned fixing device, in both the heat roller system and the fixing film system, a frictional portion is formed in the main component and also in the main part. In the former heat roller method, it is a contact portion on the surface of the fixing roller with the thermistor, and in the latter fixing film method, it is a contact portion with the heating member on the inner surface of the fixing film.

In the former thermal fixing system, the higher the speed of the image forming apparatus, the faster the rotation speed of the fixing roller and the longer the life of the fixing roller are set. The quantity increases dramatically. Therefore, in a high-speed machine, by positively moving the thermistor that contacts the surface of the fixing roller in the axial direction of the fixing roller,
We are trying to reduce the amount of wear. That is, the thermistor is brought into contact with the surface of the fixing roller, and the reciprocating operation is carried out in the axial direction, so that the thermistor is brought into contact with the same portion in the axial direction of the fixing roller for a long time, and only that portion is locally worn. To prevent it. As a result, the fixing roller has a long service life. However, according to this structure, a special mechanism for performing the reciprocating operation of the thermistor is required, and there is a problem that the structure of the entire fixing device becomes complicated.

On the other hand, in the latter fixing film system, since the inner surface of the fixing film is constantly in contact with the heating member, the fixing film is worn out with use over a long period of time, and the fixing film is frequently used. There is the problem of having to replace it. In order to eliminate frequent replacement, it is conceivable to increase the thickness of the fixing film, but if it is increased, the thermal conductivity decreases and the efficiency for heating deteriorates.

It is also conceivable to apply grease or the like to the friction surface to reduce the frictional resistance, but particularly in a low temperature environment, the driving torque of the fixing film increases due to the influence of grease. Further, it is difficult to keep the grease on the friction surface for a long period of time, which makes it unsuitable for a high-speed machine or the like aiming for a long life.

Therefore, an object of the present invention is to provide an image forming apparatus having a simple structure and extending the service life of the fixing device without lowering the thermal conductivity and increasing the driving torque. It is what

[0011]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and is a sheet material including a fixing member having a movable moving surface and a pressure member pressed against the fixing member. In a fixing device that heats and pressurizes an unfixed toner image on a sheet material while nipping and conveying the sheet, the moving surface of the fixing member is disposed in contact with the moving surface of the fixing member, and the moving surface is moved along with the movement of the moving surface. A contact member that rubs, a drive unit that can switch speeds that moves the moving surface of the fixing member, and a sheet material that is arranged upstream of the fixing device in the sheet material conveyance direction and that moves the sheet material with respect to the fixing device. And a speed switching unit that switches the driving unit to a low speed side when the non-sheet passing of the sheet material is detected by the detecting unit. To do.

Further, the fixing member is a fixing roller which is formed in a cylindrical shape and has a heat generating member inside thereof.
The contact member may be a temperature detection member that detects the surface temperature of the fixing roller.

Further, the fixing member is a heat-resistant fixing film formed in an endless shape, and the contact member is a heating member arranged in contact with the inner surface of the fixing film. The fixing film may be circulated between the pressure member and the pressure member.

[Operation] Based on the above-mentioned configuration, when the sheet material does not pass through the fixing device, the driving means is switched to the low speed side to slow down the moving speed of the moving surface. As a result, it is possible to reduce the abrasion of the moving surface due to the rubbing of the contact member.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. <Embodiment 1> FIG. 1 is a longitudinal sectional view showing a schematic configuration of an image forming apparatus according to the present invention.

The image forming apparatus 1 shown in FIG. 1 includes an image reading section 10 and an image forming section 2 at the upper, middle and lower portions of an image forming apparatus main body (hereinafter simply referred to as "apparatus main body") 2, respectively.
0, the feeding / conveying unit 30 is provided.

The image reading section 10 includes an original placing table 11 on which an original to be read is placed with its image surface facing downward, a light source 12 which moves in the left-right direction in the drawing while illuminating the image surface from below, A mirror 13, a lens 14 for guiding the reflected light emitted from the light source 12 and reflected by the image surface of the original, and a CCD 15 for reading the reflected light are provided.

