Image forming apparatus

Abstract

To provide an image forming apparatus capable of drastically suppressing power consumption and noise.SOLUTION: The fixing device 14, the duct 26 that discharges air from the fixing device 14 to the outside of the apparatus, the exhaust unit 27 that can be operated with at least one of a small output and a large output, the first filter 28 that collects substances other than ultrafine particles, the second filter 29 that collects substances including ultrafine particles, the first exhaust path 32 provided with the first filter 28, the second exhaust path 33 provided with the first filter 28 and the second filter 29, and the exhaust switching unit 31 that switches the exhaust path to either the first exhaust path 32 or the second exhaust path 33; The image forming apparatus 1 is equipped with a control means 24 for controlling the operation of the exhaust switching means 31 in accordance with the number of image forming sheets, and the control means 34 operates the exhaust switching means 31 when the number of image forming sheets reaches a specified number, switches the second exhaust path 33 to the first exhaust path 32, and operates the exhaust means 27 with small output.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus. [Background technology]

[0002] It has been known that electrophotographic image forming apparatuses emit several types of chemical substances into the atmosphere during image formation. Examples of the chemical substances that are emitted include ozone generated when the photoreceptor is charged, and toner dust generated during development and fixing operations. Measures have been taken to address the sources of these chemical substances, such as reducing the amount of chemical substances emitted or preventing the chemical substances from being emitted into the atmosphere.

[0003] However, in recent years, the generation of ultrafine particles (also known as UFPs) from electrophotographic image forming apparatuses, which are different from ozone and toner dust, has become a problem. These ultrafine particles are generated from substances constituting the fixing member and components of toner wax in a fixing device that uses heat to fix unfixed images transferred onto a sheet. It has been found that the amount of UFPs generated is high in the initial stage, from when the heater is turned off until it is turned on for a predetermined period of time, and decreases after the predetermined period of heating. As a countermeasure, a technology has been proposed in which multiple filters are placed to capture ultrafine particles when the power is turned on, when the amount of ultrafine particles generated is high, or when the fixing temperature is restored from a low temperature (see, for example, Patent Document 1). Summary of the Invention [Problem to be solved by the invention]

[0004] The filters used to capture ultrafine particles described above have a large pressure loss, so the fan used for exhausting the air needs to rotate at high speed, which poses the problem of increased power consumption and noise. The present invention aims to solve the above-mentioned problems and provide an image forming apparatus that can significantly reduce power consumption and noise caused by the operation of exhaust means such as a fan, even when a filter for capturing ultrafine particles is installed. [Means for solving the problem]

[0005] The invention of claim 1 comprises a fixing device that fixes a toner image on a sheet by heat, a duct that takes in air containing ultrafine particles generated from the fixing device while the fixing device is operating and discharges the taken-in air to the outside of the machine, exhaust means that operates to take in the air into the duct and can be selectively operated with at least one of low output and high output, a first filter that collects substances in the air excluding the ultrafine particles, a second filter that collects substances in the air including the ultrafine particles, and the first filter through which the air passes. a first exhaust path provided with the first filter and the second filter through which the air passes; an exhaust switching means for switching the exhaust path of the air to either the first exhaust path or the second exhaust path; and a control means for controlling the operation of the exhaust switching means in accordance with the number of sheets on which images are formed, wherein when the number of sheets on which images are formed reaches a predetermined number, the control means operates the exhaust switching means to switch the exhaust path of the air from the second exhaust path to the first exhaust path and operate the exhaust means at the low output. [Effects of the Invention]

[0006] According to the present invention, when the number of images formed reaches a predetermined number, the control means activates the exhaust switching means to switch the air exhaust path from the second exhaust path to the first exhaust path, and operates the exhaust means at a low output, thereby providing an image forming apparatus that can significantly reduce power consumption and noise generation. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a schematic front view of an image forming apparatus to which an embodiment of the present invention can be applied; [Figure 2] FIG. 2 is a schematic diagram illustrating a fixing device and a duct according to an embodiment of the present invention. [Figure 3] 2 is a schematic diagram illustrating the internal structure of a duct body according to an embodiment of the present invention. FIG. [Figure 4] 1 is a graph showing the correlation between the amount of ultrafine particles generated and the number of images formed when images formed under certain image forming conditions are continuously formed in one embodiment of the present invention. [Figure 5] FIG. 1 is a schematic diagram showing (a) a pleated filter and (b) a thick pleated filter used in a modified example of one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0008] 1 shows a color copier as an image forming apparatus according to one embodiment of the present invention. Process cartridges 3Y, 3C, 3M, and 3K for forming toner images of yellow (Y), cyan (C), magenta (M), and black (K) are arranged in the center of a main body 2 of the color copier 1. Each process cartridge 3 is provided with a corresponding photosensitive drum 4Y, 4C, 4M, or 4K. 1, charging devices 5Y, 5C, 5M, and 5K, developing devices 6Y, 6C, 6M, and 6K, and photosensitive drum cleaning devices 7Y, 7C, 7M, and 7K are arranged around each photosensitive drum 4 that rotates clockwise. An optical unit 8 that irradiates each photosensitive drum 4 with laser light is arranged below each process cartridge 3.

