JP2011209444A - Image heating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image heating device capable of achieving a reduction in size and cost thereof by preventing an increase in a take-up amount of a web, and satisfactorily performing cleaning even in the case where a mode is erroneously specified.SOLUTION: The fixing device 30 is configured to, when the cleaning surface of the fixing web 40 for cleaning the surface of a fixing roller 31 gets dirty, convey the fixing web 40 by a take-up roller 41 so as to refresh the cleaning surface of the fixing web 40. The fixing device 30 includes a CPU 200 configured to convey the fixing web 40 by means of the take-up roller 41 and refresh the cleaning surface when a fixing drive motor current value I being a physical quantity that varies according to an increase in frictional force on the cleaning surface of the fixing web 40 exceeds a predetermined threshold Iduring the rotation of the fixing roller 31 and a pressure roller 32.

Description

  The present invention relates to an image heating apparatus such as a fixing apparatus for fixing a toner image used in an image forming apparatus such as a copying machine, a laser beam printer, a facsimile, or a multifunction machine combining these functions. The fixing device is used for timely image forming processes such as an electrophotographic system, an electrostatic recording system, and a magnetic recording system. That is, the fixing device uses a toner made of heat-meltable resin or the like to transfer an unfixed toner image formed on the surface of the recording material corresponding to the target image information by a transfer method or a direct method. This is an apparatus of a system that heat-fixes the image as a permanently fixed image. Examples of the recording material include paper, printing paper, transfer material sheet, OHT sheet, glossy paper, glossy film, electrofax paper, and electrostatic recording paper. Here, the image heating apparatus of the present invention includes not only the above-described fixing apparatus but also an image heating apparatus that presupposes an unfixed image on a recording material, and an image such as a gloss by reheating a recording material that bears the image. An image heating apparatus for modifying the surface property is also included.

In general, an image forming apparatus includes a fixing device that fixes an unfixed toner image carried on a recording material on the recording material by heat and pressure. In such a fixing device, a recording material carrying toner is fed into a fixing nip portion formed by press-contacting a fixing roller and a pressure roller, conveyed while being nipped, and the toner is transferred onto the recording material by heat and pressure. What fixes is common.
However, in such a fixing device, as the image formation is continued, a phenomenon occurs in which the toner gradually transfers and adheres to the surface of the fixing roller in contact with the toner carrying surface of the recording material. This is caused by deterioration of the surface property of the surface of the fixing roller, electrostatic action, excessive or insufficient amount of heat given from the fixing roller to the recording material, and the like. In particular, this phenomenon is likely to occur when the temperature of the fixing roller is higher or lower than an appropriate temperature, and the amount of toner transferred to the surface of the fixing roller increases. The toner adhering to the surface of the fixing roller is transferred again to the recording material at the fixing nip portion, and becomes a stain that contaminates the recording material.
Therefore, in order to prevent the recording material from being stained, a web cleaning device is provided that removes toner adhering to the surface of the fixing roller from the surface of the fixing roller by sliding the web against the fixing roller.

A conventional web cleaning apparatus is shown in FIG. The fixing web 140 is stretched and held around a feed roller 142, a contact roller 130, and a take-up roller 141. The fixing web 140 rubs against the fixing roller 131 at a cleaning nip N formed by the fixing roller 131 and the contact roller 130 in which the heater 133 is disposed. A portion of the cleaning nip N of the fixing web 140 forms a cleaning surface. The abutting roller 130 is urged by a spring 150 that is a pressing unit and presses against the fixing roller 131. The toner adhering to the surface of the fixing roller 131 is collected (wiped off) by the fixing web 140 at the cleaning nip N.
However, as image formation continues and the amount of toner collected in the cleaning nip N increases, the cleaning surface of the fixing web 140 becomes dirty, the toner collecting performance from the fixing roller 131 to the fixing web 140 gradually decreases, and the recording material becomes dirty. Will occur.
In order to solve this problem, in recent years, based on information such as the number of prints and the number of rotations of the fixing roller, the take-up roller 141 is rotated by a predetermined amount at a predetermined timing, and a new fixing web is brought into the cleaning nip N. Devices that perform predictive control for supplying 140 are known.
For example, a method of performing a fixing web winding operation every time a series of fixing jobs is completed has been proposed (see Patent Document 1).
Further, when an abnormality such as JAM occurs, a large amount of toner may be transferred to the surface of the fixing roller 131 and a large amount of toner may enter the cleaning nip N. In such a case, there is a problem that cleaning failure occurs or abnormal noise due to stick-slip occurs. As a countermeasure, when an abnormality such as JAM is detected, an apparatus that performs predictive control for supplying a larger number of fixing webs than when forming a normal image, assuming a large amount of dirt on the surface of the fixing roller. Are known.

Japanese Patent Laid-Open No. 11-24484

  The technique of Patent Document 1 is predictive control in which a fixing web is wound up every time a series of fixing jobs are completed. For this reason, even if the amount of toner collected in the cleaning nip N is small and the cleaning surface of the fixing web is not very dirty, the fixing web is fed by a predetermined amount. Therefore, in order to be able to perform cleaning over a long period of time, it is necessary to increase the initial fixing web winding amount wound beforehand on the feed roller, which causes problems that increase the size and cost of the apparatus.

