JP2000131978A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correctly estimate the life of a fixing device irrespective of a sheet passage mode or a state of sheet passage and to promote replacement at proper time by integrating the number of passed sheets which is weighted according to the sheet passage mode and the state of sheet passage. SOLUTION: After the finish of image formation for one page, whether a sheet with the image on is passed in a plain-sheet mode or an OHT mode is judged. Further, in the case of the plain-sheet mode, whether it is printed in monochromatic color or full color is judged. Then, a coefficient corresponding to the degree of thermal damage to a fixing device in each sheet passage mode is multiplied by the count of the one page, thereby weighting it. The coefficient of weighing at the time is determined on the basis of the number of sheets passable until the expiration of the life in a certain mode (for example, plain sheet mode, full color). The value of the lastly weighted count is integrated into the number of the total count. Then in the case the number of the total count reaches a given number of sheet or larger, the advance notice of the expiration of the fixing device is promoted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using an electrophotographic process, such as a copying machine, a facsimile, and a laser printer.

[0002]

2. Description of the Related Art An image forming apparatus employing an electrophotographic process system mainly includes a photosensitive drum unit, a developing device, a transfer device, a fixing device, and the like. These units and devices are designed as consumables depending on the model of the image forming apparatus.In this case, the life of these consumables must be set to an appropriate value in order to always provide users with stable and high-quality print images. It is important that the user be notified of the life expectancy and replace the consumables.

Incidentally, in the case of a fixing device, if the fixing device is used for a long period of time, image quality defects and fixing defects occur due to deterioration of components in the fixing device. Particularly, in a fixing roller or the like having an ultra-low hardness rubber layer in the elastic layer, a phenomenon occurs in which the rubber layer peels off from the core shaft due to thermal deterioration of the rubber.
At this time, there is a possibility that the conveyance system on the fixing and discharging side is stained by the separated rubber, and the driving system is damaged because the fixing roller cannot be driven to rotate with a normal driving torque.

In order to prevent the above phenomenon, it is necessary to accurately predict the life of the fixing device. As a method of detecting the deterioration and life of the fixing device used in the main body, a method of monitoring the number of recording materials passed and the time of passing the recording material is general and easy. When the paper passing time is exceeded, a message such as a notice of the life expectancy or a replacement of the fixing device is displayed on the image forming apparatus main body or the connected PC.

[0005]

However, in an image forming apparatus having a plurality of paper passing modes having different fixing temperatures, process speeds, and throughputs, thermal damage to the fixing device differs depending on the paper passing modes. Therefore, the number of lifespans of the fixing device may vary depending on the paper passing mode. Since the types of the paper passing modes used in the actual market and the usage ratios thereof differ depending on the user, the number of lifespans of the fixing device greatly varies. In such a case, there is a problem that the service life of the fixing device cannot be accurately detected by simply monitoring the number of sheets passed as in the related art as the life detection of the fixing device.

The above problem can be avoided by setting the life of the fixing device to the shortest life under the strictest sheet passing conditions. However, it is rare that all users use the apparatus under such severe conditions. is there. Therefore, in such a method, there is a case where a normal user is urged to give a very early notice of the service life, so that there is a problem that the fixing device cannot be effectively used just before the service life.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a paper feed mode and a paper feed state even when the life of the fixing device differs depending on the paper feed mode and the paper feed state. Regardless, an object of the present invention is to provide an image forming apparatus that can accurately predict the life of the fixing device and prompt the user to replace the fixing device at an appropriate time.

[0008]

According to a first aspect of the present invention, there is provided an image forming apparatus having a fixing device life detecting means for predicting the life of a fixing device from the number of sheets passed through a recording material. When there is a difference in the number of lifespans of the fixing device depending on the sheet passing mode and the sheet passing state, the number of sheets passed is weighted according to the sheet passing mode and the sheet passing state.

According to a second aspect of the present invention, in the first aspect of the present invention, when there is a difference between the number of lifespans of the fixing device due to the paper passing mode and the paper passing state, a certain paper passing mode or the paper passing state is used. A coefficient for normalizing the number of life sheets in another paper passing mode or paper passing state is provided for the number of life sheets in the paper passing mode, and weighting is performed by multiplying the coefficient by the number of paper passing sheets in accordance with the paper passing mode or the paper passing state. Features.