[0009] Above each process cartridge 3, an intermediate transfer unit 10 is provided, which has an intermediate transfer belt 9, which is a belt member, onto which a toner image formed by each process cartridge 3 is transferred. The intermediate transfer unit 10 has a plurality of rollers that support the intermediate transfer belt 9, and the intermediate transfer belt 9 is stretched over a secondary transfer opposing roller 20, a tension roller 21, and an entrance roller 22. Of the rollers 20, 21, and 22, the secondary transfer opposing roller 20 is driven to rotate by a drive motor (not shown), thereby driving the intermediate transfer belt 9 to run in the counterclockwise direction in FIG. 1. The intermediate transfer belt 9 may have a single-layer structure or a multi-layer structure, and in the case of a single-layer structure, it is preferably formed from polyvinylidene fluoride, polycarbonate, polyimide, etc. In the case of a multi-layer structure, it is preferable that the base layer is formed from a fluororesin, polyvinylidene fluoride sheet, or polyimide resin with low elongation, and the surface is covered with a coating layer with good smoothness, such as a fluororesin.

[0010] Primary transfer rollers 11Y, 11C, 11M, and 11K are provided on the inner circumferential side of the intermediate transfer belt 9 at positions facing the respective photosensitive drums 4, for primarily transferring the toner images formed on the respective photosensitive drums 4 onto the intermediate transfer belt 9. Here, the formation of each color toner image on each photosensitive drum 4 and the primary transfer of the toner images onto the intermediate transfer belt 9 will be described. 1, each photosensitive drum 4 is rotated clockwise, and each surface is irradiated with discharging light from a discharging device to initialize the surface potential of each photosensitive drum 4. The initialized surface potential of each photosensitive drum 4 is uniformly charged to a predetermined polarity (negative polarity in this embodiment) by each charging device 5. A laser beam emitted from an optical unit 8 is irradiated onto the charged surface of each photosensitive drum 4, and an electrostatic latent image corresponding to each color image is formed on the surface of each photosensitive drum 4.

[0011] The electrostatic latent image formed on each photosensitive drum 4 is visualized as a toner image by each developing device 6. Meanwhile, a transfer voltage of the opposite polarity (positive polarity in this embodiment) to the toner image formed on each photosensitive drum 4 is applied to each primary transfer roller 11. This forms a transfer electric field between each photosensitive drum 4 and its corresponding primary transfer roller 11, and each color toner image on each photosensitive drum 4 is electrostatically transferred onto the intermediate transfer belt 9. At this time, each color toner image is superimposed and transferred onto the intermediate transfer belt 9, forming a full-color toner image on the intermediate transfer belt 9, and the intermediate transfer belt 9 functions as an image carrier that carries the image on its surface. After each color toner image has been transferred onto the intermediate transfer belt 9, the photosensitive drum 4 has any residual toner adhering to its surface removed by each photosensitive cleaning device 7, preparing it for new image formation.

[0012] A secondary transfer roller 12 is provided downstream of the primary transfer roller 11K in the direction of travel of the intermediate transfer belt 9, and performs a secondary transfer of the toner image, which has been primarily transferred onto the intermediate transfer belt 9, onto the transfer sheet S. The secondary transfer opposing roller 20 and the secondary transfer roller 12 contact each other via the intermediate transfer belt 9, forming a secondary transfer nip. A predetermined transfer voltage is applied to the secondary transfer roller 12, thereby performing a secondary transfer of the toner image formed on the intermediate transfer belt 9 onto the transfer sheet S. A belt cleaning device 13 is provided upstream of the primary transfer roller 11Y in the direction of travel of the intermediate transfer belt 9, and removes residual toner remaining on the intermediate transfer belt 9 after image transfer. The intermediate transfer unit 10, the primary transfer rollers 11, the secondary transfer roller 12, and the belt cleaning device 13 form a transfer device 23. A fixing device 14, which includes a heating roller 14A and a pressure roller 14B, is provided above the secondary transfer roller 12, and fixes the toner image, which has been secondarily transferred onto the transfer sheet S. The fixing device 14 is detachable from the apparatus main body 2, that is, replaceable, and is replaced when the fixing function deteriorates due to deterioration of the components.

