JP7470290B2 - Cooling device, fixing device and image forming apparatus - Google Patents

Description

The present invention relates to a cooling device, a fixing device, and an image forming apparatus, and in particular to a cooling device that cools a heating member having a longitudinal direction, and a fixing device and an image forming apparatus that are equipped with the cooling device.

There are various types of fixing devices used in electrophotographic image forming devices, one of which is the Surf fixing method, which is highly energy-efficient and has a short warm-up time. In this Surf fixing method, a thin fixing belt with low heat capacity is contact heated from the inside by a planar heater, and the sheet member passing through the fixing nip is heated by the fixing belt, thereby heat-fixing the unfixed toner image carried on the sheet member.

When small-size paper is continuously printed using such a fixing device, the temperature of the longitudinal end (non-paper passing area) of the fixing belt may rise. If the end temperature rises, when switching from printing small-size paper to printing large-size paper, problems such as offset (high temperature) due to excessive fixing heat supply at the end or jamming due to paper wrapping around the fixing belt may occur. As a measure to suppress the rise in end temperature, Patent Document 1 (Patent Publication No. 5930779) discloses a cooling device in which blower fans are provided at both ends of the fixing belt and part of the blower fan's air outlet is covered with a shutter depending on the paper size.

Such cooling devices are effective in preventing temperature increases at both ends of the fixing belt, but they have the problem of being complicated in structure because a blower fan must be installed at each end of the fixing belt.

The present invention was made in consideration of this situation, and aims to simplify the configuration of the cooling device.

In order to solve the above problem, the cooling device of the present invention is a cooling device that cools a heating member having a longitudinal direction with air, characterized in that it has a blowing member, an air duct through which the air passes, the air duct having a first opening through which the air is supplied by the blowing member, a second opening facing a part of the heating member, and a third opening facing another part of the heating member, and an air volume variable mechanism that varies the volume of air discharged from the second and third openings.

According to the present invention, the configuration of the cooling device can be simplified.

1 is a schematic diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. 1 is a diagram illustrating the principle of an image forming apparatus according to an embodiment of the present invention. 1 is a cross-sectional view of a first fixing device according to an embodiment of the present invention. FIG. 4 is a cross-sectional view of a second fixing device according to an embodiment of the present invention. FIG. 11 is a cross-sectional view of a third fixing device according to an embodiment of the present invention. FIG. 11 is a cross-sectional view of a fourth fixing device according to an embodiment of the present invention. FIG. 11 is a cross-sectional view of a fixing device with a cooling device that blows air from the side. FIG. 4 is a cross-sectional view of a fixing device with a cooling device that blows air from above. FIG. 2 is a plan view of a resistance member used in the fixing device. FIG. 2 is a plan view of a resistance member used in the fixing device. FIG. 11 is a cross-sectional view of a fixing device with a cooling device that blows air from the side. FIG. 4 is a cross-sectional view of a fixing device with a cooling device that blows air from above. FIG. 2 is a cross-sectional view illustrating an embodiment of a cooling device. FIG. 2 is a plan view showing an embodiment of a cooling device. FIG. 2 is a diagram showing the configuration of a control unit that controls drive motors M1 and M2 of the cooling device. FIG. 11 is a cross-sectional view showing a modified embodiment of the slide member of the cooling device. 6 is a graph showing the temperature of the fixing belt and the operation of the sliding member. 6 is a graph showing the temperature of the fixing belt and the operation of the blower fan and the sliding member. FIG. 11 is a cross-sectional view showing a modified example of the air volume varying mechanism. FIG. 11 is a cross-sectional view showing a modified example of the air volume varying mechanism. FIG. 11 is a cross-sectional view showing a modified example of the fixing device with a cooling device.

Below, a cooling device according to an embodiment of the present invention, and a fixing device and an image forming device (laser printer) using the cooling device will be described with reference to the drawings. A laser printer is one example of an image forming device, and the image forming device is of course not limited to a laser printer. In other words, the image forming device can be configured as any one of a copier, facsimile, printer, printing machine, and inkjet recording device, or as a multifunction device that combines at least two or more of these.

The same or corresponding parts in each drawing are given the same reference numerals, and their repeated explanations are appropriately simplified or omitted. Furthermore, the dimensions, materials, shapes, relative positions, etc. in the explanations of each component are merely examples, and are not intended to limit the scope of this invention unless otherwise specified.

In the following embodiment, the "recording medium" will be described as "paper", but the "recording medium" is not limited to paper. The "recording medium" includes not only paper, but also overhead projector sheets, fabric, metal sheets, plastic films, and prepreg sheets made of carbon fibers pre-impregnated with resin.

"Recording media" includes all media onto which developer or ink can be attached, recording paper, and recording sheets. In addition to plain paper, "paper" also includes cardboard, postcards, envelopes, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, etc.

In addition, "image formation" as used in the following description does not only mean applying images such as letters and figures to a medium, but also means applying patterns or other designs to a medium.

(Laser printer configuration)
Fig. 1A is a schematic diagram showing the configuration of a color laser printer as an embodiment of an image forming apparatus 100 equipped with a cooling device or fixing device 300 of the present invention. Fig. 1B shows a simplified diagram of the principle of the color laser printer.

Image forming apparatus 100 has four process units 1K, 1Y, 1M, and 1C as image forming means. These process units form images using developers of the colors black (K), yellow (Y), magenta (M), and cyan (C), which correspond to the color separation components of a color image.

Each process unit 1K, 1Y, 1M, and 1C has the same configuration, except that it has toner bottles 6K, 6Y, 6M, and 6C that contain unused toner of different colors. For this reason, the configuration of one process unit 1K will be described below, and descriptions of the other process units 1Y, 1M, and 1C will be omitted.

The process unit 1K has an image carrier 2K (e.g., a photosensitive drum), a drum cleaning device 3K, and a charge removal device. The process unit 1K further has a charging device 4K as a charging means for uniformly charging the surface of the image carrier, and a developing device 5K as a developing means for performing visible image processing of the electrostatic latent image formed on the image carrier. The process unit 1K is detachably attached to the main body of the image forming apparatus 100, and consumable parts can be replaced at the same time.