In general, the user designates a print mode in accordance with the paper type, and sets the temperature of the fixing roller optimal for the paper type, thereby ensuring good fixability. However, when the user selects a print mode that is not the print mode that should be selected (hereinafter referred to as mode misdesignation), the temperature of the fixing roller may be significantly different from the appropriate temperature. For example, when printing thick paper in the normal mode for plain paper, a large amount of cold offset toner may be generated because the amount of heat supplied from the fixing device is insufficient. When plain paper is printed in the thick paper mode for thick paper, the amount of heat supplied from the fixing device becomes excessive, and in this case, a large amount of hot offset toner may be generated.
In such a case, a large amount of toner may be transferred to the surface of the fixing roller, and a large amount of toner may enter the cleaning nip N.
However, when such a mode is erroneously specified, an abnormality such as JAM is generally not detected, and a new fixing web is not supplied as after an abnormality has occurred. For this reason, defective cleaning may occur, or abnormal noise may occur due to stick-slip. In some cases, excessive stress is applied to the inside of the fixing device, which may cause damage to parts such as a motor, parts, or a fixing web.

  An object of the present invention is to reduce the size of the apparatus and reduce the cost without increasing the web winding amount, and to achieve good cleaning even when the mode is incorrectly specified.

In order to solve the above problems, an image heating apparatus according to the present invention includes:
In an image heating apparatus for heating a toner image on a recording material,
A web for cleaning toner adhering to the rotating body from above the recording material;
Conveying means for conveying the web;
With
When the cleaning surface that rubs against the rotating body of the web gets dirty, the image heating device transports the web by the transport means and renews the cleaning surface of the web,
When a physical quantity that changes due to an increase in frictional force on the cleaning surface of the web during rotation of the rotating body exceeds a predetermined threshold, the web is transported by the transport means and the cleaning is performed. It has a control means for renewing the surface.

  According to the present invention, it is possible to reduce the size and cost of the apparatus without increasing the web winding amount, and it is possible to satisfactorily perform cleaning even when the mode is incorrectly specified.

7 is a flowchart illustrating a fixing web conveyance control routine according to the first embodiment. 1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment. 1 is a schematic configuration diagram of a fixing device according to a first embodiment. FIG. 6 is a diagram illustrating control of the fixing drive motor and the fixing web conveyance motor according to the first embodiment. 1 is an external view of a fixing drive motor according to Embodiment 1. FIG. 1 is a circuit configuration diagram of a fixing drive motor according to a first embodiment. FIG. 10 is a diagram illustrating a relationship between a torque and a current value of the fixing drive motor according to the first embodiment. The figure which shows the relationship between the toner amount in _NCL , and the electric current value I The figure which shows transition of the electric current value I at the time of image formation operation The figure which shows transition of the electric current value I at the time of fixing web conveyance control implementation The figure which shows transition of the electric current value I at the time of fixing web conveyance control implementation Schematic configuration diagram of a torque sensor according to Embodiment 2 The figure which shows the relationship between the twist angle of the torque sensor which concerns on Example 2, and the output value T. FIG. FIG. 10 is a diagram illustrating control of a fixing drive motor and a fixing web conveyance motor according to the second embodiment. The figure which shows the relationship between the toner amount in _NCL , and the output value T 8 is a flowchart illustrating a fixing web conveyance control routine according to the second embodiment. The figure which shows transition of the output value T at the time of fixing web conveyance control implementation The figure which shows transition of the output value T at the time of fixing web conveyance control implementation Schematic configuration diagram of a conventional fixing device

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be exemplarily described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention only to those unless otherwise specified. .

