Image forming apparatus

Abstract

To reduce the occurrence of image formation failure.SOLUTION: An image forming apparatus comprises: a first air supply unit that supplies air to a post-fixing conveying unit from the outside of an apparatus body; a first exhaust unit that exhausts air from an image forming unit to the outside of the apparatus body; and a control unit. When controlling the amount of air supplied by the first air supply unit to be a first air supply amount (YES in S308), the control unit controls the amount of air exhausted from the first exhaust unit to be a first exhaust amount (S309), and when controlling the amount of air supplied by the first air supply unit to be a second air supply amount larger than the first air supply amount (NO in S308), controls the amount of air exhausted from the first exhaust unit to be a second exhaust amount smaller than the first exhaust amount (S310).SELECTED DRAWING: Figure 11

Description

Technical Field

[0001] The present invention relates to an image forming apparatus that forms an image on a sheet.

Background Art

[0002] In recent years, in image forming apparatuses such as printers, copiers, and multifunction devices, there has been a demand to support a variety of sheets. For example, it is desired to support sheets with a large basis weight and a high moisture content. When heating and fixing an image formed on such a moisture-rich sheet, a large amount of water vapor is released. If this water vapor condenses on the surface of the guide that guides the sheet as a conveyance path, there is a risk of problems such as paper jams due to the sheet sticking and poor image formation (transfer failure). Therefore, a configuration has been proposed that includes a blower fan that blows (draws in) external air to the post-fixing conveyance unit that conveys the sheet that has passed through the fixing unit, and a suction fan that exhausts air to the outside from the post-fixing conveyance unit.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in recent years, further miniaturization and productivity improvement of image forming apparatuses have been demanded, and there is a problem that it is difficult to reduce the occurrence of image formation defects with the configuration as in Patent Document 1. That is, due to the miniaturization of the image forming apparatus, the conveyance path after fixing and the image forming unit that forms an image become closer. Then, water vapor easily flows to components constituting the image forming unit such as a transfer belt, a cleaning device, and a secondary transfer roller, and there is a problem that the occurrence of image formation defects is likely to occur. Further, when the cooling ability of the sheet is improved for productivity improvement, if the intake air volume by a blower fan or the like is increased, the exhaust air volume by a suction fan or the like cannot catch up, and water vapor easily flows from the conveyance path after fixing to the image forming unit, and there is also a problem that the occurrence of image formation defects is likely to occur.

[0005] Therefore, an object of the present invention is to provide an image forming apparatus capable of reducing the occurrence of image formation defects.

Means for Solving the Problems

[0006] One aspect of the present invention includes an image forming unit that forms an image on a sheet, a fixing unit that heats the sheet on which the image is formed by the image forming unit and fixes the image on the sheet, a post-fixing conveyance unit that conveys the sheet that has passed through the fixing unit, a first air supply unit that supplies air from the outside of the apparatus main body to the post-fixing conveyance unit, a first exhaust unit that exhausts air from the image forming unit to the outside of the apparatus main body, and a control unit that controls the first air supply unit and the first exhaust unit. When the control unit controls the air supply amount of the first air supply unit to a first air supply amount, the control unit controls the exhaust amount of the first exhaust unit to a first exhaust amount, and when the control unit controls the air supply amount of the first air supply unit to a second air supply amount that is larger than the first air supply amount, the control unit controls the exhaust amount of the first exhaust unit to a second exhaust amount that is smaller than the first exhaust amount. The image forming apparatus is characterized by this.

Effects of the Invention

[0007] According to the present invention, the occurrence of image formation defects can be reduced.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

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Figure 10

Figure 11

Figure 12

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Figure 14

Mode for Carrying Out the Invention

[0009] Hereinafter, the image forming apparatus according to the present embodiment will be described with reference to the drawings. The image forming apparatus includes a printer, a copier, a facsimile machine, and a multifunction peripheral. In the present embodiment, as an example of the image forming apparatus 1, a full-color laser copier that forms an image on a sheet used as a recording medium based on image information input from an external PC or image information read from a document will be described. The sheets used as the recording medium include paper such as plain paper and thick paper, plastic films such as overhead projector sheets, sheets of special shapes such as envelopes and index papers, and cloth.

[0010] [Configuration of Image Forming Apparatus] FIG. 1 is a schematic cross-sectional view showing the entirety of the image forming apparatus 1 according to the present embodiment. FIG. 2 is a block diagram showing the control configuration of the image forming apparatus according to the present embodiment. The image forming apparatus 1, which is a full-color laser copier, includes a sheet feeding unit 2, a fixing device 3 as a fixing unit, a toner storage unit T (TY, TM, TC, TK), a reversing discharge unit 4 as a post-fixing conveyance unit, and an image forming engine 8 inside the apparatus main body 1A. Among these, an image forming engine 8 that forms (transfers) an image on a sheet, a toner storage unit T that stores toner supplied to the image forming engine 8, and a fixing device 3 that fixes the image formed on the sheet constitute an image forming unit 9. Further, the image forming apparatus 1 includes a sheet stacking unit 5 on the upper surface of the apparatus main body 1A, and further includes a control unit 6 and a document reading device 7 disposed above the apparatus main body 1A. Note that the reversing discharge unit 4 conveys the sheet that has passed through the fixing device 3 to the sheet stacking unit 5, or more specifically, reverses it by a re-conveyance unit described later and re-conveys it to the image forming unit 9.

[0011] In the electrophotographic image forming unit 9 of the image forming apparatus 1, four-color toner images of yellow (Y), magenta (M), cyan (C), and black (Bk) are formed by the image forming engine 8. That is, the image forming engine 8 is a so-called intermediate transfer tandem type electrophotographic unit in which four drum units 11 (11Y, 11M, 11C, 11K) are arranged along the intermediate transfer belt 13a of the intermediate transfer unit 13. Further, toner storage units T (TY, TM, TC, TK) store toners (fresh toners) of yellow (Y), magenta (M), cyan (C), and black (K), respectively.

[0012] The image forming engine 8 includes drum units 11 (11Y, 11M, 11C, 11K), an intermediate transfer unit 13, and a secondary transfer roller 24 as a transfer unit. Each drum unit 11 (11Y, 11M, 11C, 11K) has a photosensitive drum 110 (110Y, 110M, 110C, 110K) as a photoreceptor. A developing unit 10 (10Y, 10M, 10C, 10K) for developing a toner image is arranged around the photosensitive drum 110 (110Y, 110M, 110C, 110K).

[0013] Each photosensitive drum 110 is configured to be irradiated with laser light from an exposure device 12 provided at its lower part. When the image forming process is started, the photosensitive drum 110, which has been uniformly charged on its surface in advance by a charger (not shown), is irradiated with laser light from the exposure device 12 and exposed. At this time, the exposure device 12 receives a signal (video signal) corresponding to the image data to be printed, and irradiates the photosensitive drum 110 with laser light modulated according to the video signal through a scanning optical system including a polygon mirror. Thereby, an electrostatic latent image corresponding to the image data is formed on the drum surface.

[0014] A developing device (not shown) supplies toner to the electrostatic latent image formed on the photosensitive drum 110 to visualize (develop) the latent image into a toner image. Then, a predetermined pressing force and an electrostatic load bias are applied by a primary transfer device (not shown), and the toner image is primarily transferred from the photosensitive drum 110 to the intermediate transfer belt 13a. The residual toner remaining on the photosensitive drum 110 after primary transfer is collected by a cleaning device (not shown), and the drum surface of the photosensitive drum 110 is cleaned.

[0015] The above-described toner image forming operation is performed in parallel in each drum unit 11. Also, primary transfer is performed so that the toner image formed by the upstream drum unit 11 overlaps the toner image formed by the downstream drum unit 11 on the rotating intermediate transfer belt 13a. As a result, a full-color toner image is finally formed on the intermediate transfer belt 13a, is carried while being supported by the intermediate transfer belt 13a, and is conveyed to the secondary transfer roller 24 as transfer. At the secondary transfer roller 24, the toner image is transferred from the intermediate transfer belt 13a to the sheet S while sandwiching and conveying the sheet S.

