JP2022030888A - Fixing device and image forming apparatus - Google Patents

Abstract

To prevent a reduction in the life of a fixing device as much as possible, while preventing the generation of abnormal noise due to stick slip during idling of a fixing rotating body.SOLUTION: A fixing device passes a sheet on which an unfixed toner image is formed through a nip part between a heating rotating body and a pressure rotating body to execute a fixing job. At the timing to start idling, when the total number of prints is determined to be less than a threshold Mth (No in S12), the fixing device executes idling with the rotation speed of the heating rotating body as V1, and when the total number of prints is equal to or more than the threshold Mth (Yes in S12) and when a heat storage index indicating a warming up degree of nip part forming members is equal to or more than Tth (Yes in S15), the fixing device sets the rotation speed of the heating rotating body to V2 faster than V1 (S16) before executing idling.SELECTED DRAWING: Figure 10

Description

The present disclosure relates to a fixing device for thermally fixing an unfixed image on a sheet and an image forming device provided with the fixing device.

The electrophotographic image forming apparatus includes a fixing apparatus for thermally fixing an unfixed toner image formed on a sheet. This fixing device has a configuration in which a pressurized rotating body is pressed against the peripheral surface of a heated rotating body heated by a heat source to form a nip portion, and an unfixed sheet is passed through the nip portion.

The width of the nip portion in the sheet passing direction (hereinafter referred to as "nip width") is required to have a predetermined size so as not to cause uneven fixing in heat fixing. Elastic layers are formed on both or one of the bodies.

Immediately after fixing the sheet, when the rotation of the heated rotating body and the pressurized rotating body (hereinafter, both may be collectively referred to as "nip portion forming rotating body") is stopped, the nip portion becomes hot and the nip Since the part-forming rotating body deteriorates, the heat of the nip part is usually diffused by idling (rotating the sheet without passing paper) for a predetermined time.

The nip portion forming rotating body is configured to rotate and drive only one of the rotating bodies (usually a pressurized rotating body), and the other rotating body is driven to rotate. During idle rotation without passing the sheet through the sheet, a so-called "stick slip" phenomenon in which minute slips occur intermittently between the rotating bodies in the elastic layer of the nip portion may occur, and abnormal noise may occur.

When abnormal noise is generated, it is very jarring, especially in a quiet office, and it may be misunderstood that the image forming device is out of order. Therefore, the generation of such abnormal noise is suppressed as much as possible. It is desirable to do.

Empirically, the higher the traveling speed (feeding speed in the sheet passing direction) of the nip portion forming rotating body, the less abnormal noise due to the stick-slip phenomenon (hereinafter, simply referred to as "stick-slip sound") is generated. For example, in Patent Document 1, the traveling speed at idling is controlled to be relatively high.

Japanese Unexamined Patent Publication No. 2008-20533 Japanese Unexamined Patent Publication No. 2017-107086

However, according to the configuration of Patent Document 1, the rotation speed of the nip portion forming rotating body is mechanically increased during idling without specifically considering the condition for stick slip generation, so that it is unnecessary. Nip portion formation The mileage of the rotating body is increased, wear and deterioration of the elastic properties of the material are promoted, and it is inevitable that the life of the fixing device is shortened.

Further, in Patent Document 2, the total number of jobs in the past and the number of sheets to be passed are stored, and the value of (total number of jobs) / (number of sheets to be passed) (that is, the average number of jobs per sheet to be passed) is stored. However, even in such a case, it cannot be said that the conditions for the occurrence of stick slip are sufficiently evaluated, and the spinning speed is unnecessarily high. As a result, its life is shortened.

The present disclosure has been made in view of the above-mentioned problems, and is a fixing device capable of preventing the generation of stick-slip noise during idling and suppressing the shortening of the life of the fixing device as much as possible, and the fixing. It is an object of the present invention to provide an image forming apparatus having an apparatus.

In order to achieve the above object, in the fixing device according to one aspect of the present disclosure, a pressure member is pressed against a heated rotating body heated by the heating portion to form a nip portion, and an unfixed toner image is formed on the nip portion. A fixing device that executes a fixing job by passing the formed sheet through a sheet, and is a first acquisition unit that acquires a first index value that indicates the amount of change in the friction coefficient between the heating rotating body and the pressurizing member. And the second acquisition unit for acquiring the second index value for indexing the amount of change in the rigidity of the elastic layer in the heating rotating body and / or the pressurizing member, and the first index value and the second index value. Based on this, it is characterized by including a control unit for controlling the rotation speed of the heating rotating body at the time of idling rotation.

Further, in another aspect of the present disclosure, the first index value is at least one of the total mileage of the heated rotating body and the total number of sheets to be passed through the nip portion, and the second index value is. The control unit includes the first parameter indicating the warmth of the heating rotating body and the nip portion forming member including the pressurizing member, and the control unit has the first index value equal to or higher than the first threshold value and the second. When the index value is equal to or higher than the second threshold value, it is characterized in that the rotation speed of the heated rotating body at the time of idling rotation is controlled to be higher than the initial setting condition.

Further, in another aspect of the present disclosure, the second acquisition unit is based on the history of the rotation time of the heated rotating body rotated prior to the idle rotation and the stop time of the heated rotating body stopped. , The first parameter is acquired.

Further, in another aspect of the present disclosure, the second acquisition unit measures at least the rotation time of the heated rotating body at the time of executing the fixing job, and stores the measured rotation time as a history at the first timing. When the rotation stop time of the heated rotating body intervenes between the storage unit and the start of idle rotation, the sum of the history of the rotation time immediately before the rotation stop is calculated according to the length of the rotation stop period immediately after that. A rotation time correction unit for correcting and obtaining a corrected rotation time is provided, and the total rotation time obtained by adding the history of subsequent rotation times to the corrected rotation time is acquired as the first parameter.

Further, in another aspect of the present disclosure, the first timing includes any one of the end of the fixing job, the end of power supply to the apparatus, and the stop of rotation of the heating rotating body. And.

Further, in another aspect of the present disclosure, the rotation time correction unit adds up the total rotation time history immediately before the rotation stop, based on the first table or the first calculation formula obtained in advance, immediately after that. It is characterized in that it is corrected according to the length of the rotation stop period.

Further, in another aspect of the present disclosure, the second acquisition unit acquires the second parameter based on the heating control time of the heating unit executed prior to the idle rotation in addition to the first parameter. , The second index value is acquired based on the value of the first parameter and the value of the second parameter.

Further, in another aspect of the present disclosure, the second acquisition unit measures at least the heating control time of the heating unit at the time of executing the fixing job, and controls to store the measured heating control time as a history at the second timing. A control time correction unit that obtains a correction control time by correcting the sum of the history of the heating control time immediately before the warm-up based on the temperature of the time storage unit and the heating unit at the start of warm-up immediately after the second timing. And, further, the total heating control time obtained by adding the subsequent heating control time to the correction control time is acquired as the second parameter.

Further, in another aspect of the present disclosure, the second acquisition unit detects the temperature of the heating unit at the start of heating control of the heating unit, and when the detected temperature is equal to or less than a predetermined threshold value, the said second acquisition unit. It is characterized in that the history of the corrected rotation time is reset to acquire the first parameter.

Further, in another aspect of the present disclosure, when the correction control time is shorter than the correction rotation time at the time when the heating control of the heating unit is started, the second acquisition unit substitutes for the correction rotation time. It is characterized in that the first parameter is acquired by using the correction control time.

Further, in another aspect of the present disclosure, the time point of disclosure of the heating control of the heating unit is the start of warm-up control.

Further, in another aspect of the present disclosure, the second timing includes any one of the start time of the fixing job, the end time of the fixing job, and the end time of power supply to the heating unit. ..

Further, in another aspect of the present disclosure, the control time correction unit uses a second table or a second arithmetic expression obtained in advance to warm the sum of the history of the heating control time immediately before the warm-up. It is characterized in that correction is performed based on the temperature of the heating unit at the start of up control.

Further, in another aspect of the present disclosure, the second acquisition unit acquires the second parameter based on the heating control time of the heating unit executed prior to the idling, instead of the first parameter. , The second parameter value is used as the second index value.

Further, in another aspect of the present disclosure, a third acquisition unit for acquiring a third index value for indexing a relative pressure contact force between the heating rotating body and the pressurizing member is further provided, and the control unit is the control unit. It is characterized in that the rotation speed of the heated rotating body at the time of idling is controlled based on the first index value, the second index value, and the third index value.

Further, in another aspect of the present disclosure, instead of the first acquisition unit or the second acquisition unit, a third index value for indexing the relative pressure contact force between the heating rotating body and the pressurizing member is acquired. The control unit includes three acquisition units, and the control unit controls the rotation speed of the heated rotating body at the time of idle rotation based on the first index value and the third index value, or the second index value and the third index value. It is characterized by that.

Further, in another aspect of the present disclosure, the pressurizing member is a pressurized rotating body, and one of the pressurized rotating body and the heated rotating body is rotationally driven by a drive source and the other. The rotating body is driven to rotate, and is provided with a torque detecting unit for detecting the driving torque of one of the rotating bodies to be rotationally driven, and the third index value is the detected driving torque. It is characterized by.

Further, in another aspect of the present disclosure, the heating rotating body is an endless belt that orbits, and the heating portion is separated from the nip portion in the orbiting direction in one round of the belt. It is characterized by heating the area in which it is present.

Further, in another aspect of the present disclosure, the image forming apparatus includes an image forming portion for forming an unfixed toner image on a sheet and a fixing portion for heat fixing the unfixed toner image on the sheet. The fixing device is characterized in that the fixing device is used as the fixing portion.

According to the above-described embodiment, the first index value for indexing the amount of change in the friction coefficient between the heated rotating body and the pressurizing member, which has a great influence on the conditions for generating stick slip in the nip portion, and the heated rotating body and / Alternatively, since the rotation speed of the heated rotating body during idling is controlled based on the second index value that indicates the amount of change in the rigidity of the elastic layer of the pressure member, the generation of stick-slip noise is effectively prevented. At the same time, it is possible to suppress unnecessary increase in the rotation speed at the time of idling rotation as much as possible, and it is possible to prevent shortening of the service life.

