Laser printer

Abstract: A laser printer is disclosed in which the laser printer includes a photosensitive belt (22) of a loop type having a seam (22a) at a portion where the ends overlap, circulating around a driving roller (21c), a steering roller (21b) and a transfer backing roller (21a), and passing between the transfer backing roller (21a) and a transfer roller (27); and a distance controller (30) for moving the transfer backing roller (21a) toward or away from the transfer roller (27).

Description: The present invention relates to a laser printer, and more particularly, to a laser printer using a photosensitive belt having a seam. In general, in a laser printer, developer is coated on a photosensitive belt to form an image, and then the image developed on the photosensitive belt is transferred to a roller to print the image on a sheet of paper. An example of the laser printer is schematically illustrated in Figure 1. The laser printer includes a transfer backing roller 11a, a steering roller 11b and a driving roller 11c. A photosensitive belt 12 is rotatably installed around the rollers 11a, 11b and 11c. At one side of the photosensitive belt 12, there is an eraser 23 for erasing image information of a previous step, and a charger 24 for uniformly electrifying the photosensitive belt 12 passing through the eraser 23. The image information recorded on the photosensitive belt 12 of the previous step is erased by the eraser 23, and then the charger 24 applies a predetermined voltage to the photosensitive belt 12 to be charged. Also, at one side of the photosensitive belt 22 of a color printer passing between the steering roller 11b and the driving roller 11c, there is a plurality of laser scanners 25 and developing devices 26 for combining colors. The laser scanner 25 scans light corresponding to received image information to form an photosensitive region on the photosensitive belt 12. In the developing device 26, a developer is coated on the photosensitive region formed by the laser scanner 25. The image developed on the photosensitive belt 12 is transferred to a transfer roller 17 to print an image on a sheet of paper 19 by being pressed by a pressure roller 18. Here, the photosensitive belt 12 is a loop type belt, and has a seam 12a where end portions of the belt 12 overlap. Accordingly, as the photosensitive belt 12 circulates along the rollers 11a, 11b and lie, the seam 12a of the photosensitive belt 12 can be caught between the transfer backing roller 11a and the transfer roller 17. Also, some of the developer may remain at the seam 12a, to thereby contaminate the paper 19. Accordingly, in the conventional art, when the photosensitive belt 12 passes between the transfer backing roller 11a and the transfer roller 17, the transfer roller 17 and the pressure roller 18 separate a predetermined distance from the backing roller 11a, to thereby prevent the seam 12a from being caught. During printing, since the transfer roller 17 is coupled with the pressure roller 18, the two rollers 17 and 18 should simultaneously operate. Thus, much time is required for operation, and the structure of the mechanism for controlling the distance between the transfer roller 17 and the backing roller 11a is complicated. EP-A-0,159,740 (OCE Nederland BV) discloses an electrophotographic apparatus provided with a photoconductive belt having a seam, the belt passing over a roller which is moveable from a rest position separated from an intermediate transfer belt, to an image forming position where the roller is pressed against the intermediate transfer belt. With a view to solve or reduce the above problems, it is an aim of embodiments of the present invention to provide a laser printer capable of easily passing a seam of an photosensitive belt between a transfer roller and a transfer backing roller. According to an aspect of the present invention there is provided a laser printer comprising: a photosensitive belt of a loop type having a seam at a portion where the ends overlap; the photosensitive belt circulating around a driving roller, a steering roller and a transfer backing roller, and passing between the transfer backing roller and a transfer roller; and a distance controller for moving the transfer backing roller toward or away from the transfer roller, characterised in that the distance controller is adapted to separate the transfer backing roller from the transfer roller when the seam of the photosensitive belt passes between the transfer roller and the transfer backing roller. Preferably, the distance controller comprises a cam unit for separating the transfer backing roller from the transfer roller when the seam of the photosensitive belt passes between the transfer roller and the transfer backing roller. It is also preferable that the cam unit comprises a connection member connected to a rotation shaft of the transfer backing roller, a cam contacting the bottom of the connection member and having flat and rounded portions to lower and raise the connection member, and a driving means for driving the cam. The laser printer preferably further comprises a tension controller for controlling the tension of the photosensitive belt according to the movement of the transfer backing roller. The tension controller preferably