The image forming section 20 has a photosensitive layer on the surface thereof and is driven to rotate in the direction of arrow R21, a charger 22 for charging the surface of the photosensitive drum 21 to a predetermined potential, and an image read by the CCD 15 described above. Photosensitive drum 2 based on information
1 is irradiated with light to form an electrostatic latent image, an exposure device 23, developing devices 24 and 25 for developing by attaching toner to the electrostatic latent image to develop it as a toner image, and a toner image on the photosensitive drum 21 as a sheet. A transfer charger 26 for transferring to the material P, a separation charger 27 for separating the sheet material P after the toner image transfer from the surface of the photosensitive drum 21, a cleaner 28 for removing transfer residual toner on the surface of the photosensitive drum 21 after the toner image transfer, A fixing device 50 that heats and pressurizes the sheet material P after the toner image transfer to fix the toner image on the surface thereof is provided. The fixing device 50 will be described in detail later.

The sheet feeding / conveying unit 30 stores a sheet feeding cassette 31 for stacking and storing sheet materials P such as sheets used for image formation, a conveying path 32 from the sheet feeding cassette 31 to the photosensitive drum 21, and recording from the sheet feeding cassette 31. A paper feed roller 33 for feeding the material P,
A pair of separation paper feed rollers 34 for preventing the double feeding of the fed sheet material P, conveyance rollers 35, 36 for conveying the sheet material P,
A registration roller 37 that supplies the sheet material P to the photosensitive drum 21 in synchronization with the toner image on the photosensitive drum 21, a conveyor belt 38 that conveys the sheet material P after the toner image transfer, and a conveyance that guides the sheet material P after fixing. A path 39, a conveyance roller 40 that conveys the sheet material P, a discharge roller 41 that discharges the sheet material P to the outside of the apparatus body 2, and the like are provided. Below the transport belt 38, the sheet material P after the toner image is fixed is fixed.
A re-feeding / conveying path 42 is provided to convey the sheet to the image forming unit 20 again to form a multiplex or double-sided image.

The above-described feeding / conveying unit 30 is provided with a plurality of sensors for detecting the sheet material P in order to detect a jam. The sheet material feeding detection first sensor S ₁ , the sheet material feeding detection second in order from the upstream side in the sheet material P conveyance direction.
A sensor S ₂ , a sheet material registration detection sensor S ₃ , a sheet material fixing device ejection detection sensor S ₄ , and a sheet material ejection detection sensor S ₅ .

The operation of the image forming apparatus 1 having the above configuration will be briefly described.

The surface of the photosensitive drum 21, which is driven to rotate in the direction of arrow R21, is uniformly charged by the charger 22, and the surface of the photosensitive drum 21 is exposed by the exposure device 23 based on the image information read by the image reading device 10. An electrostatic latent image is formed. This electrostatic latent image is developed by the developing device 24 or the developing device 25.
The toner adheres to and is developed as a toner image. The toner image is transferred onto the sheet material P by the transfer charger 26. This sheet material is fed from the paper feed cassette 31 by the paper feed roller 33, conveyed to the registration roller 37 by the conveyance roller 35, etc., and supplied by the registration roller 37 in synchronization with the toner image on the photosensitive drum 21. It was done.

The sheet material P after the transfer of the toner image is heated and pressed to fix the unfixed toner image on the surface thereof by the fixing device 50, and then discharged by the discharging roller 41 to the outside of the apparatus main body 2.

On the other hand, the photosensitive drum 21 after the toner image transfer
The transfer residual toner remaining on the surface is removed by the cleaner 28, and is subjected to the next image forming process starting from the charging by the charger 22.

