Electrophotographic printer

Abstract: An electrophotographic printer is disclosed. The printer includes first and second transcription rollers (11,12) for printing an image transcribed from a photosensitive drum (30) on a first surface of a paper (70), and third and fourth transcription rollers (21,22) elevated onto one sides of the first and second transcription rollers (11,12) and selectively contacting the photosensitive drum (30), to print the image transcribed from the photosensitive drum (30) on a second surface thereof. Accordingly, both surfaces of the paper (70) can be printed by passing a paper (70) through the printer only once.

Description: The present invention relates to an electrophotographic printer, and more particularly, to an electrophotographic printer capable of printing opposite surfaces of a paper. In general, an electrophotographic printer such as a laser printer, includes a high speed rotating mirror for reflecting a laser beam onto a photosensitive drum, a feed roller for supplying paper to the photosensitive drum, a compression roller for pressing against a rear surface of the supplied paper as the paper passes through the photosensitive drum being in contact therewith, and an output roller for outputting the printed paper. However, in the conventional electrophotographic printer, only one surface of the paper can be printed. That is, an image reflected on the rotating mirror is transcribed to one surface of the supplied paper through the photosensitive drum. In order to print both surfaces of the paper, the paper with one printed surface should be re-supplied to the printer. Therefore, a complicated and lengthy process is required for two-sided printing. US-A-4,688,925 discloses an electrographic reproduction apparatus according to the pre-characterising portion of claim 1 herein. The printer of US-A-4,688,925 can print simplex images on either the upper of lower side of a sheet of paper. It is an aim of preferred embodiments of the present invention to provide an electrophotographic printer capable of printing both surfaces of a paper by supplying paper to the printer only once. According to the present invention in a first aspect, there is provided an electrophotographic printer comprising: photosensitive means in which first and second surface images for first and second surfaces respectively, of a supplied paper to be printed become photosensitive; a first print means for printing said one surface image transcribed by contact with said photosensitive means on a first surface of a supplied paper; and a second print means, installed to one side of said first print means to selectively contact said photosensitive means, for printing said second surface image transcribed from said photosensitive means on the second surface of said supplied paper; characterised in that said first transcription roller rotating in contact with said photosensitive drum and transcribing said first surface image from said photosensitive drum, and a second transcription roller rotating in contact with said first transcription roller to pass said supplied paper therebetween; and said second print means comprises a third transcription roller rotating selectively in contact with said photosensitive drum, and transcribing said second surface image from said photosensitive drum, a fourth transcription roller having a circumferential length that is longer than the length of said supplied paper, rotating in contact with said third transcription roller and transcribing said second surface image from said third transcription roller, a bracket supporting said third and fourth transcription rollers and capable of being lifted and lowered with respect to said photosensitive drum, elevating means for elevating said bracket, to thereby enable said third transcription roller to selectively contact said photosensitive drum, and a driving source for driving at least one of said third and fourth transcription rollers. Preferably, the photosensitive means is a rotatable photosensitive drum. The present invention will become more apparent by describing in detail a preferred embodiment thereof, by way of example only, with reference to the attached drawings; in which: Figure 1 is a schematic perspective view showing an electrophotographic printer according to the present invention; and Figures 2A and 2B are side views illustrating the operation of the electrophotographic printer according to the present invention. Referring to Figure 1, the electrophotographic printer according to a preferred embodiment of the present invention includes first and second transcription rollers 11 and 12 rotating along a proceeding direction "C" of a supplied paper 70, being in contact with each other, and a photosensitive drum 30 contacting the first transcription roller 11. The photosensitive drum 30 has an outer surface which becomes photosensitive by a laser reflected on the rotating mirror (not shown), so that an image to be printed is transcribed to the first transcription roller 11. Third and fourth transcription rollers 21 and 22 are installed at one sides of the first and second transcription rollers 11 and 12 along a proceeding direction of the paper 70. The third transcription roller 21 contacts the outer surface of the photosensitive drum 30. Rotation shafts 21a and 22a of the third and fourth transcription rollers 21 and 22 are rotatably supported by a bracket 40. An elevating motor 50 is installed at one side of the bracket 40, and a pinion 51 connected to the rotation shaft of the elevating motor 50 engages with a rack 41 formed on the bracket 40. Accordingly, the bracket 40 is elevated vertically by the rotation of the elevating motor 50, and thus the third transcription roller 21 selectively contacts the photosensitive drum 30. The fourth transcription roller 22 is rotated by a driving motor 60. Also, preferably, the circumferential length of the photosensitive drum 30 is two or more times the length of the supplied paper 70. The above electrophotographic printer operates as follows. First, in order to transmit an image to be printed on the front surface of the paper 70 to the fourth transcription roller 22, the elevating motor 50 of Figure 2A rotates clockwise to lower the bracket 40. Thus, the third transcription roller 21 contacts the photosensitive drum 30 and rotates. Accordingly, the image transcribed on the photosensitive drum 30 is transcribed to the third transcription roller 21, and then to the fourth transcription roller 22. At this time, the circumferential length of the fourth transcription roller 22 is greater than the length of the paper 70. As described above, when the image to be printed on the front surface of the paper 70 is transcribed to the fourth transcription roller 22, as shown in Figure 2B, the elevating motor 50 rotates counterclockwise, to elevate the bracket 40 such that the third and fourth transcription rollers 21 and 22 reach a height where the paper is supplied, which is represented by the horizontal dotted line. Accordingly, the third transcription roller 21 is detached from the photosensitive drum 30, where a driving motor 60 driving the fourth transcription roller 22 stops, to thereby stop the rotation of the third and fourth transcription rollers 21 and 22. Subsequently, an image to be printed on a rear surface of the paper 70 begins to be transmitted to the first transcription roller 11 through the driving photosensitive drum 30. The circumferential length of the photosensitive drum 30 is at least twice the length of the paper 70, so that an image to be printed on the front and rear surfaces of the paper 70 can be transcribed during one rotation of the photosensitive drum 30. When the image transcribed to the first transcription roller 11 reaches a point "A" contacting the second transcription roller 12, the paper 70 is supplied in a direction "C", to print an image of the first transcription roller 11 on the rear surface of the paper. When the paper 70 passing through the first and second transcription rollers 11 and 12 reaches a point "B" contacting the third and fourth transcription rollers 21 and 22, the driving roller 60 is driven, which drives the third and fourth transcription rollers 21 and 22. Accordingly, an image transcribed on the fourth transcription roller 22 is printed on the front surface of the paper 70. As described above, images transcribed onto the photosensitive drum 30 are sequentially printed on the rear and front surfaces of the paper 70. The photosensitive drum 30, which is employed for a photosensitive means in an embodiment of the present invention, can be replaced by a photosensitive belt such as an OPC-belt. According to the electrophotographic printer of preferred embodiments of the present invention, an image to be printed can be simultaneously printed on the front and rear surfaces of the paper by supplying paper to the printer only once.

