JP2003295731A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent an image failure due to flaws of a photoreceptor drum and a transfer roll and damage to a driving system due to a loss of synchronism or breakage, etc., of a driving motor and gear in the cleaning mode of a step feeding type fixing device in a two-motor system image forming apparatus. <P>SOLUTION: In the two-motor system image forming apparatus, the step feeding quantity in transferring is made to be more than step feeding quantity in fixing, or the step feeding is started after the end of paper passed a transfer nip, or a clutch is provided to the driving system of the photoreceptor drum. <P>COPYRIGHT: (C)2004,JPO

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 using a printer such as a laser beam printer or an LED printer, an electrophotographic system such as a digital copying machine, or an electrostatic recording system.

[0002]

2. Description of the Related Art Conventionally, as a fixing device in an image forming apparatus such as an electrophotographic copying machine or a laser beam printer, a heat roller type or an on-demand type is known.

In the heat roller type fixing device, a pair of rollers (a fixing roller and a pressure roller) having a heating device are brought into pressure contact with each other, and a sheet, which is a recording material such as paper, is passed through the nip so that a sheet is formed. The above toner is melted and fixed.

Of the above-mentioned pair of rollers, the fixing roller which comes into contact with the sheet surface (which means the side carrying the toner) is a cylindrical roller whose surface is made of a material having a good releasability. The toner is heated by the halogen heater (heating device) arranged in the. On the other hand, the pressure roller that comes into contact with the back surface of the sheet is configured by providing an elastic layer on the core metal and applies appropriate pressure to the toner layer.

Ideally, all of the toner on the surface of the sheet is heated and melted and fixed on the surface of the sheet. However, the toner is in a cold offset state that does not completely melt, and the toner is in a hot offset state that is too melted. If there is toner (hereinafter referred to as "toner stain") that is electrostatically offset on the fixing roller, these toner stains adhere to the surface of the fixing roller or the pressure roller, which has the poorer releasability. Resulting in.

When the releasing property of the fixing roller is lower than that of the pressure roller, toner stains adhere to the fixing roller.
Since the fixing roller is constantly heated to the toner melting temperature during image formation, toner stains are in a melted state, and when the next sheet arrives, it is mixed with the toner image on the surface and moves to the sheet. It is unlikely that the fixing roller is continuously soiled. However, in some cases, toner stains may exist on the surface of the fixing roller, and in such a case, the image may be stained.

On the other hand, when the releasing property of the pressure roller is lower than that of the fixing roller, the toner stains once offset on the fixing roller are transferred to the pressure roller. The temperature of the pressure roller is lower than that of the fixing roller, and the transferred toner stain does not always exist on the pressure roller in a completely melted state. Further, since the toner image on the surface of the sheet does not come into contact with the pressure roller, toner stains are rarely carried on the toner image, and there is a drawback that stains are accumulated once they are soiled. When toner stains are accumulated on the pressure roller, the releasability of the pressure roller deteriorates, so that the sheet (particularly when the sheet is an OHP film) is wound around the pressure roller or accumulated in some cases. There is a problem that toner stains stain the back surface of the sheet at a stretch.

Next, on-demand (On Deman)
The d) type fixing device enables quick start and power saving as compared with the above-mentioned heat roller type fixing device. In the on-demand method, instead of the halogen heater and fixing roller in the heat roller method, a heater such as ceramics and a thin film such as polyimide are used to reduce the heat capacity of the fixing device to enable quick start and power saving. There is.

In such an on-demand type fixing device, since the heat capacity is small and the temperature response is good, it is not necessary to preheat the fixing device and fine temperature control can be performed. You can now turn off the power.

However, in the on-demand type fixing device, when the temperature control as described above is performed, the pressure roller is not heated except when the paper is passed, so that the temperature is less likely to rise than in the heat roller type. For this reason, the toner stains offset to the fixing film and transferred to the pressure roller do not melt on the pressure roller, but remain almost fixed on the pressure roller.

Due to this state, the toner stains on the pressure roller could hardly be cleaned when the sheet was passed. For example, the toner stain is described in JP-A-3-5.
Even if the cleaning paper disclosed in Japanese Patent No. 8074, that is, the paper on which the solid image is fixed, is cleaned, it cannot be completely removed. In some cases, the toner of the solid image on the cleaning paper may be peeled off by the toner on the pressure roller to accelerate the contamination of the pressure roller.

Therefore, a step-feed cleaning mode is adopted in which heating is performed with the fixing device stopped to melt the toner on the pressure roller and then the toner is rotated by the fixing nip.

The step feed cleaning mode will be described with reference to the flowchart of FIG. 5 and the drawing of the fixing device in FIG.