<Example 1>
(Image forming device)
First, the operation of the image forming unit of the color image forming apparatus according to this example will be described. FIG. 2 shows an image forming unit of the color image forming apparatus according to this example.
The image forming unit forms an electrostatic latent image with exposure light that is turned on based on the exposure time converted by the image processing unit, and develops the electrostatic latent image to form a single color toner image. The single color toner images are superimposed to form a multicolor toner image. The multicolor toner image is transferred to a recording material. Thereafter, the multicolor toner image on the recording material is fixed. The CPU 200 controls the operation of the image forming unit.
Photosensitive drums 22Y, 22M, 22C, and 22K as photoconductors are arranged for each station that forms each monochrome toner image of yellow (Y), magenta (M), cyan (C), and black (K). The photosensitive drums 22Y, 22M, 22C, and 22K are configured by applying an organic optical transmission layer to the outer periphery of an aluminum cylinder, and rotate by receiving a driving force of a driving motor (not shown). The drive motor rotates the photosensitive drums 22Y, 22M, 22C, and 22K in the counterclockwise direction shown in the drawing according to the image forming operation.
Four chargers 23Y, 23M, 23C, and 23K for charging each photosensitive drum for each station are provided as primary charging means. Chargers 23Y, 23M, 23C, 23K
Are provided with sleeves 23YS, 23MS, 23CS, and 23KS, respectively. Each photosensitive drum is charged with each sleeve.
Exposure light to the photosensitive drums 22Y, 22M, 22C, and 22K charged by the chargers is sent from the scanner units 24Y, 24M, 24C, and 24K, respectively. Thus, each scanner unit selectively exposes the surface of each charged photosensitive drum, whereby an electrostatic latent image is formed on each photosensitive drum.
As developing means, in order to visualize the electrostatic latent image, four developing units 26Y, 26M, 26C, and 26K are provided for developing each single color toner for each station. The developing devices 26Y, 26M, 26C, and 26K are provided with sleeves 26YS, 26MS, 26CS, and 26KS, respectively. In this example, toner having a negative charge property is used. A developing bias is applied between the sleeves 26YS, 26MS, 26CS, and 26KS and the corresponding photosensitive drums 22Y, 22M, 22C, and 22K from a power source (not shown). Each single color toner is supplied from each developing device to each photosensitive drum by the developing bias. Thereby, each monochrome toner image is formed on each photosensitive drum. Each developing device is detachable from the image forming apparatus.
The intermediate transfer member 28 is in contact with the photosensitive drums 22Y, 22M, 22C, and 22K, and rotates in the clockwise direction in the figure when the photosensitive drums 22Y, 22M, 22C, and 22K are rotated. The image is transferred. A primary transfer bias is applied between the primary transfer rollers 27Y, 27M, 27C, and 27K and the corresponding photosensitive drums 22Y, 22M, 22C, and 22K from a power source (not shown). Each single color toner image is transferred from each photosensitive drum to the intermediate transfer member 28 by the primary transfer bias. Each single-color toner image is transferred to the same position on the rotating intermediate transfer body 28 to be superimposed, and a multicolor toner image is formed on the intermediate transfer body 28.
The paper feed unit as the paper feed means includes a paper feed cassette 21a and a paper feed tray 21b, in which the recording material 11 is accommodated. The accommodated recording material 11 is conveyed by the paper feed rollers 20 a and 20 b and reaches the registration roller 16. The fact that the recording material 11 has reached the registration roller 16 is detected by a pre-registration sensor 17. At the time of image formation, the registration roller 16 stops the recording material 11 for a predetermined time in accordance with the timing at which the multicolor toner image formed on the intermediate transfer body 28 reaches the secondary transfer rollers 29a and 29b, and then the secondary transfer roller. Transport to 29a, b.
The secondary transfer rollers 29a and 29b are in contact with the intermediate transfer body 28 to convey the recording material 11 while sandwiching them, transfer a multicolor toner image from the intermediate transfer body 28 to the recording material 11, and serve as an image heating device. It is conveyed to the fixing device 30. The secondary transfer rollers 29a and 29b are pressed against the recording material 11 at the position 29a while the multicolor toner image is being transferred onto the recording material 11, and are separated to the position 29b after the image forming process. A secondary transfer bias is applied between the secondary transfer rollers 29a and 29b and the intermediate transfer member 28 from a power source (not shown). A multicolor toner image is transferred from the intermediate transfer member 28 to the recording material 11 by the secondary transfer bias.
The fixing device 30 heats and melts the multicolor toner image transferred onto the recording material 11 (on the recording material) while conveying the recording material 11, and fixes the fixing roller 31 as a pair of conveying rotating bodies. The pressure roller 32 is in pressure contact with the fixing roller 31. The recording material 11 carrying the multicolor toner image is applied with heat and pressure at a fixing nip formed by the fixing roller 31 and the pressure roller 32, so that the toner is fixed on the surface of the recording material 11 and the paper discharge roller 61. It is conveyed to. The surface of the fixing roller 31 is cleaned by the web cleaning device 34. The configuration of the fixing device 30 will be described later.
The paper discharge roller 61 discharges the recording material 11 to a paper discharge tray (not shown), and the image forming unit ends a series of image forming operations.
In this example, the recording material 11 is conveyed at a conveyance speed of 40 mm / sec.

(Fixing device)
FIG. 3A shows a cross-section of the basic configuration of the fixing device 30 according to this example. In the fixing roller 31, a silicone rubber layer 31b as an elastic layer is covered with 2 mm on a hollow 1.5 mm-thick iron core 31a as a base layer. The outermost layer is coated with 50 μm of a fluororesin layer 31c as a toner release layer. The outer diameter of the fixing roller 31 is 35 mm. A gear (not shown) for transmitting a rotational driving force from the fixing driving motor 50 as a driving means is provided at the end of the cored bar 31a of the fixing roller 31. Thereby, the fixing roller 31 rotates.
The pressure roller 32 has the same configuration as the fixing roller, and a 2 mm thick silicone rubber layer 32b is coated as an elastic layer on a hollow 1.5 mm thick iron cored bar 32a as a base layer. The outermost layer is coated with 50 μm of a fluororesin layer 32c as a toner release layer. The outer diameter of the pressure roller 32 is 35 mm like the fixing roller 31. The pressure roller 32, by a spring and a support member (not shown) is pressurized by the pressurizing force of about 400N against the fixing roller 31, to form a heating nip N _F for heating and melting the toner onto the recording material 11 Yes.
The halogen heater 33 is a heating source for heating the fixing roller 31 and is installed inside the fixing roller 31 having a hollow shape. The surface temperature of the fixing roller 31 is detected by a thermopile 73 that is a non-contact temperature detecting unit and is disposed opposite to the surface of the fixing roller 31, and is A / D converted by the CPU 200. The CPU 200 determines ON / OFF of the power supply circuit 201 that is a power supply means to the halogen heater 33 based on the temperature detection result, and controls the surface temperature of the fixing roller 31 to be maintained at a predetermined temperature.

(Web cleaning device)
Next, the web cleaning device 34 as a cleaning device according to this example will be described. The fixing web 40 that is a web is a web sheet made of a nonwoven fabric of aramid fibers. The fixing web 40 is stretched around a take-up roller 41 and a feed roller 42. The fixing web 40 cleans dirt on the fixing roller 31 when the feed roller 42 around which the fixing web 40 is wound comes into contact with the surface of the fixing roller 31 with a pressure of 4.9 N. That is, the fixing web 40 cleans the surface of the fixing roller 31 that is at least one of the pair of transport rotating bodies. Hereinafter, the contact portion between the fixing roller 31 and the fixing web 40 is referred to as a cleaning nip _NCL . Site of the cleaning nip N _CL of the fixing web 40 to form a cleaning surface. In this example, the cleaning nip _NCL is 2.0 mm. The fixing web 40 is wound around the fixing roller 40 by the fixing web conveyance motor 60 based on the control of the CPU 200. At this time, the fixing web 40 wound around the feed roller 42 is conveyed while sequentially pulling out the new surface, and the cleaning surface is renewed. The outer diameters of the take-up roller 41 and the feed roller 42 are 8 mm, and the longitudinal width of the fixing web 40 (the direction perpendicular to the recording material conveyance direction) is 224 mm. The winding roller 41 corresponds to the conveying means of the present invention.