A third aspect of the present invention is characterized in that, in the first or second aspect of the invention, a coefficient for multiplying the number of sheets to be passed is changed according to a sheet passing mode having a different throughput number.

According to a fourth aspect of the present invention, in the first or second aspect of the present invention, a coefficient for multiplying the number of sheets to be passed is changed in accordance with a sheet passing mode having a different fixing temperature.

According to a fifth aspect of the present invention, in the first or second aspect of the invention, a coefficient for multiplying the number of passed sheets is changed according to the number of continuous sheets.

According to a sixth aspect of the present invention, in the first or second aspect of the present invention, the coefficient multiplied by the number of sheets to be passed is changed according to the temperature of the non-roller passing area of the fixing device during the passing of the sheet. Features.

According to a seventh aspect of the present invention, there is provided an image forming apparatus having a fixing device life detecting means for estimating the life of the fixing device from the number of sheets. If this occurs, a coefficient for standardizing the life number of parts of another manufacturer is provided to the life number of parts of one manufacturer, and the number of sheets passed is multiplied by the coefficient according to the manufacturer of the installed part. It is characterized by doing.

[0015]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

<Embodiment 1> This embodiment shows an example in which the present invention is applied to a full-color laser printer. The full-color laser printer according to the present embodiment employs a rotary development system, The developing and transfer steps are sequentially repeated while rotating the rotary containing the magenta, cyan and black toner cartridges to form a full-color image composed of four color toners.
Therefore, the throughput number of full-color printing is smaller than that of mono-color printing that requires only one color toner. In the case of this printer, the throughput number of A4 size plain paper is 24 ppm for mono color and 6 ppm for full color
It is.

Further, the present printer has two types of fixing speeds for plain paper and OHT film. The fixing speed in the plain paper mode is 177 mm / sec, and the fixing speed in the OHT mode is 30 mm, which is about 1/4 of the plain paper mode.
/ Sec. In the OHT mode, the transparency of the OHT is improved by lowering the fixing speed and sufficiently dissolving the toner.

Next, the hardware configuration of the fixing device will be described.

FIG. 4 is a schematic sectional view of a fixing device of the present printer. The illustrated fixing device is a general fixing device employing a heat roller system. Oil-less fixation that does not require Accordingly, since no oil and oil application mechanism or cleaning mechanism is required, the configuration of the fixing device is very simple, and operability is improved and cost is reduced.

This fixing device is a 550 W (12 W) heat source.
Rollers 1 and 2 are provided, which are rotating bodies each containing halogen heaters 1a and 2a (when 0 V is input). Here, for convenience, the upper roller 1 that directly contacts the unfixed toner image T on the recording material P is referred to as a fixing roller, and the lower roller 2 that contacts only the recording material P is referred to as a pressure roller.
Arrows in the drawing indicate the conveyance path of the recording material P.

The recording material P to which the unfixed toner image T has been transferred is conveyed to the nip between the fixing roller 1 and the pressure roller 2 along the entrance guide 6 and is fixed. And
The recording material P is discharged to the outside of the main body by activating a paper discharge sensor 7 composed of a flag and a photo interrupter (not shown) when passing through the conveying roller 8.

The fixing roller 1 and the pressure roller 2 are made of Al
Elastic layers 1c and 2c made of a silicone rubber material are provided on core shafts 1b and 2b made of a resin, and release layers 1d and 2d made of a fluororesin tube are formed on the surface layer.
Thickness of multi-color toner of single color to four colors of color image (number to number 1)
0 μm), it is necessary to set the thickness of the elastic layers 1 c and 2 c to several tens μm or more. If the elasticity of the fixing roller 1 and the pressure roller 2 is small, the resolution is lowered due to the unfixed toner concave portion and the collapse of the toner. As the material of the elastic layers 1c and 2c, RTV and LTV types of methyl rubber and methyl vinyl silicone rubber are suitable because they have elasticity.

In this embodiment, the elastic layers 1c, 2c
A dimethyl silicone rubber having a rubber hardness of 1 ° or less according to the JISA standard was used as a material for the above. The layer thickness of the fixing roller 1 was 2.1 mm, and that of the pressure roller 2 was 2.3 mm. Release layers 1d, 2 of 50 μm thick PFA tube
The hardness of the fixing roller 1 and the pressure roller 2 provided with d are 62 to 65 ° and 61 to 64 °, respectively.