It is a schematic diagram which shows the whole structure of the printer which concerns on embodiment. It is sectional drawing which shows the schematic structure of the fixing part of the said printer. It is a model diagram for demonstrating the generation mechanism of a stick-slip phenomenon. It is a graph which shows the relationship between the rotation time of a fixing belt, and the change of a nip width. It is a graph which shows the relationship between the stop time of a fixing belt, and the change of a nip width. It is a time chart for explaining the execution of the fixing job and the state of rotation and stop of the fixing belt. It is a graph which shows the correlation between the correction rotation time Tδ and the stop time Ts of a fixing belt. It is a graph which shows the change of the index value of the heat storage amount at the time of rotating again with a stop time after the rotation of the fixing belt last time. It is a block diagram which shows the control system of the whole printer. It is a flowchart which shows the procedure of running speed control at idling rotation executed by a control part. It is a block diagram which shows the circuit for detecting the drive torque of a fixing motor by the change of the drive current. It is a figure which shows the structure for detecting the load (pressure contact force) with respect to the fixing belt of a pressure roller. It is a table which shows the result of the simulation when the degree of warming of a fixing part is corrected by the temperature of a heating roller at the start of warm-up. It is a graph which shows the result of having corrected the degree of warming of a fixing part by the temperature of a heating roller at the start of warm-up.

Hereinafter, as the image forming apparatus according to the embodiment of the present disclosure, a tandem type color printer (hereinafter, simply referred to as “printer”) will be described as an example with reference to the drawings.

(1) Overall Configuration of Printer FIG. 1 is a schematic cross-sectional view showing the overall configuration of printer 1.

As shown in the figure, the printer 1 is an electrophotographic method, includes a feeding section 10, an image forming section 20, a fixing section 30, a discharging section 40, and a double-sided transport section 50, and is one side of a recording sheet S. It is possible to execute a single-sided print job that prints an image only on the (front side) and a double-sided print job that prints an image on both sides (front side and back side) of the sheet S.

The feeding unit 10 supplies a paper feed tray 11 for accommodating the sheet S, a feeding roller 12P provided on the paper feeding tray 11 for feeding the sheet S one by one toward the transport path 19, and the fed sheet S. It is provided with a paper feed roller 12F for transporting paper, a timing roller 13 for timing the sheet S to be fed to the secondary transfer position 29, and the like.

The image forming unit 20 forms a toner image on the sheet S sent from the feeding unit 10. Specifically, in the four image forming units 21Y, 21M, 21C, 21K, the surfaces of the charged photoconductor drums 25Y, 25M, 25C, 25K are modulated and driven by the laser from the exposure unit 26 based on the image data. It is exposed to light to create an electrostatic latent image on its surface, and the electrostatic latent image is developed with toners of each color of yellow (Y), magenta (M), cyan (C) and black (K).

The four-color toner images visualized by development are the photoconductor drums 25Y, 25M, 25C, 25K, and the primary transfer rollers 22Y, 22M, 22C, 22K facing the photoconductor drums 23 via the intermediate transfer belt 23. The electric field between them causes primary transfer from the surface of each photoconductor drum to the surface of the intermediate transfer belt 23. In this primary transfer, the toner image formation timing is shifted in the image forming units 21Y to 21K so that the toner images of each color Y to K are transferred to the same position on the intermediate transfer belt 23. As a result, a color toner image formed by multiple transfer of Y to K color toner images is formed on the intermediate transfer belt 23.

The intermediate transfer belt 23 is located above the photoconductor drums 25Y to 25K, is stretched on a plurality of rollers including the drive roller 23R and the driven roller 23L, and travels in the direction of arrow A. The color toner image on the intermediate transfer belt 23 moves to the secondary transfer position 29, which is the contact position between the intermediate transfer belt 23 and the secondary transfer roller 24, by traveling around the intermediate transfer belt 23.

The color toner image on the intermediate transfer belt 23 is the intermediate transfer of the sheet S conveyed from the feeding unit 10 by the electric field between the intermediate transfer belt 23 and the secondary transfer roller 24 at the secondary transfer position 29. When passing between the belt 23 and the secondary transfer roller 24, the secondary transfer is performed on the surface (first surface) of the sheet S. The sheet S on which the color toner image is secondarily transferred is conveyed in the direction of arrow E by the secondary transfer roller 24 and heads toward the fixing portion 30.

The fixing portion 30 includes a fixing belt 311 (heating rotating body) and a pressure roller 32 (pressurizing member), and the sheet S is passed through a nip portion Np formed between the fixing belts 30 to obtain toner. The image is heat-fixed on the sheet S.

The discharge unit 40 includes a discharge roller 41 and a paper discharge port 45, and discharges the sheet S on which the color toner image is fixed from the paper discharge port 45. The ejection roller 41 is arranged inside the paper ejection port 45, and while rotating (normal rotation) in the direction of arrow B, the sheet S conveyed from the fixing portion 30 is conveyed from the paper ejection port 45 to the outside of the machine. Discharge. The ejected paper S is stored in the output tray 46. This completes single-sided printing to print only on the first side of the sheet S.

Further, in the case of a double-sided print job, the sheet S that has passed through the secondary transfer position 29 at the time of printing on the front surface (first surface) is conveyed from the fixing portion 30 to the discharge roller 41. When the rear end of the sheet S transported by the discharge roller 41 in the transport direction passes through the detection position of the discharge sensor ES including the optical sensor, the discharge roller 41 switches from normal rotation to reverse rotation (rotation in the direction of arrow C).

Due to the reversal of the discharge roller 41, the sheet S is inverted and guided to the double-sided transfer section 50, and the double-sided transfer rollers 51, 52, 53, 54, 55 convey the double-sided transfer path in the arrow D direction to cause the timing roller 13. The color toner image is secondarily transferred to the back surface (second surface) of the sheet S, thermally fixed by the fixing portion 30, and then thermally fixed via the discharge roller 41. It is discharged to the output tray 46.

In the feeding section 10 and the image forming section 20, the rotating members including the rollers for feeding and transporting, the drive roller 23R, the photoconductor drums 25Y to 25K, etc. are the driving force of the drive motor M1 arranged in the image forming section 20. Rotates by. Further, the pressure roller 32 in the fixing unit 30 is rotationally driven by the drive motor (fixing motor) M2, and the discharge roller 41 is forward-reversed by the driving force of the drive motor M3 arranged in the discharge unit 40, and the double-sided transfer roller. 51 to 55 are rotated by the driving force of the driving motor M4 arranged in the double-sided transport portion 50.

Further, the control unit 100 is connected to an external terminal device via a network (not shown) through the network interface (I / F) 110, and receives and receives print job data sent from this terminal device. Image data to be printed is generated from the data of the print job, and the generated image data is used for printing.

(2) Configuration of fixing portion FIG. 2 is a schematic cross-sectional view showing the configuration of the fixing portion 30.

As shown in the figure, the fixing portion 30 has a heating unit 31 and a pressure roller 32. The heating unit 31 includes an endless fixing belt 311 (heating rotating body), a heating roller 312 and a fixing roller 313 for tensioning the fixing belt 311, a heater unit 314 for applying heat to the heating roller 312, and a belt 31. Includes a temperature sensor 315 for detecting temperature.

The fixing belt 311 has an elastic layer made of a highly heat-resistant material such as silicone rubber and fluororubber on a base layer made of polyimide or SUS (stainless steel), and a fluoropolymer such as PFA (perfluoroalkoxy alkane resin). The releasable layer made of resin and imparted releasability is laminated in this order.

The heating roller 312 (heating portion) is formed by laminating a coat layer made of PTFE (polytetrafluoroethylene) on the outer peripheral surface of a cylindrical aluminum hollow core metal. The fixing roller 313 is formed by laminating an elastic layer such as silicone rubber or fluororubber on the outer peripheral surface of a columnar solid core metal made of aluminum or iron. Each of the heating roller 312 and the fixing roller 313 is rotatably supported at both ends in the axial direction by a frame (not shown) constituting the housing of the fixing portion 30.

The heater unit 314 includes a first heater 3141 that heats almost the entire range in the axial direction (longitudinal direction: the back direction of the paper in FIG. 2) of the heating roller 312, and a second heater 3142 that heats the central portion in the axial direction. The heating roller 312 is heated by generating heat by supplying electric power from a power source (not shown). In the present embodiment, the first heater 3141 and the second heater 3142 are composed of halogen heaters, but other heating sources may be used.

The pressure roller 32 is formed by laminating an elastic layer such as silicone rubber and a mold release layer such as PFA on the outer peripheral surface of a cylindrical core metal made of aluminum or iron in this order. Both ends of the pressurizing roller 32 in the axial direction are rotatably supported by the above frame, and the pressurizing roller 32 is subjected to a predetermined load (nip pressure) by a urging force from an elastic member (not shown) such as a spring. The outer peripheral surface is pressed against the outer peripheral surface of the fixing belt 311. By this pressure contact, a nip portion Np is formed between the outer peripheral surface of the pressure roller 32 and the outer peripheral surface of the fixing belt 311.

The pressurizing roller 32 is rotationally driven at a predetermined rotational speed in the arrow F direction by the rotational driving force of the fixing motor M2 (FIG. 1). Due to the rotation of the pressure roller 32, the fixing belt 311 stretched on the heating roller 312 and the fixing roller 313 is driven (runs) in the arrow G direction (belt circumferential direction). When the fixing job is executed, the rotation speed of the fixing motor M2 is controlled so that the transport speed of the sheet S passing through the nip portion Np stabilizes at a predetermined system speed (reference speed) (in some cases, heating rotation). There may be a configuration in which the body side is driven and the pressurized rotating body is driven to rotate.)

When the heater unit 314 is energized during the orbital traveling of the fixing belt 311, the heat generated from the heater unit 314 is transmitted from the heating roller 312 (heating unit) to the fixing belt 311, and the nip portion Np is transmitted by the orbiting traveling of the fixing belt 311. To.

As a result, the heat of the fixing belt 311 is supplied to the pressure roller 32 and the fixing roller 313, and the temperature of the nip portion Np, which is the contact region between the fixing belt 311 and the pressure roller 32, rises.