In this example, the web cleaning device 34 is disposed so as to contact the fixing roller 31. For this reason, in this example, the fixing roller 31 corresponds to the rotating body of the present invention.
However, as shown in FIG. 3B, the web cleaning device 34 may be arranged so as to contact the pressure roller 32. In this case, the contact portion between the pressure roller 32 and the fixing web 40 becomes the cleaning nip _NCL . Site of the cleaning nip N _CL of the fixing web 40 to form a cleaning surface. In this case, the pressure roller 32 corresponds to the rotating body of the present invention.
In addition, as shown in FIGS. 3C and 3D, the fixing web 40 may be disposed so as to come into contact with the roller 43 that contacts the fixing roller 31 or the pressure roller 32. In this case, the roller 43 corresponds to the contact rotating body of the present invention. Examples of the roller 43 that contacts the fixing roller 31 or the pressure roller 32 include a primary recovery roller and an external heating roller. The primary collection roller rotates to press against the fixing member and primarily collects dirt on the surface of the fixing member, and then the dirt on the primary collection roller is secondarily collected by the fixing web. . The external heating roller has a heat source inside or outside, rotates while being pressed against the fixing member, and heats the fixing member from the surface side. In these cases, the contact portion between the roller 43 and the fixing web 40 becomes the cleaning nip _NCL . Site of the cleaning nip N _CL of the fixing web 40 to form a cleaning surface.

(motor)
FIG. 4 shows a control block configuration of the fixing drive motor 50 and the fixing web conveyance motor 60.
The fixing drive motor 50 is a DC brushless motor that is driven to rotate, and its operation is controlled by the CPU 200. The fixing drive motor control unit 51 controls the driving of the fixing drive motor 50. The fixing drive motor control unit 51 receives a rotation state signal from the fixing drive motor 50 and controls the rotation speed to be suitable for image formation. The fixing drive motor current detector 52 detects the consumption current of the fixing drive motor 50, and the output is input to the CPU 200 and A / D converted.
The fixing web conveyance motor 60 is a stepping motor that is driven to rotate, and its operation is controlled by the CPU 200. The fixing web conveyance motor controller 61 controls the driving of the fixing web conveyance motor 60 and controls the conveyance amount of the fixing web 40 to be a predetermined amount indicated by the CPU 200.

  FIG. 5 shows the appearance of the fixing drive motor 50 (DC brushless motor) according to this example. The outer diameter A of the rotor portion 53 is 55 mm, and the thickness B from the end surface of the attachment portion 54 to the image forming apparatus main body to the end surface of the rotor portion 53 is 23 mm. The fixing drive motor 50 is attached to the main body of the image forming apparatus through a screw hole 56, and the pinion gear 55 transmits the rotational force of the fixing drive motor 50 to the fixing roller 31 of the fixing device 30 by a gear (not shown).

Next, a current detection method of the fixing drive motor current detection unit 52 will be described with reference to FIG. FIG. 6 shows a circuit configuration of the fixing drive motor 50.
The fixing drive motor 50 is a three-phase (LU, LV, LW) DC brushless motor, and is configured to output an FG signal from an FG pattern directly below the rotor magnet. The FG signal is input to the motor driver IC 308, amplified and compared by an FG amplifier provided in the motor driver IC 308, and output to the fixing drive motor control unit 51 as an FGOUT signal. Hall elements 310 to 312 are provided to detect the switching timing to each phase of the motor. The high-side drive FETs 302 to 304 have their drain terminals connected to a motor drive power supply, their gate terminals connected to a motor driver IC 308, and their source terminals connected to each phase. The low side drive FETs 305 to 307 have their drain terminals connected to each phase, their gate terminals connected to the motor driver IC 308, and their source terminals connected to the motor driver IC 308, the resistor RS, and the fixing drive motor current detection unit 52. ing. The resistor RS is a resistor for detecting the current flowing through the motor, and the motor driver IC 308 detects the voltage IV-converted by the resistor RS and limits the current flowing through the motor winding. The torque designation voltage capacitor 309 has its voltage determined by an ACC (acceleration) signal and a DEC (deceleration) signal, which are output signals from the fixing drive motor control unit 51, and controls the motor output. The fixing drive motor current detection unit 52 mainly includes a resistor 322, a capacitor 323, and an OP amplifier 321. The fixing drive motor current detecting unit 52 averages and amplifies the voltage obtained by IV conversion of the fixing drive motor current flowing through the resistor RS, and outputs the voltage to the CPU 200. The output is A / D converted, thereby fixing the fixing drive motor. The current value I can be recognized. The fixing drive motor current detection unit 52 corresponds to the current value detection means of the present invention.

  The rotational speed of the fixing drive motor 50 is determined so that the speed of the fixing roller 31 is 40 mm / sec. The number of rotations of the fixing drive motor 50 is T1. FIG. 7 shows the relationship between the fixing drive motor current value I and the torque according to this example.

