Image forming apparatus having flash light fixing apparatus

Abstract: An image forming apparatus has a flash light fixing apparatus (32) comprising a flash light fixing unit (33) to irradiate a flash light to paper to which toner has been transferred, and a paper feed apparatus (34) provided opposite the flash light fixing unit (33). The paper feed apparatus (34) comprises a paper feed mechanism (50) and a paper guide mechanism (60) that guides paper that is fed by the paper feed mechanism (50). The paper guide mechanism (60) comprises a plural number of metal plates (61) disposed so that end surfaces (61a) thereof oppose the flash light fixing unit (33), and arranged so as to extend in the same direction as the direction of paper feed. The end surfaces (61a) of said metal plates (61) guide the paper.

Description: BACKGROUND OF THE INVENTION The present invention relates to an image forming apparatus having a flash light fixing apparatus. One type of image forming apparatus is configured to form a latent image on a surface of a photosensitive drum, transfers toner on that latent image to paper and fix that toner to said paper. The portion that performs the fixing in the image forming apparatus described above has a fixing apparatus incorporated to it. One type of fixing apparatus is a flash light fixing apparatus that irradiates a flash light and fixes the toner image onto the paper. In this flash light fixing apparatus, the temperature of the surface in the member that guides the paper can have its temperature raised easily because of the irradiated flash light. When the temperature of the paper guide surface rises to above a predetermined temperature, various types of problems that will be described later, occur so that it is necessary for the paper guide mechanism to have a structure whereby the temperature does not rise easily. FIG. 1 shows an outline configuration of one example of a conventional image forming apparatus 10 such as described in EP-A- 0 313 088. The numeral 11 represents a photosensitive drum, and 12 represents a flash light fixing apparatus 12. The flash light fixing apparatus 12 comprises a flash light fixing unit 13 and a paper feed apparatus 14 provided to the lower side of the flash light fixing unit 13. The paper feed apparatus 14 comprises a paper feed mechanism 15 comprising suction rotating rollers and a plurality of paper guide apparatus 16 that smoothly guide the fed paper above them. The paper guide apparatus 16 has a configuration whereby a plurality of long, thin guide plates 17 with a width W1 of about 40mm are arranged parallel to each other in the direction of paper feed indicated by the arrow 18. The paper 19 to which the toner on the latent image formed on the surface of the photosensitive drum 11 has been transferred is fed by the paper feed mechanism 15 and is fed through inside the flash light fixing apparatus 12, in a state of being guided by the paper guide apparatus 16. While it is being fed, a flash light is irradiated from the flash light fixing unit 13 to fix the image. When there is to be printing on both sides of the paper, the paper 19a that is sent from the flash light fixing apparatus 12 is fed in the direction shown by the arrow 20. The rear surface of the paper 19a is in contact with the photosensitive drum 11 and toner is transferred to the rear surface and then the paper passes through the flash light fixing apparatus 12 and the toner is fixed to the rear of the paper 19a. A flash light is irradiated to the paper guide apparatus 16 and the temperature of the guide surfaces 17a of the guide plates 17 rises. The following problems occur when the temperature of the guide surfaces 17a of the guide plates 17 rises. (1) Of the actions to perform printing on both sides, when there is the process to fix the image on the rear side of the paper, the toner on the front side (lower side) adheres to the guide surfaces 17a of the guide plates 17. This adhered toner adheres to the paper that is fed next and dirties the paper and causes the print quality to deteriorate. (2) There is the danger of the fingers of the operator being burnt when there is operation to remove misfed paper from the flash light fixing apparatus 12. SUMMARY OF THE INVENTION Accordingly, it is a general object of the present invention to provide a novel and useful an image forming apparatus having a flash light fixing apparatus in which the problems described above are eliminated. Another and more specific object of the present invention is to provide an image forming apparatus having a