The operation when the image formation is performed once on one side of the sheet material P has been described. However, when the image formation is performed on one side of the sheet material P in a multiple manner or on both sides, the above-mentioned operation is performed. The sheet material P after fixing is not discharged to the outside of the apparatus main body 2 but is fed to the re-feeding / conveying path 42, and the image forming unit 2
0, the toner image is transferred again, and the fixing device 5
After being fixed by 0, it is discharged to the outside of the apparatus main body 2.

FIG. 2 shows a perspective view of a heat roller type fixing device 50 as an example of the above-mentioned fixing device.

The fixing device 50 shown in the figure includes a fixing roller (fixing member) 51, a pressure roller (pressurizing member) 52, a heater (heating member) 53, a cleaning device 55, and a thermistor (temperature detecting member) as a contact member. (Member) 56 as a main constituent member.

The fixing roller 51 is formed in a cylindrical shape, and has a rod shape in which both ends are supported by a supporting member 57 (only one supporting member 57 is shown in FIG. 2) at the inner center portion thereof. The heater 53 is disposed. The fixing roller 51 is connected to a motor (driving means) 60 whose rotation is controlled by a control device (speed switching means) 59, and is rotationally driven by this motor 60 at a predetermined peripheral speed in the direction of arrow R51. The motor 60 is at least
It is possible to switch between a normal mode at a normal speed and a low speed mode (low speed side) slower than this.

The pressure roller 52 includes a core metal 52a and a roller member 52b surrounding the metal core 52a and having an appropriate elasticity. In the pressure roller 52, both ends of the cored bar 52a are urged toward the fixing roller 51 by urging members (not shown), whereby the surface of the roller member 52b is pressed against the surface of the fixing roller 51, and A belt-shaped fixing nip portion N is formed between the two. The pressure roller 52 is driven to rotate by the rotation of the fixing roller 51 in the direction of arrow R51. While the sheet material P carrying the unfixed toner image transferred from the photosensitive drum 21 is nipped and conveyed in the fixing nip portion N, the toner image is melted and fixed and fixed.

The cleaning device 55 includes a fixing roller 51.
It is provided with two rollers arranged obliquely above, namely, a supply roller 55a and a take-up roller 55b, and a cleaning web 55c wound around the supply roller 55a and unwound by the take-up roller 55b. The cleaning web 55c is configured to contact the surface of the fixing roller 51 between the supply roller 55a and the take-up roller 55b described above. The cleaning web 55c is impregnated with silicone oil or the like.
At the time of fixing, a part of the toner of the toner image on the sheet material P adheres to the surface of the fixing roller 51. Cleaning web 5
5c shows an arrow R55 by rotation of the take-up roller 55b.
The surface of the fixing roller 51 is rubbed while moving in the direction.
As a result, the adhered matter on the surface of the fixing roller 51 is wiped off. The take-up roller 55b is, for example, decelerated from a motor 60 that drives the fixing roller 51 via a gear unit (not shown), and is driven at a sufficiently reduced speed. Further, in this drive, in order to prevent unnecessary consumption of the cleaning web 55c, ON / OFF control is performed by a solenoid (not shown), and the winding operation is performed only when the sheet material P passes through the fixing nip portion N. Done.

The thermistor 56 as a temperature detecting member is
It is arranged in contact with the surface of the fixing roller 51. Based on the temperature detected by the thermistor 56, ON / OFF control of the heater 53 described above is performed via a temperature control device (not shown) to keep the fixing roller 51 at a predetermined fixing temperature. Conventionally, in order to prevent a part of the surface of the fixing roller 51 in the axial direction from being locally worn by sliding friction with the thermistor 56, the thermistor 56 is fixed as shown by an arrow A in FIG. The reciprocating operation was performed in the axial direction of the roller 51. Traditionally, this has been provided with a special mechanism for reciprocating operation.

In the present embodiment, as described later,
By controlling the rotational speed of the fixing roller 51 by the control device 59, the above-mentioned reciprocating operation, and further, the mechanism for performing this, is eliminated.