(Fixing web conveyance control)
8, a fixing driving motor 50 as the rotation number T1, the case of rotating the temperature of the fixing roller 31 in the thermopile 73 at 180 ° C., the relationship between the toner amount and the fixing motor current value I in the cleaning nip N _CL Indicates. As shown in FIG. 8, as the amount of toner in the cleaning nip _NCL increases, the fixing drive motor current value I increases. In other words, the amount of toner accumulated in the cleaning nip N _CL increases, and the adhesion between the surface of the fixing roller 31 and the melted or fixed toner in the cleaning nip N _CL that rubs against the surface of the fixing roller 31 causes the inside of the cleaning nip N _CL . The frictional force increases. As a result, since the load on the fixing drive motor 50 increases, the fixing drive motor current value I increases. In other words, fixing driving motor current value I is a physical quantity that varies due to an increase in frictional force in the cleaning nip N _CL.
Also at the location where the fixing motor current value I exceeds the I _a In this example, the center frequency from the cleaning nip _{N CL} allophone 100~200Hz occurs. In this example, I _a = 1400 mA, and at that time, the recovered toner amount Ka in the cleaning nip N _CL was 2.0 mg. This abnormal sound is caused by stick-slip phenomenon in the cleaning nip N _CL, generated with the increase of the frictional force in the cleaning nip N _CL. Further toner amount increases, the frictional force in the cleaning nip N _CL is gradually increased, increased incidence of abnormal noise, and also increases the volume of noise. The amount of toner in the cleaning nip N _CL is further increased, the rotational speed by the output shortage of fixing the drive motor 50 is no longer maintained a predetermined speed, or JAM occurs due to paper transport failure, parts of the fixing device 30 has failed There is also a case of doing.
Here, in FIG. 8, I _b is a control threshold value used for fixing web conveyance control in this example, and in this example, I _b = 1200 mA. I _c is the fixing drive motor current value when no toner is attached to the fixing web 40 in this example, and in this example, I _c = 1000 mA.

Here, an outline of operation control during the image forming operation of the fixing device 30 will be described. Operation control during the image forming operation is mainly classified into a pre-rotation operation, a paper transport operation, an inter-paper operation, and a post-rotation operation.
The pre-rotation operation indicates operation control of the fixing device 30 before the recording material 11 is carried into the fixing device 30. The paper transport operation indicates operation control of the fixing device 30 when the recording material 11 is transported by the fixing device 30. The inter-sheet operation refers to operation control of the fixing device 30 that is performed between the sheet conveying operations when a plurality of recording materials 11 are printed. The post-rotation operation indicates operation control of the fixing device 30 after the recording material 11 is carried out from the fixing device 30 until the fixing device 30 stops.
In this example, when the main power supply of the image forming apparatus is turned on, the fixing device 30 is controlled by the CPU 200 so that the temperature of the thermopile 73 is maintained at 180 ° C. in the standby state and the image forming operation state. Further, during the image forming operation, the fixing roller 31 is controlled by the CPU 200 so that the conveying speed is 40 mm / sec.

  FIG. 9 shows changes in the fixing drive motor current value I during a normal image forming operation such as a pre-rotation operation, a paper transport operation, a sheet-to-paper operation, a post-rotation operation, and a stop. It can be seen that the fixing drive motor current value I is more stable during the pre-rotation operation, the inter-sheet operation, and the post-rotation operation than during the paper conveyance operation for conveying the recording material 11. During the paper transport operation, the load applied to the fixing drive motor 50 differs depending on the basis weight, surface property, thickness, and the like of the recording material 11, and the fixing drive motor current value I is not stable. For this reason, in this example, the fixing web conveyance control by the fixing driving motor current value I, which will be described later, is performed only during the pre-rotation operation, the sheet interval operation, and the post-rotation operation. In other words, the fixing web conveyance control is performed when the fixing roller 31 and the pressure roller 32 are not sandwiching the recording material 11 during the pre-rotation operation, the sheet-to-sheet operation, or the post-rotation operation. Implemented when 32 rotates.

Next, the fixing web conveyance control according to this example will be described with reference to the flowchart of FIG. FIG. 1 shows a flowchart of a routine for executing fixing web conveyance control according to this example.
The CPU 200 that executes this routine corresponds to the control means of the present invention.
First, this routine is started when the image forming apparatus main body is turned on or when a predetermined time elapses from the previous execution of the routine.
In step 1, the CPU 200 determines whether or not it is the current value detection timing of the fixing drive motor current value I. Specifically, the current value detection timing is determined when the image forming operation of the fixing device 30 is a pre-rotation operation, a sheet-to-sheet operation, or a post-rotation operation. If an affirmative determination is made in step 1 that the current value detection timing is reached, the process proceeds to step 2. If it is determined in step 1 that the current value detection timing is not reached, this routine is temporarily terminated.
In step 2, the CPU 200 determines whether or not it is the execution timing of fixing web conveyance. Specifically, it is determined whether or not the fixing drive motor current value I exceeds the threshold value I _b (I> I _b ).
Here, the threshold value I _b is a predetermined value of the fixing drive motor current value I that changes due to an increase in frictional force on the cleaning surface of the fixing web 40 when the fixing roller 31 and the pressure roller 32 rotate. The current value corresponds to the threshold value. Note that the threshold value I _b corresponds to a threshold value of the frictional force that is lower than the value of the frictional force when the cleaning surface of the fixing web 40 becomes dirty enough to cause a problem due to the frictional force.
If an affirmative determination is made in step 2 that it is the execution timing, the process proceeds to step 3. If it is determined in step 2 that the execution timing is not reached, this routine is temporarily terminated.
In step 3, the CPU 200 conveys the fixing web 40 and renews the cleaning surface of the fixing web 40. In this example, the cleaning nip _{N CL} min (2.0 mm) transports. After this step, this routine is temporarily terminated.
In this example, one threshold _Ib is set as the threshold of the fixing drive motor current value I for conveying the fixing web 40. However, a plurality of threshold values are set as threshold values of the fixing drive motor current value I, and the fixing web conveyance amount is reduced when the low threshold value is exceeded, and the fixing web conveyance amount is increased when the high threshold value is exceeded. The web conveyance amount may be set in multiple stages.