The exposure device 7 is disposed above each of the process units 1K, 1Y, 1M, and 1C installed in the image forming apparatus 100. The exposure device 7 is configured to perform writing scanning according to image information, i.e., to reflect laser light L from a laser diode by a mirror 7a based on image data and irradiate the image carrier 2K.

In this embodiment, the transfer device 15 is disposed below each of the process units 1K, 1Y, 1M, and 1C. This transfer device 15 corresponds to the transfer means TM in FIG. 1B. Primary transfer rollers 19K, 19Y, 19M, and 19C are disposed in contact with the intermediate transfer belt 16, facing each of the image carriers 2K, 2Y, 2M, and 2C.

The intermediate transfer belt 16 is adapted to circulate around the primary transfer rollers 19K, 19Y, 19M, and 19C, the drive roller 18, and the driven roller 17. The secondary transfer roller 20 is disposed opposite the drive roller 18 and in contact with the intermediate transfer belt 16. If the image carriers 2K, 2Y, 2M, and 2C are the first image carriers for each color, then the intermediate transfer belt 16 is the second image carrier that combines these images.

The belt cleaning device 21 is installed downstream of the secondary transfer roller 20 in the running direction of the intermediate transfer belt 16. In addition, a cleaning backup roller is installed on the opposite side of the intermediate transfer belt 16 from the belt cleaning device 21.

A paper feeder 200 having a tray for stacking paper P is installed below the image forming device 100. This paper feeder 200 constitutes the recording medium supply section, and is capable of storing a large number of sheets of paper P as recording media in a bundle, and is unitized with a paper feed roller 60 and a roller pair 210 as a means for transporting paper P.

The paper feeder 200 can be inserted into and removed from the main body of the image forming device 100 for paper replenishment, etc. The paper feed roller 60 and the roller pair 210 are disposed above the paper feeder 200, and are configured to transport the topmost paper P of the paper feeder 200 toward the paper feed path 32.

The pair of registration rollers 250, which serve as a separation and transport means, are disposed immediately upstream of the secondary transfer roller 20 in the transport direction, and can temporarily stop the paper P fed from the paper feed device 200. This temporary stop creates slack in the leading edge of the paper P, correcting any skew in the paper P.

A registration sensor 31 is disposed immediately upstream of the registration roller pair 250 in the conveying direction, and this registration sensor 31 detects the passage of the leading edge of the paper. After the registration sensor 31 detects the passage of the leading edge of the paper, when a predetermined time has elapsed, the paper is abutted against the registration roller pair 250 and temporarily stopped.

At the downstream end of the paper feeder 200, a transport roller 240 is provided to transport the paper transported to the right from the roller pair 210 upward. As shown in FIG. 1A, the transport roller 240 transports the paper upward toward the registration roller pair 250.

The roller pair 210 is composed of a pair of upper and lower rollers. The roller pair 210 can be of the FRR separation type or the FR separation type.

The FRR separation method presses a separation roller (return roller) to which a constant torque is applied in the counter-feed direction by the drive shaft via a torque limiter against the feed roller, separating the paper at the nip between the rollers. The FR separation method presses a separation roller (friction roller) supported on a fixed shaft against the feed roller via a torque limiter, separating the paper at the nip between the rollers.

In this embodiment, the roller pair 210 is configured using the FRR separation method. That is, the roller pair 210 is configured with an upper feed roller 220 that transports paper into the machine, and a lower separation roller 230 that is given a driving force by a drive shaft via a torque limiter in the opposite direction to the feed roller 220.

The separation roller 230 is biased toward the feed roller 220 by a biasing means such as a spring. The feed roller 60 rotates counterclockwise in FIG. 1A by transmitting the driving force of the feed roller 220 via a clutch means.

The paper P, which has been struck by the pair of registration rollers 250 and has a slack at its leading edge, is sent to the secondary transfer nip (transfer nip N in FIG. 1B) between the secondary transfer roller 20 and the drive roller 18 in time for the toner image formed on the intermediate transfer belt 16 to be suitably transferred. The toner image formed on the intermediate transfer belt 16 is then electrostatically transferred to the desired transfer position with high precision by the bias applied to the secondary transfer nip.

The post-transfer transport path 33 is disposed above the secondary transfer nip between the secondary transfer roller 20 and the drive roller 18. The fixing device 300 is installed near the upper end of the post-transfer transport path 33.

The fixing device 300 is equipped with a fixing belt 310 as a heating member containing a heat generating member, and a pressure roller 320 as a pressure member that rotates while contacting the fixing belt 310 with a predetermined pressure. The fixing device 300 can be of various types as shown in Figures 2A to 2D described later, but we will first explain it based on the type in Figure 2A.

The post-fixing transport path 35 is disposed above the fixing device 300, and at the upper end of the post-fixing transport path 35, it branches into a paper discharge path 36 and a reversing transport path 41. A switching member 42 is disposed at this branching point, and the switching member 42 is adapted to swing around its swing shaft 42a. In addition, a pair of paper discharge rollers 37 is disposed near the open end of the paper discharge path 36.

The reverse transport path 41 merges with the paper feed path 32 at the other end opposite the branching point. A pair of reverse transport rollers 43 is disposed midway along the reverse transport path 41. The paper output tray 44 is disposed on the top of the image forming device 100, forming a concave shape facing inward of the image forming device 100.

The powder container 10 (e.g., a toner container) is disposed between the transfer device 15 and the paper feed device 200. The powder container 10 is removably attached to the main body of the image forming device 100.

The image forming device 100 of this embodiment requires a certain distance between the paper feed roller 60 and the secondary transfer roller 20 due to the transfer paper transport. The powder container 10 is installed in the dead space created by this distance, making the entire laser printer smaller.

