JP7046520B2 - Fixing device - Google Patents

Description

The present invention relates to a fixing device used in an image forming apparatus such as a copying machine or a printer using an electrophotographic method.

In the electrophotographic image forming apparatus, a fixing device is used to fix the unfixed toner image formed on the recording material on the recording material. In the fixing device, a heated fixing member and a pressure member are pressed against each other to form a fixing nip portion, and a recording material is sandwiched and conveyed to the nip portion to heat and pressurize an unfixed toner image to fix it on the recording material.

As a fixing device, a belt heating type fixing device using a cylindrical rotatable fixing belt (hereinafter referred to as a belt) as a fixing member has been put into practical use. In the belt heating type fixing device, a plate-shaped heater extending in the direction of the belt rotation axis is fixedly arranged inside the belt, and the heater and the pressure roller, which is a pressure member, are pressed against each other via the belt to form a fixing nip portion. By rotating the belt drivenly by the pressurizing roller, the recording material is conveyed to the fixing nip portion and the toner image is heated and fixed. As the heater, a plate-shaped heating element in which a resistor pattern that generates heat by energization is closely adhered to an insulating base material such as ceramic is used.

The heater gradually deteriorates due to durable use. In the deteriorated state, the resistance value of the resistor may increase due to repeated energization, the current may decrease, and the power consumption of the heater, that is, the calorific value may decrease. In Patent Document 1, the current value flowing through the heater is detected and the heater life is determined based on the current value.

Further, in a heater in which a thermistor for temperature detection is brought into contact with the surface opposite to the surface rubbing against the belt of the heater, the elastic member made of a heat insulating material that presses the thermistor against the heater is crushed due to durability and the pressing pressure is reduced. The detection temperature of is lower than the actual temperature of the heater. In addition, in order to reduce the rubbing resistance between the belt and the heater during belt rotation, the lubricant initially applied to the inner surface of the belt or the rubbing surface of the heater permeates the elastic member during durability, and the heat insulating effect is reduced to the actual heater temperature. The difference between the temperature detected by the thermistor and the temperature detected by the thermistor increases. Therefore, in Patent Document 2, the thermistor detection temperature for determining the start of image formation is controlled to be set stepwise lower than the cumulative number of image formations.

Japanese Unexamined Patent Publication No. 2006-39773 Japanese Unexamined Patent Publication No. 2016-42112

Other than the above, there is dirt on the rubbing surface of the heater as a durability deterioration. This occurs when the wear debris on the inner surface of the belt and the deteriorated grease, which has become highly viscous due to the liberation of the base oil contained in the grease of the lubricant, accumulates on the rubbing surface of the heater. Such dirt hinders heat transfer from the heater to the belt, which reduces the heating efficiency of the belt. As the durability increases, dirt accumulates and gradually, but the temperature rise time from when the heater is energized at the start of image formation until the belt is heated to a desired temperature becomes longer. In addition, the heater is heated more than necessary, and at the end of durability, the device is stopped by detecting the overheating of the heater, or the energization cutoff element such as a fuse made in the energization circuit near the heater is operated to stop the device.

In the above-mentioned Patent Document 1, the life of the heater due to such dirt cannot be determined. Further, in Patent Document 2, since the temperature change of the heater and the belt due to dirt is not assumed, the belt temperature cannot be appropriately controlled.

In addition, when the device is stopped, it is necessary to clean the heater or replace the heater so that the device can be reused. It is inconvenient for users.

An object of the present invention is to estimate the heater life due to stains on the heater and to shorten the stop time by performing maintenance before stopping the device based on the estimation result. The purpose of the present invention is to properly control the belt temperature even if the heater is dirty at the end of durability to prevent poor fixing of the toner image.

In the present invention, an image forming portion for forming a toner image on a recording material, a tubular fixing film, a heated body in contact with the inner surface of the fixing film, and a fixing nip portion together with the heating body via the fixing film are provided. It has a roller to be formed and a temperature detecting element for detecting the temperature of the heating body, and the fixing nip portion sandwiches and conveys the recording material while fixing the toner image formed on the recording material to the recording material. In an image forming apparatus having a unit and a control unit, when the temperature of the heating body is raised, the control unit has a detecting means for detecting the time until the temperature of the heating body reaches a predetermined temperature. Determines that the life of the fixing unit is when the time when the cumulative usage increases is shorter than the threshold value with respect to the time when the cumulative usage of the fixing unit is initial. It is characterized in that the image forming operation can be continued by raising the target temperature of the heating body when fixing the toner image on the recording material as compared with before the temperature becomes shorter than the threshold value .