Also, the diameter of the fixing roller 1 and the pressure roller 2 is A3 or Ledger-size paper (the maximum vertical length of the paper that can be passed by the machine is 432 of Ledger-size paper).
mm) is set to φ46.0 mm as a dischargeable diameter. The length in the longitudinal direction of the portion having the elastic layers 1c and 2c is set to 313 mm in order to cover LDR bleed size paper of 12 × 18.5 inches. The fixing roller 1 and the pressing roller 2 are brought into contact with each other with a total pressure of 45 kgf so that the nip width is about 9 m.
m.

By the way, in order to prevent electrostatic offset,
A voltage of about -1 kV is applied to the fixing roller 1 by a power supply 3 to the core shaft 1 b, and the potential of the core shaft 2 b of the pressure roller 2 is controlled by a diode 4.

With respect to the temperature control of the fixing roller 1 and the pressure roller 2, the thermistors 5a and 5b, which are temperature detecting elements, are arranged in contact with the fixing roller 1 and the pressure roller 2, respectively. Thus, the lighting control of the halogen heaters 1a and 2a is performed so that the roller surface temperature becomes a predetermined temperature. The temperature control temperature during standby is 165 ° C., and the temperature control temperature during printing is 170 ° C.

The image forming apparatus (full-color laser printer) has the same fixing temperature for full-color / mono-color paper passing as described above, but differs in the throughput number. Since the temperature control is controlled by the thermistors 5a and 5b abutting on the respective surfaces of the fixing roller 1 and the pressing roller 2, the surface temperature of the fixing roller 1 and the pressing roller 2 is 170 ° C. for both full color and mono color. It is.

However, since the thermal conductivity of rubber is considerably lower than that of a metal such as a hard roller, the greater the throughput number, the greater the temperature gradient in the radial direction of the rubber layer. As a result, even when the surface temperature is the same, the higher the throughput number, the higher the temperature of the rubber layer near the core axis, and the faster the thermal deterioration of the rubber. For this reason, the life of the fixing device when the paper is passed in the mono-color mode is shorter than that when the paper is passed in the full-color mode.

Although the fixing temperature is the same in the plain paper mode and the OHT mode, the fixing speed in the OHT mode is lower than that in the plain paper mode. Therefore, in the plain paper mode having a large number of throughputs, the number of rollers in the OHT mode is shorter than that in the OHT mode for the above-described reason.

In this embodiment, even when the number of lifespans of the fixing device differs in each paper passing mode, the life of the fixing device can be accurately detected by counting the number of papers passed.

FIG. 1 shows a routine of a fixing device life detecting sequence according to this embodiment.

In the fixing device life detecting sequence according to the present embodiment, a sheet passing count is performed on the controller side of the image forming apparatus main body every time image formation for one page is completed. Therefore, each time one page is printed, the controller executes the fixing device life detecting routine shown in FIG. Since the count for one page is based on A4 size paper, large size paper such as A3 is counted as 2 pages in A4 conversion.

First, after the image formation for one page is completed, it is determined whether the image has passed in the plain paper mode or the OHT mode. In the case of the plain paper mode, it is further determined whether or not the printing has been performed in mono color or full color.
In this way, the paper passing mode is changed to “plain paper mode full color”, “plain paper mode mono color”, “OHT mode”.
Are divided into three types. In the OHT mode, there was not much difference in life between full-color and mono-color paper passages. Therefore, in this embodiment, full-color and mono-color OHT modes are not classified. If there is a remarkable difference in life between the two even in the OHT mode, it is better to divide the cases into full color and mono color.

Next, weighting is performed on the sheet passing count according to each sheet passing mode. One page count is multiplied by a coefficient corresponding to the magnitude of thermal damage to the fixing device in each paper passing mode, and weighting is performed. The weighting coefficient at this time is determined based on the number of lifespan in a certain mode (here, “plain paper mode full color”). In other words, it is preferable to calculate a value that normalizes the life number in the other paper passing mode to the life number in the “plain paper mode full color”.

For example, it is assumed that the number of lifespans of the fixing roller when the paper is passed in each paper passing mode is as follows.

“Plain paper mode full color”… P (full) sheets “Plain paper mode monocolor”… P (mono) sheets “OHT mode”… P (OHT) sheets “Plain paper mode full color” lifespan P (full) ), The weighting coefficient (monocolor) of “plain paper mode monocolor” is P (full) / P (mono), and “O”
The weighting coefficient (OHT) of the “HT mode” is P (full) /
It is calculated as P (OHT).