The temperature sensor 315 is, for example, a thermistor, which is arranged near a portion of the fixing belt 311 in contact with the outer peripheral surface of the heating roller 312, detects the surface temperature of the fixing belt 311 and outputs the detection result to the control unit 100. send.

Based on the detection result, the control unit 100 turns on / off the electric power supplied to the first heater 3141 and the second heater 3142 in the heater unit 314, and controls the fixing belt 311 to reach the target temperature.

Specifically, for example, assuming that the temperature detected by the temperature sensor 315 is Tw, the position of the temperature sensor 315 and the nip portion Np are separated by a predetermined distance, so that the temperature TN in the nip portion Np is the same as the detected temperature Tw. However, it is corrected by multiplying this by a constant temperature adjustment correction coefficient A1 (A1 <1) (TN = A1 * Tw).

Therefore, the control unit 100 controls on / off of each heater 3141 and 3142 in the heater unit 314 so that the corrected temperature TN becomes equal to the target set temperature.

Temperature control (warm-up control) that raises the temperature of the nip part Np to a fixable target temperature is performed when the device is turned on, after a jam occurs, after job processing by the user is completed, a front door for maintenance, etc. Is executed when is closed, when returning from sleep mode to save power consumption, and so on.

In this warm-up control, the first heater 3141 (long heater) is turned on in order to raise the temperature to a fixable temperature at an early stage. If the target set temperature TN for fixing is, for example, 155 ° C, the TN is input so that the target heating temperature of the heating roller 312 (TN / A1: for example, about 170 ° C) is reached in the first heater 3141. The nip portion Np is heated by controlling the on / off control and rotating the fixing belt 311 at a predetermined traveling speed (linear speed) (for example, 135 mm / s).

After the warm-up is completed, the printing job is executed by switching to the heating control by the second heater 3142 (short heater). After that, if there is no print instruction, the target set temperature of the heating roller 312 is set again by the first heater 3141 to a standby temperature (about 150 ° C to 155 ° C) lower than that at the time of executing the fixing job, and the temperature is controlled for a predetermined time. After executing the idle rotation, the fixing belt 311 is stopped to shift to the standby mode. During this time, the heating roller 312 is maintained at the standby temperature.

When a large amount of small-sized sheets are output in a print job, only the amount of heat in the central part in the axial direction may be deprived and the temperature at the end in the axial direction may rise excessively. (Scanning direction) In addition to the temperature sensor 315 that detects the temperature at the center, a temperature sensor that detects the temperature at the axial end is separately provided so that the temperature at the end does not rise excessively. It is desirable to switch between and the second heater 3142 to heat.

(3) Conditions for generating stick slip Next, the conditions for generating stick slip in the nip portion Np of the fixing portion 30 will be considered.

FIG. 3 is a model diagram for explaining a generalized mechanism of occurrence of the stick-slip phenomenon.

In the figure, the second member 302 (corresponding to the pressure roller 32 in the present embodiment) is pressed against the elastic first member 301 (corresponding to the fixing belt 311 in the present embodiment) with the load W. Then, the second member 302 is moved in the direction of the arrow at a speed V (FIG. 3 (a)).

Under the load W, the upper surface of the first member 301 and the lower surface of the second member 302 are initially in a state of sticking, and as the second member 302 moves in the horizontal direction, the first member 301 The surface layer portion is elastically deformed (FIG. 3 (a)).

Then, when the elastic restoring force of the surface layer portion of the first member 301 exceeds the static friction force with the lower surface of the second member 302, it slips between the surface layer portion of the first member 301 and the lower surface of the second member 302. ) Occurs, and the surface layer portion of the first member 301 returns to its original posture (FIG. 3 (c)). At this time, it is considered that a stick slip sound is generated.

Hereinafter, the behaviors of FIGS. 3A to 3C are repeated.

In such a model case, the parameter λ indicating the susceptibility to the stick-slip phenomenon is expressed by the following equation (1).

・・・式（１）
式（１）において、Δμ＝μs－μk
ここで、μs：第１部材と第２部材間の静止摩擦係数
μk：第１部材と第２部材間の動摩擦係数
また、Ｗ：第２部材から第１部材に加えられる荷重
ｍ：第２部材の質量
ｋ：ばね剛性係数（剛性率）
Ｖ：第２部材の初速
上記式（１）で定義されるパラメーターλの値が小さいほど、スティックスリップが発生じにくいことが知られており、この式（１）を、定着部３０のニップ部Ｎｐにおけるスティックスリップ現象の解析に適用すると、次のようになる。

... Equation (1)
In equation (1), Δμ = μs-μk
Here, μs: coefficient of static friction between the first member and the second member
μk: Coefficient of dynamic friction between the first member and the second member W: Load applied from the second member to the first member
m: Mass of the second member
k: Spring rigidity coefficient (rigidity)
V: Initial velocity of the second member It is known that the smaller the value of the parameter λ defined in the above equation (1), the less likely it is that stick slip will occur. When applied to the analysis of the stick-slip phenomenon in Np, it becomes as follows.

(A) The larger the total number of prints (total number of sheets to be printed) and / or the total mileage on the fixing unit 30, the larger Δμ.

Normally, in the fixing portion 30, the outer surface of the rotating body that comes into contact with the toner (in the present embodiment, the outer surface of the fixing belt 311) is coated with a fluorine-based resin or the like in order to improve the releasability of the toner. ing.

As the number of prints and the mileage increase, the coating on the outer surface of the fixing belt 311 gradually peels off due to wear, and the friction coefficient on the surface of the fixing belt 311 gradually increases.

At this time, both the static friction coefficient μs and the dynamic friction coefficient μk become large, but it is empirically known that the static friction coefficient μs is larger than the dynamic friction coefficient μk, and therefore Δμ The value of tends to increase with durability.

Since this Δμ cannot be directly measured in the image forming apparatus, in the present embodiment, the total number of printed sheets and / or the total mileage is used as an index value for indexing the value of Δμ. ..

(B) Normally, the rigidity k of an elastic body has a characteristic that the larger the amount of heat storage, the smaller (the elasticity increases).

This rigidity is a physical characteristic value that determines the difficulty of deformation due to shearing force, and the elastic material such as rubber used for the nip-forming rotating body of the fixing portion 30 has a small rigidity as the temperature of the member rises. It is known to be.

As a condition for generating stick slip, the rigidity of the elastic material facing the contact surface between the first member 301 and the second member 302 becomes a problem, but when this rigidity is indexed by temperature, the temperature of the surface thereof is a problem. It is not enough by itself, but the warming condition (hereinafter referred to as "heat storage amount") of the entire portion forming the nip portion (hereinafter referred to as "nip portion forming member") is an important parameter.

In the present embodiment, the fixing roller 313, the pressure roller 32, and the fixing belt 311 are included as the nip portion forming member.

Therefore, the larger the amount of heat stored in the nip portion forming member in the fixing portion 30, the smaller the rigidity.

From the consideration of the formula (1) and the above (a) and (b), the value of λ increases as the total number of printed sheets (or the total mileage) increases or the amount of heat stored in the nip portion forming member increases. It can be seen that stick slip is likely to occur.

(4) Acquisition of each index value (4-1) Index value of the fluctuation amount of Δμ As described above, the fluctuation amount of Δμ has a correlation with the total number of printed sheets and / or the total mileage. It can be used as an index value.

Here, the total number of prints is the cumulative number of prints (that is, fixed) from the first drive of the new image forming apparatus or the replacement of the unit of the fixing unit with a new one to the latest printing. It means the cumulative number of sheets passed through the nip portion Np in the job).

In this embodiment, as a general rule, the number of prints on a standard A4 size horizontal sheet is counted. In the case of printing on other sheet sizes, for example, it may be converted into the number of A4 horizontal sheets according to the area ratio, or if there is not much difference in size, it may be counted as one sheet as it is.

The total mileage is added to the total number of revolutions of the pressure roller 32 from the first drive of the new image forming device or the replacement of the fixing unit with a new one to the latest printing. It can be obtained by multiplying the peripheral length of the pressure roller 32.

In the following, the total number of printed sheets and / or the total mileage may be collectively referred to simply as "durability index value" (first index value).

(4-2) Index value of the fluctuation amount of the rigidity The rigidity of the elastic layer for forming the nip portion Np shall be estimated from the heat storage amount (warming condition) of the entire nip portion forming member as described above. (Specifically, the amount of fluctuation is used as an index, not the absolute value of the rigidity).

However, since the heat storage amount of the nip portion forming member cannot be actually measured in the apparatus, it is necessary to set a parameter (first parameter) that can quantitatively estimate this.

Therefore, the inventors of the present application determine that the traveling time of the fixing belt 311 heated and controlled via the heating roller 312 (heating portion) (hereinafter, referred to as “belt rotation time”) is the heat storage amount of the nip portion forming member. I thought that it would be one of the indicators to evaluate.

This is because the amount of heat applied to the fixing belt 311 by the heating roller 312 is eventually propagated to the fixing roller 313, the pressure roller 32, and the like due to the rotation thereof, and influences the warming condition of the nip portion forming member.

In the present embodiment, the belt rotation time generated when one fixing job is executed is, in principle, not only the rotation time for fixing the sheet passed through the nip portion Np (fixing job in a narrow sense) but also fixing. It also includes the idle rotation time during warm-up before job execution and the idle rotation time after fixing job execution (fixing job in a broad sense).

This is because the amount of heat supplied by the heating roller 312 is supplied to the nip portion Np via the fixing belt 311 through the rotation of the fixing belt 311 even during idle rotation before and after such a fixing job.

Strictly speaking, the unit time supplied from the heating roller 312 to the fixing belt 311 in (i) pretreatment idle rotation, (ii) fixing job execution (narrow sense), and (iii) post-processing idle rotation. Although the amount of heat per unit is different, it can be considered that a uniform amount of heat is supplied per unit time on average over the entire belt rotation time.

However, since the set temperature at the time of executing the fixing job in a narrow sense is the highest and it is considered that the influence on the heat storage amount of the nip portion forming member is large, at least the execution time of this fixing job is selectively measured as the belt rotation time. It doesn't matter.