According to the fixing device according to the present invention, the heater dirt life is calculated and displayed based on the change over time of the heater temperature rise time, so that the time when maintenance is required before the device is stopped due to dirt. Can now be judged. In addition, the setting of the fixing device can be appropriately changed according to the progress of the life, and the occurrence of fixing failure can be suppressed.

Cross-sectional view of the fixing device Side view and block diagram of the fixing device Image forming device Heater temperature rise transition Durability transition of heater temperature rise time Flowchart for calculating heater life Cross-sectional view of fixing device (Example 2) Relationship between heater dirt and temperature distribution (Example 2) Flowchart for calculating heater life (Example 2) Cross-sectional view of other fixing devices

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

(Image forming device)
The schematic configuration of the image forming apparatus to which the present invention is applied will be described. FIG. 3 is an overall cross-sectional view of the color image forming apparatus.

The first, second, third, and fourth image forming portions Py, Pm, Pc, and Pk are arranged in the apparatus, and toner images of different colors are formed through the processes of latent image, development, and transfer. Will be done. Photosensitive drums 1a, 1b, 1c, and 1d, which are image carriers, are rotatably supported, and on the outer periphery thereof, a charger 2a, 2b, 2c, 2d, a developer 3a, 3b, 3c, 3d, and a primary transfer means. 4a, 4b, 4c, and 4d are provided, and exposure devices 5a, 5b, 5c, and 5d are further arranged below the image forming portion.

The photosensitive drums 1a to 1d are rotationally driven by a drum motor (not shown), charged to a predetermined potential by the chargers 2a to 2d, and then emit laser light corresponding to the image signal from the exposure devices 5a to 5d to emit the photosensitive drums 1a to 1d. An electrostatic latent image is formed on the photosensitive drums 1a to 1d by condensing and exposing the light on the bus.

The developers 3a to 3d are filled with a predetermined amount of yellow, magenta, cyan, and black toner as developer, respectively, and the latent images on the photosensitive drums 1a to 1d are developed to develop the yellow, magenta, and magenta, respectively. Visualize as a cyan and black toner image.

Then, the intermediate transfer body 25 stretched by the tension roller 21, the drive roller 22, and the backup roller 23 is rotationally driven in the direction of arrow G by the drive roller 22, and the primary transfer means 4a is charged with toner by a high-voltage power supply (not shown). A transfer voltage having a polarity opposite to that of the polarity is applied, and the yellow toner image of the first color on the photosensitive drum 1a is transferred to the intermediate transfer body 25 (primary transfer). Similarly, for the second color, the third color, and the fourth color, the toner image developed on the photosensitive drum is superposed on the intermediate transfer body 25 and transferred to obtain a color image on which the toner images of the four colors are superimposed.

Residual transfer toner remains on the surfaces of the photosensitive drums 1a to 1d after transfer, and the residual transfer toner is removed by the cleaning devices 6a, 6b, 6c, 6d and collected in a toner recovery container (not shown). After that, the residual charges of the photosensitive drums 1a to 1d are eliminated by the preexposure devices 7a, 7b, 7c, and 7d to prepare for the next latent image formation.

The recording material P is sent to the secondary transfer unit where the backup roller 23 grounded to the secondary transfer means 24 is in contact with the secondary transfer means 24 by a recording material transfer device (not shown), and the recording material P is sent to the secondary transfer means 24 in the opposite direction to the charging polarity of the toner. When a polar secondary transfer voltage is applied, the four-color toner images on the intermediate transfer body 25 are collectively transferred to the recording material P (secondary transfer).

The recording material P to which the toner image is transferred is conveyed to the fixing device 10, and the toner image is heated and melted and fixed to the recording material to form a full-color image.

The transfer residual toner remaining on the intermediate transfer body 25 moves with the rotation of the intermediate transfer body 25, is removed by the cleaning blade 20, and is collected in a collection container (not shown).

(Fixing device)
FIG. 1 is a cross-sectional view of a fixing device 10 using a fixing belt to which the present invention is applied.