[0016] Thereafter, the sheet S is conveyed to a fixing device 3 as a fixing unit that heats and presses the toner image for fixing. The fixing device 3 has a fixing roller pair 31 as a fixing rotating body pair. The fixing roller pair 31 is composed of a heater roller 31a as a heating rotating body having a built-in heating heater (not shown) and a pressure roller 31b that is pressed against the heater roller 31a. By these heater roller 31a and pressure roller 31b, heat and pressure are applied to the toner image while sandwiching and conveying the sheet S. As a result, the toner melts, then solidifies and adheres to the sheet S, and the image is fixed on the sheet S.

[0017] On one hand, the sheet S used as a recording medium is supplied to the image forming unit 9 (image forming engine 8 and fixing device 3) by the sheet feeding unit 2. The sheet feeding unit 2 includes a cassette 21 having a lift-up device that moves up and down with the sheet S loaded thereon, and the sheet S is fed out one by one from the cassette 21. The sheet S fed from the cassette 21 is conveyed to the pre-registration roller pair 22 via the conveyance path 2a, and then conveyed to the registration roller pair 23 via the conveyance path 2b. The registration roller pair 23 corrects the skew of the sheet S and conveys the sheet S to the secondary transfer roller 24 via the conveyance path 2c at a timing determined in accordance with the toner image forming operation by the image forming engine 8.

[0018] The sheet S with the toner image transferred at the secondary transfer roller 24 is conveyed to the fixing device 3 via the conveyance path 2d. The sheet S having the fixed image fixed by the fixing device 3 is conveyed to the reverse discharging unit 4 through the conveyance path 3a. In the reverse discharging unit 4, the sheet S conveyed from the fixing device 3 through the conveyance path 3a is conveyed by the fixing discharge roller pair 42 as the first rotating body pair and reaches the branch portion where the first switching flap FL1 (see FIG. 9) is arranged. The first switching flap FL1 guides the sheet S to either the conveyance path 4a leading to the discharge roller pair 44 or the conveyance path 4b leading to the reverse discharge roller pair 45 as the second rotating body pair. The sheet S heading for the conveyance path 4a is conveyed to the discharge roller pair 44 by the fixing discharge roller pair 42. The sheet S reaching the discharge roller pair 44 is discharged onto the sheet stacking unit 5 by the discharge roller pair 44.

[0019] On one hand, the sheet S moving towards the conveyance path 4b is conveyed along the conveyance path 4b by the branch conveyance roller pair 43, and is conveyed to the reverse discharge roller pair 45 which also functions as a re-conveyance unit arranged at an upper position relative to the discharge roller pair 44. The sheet S reaching the reverse discharge roller pair 45 is either directly discharged to the sheet stacking unit 5 by the reverse discharge roller pair 45, or when double-sided printing is to be performed, the conveyance direction of the sheet S is reversed by the reverse operation of the reverse discharge roller pair 45 and then conveyed. When double-sided printing is performed, the reversed sheet S is guided to the re-conveyance path 4c as a re-conveyance unit by the second switching flap FL2 (see FIG. 9). The sheet S guided to the re-conveyance path 4c has its front and back sides reversed, and is conveyed to the double-sided merging conveyance path 4d as a re-conveyance unit by the double-sided conveyance roller pairs 46, 47 and the double-sided pre-registration roller pair 48, and then re-conveyed to the registration roller pair 23. The sheet S reaching the registration roller pair 23 has an image formed on its second side in the same process as the already image-formed first side, and then is discharged to the sheet stacking unit 5.

[0020] [Control Configuration of Image Forming Apparatus] Next, the control unit 6 of the image forming apparatus 100 will be described. As shown in FIG. 2, the control unit 6 as a control device of the image forming apparatus 100 includes a CPU 111, an image memory 115, a ROM 112, and a RAM 113. The CPU 111 centrally controls each part of the image forming apparatus 100, and executes various processes by expanding various programs stored in the ROM 108 into the RAM 112. In the image memory 115, the image read by the document reading device 7 or the image transmitted as a print job from an external computer is temporarily stored as image information. The CPU 111 transmits the image stored in this image memory 115 to the image forming engine 8 to form an image on the sheet S.

[0021] Further, an external temperature sensor Ts1 as an external temperature detection unit and an internal temperature sensor Ts2 as an internal temperature detection unit provided in the image forming apparatus 1 are respectively connected to the CPU 111. Further, an exhaust unit supply fan F1 as a first supply unit, an exhaust unit supply fan F2 as a first supply unit, and an exhaust unit exhaust fan F3 as a first exhaust unit are respectively connected to the CPU 111. Further, a toner unit supply fan F4 as a second supply unit, a developing unit supply fan F5 as a second supply unit, and an image forming unit exhaust fan F6 as a second exhaust unit are respectively connected to the CPU 111.

[0022] The external temperature sensor Ts1 is disposed inside the apparatus main body 1A near the outer wall (see FIG. 1), detects the temperature (ambient temperature) outside the image forming apparatus 1, and outputs a signal of the detection result to the CPU 111. The internal temperature sensor Ts2 is attached and disposed on the side surface of, for example, the black developing unit 10K (see FIG. 1), detects the temperature (ambient temperature) inside the image forming apparatus 1 (image forming unit 9), and outputs a signal of the detection result to the CPU 111.

[0023] [Configuration of Each Fan] Subsequently, with reference to FIG. 1, the arrangement of each of the above-described fans and the relationship between the air supply or exhaust by the fans will be described with reference to FIGS. 3 to 7. FIG. 3 is a perspective view showing the arrangement of each fan in the image forming apparatus according to the present embodiment. FIG. 4 is a perspective view showing the air supply by the exhaust unit supply fans F1 and F2 and the exhaust by the exhaust unit exhaust fan F3. FIG. 5 is a perspective view showing the air supply by the toner unit supply fan F4. FIG. 6 is a perspective view showing the air supply by the developing unit supply fan F5. FIG. 7 is a perspective view showing the exhaust by the image forming unit exhaust fan F6. In FIGS. 3 to 7, the X1 direction is the left direction of the image forming apparatus 1, the X2 direction is the right direction of the image forming apparatus 1, the Y1 direction is the front direction of the image forming apparatus 1, the Y2 direction is the rear direction of the image forming apparatus 1, the Z1 direction is the upward direction of the image forming apparatus 1, and the Z2 direction is the downward direction of the image forming apparatus 1.

[0024] As shown in FIG. 3, the image forming apparatus 1 is provided with intake fans F1 and F2 for the discharge unit to cool the sheet S after fixing the image passing through the reverse discharge unit 4. The intake fans F1 and F2 for the discharge unit take in outside air and supply it to the reverse discharge unit 4 inside the apparatus main body 1A without passing through the image forming unit 9. Further, the image forming apparatus 1 is provided with an exhaust fan F3 for the discharge unit that exhausts the air near the reverse discharge unit 4 that has cooled the sheet S in the reverse discharge unit 4 without passing through the image forming unit 9.

[0025] In addition, the image forming apparatus 1 is provided with a toner unit intake fan F4 that takes in outside air and supplies it to the toner storage unit T inside the apparatus main body 1A without passing through the reverse discharge unit 4 or the fixing device 3 in order to cool the toner storage unit T of the image forming unit 9. That is, the toner unit intake fan F4 supplies the taken-in outside air to the toner storage unit T from between the toner storage unit T and the sheet stacking unit 5 (see FIG. 1).

[0026] Furthermore, the image forming apparatus 1 is provided with a developing unit intake fan F5 that cools the image forming engine 8 (see FIG. 1) of the image forming unit 9. The developing unit intake fan F5 takes in outside air and supplies it to the image forming engine 8 inside the apparatus main body 1A without passing through the reverse discharge unit 4 or the fixing device 3. That is, the developing unit intake fan F5 supplies the taken-in outside air to the drum units 11 and the developing units 10 of each color and cools them.