First, in the start state (S1), the fixing device 11 is in the standby state. In this state, when the user determines that cleaning is required, the image forming apparatus is switched to the cleaning mode by a signal from the operation panel of the apparatus main body M, the host computer (not shown), or the like (S).
2). In the image forming apparatus in the cleaning mode, a cleaning sheet P (which means a sheet P used for cleaning and is generally the same as an ordinary recording material P. Hereinafter, appropriately referred to as “paper”) is fed. Start (S
3), one sheet of paper on which an image as shown in FIG. 6 is formed is sent to the fixing device 11. In Figure 6, the black belt is diagonal
This is to prevent the pressure roller from being wrapped around. Furthermore,
The user may be notified by including an article such as “cleaned”.

Here, the time for the leading edge of the paper to reach the fixing nip N is the transportation speed of the paper and the top sensor 9 for the leading edge of the paper.
Can be calculated from the time when the paper has passed through, and similarly, the time when the leading edge of the paper leaves the nip N can be calculated. The detection of whether or not the leading edge of the paper has exited the fixing nip N may be performed by disposing a sensor downstream of the fixing nip and detecting the leading edge of the paper. When it is detected that the leading edge of the paper leaves the nip N (S4), the motor 2
9 is stopped to stop the rotation of the fixing film 25 and the pressure roller 26, the ceramic heater 20 (hereinafter appropriately referred to as "heater 20") is turned on (S5), and the timer time t is set to 0. Then, heating by the heater 20 in the nip is started (S6, S7).

Although the heater 20 is turned on at this point in the flow chart of FIG. 5, it is turned on before that.
The sliding torque of the fixing film 25 may be reduced by adjusting the temperature at a temperature lower than that during printing. this is,
This utilizes that the viscosity of the grease applied to the inner surface of the fixing film 25 decreases as the temperature rises. Furthermore, in order to soften the adhered substances such as toner on the surface of the pressure roller 26 and make it easy to attach to the paper which is a cleaning sheet, the surface of the pressure roller 26 is warmed to some extent before the paper enters the nip N. You can leave it. In this case, it is necessary to rotate the pressure roller 26 for a few rotations while maintaining the heater 20 at the same high temperature as during printing.

In any case, the timer starts counting at the same time when the motor 29 is stopped (that is, the rotation of the fixing film 25 and the pressure roller 26 is stopped). It is checked whether or not the time t of the timer has exceeded the heating time t1 for softening the toner or the like adhering to the surface of the pressure roller 26 and adhering it to the paper (S8). Alternatively, it may be determined that the temperature of the heater 20 detected by the thermistor 21 exceeds a predetermined temperature. The predetermined temperature is preferably the softening point or melting point of the toner. After once softening the adhering material on the surface of the pressure roller in this way, the motor 29 is activated to convey the paper by the nip width a (S9), and the adhering material is peeled off from the surface of the pressure roller 26 to remove the paper. Transfers to the back side.

As described above, the pressure roller 26 is operated while the paper is stopped.
By softening the toner on the surface, the softened toner can enter the unevenness of the paper and be attached to the paper.

It is possible to clean the entire surface of the pressure roller 26 by repeating the above-described softening of the deposit and feeding of the paper for the nip width a for one rotation of the pressure roller 26.

In this conventional example, after the paper is fed by the nip width a in S9, the motor 29 is stopped to stop the rotation of the pressure roller 26 and the fixing film 25 (S10).
Until the trailing edge of the paper enters the nip N, S6 to S11
repeat.

The rear end of the paper used for cleaning has a nip N.
When it is entered (S11), the motor 29 is rotated at a regular constant speed (S12), and when it is determined that the discharge from the nip N is completed (S13), the cleaning mode is ended (S14). The timing for ending this cleaning may be such that the entire surface of the pressure roller 26 is stopped at least once in the nip N even after the trailing edge of the paper has entered the nip N.

By the above method, the fixing member such as the pressure roller and the fixing film can be effectively cleaned.

[0023]

In recent years, the speed of printers has increased and the drive torque of the main body has increased.
In high speed printers, it is necessary to increase the size of the drive motor. However, when a drive motor of a certain size or more is needed, it is better to use two small drive motors and drive the photosensitive drum and the fixing device separately than to drive the entire printer body with a single motor. A two-motor system is adopted because it can reduce the cost and space. Further, in the two-motor system, since the abrasion of the drum can be suppressed by the independent drive control of the photosensitive drum, the two-motor system is often adopted also from the viewpoint of extending the life of the CRG.