In FIG. 1, the fixing belt 11 is provided with an elastic layer made of silicone rubber having a thickness of about 200 μm on the outer peripheral surface of a cylindrical base layer having a thickness of about 50 μm made of stainless steel, and has a thickness of about 30 μm from PFA on the outer peripheral surface of the elastic layer. It is an endless belt-shaped fixing member that covers the tube. Reference numeral 14 is a heater holder as a heater holding member, which is made of a liquid crystal polymer resin having heat resistance and rigidity.

Reference numeral 13 is a heater, in which a resistor that rapidly generates heat when energized is formed in the shape of an elongated plate-shaped ceramic substrate along the longitudinal direction of the substrate, the resistor is covered with a glass protective layer, and the end in the longitudinal direction of the resistor is formed. It has a conductor electrode part for applying a voltage to the part.

The heater 13 is arranged in a recess formed along the longitudinal direction on the side surface of the belt of the heater holder 14. The fixing belt 11 is loosely fitted to the heater holder 14.

The stay 15 is a highly rigid support formed by molding a stainless steel sheet metal into a U shape, and the heater holder 14 is fixed to the stay 15 to reinforce the heater holder 14.

Reference numeral 19 is a pressure roller as a pressure member. A silicone rubber layer having a thickness of about 3 mm is formed on the peripheral surface of a stainless steel core metal by injection molding, and a PFA resin tube having a thickness of about 40 μm is coated on the silicone rubber layer. .. The pressure roller 19 is arranged so that both ends of the core metal are rotatably held by the side plates on the back side and the front side of the fixing device frame (not shown). The heater 13 is fixed by arranging the heater holder 14 in parallel with the pressurizing roller 19 and urging both ends of the heater holder 14 in the axial direction of the pressurizing roller 19 with a predetermined force by a pressurizing mechanism (not shown). A fixing nip portion N having a predetermined width required for fixing is formed by pressure contacting the pressure roller 19 via the 11.

The pressure roller 19 is rotationally driven in the direction of arrow A at a predetermined peripheral speed by a drive device described later. As a result, the fixing belt 11 pressed against the outer surface of the pressure roller 19 receives the frictional force from the pressure roller 19 and rotates drivenly. The inner surface of the fixing belt 11 is in close contact with the fixing heater 13 and rotates while rubbing. Silicone oil and fluororesin-containing grease are applied to the inner surface of the fixing belt 11 and the rubbing surface of the heater 13 as a heat-resistant lubricant in order to ensure the slipperiness of the heater 13 and the belt 11.

Reference numeral 18 is a thermistor as a temperature detecting means. The thermistor 18 is arranged near the center where recording materials of all sizes pass along the width direction of the belt and at a plurality of positions other than the center, detects the temperature of the heater 13, and makes the detected temperature of the central thermistor the target temperature. The electric power supplied to the heater 13 is controlled.

The recording material P carrying the unfixed toner image is conveyed to the nip portion N in a state where the pressurizing roller 19 and the belt 11 are rotationally driven and the fixing heater 13 is controlled to the target temperature. The recording material P is heated by receiving heat from the fixing heater via the fixing belt 11, and at the same time, the toner image is pressed onto the recording material by being sandwiched by the nip portion. As a result, the toner image is fixed to the recording material P.

(Control device)
FIG. 2 shows a side view of the fixing device 10 (a view seen from the transport direction of the recording material) and a control block diagram of the fixing device.

Support members 12a and 12b molded from heat-resistant resin are attached to both ends of the heater holder 14, and a part of the support members 12a and 12b is inserted inside both ends of the belt 11 so that the support members 12a and 12b are inserted into a fixing device frame (not shown). The belt 11 is supported by fixing the 12b. The support members 12a and 12b have wall portions 12c and 12d along the peripheral direction of the belt, and the belt 11 offset to the left or right in the axial direction abuts on the wall portions 12c or 12d in the axial direction of the belt 11. The position is regulated.

A power supply 85 and a control circuit 84 for controlling the amount of energization are connected to the heater 13. A plurality of thermistors 18a, 18b, 18c are pressed as heater temperature detecting means on the side opposite to the surface of the heater 13 in contact with the belt. In this embodiment, thermistors are placed near the center (18b) and near both ends (18a, 18c) through which recording materials of all sizes pass. The central thermistor 18b is used to control the heater 13 to the target temperature, and all thermistors are used for dirt estimation described later. The reason why the thermistors are arranged near both ends is that a relatively large amount of abrasion powder on the inner surface of the belt and the end surface of the belt, which causes stains, is generated near the ends where the belt 11 and the support members 12a and 12b rub against each other.