In the following, for convenience of explanation, the idle rotation at the time of warm-up before the fixing job is executed is referred to as “pre-processing idle rotation”, and the idle rotation after the fixing job is executed is referred to as “post-processing idle rotation” to distinguish between the two. Further, unless otherwise specified, "fixing job" means a fixing job in a narrow sense.

The post-processing idle rotation is stopped after a preset time elapses and shifts to the standby mode. During this standby mode, the temperature of the heating roller 312 reaches the fixing temperature immediately after accepting the next print job. It is maintained at a temperature that allows it (standby temperature).

In the present embodiment, the standby temperature is set to be about 10 ° C. to 30 ° C. lower than the heating temperature of the heating roller 312 at the time of executing the fixing job.

Here, first, the index value (second index value) of the heat storage amount of the nip portion forming member at the start of the post-treatment idle rotation will be described.

At the timing of the start of post-processing idle rotation, the immediately preceding belt rotation time Tr (however, here, the post-processing idle rotation time is excluded) performed when the fixing job (hereinafter referred to as "immediately preceding job") executed immediately before is executed. ) Is an index that most affects the amount of heat stored in the nip portion Np.

However, there is a high possibility that the amount of heat applied when the fixing job (hereinafter referred to as "preceding job") executed prior to the immediately preceding job is executed also remains.

In the present embodiment, the total rotation time R (= Tr + Tδ) obtained by adding the corrected rotation time Tδ obtained by converting the residual heat storage amount in the preceding job to the belt rotation time in the immediately preceding job to the belt rotation time Tr in the immediately preceding job is calculated. This is used as the first parameter for indexing the amount of heat stored in the nip portion forming member.

This corrected rotation time Tδ can be obtained by correcting the belt rotation time in the preceding job in consideration of the length of the subsequent stop time.

The inventors of the present application focused on the amount of change in the width (nip width: FIG. 2) Nd of the nip portion Np in the sheet transport direction in order to obtain the corrected rotation time Tδ that indicates the residual heat storage amount in the preceding job.

Specifically, the larger the amount of heat stored in the nip portion forming member, the larger the thermal expansion of the pressure roller 32, and the larger the degree of thermal expansion of the pressure roller 32, the larger the contact with the fixing belt 311 in the sheet transport direction. The nip width Nd (FIG. 2), which is the length, becomes wider.

The thermal expansion of the pressure roller 32 varies depending on the amount of heat applied from the heated fixing belt 311 to the pressure roller 32, and the amount of heat applied to the pressure roller 32 differs depending on whether the fixing belt 311 is rotating or stopped. ..

Since the heating roller 312 heated by the heater portion 314 of the heat source and the pressurizing roller 32 forming the nip portion Np are separated from each other, if the fixing belt 311 rotates as in the case of printing, the heater portion 314 This is because the heat of the heating roller 312 heated by the above is directly transferred from the fixing belt 311 to the nip portion Np.

On the contrary, if the fixing belt 311 is stopped while waiting for a print job or the like, the heat transferred to the nip portion Np away from the heating roller 312 is greatly reduced.

The nip width Nd fluctuates as shown in FIGS. 4 and 5 depending on whether the fixing belt 311 is rotating or stopped. FIG. 4 shows a case where a predetermined amount of heat is applied to the fixing belt 311 by the heating roller 312 and the temperature of the nip portion Np is controlled to be a high temperature of a predetermined value or more (for example, 100 ° C. or more) (hereinafter, the present invention). It is a figure which shows the relationship between the belt rotation time (second) of the fixing belt 311 and the nip width Nd (mm) in "during heating control").

Further, FIG. 5 is a diagram showing the relationship between the stop time of the fixing belt 311 (fixing belt stop time Ts) and the nip width Nd after heat is stored by the rotation of the fixing belt 311.

4 and 5 show an example of actual measurement of the relationship between the belt rotation time Tr, the fixing belt stop time Ts, and the nip width Nd, respectively.

As shown in FIG. 4, it can be seen that the nip width Nd becomes wider as the belt rotation time Tr increases. Specifically, at the start of rotation of the fixing belt 311, the nip width Nd is 4.85 mm, but after 300 seconds, the nip width Nd becomes 5.4 mm, and after 900 seconds, the nip width Nd is 5.6 mm. It has spread to.

When the rotation of the fixing belt 311 is stopped from this state, the amount of heat transferred to the pressurizing roller 32 decreases, so that the nip width Nd becomes narrower as the fixing belt stop time Ts increases as shown in FIG. Specifically, the nip width Nd, which was 5.6 mm when the fixing belt 311 was stopped, became 5.4 mm after 600 seconds and narrowed to 5.2 mm after 1800 seconds.

In FIG. 5, the reason why the nip width Nd does not return to the original size of 4.8 mm is that even if the rotation of the fixing belt 311 is stopped, the heat from the heating roller 312 is pressed through the stopped fixing belt 311. It is considered that this is because the radiant heat of the heating roller 312 is also transmitted to the pressure roller 32 as well as being transmitted to the roller 32.

It should be noted that the size of the nip width Nd is an example, and it goes without saying that the size of the nip width Nd may be different if the device configuration of the fixing portion 30 is different.

In this way, the nip width Nd increases according to the rotation time of the fixing belt 311 heated by the heater unit 314, and decreases according to the stopping time of the fixing belt 311.

Then, as the rotation time of the fixing belt 311 increases, the amount of heat supplied to the nip portion forming member via the nip portion Np increases, so that the amount of heat stored in the nip portion forming member increases accordingly, and the fixing belt 311 is stopped thereafter. Since there is a relationship that the longer the time is, the amount of heat stored in the nip portion forming member decreases due to heat dissipation, it can be said that the amount of heat stored in the nip portion forming member has a clear correlation with the rotation time and the stop time of the fixing belt 311.

FIG. 6 is a time chart showing an example of the rotation / stop operation of the fixing belt 311 for the fixing jobs executed for the (n-1) th and nth print jobs received after a predetermined time. .. Note that "n" is a natural number, and in this example, the print jobs immediately after the power is turned on to the apparatus are counted up in order with the initial value "1".

First, when the execution start of the (n-1) th print job is accepted (time t1), the warm-up woo1 (preprocessing idle rotation) is started, and when the nip portion Np reaches a predetermined fixing temperature (time t2), The (n-1) th fixing job is executed in which the unfixed toner image in the (n-1) th print job is thermally fixed to the sheet.

When the (n-1) th fixing job is completed (time t3), the post-processing idle rotation 1 is executed to diffuse the heat in the nip portion Np, and then the rotation of the fixing belt 311 is stopped at the time t4. Move to standby mode.

Then, the warm-up woo2 is started (time t5) in accordance with the start of execution of the next nth print job n, and then the execution of the nth fixing job is started at time t6, and after the end (time t7). ), After the post-processing idle rotation 2 is executed, the rotation of the fixing belt 311 is stopped at time t8, and the mode shifts to the standby mode.

Now, when determining whether or not it is necessary to change the idle rotation conditions (set temperature and idle rotation time) in the post-processing idle rotation 2 at the time t7 when the post-processing idle rotation 2 is started, the nip at that time. As an index of the heat storage amount of the part forming member, the belt rotation time Tr (n) (= t7-t5) performed at the time of executing the immediately preceding fixing job (n) has the greatest influence, but is more accurate. In order to reflect the amount of heat storage, it is desirable to take into consideration the amount of residual heat remaining in the nip portion Np when the fixing job executed before that is executed.

When the fixing belt stop time intervenes after the fixing job is completed, heat is dissipated according to the fixing belt stop time and the nip width Nd becomes smaller as described in FIG. 5, so that the previous fixing job (n-) It is not desirable to add the belt rotation time T (n-1) in 1) to the belt rotation time Tr (n) as it is using the heat storage amount as an index, and some correction is necessary.

FIG. 7 shows a change in the nip width Nd with respect to the subsequent stop time Ts of the fixing belt 311 when the belt rotation time Tr (n-1) made in connection with the previous fixing job (n-1) is 30 seconds. Is a graph obtained by calculating and plotting a value (corrected rotation time Tδ) converted into a belt rotation time in a immediately preceding job having a nip width Nd equal to the nip width Nd based on the experimental results of FIG. 5, and the horizontal axis is a fixing belt stop. The time Ts is shown, and the vertical axis shows the corrected rotation time Tδ.

In this experiment, almost no change in the width of the nip width Nd was observed for about 100 seconds after the rotation of the fixing belt 311 was stopped. Therefore, as shown in FIG. 7, until the stop time (Ts) reached 100. The corrected rotation time Tδ does not change at 30 seconds, but when it exceeds 100 seconds, the corrected rotation time Tδ gradually decreases.

Such a correlation between the corrected rotation time Tδ and the stop time Ts is obtained in advance for each value of the rotation time that indicates the amount of heat storage at the time of rotation stop, and is converted into, for example, ROM 103 (see FIG. 9) of the control unit 100. It is stored as (first table).

Now, the belt rotation time, which is an index of the residual heat amount at the end of the previous (n-1) th fixing job, is set to R (n-1), and then decays after the fixing belt rotation stop time Ts (n) has elapsed. Assuming that the corrected rotation time Tδ (n) for indexing the amount of residual heat later, Tδ (n) can be approximated by the following equation (2) (first arithmetic equation) from the above experimental results.

…式（２）
ここで、「Ｔｄ（ｎ）」は、ｎ番目の定着ジョブの実行開始直前の定着ベルト回転停止時間Ｔｓ（ｎ）のうち、実質的に残留蓄熱量の減衰に寄与する時間（以下、「減衰寄与時間」という。）を示すものである。

… Equation (2)
Here, "Td (n)" is the time (hereinafter, "attenuation") that substantially contributes to the attenuation of the residual heat storage amount in the fixing belt rotation stop time Ts (n) immediately before the start of execution of the nth fixing job. It is called "contribution time").

Based on the above experimental results, since the nip width Nd did not change 100 seconds after the rotation was stopped, the damping contribution time Td (n) is as follows.