When the step feed type cleaning mode of the fixing device as in the above-mentioned conventional example is performed in the two-motor system as described above, the feed amount for one step is different due to the variation of the starting characteristics of the two motors, and the transfer is performed. If the feed amount is less than the feed amount for fixing, the paper may be attracted between the transfer and the fixing, and the photosensitive drum or the transfer roller may be scratched, resulting in an image defect. Furthermore, there is a problem in that the drive system is damaged due to step-out or breakage of the drive motor / gear due to the drawing of the paper between the transfer and the fixing.

[0025]

In order to solve the above problems, in the present invention, a uniformly charged photosensitive member is exposed to form an electrostatic latent image, and the electrostatic latent image is developed with a developer. Then, the developed image is transferred onto the transfer material by the transfer nip formed by the photoreceptor and the transfer material, and the image of the transfer material is formed with a fixing nip between a pair of fixing members at least one of which is rotatable, In an electrophotographic image forming apparatus which heats and fixes by inserting into the fixing nip and outputs the image, the image forming apparatus includes a photoconductor driving motor and a fixing member driving motor, and the rotatable fixing member. Has a fixing member cleaning mode that holds the sheet in the fixing nip and conveys the sheet while repeating rotation and stop. The relationship between the sheet feeding amount during rotation of the fixing member cleaning mode is By a ram drive motor ≧ fuser drive motor, transfer - inquiry of paper between the fixing can be prevented, there is no damage the photoreceptor and the transfer roller, it is possible to prevent the occurrence of image defects. Further, it is possible to prevent damage such as step-out and breakage of the drive motor and gear.

Further, the uniformly charged photoconductor is exposed to form an electrostatic latent image, the electrostatic latent image is developed with a developer, and the developed image is formed by the photoconductor and the transfer material. An electrophotographic apparatus which transfers a transfer nip onto a transfer material, forms a fixing nip between a pair of fixing members, at least one of which is rotatable, and inserts the image of the transfer material into the fixing nip for heating and fixing to output the image. In the image forming apparatus of the type, the image forming apparatus has a photosensitive member driving motor and a fixing member driving motor separately, and the rotatable fixing member holds the sheet at the fixing nip, and then rotates and stops. A fixing member cleaning mode in which the sheet is conveyed while repeating the above, and the driving of the motor is precisely controlled by repeating the rotation and stop of the fixing member after the trailing edge of the sheet passes the photoconductor. Ku, thereby preventing damage to the image defects and the drive system of the photosensitive member and transfer roller scratches caused at a low cost.

Further, the uniformly charged photoconductor is exposed to form an electrostatic latent image, the electrostatic latent image is developed with a developer, and the developed image is formed by the photoconductor and the transfer material. An electrophotographic apparatus which transfers a transfer nip onto a transfer material, forms a fixing nip between a pair of fixing members, at least one of which is rotatable, and inserts the image of the transfer material into the fixing nip for heating and fixing to output the image. In the image forming apparatus of the type, the image forming apparatus has a photosensitive member driving motor and a fixing member driving motor separately, and the rotatable fixing member holds the sheet at the fixing nip, and then rotates and stops. By having a fixing member cleaning mode that conveys the sheet while repeating the above, and by providing a mechanism that releases the drive of the photoconductor during the fixing member cleaning mode and makes it rotatable.
It is possible to take a long cleaning area in the sheet without precisely controlling the drive of the motor, and
It is possible to prevent image defects and damage to the drive system due to scratches on the photoconductor / transfer roller.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION (Example) (First Example) Hereinafter, an embodiment of the present invention will be described.

FIG. 1 shows an image forming apparatus according to the present invention, that is, an image forming apparatus provided with a fixing device according to the present invention. It should be noted that FIG. 1 is a vertical cross-sectional view showing a schematic configuration of a laser beam printer as an example of an image forming apparatus according to the present invention. In the following description, among the recording materials, those used for normal fixing are referred to as “recording material P”, and those used for cleaning the fixing member are referred to as “sheet P”.

First, the structure of a laser beam printer (hereinafter referred to as "image forming apparatus") will be described with reference to FIG.

The laser beam printer shown in the figure includes a drum type electrophotographic photosensitive member (hereinafter referred to as "photosensitive drum") 1 as an image bearing member. The photosensitive drum 1 is rotatably supported by the apparatus main body M, and is rotationally driven in the direction of arrow R1 at a predetermined process speed by a driving unit (not shown).

Around the photosensitive drum 1, a charging roller (charging device) 2, an exposing means 3, and an exposing means 3 in order along the rotation direction thereof.
A developing device 4, a transfer roller (transfer device) 5, and a cleaning device 6 are provided.