[0027] And the image forming apparatus 1 is provided with an exhaust fan F6 for the image forming unit that exhausts the air near the image forming unit 9 that has cooled the image forming unit 9 without passing through the reverse discharge unit 4 or the fixing device 3.

[0028] Next, the functions of each fan will be specifically described. The discharge section air supply fans F1 and F2 have the function of cooling the sheet S on which the image is fixed by the fixing device 3, and the function of diffusing the moisture released from the sheet S and preventing condensation on the guide surface that forms the sheet conveyance path. Specifically, as shown in FIGS. 1 and 4, the discharge section air supply fans F1 and F2 are in the Z1-Z2 direction (vertical direction) and are approximately at the same height as the lower part of the inversion discharge section 4, and are arranged on the Y1 direction side (front side) of the image forming apparatus 1. The discharge section air supply fan F1 blows the taken-in outside air in the wind direction of arrow A1, and the discharge section air supply fan F2 blows the taken-in outside air in the wind direction of arrow A2. The air blown in the wind direction of arrow A1 is blown (supplied) to the surface (first surface) of the passing sheet S in the form of using the inside of the conveyance guide G1 (see FIG. 1) as a duct. The air blown in the wind direction of arrow A2 is blown (supplied) to the surface (second surface) of the passing sheet S in the form of using the inside of the conveyance guide G2 (see FIG. 1) as a duct.

[0029] The discharge section exhaust fan F3 has the function of collecting the highly humid air diffused to the inversion discharge section 4 particularly by the discharge section air supply fans F1 and F2 and exhausting it to the outside of the image forming apparatus 1. Specifically, as shown in FIGS. 1 and 4, the discharge section exhaust fan F3 is in the Z1-Z2 direction (vertical direction) and is approximately at the same height as the upper part of the inversion discharge section 4, and is arranged on the Y2 direction side (rear side) of the image forming apparatus 1. The discharge section exhaust fan F3 sucks the air of the inversion discharge section 4 (or the air in the vicinity of the inversion discharge section 4) and exhausts it to the outside of the image forming apparatus 1 in the wind direction of arrow A3.

[0030] As shown in FIGS. 1 and 5, the toner section air supply fan F4 is arranged in the Z1-Z2 direction (vertical direction) and is approximately at the same height as the toner storage section T, and is arranged on the Y1 direction side (front side) of the image forming apparatus 1. The toner section air supply fan F4 blows the taken-in outside air in the wind direction of arrow A4 through the toner cooling duct F4D. The air blown in the wind direction of arrow A4 cools the surface of the toner storage section T and prevents the heat of the sheet S stacked on the sheet stacking section 5 from being transmitted to the toner storage section T.

[0031] As shown in FIGS. 1 and 6, the developing unit air supply fan F5 is disposed in the Z1-Z2 direction (vertical direction) at substantially the same height as the developing unit 10 of the image forming unit 9, and is disposed on the Y1 direction side (front side) of the image forming apparatus 1. The developing unit air supply fan F5 blows the taken-in outside air through the developing cooling duct F5D in the direction of arrow A5. The air blown in the direction of arrow A5 is blown (supplied) between the developing unit 10 and the exposure device 12 in the image forming unit 9 to cool the surfaces of the developing unit 10 and the drum unit 11.

[0032] As shown in FIGS. 1 and 7, the image forming unit exhaust fan F6 is disposed in the Z1-Z2 direction (vertical direction) at substantially the same height as the exposure device 12 of the image forming unit 9, and is disposed on the X1 direction side (left side) of the image forming apparatus 1. The image forming unit exhaust fan F6 takes in the air in the space of the image forming unit 9 including the developing unit 10, the drum unit 11, the intermediate transfer unit 13, and the toner storage unit T, and exhausts it toward the outside of the image forming apparatus 1 in the direction of arrow A6.

[0033] [Regarding the movement of moisture inside the sheet due to heating of the fixing device] Next, the movement of moisture inside the sheet S due to heating of the fixing device 3 will be described with reference to FIG. 8. FIG. 8(a) is a schematic diagram showing the state of moisture in the sheet before fixing, and FIG. 8(b) is a schematic diagram showing the state of moisture in the sheet during fixing. Further, FIG. 8(c) is a schematic diagram showing the state of moisture in the sheet immediately after fixing, and FIG. 8(d) is a schematic diagram showing the state in which moisture is released from the sheet after fixing.

[0034] As shown in FIG. 8(a), the sheet S has a first surface A and a second surface B on the back side thereof. For example, in single-sided printing, the toner image Tim is transferred to the first surface A. Moisture Wa is contained inside this sheet S. In the state before being heated by the fixing device 3, the moisture Wa inside the sheet S is uniformly dispersed in the thickness direction.

[0035] As shown in FIG. 8(b), heat is applied to the sheet S by the heater roller 31a of the fixing device 3, and pressure is applied by the pressure roller 31b, thereby fixing the toner image Tim on the first surface A of the sheet S. At this time, the moisture Wa inside the sheet S moves from the first surface A toward the second surface B due to the heat applied from the heater roller 31a. The moisture Wa that has moved to the second surface B is prevented from being released into the air by the pressure roller 31b, so the moisture Wa inside the sheet S tends to be biased toward the second surface B side.

[0036] Therefore, as shown in FIG. 8(c), the sheet S immediately after passing through the fixing device 3 is in a state of containing more moisture Wa on the second surface B side than on the first surface A side. Therefore, as shown in FIG. 8(d), the moisture Wa released from the sheet S into the air is released more from the second surface B side than from the first surface A side. As a result, high-humidity air tends to be unevenly distributed on the side where the conveyance guide is located on the second surface B side, which is the non-image surface side, and the diffusion of the high-humidity air also tends to spread to the non-image surface side or the side of the re-conveyance path 4c.

[0037] [Fixing Device and Configuration of Conveyance Path on Downstream Side in Its Conveyance Direction] Next, the configuration of the fixing device 3 and the guide members that form the conveyance paths 3a, 4a, 4b, and the re-conveyance path 4c on the downstream side in the sheet conveyance direction will be described with reference to FIG. 9. FIG. 9 is a schematic cross-sectional view showing a portion from the fixing device to the inversion discharge roller pair in the image forming apparatus according to the present embodiment.

[0038] As shown in FIG. 9, the fixing device 3 includes a case 30, and the case 30 houses the fixing roller pair 31 composed of the above-described heater roller 31a and pressure roller 31b. These heater roller 31a and pressure roller 31b are in contact with each other with a width larger than the width of the sheet conveyance path in the width direction orthogonal to the sheet conveyance direction. That is, these rollers are configured to be in a contact state with the full width larger than the width of the largest-size sheet that can be conveyed by the image forming apparatus 1. Therefore, the nip formed by the contact of these heater roller 31a and pressure roller 31b blocks the air flow in the sheet conveyance direction.

[0039] Further, the fixing discharge roller pair 42 has a driving roller 42a and a driven roller 42b. These driving roller 42a and driven roller 42b are each formed of, for example, a single cylindrical shape (wide roller) made of rubber, and both ends thereof are arranged so as to be outside both ends of the conveyance path 182 in the width direction. That is, these driving roller 42a and driven roller 42b are in contact with a width larger than the width of the sheet conveyance path in the width direction orthogonal to the sheet conveyance direction. That is, these rollers are also configured to be in contact with the full width that is larger than the width of the sheet of the maximum size that can be conveyed by the image forming apparatus 1. Therefore, the nip formed by the contact of these driving roller 42a and driven roller 42b blocks the air flow in the sheet conveyance direction.

[0040] On the downstream side in the sheet conveyance direction from the fixing device 3, a conveyance path 3a, a fixing discharge roller pair 42, a conveyance path 4b, and a reverse discharge roller pair 45 are arranged. Further, a conveyance path 4a is arranged from the fixing discharge roller pair 42 to the discharge roller pair 44. Furthermore, a re-conveyance path 4c as a third conveyance path is arranged from the reverse discharge roller pair 45 to the secondary transfer roller 24.