FIG. 10 shows the transition of the fixing drive motor current value I when the fixing web conveyance control according to this example is performed. After fixing the drive motor current value I is determined that exceeds the threshold value I _b carries the fixing webs 40, new look clean surface of the fixing web 40, the frictional force in the cleaning nip N _CL is reduced . This control can be seen that fixing the drive motor current value I has remained to be below the threshold I _b. During this way pre-rotation operation, when the sheet interval operation, and, during the post-rotation operation, by controlling the fixing driving motor current value I below the threshold I _b, noise and other by fixing web 40 which cleaning surface is contaminated The occurrence rate of this problem can be reduced.

FIG. 11 shows the transition of the fixing drive motor current value I when the user prints with the mode specified incorrectly. Here, a case where thick paper is set and printing is performed in the plain paper mode is described as an example. In this case, a large amount of offset toner adheres to the fixing roller 31 by the insufficient heating, finally reaches the cleaning nip N _CL. Timing X in FIG. 11 is a timing offset toner reaches the cleaning nip N _CL.
Here, in the case of the conventional control, as shown in FIG. 11A, the fixing drive motor current value I suddenly increases after the timing X. At this time, the fixing drive motor 50 is used in a state exceeding the normally used current value due to the frictional force caused by a large amount of toner in the cleaning nip _NCL , and as a result, abnormal noise and other problems occur. Risk increases.
However, in the present embodiment shown in FIG. 11 (b), conveying the fixing web 40 at the stage it is detected that the fixing driving motor current value I in the subsequent timing X has exceeded the threshold value I _b, fixing driving motor current value can be kept I below the threshold I _b. As a result, the cleaning nip N
_The amount of toner in the _CL can be controlled to a predetermined amount or less, and the occurrence of abnormal noise and other problems can be avoided.

In this example, the control for conveying the fixing web 40 only based on the detection result of the fixing drive motor current value I has been described. However, the conventional predictive control method and the fixing web conveyance control method according to this example may be combined. In this case, normally, the minimum necessary amount of fixing web is conveyed for each print page or print job. Then, only when the toner exceeding the predetermined amount is supplied into the cleaning nip _NCL , it is detected by the fixing drive motor current value I as in this example, and the fixing web 40 is conveyed. Even in this case, it is possible to prepare for a situation in which a large amount of toner is supplied unexpectedly, such as erroneous specification of the mode, while the fixing web conveyance amount necessary for the prediction control can be set as small as possible.

As described above, by detecting the fixing driving motor current value I as in this example, is conveyed a predetermined distance fixing web 40 when the fixing motor current value I exceeds the threshold value I _b, cleaning nip N _The amount of toner collected in the _CL can be reduced to a predetermined amount or less. Further, even when a large amount of toner adheres to the fixing web 40 due to erroneous mode designation or the like, the fixing web 40 can be conveyed immediately and the cleaning surface of the fixing web 40 can be renewed. As a result, it is possible to reduce problems such as generation of abnormal noise due to excessive amount of toner collected in the cleaning nip _NCL , recording material contamination due to poor cleaning, damage to parts of the fixing device 30, and the like.
Such as when carrying out the low print JOB of printing rate Further, when the toner in the fixing web 40 unexpectedly is not recovered, the fixing web 40 until the toner recovery amount in the cleaning nip N _CL reaches a predetermined amount is not conveyed . For this reason, the fixing web surface can be effectively used as compared with the conventional predictive control, and the consumption of the fixing web 40 can be reduced. Therefore, the apparatus can be reduced in size and cost.

<Example 2>
In this example, estimate the amount of toner in the cleaning nip N _CL rotational force applied to the stretched axis of the fixing web is detected by the torque sensor is a torque detecting means, a fixing web for conveying the fixing web on the basis of the detection result The conveyance control will be described.
In addition, in this example, description of the part which overlaps with the said Example 1 is abbreviate | omitted.

(Torque sensor)
FIG. 12A is a perspective view showing a schematic configuration of the torque sensor 90 according to this example. The torque sensor 90 is installed on the shaft of a take-up roller 41 as a web conveyance rotating body for conveying the fixing web 40. The torque sensor 90, the frictional force applied to the fixing web 40 in the cleaning nip N _CL, it detects the Figure 12 rotational force applied in the direction of B in (a) the rotational axis of the take-up roller 41 is subjected. Here, the direction A in FIG. 12A is the winding direction of the fixing web 40 by the fixing drive motor 50.

  FIG. 12B shows a side surface of the internal structure of the torque sensor 90 according to this example. In this example, the torque sensor 90 uses a phase difference detection method. The take-up roller shafts 93a, 93b on the gear side and the fixing web side are connected to the torque transmission shaft 92 by couplings 94a, 94b. The rotational force received by the rotary shaft of the winding roller 41 causes the torque transmission shaft 92 to generate a twist angle. The twist angle is detected by the sensors 95a and 95b based on the rotation amounts of the gears 91a and 91b, and the detection result is A / D converted by the CPU 200 and recognized as torque.

FIG. 13 shows the relationship between the twist angle of the torque sensor 90 and the torque. The torsion angle is positive in the direction B in FIG. In the detection result by the torque sensor 90 used in this example, when the twist angle of the shaft of the take-up roller 41 increases as shown in FIG. 13, the torque tends to increase. That is, the torque to be detected is a physical quantity that varies due to an increase in frictional force in the cleaning nip N _CL.