A paper feed cassette 7 containing a recording material P such as paper is arranged below the main body M of the apparatus, and the paper feed roller 15 and the paper feeding roller 15 are carried in order along the carrying path of the recording material P. A roller 8, a top sensor 9, a conveyance guide 10, a fixing device 11 according to the present invention, a conveyance roller 12, a paper discharge roller 13, and a paper discharge tray 14 are arranged.

Next, the operation of the image forming apparatus having the above configuration will be described.

The photosensitive drum 1 rotatively driven in the direction of arrow R1 by the photosensitive drum driving means (not shown) is uniformly charged by the charging roller 2 to have a predetermined polarity and a predetermined potential. The surface of the photosensitive drum 1 after charging is subjected to image exposure L based on image information by the exposing means 3 such as a laser optical system, and the charge of the exposed portion is removed to form an electrostatic latent image. The electrostatic latent image is developed by the developing device 4. The developing device 4 has a developing roller 4a, and applies a developing bias to the developing roller 4a to attach toner to the electrostatic latent image on the photosensitive drum 1 to develop (visualize) a toner image.

The toner image is transferred onto the recording material P such as paper by the transfer roller 5. The sheet P is housed in the sheet feeding cassette 7, fed by the sheet feeding roller 15, conveyed by the conveying roller 8, and passes through the top sensor 9 to transfer nip between the photosensitive drum 1 and the transfer roller 5. Transported to the department. At this time, the leading edge of the recording material P is detected by the top sensor 9, and the recording material P is synchronized with the toner image on the photosensitive drum 1. A transfer bias is applied to the transfer roller 5, whereby the toner image on the photosensitive drum 1 is transferred to a predetermined position on the recording material P.

The recording material P, which has an unfixed toner image on the surface by transfer, is fixed to the fixing device 11 along the conveyance guide 10.
Then, the unfixed toner image is heated and pressed to be fixed on the surface of the recording material P. The fixing device 11 will be described in detail later.

The recording material P on which the toner image has been fixed is conveyed by the conveying roller 12, and is ejected by the paper ejection roller 13 onto the paper ejection tray 14 on the upper surface of the apparatus main body.

On the other hand, the photosensitive drum 1 after the toner image transfer is
Toner remaining on the surface without being transferred to the recording material P (transfer residual toner) is removed by the cleaning blade 6a of the cleaning device 6 and is used for the next image formation.

By repeating the above operation, it is possible to form images one after another. The image forming apparatus according to the present exemplary embodiment is 600 dpi, 45 sheets / minute (process speed of about 2
Printing can be performed at a printing speed of 66 mm / sec).

Next, an example of the fixing device 11 according to the present invention will be described in detail with reference to FIG. The drawing is a vertical cross-sectional view taken along the conveying direction of the recording material P (direction of arrow K).

The fixing device 11 shown in the figure includes a fixing film 25, which is a film-like fixing rotating member, and a fixing film 2.
A pressure roller 26 as a fixing rotary member, which is in contact with 5;
A ceramic heater (heater) 20 that heats the toner through the fixing film 25, a temperature control unit 27 that controls the temperature of the ceramic heater 20, and a fixing unit rotation control unit 28 that controls the conveyance of the recording material P used for cleaning. And are configured as main constituent members.

The ceramic heater 20 is a resistance heating element, and is formed by forming a resistor pattern 20b on a heat-resistant substrate 20a such as alumina by printing, and coating the surface thereof with a glass layer 20c. It is formed to be long in the left-right direction (that is, the direction perpendicular to the paper surface) toward the conveyance direction of the material P (arrow K direction), that is, longer than the width of the recording material P. The ceramic heater 20 is a device main body M.
It is supported by a heater holder 22 attached to the. The heater holder 22 is a member formed of heat-resistant resin in a semicircular shape, and also functions as a guide member for guiding the rotation of the next fixing film 25.

The heat capacity of the fixing film 25 is smaller than that of the pressure roller 26. The fixing film 25 is formed of a heat-resistant resin such as polyimide in a cylindrical shape, and has a release layer such as a fluororesin on the surface. Fixing film 2
Reference numeral 5 has a total thickness of 100 μm or less, and is loosely fitted to the above-mentioned ceramic heater 20 and heater holder 22. The fixing film 25 is pressed against the ceramic heater 20 by a pressure roller 26 described later, so that the back surface of the fixing film 25 is brought into contact with the lower surface of the ceramic heater 20. The fixing film 25 is configured to rotate in the arrow R25 direction as the recording material P is conveyed in the arrow K direction by the rotation of the pressure roller 26 in the arrow R26 direction. The fixing film 25
The left and right ends of the ceramic heater 20 are regulated by guide portions (not shown) of the heater holder 22 so as not to shift in the longitudinal direction of the ceramic heater 20. Grease is applied to the inner surface of the fixing film 25 in order to reduce sliding resistance between the fixing film 25 and the ceramic heater 20 or the heater holder 22.