[0041] Between these conveyance paths 4b and the re-conveyance path 4c, a conveyance guide G2 and a conveyance guide G4 are arranged. The conveyance guide G2 is arranged above the fixing device 3. Also, the conveyance guide G4 is arranged above the conveyance guide G2. On the other hand, at positions facing the conveyance guide G2 and the conveyance guide G4 with the re-conveyance path 4c in between, and inside the exterior cover 49 (see FIG. 1) of the apparatus main body 1A, a conveyance guide G6 and a conveyance guide G7 are arranged. Further, a conveyance guide G5 is arranged on the side of the sheet stacking portion 5 in the horizontal direction of the conveyance guide G6. Furthermore, below the conveyance guide G5, a conveyance guide G3 and a conveyance guide G1 are arranged. The conveyance guide G3 and the conveyance guide G1 are arranged at positions facing the conveyance guide G2, the conveyance guide G4, and the conveyance guide G5 with the conveyance path 3a and the conveyance path 4b in between, and on the side of the sheet stacking portion 5 in the horizontal direction of the conveyance guide G2 and the conveyance guide G4. The conveyance guide G3 is arranged below the conveyance guide G5 and has the conveyance path 4b between them. And the conveyance guide G1 is arranged below the conveyance guide G3 and has the conveyance path 4a between them. As described above, the conveyance guides G1 and G2 have the role of blowing the air blown by the discharge portion air supply fans F1 and F2 from inside the guide to the conveyance path side.

[0042] The conveyance guides G1 to G7 described above each have a guide surface that forms the conveyance paths 4a, 4b, and 4c along which the sheet S is conveyed. Note that the guide surfaces forming the respective conveyance paths of these conveyance guides G1 to G7 are not necessarily formed in a flat surface shape without irregularities, but mean a surface along which the sheet S is contacted and guided, such as a surface connecting the vertices of a plurality of ribs.

[0043] [Regarding the movement of high-humidity air] As shown in FIG. 9, the air blown from the discharge section air supply fan F1 described above flows inside the conveyance guide G1 and blows out from the opening C toward the sheet S in the wind direction of arrow A1a. Thereby, it flows along the image surface (first surface A) side of the sheet S to cool the surface on the image surface side of the sheet S. Further, the air blown from the discharge section air supply fan F2 flows inside the conveyance guide G2 and blows out from the opening D toward the sheet S in the wind direction of arrow A2a. Thereby, it flows along the non-image surface (second surface B) side of the sheet S to cool the surface on the non-image surface side of the sheet S and to diffuse the moisture discharged from the surface on the non-image surface side of the sheet S (see FIG. 8). Note that the openings C and D are arranged as a plurality of slit-shaped openings in the width direction perpendicular to the conveyance direction on the surfaces of the conveyance guides G1 and G2, respectively.

[0044] Further, in addition to the blowing out from the opening D, the air blown from the discharge section air supply fan F2 blows out from the slit-shaped opening E formed in the gap between the driving roller 42a having a single cylindrical shape and the conveyance guide G2 in the wind direction of arrow A2b. Then, the air blown out in the wind direction of arrow A2b flows along the surface of the sheet S toward the fixing device 3, thereby diffusing the moisture discharged from the surface on the non-image surface side of the sheet S.

[0045] As described above, the water vapor diffused into the reverse discharge section 4 by the blowing of the discharge section air supply fans F1 and F2 is basically recovered by the discharge section exhaust fan F3 and exhausted to the outside of the image forming apparatus 1. However, since there is a possibility that the water vapor diffused into the reverse discharge section 4 also diffuses into the inside of the image forming section 9, in the present embodiment, the diffusion of the water vapor into the image forming section 9 is reduced by the image forming section fan control described later.

[0046] [Discharge Section Fan Control] Next, the exhaust section fan control for controlling the intake fans F1 and F2 and the exhaust fan F3 of the exhaust section by the control unit 6 will be described with reference to FIG. 10. FIG. 10 is a flowchart showing the exhaust section fan control in the present embodiment. In the exhaust section fan control according to the present embodiment, on the premise that each fan has a function of cooling each section, the minimum necessary rotation speed (rotation speed) for each operation mode is set for the purpose of suppressing the operation noise and power consumption of the fans.

[0047] When the control unit 6 determines the start of a print job, for example, by a command from an external computer or an operation of the start key of the operation unit, the exhaust section fan control is started. Then, as shown in FIG. 10, the control unit 6 first measures the outside temperature Tm1 as the outside temperature of the image forming apparatus 1 by the above-described outside temperature sensor Ts1 (S101). Subsequently, the control unit 6 determines whether the type of the sheet for forming an image in the print job is a normal sheet such as plain paper as the first type (S102). When it is determined that the type of the sheet is a normal sheet (YES in S102), it is determined whether the outside temperature Tm1 is less than 25 degrees as the second set temperature (S103). In the present embodiment, the information regarding the type of the sheet will be described as using the type of the sheet set by the user via the operation unit, an external computer, or the like. However, the present invention is not limited to this, and a type detection sensor that detects the type of the sheet using impact, ultrasonic waves, or the like may be provided, and the result of the sensor may be used.

[0048] When the control unit 6 determines that the outside temperature Tm1 is less than 25 degrees (lower than the second set temperature) (YES in S103), it executes the low paper temperature mode on the assumption that the temperature of the sheet S is low (S104). In this low paper temperature mode, the control unit 6 stops the discharge unit air supply fan F1, drives the rotation speed of the discharge unit air supply fan F2 at 50% of the maximum performance, and controls to drive the rotation speed of the discharge unit exhaust fan F3 at 100% which is the maximum performance. That is, the air supply amount to the reverse discharge unit 4 by the discharge unit air supply fan F1 and the discharge unit air supply fan F2 is controlled to be small. Then, in the print job, it is determined whether there is a job to print (print) on the subsequent sheet (S105). If there is a job to continue printing (NO in S105), it returns to the above step S101. If there is no job to print (YES in S105), the print job is terminated (S106), the discharge unit air supply fans F1, F2 and the discharge unit exhaust fan F3 are stopped (S107), and this control is terminated.

[0049] On the other hand, in step S103, if it is determined that the outside temperature Tm1 is 25 degrees or higher (higher than the second set temperature) (NO in S103), the process proceeds to step S108. Then, it is determined whether the print job for the sheet to be printed is a single-sided print job (printing only on the first side of sheet S) (S108). If it is determined that the print job is a single-sided print job (YES in S108), assuming that the temperature of sheet S is medium, the medium paper temperature mode is executed (S109). In this medium paper temperature mode, the control unit 6 controls to drive the rotation speeds of the discharge unit supply fan F1 and the discharge unit supply fan F2 at 50% of the maximum performance, and drive the rotation speed of the discharge unit exhaust fan F3 at 100% which is the maximum performance. That is, the air supply amount to the reverse discharge unit 4 by the discharge unit supply fan F1 and the discharge unit supply fan F2 is controlled to be a medium amount which is more than that in the above-mentioned low paper temperature mode. Then, in the same manner as described above, in the print job, it is determined whether there is no job to print on the subsequent sheets (S105). If there is a job to continue printing (NO in S105), the process returns to the above step S101. Also, if there is no job to print (YES in S105), the print job is terminated (S106), the discharge unit supply fans F1, F2 and the discharge unit exhaust fan F3 are stopped (S107), and this control is terminated.