The transfer cover 8 is installed on top of the paper feed device 200, directly in front of the paper feed device 200 in the pull-out direction. By opening this transfer cover 8, the inside of the image forming device 100 can be inspected. The transfer cover 8 is equipped with a manual feed roller 45 for manual paper feed, and a manual feed tray 46 for manual paper feed.

(Laser printer operation)
Next, the basic operation of the laser printer according to this embodiment will be described below with reference to Fig. 1A. First, single-sided printing will be described.

As shown in FIG. 1A, the paper feed roller 60 rotates in response to a paper feed signal from the control unit of the image forming device 100. The paper feed roller 60 then separates only the topmost sheet of the stack of paper P loaded in the paper feed device 200 and sends it to the paper feed path 32.

When the leading edge of the paper P sent out by the paper feed roller 60 and the roller pair 210 reaches the nip of the registration roller pair 250, it forms a slack and waits in that state. Then, the toner image formed on the intermediate transfer belt 16 is transferred to the paper P at the optimal timing (synchronization), and the leading edge skew of the paper P is corrected.

When feeding paper manually, a stack of paper sheets stacked on the manual feed tray 46 is transported one by one, starting from the topmost sheet, through a part of the inverted transport path 41 by the manual feed roller 45 to the nip of the registration roller pair 250. The subsequent operation is the same as when feeding paper from the paper feed device 200.

Here, the image forming operation will be explained for one process unit, 1K, and explanations for the other process units, 1Y, 1M, and 1C, will be omitted. First, the charging device 4K uniformly charges the surface of the image carrier 2K to a high potential. Then, the exposure device 7 irradiates the surface of the image carrier 2K with laser light L based on the image data.

When the surface of the image carrier 2K is irradiated with the laser light L, the potential of the irradiated area decreases, forming an electrostatic latent image. The developing device 5K has a developer carrier that carries a developer containing toner, and transfers unused black toner supplied from the toner bottle 6K via the developer carrier to the surface portion of the image carrier 2K on which the electrostatic latent image is formed.

The image carrier 2K to which the toner has been transferred forms (develops) a black toner image on its surface. The toner image formed on the image carrier 2K is then transferred to the intermediate transfer belt 16.

The drum cleaning device 3K removes residual toner adhering to the surface of the image carrier 2K after the intermediate transfer process. The removed residual toner is sent by a waste toner transport means to a waste toner storage section in the process unit 1K for collection. In addition, the charge removal device removes residual charge from the image carrier 2K from which the residual toner has been removed by the cleaning device 3K.

In the process units 1Y, 1M, and 1C for each color, toner images are formed on the image carriers 2Y, 2M, and 2C in the same manner, and the toner images of each color are transferred to the intermediate transfer belt 16 so that they are superimposed.

The intermediate transfer belt 16, on which the toner images of each color have been transferred so as to overlap, travels to the secondary transfer nip between the secondary transfer roller 20 and the drive roller 18. Meanwhile, the pair of registration rollers 250 rotates, nipping the paper that is abutted against them at a predetermined timing, and transports the paper to the secondary transfer nip of the secondary transfer roller 20 in accordance with the timing at which the toner images formed by superimposing and transferring onto the intermediate transfer belt 16 are appropriately transferred. In this way, the toner image on the intermediate transfer belt 16 is transferred to the paper P sent out by the pair of registration rollers 250.

The paper P with the toner image transferred thereto is transported through post-transfer transport path 33 to fixing device 300. The paper P transported to fixing device 300 is then sandwiched between fixing belt 310 and pressure roller 320, where the unfixed toner image is fixed to the paper P by applying heat and pressure. The paper P with the fused toner image is sent from fixing device 300 to post-fixing transport path 35.

When the paper P is sent out from the fixing device 300, the switching member 42 is in a position that opens the vicinity of the upper end of the post-fixing transport path 35, as shown by the solid line in FIG. 1A. The paper P sent out from the fixing device 300 is then sent out to the paper discharge path 36 via the post-fixing transport path 35. The paper discharge roller pair 37 clamps the paper P sent out to the paper discharge path 36 and rotates to discharge the paper onto the paper discharge tray 44, thereby completing single-sided printing.

Next, the case of double-sided printing will be described. As in the case of single-sided printing, the fixing device 300 sends the paper P to the paper discharge path 36. Then, when performing double-sided printing, the pair of paper discharge rollers 37 are driven to rotate to transport a portion of the paper P outside the image forming device 100.

Then, when the rear end of the paper P passes through the paper discharge path 36, the switching member 42 swings about the swing shaft 42a as shown by the dotted line in FIG. 1A, and closes the upper end of the post-fixing transport path 35. Almost simultaneously with the closing of the upper end of the post-fixing transport path 35, the pair of paper discharge rollers 37 rotates in the direction opposite to the direction in which the paper P is transported out of the image forming device 100, and sends the paper P to the reverse transport path 41.

The paper P sent to the reverse transport path 41 passes through the reverse transport roller pair 43 and reaches the registration roller pair 250. The registration roller pair 250 then determines the optimal timing (synchronization) for transferring the toner image formed on the intermediate transfer belt 16 to the non-transferred surface of the paper P, and sends the paper P to the secondary transfer nip.

Then, the secondary transfer roller 20 and the drive roller 18 transfer the toner image to the non-transferred side (reverse side) of the paper P as the paper P passes through the secondary transfer nip. The paper P with the transferred toner image is then transported to the fixing device 300 via the post-transfer transport path 33.

The fixing device 300 clamps the transported paper P between the fixing belt 310 and the pressure roller 320, and applies heat and pressure to fix the unfixed toner image to the back side of the paper P. In this way, the paper P with the toner images fixed on both sides is sent from the fixing device 300 to the post-fixing transport path 35.

When the paper P is sent out from the fixing device 300, the switching member 42 is in a position that opens the vicinity of the upper end of the post-fixing transport path 35, as shown by the solid line in FIG. 1A. The paper P sent out from the fixing device 300 is then sent out to the paper discharge path 36 via the fixing transport path. The paper discharge roller pair 37 clamps the paper P sent out to the paper discharge path 36, and rotates to discharge the paper to the paper discharge tray 44, completing double-sided printing.