The pressure roller 26 comprises a metal cored bar 26a and a heat-resistant release layer 26b having elasticity such as silicone rubber provided on the outer peripheral surface of the metal cored bar 26a. From fixing film 25 to ceramic heater 2
It is pressed against 0 to form a fixing nip portion N (hereinafter simply referred to as “nip N”) with the fixing film 25. If the width (nip width) of the nip N in the rotation direction of the pressure roller 26 (that is, the conveying direction of the recording material P) is a, then the nip width a preferably heats the toner on the recording material P. The pressure is set so that it can be pressurized.

The fixing device rotation control means 28 includes the pressure roller 2
It has a motor 29 for rotating 6 and a CPU 30 for controlling the rotation of the motor 29. As the motor 29, for example, a stepping motor, a DC motor, or the like can be used, and the rotation of the pressure roller 26 can be continuously performed in the direction of arrow R26 or intermittently at a predetermined angle. That is, the sheet P described later can be stepwise fed while repeating the rotation and stop of the pressure roller 26.

The temperature control means 27 is the ceramic heater 2
It has a thermistor 21 which is a temperature detecting means attached to the back surface of 0, and a CPU 23 which controls the triac 24 based on the temperature of the ceramic heater 20 detected by the thermistor 21 and controls the energization of the ceramic heater 20.

As described above, in the fixing device 11, the recording material P carrying the unfixed toner is nipped and conveyed by the nip N by the rotation of the pressure roller 26 in the direction of the arrow R26, and the sheet is moved by the ceramic heater 20. Heat the upper toner. At this time, by controlling the rotation of the pressure roller 26 by the fixing device rotation control means 28, the feeding of the sheet P can be appropriately controlled, and the temperature control means 27 appropriately controls the temperature of the ceramic heater 20. It is something that can be controlled.

Next, the cleaning mode of this embodiment will be described with reference to the flowchart of FIG.

First, in the start state (S101), the fixing device 11 is in the standby state. In this state, when the user determines that cleaning is required, the image forming apparatus is switched to the cleaning mode by a signal from the operation panel of the apparatus main body M, a host computer (not shown), or the like (S102). The image forming apparatus in the cleaning mode starts feeding the cleaning sheet P (paper) (S103) and sends one sheet of paper on which an image as shown in FIG. 6 is formed to the fixing device 11. The black belt is oblique in the figure to prevent the black belt from being wound around the pressure roller. Further, an article such as “cleaned” may be included to notify the user.

Here, the time required for the front end of the paper to reach the fixing nip N can be calculated from the paper conveyance speed and the time taken for the front end of the paper to pass the top sensor 9. Incidentally, the detection of whether or not the leading edge of the paper has exited the nip N may be performed by disposing a sensor downstream of the nip and detecting the leading edge of the paper. If it is detected that the leading edge of the paper has exited the fixing nip N (S104), then it is detected that the trailing edge of the paper has exited the transfer nip by the same method (S105), and the photosensitive drum motor and the fuser motor are turned on. Stop and fix film 2
The rotation of 5 and the pressure roller 26 is stopped, the energization of the heater 20 is turned on (S106), the time t of the timer is set to 0, and heating by the heater 20 in the nip is started. (107, 108).

Although the heater 20 is turned on at this point in the flow chart of FIG. 3, the heater 20 is turned on before that, and the fixing film 2 is adjusted at a temperature lower than that at the time of printing.
The sliding torque of 5 may be reduced. This utilizes the fact that the viscosity of the grease applied to the inner surface of the fixing film 25 decreases as the temperature rises.
Furthermore, in order to soften the adhered substances such as toner on the surface of the pressure roller 26 and make it easy to attach to the paper which is a cleaning sheet, the surface of the pressure roller 26 is warmed to some extent before the paper enters the nip N. You can leave it. In this case, it is necessary to rotate the pressure roller 26 for a few rotations while maintaining the heater 20 at the same high temperature as during printing.

In any case, the timer starts counting at the same time when the fixing device drive motor 29 is stopped (that is, the rotations of the fixing film 25 and the pressure roller 26 are stopped). It is checked whether or not the time t of the timer has exceeded the heating time t1 for softening the toner or the like adhering to the surface of the pressure roller 26 and adhering it to the paper (S108). Alternatively, it may be determined that the temperature of the heater 20 detected by the thermistor 21 exceeds a predetermined temperature. The predetermined temperature is preferably the softening point or melting point of the toner. In this way, after temporarily softening the adhered matter on the surface of the pressure roller, the motor 29 is started to move the paper to the nip width a.
After being conveyed by the amount (S109), the adhered matter is separated from the surface of the pressure roller 26 and transferred to the back surface of the paper.