When Ts (n)> 100, Td (n) = Ts (n) -100
When Ts (n) ≤ 100, Td (n) = 0
Further, "β" is a positive constant for determining the degree of attenuation, and varies depending on the structure of the fixing portion 30, the material and shape of the fixing roller, the fixing belt, the pressure roller, etc., and is a specific numerical value. Is obtained by experiments.

Therefore, assuming that the belt rotation time R (n) for indexing the heat storage amount (residual heat storage amount) of the nip portion Np at the end of the nth fixing job, R (n) is at the end of the nth fixing job. The sum of the belt rotation time Tr (n) and the corrected rotation time Tδ (n) obtained by converting the amount of residual heat remaining in the nip portion Np by the fixing job before the previous time into the rotation time in the nth fixing job immediately before. Can be obtained as.

・・・式（３）
この式（３）に上記式（２）を代入すると、次の式（４）が得られる。

... formula (3)
By substituting the above equation (2) into this equation (3), the following equation (4) is obtained.

・・・式（４）
上述のように、ｎは、自然数（１，２，３・・・）であって、通常は、朝一番に装置に電源が投入された後に実行したプリントジョブの順を示す。

... Equation (4)
As described above, n is a natural number (1, 2, 3 ...), Which usually indicates the order of print jobs executed after the device is turned on first in the morning.

The stop time from the end of the (n-1) th fixing job in the middle to the start of execution of the next (n) th fixing job is very long, which is equal to or more than a predetermined threshold value (for example, 2 hours or more). In such a case, the residual heat amount from the previous fixing job is almost dissipated and may be ignored. In this case, it may be reset to n = 1. At this time, it is considered that R (0) = 0.

Further, even when the sleep mode time (non-heating control time) for power saving is long and the heat dissipation of the nip portion forming member is progressing, the temperature of the heating roller 312 is also lowered, so that the heating roller by the temperature sensor 315 is used. Even when the detection temperature of 312 is a predetermined temperature (for example, 50 ° C.), it may be reset to n = 1.

On the contrary, even if the power of the main body of the device is turned off, the control unit 100 continuously counts the rotation stop time, and then the power is turned on until the execution of the next fixing job is started. If the stop time of is not equal to or greater than the above threshold value, the total rotation time R (n) (n) which is an index of the heat storage amount of the nip portion Np in consideration of the residual heat amount before the power is turned off without resetting n. The first parameter) can be obtained.

Further, the values of Tr (n) and Td (n) are counted by the counter 104 (see FIG. 9) in the control unit 100 and stored in the backup memory 105 at a predetermined timing (first timing) (for example). , Tr (n) at the end of the nth fixing job or when the post-processing idle rotation is stopped, and Td (n) at the start of warm-up in the next fixing job, Ts (n), Tδ ( With respect to n), the count value at the counter 104 is reset while being backed up at the time of transition from the rotation stop state to the next rotation start). It should be noted that each of the above counter values is backed up even when the printer is suddenly turned off so that its history is not deleted.

FIG. 8 is a graph showing changes in the index value R of the heat storage amount of the nip portion Np when the (n-1) th and nth fixing jobs are executed as shown in FIG. 6, and the vertical axis is the heat storage. The index value of the quantity is R [seconds], and the horizontal axis indicates the elapsed time [seconds].

The (n-1) th fixing job is executed from time t1, and at this point, the corrected rotation time Tδ (n-1), which is an index of the residual heat amount by the (n-2) th and earlier fixing jobs, is set to (n-1). -1) The history of the belt rotation time of the third fixing job (broad definition) is gradually added, and the index value R (n-1) = Tr (n-1) + Tδ at the time when the rotation stops at time t4. It becomes (n-1).

After that, when the rotation stop time elapses and the execution of the next nth fixing job is started at time t5, the belt rotation time Tr in the nth fixing job is set to the corrected rotation time Tδ (n) at that time. (N) is gradually added.

Then, the index value R (n) = Tr (n) + Tδ (n) indicating the amount of heat stored in the nip portion Np at the end of the nth fixing job. The correction rotation time Tδ (n) is obtained by the above equation (2).

In this way, the index value of the heat storage amount of the nip portion forming member is basically obtained by the sum of the history of the rotation time of the fixing belt 311 in the fixing job executed up to the immediately preceding fixing job, and is obtained by the preceding fixing job and the next fixing job. If the stop time of the fixing belt 311 intervenes between the fixing job and the fixing job, the total rotation time up to that point is corrected and added according to the length of the stop time (damping contribution time). Thereby, an index value (hereinafter, may be referred to as “heat storage index value”) that more reflects the amount of heat storage of the actual nip portion forming member can be obtained.

As described above, the parameter λ (see equation (1)) indicating the occurrence rate of the stick-slip phenomenon increases as the rigidity k of the member forming the nip portion becomes smaller, and the rigidity k forms the nip portion. Since there is a correlation that the larger the heat storage amount of the member (the larger the heat storage index value R (n)), the smaller the heat storage amount, the stick at the time of idling stop based on the heat storage index value R (n) of the nip portion forming member. It is possible to accurately determine the probability of occurrence of slip noise.

(5) Control system FIG. 9 is a block diagram showing the configuration of the entire control system of the printer 1 according to the present embodiment.

As shown in the figure, the control unit 100 includes a CPU (Central Processing Unit) 101, a RAM (RandoMthccess Memory) 102, a ROM (Read Only Memory) 103, a counter 104, and a backup memory 105.

The CPU 101 can communicate with each other with the feeding unit 10, the image forming unit 20, the fixing unit 30, the discharging unit 40, the double-sided transport unit 50, and the network I / F 110.

The ROM 103 stores in advance a control program or the like for executing a print job.

When the network I / F 110 receives print job data sent from an external terminal device via a network (for example, LAN), the CPU 101 reads a necessary program from the ROM 103 and feeds the RAM 102 as a work area. The operations of the unit 10, the image forming unit 20, the fixing unit 30, the discharging unit 40, and the double-sided transport unit 50 are collectively controlled to smoothly execute the print job based on the received print job data.

The counter 104 counts the belt rotation time Tr and the rotation stop time Ts of the fixing belt 311. The backup memory 105 is composed of a non-volatile memory, and backs up the count value of the counter 104, the number of printed sheets, and the like at the predetermined timing (first timing) described above. When backing up, the number of prints and the like are cumulatively added, but the belt rotation time Tr, the rotation stop time Ts, the correction rotation time Tδ, and the like are overwritten.

When backed up to the backup memory 105, the counter 104 resets each count value and starts counting for the next fixing job.

Based on the detection result of the temperature sensor 315, the CPU 101 controls the supply of electric power to the heater unit 314 to maintain the temperature of the nip unit Np at the target temperature. Further, the rotation speed of the fixing motor M2 is controlled when the fixing job is executed.

Further, based on the durability index value and the heat storage index value calculated by the numerical values stored in the backup memory 105, the idle rotation speed control that controls the rotation speed of the fixing belt 311 so that the stick slip sound does not occur at the time of idle rotation. To execute. In addition, in this specification, "rotational speed" is expressed by running speed (line speed) mm / s instead of rpm (rotational speed / minute).

(6) Free rotation speed control FIG. 10 is a flowchart showing the procedure of the idle rotation speed control executed by the control unit 100.

First, it is determined whether or not the timing of the start of idle rotation is present (step S11). In the present embodiment, the idle rotation is performed when the power of the device is turned on, at the time of warming up for accepting the print job and raising the fixing belt 311 from the standby mode to the fixing temperature, and immediately after the fixing job is executed. It is executed to diffuse the heat of the nip portion Np.

When it is the timing of the start of idle rotation (“Yes” in step S11), it is determined whether or not the total number of prints stored in the backup memory 105 is equal to or greater than the threshold value Mth (step S12).

As described above, as the total number of printed sheets increases, Δμ increases, so that the parameter λ indicating the possibility of stick slip in the equation (1) increases. Conversely, if the total number of printed sheets is less than the threshold value, stick slip noise may occur even if the amount of heat stored in the nip portion Np is slightly large while the rotation speed of the fixing belt 311 is low to some extent. A threshold value Mth that does not exist is set.

As the threshold value Mth in this case, for example, in the present embodiment, the number of sheets is set to about 300,000, but an appropriate value within 200,000 to 300,000 is determined by an experiment or the like in advance for each model. May be done. The value of this threshold value Mth is stored in ROM 103 in advance.

If the total number of printed sheets is less than the threshold value Mth (“No” in step S12), there is little possibility that a stick slip sound will occur as described above. Start. In this embodiment, V1 (initial setting) is, for example, 70 mm / s.

Then, after the lapse of a predetermined time, the rotation of the fixing belt 311 is stopped (step S17), and the idle rotation speed control is terminated.

Further, if the total number of prints is equal to or greater than the threshold value Mth in step S12 (“Yes” in step S12), Δμ becomes large as described above, and there is a high possibility that a stick slip sound is generated. , Step S14 to acquire the heat storage index value of the nip portion Np (step S14).

This heat storage index value differs depending on whether the idle rotation is warm-up (pretreatment idle rotation) or post-treatment idle rotation.

As shown in FIG. 6, for example, when the nth fixing job is started to be executed, the warm-up is started at time t5, and the index value of the heat storage amount of the nip portion Np at that time is shown in FIG. As described above, the corrected rotation time Tδ (n).

On the other hand, when the idle rotation is a post-processing idle rotation performed at time t7 after the end of the fixing job in the narrow sense, the index value is from R (n) (= Tr (n) + Tδ (n)). The value is obtained by deducting the post-processing idle rotation time (t8-t7).

That is, the belt rotation time is the index value, which is the sum of the correction rotation time Tδ (n), the warm-up time for the nth fixing job, and the execution time of the fixing job in a narrow sense.

Then, in step S15, it is determined whether or not the acquired index value is equal to or greater than the threshold value Tth seconds.

Here, as the threshold value Tth, a numerical value that increases the probability that stick slip will occur when the rotation speed of the fixing belt 311 is V1 is obtained in advance by an experiment or the like and stored in the ROM 103. In the present embodiment, the threshold value Tth is set to 300 seconds.