The control device 81 controls the control circuit 84 based on the detection temperature of the thermistor 18b to control the amount of energization. This causes the heater 13 to converge to the target temperature. The drive device 83 is a motor connected to a gear 17 that rotates the pressure roller 19, and is controlled by the control device 81 to control the rotation and stop of the pressure roller 19.

Further, the control device 81 calculates the heater dirt life by the method described later based on the detection results of the thermistors 18a, 18b, 18c and the temperature rise time of the heater 13 measured by the timer 87, and stores the calculation result in the storage device 86. ..

The timer 87 may be built in the control device 81. Further, the calculated heater dirt life is displayed on the display device 82 provided in the operation unit or the like of the image forming apparatus. In addition to displaying on the display device 82, information on the life of the heater dirt may be transmitted to the monitoring host computer installed at an external service base or the like via a communication line.

Next, the features of the present invention will be described with reference to FIGS. 4, 5, and 6.

FIG. 4 shows an example of the temperature transition detected by the thermistor 18a immediately after the start of energization from the state where the temperature of the heater 13 is near room temperature.

T0 is the case where the fixing device is new, and T20 is the temperature transition after the integrated printing operation of 200,000 sheets is performed. It has been confirmed that dirt has adhered to the heater rubbing surface, which has been subjected to a total of 200,000 sheets, at the position corresponding to the thermistor 18a. The temperature rise time until the thermistor detection temperature reaches 200 ° C. is 8 seconds (ta (0)) for a new product, but it is shortened to 6 seconds after 200,000 sheets. It is considered that this is because the adhered dirt becomes a thermal resistor, the amount of heat transfer from the heater 13 to the belt 11 is reduced, and the heating rate of the heater 13 is increased.

FIG. 5 shows an example of the change in the temperature rising time with respect to the cumulative number of prints since the start of use of the fixing device. The temperature rise time is gradually shortened with durability. It is considered that this is because the amount of dirt accumulated in the heater 13 gradually increases and the amount of heat transfer gradually decreases. Since the wear of the belt 11 occurs with the rotation of the belt, it is considered that the accumulated amount depends on the integrated rotation time of the belt.

Based on the above, the heater dirt life L is defined by the following formula. Here, ta (n) is the temperature rise time measured by the thermistor 18a at any time during durability, ta (0) is the temperature rise time initially measured by the thermistor 18a, and K is the maximum allowable amount of dirt. It is the amount of decrease from the initial stage of the temperature rise time. K is subjected to a durability test in advance and stored in the storage device 86. The maximum allowable amount of stain is the upper limit amount at which the fixing failure of the toner image does not occur due to the decrease in the belt temperature.
Heater dirt life L = min (La, Lb, Lc) ... Minimum value of La, Lb, Lc La = 100 × [ta (0) -ta (n)] / K (unit:%)
Lb = 100 × [tb (0) -tb (n)] / K
Lc = 100 × [tc (0) -tc (n)] / K
Table 1 shows the results of the authors' investigation of the durability change and the cause of the temperature rise time. There are multiple causes for the change in the temperature rise time, and the state of change is different for each. Of the causes, the only reason why the temperature rise time is short is that the heater is dirty and the belt is damaged, so it can be distinguished from other causes. In rare cases, belt breakage may occur at the end of durability, but in that case, since the belt 11 does not adhere to the heater 13 at the damaged portion, heat transfer to the belt 11 is almost eliminated and the heater 13 rapidly overheats. Therefore, since the temperature rise time is suddenly shortened, it can be determined that the belt is damaged from the rate of change of the temperature rise time.

In this way, it is possible to distinguish the cause from the state of the change over time in the temperature rise time.