After the toner image on the intermediate transfer belt 16 is transferred to the paper P, residual toner remains on the intermediate transfer belt 16. The belt cleaning device 21 removes this residual toner from the intermediate transfer belt 16. The toner removed from the intermediate transfer belt 16 is transported by the waste toner transport means to the powder container 10 and collected in the powder container 10.

(Fixing device)
Next, a further description will be given of the cooling device according to the embodiment of the present invention and the first to fourth fixing devices 300. The cooling device of this embodiment is for cooling both ends of the fixing belt 310 of the fixing device 300.

As shown in FIG. 2A, the first fixing device is composed of a thin fixing belt 310 with low heat capacity and a pressure roller 320. The fixing belt 310 has a cylindrical body made of polyimide (PI) with an outer diameter of 25 mm and a thickness of 40 to 120 μm, for example.

A release layer made of fluororesin such as PFA or PTFE and having a thickness of 5 to 50 μm is formed on the outermost surface of the fixing belt 310 to improve durability and ensure releasability. An elastic layer made of rubber or the like and having a thickness of 50 to 500 μm may be provided between the base and the release layer.

The base material of the fixing belt 310 is not limited to polyimide, and may be a heat-resistant resin such as PEEK or a metal base material such as nickel (Ni) or SUS. The inner surface of the fixing belt 310 may be coated with polyimide, PTFE, or the like as a sliding layer.

The pressure roller 320 has an outer diameter of, for example, 25 mm, and is composed of a solid iron core 321, an elastic layer 322 formed on the surface of the core 321, and a release layer 323 formed on the outside of the elastic layer 322. The elastic layer 322 is made of silicone rubber and has a thickness of, for example, 3.5 mm.

To improve releasability, it is desirable to form a release layer 323 made of a fluororesin layer having a thickness of, for example, about 40 μm on the surface of the elastic layer 322. The pressure roller 320 is pressed against the fixing belt 310 by a biasing means.

A stay 350 and a heater holder 340 are arranged in the axial direction inside the fixing belt 310. The stay 350 is made of a metal channel material, and both ends are supported by both side plates of the fixing device 300. The stay 350 reliably receives the pressing force of the pressure roller 320 to stably form the fixing nip SN.

The heater holder 340 is for holding the base material 341 of the fixing device 300, and is supported by the stay 350. The heater holder 340 is preferably formed from a heat-resistant resin with low thermal conductivity, such as LCP, which reduces heat transfer to the heater holder 340 and allows the fixing belt 310 to be heated efficiently.

The heater holder 340 is shaped to support only two points near both ends of the substrate 341 in the short direction to avoid contact with the high-temperature parts of the substrate 341. This further reduces the amount of heat flowing to the heater holder 340, allowing the fixing belt 310 to be heated efficiently.

The fixing device 300 can be of various types, and the first fixing device in FIG. 2A is one example. The second to fourth fixing devices 300 will be described below with reference to FIGS. 2B to 2D. As shown in FIG. 2B, the second fixing device 300 has a pressure roller 390 on the opposite side to the pressure roller 320, and heats the fixing belt 310 by sandwiching it between the pressure roller 390 and the resistance member 370.

The heat-generating member described above is disposed inside the fixing belt 310. An auxiliary stay 351 is attached to one side of the stay 350, and a nip-forming member 381 is attached to the other side. The heat-generating member is held by this auxiliary stay 351. The nip-forming member 381 abuts against the pressure roller 320 via the fixing belt 310 to form the fixing nip SN.

As shown in FIG. 2C, the third fixing device 300 has a heat generating member disposed inside the fixing belt 310. Instead of omitting the pressure roller 390 described above, this heat generating member has a base material 341 and an insulating layer 385 with an arc-shaped cross section to match the curvature of the fixing belt 310 in order to increase the circumferential contact length with the fixing belt 310. The resistance member 370 is disposed in the center of the arc-shaped base material 341. The rest is the same as the second fixing device in FIG. 2B.

The fourth fixing device 300, as shown in FIG. 2D, is configured to be divided into a heating nip HN and a fixing nip SN. That is, a nip forming member 381 and a stay 352 made of a metal channel material are arranged on the opposite side of the pressure roller 320 from the fixing belt 310, and the pressure belt 334 is arranged so that it can rotate around the nip forming member 381 and the stay 352. Then, paper P is passed through the fixing nip SN between the pressure belt 334 and the pressure roller 320 and heated and fixed. The rest is the same as the first fixing device in FIG. 2A.

The fixing device 300 in Figures 2A to 2D has a resistance member 370 composed of a resistive heating element (planar heater). This resistance member 370 can be formed in a number of types, such as the resistance member 330 shown as an example in Figures 3C and 3D. In either type, the resistance members 370 and 330 are formed on a substrate 341 made of a thin, elongated metal plate member covered with an insulating material. In a fixing method that uses a planar heater to heat the fixing nip SN, the resistance member, which is a heating element, is divided into multiple parts in the paper width direction and heated and controlled individually, allowing multiple types of paper widths to be heated uniformly.

The preferred material for the substrate 341 is low-cost aluminum or stainless steel. The substrate 341 is not limited to being made of metal, and can be made of ceramics such as alumina or aluminum nitride, or non-metallic materials with excellent heat resistance and insulation properties, such as glass or mica.

To improve the thermal uniformity of the resistive members 330 and 370 and enhance image quality, the substrate 341 may be made of a material with high thermal conductivity, such as copper, graphite, or graphene. In this embodiment, an alumina substrate with a short side width of 8 mm, a long side width of 270 mm, and a thickness of 1.0 mm is used.

The resistance member 330 in Figs. 3C and 3D can be configured as a multi-type in which PTC elements 371 to 378 are electrically connected in parallel. If the resistance value between electrodes 370c and 370d at both ends in Figs. 3C and 3D is 10 Ω, the resistance value of each of the PTC elements 371 to 378 will be as high as 80 Ω due to the parallel connection.