As described above, the pressure roller 26 is operated while the paper is stopped.
By softening the toner on the surface, the softened toner can enter the unevenness of the paper and be attached to the paper.

It is possible to clean the entire surface of the pressure roller 26 by repeating the above-described softening of the adhered matter and feeding for the nip width a of the paper for one rotation of the pressure roller 26.

In this embodiment, the photosensitive drum is set to 2 in S109.
After feeding the fixing device motor for 20 ms for 5 ms, both motors are stopped to stop the rotation of the pressure roller 26 and the fixing film 25 (S110). Then, S106 to S111 are repeated until the trailing edge of the paper enters the nip N.

The rear end of the paper used for cleaning has a nip N.
When it is entered (S111), the photosensitive drum motor and the fixing motor are rotated at a regular constant speed (S112), and when it is determined that the discharge from the nip N is completed (S113), the cleaning mode is ended (S114). ). The timing of ending this cleaning may be such that the entire surface of the pressure roller 26 is stopped at least once in the fixing nip N even after the trailing edge of the paper has entered the nip N.

In this embodiment, the step feed amount in transfer is made larger by making the drive time of the photosensitive drum drive motor slightly longer than the drive time of the fixing device drive motor. As a result, it is possible to prevent the drawing of the paper between the transfer and the fixing, and to prevent the photosensitive drum and the transfer roller from being damaged. Further, it is possible to prevent damage to the drive system such as step-out and damage of the drive motor and gears.

Table 1 shows the relationship between the driving time of the photosensitive drum drive motor and the fixing device drive motor and the step feed amount.

[0060]

[Table 1]

As can be seen from Table 1, in order to reliably feed the paper stepwise, the drive time of the fixing device drive motor is set to 10
It must be more than ms. Further, a step feed amount slightly smaller than the nip width (about 8 mm) is desirable in order to effectively perform the fixing device cleaning. For this reason, the driving time of the fixing device drive motor is preferably about 20 ms. Therefore, in order to surely increase the step feed amount in the transfer from the fixing, it is necessary to set the driving time to about 25 ms or more so that the feed amount larger than the maximum value of 10 mm in the step feeding amount in the fixing can be obtained. It should be noted that in Table 1, the step feed amount varies with the same motor drive time because of variations in the motor start-up characteristics and variations in the load torque. The photosensitive drum motor having a smaller load torque than the fuser drive motor However, the step feed amount is large.

Next, in the case where the step feed amount of the photosensitive drum is equal to or larger than the fixing device as in the present embodiment and in the case where it is not, the image defect and the damage to the drive system due to the scratches on the photosensitive drum and the transfer roller occur. Table 2 shows the results of examining whether there is a difference.

[0063]

[Table 2]

From the above table, it can be seen that when the step feed amount of the fixing device is made larger than that of the photosensitive drum in the fixing device cleaning mode, a defective image (particularly a graphic image) is generated due to scratches on the photosensitive drum / transfer roller. In addition, the drive system is greatly damaged, and the drive gear may be damaged during step out of the drive gear or in the latter half of the life of the main body.

In this embodiment, the relationship between the step feed amount of transfer and fixing is controlled by changing the driving time of the photosensitive drum and the fixing device. However, the method of controlling the step feed amount by combining motors having different starting characteristics is used. However, the same effect was obtained.

As described above, in the step feed type fixing device cleaning mode, by setting the photosensitive drum feed amount ≧ the fixing device feed amount, the image defect due to the damage of the photosensitive drum / transfer roller, the drive motor / gear It is possible to prevent damage to the drive system such as step out and damage.

(Second Embodiment) In this embodiment, after the front end of the paper passes through the fixing nip, the paper is fed at a constant speed until the rear end of the paper passes through the transfer nip, and then the step feed is started to perform cleaning. It was The other conditions are the same as those in the above-mentioned embodiment, and the repetitive description will be omitted.

FIG. 4 shows the cleaning mode method of this embodiment.
Will be explained.