3 and 4 show the image forming apparatus 1 having the above-mentioned configuration.
6 is a flowchart showing control in the fixing device 50 in FIG.

When the operation start command signal is input by the copy key provided on the operation unit (not shown), the apparatus body 2 starts the operation (S1). At the same time, the control device 59 sets the speed of the motor 60 for driving the fixing device 50 to the low speed side (S2). The sheet material P fed from the sheet feeding cassette 31 is detected by the sheet material registration detection sensor S ₃
(Hereinafter simply referred to as "sensor S _3") monitors until reaching the (S3), when the arrival of the sheet material P is detected, the conveying operation of the sheet material P on standby, the sheet material by the registration rollers 37 P loop amount and exposure device 2
3. It is monitored whether all the image forming conditions of the developing devices 24 and 25 have been met (S4). Once you have them, the registration roller 3
7 is transmitted (S5). This registration roller 37
The transportation time t ₁ of the sheet material P from the transportation speed of the sheet material P to the front side of the fixing device 50 is set in advance. Then, the time t is measured at the same time as the conveyance by the registration rollers 37 is started (S6). If the sensor S ₃ is turned off before the predetermined transport time t ₁ elapses (S7),
A timer for measuring the time t ₂ is operated (S8). When the conveyance time t ₁ has passed, the fixing device 50 is driven,
The normal transportation speed that is the same as the transportation speed of the sheet material P is switched (S9). It should be noted that the above-described transport time t ₁ is equal to
Is a time that is set in consideration of a time sufficient for the speed of the fixing device 50 to stabilize before it enters the fixing device 50.

On the other hand, if the sensor S ₃ is not turned off at a predetermined time t ₁ , the sensor is monitored until it is turned off (S10 in FIG. 4), and from the time of turning it off, the preset time t is set as in S8. Count ₂ (S11).

Here, the time t ₂ is from the time when the sheet material P completely passes the sensor S ₃ (S _{3 is} off).
The distance to completely pass through the fixing device 50 is set in advance by converting the transport speed into time.

When the time t ₂ has elapsed (S11), it is judged that the sheet is not passed and the mode is switched to the low speed mode (S12).

It is judged whether or not the initially set number of copies has been completed (S13). If it is judged not to be completed, the process returns to S3 again, and if it is judged to be completed, the copying is ended (S14). .

In the image forming apparatus 1 having the configuration shown in FIG. 1, the motor 60 is switched to the low speed mode from the state in which the sheet material fixing device discharge detection sensor S ₄ is turned off without counting the time t _2. You may

As described above, when the sheet material P is not in the sheet passing state (non-sheet passing state) with respect to the fixing device 50, the motor 60 is switched to the low speed mode via the control device 59 to fix the fixing roller. Reduce the rotation speed of 51. As a result, it is possible to significantly reduce the wear of the contact portion with the thermistor 56 on the surface of the fixing roller 51 without providing a special mechanism. <Second Embodiment> FIG. 5 is a perspective view of a fixing device 70 using a heat-resistant fixing film (fixing member).

The fixing device 70 includes a heater (heating member).
71, a drive roller 72, a tension roller 73,
The pressure roller 75 is a main component.

The heater 71 is constructed by printing a resistor on a long plate-shaped ceramic substrate along the longitudinal direction thereof, and electrodes are provided at both ends in the longitudinal direction of the resistor. The heater 71 is supported by a heat resistant plastic supporter 74. Further, a metal stay is attached to the plastic supporter 74 to strengthen it. The fixing film 75 is a heat-resistant film formed in an endless shape, and is stretched over the heater 71, the driving roller 72, and the tension roller 73. The above metal stay has a thermistor (temperature detecting element)
77 is attached, and the thermistor 77 is in direct contact with the back surface of the heater 71. The other thermistor 78 is also arranged in contact with the back surface of the heater 71, like the thermistor 77. The thermistor 78 is attached near the end of the heater 71. This is because, when the small-width sheet material P is passed, the paper passing width becomes higher than the temperature of a portion where the sheet material P is absent, and therefore, the temperature is detected and, for example, continuous paper passing is performed. It is sometimes used to increase the time interval for paper passing. Fixing film 7
5 is pressed against the heater 71 from below by the pressure roller 76. When fixing the unfixed toner image on the sheet material P, the pressure roller 76 is rotated in the direction of arrow R76, and the fixing film 75 is rotated by the drive roller 72 in the direction of arrow R75. As a result, the sheet material P is nipped and conveyed between the fixing film 75 and the pressure roller 76, and the toner image on the sheet material P is heated and melted by the heater 71 to be fixed.