The PTC element is made of a material with a positive temperature coefficient of resistance, and has the characteristic that the resistance value increases as the temperature T increases (the current I decreases and the heater output decreases). The temperature coefficient of resistance (TCR) can be, for example, 1500 PPM (parts per million).

The PTC elements 371-378 in Figures 3C and 3D are arranged linearly and at equal intervals in the longitudinal direction of the substrate 341. Low resistance power supply lines 370a, 370b are linearly arranged parallel to each other on both sides of the short sides of each PTC element 371-378, and both ends of each PTC element 371-378 are connected to these power supply lines 370a, 370b. AC power is supplied to electrodes 370c, 370d formed at one end of each of the power supply lines 370a, 370b.

The PTC elements 371-378 and the power supply lines 370a, 370b are covered with a thin insulating layer 385. This insulating layer 385 can be made of heat-resistant glass with a thickness of, for example, 75 μm. The insulating layer 385 insulates and protects the PTC elements 371-378 and the power supply lines 370a, 370b, while maintaining sliding ability with the fixing belt 310.

The PTC elements 371 to 378 can be formed, for example, by applying a paste made of silver palladium (AgPd) and glass powder to the substrate 341 by screen printing or the like, and then firing the substrate 341. In this embodiment, the resistance value of each of the PTC elements 371 to 378 is set to 80 Ω at room temperature (total resistance value is 10 Ω).

Resistive materials such as silver alloy (AgPt) and ruthenium oxide (RuO ₂ ) may be used as the materials for the PTC elements 371 to 378. The materials for the power supply lines 370a, 370b and the electrodes 370c, 370d can be formed by screen printing or the like using silver (Ag) or silver palladium (AgPd).

The insulating layer 385 side of the PTC elements 371-378 comes into contact with the fixing belt 310 and heats up, increasing the temperature of the fixing belt 310 through heat transfer, and heating and fixing the unfixed image conveyed to the fixing nip SN. By using the PTC elements 371-378, when the temperature of the PTC elements in non-paper passing areas increases due to the passage of small-sized paper, etc., the amount of heat generated by the PTC elements decreases due to the temperature resistance dependency of the resistive heating element, making it possible to suppress the temperature increase.

Due to this feature, for example, if a piece of paper narrower than the overall width of PTC elements 371-378 (for example, within the width of PTC elements 373-376) is printed, the temperature of PTC elements 371, 372, 377, and 378 outside the paper width will rise because the heat is not absorbed by the paper. This causes the resistance value of those PTC elements 371, 372, 377, and 378 to rise.

Since the voltage applied to the PTC elements 371-378 is constant, the output of the PTC elements 371, 372, 377, and 378 outside the paper width is relatively lower, suppressing the rise in temperature at the ends. If the PTC elements 371-378 are electrically connected in series, the only way to suppress the temperature rise of the resistive heating elements outside the paper width during continuous printing is to slow down the printing speed. By electrically connecting the PTC elements 371-378 in parallel, it is possible to suppress the temperature rise in non-paper passing areas while maintaining the printing speed.

If there are gaps between the PTC elements 371-378 in the short direction, the amount of heat generated will decrease in the gaps, which will likely cause uneven fixing. Therefore, in Figures 3C and 3D, the ends of the PTC elements 371-378 are overlapped in the long direction.

In Fig. 3C, steps are formed by L-shaped cutouts at the ends of PTC elements 371-378, and these steps overlap with the steps at the ends of adjacent resistive heating elements. In Fig. 3D, inclined portions are formed by diagonal cutouts at the ends of PTC elements 371-378, and these inclined portions overlap with the inclined portions at the ends of adjacent resistive heating elements. By overlapping the ends of PTC elements 371-378 in this way, the effect of reduced heat generation in the gaps between the resistive heating elements can be suppressed.

Also, the electrodes 370c and 370d can be arranged on either end of the PTC elements 371 to 378, or on one side of the PTC elements 371 to 378. By arranging the electrodes 370c and 370d on one side in this way, space can be saved in the longitudinal direction.

Each PTC element 371-378 in Figures 3C and 3D is composed of a rectangular sheet heating element, but to obtain the desired output (resistance value), it can also be composed of multiple PTC elements formed in a narrow serpentine shape and electrically connected in parallel.

(Cooling system)
As shown in Fig. 3A, cooling device 400, which cools both ends of fixing belt 310 of fixing device 300 with air, has air duct 410, blower fan 430 as a blower member, and slide member 450. Air duct 410 extends in the longitudinal direction of fixing belt 310, i.e., in a direction perpendicular to the paper surface of Fig. 3A. Slide member 450 constitutes an air volume variable mechanism, as described below. In this document, the term "air volume" refers to the volume of gas flowing per unit time ( ^m3 /sec) unless otherwise specified.

As shown in FIG. 5A, a first opening 411 having an air passage in the vertical direction is formed in the longitudinal center of the air duct 410. A second opening 412 and a third opening 413 are formed at both longitudinal ends of the air duct 410. The first opening 411 is not limited to being formed exactly in the longitudinal center of the air duct 410, but can also be formed in a position (middle part) that is off-center to the left or right of the center. In short, the first opening 411 can be formed in the middle part between the second opening 412 and the third opening 413.

A blower fan 430 is disposed within the first opening 411. The blower fan 430 is driven by a drive motor M1, as shown in FIG. 5C. By disposing the blower fan 430 within the first opening 411, it is possible to save space and reduce the number of parts.

The blower fan 430 may be disposed outside the first opening 411, in which case the blower fan 430 and the first opening 411 are connected by a blower duct. Although a propeller type blower fan 430 is illustrated in FIG. 5A, the blower fan 430 is not limited to this, and various types of blower fans such as a centrifugal fan, a turbo fan, an airfoil fan, and a plate fan can be used.

A partition-shaped slide member 450 is disposed immediately downstream of the blower fan 430, perpendicular to the longitudinal direction of the air duct 410. The air introduced into the first opening 411 by the blower fan 430 is distributed to the left and right in a predetermined ratio by the slide member 450, and is configured to be blown out from the second opening 412 and the third opening 413 toward both ends of the fixing belt 310.