If the index value is Tth seconds or more (“Yes” in step S15), the idle rotation speed is set to V2 larger than V1 to start idle rotation (step S16), and the process proceeds to step S17.

This speed V2 is set to a speed at which a stick slip sound is not generated even if the heat storage index value increases within the range of normal use when the total number of printed sheets becomes Mth or more. It is obtained by an experiment or the like and stored in the ROM 103. Specifically, in this embodiment, V2 is set to 120 mm / s.

If the index value is less than Tth seconds (“No” in step S15), it is determined that there is no possibility of stick slip sound even if the idle rotation speed is V1, and the process proceeds to step S13.

Then, when the predetermined time elapses, the idle rotation is stopped (“Yes” in step S17, step S18), and the idle rotation speed control is terminated.

As described above, according to the present embodiment, the heat storage index value is comprehensively obtained in consideration of the rotation time of the fixing belt 311 during heating control and the rotation stop time, so that the nip portion Np can be more accurately obtained. The amount of heat storage can be reflected, and it is judged in two stages of the total number of printed sheets (durability index value) and the heat storage index value. It is possible to prevent the generation of sound.

It is necessary to unnecessarily increase the idle rotation speed compared to the conventional case where the rotation speed is always increased during idle rotation or the rotation speed is mechanically controlled by the number of jobs per sheet of paper. It is possible to suppress the shortening of the life of the fixing portion 30 as much as possible while avoiding the generation of abnormal noise due to stick slip.

<Modification example>
Although the above description has been made based on the embodiments, the present disclosure is not limited to the above-described embodiments, and the following modifications can be considered.

(1) In the idle rotation speed control in the above embodiment, the total number of printed sheets is adopted as the index value of Δμ in Equation 1, but instead of the total number of printed sheets, the total mileage of the fixing belt 311 (heated rotating body) is used. It may be set as an index value of Δμ. Needless to say, in this case, another threshold value is set. Since the fixing belt 311 is rotating in addition to actually fixing the seat, it is more likely that the total mileage reflects the amount of change of Δμ.

Further, the probability of occurrence of the stick slip sound may be determined by comparing with each threshold value in two stages of the total number of printed sheets and the total mileage.

(2) In the above embodiment, of the stick slip generation conditions represented by the equation (1), two parameters are Δμ (difference between the static friction coefficient and the dynamic friction coefficient) and the rigidity k of the elastic material in the nip portion forming member. The respective index values (durability index value and heat storage index value) were obtained, and these index values were compared with the threshold value to determine the probability of stick-slip sound generation. In addition, if an index value for indexing W (load) in the equation (1) is added as a parameter for determination, it is considered that the probability of occurrence of stick-slip sound can be determined more accurately.

As described above, normally, the heated rotating body and the pressurized rotating body are urged to the other side by an elastic material such as a spring with a constant pressure contact force (corresponding to the above load W), and the nip portion forming member is formed. By being heated and expanding against the urging force of the spring, the displacement amount of the spring increases and the load increases.

As can be seen from the equation (1), as the load (W) increases, the value of the parameter λ also increases, so that the probability that a stick-slip sound is generated also increases.

When the load in the nip portion Np increases, it is necessary to rotationally drive the rotating body (in the embodiment, the pressurizing roller 32) with a larger driving torque in order to maintain the target rotational speed. Therefore, the magnitude of the load W can be estimated by detecting the fluctuation of the drive torque.

In order to detect the fluctuation of the drive torque, a torque sensor may be provided on the drive shaft of the fixing motor M2 (FIGS. 1 and 9), but in this modification, the pressurizing roller 32 is provided at a predetermined rotation speed. The change in the drive current is acquired by the drive current detection unit (not shown) that detects the current supplied to the fixing motor M2, and the fluctuation amount of the drive torque is acquired based on this value. ..

The rotation speed of the fixing motor M2 can be obtained, for example, by the number of output pulses per unit time from the optical encoder built in the motor M2. The control unit 100 controls the current supplied by the fixing motor M2 so as to have a constant rotation speed with reference to the output pulse.

If the drive torque increases, the amount of current that should be supplied to the fixing motor M2 to maintain a constant rotation speed also increases. Therefore, if the fluctuation amount is detected, the fluctuation amount of the drive torque and the magnitude of the load can be determined. Can be estimated.

Therefore, in this modification, as the index value (third index value) for indexing the magnitude of the load, the fluctuation amount of the drive current of the fixing motor at the time of constant speed rotation control is used as the index value (hereinafter, "load index value"). ").

In this modification, it is assumed that the drive current at the time of constant speed rotation control at the time of executing the fixing job executed immediately before the idle rotation is acquired as the load index value.

FIG. 11 is a block diagram in which only the portion related to the detection of the drive torque is extracted from the control unit 100 for carrying out this modification.

For example, at the time of executing the fixing job, the CPU 101 acquires the value of the rotation speed of the fixing motor M2 for obtaining a constant rotation speed (system speed) at that time from the ROM 103, and instructs the motor drive circuit 106. The motor drive circuit 106 supplies a predetermined current to rotate the fixing motor M2 at the rotation speed.

The rotation speed of the fixing motor M2 is detected by the rotation speed detection unit 107 (optical encoder) and input to the motor drive circuit 106. As a result, the rotation speed of the fixing motor M2 is feedback-controlled and controlled to a target rotation speed.

The drive current detection unit 108 detects the current value supplied from the motor drive circuit 106 to the fixing motor M2. The torque table storage unit 109 is composed of a non-volatile memory, and a table showing the relationship between the magnitude of the drive current value and the drive torque of the pressurizing roller 32 is obtained and stored in advance, and the CPU 101 stores the table. The drive torque value obtained with reference to the reference is sampled during the fixing job, and the sampling value at the end of the fixing job or the average value of the sampled values during the fixing job is set as a predetermined memory in the backup memory 105. Make the area back up.

In the idle rotation speed control in this modification, for example, in the flowchart of FIG. 10, a load index value determination step is interposed between steps S15 and S16.

The relationship between the amount of change in the drive current of the fixing motor M2 and the amount of change in the drive torque is obtained in advance and stored as a table in the ROM 103, and the drive torque is set to a predetermined threshold value (for example, with reference to the table). If it becomes 0.8 Nm) or more, it may be determined that the probability of the stick slip sound being generated is further increased, and the process proceeds to step S16 so that the idle rotation speed is set to V2.

If the drive torque is less than a predetermined threshold value, the process proceeds to step S13 and the idle rotation speed is set to V1, which is the initial setting condition.

In this modification, W (load) is used as an index in addition to the durability index value and heat storage index value of two parameters, Δμ (difference between static friction coefficient and dynamic friction coefficient) and k (rigidity coefficient) of the nip forming member. The probability of stick-slip sound was judged by judging the load index value to be applied, and the rotation time and target set temperature during idle rotation were controlled, but either the durability index value or the heat storage index value was used. It is also possible to replace it with one judgment and make a judgment on the load index value.

That is, the idle rotation time and the target set temperature may be controlled by a two-step determination based on the load index value and the heat storage index value, or a two-step determination based on the durability index value and the load index value.

(3) In the modified example of (2) above, the drive torque of the pressurized rotating body (pressurized roller) is obtained from the fluctuation amount of the drive current as the parameter of the load W in the equation (1) and used as the load index value. However, it is also possible to measure the displacement amount of the tension spring (or compression spring) that urges the pressurized rotating body toward the heated rotating body, and obtain the urging force of the spring from the displacement amount and the spring coefficient. ..

FIG. 12 is a schematic view showing an example of the configuration of the fixing portion 30 in this case.

The shaft 321 of the pressure roller 32 is rotatably supported by a pair of swing arms 33 (only the swing arm on the front side is visible in the figure) at both ends in the axial direction, and the swing arm 33 is rotatably supported. At its lower end, it is swingably supported by a frame (not shown) of the fixing portion 30 via a support shaft 331.

The upper end of the swing arm 33 is urged in the direction of arrow F by the tension spring 34. Similarly, a detection plate 35 is erected on the upper part of the swing arm 33, and by detecting and sampling the position of the detection plate 35 by the displacement detector 36, the amount of change in the position of the detection plate 35 is achieved. Therefore, it is possible to obtain a change in the amount of elongation of the tension spring 34 due to expansion / contraction of the pressurized rotating body, and the urging force of the heated tension spring 34 can be obtained by calculation.

In this case, if the urging force of the tension spring 34 is obtained, the pressure roller 32 is determined by the ratio of the distance from the support shaft 331 to the shaft 321 and the distance from the support shaft 331 to the locking position 341 of the tension spring 34. Since the relative pressure contact force to the fixing belt 311 can be obtained, this can be directly regarded as a load index value.

In this modification, a table corresponding to the load W in the nip portion Np and the displacement amount of the detection plate 35 is obtained in advance, stored in ROM 103 or the like, and by referring to this table, the actual elongation fluctuation of the tension spring 34 fluctuates. The load W based on the quantity is acquired.

In this way, the threshold value (third threshold value) when the load (pressure contact force) of the pressure roller 32 directly on the fixing belt 311 is used as an index value is set to, for example, 100N.

If the acquired load is larger than 100 N, it is judged that the probability of occurrence of the stick slip sound is sufficiently high, the target set temperature during idling rotation is lowered, and the rotation time is lengthened.

As the displacement detector 36, an optical displacement sensor, a magnetic proximity sensor, an ultrasonic displacement sensor, a differential transformer displacement sensor, or the like is appropriately used.

(4) Relationship between drive torque and Δμ In the modified example of (2) above, the drive torque of the pressurized rotating body (pressurized roller) is calculated from the fluctuation amount of the drive current as the parameter of the load W in the equation (1). Although it was obtained and used as a load index value, the fluctuation amount of the drive torque can also be an index value of the fluctuation amount of Δμ.

That is, it is known that when the coating on the surface layer of the heated rotating body (fixing belt 311) is peeled off due to the deterioration of durability and the friction coefficient μ becomes large, the driving torque of the pressurized rotating body (pressurizing roller 32) also tends to increase. In particular, since the drive torque at the moment when the drive is started becomes large, it is understood that the static friction force is larger than the dynamic friction coefficient due to the deterioration of durability. As a result, it has been found by the inventor of the present application that Δμ becomes large and stick-slip sound is likely to occur.