comprises a photosensitive belt tensioning roller adjacent to the transfer backing roller, contacting the photosensitive belt to rotate, and an elastic member for biasing the photosensitive belt tensioning roller toward the photosensitive belt. The tension controller comprises an elastic member for biasing the steering roller toward the photosensitive belt. The tension controller may comprise a support frame for supporting a shaft of the steering roller, an auxiliary support roller installed at both sides of the support frame parallel to the steering roller, contacting the photosensitive belt, and an elastic member for applying a biasing force to the support frame. The distance controller preferably makes the transfer backing roller separate from the transfer roller during a standby mode of printing. For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings, in which: Figure 1 is a diagram schematically illustrating the photosensitive belt and related portions of a conventional laser printer; Figure 2 is a diagram schematically illustrating the photosensitive belt and related portions of a laser printer according to an embodiment of the present invention; Figure 3 is a perspective view showing a distance controller of a transfer backing roller used for the laser printer of Figure 2; and Figure 4 is a perspective view showing a tension controller of a photosensitive belt used for the laser printer of Figure 2. Referring to Figure 2, a laser printer according to an embodiment of the present invention includes a transfer backing roller 21a, a steering roller 21b and a driving roller 21c. An photosensitive belt 22 in a loop on which image information is recorded is rotatably installed around the rollers 21a, 21b and 21c. The photosensitive belt 22 includes a seam 22a where end portions of the photosensitive belt 22 overlap. Throughout the drawings, the same reference numerals represent the same elements as Figure 1. The transfer roller 27 rotates coupled with the transfer backing roller 21a with the photosensitive belt 22 interposed therebetween. Accordingly, the image information formed on the photosensitive belt 22 is transferred to the transfer roller 27. The transfer roller 27 rotates with the pressure roller 28 between which a sheet of paper 29 passes. Thus, the paper 29 pressed by the pressure roller 28 against the transfer roller 27 is printed with the image information on the transfer roller 27. When the photosensitive belt 22 passes between the transfer backing roller 21a and the transfer roller 27, the transfer backing roller 21a separates from the transfer roller 27 to prevent the seam 22a formed at overlapped portion of the photosensitive belt 22 from being caught by the rollers 21a and 27. A distance controller 30 for elevating the transfer backing roller 21a is required such that the transfer backing roller 21a separated by a predetermined distance. It is preferable to connect the distance controller 30 to a rotation shaft of the transfer backing roller 21a. A cam unit can be used for the distance controller 30, also, e.g., a rack and pinion may be used as a means for elevating the transfer backing roller 21a. Figure 3 shows the distance controller 30. In detail, the distance controller includes a connection member 31, a cam 32 and a driving means 33. That is, the connection member 31 is connected to the rotation shaft of the transfer backing roller 21a, and is moved downwards along a guide (not shown). The cam 32 having an outer circumference composed of a flat portion 32a and a rounded portion 32b is installed below the surface of the connection member 31, and the cam 32 is rotated by the driving means 33, e.g., a driving motor. That is, when the seam 22a of the photosensitive belt 22 is close to the portion between the transfer backing roller 21a and the transfer roller 27, the flat portion 32a of the cam 32 contacts with the bottom surface of the connection member 31 to lower the connection member 31. Accordingly, the transfer backing roller 21a connected to the connection member 31 separates from the transfer roller 27 a predetermined distance, so that the seam 22a of the photosensitive belt 22 does not contact the transfer roller 27. At this time, the tension controller 40 operates to prevent the photosensitive belt 22 from becoming loose due to the lowering of the transfer backing roller 21a. The tension controller 40 is installed to operate together with the steering roller 21b. The tension controller 40 includes an elastic member 41 such as a spring for applying a biasing force to the steering roller 21b to prevent the photosensitive belt 22 from becoming loose. In the tension controller 40 of Figure 4, a support frame 43 supports the shaft of the steering roller 21b, and the elastic member 41 is connected to the support frame 43 to press the steering roller 21b toward the photosensitive belt 22. Also, it is preferable to install auxiliary support rollers 45 parallel to the steering roller 21b and contacting the photosensitive belt 22 on both sides of the support frame 43. Thus, the elastic member 41 fixed to a fixing plate 42 applies a biasing force to the support frame 43, to move the steering roller 21b toward the photosensitive belt 22 and further elastically supports the