[0050] Also, in the above step S108, if it is determined that the print job is not a single-sided print job but a double-sided print job that also prints on the second side opposite to the first side of the sheet S (NO in S108), the process proceeds to step S109. Then, assuming that the temperature of the sheet S is high, the paper temperature high mode is executed (S109). In this paper temperature high mode, the control unit 6 controls to drive the rotation speeds of the discharge unit air supply fans F1 and F2 at 100%, which is the maximum performance, and also drives the rotation speed of the discharge unit exhaust fan F3 at 100%, which is the maximum performance. That is, the air supply amount to the reverse discharge unit 4 by the discharge unit air supply fans F1 and F2 is controlled to be a large amount larger than that in the above paper temperature medium temperature mode. Then, in the same manner as described above, in the print job, it is determined whether there is no job to print (print) on the subsequent sheets (S105). If there is a job to continue printing (NO in S105), the process returns to the above step S101. Also, if there is no job to print (YES in S105), the print job is terminated (S106), the discharge unit air supply fans F1, F2, and the discharge unit exhaust fan F3 are stopped (S107), and this control is terminated.

[0051] On the other hand, in the above step S102, if it is determined that the type of the sheet is not ordinary paper (NO in S102), it is determined whether it is a resin sheet such as an OHP sheet as the second type (S111). Here, if it is determined that it is a resin sheet (YES in S111), the process proceeds to the above step S110. Assuming that the temperature of the sheet S is high, the paper temperature high mode is executed (S109). Then, in the same manner as described above, in the print job, it is determined whether there is no job to print (print) on the subsequent sheets (S105). If there is a job to continue printing (NO in S105), the process returns to the above step S101. Also, if there is no job to print (YES in S105), the print job is terminated (S106), the discharge unit air supply fans F1, F2, and the discharge unit exhaust fan F3 are stopped (S107), and this control is terminated.

[0052] Also, in the above step S111, if it is determined that the type of the sheet is not a resin sheet (NO in S111), assuming that the type of the sheet is special paper as the third type, the special paper mode is executed (S112). In this special paper mode, the control unit 6 drives the discharge unit air supply fans F1 and F2 to rotate at rotation speeds individually set in advance for each sheet, and controls the discharge unit exhaust fan F3 to rotate at 100% which is the maximum performance. Then, as described above, in the print job, it is determined whether there is a job to print (print) on the subsequent sheets (S105). If there is a job to continue printing (NO in S105), the process returns to the above step S101. Also, if there is no job to print (YES in S105), the print job is terminated (S106), the discharge unit air supply fans F1, F2, and the discharge unit exhaust fan F3 are stopped (S107), and this control is terminated.

[0053] As described above, in the discharge unit fan control, the discharge unit air supply fans F1 and F2 that supply air to the reverse discharge unit 4 and the discharge unit exhaust fan F3 that exhausts air from the reverse discharge unit 4 have their air volumes (air supply volume and exhaust volume) set by selectively executing a plurality of modes. Also, in the discharge unit fan control, one mode is selected from a plurality of modes based on the type of the sheet, the outside temperature Tm1, and single-sided / double-sided printing. Therefore, the air supply volume of the discharge unit air supply fans F1 and F2 and the exhaust volume of the discharge unit exhaust fan F3 are controlled based on the type of the sheet, the outside temperature Tm1, and single-sided / double-sided printing.

[0054] [Image forming unit fan control of the comparative example] Here, the image forming unit fan control of the comparative example that controls the toner unit air supply fan F4, the developing unit air supply fan F5, and the image forming unit exhaust fan F6 that supply and exhaust air to and from the image forming unit 9 by the control unit 6 will be described with reference to FIGS. 13 and 14. FIG. 13 is a flowchart showing the image forming unit fan control of the comparative example. FIG. 14 is a schematic cross-sectional view showing the air flow when the intake air volumes of the discharge unit air supply fans F1 and F2 of the comparative example are increased.

[0055] When the control unit 6 determines the start of a print job, it starts the image forming unit fan control together with the discharge unit fan control described above. Then, as shown in FIG. 13, the control unit 6 first measures the internal temperature Tm2 of the image forming apparatus 1 as the internal temperature by the above-described internal temperature sensor Ts2 (S201), and determines whether or not the internal temperature Tm2 is less than 40 degrees (S202).

[0056] If it is determined that the internal temperature Tm2 is less than 40 degrees (YES in S203), the control unit 6 executes the image forming unit low temperature mode assuming that the temperature of the image forming unit 9 is low (S204). In this image forming unit low temperature mode, the control unit 6 controls the rotation speeds of the toner unit air supply fan F4, the developing unit air supply fan F5, and the image forming unit exhaust fan F6 to be driven at 50% of the maximum performance. That is, the exhaust amount from the image forming unit 9 by the image forming unit exhaust fan F6 is controlled to be medium. Then, in the print job, it is determined whether there is no job to perform printing (printing) on the subsequent sheet (S204). If there is a job to continue printing (NO in S204), the process returns to the above step S201. If there is no job to print (YES in S204), the print job is terminated (S205), the toner unit air supply fan F4, the developing unit air supply fan F5, and the image forming unit exhaust fan F6 are stopped (S206), and this control is terminated.

[0057] On the other hand, when it is determined that the in-cabin temperature Tm2 is 40 degrees or higher (NO in S203), the control unit 6 executes the image forming unit high-temperature mode assuming that the temperature of the image forming unit 9 is high (S207). In this image forming unit high-temperature mode, the control unit 6 controls the rotation speeds of the toner unit supply fan F4, the developing unit supply fan F5, and the image forming unit exhaust fan F6 to be driven at 100%, which is the maximum performance. That is, the exhaust amount from the image forming unit 9 by the image forming unit exhaust fan F6 is controlled to be larger than that in the above-described image forming unit low-temperature mode. Then, in the same manner as described above, in the print job, it is determined whether there is no job to print (print) on the subsequent sheet (S204). If there is a job to continue printing (NO in S204), the process returns to step S201. If there is no job to print (YES in S204), the print job is terminated (S205), the toner unit supply fan F4, the developing unit supply fan F5, and the image forming unit exhaust fan F6 are stopped (S206), and this control is terminated.

[0058] As described above, in the image forming unit fan control of the comparative example, the rotation speeds of the toner unit supply fan F4, the developing unit supply fan F5, and the image forming unit exhaust fan F6 that supply air to and exhaust air from the image forming unit 9 are controlled based on the in-cabin temperature Tm2. However, the above-described discharge unit fan control and the image forming unit fan control are executed as separate controls and have different sequences. Therefore, when the in-cabin temperature Tm2 is low and a print job for printing a resin sheet is executed, etc., the rotation speeds of the discharge unit supply fans F1 and F2 may be high and the rotation speed of the discharge unit exhaust fan F3 may be low.

[0059] Then, the air pressure in the inversion discharge unit 4 becomes relatively higher than that in the image forming unit 9. When such a pressure relationship occurs, due to the pressure difference, a phenomenon occurs where air flows from the side with higher air pressure to the side with lower air pressure. Therefore, the wind direction of arrow A7 in FIG. 14 indicates the air flow in such a pressure relationship. That is, a part of the air supplied from the discharge unit air supply fans F1 and F2 to the inversion discharge unit 4 is discharged outside the machine from the discharge ports where the discharge roller pair 44 and the inversion discharge roller pair 45 are arranged. Also, another part of the air in the inversion discharge unit 4 is collected by the discharge unit exhaust fan F3 and exhausted outside the machine.

[0060] However, a part of the other air in the inversion discharge unit 4, while containing the moisture released from the sheet S, flows into the vicinity of the secondary transfer roller 24 and the intermediate transfer belt 13a in the image forming unit 9 through the gaps in the fixing device 3, the re-conveying path 4c, etc. In the vicinity of the secondary transfer roller 24 and the intermediate transfer belt 13a that are less affected by the temperature of the fixing device 3, the temperature is lower compared to the inversion discharge unit 4 that is easily affected by the temperature of the fixing device 3. Therefore, when high-temperature and high-humidity air flows in from the inversion discharge unit 4, it is cooled on the surfaces of the secondary transfer roller 24 and the intermediate transfer belt 13a, the relative humidity of the air increases, and when the relative humidity exceeds 100%, condensation occurs. And when the condensed water adheres to the secondary transfer roller 24 and the intermediate transfer belt 13a, there is a risk of causing image defects due to transfer defects, poor cleaning of the intermediate transfer belt 13a, etc. Therefore, in the present embodiment, the image forming unit fan control described below is executed.