Claims: An electrophotographic printer comprising: photosensitive means (30) in which first and second surface images for first and second surfaces respectively, of a supplied paper (70) to be printed become photosensitive; a first print means (11,12) for printing said one surface image transcribed by contact with said photosensitive means (30) on a first surface of a supplied paper (70); and a second print means (21,22,30,40,41,50,51,60), to selectively contact said photosensitive means (30), for printing said second surface image transcribed from said photosensitive means (30) on the second surface of said supplied paper; characterised in that said first print means (11,12) comprises: a first transcription roller (11) rotating in contact with said photosensitive drum (30) and transcribing said first surface image from said photosensitive drum (30); and a second transcription roller (12) rotating in contact with said first transcription roller to pass said supplied paper (70) therebetween; and said second print means (21,22,30,40,41,50,51,60) comprises: a third transcription roller (21) rotating selectively in contact with said photosensitive drum (30), and transcribing said second surface image from said photosensitive drum (30); a fourth transcription roller (22) having a circumferential length that is longer than the length of said supplied paper (70), rotating in contact with said third transcription roller (21) and transcribing said second surface image from said third transcription roller (21); a bracket (40) supporting said third and fourth transcription rollers (21,22) and capable of being lifted and lowered with respect to said photosensitive drum; elevating means (41,50,51) for elevating said bracket (40), to thereby enable said third transcription roller (21) to selectively contact said photosensitive drum (30); and a driving source (60) for driving at least one of said third and fourth transcription rollers. An electrophotographic printer according to claim 1, wherein said photosensitive means (30) is a rotatable photosensitive drum (30). An electrophotographic printer according to claim 1, wherein said elevating means (41,50,51) comprises: a driving motor (50); a pinion (51) connected to a rotation shaft of said driving motor (50); and a rack (41) formed on said bracket (40) to engage with said pinion (51). An electrophotographic printer according to claim 2 or claim 3, wherein the circumferential length of said photosensitive drum (30) is two or more times the length of said supplied paper (70).

Inventors: PARK GEUN-YONG, PARK, GEUN-YONG
Applicants: SAMSUNG ELECTRONICS CO LTD, SAMSUNG ELECTRONICS CO., LTD.
Application year: 1997
Main classification: G03G15
IPC codes: G03G15, H04N1