Therefore, the fluctuation amount of the drive torque can be an index of the fluctuation amount of Δμ. Specifically, as a method of determining the probability of stick slip occurrence from the drive torque, for example, the drive torque at the start of drive (affected by static friction force) and the drive torque during subsequent rotation (affected by dynamic friction force) This can be done by estimating the amount of variation of Δμ by obtaining the difference and comparing it with a predetermined threshold value.

Of course, as described above, the change in the load W also appears as the change in the drive torque, so that the drive torque can be used as an index of both the load W and Δμ parameters.

(5) Effect of radiant heat from the heating roller The heat source (heater section 314) and the nip section Np are separated from each other as in the fixing section 30 of the above embodiment, and the nip section Np is heated via the fixing belt 311. In this configuration, the heat storage amount of the nip portion forming member has a great influence on the rotation time of the fixing belt 311 during heating control. Therefore, the heat storage index value of the nip portion forming member is determined based on the history of the belt rotation time. I asked.

However, even if the fixing belt 311 is not rotated, the entire fixing portion 30 is warmed by radiant heat from the heating roller 312, heat conduction via air, and convection (hereinafter referred to as "radiant heat or the like"). Since heat is also stored in the fixing roller 313, the fixing belt 311 and the pressure roller 32, the amount of heat stored in the nip portion forming member can be more accurately reflected by considering the degree of warming due to such radiant heat. You can expect to get it.

Now, the time to heat control the heating roller 312 (heating part) so that it becomes relatively high temperature, such as when executing a fixing job in a broad sense including warm-up control and idle rotation, or in the standby mode, is called "heating control time". When defined as, since the amount of heat generated by the radiant heat from the heating roller 312 is also applied to the nip portion forming rotating body during this heating control time, the history of this heating control time is added to obtain the total heating control time. As a result, it can be a parameter (second parameter) indicating the degree of warming due to the radiant heat or the like.

Such a heating control time is counted by the counter 104 (FIG. 9) from the start of the heating control, and is, for example, one of the end of the warm-up, the end of the fixing job, and the end of the power supply to the heating unit. It is backed up to the backup memory 105 at a timing including one (second timing), and at a timing such as when the post-processing idle rotation is stopped or when the standby mode ends.

It should be noted that this "heating control time" does not necessarily have to measure all the heating times of the heating roller 312, and the set temperature at the time of executing the fixing job in a narrow sense is the highest, and is given to the heat storage amount of the nip portion forming member. Since it is considered that the influence is the largest, at least the heating control time in the execution time of this fixing job may be selectively measured.

However, the heating roller 312 is not always controlled for heating, and normally, when a predetermined time elapses after shifting to the standby mode, the heating roller 312 executes a so-called sleep mode for power saving.

When this sleep mode is executed, the heating control is completely stopped, or the temperature is maintained at an extremely low temperature even when heated, so that the degree of warming due to radiant heat or the like gradually decreases, and the total temperature at the start of the sleep mode is reduced. The time obtained by adding correction to the heating control time (hereinafter referred to as "correction control time") is added to the subsequent heating control time, and the current total heating control time is used as an index of the degree of warming (heat storage amount) due to radiant heat or the like. It is desirable to obtain it as a value.

Now, the heating control time executed when the nth fixing job (broad definition) is executed is set to Ct (n), and it is executed in relation to the fixing job before that, and is corrected by the passage of time in the sleep mode before the previous time. The correction control time obtained by adding the correction to the total heating control time in the fixing job execution is set to Cδ (n), and the warming condition of the entire fixing unit 30 at the end of the heating control executed in connection with the nth fixing job is determined. Assuming that the total heating control time to be indexed is S (n), it is possible to express S (n) = Ct (n) + Cδ (n) by the same idea as considered in the belt rotation time.

Here, Cδ (n) is a correction of the total heating control time P (n-1) backed up at the end of the previous standby mode in consideration of the heat dissipation state due to the subsequent elapsed time (including the sleep time). In this modification, the correction is made based on the temperature of the heating roller 312 detected by the temperature sensor 315 at the start of warm-up after backup.

This is because it is considered that the decrease in the temperature of the heating roller 312 reflects the amount of heat radiated from the time of the previous backup.

Strictly speaking, as shown in FIG. 2, the temperature sensor 315 detects the surface temperature of the fixing belt 311. However, at the detection position of the temperature sensor 315, the fixing belt 311 and the heating roller 312 are located. Since they are almost in close contact with each other and the thickness of the fixing belt 311 is small, the temperature detected by the temperature sensor 315 can be regarded as the temperature of the heating roller 312.

FIG. 13 shows a correction value Cδ in which the total heating control time S (n-1) backed up at the end of the standby mode in the previous fixing job is corrected based on the surface temperature of the heating roller 312 at the start of the subsequent warm-up (WU). It is a table showing (n) (note that some notations are omitted in the figure for the sake of brevity).

For example, in this example, when the temperature of the heating roller 312 at the start of warm-up is 30 ° C. or lower, the temperature of the heating roller 312 drops to almost room temperature, so that the amount of heat stored by the heating control before that is The correction control time Cδ (n) is set to “0” regardless of the size of the backed up S (n-1), assuming that the heat is almost dissipated.

Then, as the surface temperature of the heating roller 312 at the start of warm-up gradually rises from 30 ° C. (that is, as the elapsed time from shifting to the previous sleep mode to starting warm-up decreases). The amount of heat radiation is also reduced, and the value of the correction control time Cδ is also increased according to the magnitude of the total heating control time S (n-1) backed up last time.

FIG. 14 is a graph of the table of FIG. 13 above. In the graph, the horizontal axis shows the surface temperature [° C.] of the heating roller 312 at the start of warm-up (WU), and the vertical axis shows the value of the correction control time Cδ (n) after the surface temperature is corrected. show.

In the graphs BU0 to BU9, the time [S] of the previous total heating control time S (n-1) before correction is 1000, 800, 600, 480, 300, 210, 150, 90, 30, 0, respectively. The change of the correction control time Cδ (n) in a certain case is shown.

Therefore, a table (second table) showing the correlation as shown in FIG. 13 and an approximate expression (second arithmetic expression: a relational expression based on the graph for each total heating control time shown in FIG. 14) are obtained in advance. For example, if stored in the ROM 103, the total heating control time S (n-1) backed up in the backup memory 105 immediately before the previous sleep mode transition and the temperature of the heating roller 312 at the start of warm-up in the nth fixing job. Based on the above, the correction control time Cδ can be obtained.

Further, the heating control time Ct (n) after the start of warm-up is the heating control time performed in connection with the nth fixing job, and is the time backed up in connection with the nth fixing job. As a result, the total heating control time S (n) = Ct (n) + Cδ (n) can be obtained as an index indicating the degree of warming of the nip portion forming rotating body due to the radiant heat of the heating roller 312.

As described above, in this modification, the heat storage index value of the nip portion forming member is set to the parameter (first parameter) indicated by the total rotation time R (n) of the fixing belt 311 with respect to the heating roller 312 (heating source). By adding the parameter (second parameter) indicated by the total heating control time S (n), in particular, as shown in FIG. 2, the heating roller 312 is used, and the heating position of the heating roller 312 which is a heating source is used. It is understood that when the distance between the nip portion and the nip portion Np is separated, a more accurate heat storage index value can be obtained.

In normal control, if the fixing belt 311 does not rotate when the heating control of the heater unit 314 is not performed, "heating control time"> "belt rotation time", so that heating control is performed. Inconsistencies may occur due to the calculation of time and belt rotation time, so adjustments may be made as follows.

(I) For example, if the device is cooled to some extent when the counting of the heating control time is started (at this time, for example, the detected temperature of the temperature sensor 315 is referred to), once the belt rotation time is started. You may reset the history. That is, the correction rotation time Tδ is set to “0”.

This is because if the apparatus temperature is low, the residual heat storage amount of the nip portion Np is sufficiently small, and it is not necessary to consider the history of the past rotation time.

(Ii) Further, for example, when the heating control is started by intermittently turning off and on the power supply while the device is not cooled to some extent, "substantial heating control time (time during which the energization is turned on)). Since there may be a relationship of <"belt rotation time", the value of the correction control time Cδ should be substituted instead of the correction rotation time Tδ indicating the history of the rotation time to avoid inconsistency. You may.

The adjustment for avoiding the inconsistency between the first parameter and the second parameter as described in (i) and (ii) above is particularly effective when the warm-up control is started.

That is, when the temperature of the temperature sensor 315 is, for example, less than 50 ° C. at the start of warm-up control, the correction belt rotation time Tδ indicating the history of the belt rotation time is set to “0”, and the subsequent belt rotation time is set to “0”. One parameter.

If the correction control time Cδ is smaller than the correction rotation time Tδ at the start of the warm-up control, the correction control time Cδ is used instead of the correction rotation time Tδ to obtain the first parameter.

Strictly speaking, since this total heating control time only indicates the degree of warming of the nip portion forming member due to radiation or the like, the nip portion Np is directly heated via the rotation of the fixing belt 311 as described above. Compared with the case, the degree of contribution to the increase in the heat storage amount of the nip portion Np is different.

Therefore, the amount of heat stored in the nip portion forming member due to radiant heat or the like is converted into the belt rotation time and added to the index value R (n) obtained in the above embodiment to obtain the current nip portion Np. An index value that more accurately reflects the amount of heat storage may be obtained.

To convert the index value (total heating control time) of the heat storage amount accumulated in the nip portion Np by radiant heat or the like into the index value (total rotation time) of the heat storage amount based on the belt rotation time in the above embodiment, for example. The amount of heat given to the nip-forming rotating body per unit time by radiant heat or the like when the heating roller 312 is heated and controlled to a target temperature, and the amount of heat given to the nip-forming rotating body per unit time by belt rotation. Are obtained in advance by experiments or simulations, the ratio of the amount of heat applied per unit time of both is obtained, and the ratio is multiplied by the "total heating control time" and converted into an index value based on the "total rotation time". You just have to do it.