[0013] A paper feed unit 15 is disposed at the bottom of the apparatus main body 2. The paper feed unit 15 has a paper feed cassette 16, a paper feed roller 17, and a pair of registration rollers 18, and a transfer sheet S stored in the paper feed cassette 16 is fed by the paper feed roller 17 toward the pair of registration rollers 18. The pair of registration rollers 18 feeds the transfer sheet S toward the secondary transfer nip portion where the secondary transfer roller 12 and the intermediate transfer belt 9 come into contact with each other at a predetermined timing when the toner image formed on the intermediate transfer belt 9 matches a predetermined position on the transfer sheet S. Toner bottles 19Y, 19C, 19M, and 19K, each containing a corresponding color toner to be supplied to each developing device 6, are disposed at the top of the apparatus main body 2.

[0014] When a full-color toner image is formed on the intermediate transfer belt 9, a transfer sheet S in a paper feed cassette 16 is separated and fed by the operation of a paper feed roller 17 in the paper feed unit 15. The fed transfer sheet S is sent to the secondary transfer nip at a predetermined timing by the operation of a pair of registration rollers 18. The transfer sheet S, onto which the full-color toner image formed on the intermediate transfer belt 9 is transferred at the secondary transfer nip, is sent to the fixing device 14, where the transferred image is fixed. After that, the transfer sheet S is discharged onto a paper discharge tray 25 formed on the upper part of the device main body 2 by a pair of discharge rollers 24 located downstream of the fixing device 14 in the sheet conveyance direction. As with each photosensitive drum 4, residual toner remaining on the intermediate transfer belt 9 is cleaned by a belt cleaning device 13. A predetermined amount of the toner of each color contained in each toner bottle 19 is replenished to the corresponding developing device 6 as needed via a toner conveyance path (not shown).

[0015] Here, a characteristic feature of the present invention will be described. In FIG. 1, a duct 26 is provided above the fixing device 14. The duct 26 takes in air generated by the fixing device 14 during operation and discharges the air to the outside of the device main body 2. As also shown in FIG. 2, the duct 26 is composed of a connection portion 26A connected to the fixing device 14 and a duct main body 26B. In the illustrated example, the connection portion 26A, which is a hollow pipe, is a square pipe, but the shape is not limited thereto and may be, for example, a round pipe. The connection portion 26A is connected to the vicinity of both longitudinal ends of the fixing device 14 and to the duct main body 26B, respectively, so that air inside the fixing device 14 flows into the duct main body 26B via the connection portion 26A.

[0016] Duct body 26B, which has a rectangular cross section, has, at both longitudinal ends, air intake port 26a, to which connecting portion 26A is connected and through which air is taken in, and air exhaust port 26b, through which the taken-in air is discharged, as shown in Fig. 3. An exhaust fan 27 is provided near air exhaust port 26b of duct body 26B as exhaust means that, when activated, generates an air flow from air intake port 26a to air exhaust port 26b to take air into duct body 26B. Exhaust fan 27 is configured so that its output, in other words, the number of rotations per unit time, can be switched between at least two levels: high and low. A partition wall 26c is provided near the intake port 26a of the duct main body 26B, which in this example divides the air taken in through the intake port 26a into upper and lower halves. The upper space, which is the upper space separated by the partition wall 26c, is provided with a first filter 28 that collects matter from the taken in air except for ultrafine particles (the above-mentioned UFP (a type of PM (particulate matter) that is suspended particulate matter (SPM) floating in the air and has a diameter of 50 nm or less)). The lower space, which is the lower space separated by the partition wall 26c, is provided with the first filter 28 and a second filter 29 that collects matter from the taken in air, including ultrafine particles. The first filter 28 may be, for example, an ozone removal filter that removes ozone generated by the process cartridge 3.