[0061] [Image Forming Unit Fan Control According to the Present Embodiment] Next, the image forming unit fan control according to the present embodiment will be described with reference to FIG. 11. FIG. 11 is a flowchart showing the image forming unit fan control in the present embodiment.

[0062] When the control unit 6 determines the start of a print job, it starts the image forming unit fan control together with the discharge unit fan control described above. Then, as shown in FIG. 11, the control unit 6 first measures the internal temperature Tm2 of the image forming apparatus 1 as the internal temperature by the above-described internal temperature sensor Ts2 (S301), and determines whether or not the internal temperature Tm2 is less than 40 degrees as the first set temperature (S302).

[0063] Here, when it is determined that the measured internal temperature Tm2 is 40 degrees or higher (higher than the first set temperature) (NO in S302), the control unit 6 executes the high temperature mode for the image forming unit (S311). That is, in this high temperature mode for the image forming unit, the control unit 6 controls the rotation speeds of the toner unit air supply fan F4, the developing unit air supply fan F5, and the image forming unit exhaust fan F6 to be driven at 100% which is the maximum performance. That is, the exhaust amount from the image forming unit 9 by the image forming unit exhaust fan F6 is controlled to be large. Then, in the print job, it is determined whether there is no job for printing on the subsequent sheet (S305). If there is a job for continuous printing (NO in S305), the process returns to the above step S301. If there is no job for printing (YES in S305), the print job is terminated (S306), the toner unit air supply fan F4, the developing unit air supply fan F5, and the image forming unit exhaust fan F6 are stopped (S307), and this control is terminated.

[0064] On the other hand, in the present embodiment, when it is determined that the internal temperature Tm2 is less than 40 degrees (lower than the first set temperature) (YES in S302), the control unit 6 checks the rotation speeds of the discharge unit air supply fans F1 and F2 (S303, S308). That is, the control unit 6 calculates the average rotation speed of the rotation speeds of the two discharge unit air supply fans F1 and F2 (for example: when F1: 0% + F2: 50%, it is calculated as 25%) (S303). When it is determined that the average rotation speed is less than 50% (YES in S303), the low temperature mode for the image forming unit (S304) is executed.

[0065] That is, in this image forming unit low temperature mode, the control unit 6 controls the rotation speeds of the toner unit air supply fan F4, the developing unit air supply fan F5, and the image forming unit exhaust fan F6 to be driven at 50% of the maximum performance. That is, the exhaust amount from the image forming unit 9 by the image forming unit exhaust fan F6 is controlled to be medium. Then, in the print job, it is determined whether there is a job to perform printing (printing) on the subsequent sheet (S305). If there is a job to continue printing (NO in S305), the process returns to step S301 above. If there is no job to print (YES in S305), the print job is terminated (S306), the toner unit air supply fan F4, the developing unit air supply fan F5, and the image forming unit exhaust fan F6 are stopped (S206), and this control is terminated.

[0066] And in this embodiment, when it is determined in steps S303 and S308 that the average rotation speed is 50% or more and less than 100%, the control unit 6 executes the first image unit dew condensation countermeasure mode (S309). That is, in this first image unit dew condensation countermeasure mode, the control unit 6 drives the rotation speeds of the toner unit air supply fan F4 and the developing unit air supply fan F5 at 50% of the maximum performance, and controls the rotation speed of the image forming unit exhaust fan F6 to be driven at 25% of the maximum performance. That is, the exhaust amount from the image forming unit 9 by the image forming unit exhaust fan F6 is controlled to be a small and medium amount (an amount between a small amount and a medium amount) less than that in the above image forming unit low temperature mode. Thereby, the rotation speed of the image forming unit exhaust fan F6 is lowered, the discharge of air from the image forming unit 9 is suppressed, and the air pressure of the image forming unit 9 is relatively increased with respect to the reverse discharge unit 4.

[0067] Similarly, in the print job, it is determined whether there is a job to perform printing (printing) on the subsequent sheet (S305). If there is a job to continue printing (NO in S305), the process returns to step S301 above. If there is no job to print (YES in S305), the print job is terminated (S306), the toner unit air supply fan F4, the developing unit air supply fan F5, and the image forming unit exhaust fan F6 are stopped (S206), and this control is terminated.

[0068] Also, in this embodiment, when it is determined in the above steps S303 and S308 that the average rotation speed is 100%, the control unit 6 executes the second image unit dew condensation countermeasure mode (S310). That is, in this second image unit dew condensation countermeasure mode, the control unit 6 drives the rotation speeds of the toner unit air supply fan F4 and the developing unit air supply fan F5 at 100% which is the maximum performance, and controls to stop the image forming unit exhaust fan F6. That is, the exhaust amount from the image forming unit 9 by the image forming unit exhaust fan F6 is controlled to be a small amount (here, substantially 0) less than that in the above first image unit dew condensation countermeasure mode. Thereby, the rotation speed of the image forming unit exhaust fan F6 is further lowered (stopped) compared to the first image unit dew condensation countermeasure mode, the discharge of air from the image forming unit 9 by the image forming unit exhaust fan F6 is suppressed, and the air pressure of the image forming unit 9 is further increased relatively with respect to the reverse discharge unit 4.

[0069] Similarly, in the print job, it is determined whether there is no job for printing (printing) on the subsequent sheet (S305). If there is a job for continuous printing (NO in S305), the process returns to the above step S301. If there is no job for printing (YES in S305), the print job is terminated (S306), the toner unit air supply fan F4, the developing unit air supply fan F5, and the image forming unit exhaust fan F6 are stopped (S206), and this control is terminated.

[0070] [Air flow during execution of the first and second image unit dew condensation countermeasure modes] Subsequently, the air flow inside the image forming apparatus 1 during the execution of the above-described first and second image unit dew condensation countermeasure modes will be described with reference to FIG. 12. FIG. 12 is a schematic cross-sectional view showing the air flow during the execution of the first and second image unit dew condensation countermeasure modes in this embodiment.

[0071] As described above, for example, in the case of the image forming unit low temperature mode, the average rotational speed of the exhaust unit supply fans F1 and F2 is less than 50% of the maximum performance, while the rotational speed of the image forming unit exhaust fan F6 is 50% of the maximum performance (see S303 and S304). On the other hand, in the first image unit dew condensation countermeasure mode, the average rotational speed of the exhaust unit supply fans F1 and F2 is 50% or more and less than 100% of the maximum performance, while the rotational speed of the image forming unit exhaust fan F6 is 25% of the maximum performance (see S303, S308, and S309). That is, considering the image forming unit low temperature mode as a reference, in the first image unit dew condensation countermeasure mode, the average rotational speed of the exhaust unit supply fans F1 and F2 increases, the air supply amount to the reverse exhaust unit 4 increases, and the air pressure of the reverse exhaust unit 4 tends to rise. However, the rotational speed of the image forming unit exhaust fan F6 is decreased, the exhaust amount of the image forming unit 9 is reduced, the air pressure of the image forming unit 9 rises, and the air pressure of the image forming unit 9 becomes relatively higher than the air pressure of the reverse exhaust unit 4.

[0072] Similarly, in the second image unit dew condensation countermeasure mode, the average rotational speed of the exhaust unit supply fans F1 and F2 is 100% of the maximum performance, while the image forming unit exhaust fan F6 is stopped (see S303, S308, and S310). That is, considering the image forming unit low temperature mode and the first image forming unit dew condensation countermeasure mode as references, in the second image unit dew condensation countermeasure mode, the average rotational speed of the exhaust unit supply fans F1 and F2 increases, and the air pressure of the reverse exhaust unit 4 tends to rise. However, the image forming unit exhaust fan F6 is stopped, the exhaust amount of the image forming unit 9 is reduced (to zero), the air pressure of the image forming unit 9 rises, and the air pressure of the image forming unit 9 becomes relatively higher than the air pressure of the reverse exhaust unit 4.