ヒータ汚れ寿命Ｌの定義より定着不良が発生しない許容最大寿命は１００％（Ｋ＝ｔ（０）－ｔ（ｎ）のとき）である。したがってＬが１００％に到達する前にメンテナンスすることが必要である。しかし何らからの理由でメンテナンスができない場合も有り得る。そのためＬが１００％に到達した後も定着装置の設定を自動変更して少なくともプリント動作が可能な状態を維持することがユーザー立場にとって好ましい。

According to the definition of the heater dirt life L, the maximum allowable life at which fixing failure does not occur is 100% (when K = t (0) -t (n)). Therefore, maintenance is required before L reaches 100%. However, there may be cases where maintenance is not possible for some reason. Therefore, even after L reaches 100%, it is preferable from the user's point of view to automatically change the setting of the fixing device to maintain at least a state in which printing operation is possible.

Table 2 shows the settings when the life L exceeds 100%. However, the setting is not limited to this embodiment and may be appropriately changed according to the device specifications and the fixing device configuration. After exceeding 100%, if it is less than 110% (condition 1), the target temperature is raised by 10 ° C. to suppress a decrease in belt temperature and prevent fixing failure. If it is less than 120% (condition 2), the printing speed is further reduced by 10 to reduce the number of recording materials passing through the fixing nip per unit time and suppress the decrease in belt temperature due to heat transfer to the recording material. If it becomes 120% or more, the temperature rise of the heater at the dirty position approaches the heat resistance limit of 280 ° C. of the heater holder, and the device is stopped. Optimal values for these settings are obtained in advance by experiments and stored in the storage device 86.

上記で説明した汚れの判定、寿命算出、および寿命が１００％超えた後の定着設定変更の制御フローについて図６により説明する。

The stain determination, the life calculation, and the control flow for changing the fixing setting after the life exceeds 100% will be described with reference to FIG.

When the image forming apparatus receives the print command signal, the flow is started. The operation of each step is all controlled by the control device 81.

At the start time, the thermistors 18a, 18b, 18c detect the heater temperature (Tha0, Thb0, Thc0) at each position and temporarily store it in the storage device 86 <S1>. This detected temperature is later used to determine if the heater temperature at the start was near room temperature.

Next, the control circuit 84 and the drive device 83 are turned on to energize the heater 13 and start the rotation of the pressurizing roller 19 and the belt 11 <S2>. At this time, the energization ratio is set to 100% for the heater 13 so that the heater 13 is always energized (energization ratio 0% is energization OFF).

Next, the timer 87 starts measuring the temperature rise time <S3>, detects the heater temperature at predetermined time intervals, and sets the elapsed time when the heater temperature at each position reaches the target temperature Tt (200 ° C.). (S4 to S6) determined to be (ta (n), tb (n), tc (n)). As the temperature rise time, only the elapsed time at the time when one of the thermistors reaches the target temperature Tt may be used.

Next, the amount of change between the temperature rise time ta (n-1) measured at the time of the previous temperature rise and the temperature rise time ta (n) this time is compared with the predetermined value A (= 4 sec), and the change in the temperature rise time is rapid. <S7> to determine whether or not. The same judgment is made for tb and tc. If the amount of change is A or more, it is abrupt and the device is stopped because it is regarded as a sign that belt breakage or the like occurs or occurs <S18>. If it is less than A, it is continuously compared with the initial value ta (0) <S8>, and if it is shorter than the initial value, it is judged that the temperature rising time is gradually shortened, and it is judged that the heater contamination is progressing.

Before calculating the dirt life, check whether the heater temperature at the start is near room temperature <S9>. For example, it is indistinguishable from the case where the heater temperature is high when the printing is completed last time and the temperature rise time is short and the temperature is shortened due to stains. Therefore, when the heater temperature is Tr (= 30 ° C.) or higher, it is determined that the temperature is not near room temperature, and the stain life is not calculated thereafter, and printing is immediately performed.

If the heater temperature is less than Tr (= 30 ° C), it is judged that it was near room temperature, the memory of the temperature rise time this time, the calculation of the dirt life L, the life update, and the display of the life value updated on the display device 82. <S10 to S12>. This enables the service person to judge the necessity of maintenance by looking at the displayed value. When maintenance is performed, the serviceman resets the life to 0% from the operation unit (not shown).

If the life is less than 100%, it shifts to printing, but if it exceeds 100% and maintenance is not performed, the setting of the fixing device is changed according to the progress of the life value and controlled so that fixing failure does not occur. <S15 to S18>.