In this way, by arranging one blower fan 430 in the longitudinal center of the air duct 410, it is possible to significantly reduce the space and number of parts compared to the conventional arrangement of multiple fans as in Patent Document 1. In addition, excessive temperature rise at the end of the fixing belt 310, which has a small heat capacity, can be efficiently suppressed in accordance with the temperature rise.

The direction of blowing the cooling air from the second opening 412 and the third opening 413 can be blown from the horizontal lateral direction of the fixing belt 310 as shown in FIG. 3A, or blown downward from above the fixing belt 310 as shown in FIG. 3B. By providing the second opening 412 and the third opening 413, the cooling air can be effectively supplied to the part of the fixing belt 310 that is to be cooled. Also, instead of a planar heater using a resistance member 370 as shown in FIG. 3A and FIG. 3B, a halogen heater 314 can be disposed inside the fixing belt 310 as shown in FIG. 4A and FIG. 4B as a heating source. FIG. 4A is an example in which the cooling air is blown from the horizontal lateral direction of the fixing belt 310 as in FIG. 3A, and FIG. 4B is an example in which the cooling air is blown downward from above the fixing belt 310 as in FIG. 3B.

(Details of the cooling device)
Next, an embodiment of the cooling device will be described in more detail with reference to Figures 5A to 5C. As shown in Figure 5A, air duct 410 extends in the longitudinal direction of fixing belt 310. Figure 5B is a plan view of air duct 410 seen from above, in which air duct 410 has a rectangular shape that is long in the longitudinal direction of fixing belt 310.

The second opening 412 at the left end of the air duct 410 and the third opening 413 at the right end are approximately square and of the same size in the plan view of FIG. 5B, and open toward the outer peripheral surface of both ends of the fixing belt 310. The gaps formed between the outer peripheral surfaces of both ends of the fixing belt 310 and the second opening 412 and the third opening 413 need only be large enough not to impede the rotation of the fixing belt 310, but if these gaps are larger than necessary, air will leak out unnecessarily, reducing the cooling effect. Therefore, it is desirable for the size of the gap to be, for example, around 2 mm to 3 mm at most.

The second opening 412 and the third opening 413 are preferably shaped to cover the outer peripheral surface of both ends of the fixing belt 310 in an arc shape. This makes it possible to keep the gap between the outer peripheral surface of both ends of the fixing belt 310 constant in the circumferential direction and enhance the cooling effect.

The longitudinal center of the air duct 410 is spaced upward from the outer periphery of the fixing belt 310 in the side view of FIG. 5A, and is bent at an obtuse angle into an inverted V shape overall. This shape allows the cooling air supplied to the first opening 411 in the longitudinal center to flow smoothly in the directions of the arrows E2 and E3 to the second opening 412 and the third opening 413, and is effectively blown onto both ends of the fixing belt 310.

A slide member 450 is disposed at a right angle to the longitudinal direction of the air duct 410 on the bottom surface of the longitudinal center of the air duct 410. This slide member 450 is disposed so as to be slidable in the longitudinal direction of the air duct 410, i.e., the left-right direction in FIG. 5A, by a rack and pinion in FIG. 5B. The rack and pinion has a pinion gear 471 that is rotated by a drive motor M2, and a rack 473 that meshes with this pinion gear 471.

The rack 473 extends in the longitudinal direction of the air duct 410, and the pinion gear 471 meshes with the rack teeth 473a formed on the lower edge of the rack 473. Long holes 473b extending in the left-right direction are formed on the left and right sides of the rack 473, and a guide pin 475 extending from the fixed side is slidably inserted into these long holes 473b.

The longitudinal center of rack 473 is connected to the side end of slide member 450 via fixed member 473c. In FIG. 5B, when pinion gear 471 rotates left, rack 473 and slide member 450 slide in direction A2 (leftward), and when pinion gear 471 rotates right, rack 473 and slide member 450 slide in direction A3 (rightward). Because slide member 450 can be moved simply by rotating pinion gear 471 of the rack and pinion, cooling to eliminate the temperature difference between both ends of fixing belt 310 can be performed with a simple mechanism.

Thermistors TH1 to TH3 are arranged close to the outer peripheral surface of the fixing belt 310 as temperature detection members that detect the temperature of the fixing belt 310. Thermistor TH1 is arranged close to the outer peripheral surface of the longitudinal center of the fixing belt 310, with thermistor TH1 located in the center of the narrow paper width of small size paper. Thermistors TH2 and TH3 are arranged close to the outer peripheral surface of both ends of the fixing belt 310, with thermistors TH2 and TH3 located at the wide paper width ends of large size paper.

The temperatures detected by thermistors TH1 to TH3 are input to the control unit 480 in FIG. 5C. Based on the temperature information of the fixing belt 310 obtained from thermistors TH1 to TH3, the control unit 480 controls the drive of the drive motor M1 of the blower fan 430 and the slide drive motor M2 of the slide member 450. Therefore, the control unit 480 constitutes a part of the cooling device 400.

The slide member 450 is preferably a wedge-shaped slide member 451 with inclined surfaces 451a, 451b on the left and right as shown in Figures 6(a) and (b). If the slide member 451 has inclined surfaces 451a, 451b on the left and right, the air introduced vertically into the first opening 411 by the blower fan 430 is smoothly guided horizontally by the inclined surfaces 451a, 451b as shown in Figure 6(b). This reduces the air resistance in the slide member 451, and allows a sufficient amount of air to be stably supplied to the second opening 412 and the third opening 413.

7A shows a state in which the controller 480 controls the sliding movement of the sliding member 450 (451) when the temperature at both ends of the fixing belt 310 detected by thermistors TH2 and TH3 rises (vertical axis) as the machine operating time (horizontal axis) elapses when small size paper is continuously fed. In the illustrated example, the temperature rise is more rapid for the thermistor TH2 (solid line) on the left end than for the thermistor TH3 (dotted line) on the right end. As a result, the temperature difference ΔT detected by both thermistors TH2 and TH3 increases to _ΔT1 .