[0073] In this way, when the first and second image unit condensation prevention modes are being executed, the air pressure in the image forming unit 9 can be increased in conjunction with the increase in air pressure in the reversing and discharging unit 4. This makes it possible to reduce or suppress the flow of air from the reversing and discharging unit 4 to the image forming unit 9 due to the air pressure difference, and conversely, to make the air pressure in the image forming unit 9 higher than that of the reversing and discharging unit 4. As a result, as shown by the wind direction of the arrow A8 in FIG. 12, by making the air pressure in the image forming unit 9 higher than that of the reversing and discharging unit 4, it is possible to create an air flow from the image forming unit 9 to the reversing and discharging unit 4.

[0074] Then, when the air pressure in the image forming section 9 is higher than that in the reversing and discharging section 4, air flows from the vicinity of the secondary transfer roller 24 and the intermediate transfer belt 13a toward the reversing and discharging section 4 via the fixing device 3 and the re-conveying path 4c. This makes it possible to keep the high-temperature and high-humidity air in the reversing and discharging section 4 in the reversing and discharging section 4, and it is possible to increase the efficiency of discharging the moisture released from the sheet S in the discharge section exhaust fan F3, even if, for example, a large dedicated exhaust duct space is not provided in the reversing and discharging section 4. As a result, it is possible to prevent the diffusion of moisture from the reversing and discharging section 4 to the image forming section 9, reduce condensation in the image forming section 9, and reduce the occurrence of image defects.

[0075] [Summary of this embodiment] (When the exhaust volume of the image formation unit exhaust fan F6 is medium (50%)) As described above, in the image forming apparatus 1 according to this embodiment, when the control unit 6 controls the supply air volume of the exhaust section air supply fans F1, F2 to a small volume (first supply air volume) (see S104), the control unit 6 controls the exhaust volume of the image forming section exhaust fan F6 to a medium volume (first exhaust volume) (see S304). On the other hand, when the control unit 6 controls the supply air volume of the exhaust section air supply fans F1, F2 to a medium volume (second supply air volume) (see S109), the control unit 6 controls the exhaust volume of the image forming section exhaust fan F6 to a small-medium volume (second exhaust volume) smaller than the medium volume (see S304).

[0076] (When the exhaust volume of the image formation unit exhaust fan F6 is low to medium (25%)) Further, when the control unit 6 controls the air supply amounts of the exhaust unit air supply fans F1 and F2 to a medium amount (first air supply amount) (see S109), the control unit 6 controls the exhaust amount of the image forming unit exhaust fan F6 to a small to medium amount (first exhaust amount) (see S309). On the other hand, when the control unit 6 controls the air supply amounts of the exhaust unit air supply fans F1 and F2 to a large amount (second air supply amount) (see S110), the control unit 6 controls the exhaust amount of the image forming unit exhaust fan F6 to a small amount (second exhaust amount) smaller than the small to medium amount (see S310).

[0077] Note that the first air supply amount, the first exhaust amount, the second air supply amount, and the second exhaust amount mentioned here represent relative magnitude relationships and are not quantitative values.

[0078] (When taking the image forming unit low temperature mode as a reference) Also, in the present embodiment, the exhaust amount of the image forming unit exhaust fan F6 is controlled by selectively executing one from a plurality of modes according to the air supply amounts of the exhaust unit air supply fans F1 and F2. That is, when the air supply amounts of the exhaust unit air supply fans F1 and F2 are controlled to a small amount (first air supply amount) in the paper temperature low temperature mode (see S104), the image forming unit low temperature mode (first mode) is selected and the exhaust amount of the image forming unit exhaust fan F6 is controlled to a medium amount (first exhaust amount) (see S304). On the other hand, when the air supply amounts of the exhaust unit air supply fans F1 and F2 are controlled to a medium amount (second air supply amount) in the paper temperature medium temperature mode (see S109), the first image unit dew condensation countermeasure mode is selected and the exhaust amount of the image forming unit exhaust fan F6 is controlled to a small to medium amount (second exhaust amount) (see S304).

[0079] (When taking the first image unit dew condensation countermeasure mode as a reference) When the air supply amounts of the exhaust unit air supply fans F1 and F2 are controlled to a medium amount (first air supply amount) in the medium paper temperature mode (see S109), the first image unit dew condensation countermeasure mode (first mode) is selected and the exhaust amount of the image forming unit exhaust fan F6 is controlled to a small to medium amount (first exhaust amount) (see S309). On the other hand, when the air supply amounts of the exhaust unit air supply fans F1 and F2 are controlled to a large amount (second air supply amount) in the high paper temperature mode (see S110), the second image unit dew condensation countermeasure mode is selected and the exhaust amount of the image forming unit exhaust fan F6 is controlled to a small amount (second exhaust amount) (see S310). Further, in contrast to this, when the air supply amounts of the exhaust unit air supply fans F1 and F2 are controlled to a small amount (third air supply amount) in the low paper temperature mode (see S104), the image forming unit low temperature mode is selected and the exhaust amount of the image forming unit exhaust fan F6 is controlled to a large amount (third exhaust amount) (see S304).

[0080] In the image forming unit low temperature mode and the first image unit dew condensation countermeasure mode, the air supply amounts of the toner unit air supply fan F4 and the developing unit air supply fan F5 are controlled to a medium amount (fourth air supply amount), and in the second image unit dew condensation countermeasure mode, the air supply amounts of the toner unit air supply fan F4 and the developing unit air supply fan F5 are controlled to a large amount (fifth air supply amount) that is larger than the medium amount. Also, when the internal temperature Tm2 is 40 degrees or higher, the image forming unit high temperature mode (fourth mode) is selected and the exhaust amount of the image forming unit exhaust fan F6 is controlled to the maximum (see S311).

[0081] Note that the first air supply amount, the first exhaust amount, the second air supply amount, the second exhaust amount, the third air supply amount, the third exhaust amount, the fourth air supply amount, and the fifth air supply amount mentioned here express relative magnitude relationships and are not quantitative values. Also, the first mode, the second mode, and the third mode mentioned here are for explaining the relationship of the selected modes and do not specify any of the modes for controlling the above-described fans.

[0082] (Summary) As described above, in the image forming apparatus 1 according to the present embodiment, when the air supply amounts of the discharge unit air supply fans F1 and F2 are increased, the exhaust amount of the image forming unit exhaust fan F6 is decreased. In short, when the air pressure in the reverse discharge unit 4 increases, the air pressure in the image forming unit 9 is also increased, and the air pressure in the image forming unit 9 is controlled to be relatively higher than the air pressure in the reverse discharge unit 4. Thereby, it is possible to prevent the diffusion of moisture from the reverse discharge unit 4 to the image forming unit 9, reduce the dew condensation in the image forming unit 9, and reduce the occurrence of image defects.

[0083] [Possibility of other embodiments] In the present embodiment described above, an example has been described in which two air supply fans and one exhaust fan are arranged for the reverse discharge unit 4, and two air supply fans and one exhaust fan are arranged for the image forming unit 9. However, the present invention is not limited to this, and at least one air supply fan for the reverse discharge unit 4 and one exhaust fan for the image forming unit 9 are sufficient, and further, the number of fans arranged for the reverse discharge unit 4 and the image forming unit 9 may be any number.

[0084] Also, in the present embodiment, an example has been described in which the discharge unit air supply fans F1 and F2 and the discharge unit exhaust fan F3 are controlled based on the outside temperature Tm1 and the sheet type. However, the present invention is not limited to this, and for example, other information such as the outside humidity, information from other sensors, operation information of the main body of the image forming apparatus 1, etc. may be used. Further, an example has been described in which the toner unit air supply fan F4, the developing unit air supply fan F5, and the image forming unit exhaust fan F6 are controlled based on the inside temperature Tm2. However, the present invention is not limited to this, and for example, other information such as the outside humidity, information from other sensors, operation information of the main body of the image forming apparatus 1, etc. may be used.