First, in the start state (S201), the fixing device 11 is in the standby state. In this state, when the user determines that cleaning is required, the image forming apparatus is switched to the cleaning mode by a signal from the operation panel of the apparatus main body M, the host computer (not shown), or the like (S202). The image forming apparatus in the cleaning mode starts feeding the cleaning sheet P (paper) (S203), and sends one sheet of paper on which an image as shown in FIG. 6 is formed to the fixing device 11. When it is detected that the leading edge of the paper has exited the fixing nip N (S204), then it is detected that the trailing edge of the paper has exited the transfer nip (S205), the photosensitive drum and the fixing unit motor are stopped, and the fixing film is stopped. 25, the rotation of the pressure roller 26 is stopped, the heater 20 is energized (S206), the timer time t is set to 0, and
The heating by the heater 20 in the nip is started. (20
7, 208). It is checked whether or not the time t of the timer has exceeded the heating time t1 for softening the toner or the like adhering to the surface of the pressure roller 26 and adhering it to the paper (S209). In this way, once the adhered matter on the surface of the pressure roller is softened, the motor 29 is activated to convey the paper by the nip width a (S210), and the adhered matter is
It peels from the surface of the pressure roller 26 and transfers to the back surface of the paper.

It is possible to clean the entire surface of the pressure roller 26 by repeating the above-described softening of the adhered matter and feeding for the nip width a of the paper for one rotation of the pressure roller 26.

The rear end of the paper used for cleaning has a nip N.
When entering (S211), the photosensitive drum motor and the fixing device motor are rotated at a regular constant speed (S212), and it is determined that the paper discharge from the fixing nip N is completed (S21).
3) Then, the cleaning mode is ended (S214).

According to the method of this embodiment, it is not necessary to precisely control the photosensitive drum motor and the fixing device motor.
It is not necessary to use an expensive drive motor such as a stepping motor, and even when using a DC motor, it is not necessary to manage the motor starting characteristics in detail in order to set the step feed amount to a predetermined amount, and it is possible to realize at low cost. It is possible.

Table 3 shows the results of examining the difference in the presence or absence of image defects between the case where the cleaning is performed by the fixing device cleaning method of this embodiment and the case where the cleaning is performed while holding the paper in both the transfer / fixing nip as in the conventional case. Indicates.

[0074]

[Table 3]

From Table 3, in the conventional cleaning method, when the step feed amount is larger than the transfer amount for the fixing,
In contrast to the case where a defective image is generated due to scratches on the photosensitive drum / transfer roller, the cleaning method according to the present embodiment does not cause a defective image due to scratches on the photosensitive drum / transfer roller even when the feeding amount is larger in fixing than in transfer. I understand.

Next, Table 4 shows the results of examining the presence or absence of damage to the drive system.

[0077]

[Table 4]

From Table 4, in the conventional cleaning method, when the step feed amount is larger than the transfer amount for the fixing,
The load on the drive motor / gear causes step-out / cracking, while the cleaning method of this embodiment causes step-out of the drive motor / gear even when the feeding amount is larger in fixing than in transfer.・ It can be seen that no cracks occur.

As described above, in the fixing device cleaning mode, the step feed start position is set after the trailing edge of the paper has passed through the transfer nip, and the surface of the photosensitive drum or the transfer roller is attracted by the attraction of the paper between the transfer and the fixing. Hurt,
It is possible to prevent image defects from occurring. Further, it is possible to prevent damage to the drive system such as step-out and damage of the drive motor and gear.

(Third Embodiment) In this embodiment, a clutch is provided in the drive system of the photosensitive drum, the clutch is turned off during the step feed in the cleaning mode, and the photosensitive drum is driven to rotate by the paper pulled by the fixing device. did. still,
The other conditions are the same as those in the above-mentioned embodiment, and the repetitive description is omitted.

By providing a clutch in the drive system of the photosensitive drum as in this embodiment, the photosensitive drum and the transfer roller are damaged or driven because the photosensitive drum is driven to rotate according to the step feed amount of the fixing device. It does not damage the drive system such as motors and gears. Further, since it is not necessary to control and manage the variation in the step feed amount of the motor, and the step feed start position can be advanced as compared with the second embodiment, the cleaning area within one sheet can be made long. it can.

Table 5 shows the presence or absence of image defects due to scratches on the photosensitive drum and the transfer roller, with and without the clutch provided in the drive system. At this time, the relationship between the feeding amounts of the photosensitive drum driving motor and the fixing device driving motor was confirmed in the state of photosensitive drum motor <fixing device motor.

[0083]

[Table 5]

As can be seen from Table 5, scratches on the photosensitive drum and the transfer roller can be prevented.

Next, Table 6 shows whether or not the drive system is damaged due to the presence or absence of the clutch.