Then, the value weighted and counted last is added to the total count number. At this time, if the total count reaches a predetermined number or more, the user is urged to announce the life of the fixing device. The predetermined number of sheets at this time is the number of life sheets when the sheet is passed in the “plain paper mode full color” as a reference. It is effective to display the fixing device replacement message on the display of the image forming apparatus main body or to display the fixing device replacement message on the PC side connected via the controller as the fixing device life notice.

According to the above method, even if the roller life differs depending on the paper passing mode, the total count number until the roller reaches the life becomes almost the same. As a result, the roller life can be accurately detected, and the user can be prompted to replace the fixing device at an appropriate timing.

Second Embodiment Next, a second embodiment of the present invention will be described.

For a soft roller or the like having a thick rubber layer, if the throughput number is large, the thermal damage to the fixing roller may be different between the initial stage of continuous printing and the subsequent stage.

FIG. 5 shows a temperature change of the fixing roller at the time of monocolor printing of the image forming apparatus according to the present embodiment.

In FIG. 5, each of the roller surface temperature ripples during printing indicates that one sheet of A3 size paper has passed through the fixing device. Here, as can be seen from FIG. 5, the temperature of the rubber layer on the surface and the temperature of the rubber layer near the core axis are higher after continuous printing to some extent than in the initial printing, and thermal damage to the fixing roller is caused. Is big. For this reason, thermal damage to the fixing roller differs between repetition of continuous printing of about several sheets and repetition of continuous printing of several tens or more sheets, resulting in a difference in the number of rollers used.

In this embodiment, even when the number of lifespans of the fixing device differs depending on the number of continuous prints as described above, the life of the fixing device can be accurately detected by counting the number of sheets passed.

That is, in the present embodiment, in addition to the life detecting routine of the first embodiment, the weighting coefficient for counting one page is changed according to the number of continuous papers during monocolor printing. At the time of full-color printing with a small number of throughputs, since the temperature difference due to the number of continuous sheets is small, the case is not classified according to the number of continuous sheets.

FIG. 2 shows a routine of a fixing device life detecting sequence according to this embodiment.

Each time the image formation for one page is completed, the sheet passing count is performed on the controller side of the image forming apparatus main body. Therefore, every time one page is printed, the controller
The routine for detecting the life of the fixing device shown in FIG. Basically, the count for one page is based on A4 size paper, so in case of large size paper such as A3, 2 pages in A4 conversion
Count as

Hereinafter, description of the same routine part as in the first embodiment will be omitted.

The part added to the routine shown in FIG.
At the time of mono-color printing, the case is divided into "continuous sheet number L or less" and "continuous sheet number L or more". In this case, the cases are classified into two types. However, the more accurately the cases are classified, the more accurate the life can be detected.

The coefficient (mono <L) is multiplied by the coefficient (mono> L) when the number of continuous papers is L or less, and weighted by multiplying the coefficient (mono> L) when the number is continuous L or more. I do. These coefficients are values that normalize the life number of the roller in each case to the life number in the “plain paper mode full color”.

That is, the number of lifespans of the fixing device when performing intermittent printing with “the number of continuous paper passing is L or less” is P (mono <
L), the life of the fixing device when performing intermittent printing with “L or more continuous papers” is P (mono> L), and the life of the fixing device when performing continuous printing in “plain paper mode mono color” is P (mono) sheets. At this time, the coefficient (mono <L) is P (full) / P (mono <L), and the coefficient (mono)
L) is calculated as P (full) / P (mono> L). Then, the coefficient of one page is multiplied by the coefficient in accordance with the paper passing mode and the number of continuous papers to be weighted.

Finally, the value is added to the total count. At this time, if the total count reaches a predetermined number or more, the user is urged to announce the life of the fixing device. The predetermined number of sheets at this time is the number of life sheets in the “plain paper mode full color” as a reference.

According to the above method, even if the roller life is different due to the paper passing mode or continuous / intermittent printing, the total count number until the roller reaches the life becomes the same. As a result, the roller life can be accurately detected, and the user can be prompted to replace the fixing device at an appropriate timing.

<Third Embodiment> Next, a third embodiment of the present invention will be described.