[0085] In addition, in the present embodiment, it has been described that four modes are executed in the discharge unit fan control and four modes are also executed in the image forming unit fan control. However, the present invention is not limited to this, and as long as the driving (air supply amount and exhaust amount) of each fan is changed in at least two or more modes, the number of modes can be any number, and in particular, the air supply amount and exhaust amount of each fan may be subdivided so that more detailed control can be performed.

[0086] In addition, in the present embodiment, it has been described that the driving amount (air supply amount and exhaust amount) of each fan is changed by selectively executing one from a plurality of modes in the discharge unit fan control and the image forming unit fan control. However, the present invention is not limited to this, and the driving amount (air supply amount and exhaust amount) of each fan may be continuously changed based on parameters such as the outside temperature, the inside temperature, and the sheet type. In particular, the driving amount (air supply amount and exhaust amount) of each fan may be controlled in such a way as to perform linear interpolation between the above-described modes.

[0087] The present disclosure can also be realized by supplying a program that realizes one or more functions of the above-described embodiments to a system or apparatus via a network or a storage medium, and having one or more processors in the computer of the system or apparatus read and execute the program. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

Explanation of Reference Numerals

[0088] 1... Image forming apparatus / 3... Fixing device (fixing unit) / 4... Inverting discharge unit (post-fixing conveyance unit) / 4c... Re-conveyance path (re-conveyance unit) / 4d... Double-sided merging conveyance path (re-conveyance unit) / 6... Control unit / 9... Image forming unit / 45... Inverting discharge roller (re-conveyance unit) / F1... Discharge unit air supply fan (first air supply unit) / F2... Discharge unit air supply fan (first air supply unit) / F3... Discharge unit exhaust fan (first exhaust unit) / F4... Toner unit air supply fan (second air supply unit) / F5... Developing unit air supply fan (second air supply unit) / F6... Image forming unit exhaust fan (second exhaust unit) / S... Sheet / Ts2... Inside temperature sensor (internal temperature detection unit) / Ts1... Outside temperature sensor (external temperature detection unit)

Claims

1. An image forming unit that forms an image on a sheet; A fixing unit that heats the sheet on which the image is formed by the image forming unit and fixes the image on the sheet; A post-fixing conveyance unit that conveys the sheet that has passed through the fixing unit; A first air supply unit that supplies air from the outside of the apparatus main body to the post-fixing conveyance unit; A first exhaust unit that exhausts air from the image forming unit to the outside of the apparatus main body; A control unit that controls the first air supply unit and the first exhaust unit, and the control unit controls the exhaust amount of the first exhaust unit to a first exhaust amount when controlling the air supply amount of the first air supply unit to a first air supply amount, and controls the exhaust amount of the first exhaust unit to a second exhaust amount that is less than the first exhaust amount when controlling the air supply amount of the first air supply unit to a second air supply amount that is greater than the first air supply amount. An image forming apparatus characterized by the above.

2. The control unit has a first mode in which the exhaust amount of the first exhaust unit is controlled to a first exhaust amount when the air supply amount of the first air supply unit is controlled to a first air supply amount, and selectively executes one from a plurality of modes including a second mode in which the exhaust amount of the first exhaust unit is controlled to the second exhaust amount when the air supply amount of the first air supply unit is controlled to the second air supply amount. The image forming apparatus according to claim 1, characterized by the above.

3. The plurality of modes include a third mode in which the exhaust amount of the first exhaust unit is controlled to a third exhaust amount that is greater than the first exhaust amount when the air supply amount of the first air supply unit is controlled to a third air supply amount that is less than the first air supply amount. The image forming apparatus according to claim 2, characterized by the above.

4. The image forming unit is provided with a second air supply unit that supplies air from the outside of the apparatus main body, and the control unit controls the air supply amount of the second air supply unit to a fourth air supply amount in the first mode, and controls the air supply amount of the second air supply unit to a fifth air supply amount that is greater than the fourth air supply amount in the second mode. The image forming apparatus according to claim 2, characterized by the above.

5. The image forming unit is provided with a second air supply unit that supplies air from the outside of the apparatus main body, and the control unit controls the air supply amount of the second air supply unit to a fourth air supply amount in the first mode and the third mode, and controls the air supply amount of the second air supply unit to a fifth air supply amount that is greater than the fourth air supply amount in the second mode. The image forming apparatus according to claim 3, characterized by the above.

6. An internal temperature detection unit that detects the internal temperature of the apparatus main body is provided, The control unit selects and executes one from the plurality of modes based on the detection result of the internal temperature detection unit. The image forming apparatus according to claim 5, characterized in that.

7. When the internal temperature detected by the internal temperature detection unit is lower than the first set temperature, the control unit can execute the first mode and the second mode. The image forming apparatus according to claim 6, characterized in that.

8. The plurality of modes includes a fourth mode in which the air supply amount of the second air supply unit is maximized and the exhaust amount of the first exhaust unit is maximized. When the internal temperature detected by the internal temperature detection unit is higher than the first set temperature, the control unit can execute the fourth mode. The image forming apparatus according to claim 7, characterized in that.

9. An external temperature detection unit for detecting the external temperature of the apparatus main body is provided. Based on the detection result of the external temperature detection unit, the control unit controls the air supply amount of the first air supply unit, and based on the controlled air supply amount of the first air supply unit, selects and executes one from the plurality of modes. The image forming apparatus according to claim 2, characterized in that.

10. When the external temperature detected by the external temperature detection unit is higher than the second set temperature, the control unit sets the air supply amount of the first air supply unit to the first air supply amount or the second air supply amount. The image forming apparatus according to claim 9, characterized in that.

11. The post-fixing conveyance unit has a re-conveyance unit that re-conveys the sheet on which the image has been formed by the image forming unit to the image forming unit after inverting the front and back. The control unit is capable of executing a single-sided printing job for forming an image on the first surface of the sheet and a double-sided printing job for forming an image on the second surface opposite to the first surface using the first surface of the sheet and the re-conveyance unit. When executing the single-sided printing job, the control unit sets the air supply amount of the first air supply unit to the first air supply amount. When executing the double-sided printing job, the control unit sets the air supply amount of the first air supply unit to the second air supply amount. The image forming apparatus according to claim 10, characterized in that.

12. An external temperature detection unit for detecting the external temperature of the apparatus main body is provided. Based on the detection result of the external temperature detection unit, the control unit controls the air supply amount of the first air supply unit, and based on the controlled air supply amount of the first air supply unit, selects and executes one from the plurality of modes. The plurality of modes includes a third mode in which when the air supply amount of the first air supply unit is controlled to a third air supply amount smaller than the first air supply amount, the exhaust amount of the first exhaust unit is controlled to a third exhaust amount larger than the first exhaust amount. When the outside temperature detected by the outside temperature detection unit is lower than the second set temperature, the control unit sets the air supply amount of the first air supply unit to the third air supply amount. The image forming apparatus according to claim 10, characterized in that.

13. An outside temperature detection unit for detecting the outside temperature of the apparatus main body is provided. The control unit is When the type of the sheet is the first type, the air supply amount of the first air supply unit is controlled based on the detection result of the outside temperature detection unit, and based on the controlled air supply amount of the first air supply unit, one of the plurality of modes is selected and executed. When the type of the sheet is a second type different from the first type, the air supply amount of the first air supply unit is controlled to the second air supply amount, and the second mode is selected and executed. The image forming apparatus according to claim 2, characterized in that.

14. The control unit is When the type of the sheet is a third type different from the first type and the second type, the air supply amount of the first air supply unit is controlled to an air supply amount preset for the third type of sheet, and based on the controlled air supply amount of the first air supply unit, one of the plurality of modes is selected and executed. The image forming apparatus according to claim 13, characterized in that.

15. A second exhaust unit for exhausting air from the post-fixing conveyance unit to the outside of the apparatus main body is provided. The image forming apparatus according to claim 1, characterized in that.

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