[0017] A movable shielding plate 30 is provided at the air outlets of the upper and lower spaces, blocking either the upper or lower space and allowing the other to communicate with the downstream side of duct body 26B. The shielding plate 30 is selectively positioned by an exhaust switching mechanism 31, such as a motor or a solenoid, between a first position (shown by a solid line in FIG. 3 ) where the upper space communicates with the downstream side of duct body 26B, and a second position (shown by a dashed line in FIG. 3 ) where the lower space communicates with the downstream side of duct body 26B. When the shielding plate 30 is in the first position, air taken in through intake port 26a by the operation of exhaust fan 27 flows through first exhaust path 32, passing through the upper space, through the inside of duct body 26B, and toward exhaust port 26b. When the shielding plate 30 is in the second position, the air taken in through the air intake 26a by the operation of the exhaust fan 27 flows through the lower space, through the inside of the duct body 26B, and toward the exhaust outlet 26b through a second exhaust path 33. The operation of the exhaust switching means 31 is controlled by control means 34, which is a well-known microcomputer.

[0018] Based on the above-described configuration, the control of changing the exhaust path by switching the position of the shielding plate 30 by the exhaust switching means 31, which is a feature of the present invention, will be described. 3 , when air taken in through intake port 26a flows through first exhaust path 32, shielding plate 30 is positioned at the first position, and the air flowing in through intake port 26a passes through first filter 28 and is discharged from exhaust port 26b. When air taken in through intake port 26a flows through second exhaust path 33, shielding plate 30 is positioned at the second position, and the air flowing in through intake port 26a passes through first filter 28 and second filter 29 and is discharged from exhaust port 26b. Therefore, while air flowing through first exhaust path 32 passes only through first filter 28, air flowing through second exhaust path 33 passes through first filter 28 and second filter 29. Therefore, the pressure loss of air flowing through second exhaust path 33 is greater than that of air flowing through first exhaust path 32. As a result, when the incoming air flows through the second exhaust path 33, the output of the exhaust fan 27 (in other words, the number of rotations per unit time) needs to be increased compared to when the air flows through the first exhaust path 32, which increases power consumption and noise during operation.

[0019] However, in order to capture ultrafine particles, it is necessary to introduce air into the second exhaust path 33, which results in a large pressure loss. Therefore, in the present invention, the time that the air flows through the second exhaust path 33 is shortened as much as possible, thereby suppressing increases in power consumption and noise when the exhaust fan 27 is operating. Figure 4 is a graph showing the correlation between the amount of ultrafine particles (UFP) generated and the number of images formed when images formed under certain image forming conditions are continuously formed in color copier 1. The amount of ultrafine particles generated is caused by equipment factors such as the oil components used in the roller lubrication of fixing device 14, and supply factors such as toner wax. As shown in Figure 4, under these image forming conditions, the amount of ultrafine particles generated drops dramatically when the number of images formed reaches 200, and thereafter the amount of ultrafine particles generated is almost quantified.

[0020] Therefore, in this embodiment, the control unit 34 inputs the number of sheets on which images are formed, and when the number of sheets on which images are formed reaches a predetermined number, the control unit 34 activates the exhaust switching unit 31. Specifically, because a large amount of ultrafine particles are generated from the start of image formation until the number of sheets on which images are formed reaches the predetermined number of 200, the control unit 34 activates the exhaust switching unit 31 to position the shielding plate 30 at the second position, so that air flowing in from the intake port 26a passes through the second exhaust path 33. As a result, the air flowing in from the intake port 26a in the initial stage flows through the second exhaust path 33, and even ultrafine particles are captured and purified by the first filter 28 and the second filter 29. However, because the air flowing through the second exhaust path 33 has a large pressure loss, the control unit 34 must increase the output of the exhaust fan 27, which increases power consumption and noise.

[0021] Then, when the number of images formed reaches the predetermined number of 200 sheets, the control unit 34 activates the exhaust switching unit 31 to displace the shielding plate 30 from the second position to the first position. The air flowing in through the intake port 26a is redirected from the second exhaust path 33 to the first exhaust path 32, and the air containing almost no ultrafine particles is purified only by the first filter 28 and discharged to the outside of the apparatus through the exhaust port 26b. At this time, the air flowing through the first exhaust path 32 has a smaller pressure loss than the air flowing through the second exhaust path 33, so the control unit 34 controls the output of the exhaust fan 27 to be lower than it was before the number of images formed reached the predetermined number, thereby significantly reducing power consumption and noise generation.