In this example, the torque sensor 90 is installed on the shaft of the winding roller 41. However, the present invention is not limited to this, and a torque sensor may be installed on the shaft of the feed roller 42.
In this example, a phase difference detection method is used as a torque sensor for detecting the rotational force of the shaft of the winding roller 41. However, it is not limited to this. As the torque sensor, a strain gauge method using a strain gauge, a magnetic torque detection method for detecting a change in magnetic permeability, a piezoelectric torque detection method using a piezoelectric element, or the like may be used.

(motor)
FIG. 14 shows a control block configuration of the fixing drive motor 50 and the fixing web conveyance motor 60.
The fixing drive motor 50 is a DC brushless motor that is driven to rotate, and its operation is controlled by the CPU 200. The fixing drive motor control unit 51 controls the driving of the fixing drive motor 50. The fixing drive motor control unit 51 receives a rotation state signal from the fixing drive motor 50 and controls the rotation speed to be suitable for image formation.
The fixing web conveyance motor 60 is a stepping motor that is driven to rotate, and its operation is controlled by the CPU 200. The fixing web conveyance motor controller 61 controls the driving of the fixing web conveyance motor 60 and controls the conveyance amount of the fixing web 40 to be a predetermined amount indicated by the CPU 200.
The detection result by the torque sensor 90 is recognized as torque by the CPU 200 as described above.

(Fixing web conveyance control)
FIG. 15 shows the amount of toner collected in the cleaning nip _NCL and the output value T of the torque sensor 90 when the fixing drive motor 50 is rotated at a rotation speed T1 and the temperature of the fixing roller 31 in the thermopile 73 is rotated at 160 ° C. The relationship is shown. As shown in FIG. 15, when the toner recovery amount in the cleaning nip N _CL is increased, the output of the torque sensor 90 increases. This means increased toner recovery amount in the cleaning nip N _CL is the frictional force of the fixing web 40 and the fixing roller 31 increases, force applied to the shaft of the take-up roller 41 by the fixing roller 31 is increased. Since the torque sensor 90 detects the change in the rotational force of the shaft of the take-up roller 41, the torque output from the torque sensor 90 increases.
In FIG. 15, the center frequency when the torque sensor output value T has exceeded the T _a 10
An abnormal noise of 0 to 200 Hz was generated. In this example, T _a = 2.0 V (equivalent to 0.06 N · m)
, And the toner recovery amount La of the cleaning nip _{N CL} at that time was 2.0 mg. This abnormal sound is caused by stick-slip phenomenon in the cleaning nip N _CL, generated with the increase of the frictional force in the cleaning nip N _CL. Furthermore toner recovery amount is increased, the frictional force in the cleaning nip N _CL is gradually increased, increased incidence of abnormal noise, and also increases the volume of noise. Further, when the toner recovery amount in the cleaning nip N _CL is further increased, the rotational speed by the output shortage of fixing the drive motor 50 is no longer maintained a predetermined speed, or JAM occurs due to paper transport failure, parts of the fixing device 30 is Sometimes it breaks down.
Here, in FIG. 15, T _b is a control threshold value used for fixing web conveyance control in this example, and in this example, T _b = 1.5 V (0.04 N · m). In addition, T _c is a torque sensor output value when no toner adheres to the fixing web 40 in this example, and T _c = 1 in this example.
. It was 0 V (0.02 N · m).

Next, the fixing web conveyance control using the torque sensor 90 according to this example will be described with reference to the flowchart of FIG. FIG. 16 shows a flowchart of a routine for executing the fixing web conveyance control according to this example. The CPU 200 that executes this routine corresponds to the control means of the present invention.
First, this routine is started when the image forming apparatus main body is turned on or when a predetermined time elapses from the previous execution of the routine.
In step 11, the CPU 200 determines whether or not it is a torque detection timing using the torque sensor 90. Specifically, the torque detection timing is determined when the image forming operation of the fixing device 30 is a pre-rotation operation, a sheet-to-sheet operation, or a post-rotation operation. If an affirmative determination is made in step 11 that it is the torque detection timing, the routine proceeds to step 12. If it is determined in step 11 that the current value detection timing is not reached, this routine is temporarily terminated.
In step 12, the CPU 200 determines whether or not it is the execution timing of fixing web conveyance. Specifically, it is determined whether or not the output value T of the torque sensor 90 exceeds the threshold value T _b (T> T _b ).
Here, the threshold value T _b is a predetermined output value T (torque) that changes due to an increase in frictional force on the cleaning surface of the fixing web 40 when the fixing roller 31 and the pressure roller 32 rotate. The torque value corresponding to the threshold value. The threshold value T _b corresponds to the threshold of the low friction force than the friction force when cleaning surface of the fixing web 40 is contaminated enough to cause problems by frictional force.
If an affirmative determination is made in step 12 that it is the execution timing, the process proceeds to step 13. If it is determined in step 12 that the execution timing is not reached, this routine is temporarily terminated.
In step 13, the fixing web 40 is conveyed by the CPU 200 and the cleaning surface of the fixing web 40 is renewed. In this example, the cleaning nip _{N CL} min (2.0 mm) transports. After this step, this routine is temporarily terminated.
In this example, one threshold value _Tb is set as the threshold value of the torque sensor output value T. However, a plurality of threshold values are set as the threshold value of the torque sensor output value T. When the low threshold value is exceeded, the fixing web conveyance amount is decreased, and when the high threshold value is exceeded, the fixing web conveyance amount is increased. The carry amount may be set in multiple stages.