With the temperature difference _ΔT1 as a threshold, the sliding member 450 (451) slides a certain amount from the central position in the direction A3 in Figures 5A and 5B. This movement of the sliding member 450 (451) reduces the amount of air blown out from the third opening 413 on the moving side, while increasing the amount of air blown out from the second opening 412 on the opposite side to the moving side. As a result, the cooling effect of the left end of the fixing belt 310 increases, and the temperature difference decreases from _ΔT1 to _ΔT2 . Then, with the temperature difference _ΔT2 as a threshold, the sliding member 450 (451) returns to the central position from the sliding position in the A3 direction.

In this way, the amount of air supplied to the first opening 411 by one blower fan 430 is distributed to the left and right by the slidable slide member 450 (451) and blown out from the second opening 412 and the third opening 413, making the configuration much simpler than conventional cooling devices equipped with separate blower fans for the left and right. Furthermore, when the temperatures at both ends of the fixing belt 310 differ, the slide member 450 (451) slides to cool both ends so that the temperature difference at both ends is reduced, making it possible to provide a fixing device that enables high image quality at low cost and in a small space.

7B shows an example in which the rotation speed of blower fan 430 is switched between three levels in addition to the sliding movement control of slide member 450 (451) described above. That is, the drive of slide member 450 (451) and blower fan 430 is controlled by controller 480 based on the temperature change (vertical axis) at both ends of fixing belt 310 detected by thermistors TH2 and TH3 as the machine operating time (horizontal axis) elapses. In the illustrated example, the temperature difference ΔT detected by thermistors TH2 and TH3 increases from _ΔT2 to _ΔT1 to _ΔT10 ( _ΔT2 < _ΔT1 < _ΔT10 ).

The rotation speed of the blower fan 430 is low until the temperature difference reaches _ΔT2 , but increases to medium rotation speed when the temperature difference exceeds _ΔT2 . This increases the amount of air blown out from the second opening 412 and the third opening 413, and enhances the cooling effect that lowers the temperature at both ends of the fixing belt 310.

When the temperature difference exceeds _ΔT2 and becomes _ΔT1 , the rotation speed of the blower fan 430 remains at medium speed, but the sliding member 450 slides a predetermined distance in the A3 direction. This sliding movement reduces the amount of air supplied in the A3 direction, while increasing the amount of air supplied in the A2 direction, where the temperature rises sharply.

When the temperature difference exceeds _ΔT1 and becomes _ΔT10 , slide member 450 remains in the position closer to the A3 direction, but the rotation speed of blower fan 430 increases from medium to high rotation. This increases the amount of air blown out from second opening 412 and third opening 413, enhancing the cooling effect that lowers the temperature of both ends of fixing belt 310. At this time, since slide member 450 is in the position closer to the A3 direction, the cooling effect of air blown out from second opening 412 is greater than the cooling effect of air blown out from third opening 413.

As a result, the sudden rise in temperature at the left end of fixing belt 310 is suppressed from peaking at temperature difference _ΔT10 , and then gradually decreases. When the temperature difference returns to _ΔT1 , first the rotation speed of blower fan 430 decreases from high to medium. When the temperature difference further decreases to _ΔT2 , the rotation speed of blower fan 430 decreases from medium to low, and at the same time, slide member 450 returns to the center position from the position closer to A3. Now, the amount of air blown out from second opening 412 and third opening 413 becomes equal and low.

In this way, the volume of air blown out of the second opening 412 and the third opening 413 can be changed by changing the position of the slide member 450 as an air volume varying mechanism or by changing the rotation speed of the blower fan 430 based on the temperature difference between the thermistors TH2 and TH3. Therefore, it is possible to achieve energy saving effects by increasing the volume of air only when necessary and for the required time, without constantly increasing the volume of air from the blower fan 430. Note that, although the above describes how the rotation speed of the blower fan 430 is controlled based on the temperature difference between the thermistors TH2 and TH3 at both ends, it may also be controlled based on the temperature difference between the central thermistor TH1 and either of the thermistors TH2 and TH3 at both ends.

The variable airflow mechanism using the slide member 450 (451) described above can be replaced by other modified embodiments. Figure 8 shows one such modified embodiment, in which the variable airflow mechanism is configured with a swingable member 452 that can swing around a pivot point 452a.

The pivot 452a can be rotated clockwise and counterclockwise in FIG. 8 by a motor or cam, and this rotation causes the oscillating member 452 to rotate in the A2 or A3 direction. This rotation of the oscillating member 452 can change the airflow distribution ratio in the same way as the sliding movement of the sliding member 451 described above.

Figure 9 shows a modified embodiment of the variable airflow mechanism that combines a fixed partition member 453 that does not slide and a swingable blower fan 430. The partition member 453 can be configured to have a triangular wedge shape in cross section, with the tip of the wedge extending perpendicular to the longitudinal direction of the air duct 410 and facing the center of the first opening 411.

The blower fan 430 is attached to a holder 431 that can swing left and right in FIG. 9, and when the holder 431 is tilted to the right as shown by a swinging mechanism that uses a motor and a cam, the amount of air distributed to the left side increases and the amount of air supplied to the opposite side decreases. In this way, even if a fixed partition member 452 is used, the amount of air distributed to the second opening 512 and the third opening 513 can be varied by swinging the blower fan 430.

Furthermore, the fixing device 300 is not limited to the configuration shown in Figs. 2A to 2D, and may also be configured as shown in Figs. 10(a) and 10(b) in which the fixing belt 310 is wound around three rollers 311 to 313. That is, the fixing device in Figs. 10(a) and 10(b) uses a fixing belt 310, a heating roller 311, guide rollers 312 and 313, and a pressure roller 320.