(6) In the above embodiment, the total rotation time R (n) (first parameter) is used as the heat storage index value of the nip portion forming member, and in the above modification (3), the total rotation time R of the fixing belt 311 is used. In addition to (first parameter), the total heating control time S (n) (second parameter) was also used as the heat storage index value of the nip portion forming member. For example, a fixing roller was used instead of the fixing belt 311. When the heating source is arranged in the fixing roller and the nip portion Np is formed between the fixing roller and the pressurizing roller, the total heating control is performed even without the first parameter indicated by the total rotation time. It is also possible to use only the second parameter indicated by time as the heat storage index value.

(7) In the above embodiment, an example in which the image forming apparatus according to the present disclosure is applied to a tandem color printer has been described, but the present invention is not limited to this. It has a heating rotating body such as a fixing belt 311 and a pressing member such as a pressurizing roller 32, and the pressurizing member presses against the heating rotating body to form a nip portion Np between the heating rotating body and the pressurizing member. It can be applied to a fixing portion for heat fixing by passing the sheet S through the nip portion Np and an image forming apparatus provided with the fixing portion.

The image forming apparatus can be applied to those capable of performing color image forming or those capable of performing only monochrome image forming, and is not limited to printers, and is not limited to printers, for example, images of copiers, facsimile machines, MFPs (Multiple Function Peripheral) and the like. Applicable to forming equipment. The pressurizing member is not limited to a rotating body such as a pressurizing roller, and a non-rotating body such as a pressurizing pad fixed to the frame of the apparatus can also be used.

(8) Further, the fixing device is not limited to the above embodiment, and for example, instead of the fixing roller 313 (FIG. 2) as a fixing member for backing up the fixing belt 311 for forming the nip portion Np, a resin pad is used. You may use it.

Further, the heating rotating body is not limited to the fixing belt, and may be, for example, a roller shape (fixing roller). In this case, the fixing roller and the pressure roller can be regarded as a "nip portion forming member". Similar to the belt-shaped configuration, the heat source such as a heater is a region of one circumference of the roller-shaped heating rotating body that is separated from the nip portion Np in the rotation direction (the nip portion Np in the rotation direction). By arranging the portions (parts existing at different positions) at the heating positions, the speed control during idling can be effectively performed by using the heat storage index value in the above embodiment.

Further, in the above embodiment, a pressure roller (pressurized rotating body) is pressed against the fixing belt (heating rotating body) as a pressure member to form a nip portion Np, but in some cases, pressure is applied. A pressure member such as a pad may be pressure-welded to form a nip portion Np.

(9) The size, shape, material, number, etc. of each member in the above embodiment are examples, and the size, shape, material, number, etc. suitable for the device configuration are determined in advance. Further, as long as the formula can obtain an index value for indexing the amount of heat storage in the nip portion Np, for example, the formula is not strictly limited to the above formula (2), and another complicated approximate formula can be used. Is.

Further, the numerical value of the threshold value for each index value given in the above embodiment is only an example, and an appropriate numerical value is obtained in advance by an experiment or the like according to the model or the specification and stored in the ROM 103 or the like. To.

≪Supplement≫
The fixing device and the image forming apparatus according to the present invention have been described above based on the embodiments and modifications, but the present invention is not limited to the above embodiments and modifications. By arbitrarily combining the embodiments obtained by applying various modifications to the above-described embodiments and modifications, and the components and functions of the embodiments and modifications without departing from the spirit of the present invention. The realized form is also included in the present invention.

The present disclosure can be widely applied to an image forming apparatus having a fixing apparatus in which a sheet on which an unfixed image is formed is passed through a nip portion and thermally fixed.

1 Printer 20 Image drawing part 30 Fixing part 31 Heating unit 32 Pressurizing roller (pressurizing member)
33 Swing arm 34 Tension spring 36 Displacement detector 100 Control unit (also functions as 1st acquisition unit, 2nd acquisition unit, 3rd acquisition unit)
101 CPU
104 Counter 105 Backup memory (rotation time storage unit, control time storage unit)
106 Motor drive circuit 107 Rotation speed detection unit 108 Drive current detection unit 109 Torque table storage unit 311 Fixing belt (heating rotating body)
312 Heating roller (heating part)
313 Fixing member 3131 Resin pad 314 Heater part 315 Temperature sensor (Temperature detection part)
Np Nip part Nd Nip width M2 Fixing motor

Claims (19)

A fixing device that executes a fixing job by pressing a pressure member against a heated rotating body heated by the heating part to form a nip part, passing a sheet on which an unfixed toner image is formed on the nip part, and executing a fixing job. There,
The first acquisition unit for acquiring the first index value for indexing the amount of change in the coefficient of friction between the heating rotating body and the pressure member, and the first acquisition unit.
A second acquisition unit for acquiring a second index value for indexing the amount of change in the rigidity of the elastic layer in the heating rotating body and / or the pressurizing member.
A control unit that controls the rotation speed of the heated rotating body during idling based on the first index value and the second index value.
A fixing device characterized by being equipped with. The first index value is at least one of the total mileage of the heating rotating body and the total number of sheets to be passed through the nip portion, and also.
The second index value includes a first parameter indicating how warm the nip portion forming member including the heating rotating body and the pressurizing member is.
The control unit
When the first index value is equal to or higher than the first threshold value and the second index value is equal to or higher than the second threshold value, the rotation speed of the heated rotating body at the time of idle rotation is larger than the initial setting condition. The fixing device according to claim 1, wherein the fixing device is controlled so as to be. The second acquisition unit acquires the first parameter based on the history of the rotation time of the heated rotating body rotated prior to the idling rotation and the stop time of the heated rotating body stopped. The fixing device according to claim 2, wherein the fixing device is characterized. The second acquisition unit is
A rotation time storage unit that measures at least the rotation time of the heated rotating body at the time of executing a fixing job and stores the measured rotation time as a history at the first timing.
When the rotation stop time of the heated rotating body intervenes before the start of idle rotation, the total of the rotation time history immediately before the rotation stop is corrected and corrected according to the length of the rotation stop period immediately after that. A rotation time correction unit that obtains the rotation time, and
Equipped with
The fixing device according to claim 3, wherein the total rotation time obtained by adding the history of subsequent rotation times to the corrected rotation time is acquired as the first parameter. The fixing device according to claim 4, wherein the first timing includes any one of the time when the fixing job is completed, the time when the power supply to the device is finished, and the time when the rotation of the heating rotating body is stopped. .. The rotation time correction unit corrects the total sum of the rotation time history immediately before the rotation stop according to the length of the rotation stop period immediately after the rotation stop, based on the first table or the first calculation formula obtained in advance. The fixing device according to claim 4 or 5, wherein the fixing device is characterized in that. The second acquisition unit is
In addition to the first parameter, the second parameter is acquired based on the heating control time of the heating unit executed prior to the idle rotation.
The fixing device according to any one of claims 4 to 6, wherein the second index value is acquired based on the value of the first parameter and the value of the second parameter. The second acquisition unit is
A control time storage unit that measures at least the heating control time of the heating unit when the fixing job is executed and stores the measured heating control time as a history at the second timing.
Further provided with a control time correction unit for obtaining a correction control time by correcting the total of the history of the heating control time immediately before the warm-up based on the temperature of the heating unit at the start of warm-up immediately after the second timing. ,
The fixing device according to claim 7, wherein the total heating control time obtained by adding the subsequent heating control time to the correction control time is acquired as the second parameter. The second acquisition unit is
The temperature of the heating unit at the start of heating control of the heating unit is detected, and if the detected temperature is equal to or less than a predetermined threshold value, the history of the corrected rotation time is reset to acquire the first parameter. The fixing device according to claim 8. When the correction control time is shorter than the correction rotation time at the time when the heating control of the heating unit is started, the second acquisition unit uses the correction control time instead of the correction rotation time. The fixing device according to claim 8, wherein the first parameter is acquired. The fixing device according to claim 9 or 10, wherein the time of disclosure of the heating control of the heating unit is the start of warm-up control. Any one of claims 8 to 11, wherein the second timing includes any one of the start of the fixing job, the end of the fixing job, and the end of power supply to the heating unit. The fixing device described in the section. The control time correction unit uses the second table or the second arithmetic expression obtained in advance to add the sum of the history of the heating control time immediately before the warm-up to the temperature of the heating unit at the start of the warm-up control. The fixing device according to any one of claims 8 to 12, wherein the fixing device is corrected based on the above. The second acquisition unit is
Instead of the first parameter, the second parameter is acquired based on the heating control time of the heating unit executed prior to the idle rotation.
The fixing device according to claim 3, wherein the value of the second parameter is used as the second index value. Further, a third acquisition unit for acquiring a third index value for indexing the relative pressure contact force between the heating rotating body and the pressurizing member is provided.
The first aspect of the present invention, wherein the control unit controls the rotation speed of the heated rotating body at the time of idling based on the first index value, the second index value, and the third index value. Fixing device. Instead of the first acquisition unit or the second acquisition unit, a third acquisition unit for acquiring a third index value for indexing the relative pressure contact force between the heating rotating body and the pressurizing member is provided.
The claim is characterized in that the control unit controls the rotation speed of the heated rotating body at the time of idle rotation based on the first index value and the third index value, or the second index value and the third index value. Item 1. The fixing device according to Item 1. The pressurizing member is a pressurizing rotating body.
One of the pressurized rotating body and the heated rotating body is rotationally driven by a drive source, and the other rotating body is driven to rotate.
A torque detecting unit for detecting the driving torque of one of the rotating bodies to be rotationally driven is provided.
The fixing device according to claim 15, wherein the third index value is the detected drive torque. The heating rotating body is an endless belt that orbits.
The fixing according to any one of claims 1 to 17, wherein the heating portion heats a region of one round of the belt that is separated from the nip portion in the circumferential direction. Device. An image forming apparatus including an image forming portion for forming an unfixed toner image on a sheet and a fixing portion for thermally fixing the unfixed toner image to the sheet.
An image forming apparatus according to claim 1, wherein the fixing device according to any one of claims 1 to 18 is used as the fixing unit.

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