As described above, since the heater dirt life is calculated and displayed based on the change over time of the heater temperature rise time, it is possible to determine the maintenance time before the device is stopped due to dirt. In addition, as a result of the tests by the authors, the target life of the heater is 300,000 as the specification of the image forming apparatus, whereas the conventional fixing device causes fixing failure with 320,000, but the fixing to which the present invention is applied is applied. No fixing failure occurred in the apparatus even with 350,000 sheets.

In the first embodiment, the temperature rise time of the heater is measured in order to calculate the dirt life, but instead, the temperature difference between the heater and the belt may be measured. The second embodiment will be described with reference to FIGS. 7, 8 and 9.

FIG. 7 is a cross-sectional view of the fixing device 101, and the elements common to those in FIG. 3 are numbered the same.

Reference numeral 16 is a thermistor as a temperature detecting means for detecting the belt temperature. The thermistor 16 is urged toward the belt 11 by a leaf spring 161 fixed to the pedestal 162 provided on the heater holder 14 and pressed against the belt 11.

The arrangement of the thermistor 16 in the belt rotation axis direction is shown on the upper side of FIG. The thermistors for detecting the belt temperature are arranged near the center (16b) and near both ends (16a, 16c), and are arranged at substantially the same positions as the thermistors 18a, 18b, 18c for detecting the heater temperature. The thermistor 18b that detects the central temperature of the heater 13 is used to control the heater 13 to the target temperature.

An example of the temperature distribution of the heater 13 and the belt 11 when dirt D is accumulated at the end of the heater 13 is shown at the lower side of FIG. Here, the temperature distribution at the time when the temperature detected by the thermistor 18b reaches 200 ° C. after the start of energization from the state where the heater temperature is near room temperature is shown. At this time, the central belt temperature detected by the thermistor 16b is 170 ° C.

At the position where dirt D adheres (position 18a), the dirt becomes a thermal resistor and the amount of heat transfer from the heater 13 to the belt 11 decreases, so the heater temperature is higher than the position without dirt (positions 18b and 18c). Higher (225 ° C) and lower belt temperature (160 ° C). Therefore, the temperature difference between the heater and the belt is ΔTa (65 ° C.) at the position where the dirt D is attached, and ΔTb (30 ° C.) and ΔTc (30 ° C.) at the position where there is no dirt, and the dirt can be estimated based on the temperature difference.

Based on the above, the heater dirt life L2 is defined by the following formula. Here, ΔTa (n) is the temperature difference between the heater and the belt measured at any time during durability, ΔTa (0) is the temperature difference measured at the initial stage, and M is the initial temperature difference at the maximum allowable dirt amount. It is an increase from.
Heater dirt life L2 = min (L2a, L2b, L2c) ... Minimum value of L2a, L2b, L2c L2a = 100 × [ΔTa (n) −ΔTa (0)] / M (unit:%)
L2b = 100 × [ΔTb (n) −ΔTb (0)] / M
L2c = 100 × [ΔTc (n) −ΔTc (0)] / M
The amount of dirt accumulated in the heater 13 gradually increases with durability, and the amount of heat transfer to the belt 11 gradually decreases, so that the temperature difference between the heater 13 and the belt 11 also gradually increases. As shown in Table 3, the state of the change over time of the temperature difference caused by the heater contamination is different from the change due to other causes, so that it can be distinguished.

上記で説明した汚れの判定、寿命算出のフローについて図９により説明する。なお実施例１と同じ制御ステップについては図６と同じ記号を付してある。以下、実施例１と異なるステップ＜Ｓ２１～Ｓ３５＞の制御内容だけを説明する。

The flow of dirt determination and life calculation described above will be described with reference to FIG. The same control steps as in the first embodiment are designated by the same symbols as those in FIG. Hereinafter, only the control contents of the steps <S21 to S35> different from those of the first embodiment will be described.

In steps S21 to S24, the time t after the start of energization of the heater 13 is measured by the timer 87, and when the predetermined time Tm (8 sec) is reached, the heater temperature (Tha (n), Thb (n), Thc (n)). , Belt temperature (Tfa (n), Tfb (n), Tfc (n)) is detected, and the temperature difference (ΔTa (n), ΔTb (n), ΔTc (n)) is calculated from the detection result. The detection timing may be the time when any one of the thermistors 18a, 18b, and 18c for detecting the heater temperature reaches the target temperature Tt (200 ° C.).