configuration where a paper guide mechanism having a plurality of metal paper guide plates, guides the paper along the surface at the end. The paper guide mechanism has a small area which is irradiated by the flash light, and has a large area to dissipate heat and so the rise of the temperature of the paper guide surface is suppressed. Accordingly, it is possible to prevent the toner from adhering to the guided surface of the paper when printing on both sides is performed and therefore prevent the paper from becoming dirty, and thus prevent deterioration of the print quality, and therefore maintain the initial good print quality for an extended period of time. In addition, the possibility of the fingers of the operator being burnt when maintenance operation to remove misfed paper from the flash light fixing means is also eliminated. Another object of the present invention is to provide an image forming apparatus having a paper guide mechanism with a configuration provided with a heat pipe having heat sinks at its end. The heat pipe having heat sinks at its end portion effectively suppresses the rise in temperature of the paper guide surface. Accordingly, it is possible to further suppress the rise in temperature of the paper guide surface, definitely prevent the adhering of toner to the paper guide surfaces and thus effectively prevent further deterioration of the print quality. Other objects of the present invention will become clear from the following detailed description of the present invention, with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an outline configuration view of a conventional image forming apparatus; FIG. 2 is a view showing a schematic configuration of an entire image forming apparatus of one embodiment according to the present invention; FIG. 3 is a perspective view showing the major portions of a paper feed apparatus according to the present invention; FIG. 4 is a view showing the paper guide mechanism shown in FIG. 3, together with suction rollers; FIG. 5 is a partial cutaway view of the paper guide mechanism in FIG. 3; and FIG. 6 is a perspective view showing the heat pipe assembly unit of FIG. 3. DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 2 shows a schematic configuration of an entire image forming apparatus 30 of one embodiment according to the present invention. In the figure, a photosensitive drum 31 is the image retention medium. A flash light fixing apparatus 32 comprises a flash light fixing unit 33 to irradiate the flash light, and a paper feed apparatus 34 that opposes it on the lower side. As shown in FIG. 3, the paper feed apparatus 34 comprises a paper feed mechanism 50 and a paper guide mechanism 60. Around the periphery of the photosensitive drum 31 shown in FIG. 2 are disposed a precharger 35, an exposer 36, a developer 37, a transfer unit 38 and a cleaner 39. This image forming apparatus 30 performs printing in the following manner. The photosensitive drum 31 rotates in the clockwise direction indicated by the arrow 40. The surface of this photosensitive drum 31 is first uniformly charged by the precharger 35 and then the exposer 36 forms a latent image corresponding to the image to be formed. This latent image is developed by the developer 37, to become a toner image, and this toner image is transferred to the paper 42 supplied from the paper supply portion 41, by the transfer unit 38. Then, the paper 42 is fed by the feed apparatus 34 in the direction of the arrow 43, and toner image fixing is performed by the flash light fixing apparatus 32. Then, the paper 42 is discharged by the discharge roller 44 and is fed to a stacker portion (not shown). The actions described above perform printing to the front surface of the paper 42. When printing on both sides of the paper is to be performed, the paper that has been fixed by the fixing unit 32 has its feed path switched by the feed path switching means (not shown) and is fed to a paper inverter mechanism 45. Then, the paper 42 is fed along the path 46 as shown by the arrow 47, and is inverted so that the rear is now at the front, and is fed between the transfer unit 38 and the photosensitive drum 31 in the state where the surface that was the rear surface is now uppermost. Then, the image is transferred to the 'rear' surface and this image is fixed by the fixing unit 33. The following is a description of the structure of the paper feed apparatus 34 which is one portion of the flash light fixing apparatus 32, with reference to FIG. 3 through FIG. 5. As has already been described, the paper feed apparatus 34 