At this time, the back surface of the fixing film 75 is rubbed against the heater 71 and gradually worn.

Therefore, also in the present embodiment, as in the case of the above-described first embodiment, when the sheet material P is in the non-sheet passing state with respect to the fixing device 70, the peripheral speed of the fixing film 75 is slowed. To do. That is, the motor (driving means) 80 for orbiting the fixing film 75 is switched to the low speed mode by the control device (speed switching means) 79,
Thereby, the abrasion of the fixing film 75 is reduced.

[0045]

As described above, according to the present invention, when the sheet material does not pass through the fixing device, the driving means is switched to the low speed side by the speed switching means to move the moving speed of the moving surface. Slow down. As a result, it is possible to reduce the abrasion of the moving surface due to the rubbing of the contact member. That is, although the structure is simple, the life of the fixing device can be extended without lowering the thermal conductivity and increasing the driving torque.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a schematic configuration of an image forming apparatus according to the present invention.

FIG. 2 is a perspective view showing the configuration of a fixing device according to the first embodiment.

FIG. 3 is a flowchart showing the operation of the image forming apparatus according to the first embodiment.

FIG. 4 is a flowchart showing the operation of the image forming apparatus according to the first embodiment.

FIG. 5 is a perspective view showing a configuration of a fixing device according to a second embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Image forming apparatus main body (apparatus main body) 10 Image reading section 20 Image forming section 21 Photosensitive drum 30 Feeding / conveying section 50 Fixing device 51 Fixing member (fixing roller) 52 Pressing member (pressing roller) 53 Heating member (Heater) 55 Cleaning device 56 Contact member, temperature detection member (thermistor) 59 Speed switching means (control device) 60 Driving means (motor) 70 Fixing device 71 Heating member (heater) 72 Driving roller 73 Driven roller 75 Fixing member (fixing) Film) 76 Pressure member (pressure roller) 79 Speed switching means (control device) 80 Driving means (motor) P Sheet material S ₃ Detection means (sheet material registration detection sensor)

Claims (3)

[Claims] 1. A fixing member having a movable moving surface,
In a fixing device that heats and presses an unfixed toner image on a sheet material to fix the unfixed toner image on the sheet material while nipping and transporting the sheet material by a pressure member that is pressed against the fixing member, the fixing device is disposed in contact with the moving surface of the fixing member. At the same time, a contact member that rubs the moving surface along with the movement of the moving surface, a drive unit that can change the speed of moving the moving surface of the fixing member, and a fixing device of the fixing device in the conveyance direction of the sheet material. Is arranged on the upstream side, and the sheet material is passed through the fixing device,
An image forming device, comprising: a detection unit that detects non-sheet passing; and a speed switching unit that switches the driving unit to a low speed side when the detection unit detects non-sheet passing of a sheet material. apparatus. 2. The fixing member is a fixing roller that is formed in a cylindrical shape and has a heat generating member inside, and the contact member is a temperature detecting member that detects the surface temperature of the fixing roller. The image forming apparatus according to claim 1. 3. The fixing member is a heat-resistant fixing film formed endlessly, and the contact member is a heating member arranged in contact with the inner surface of the fixing film. The image forming apparatus according to claim 1, wherein the fixing film is circulated between the pressure member and the pressure member.