Next, the amount of change in the temperature difference ΔTa (n-1) measured at the time of the previous temperature rise and the temperature difference ΔTa (n) this time is compared with the predetermined value B to determine whether or not the change in the temperature difference is rapid. S25>. The same determination is made for ΔTb and ΔTc. If the amount of change is B or more, it is sudden and the device is stopped because the belt is damaged, the thermistor is broken, or the thermistor floats (contact failure). If it is less than B, it is continuously compared with the initial value ΔTa (0) <S26>, and if it is larger than the initial value, there is a possibility that the heater is contaminated. Next, the heater temperature The (n) is compared with the initial value The (0), and if it is higher than the initial value, it is determined that the cause is dirt <S27>.

Next, it was checked whether the heater temperature at the start of energization was near room temperature <S9>, and if it was near room temperature Tr, the temperature difference was stored, the dirt life L2 was calculated, the life was updated, and the display device 82 was updated. Displaying the life value <S28 to S30>.

If the life is less than 100%, the process shifts to printing <S31, S14>, and if it exceeds 100%, the setting of the fixing device is changed to control <S32 to S35> so that fixing failure does not occur. Here, the same setting change as in the first embodiment was adopted.

By the above method, the heater dirt life could be calculated based on the change over time of the temperature difference between the heater and the belt.

In Examples 1 and 2, the case where the present invention is applied to the fixing device in which the heater is arranged in the nip portion has been described, but it is clear that the heater position is not limited to the nip portion. For example, it can be applied to a fixing device 102 in which a heater is arranged in addition to the nip portion as shown in FIG. In the fixing device 102, a heater 130 having an arc-shaped cross section along the inner peripheral surface of the belt 11 is used, the heater 130 is fixed on the heater holder 131, and the heater holder 131 is moved to the belt 11 side by the spring 15 provided on the stay 132. The heater 130 is brought into contact with the inner surface of the belt by urging. Further, a thermistor 160 is provided as a temperature detecting means of the heater 131, and a non-contact temperature sensor 180 is provided as a temperature detecting means of the belt 11.

10 fixing device, 11 fixing member, 13 heater, 14 heater holding member,
16, 16a, 16b, 16c Belt temperature detecting means,
18, 18a, 18b, 18c Heater temperature detecting means, 19 Pressurizing member,
81 control device, 82 display device, 85 storage device, 87 timer,
130 heater, 131 heater holding member, 160 heater temperature detecting means,
180 Belt temperature detection means, D dirt, N nip

Claims (5)

An image forming part that forms a toner image on the recording material,
A tubular fixing film, a heating body that contacts the inner surface of the fixing film, a roller that forms a fixing nip portion together with the heating body via the fixing film, and a temperature detecting element that detects the temperature of the heating body. A fixing unit that fixes the toner image formed on the recording material to the recording material while sandwiching and transporting the recording material at the fixing nip portion.
Control unit and
In an image forming apparatus having
It has a detecting means for detecting the time until the temperature of the heating body reaches a predetermined temperature when the temperature of the heating body is raised.
The control unit determines that the life of the fixing unit is determined when the time when the cumulative usage increases is shorter than the threshold value with respect to the time when the cumulative usage of the fixing unit is initial. However, the image formation is characterized in that the image formation operation can be continued by raising the target temperature of the heating element when fixing the toner image on the recording material as compared with before it becomes shorter than the threshold value. Device. The image forming apparatus according to claim 1, further comprising a display unit for displaying the life. The image forming apparatus according to claim 1 or 2, wherein the fixing unit is integrally removable from the image forming apparatus. After it is determined that the fixing unit has reached the end of its life, the control unit sets the time when the cumulative usage increases with respect to the time when the cumulative usage of the fixing unit is initially set. When it becomes shorter than the first threshold value which is further lower than the threshold value, the number of recording materials passing through the fixing nip per unit time is reduced as compared with before it becomes shorter than the first threshold value, and the image forming operation is performed. The image forming apparatus according to claim 1 or 3, wherein the image forming apparatus is configured to be sustainable. After it is determined that the fixing unit has reached the end of its life, the control unit sets the time when the cumulative usage increases with respect to the time when the cumulative usage of the fixing unit is initially set. The image forming apparatus according to claim 4 , wherein the image forming operation is prohibited when the second threshold value is further lower than the first threshold value.

Images