comprises the paper feed mechanism 50 and the paper guide mechanism 60. The paper feed mechanism 50 comprises suction rollers 51. As shown in FIG. 3 and FIG. 4, these suction rollers 51 are provided in plural number in three rows in the direction of paper feed 43. More specifically, a plurality of the suction rollers 51 are provided in the direction perpendicular to the paper feed direction 43, with leaving a space between the suction rollers 51 adjacent with each other. Each of suction rollers 51 has, around the periphery thereof, a plurality of suction holes. The suction holes coming to the topmost position performs suction action and moves in the direction indicated by the arrow 51 thereby to impart feed force to the paper 42, which is then fed in the direction of the arrow 43. In FIG. 3, the suction rollers 51 are indicated by chain double-dashed line, due to the convenience of drawing. As shown in FIG. 4 and FIG. 5, the paper guide mechanism 60 has a structure where a plurality of paper guide plates 61, forming a shape like two letter T's side by side, are disposed vertically and parallel at equal intervals. Each of the paper guide plates 61 is disposed between suction rollers 51 so that the end surface 61a at the top of the letter T is the surface that guides the paper. The width W2 of the paper guide surfaces 61a corresponds to the plate thickness t of the paper guide plates 61 and is approximately 3 to 5mm, which is approximately 1/10 of a conventional width W1 shown in FIG. 1. In addition, the paper guide surface 61a of the paper guide plate 61 is coated with a Teflon (registered trade mark) film 62. This makes it more difficult for the toner to adhere. In addition, the paper guide plates 61 are made of copper, and have a high coefficient of thermal conductivity. Furthermore, each of the paper guide plates 61 forms a unit with a pair of leg portions 61b and 61c through which copper pipes 63 and 64 are attached to form a single unit and both ends of the copper pipes 63 and 64 are soldered to brackets 65 and 66. The portion numbered 67 is also soldered. The internal diameter of the copper pipes 63 and 64 is slightly larger than 13mm. The paper guide mechanism 60 has the brackets 65 and 66 at both ends and fixed at the brackets 65 and 66 to both side plates (not indicated in the figure) of the image forming apparatus 30. Each of the paper guide plates 61 is vertical, and in alignment in the direction 43 of paper feed and between adjacent suction rollers 51. As shown in FIG. 4, the cutout portion 61d of both sides of the leg portions 61b and 61c of the paper guide plates 61 is a portion for disposing a shaft 53 of the suction roller 51. As shown in FIG. 4, the leg portions 61c extend at portions that do not interfere with the shaft 53, downwards below the shaft 53. The paper guide surface 61a smoothly guides the paper 42 and supports it so that it is not drawn between adjacent suction rollers 51 in the paper feeding direction 42. In FIG. 3, 70 represents a heat pipe assembly unit. As shown in FIG. 6, to one end of the heat pipe 71 having a diameter of 13mm and manufactured by Furukawa Electric Co., Ltd. has fixed a plurality (7 or 8) of heat sinks 72 at 5mm intervals. These heat sinks 72 have holes 72a that are burring processed so as to fixedly engage with the heat pipe 71. Of the heat sinks 72, the heat sinks 72-1 on the inner side are formed with portions 72-1a curved in the shape of a letter Z for the sake of mounting. The heat pipe assembly unit 70A is the same as the heat pipe assembly 70 described above in that it has a configuration whereby a plural number of heat sinks 72A are fixed to one end of the heat pipe 71A. As indicated in FIG. 3, in the state where the heat pipe assemblies 70 and 70A are inserted into the copper pipes 63 and 64 respectively, the heat sinks 72-1 and 72A-1 are screw mounted and fixed by to a side plate 80 by screws 78 and 79, and the heat sinks 72 and 72A protrude on the outside of the side plate 80. A cooling fan 81 is provided on the lower side of the heat sinks 72 and 72A. The cooling fan 81 causes an air stream to blow onto the heat sinks 72 and 72A to provide forced cooling of the heat sinks 72 and 72A. The following is a description of the operation of the paper guide mechanism 60 described above. The flash light from fixing unit 33 is irradiated to the paper guide surface 61a of the paper guide mechanism 60 and the paper guide plates 61 are heated. Here, the paper guide surface 61a to which the flash light is irradiated is extremely narrow, and has a small area. In