photosensitive belt 22. That is, the tension controller 40 controls the tension of the photosensitive belt 22 loosened by the operation of the distance controller 30, to thereby prevent the photosensitive belt 22 from becoming loose. Therefore, according to the above principles, when the seam 22a of the photosensitive belt 22 passes between the transfer backing roller 21a and the transfer roller 27, the transfer backing roller 21a moves downwards according to the operation of the distance controller 30 to loosen the photosensitive belt 22 downwards. Due to the loosened photosensitive belt 22, a pressure applied to the elastic member 41 by the steering roller 21b and/or the auxiliary support roller 45 is reduced so that the elastic member 41 moves in a direction to compensate for the reduced pressure. Accordingly, loosening of the photosensitive belt 22 is prevented due to movement of the steering roller 21b along the photosensitive belt 22. One or more photosensitive belt tensioning rollers 49 having an elastic member 48 adjacent to the transfer backing roller 21a may compensate for the loosening of the photosensitive belt 22 due to movement of the transfer backing roller 21a. After the seam 22a of the photosensitive belt 22 has passed through between the transfer backing roller 21a and the transfer roller 27, the rounded portion 32b of the cam 32 is contacted instead of the flat portion 32a according as the cam 32 rotates. Thus, the connection member 31 rises to return the transfer backing roller 21a to its initial position. As described above, when the seam of the photosensitive belt passes between the transfer roller and the transfer backing roller, the distance controller connected to the rotation shaft of the transfer backing roller and the tension controller connected to the steering roller simultaneously operate. Accordingly, the seam of the photosensitive belt passes through without contacting the transfer roller by a simplified mechanism. Also, during a standby mode of printing, the flat portion 32a of the cam contacts the bottom of the connection member to lower the transfer backing roller. Then, the photosensitive belt does not contact the high-temperature transfer roller so that the photosensitive belt is protected from heat to increase its life span.

Claims: A laser printer comprising: a photosensitive belt (22) of a loop type having a seam (22a) at a portion where the ends overlap; the photosensitive belt circulating around a driving roller (21c), a steering roller (21b) and a transfer backing roller (21a), and passing between the transfer backing roller (21a) and a transfer roller (27); and a distance controller (30) for moving the transfer backing roller (21a) toward or away from the transfer roller (27), characterised in that the distance controller (30) is adapted to separate the transfer backing roller (21a) from the transfer roller (27) when the seam (22a) of the photosensitive belt (22) passes between the transfer roller (27) and the transfer backing roller (21a). The laser printer of claim 1, wherein the distance controller (30) comprises a cam unit (31-33) for separating the transfer backing roller (21a) from the transfer roller (27) when the seam (22a) of the photosensitive belt (22) passes between the transfer roller (27) and the transfer backing roller (21a). The laser printer of claim 2, wherein the cam unit comprises (31-33) a connection member (31) connected to a rotation shaft of the transfer backing roller (21a), a cam (32) contacting the bottom of the connection member (31) and having flat (32a) and rounded (32b) portions to lower and raise the connection member (31), and a driving means (33) for driving the cam (32). The laser printer of any preceding claim, further comprising a tension controller (40-49) for controlling the tension of the photosensitive belt (22) according to the movement of the transfer backing roller (21a). The laser printer of claim 4, wherein the tension controller (40-49) comprises a photosensitive belt tensioning roller (49) adjacent to the transfer backing roller (21a), contacting the photosensitive belt (22) to rotate, and an elastic member (48) for biasing the photosensitive belt tensioning roller (49) toward the photosensitive belt (22). The laser printer of claim 4 or 5, wherein the tension controller (40-49) comprises an elastic member (41) for biasing the steering roller (21b) toward the photosensitive belt (22). The laser printer of claim 4, 5 or 6, wherein the tension controller (40-49) comprises a support frame (43) for supporting a shaft of the steering roller (21b), an auxiliary support roller (45) installed at both sides of the support frame (43) parallel to the steering roller (21b), contacting the photosensitive belt (22), and an elastic member (41) for applying a biasing force to the support frame (43). The laser printer of any preceding claims, wherein the distance controller (30) makes the transfer backing roller (21a) separate from the transfer roller (27) during a standby mode of printing.

Inventors: PANG JEONG-HUN, PANG, JEONG-HUN, Pang, Jeong-hun Printer team, Central Research Ins
Applicants: SAMSUNG ELECTRONICS CO LTD, SAMSUNG ELECTRONICS CO., LTD.
Application year: 1998
Main classification: G03G15
IPC codes: G03G15, B41J2, G03G21