[0022] Furthermore, the amount of ultrafine particles generated is related to the power-on time of the color copier 1, i.e., the heating time of the fixing device 14, in addition to the number of images formed as described above, and the color copier 1 is provided with a heating time counter that accumulates the heating time of the fixing device 14. It is known that the amount of ultrafine particles generated is quantified by being high until the heating time of the fixing device 14 reaches a predetermined time and decreasing once the predetermined time has passed. The control unit 34 obtains the heating time of the fixing device 14 from the heating time counter, and when the heating time reaches a predetermined time, for example 60 seconds, it activates the exhaust switching unit 31 to move the shielding plate 30 from the second position to the first position, changing the air flow path from the second exhaust path 33 to the first exhaust path 32, and changing the output of the exhaust fan 27 to low output. With this configuration, when the heating time of the fixing device 14 reaches a predetermined time before the number of images formed reaches a predetermined number, the control means 34 activates the exhaust switching means 31 to switch the air exhaust path from the second exhaust path 33 to the first exhaust path 32 and also operates the exhaust fan 27 at low output, thereby significantly reducing power consumption and noise generation.

[0023] Furthermore, the amount of ultrafine particles generated is related to the replacement of the fixing device 14 in addition to the number of images formed and heating time described above, and the color copier 1 is provided with a replacement detection means for detecting that the fixing device 14 has been replaced. The replacement detection means is, for example, a microswitch provided in the device main body 2 to which the fixing device 14 is detached, and determines that the fixing device 14 has been replaced when a used fixing device 14 is removed from the device main body 2 and a new fixing device 14 is installed again, i.e., when the switch is turned off and then on again. As described above, the amount of ultrafine particles generated is due to device factors such as the oil components used in the roller lubrication of the fixing device 14, and is therefore known to increase when the fixing device 14 is replaced.

[0024] When the replacement detection means detects that the fixing device 14 has been replaced, the control means 34 activates the exhaust switching means 31 to displace the shielding plate 30 from the first position to the second position, changing the air flow path from the first exhaust path 32 to the second exhaust path 33, and changing the output of the exhaust fan 27 to high output. Therefore, when it is detected that the fixing device 14 has been replaced, regardless of the number of images formed or the heating time of the fixing device 14, the control means 34 activates the exhaust switching means 31 to switch the air exhaust path from the first exhaust path 32 to the second exhaust path 33, and also activates the exhaust fan 27 at high power. This makes it possible to effectively purify the air containing a large amount of ultrafine particles generated by the replaced fixing device 14. When the replacement detection means detects that the fixing device 14 has been replaced, the control device 34 resets the heating time accumulated by the heating time counting means to zero.

[0025] In the above-described configuration, at least one of the first filter 28 and the second filter 29 may be a pleated filter 35a shown in FIG. 5(a) or a pleated filter 35b shown in FIG. 5(b), which is thicker than the pleated filter 35a. The pleated filter 35b is thicker than the pleated filter 35a, i.e., its length in the airflow direction (left-right in FIG. 5) is greater. This increases the surface area of ​​the filter components and the number of air holes, as shown by the dashed lines in FIG. 5. As a result, increasing the thickness of each filter 35a, 35b can reduce pressure loss. By reducing the output of the exhaust fan 27, power consumption and noise generation can be reduced compared to the above-described embodiment. In other words, the output of the exhaust fan 27 can be set based on the thickness of the pleated filters 35a, 35b. In the above embodiment, the predetermined number of sheets at which the control unit 34 activates the exhaust switching unit 31 is set to 200 sheets, and the predetermined time is set to 60 seconds, but these are not limited to these values ​​as they can be changed depending on the image formation conditions, etc. Also, although the output of the exhaust fan 27 can be switched between two levels, low output and high output, a configuration in which the output can be switched between three or more levels may be adopted.

[0026] In the above embodiment, an example was shown in which a color copier 1 that forms full-color images was used as an image forming apparatus to which the present invention can be applied, but the image forming apparatus to which the present invention can be applied is not limited to this, and the present invention can also be applied to printers, facsimiles, multifunction devices, etc. In addition, in the above embodiment, a configuration is shown in which a transfer sheet S is used as the sheet, which is the recording medium on which an image is formed, but this transfer sheet S is not limited to recording paper, but also includes cardboard, postcards, roll paper, envelopes, plain paper, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, OHP sheets, OHP film, resin film, etc., and any sheet-like material on which an image can be formed may be used.