[0086]

[Table 6]

It can be seen from Table 6 that by providing a clutch on the drive system of the photosensitive drum, damage to the drive system such as step-out or damage of the drive motor / gear can be prevented.
In this embodiment, the clutch provided in the drive system of the photosensitive drum is one that can rotate in both forward and reverse directions. However, the photosensitive drum rotates in the forward direction only in order to prevent the photosensitive drum from rotating in the reverse direction and soiling the charging roller. It is preferable to use a one-way clutch.

As described above, by providing the photosensitive drum drive system with the clutch, it is possible to prevent image defects due to scratches on the photosensitive drum / transfer roller, and also to prevent damage to the drive system.

[0089]

As described above, when the step-feed type cleaning mode is performed in the two-motor type image forming apparatus according to the present invention, the photosensitive drum or the transfer roller is damaged or the drive system such as the motor or gear is used. It can prevent damage.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an image forming apparatus according to the present invention.

FIG. 2 is a diagram of a heat fixing device according to the first embodiment

FIG. 3 is a diagram illustrating a flowchart of a cleaning mode according to the first embodiment.

FIG. 4 illustrates a flowchart of a cleaning mode according to a second exemplary embodiment.

FIG. 5 is a diagram showing a flowchart of a cleaning mode of a conventional example.

FIG. 6 is a diagram showing an image pattern used in a cleaning mode.

[Explanation of symbols]

1. Image carrier (photosensitive drum) 5: Transfer roller 9 ... Top sensor 11. Fixing device 12: Transport roller pair 20 Heating means (ceramic heater) 21 ... Thermistor 23 ... CPU 24 Triac 25: Fixing member (fixing film) 26 ... Fixing member (pressure roller) 27 ... Temperature control means 28 ... Rotation control means 29: Fixer drive motor 30 ... CPU N: Fixing nip P: Recording material, cleaning sheet

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Wataru Nihonyanagi             3-30-2 Shimomaruko, Ota-ku, Tokyo             Non non corporation (72) Inventor Hiroto Hasegawa             3-30-2 Shimomaruko, Ota-ku, Tokyo             Non non corporation F-term (reference) 2H027 DA39 DC05 ED02 ED25 EE04                       EF13 FA30 GB05                 2H033 AA08 BA09 BA10 BA11 BA22                       BA32 BA48 BB29 BB30 BB33                       BB37 BE03 CA07 CA35 CA40                       CA44 CA57

Claims (3)

[Claims] 1. A uniformly charged photoreceptor is exposed to form an electrostatic latent image, the electrostatic latent image is developed with a developer, and the developed image is formed by the photoreceptor and a transfer material. An electrophotographic image which is transferred onto a transfer material by a transfer nip, a fixing nip is formed between a pair of fixing members, at least one of which is rotatable, and which is heated and fixed by being inserted into the fixing nip to output the image. In the image forming apparatus of the type, the image forming apparatus has a photoconductor drive motor and a fixing member drive motor separately, and the rotatable fixing member holds a sheet at the fixing nip, and then rotates and stops. And a fixing member cleaning mode in which the sheet is conveyed while repeating the above, and the relationship of the sheet feeding amount during rotation of the fixing member cleaning mode is photosensitive drum drive motor ≧ fixer drive motor An image forming apparatus. 2. A uniformly charged photosensitive member is exposed to form an electrostatic latent image, the electrostatic latent image is developed with a developer, and the developed image is formed by the photosensitive member and a transfer material. An electrophotographic image which is transferred onto a transfer material by a transfer nip, a fixing nip is formed between a pair of fixing members, at least one of which is rotatable, and which is heated and fixed by being inserted into the fixing nip to output the image. In the image forming apparatus of the type, the image forming apparatus has a photoconductor drive motor and a fixing member drive motor separately, and the rotatable fixing member holds a sheet at the fixing nip, and then rotates and stops. An image forming apparatus having a fixing member cleaning mode in which the sheet is conveyed while repeating the above steps, and the fixing member is repeatedly rotated and stopped after the trailing edge of the sheet passes through the photoconductor. 3. A uniformly charged photosensitive member is exposed to form an electrostatic latent image, the electrostatic latent image is developed with a developer, and the developed image is formed by the photosensitive member and a transfer material. An electrophotographic image which is transferred onto a transfer material by a transfer nip, a fixing nip is formed between a pair of fixing members, at least one of which is rotatable, and which is heated and fixed by being inserted into the fixing nip to output the image. In the image forming apparatus of the type, the image forming apparatus has a photoconductor drive motor and a fixing member drive motor separately, and the rotatable fixing member holds a sheet at the fixing nip, and then rotates and stops. An image forming apparatus having a fixing member cleaning mode in which the sheet is conveyed while repeating the above steps, and a mechanism for releasing the drive of the photosensitive member to rotate the photosensitive member in the fixing member cleaning mode is provided.