In the case of a soft roller or the like having a thick rubber layer, even if the roller surface temperature in the paper passing area is the same, the temperature of the rubber layer near the core axis during the paper passing greatly differs depending on the throughput number and continuous paper passing. The lifespan is also different. For this reason, in the first embodiment, weighting is performed on the count of the number of passed sheets corresponding to each paper passing mode in consideration of thermal damage to the fixing device in each paper passing mode.

However, in order to detect the degree of thermal damage to the rollers in the paper passing mode having different throughput numbers and fixing temperatures, it is only necessary to detect the temperature of the rubber layer near the core shaft. The temperature change of the rubber layer near the core axis appears in the roller surface temperature in the non-paper passing area where the media does not pass and does not take heat from the surface. Of the rubber layer can be detected.

Therefore, in the present embodiment, means for detecting the roller surface temperature in the non-sheet passing area is used, and the temperature is divided into cases to change the weight coefficient for the sheet passing count.

FIG. 6 shows the arrangement of the thermistors of the fixing device according to the present embodiment.

In the fixing device according to the present embodiment, the thermistors 5a and 5b abut the non-sheet passing area of the fixing roller 1 and the sheet passing area of the pressure roller 2, respectively. During printing, the temperature is controlled only by the central thermistor 5b on the pressure roller 2 side,
The temperature in the non-sheet passing area is constantly monitored by the end thermistor 5a on the fixing roller 1 side. The end thermistor 5a may be provided in the non-sheet passing area of the pressure roller 2. Here, the end thermistor 5a in contact with the non-sheet passing area is used as the non-sheet passing area temperature detecting means.

FIG. 3 shows a routine of a fixing device life detecting sequence according to the present embodiment.

Each time the image formation for one page is completed, the sheet passing count is performed on the controller side of the image forming apparatus main body. Therefore,
Every time one page is printed, the controller executes a fixing device life detecting routine shown in FIG. Since the count for one page is based on A4 size paper, large size paper such as A3 is counted as 2 pages in A4 conversion.

First, after the image formation for one page is completed, the detected temperature of the end thermistor 5a is confirmed, and “T1 ° C. or less”, “T1
1 to T2 ° C. ”and“ T2 ° C. or higher ”. Naturally, the finer the classification, the more accurate the roller life detection becomes. For example, if a relational expression between the detected temperature and the weighting coefficient is provided and the weighting coefficient is changed in multiple stages according to each detected temperature, more accurate roller life detection can be performed.

In the case of “T1 to T2 ° C.” and “T2 ° C. or higher”, the coefficient (T1 to T2) and the coefficient (T2) are multiplied by the sheet count. These coefficients are
The life number at “T1 to T2 ° C.” and “T2 ° C. or higher”
It is a value standardized to the number of lifespan at 1 ° C. or less.

That is, the number of lifespan at “T1 ° C. or less” is P
(T1), the life number at “T1 to T2 ° C.” is represented by P (T1 to
T2), assuming that the life number at T2 ° C. or higher is P (T2), the coefficient (T1 to T2) is P (T1) / P (T1 to T2).
2) The coefficient (T2) is calculated as P (T1) / P (T2). Then, the coefficient is multiplied by the coefficient in accordance with each temperature of the thermistor 5a at the end, weighted and counted, and the value is added to the total count. At this time, if the total count reaches a predetermined number or more, the user is urged to announce the life of the fixing device. Note that the predetermined number of sheets at this time is the life number at "T1 ° C. or lower" as a reference.

Thus, even in the present embodiment, even if the roller life differs depending on the paper passing mode and the paper passing state, the total count number until the roller reaches the life becomes the same. As a result, the roller life can be accurately detected, and the user can be prompted to replace the fixing device at an appropriate timing.

<Fourth Embodiment> Next, a fourth embodiment of the present invention will be described.

Each part of an actual product may be supplied from a plurality of manufacturers in consideration of the process capability and cost of the parts manufacturer.

However, although the parts dimensions and the design values of the physical characteristics of each manufacturer are the same, the materials used and the manufacturing methods are slightly different. For this reason, in the case of the fixing device, there may be differences between manufacturers in the characteristics of the manufactured roller. In particular, if there is a difference in the number of rollers, the life of the fixing device cannot be predicted at an accurate timing by simply counting the number of sheets passed.