[0027] The aspects of the present invention are as follows, for example. [1] A first apparatus including a fixing device that fixes a toner image on a sheet by heat, a duct that takes in air containing ultrafine particles generated from the fixing device while the fixing device is operating and discharges the taken-in air to the outside of the apparatus, an exhaust means that operates to take in the air into the duct and can be selectively operated with at least one of low output and high output, a first filter that captures substances in the air excluding the ultrafine particles, a second filter that captures substances in the air including the ultrafine particles, and the first filter through which the air passes. The image forming apparatus comprises an exhaust path, a second exhaust path provided with the first filter and the second filter through which the air passes, an exhaust switching means for switching the air exhaust path to either the first exhaust path or the second exhaust path, and a control means for controlling the operation of the exhaust switching means in accordance with the number of images formed, wherein the control means activates the exhaust switching means when the number of images formed reaches a predetermined number, switches the air exhaust path from the second exhaust path to the first exhaust path, and operates the exhaust means at the low output. [2] The image forming apparatus according to [1] is characterized in that it is provided with a heating time counting means for accumulating the heating time of the fixing device, and the control means activates the exhaust switching means when the heating time of the fixing device reaches a predetermined time before the number of image-formed sheets reaches a predetermined number, switches the exhaust path of the air from the second exhaust path to the first exhaust path, and operates the exhaust means at the low output. [3] The image forming apparatus according to [2], wherein the fixing device is replaceable and includes a replacement detection means for detecting that the fixing device has been replaced, and wherein the control means, when the replacement detection means detects that the fixing device has been replaced, resets the accumulated time of the heating time counter means and activates the exhaust switching means, switches the air exhaust path from the first exhaust path to the second exhaust path, and operates the exhaust means at the high output. [4] The image forming apparatus according to any one of [1] to [3], characterized in that the thickness of the first filter and the second filter is increased and the exhaust means is operated at the low output.

[0028] While the preferred embodiments of the present invention have been described above, the present invention is not limited to such specific embodiments, and unless otherwise specifically limited in the above description, various modifications and variations are possible within the spirit and scope of the present invention as set forth in the claims. For example, in the above embodiment, a duct body 26B having an exhaust path separated into two, upper and lower, is used, but a duct body having an exhaust path separated into two, left and right, may also be used. The effects described in the embodiments of the present invention are merely examples of the most preferable effects resulting from the present invention, and the effects of the present invention are not limited to those described in the embodiments of the present invention. [Explanation of symbols]

[0029] 1. Image forming equipment (color copiers) 14 Fixing device 26 Duct 27 Exhaust means (exhaust fan) 28 First Filter 29 Second Filter 31 Exhaust diversion means 32 First exhaust route 33 Second exhaust route 34 Control measures S sheet (transfer sheet) [Prior art documents] [Patent documents]

[0030] [Patent Document 1] Patent No. 6447004

Claims

1. a fixing device that fixes the toner image on the sheet by heat; a duct that takes in air containing ultrafine particles generated from the fixing device during operation of the fixing device and discharges the taken-in air to the outside of the device; an exhaust means operable to draw the air into the duct and selectively operable at least with either a low output or a high output; a first filter that collects substances in the air excluding the ultrafine particles; a second filter that collects substances including the ultrafine particles from the air; a first exhaust path provided with the first filter through which the air passes; a second exhaust path provided with the first filter and the second filter through which the air passes; an exhaust switching means for switching the exhaust path of the air to either the first exhaust path or the second exhaust path; a control means for controlling the operation of the exhaust switching means in accordance with the number of sheets of image formation; When the number of images formed reaches a predetermined number, the control means activates the exhaust switching means, switches the air exhaust path from the second exhaust path to the first exhaust path, and operates the exhaust means at the low output.

2. 2. The image forming apparatus according to claim 1, an image forming apparatus including a heating time counting means for accumulating a heating time of the fixing device, and wherein the control means, when the heating time of the fixing device reaches a predetermined time before the number of images formed on sheets reaches a predetermined number, activates the exhaust switching means to switch the air exhaust path from the second exhaust path to the first exhaust path and operate the exhaust means at the low output.

3. 3. The image forming apparatus according to claim 2, an image forming apparatus characterized in that the fixing device is replaceable and further comprising a replacement detection means for detecting that the fixing device has been replaced, and when the replacement detection means detects that the fixing device has been replaced, the control means resets the accumulated time of the heating time counter means and activates the exhaust switching means, switches the air exhaust path from the first exhaust path to the second exhaust path, and operates the exhaust means at the high output.

4. 4. The image forming apparatus according to claim 1, an image forming apparatus, characterized in that the thicknesses of the first filter and the second filter are increased, and the exhaust means is operated at the low output;

Images