FIG. 17 shows the transition of the torque sensor output value T when the fixing web conveyance control according to this example is performed. After determining that the torque sensor output value T exceeds the threshold T _b carries the fixing webs 40, cleaning surface is new, the frictional force in the cleaning nip N _CL is reduced. This control reduces the torque sensor output value T, it can be seen that remained to be below the threshold value T _b. During this way pre-rotation operation, when the sheet interval operation, and, during the post-rotation operation, by controlling the torque sensor output value T below the threshold T _b, cleaning surface by the fixing webs 40 in which dirt abnormal noise or other The occurrence rate of problems can be reduced.

FIG. 18 shows the transition of the torque sensor output value T in the case where the user performs the mode improper designation and prints. Here, a case where thick paper is set and printing is performed in the plain paper mode is described as an example. In this case, a large amount of offset toner adheres to the fixing roller 31 by the insufficient heating, finally reaches the cleaning nip N _CL. Timing Y in FIG. 18 is a timing offset toner reaches the cleaning nip N _CL.
Here, in the case of the conventional control, as shown in FIG. 18A, the torque sensor output value T increases rapidly after the timing Y. At this time, frictional force due to large amount of toner to be recovered in the cleaning surface of the fixing web 40 has occurred in the cleaning nip N _CL. As a result, there is an increased risk of occurrence of abnormal noise and other problems.
However, in the present embodiment shown in FIG. 18 (b), conveying the fixing web 40 at the stage it is detected that the torque sensor output value T exceeds the threshold value T _b in the subsequent timing Y, the torque sensor output value T it can be kept below the threshold T _b. As a result, the cleaning nip N _CL
The amount of collected toner can be controlled to a predetermined amount or less, and the occurrence of abnormal noise and other problems can be avoided.

In this example, the control for conveying the fixing web 40 only based on the detection result of the torque sensor output value T has been described. However, the conventional predictive control method and the fixing web conveyance control method according to this example may be combined. In this case, the minimum necessary amount of fixing web transport is transported for each print page or print job. Then, only when the toner exceeding the predetermined amount is supplied into the cleaning nip _NCL , it is detected by the torque sensor output value T as in this example, and the fixing web 40 is conveyed. Even in this case, it is possible to prepare for a situation in which a large amount of toner is supplied unexpectedly, such as erroneous specification of the mode, while the fixing web conveyance amount necessary for the prediction control can be set as small as possible.

As described above, using the torque sensor 90 in the present embodiment, by estimating the toner recovery amount in the cleaning nip N _CL from the rotational force applied to stretched axis of the fixing web 40, it is the same control as in Example 1 . That is, to detect the torque sensor output value T, by a fixing web 40 is conveyed by a predetermined amount when the torque sensor output value T exceeds the threshold value T _b, the toner recovery amount in the cleaning nip N _CL below a predetermined amount Can be reduced. Further, even when a large amount of toner adheres to the fixing web 40 due to erroneous mode designation or the like, the fixing web 40 can be conveyed immediately and the cleaning surface of the fixing web 40 can be renewed. As a result, it is possible to reduce problems such as generation of abnormal noise due to an excessive amount of toner collected in the cleaning nip _NCL , recording paper contamination due to poor cleaning, damage to parts of the fixing device 30, and the like.
Such as when carrying out the low print JOB of printing rate Further, when the toner in the fixing web 40 unexpectedly is not recovered, the fixing web 40 until the toner recovery amount in the cleaning nip N _CL reaches a predetermined amount is not conveyed . For this reason, the fixing web surface can be effectively used as compared with the conventional predictive control, and the consumption of the fixing web 40 can be reduced. Therefore, the apparatus can be reduced in size and cost.

  In the above embodiment, the fixing drive motor current value I and the torque sensor output value T are caused by an increase in frictional force when the fixing web 40 becomes dirty during rotation between the fixing web 40 and the fixing roller 31. It was a physical quantity that changed. However, the present invention is not limited to this, and other physical quantities may be detected.

DESCRIPTION OF SYMBOLS 30 ... Fixing device, 31 ... Fixing roller, 32 ... Pressure roller, 40 ... Fixing web, 41 ... Winding roller, 200 ... CPU

Claims (6)

In an image heating apparatus for heating a toner image on a recording material,
A web for cleaning toner adhering to the rotating body from above the recording material;
Conveying means for conveying the web;
With
When the cleaning surface that rubs against the rotating body of the web gets dirty, the image heating device transports the web by the transport means and renews the cleaning surface of the web,
When a physical quantity that changes due to an increase in frictional force on the cleaning surface of the web during rotation of the rotating body exceeds a predetermined threshold, the web is transported by the transport means and the cleaning is performed. An image heating apparatus comprising control means for renewing the surface. Provided with a pair of transport rotating bodies that transport while sandwiching the recording material,
The image heating apparatus according to claim 1, wherein the rotating body on which the cleaning surface of the web is rubbed is one of the pair of conveying rotating bodies. A pair of transport rotators that transport while sandwiching the recording material;
A contact rotator that contacts either one of the pair of transport rotators;
Further comprising
The image heating apparatus according to claim 1, wherein the rotating body on which the cleaning surface of the web rubs is the contact rotating body. Drive means for rotationally driving the pair of transport rotators;
Current value detecting means for detecting a current value of a current used for driving the driving means;
Further comprising
The image heating apparatus according to claim 2, wherein the physical quantity is a current value detected by the current value detection unit. The transport means includes a web transport rotating body for transporting the web,
A torque detection means for detecting a torque received by a rotation shaft of the web conveyance rotating body during rotation of the rotating body;
The image heating apparatus according to claim 1, wherein the physical quantity is a torque detected by the torque detection unit.   6. The control unit according to claim 2, wherein the control unit is implemented during rotation of the pair of transport rotators when the pair of transport rotators does not sandwich a recording material. Image heating device.

Images