addition, the leg portions 61b and 61c of the paper guide plates 61 function as heat dissipation portions. The area of the heat dissipation portions is large. Since each of the paper guide plates 61 has an extremely small area to which the flash light is irradiated and also has a relatively large area from which the heat is dissipated, the paper guide surfaces 61a is difficult to heat to a high temperature, when compared to the conventional example. Furthermore, the heat of the paper guide plates 61 is favorably conducted to the heat pipes 63,64 and 71 and is dissipated from the heat sinks 72 and 72A that are being forcedly cooled. Because of this, the rise of the temperature of the paper guide surfaces 61a is further suppressed, and held at a temperature that is sufficiently lower than the temperature at which toner dissolves. As a result, when there is to be printing on the rear surface of a sheet of paper after the front surface has been printed upon, in the process to feed the paper inside the fixing apparatus 32, toner that is already adhered to the front surface does not adhere to the paper guide surfaces 61a even if toner on the front surface rubs the paper guide surfaces 61a. The Teflon (registered trade mark) film 62 also functions to make the toner difficult to adhere to the paper guide surfaces 61a. Because of this, when there is operation to remove misfed paper from inside the flash light fixing unit 32, then there is no possibility of the fingers of the operator being burnt even if the paper guide surface 61a is touched. Moreover, the heat pipe assemblies 70 and 70A described above are units which are separated from the paper guide mechanism 60 and can also be removed so that when there is a failure of some kind in the heat pipe assembly units 70 and 70A, the paper guide mechanism 60 can be left as it is and the failed heat pipe assembly exchanged so enhance maintenability. Further, the present invention is not limited to these embodiments, but various variations and modifications may be made within the scope of the invention as claimed.

Claims: An image forming apparatus having a flash light fixing apparatus (32) comprising a flash light fixing unit (33) to irradiate a flash light to paper to which toner has been transferred, and a paper feed apparatus (34) provided opposite the flash light fixing unit (33), said paper feed apparatus (34) comprising a paper feed mechanism (50) and a paper guide mechanism (60) that guides paper that is fed by said paper feed mechanism, characterized in that said paper guide mechanism (60) comprises a plurality of metal plates (61) disposed so that end surfaces (61a) thereof which correspond to the thickness of said metal plates (61) oppose said flash light fixing unit (33), and arranged so as to extend in the same direction as the direction of paper feed, said end surfaces (61a) of said metal plates (61) guiding the paper. The image forming apparatus as claimed in claim 1, characterized in that end surfaces (61a) of said plurality of metal plates (61) are coated with a Teflon (registered trade mark) film (62). The image forming apparatus as claimed in claim 1, characterized in that said paper guide mechanism (60) forms a unit by said plurality of metal plates (61) being soldered to metal pipes (63, 64), with a heat pipe (71), having heat sinks (72) fixed at one end thereof, inserted into said metal pipes (63, 64). The image forming apparatus as claimed in claim 3, characterized in that said paper guide mechanism (60) further has a cooling fan (81) which blows an air stream onto said heat sink (72). The image forming apparatus as claimed in claim 1, characterized in that said paper feed mechanism (50) comprises a plurality of suction rollers (51) that are provided at intervals in the direction perpendicular to the direction of paper feed, said plurality of metal plates having leg portions (61b 61c) and being arranged between adjacent suction rollers (51), and said leg portions (61b, 61c) being provided to a portion that does not interfere with a shaft of said suction rollers (51). The image forming apparatus as claimed in claim 5, characterized in that said plurality of metal plates (61) is soldered, at the position of the leg portions (61b, 61c) thereof, to metal pipes (63,64) to form a unit, with a heat pipe (71), having heat sinks (72) fixed at one end thereof, inserted into said metal pipes (63, 64).

Inventors: YAGUCHI MASANORI, YAGUCHI, MASANORI
Applicants: FUJITSU LTD, FUJITSU LIMITED
Application year: 1991
Main classification: G03G15
IPC codes: G03G15