The fixing belt 310 is wound around the heating roller 311 and the guide rollers 312 and 313, and rotates around these rollers 310 to 313 in a clockwise direction. The pressure roller 320 may be rotated counterclockwise to rotate the fixing belt 310 clockwise, or either the heating roller 311 or the guide rollers 312 and 313 may be rotated clockwise to rotate the fixing belt 310 clockwise.

The air duct 510 is placed inside the fixing belt 310, and the blower fan 430 is placed in the first opening 511 in the longitudinal center of the air duct 510 as shown in FIG. 10(b). The air blown out from the second opening 512 and the third opening 513 formed at both ends of the air duct 510 cools the underside of the fixing belt 310 between the heating roller 311 and the guide roller 313.

The ratio of the air volumes blown out from the second opening 512 and the third opening 513 is changed by sliding the slide member 450 (451) slidably arranged inside the first opening 511 in the longitudinal direction of the air duct 510.

The temperatures of the center and both ends of the fixing belt 310 are detected by thermistors TH1 to TH3 arranged at three positions along the longitudinal direction of the outer circumference of the fixing belt 310. Based on the detected temperatures, the sliding member 450 (451) is slid as described above to prevent the temperature difference between both ends of the fixing belt 310 from exceeding a predetermined threshold.

The present invention has been described above based on the embodiment, but the present invention is not limited to the embodiment, and it goes without saying that various modifications can be made within the scope of the technical ideas described in the claims. For example, the air volume variable mechanism can be configured by combining slide members 450, 451 and a swing member 452, and in this configuration, the slide members 450, 451 in Figs. 5A and 6 can be swingable in the left-right direction as shown in Fig. 8. In addition, the swing mechanism in Fig. 9, which swings the blower fan 430 in the longitudinal direction of the air duct 510, can be combined with the slide members 450, 451 in Figs. 5A and 6, or the swing member 452 in Fig. 8. In addition, the cooling device of the present invention can be used for purposes other than the fixing device, such as cooling a heating member used in a drying device. In addition, the heating element that heats the fixing belt 310 can be other heating elements such as a ceramic heater in addition to the resistance member 370 and the halogen heater 314.

1K, 1Y, 1M, 1C: Process unit 2K, 2Y, 2M, 2C: Image carrier
3K, 3Y, 3M, 3C: Drum cleaning device 4K, 4Y, 4M, 4C: Charging device
5K, 5Y, 5M, 5C: Developing device 6K, 6Y, 6M, 6C: Toner bottle 7: Exposure device 7a: Mirror 8: Transfer cover 10: Powder container 15: Transfer device 16: Intermediate transfer belt 17: Driven roller 18: Drive roller
19K, 19Y, 19M, 19C: Primary transfer roller 20: Secondary transfer roller 21: Belt cleaning device 31: Registration sensor 32: Paper feed path 33: Post-transfer transport path 35: Post-fixing transport path 36: Discharge path 37: Paper discharge roller pair 41: Reverse transport path 42: Switching member 42a: Oscillating shaft 43: Reverse transport roller pair 44: Paper discharge tray 45: Paper feed roller 46: Tray 60: Paper feed roller 100: Image forming device 101: Protrusion 102: Hole 103: Image forming device main body 200: Paper feed device 210: Roller pair 220: Feeding roller 230: Separation roller 240: Transport roller 250: Registration roller pair 300: Fixing device 310: Fixing belt 311: Heating roller 312, 313: Guide roller 314: Halogen heater 320: Pressure roller 321: Core metal 322: Elastic layer 323: Release layer 330: Resistance member 334: Pressure belt 340: Heater holder 341: Base material 350: Stay 351: Auxiliary stay 352: Stay 360: Device frame 360c, 360d: Electrode 370: Resistance member 370-2: End resistance member 370a, 370b: Power supply line 370c to 370h: Electrode 371 to 378: PTC element 379a to 379h: Power supply line 381: Nip forming member 385: Insulating layer 390: Pressing roller 370a, 370b: Power supply line 370c, 370d: Electrode 400: Cooling device 410, 510: Air duct 411, 511: First opening 412, 512: second opening 413, 513: third opening 430: blower fan (blower member)
431: Holder 450, 451: Slide member (air volume variable mechanism)
452: Swinging member (air volume variable mechanism) 453: Partition member (air volume variable mechanism)
451a, 451b: Inclined surface 452a: Pivot 471: Pinion gear 473: Rack 473a: Rack teeth 473b: Long hole 473c: Fixing member 475: Guide pin 480: Control unit HN: Heating nip L: Laser light M1, M2: Driving motor N: Transfer nip P: Paper SN: Fixing nip TH1 to TH3: Thermistor

Patent No. 5930779

Claims (5)

In a cooling device for cooling a heating member having a longitudinal direction with air,
A blower member;
an air duct extending in the longitudinal direction of the heating member and through which the air passes, the air duct having a first opening formed in a longitudinal center portion and through which the air blowing member is disposed to introduce air into the air duct, a second opening formed at one longitudinal end portion and facing the one longitudinal end portion of the heating member, and a third opening formed at the other longitudinal end portion and facing the other longitudinal end portion of the heating member;
A cooling device comprising: an air volume variable mechanism that varies the volume of air discharged from the second and third openings, the air volume variable mechanism having a swing mechanism that swings the blowing member in the longitudinal direction of the air duct . 2. The cooling device according to claim 1, further comprising a temperature detection member for detecting the temperature at both longitudinal ends of the heating member, and the air volume variable mechanism operates to increase the proportion of the air volume distributed to the end of the heating member in the longitudinal direction that has a higher temperature based on the temperature detected by the temperature detection member . 3. The cooling device according to claim 1, further comprising a temperature detection member for detecting temperatures at both longitudinal ends of said heating member, and the amount of air blown by said air blowing member is changed based on the temperature detected by said temperature detection member. The heating member is provided,
4. A fixing device, comprising: a toner image carried on a sheet member, the toner image being heated and fixed by the heating member; and the heating member being cooled by the cooling device according to claim 1. 13. An image forming apparatus comprising the cooling device according to claim 1 or the fixing device according to claim 12 .

Images