Therefore, in the present embodiment, as a countermeasure, a weighting coefficient for counting the number of passed sheets is divided according to the manufacturer of the roller inserted into the main body.
Since the basic life detecting routine is the same as that of the first embodiment, a description thereof will be omitted below.

The weighting factor here is a certain manufacturer A
In the case of the main body with the rollers of, the number of sheets passed is multiplied by a coefficient calculated by (the number of rollers of the reference manufacturer) / (the number of rollers of the manufacturer A), and the number of sheets passed is counted. To be added. At this time,
When the total count reaches a predetermined number or more, the user is urged to announce the life of the fixing device. Note that the predetermined number at this time is the number of rollers used by the reference manufacturer.

According to the above-described method, even when the roller life differs depending on the manufacturer, the total count number until the life of the roller becomes the same. As a result, the roller life can be accurately detected, and the user can be prompted to replace the fixing device at an appropriate timing.

[0071]

As is apparent from the above description, according to the present invention, in the image forming apparatus having the fixing device life detecting means for estimating the life of the fixing device from the number of sheets of recording material passed, the paper feeding mode and In the case where there is a difference in the number of lifespans of the fixing device depending on the paper passing state, the number of papers weighted according to the paper passing mode and the paper passing state is added up.
Even when the life of the fixing device differs depending on the paper passing mode and paper passing status, the user can accurately predict the life of the fixing device regardless of the paper passing mode and paper passing status and replace the fixing device at an appropriate time. The effect of being able to prompt is obtained.

[Brief description of the drawings]

FIG. 1 is a flowchart illustrating a routine of a fixing device life detecting sequence according to a first embodiment of the present invention.

FIG. 2 is a flowchart illustrating a routine of a fixing device life detecting sequence according to a second embodiment of the present invention.

FIG. 3 is a flowchart illustrating a routine of a fixing device life detecting sequence according to a third embodiment of the present invention.

FIG. 4 is a schematic sectional view of a fixing device of the image forming apparatus according to the present invention.

FIG. 5 is a diagram illustrating a surface temperature of a rubber layer of a fixing roller and a temperature near a core axis during monocolor printing.

FIG. 6 is a perspective view showing a thermistor arrangement of a fixing device according to a third embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fixing roller 2 Pressure roller 1a, 2a Halogen heater 1b, 2b Core shaft 1c, 2c Elastic layer 1d, 2d Release layer 3 Power supply 4 Diode 5a, 5b Temperature detection element (thermistor) 6 Inlet guide 7 Discharge sensor 8 Transport Roller P Recording material T Toner

Claims (7)

[Claims] In an image forming apparatus having a fixing device life detecting unit for predicting the life of the fixing device from the number of sheets of recording material, when a difference occurs in the number of life of the fixing device depending on a sheet passing mode and a sheet passing state. An image forming apparatus for accumulating the number of sheets passing weighted according to a sheet passing mode and a sheet passing state. 2. When there is a difference in the number of lifespans of a fixing device depending on a paper passing mode and a paper passing state, the lifespan in a certain paper passing mode or the paper passing state is replaced with the lifespan in another paper passing mode or the paper passing state. 2. The image forming apparatus according to claim 1, wherein a coefficient for standardizing the number of sheets to be used is provided and weighting is performed by multiplying the coefficient by the number of sheets to be passed according to a sheet passing mode or a sheet passing state. 3. The image forming apparatus according to claim 1, wherein a coefficient by which the number of passed sheets is multiplied is changed in accordance with a sheet passing mode having a different throughput number. 4. The image forming apparatus according to claim 1, wherein a coefficient by which the number of passed sheets is multiplied is changed according to a sheet passing mode having a different fixing temperature. 5. The image forming apparatus according to claim 1, wherein a coefficient for multiplying the number of passed sheets is changed according to the number of continuous sheets. 6. The image forming apparatus according to claim 1, wherein a coefficient to be multiplied by the number of sheets to be passed is changed in accordance with a temperature of a roller non-sheet passing area of the fixing device during sheet passing. 7. An image forming apparatus having a fixing device life detecting means for estimating the life of the fixing device from the number of sheets, wherein a difference occurs in the number of life of the fixing device depending on a manufacturer of a component in the fixing device. It is characterized by providing a coefficient for standardizing the life number of parts of another manufacturer to the life number of parts of one manufacturer, and multiplying the number of paper passing times multiplied by the coefficient according to the manufacturer of the installed part. Image forming apparatus.