# Patent

## Title
Image forming apparatus

## Abstract

An image forming apparatus includes a printer body having a developing portion and a fixing portion therein, a plurality of sheet feeding rollers provided along a sheet discharge path successively and driven to discharge a sheet passing through the fixing portion to an upper portion of the printer body, and a rear cover provided on a side of the printer body to open and close, and having guide ribs to guide the sheet passed through the fixing portion. The image forming apparatus also includes an idle roller provided movably on the rear cover, to contact and rotate with one of the sheet feeding rollers to feed the sheet, and a supplementary guide member provided rotatably on the rear cover and positioned below the idle roller. The supplementary guide member changes a position thereof when the rear cover is open so that the sheet being discharged directly to the guide ribs is prevented from running into the idle roller.

## Background
CROSS REFERENCE TO RELATED APPLICATION
This application claims the benefit of Korean Application No. 2002-44252, filed Jul. 26, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus and, more particularly, to an image forming apparatus to prevent sheets from running into an idle roller during a discharge of special sheets.
2. Description of the Related Art
Referring to FIG. 1, a conventional image forming apparatus is provided with a sheet supply cassette 11 in which sheets are stacked on a lower end of a body 10. The sheets in the sheet supply cassette 11 are picked up one after another by a pickup roller 12. The picked up sheets are sent to a developing portion 13. The developing portion 13 includes a photosensitive drum 14, a developing roller 15 and a transfer roller 16. The photosensitive drum 14 is charged with an electric potential by a charging device, and an electrostatic latent image corresponding to a predetermined image is formed on a charged surface by light scanned from a laser scanning unit 17. The electrostatic latent image area is fed with toner supplied by the developing roller 15. Accordingly, an image is formed and then transferred to and printed on a sheet passing between the photosensitive drum 14 and the transfer roller 16.
The sheet with the printed image is fixed at an elevated temperature and under a high pressure through a fixing portion 18, so that the toner image is fused thereonto. After passing through the fixing portion 18, the sheet passes through first, second and third sheet feeding rollers 21, 22 and 23 one after another, and is then stacked on a sheet stacking surface 10a provided on an upper section of the body 10. First, second and third idle rollers 24, 25 and 26 are further provided to rotatably contact with the sheet feeding rollers 21, 22 and 23, respectively, and thus rotate together to pass the sheet.
To print on both sides of the sheet, after passing the first or second sheet feeding roller 21 or 22, the sheet is reversed and directed through a duplex feeding path 30 to be fed again.
When a special sheet like an envelope, OHP film, etc., is printed by the above image forming apparatus, the sheet is discharged from the body 10 right after being passed through the first sheet feeding roller 21 in order to reduce an occurrence of a jam, curl, etc. Here, the second sheet feeding roller 22 and the second idle roller 25 are not used for sheet feeding. In other words, during special sheet printing, a rear cover 19 of the body 10 is opened with an angle from about 40° to 60°, as shown in FIG. 1. Then, the sheet is stacked on an inner guiding ribbed-surface 19a of the rear cover 19.
In the above-described construction, the second idle roller 25 protrudes higher than the guiding ribbed-surface 19a. Therefore, during the stacking of a sheet discharged from the body 10, there is a possibility that a leading end of the sheet may run into the idle roller 25, and thus change direction. Furthermore, there may be difficulty in stacking sheets due to sheet bending.
SUMMARY OF THE INVENTION
Accordingly, it is an aspect of the present invention to provide an improved image forming apparatus to prevent sheets from running into an idle roller during discharge of special sheets.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
The foregoing and/or other aspects of the present invention are achieved by providing an image forming apparatus including a printer body having a developing portion and a fixing portion therein, a plurality of sheet feeding rollers provided along a sheet discharge path successively and driven to discharge a sheet passing through the fixing portion to an upper portion of the printer body, and a rear cover provided on a side of the printer body to open and close, and having guide ribs to guide the sheet passed through the fixing portion. The image forming apparatus also includes an idle roller provided movably on the rear cover to contact and rotate with one of the sheet feeding rollers to feed the sheet, and a supplementary guide member provided rotatably on the rear cover and positioned below the idle roller. The supplementary guide member changes a position thereof when the rear cover is open so that the sheet being discharged directly to the guide ribs is prevented from running into the idle roller.
According to an aspect of the invention, the supplementary guide member is rotatably fitted into supporting holes formed in the guide ribs and is supported by the supporting holes to pivot due to a weight thereof when the position of the rear cover changes.
According to an aspect of the invention, the supplementary guide member is supported rotatably on the guide ribs, and is arranged so that a center of gravity of the supplementary guide member is positioned below a center of rotation thereof. The supplementary guide member is rotated by a weight thereof when the position of the rear cover changes, so that an upper end of the supplementary guide member is moved to a position that extends as far as or farther than the idle roller.
According to another aspect of the invention, the supplementary guide member includes a plate-shaped body to face the rear cover, a pair of wings to extend vertically from both edges of the plate-shaped body and aligned with the guide ribs, and a rotation shaft to protrude from opposite sides of the wings and rotatably coupled to the guide ribs.
According to yet another aspect of the invention, the rotation shaft includes a latching projection formed on an end of the rotation shaft to protrude crosswise at an angle of 90° with respect to an axial direction to prevent a disengagement of the rotation shaft from the guide ribs
According to another aspect of the invention, supporting holes are formed on the guide ribs to have a shape to correspond to a shape of the rotation shaft and the latching projection, so that the rotation shaft and the latching projection pass through the supporting holes.



BRIEF DESCRIPTION OF THE DRAWINGS
The above and/or other aspects and advantages of the present invention will become apparent and more appreciated from the following detailed description of the preferred embodiments, taken in conjunction with the accompanying drawings of which:
FIG. 1 is a schematic diagram showing a conventional image forming apparatus;
FIG. 2 is a schematic diagram showing an image forming apparatus, according to an embodiment of the present invention;
FIG. 3 is a perspective view of a rear cover in FIG. 2;
FIG. 4 is a schematic diagram showing a main part of FIG. 3;
FIG. 5 is a perspective view showing a supplementary guide member as shown in FIG. 3; and
FIG. 6 is a diagram showing the rear cover of FIG. 2 in an opened state.
FIG. 7 is a view showing a main portion of the rear cover of FIG. 3.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Reference will now be made in detail to the present preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout.
Referring to FIG. 2, an image forming apparatus, according to an embodiment of the present invention includes a printer body 100 provided with a developing portion 110 and a fixing portion 120 disposed therein, a plurality of sheet feeding rollers 131, 132 and 133, a rear cover 140 disposed at a rear side of the printer body 100 to open and close, an idle roller 152 rotatably disposed at the rear cover 140, and a supplementary guide member 160 rotatably disposed at the rear cover 140.
The printer body 100 is provided with a sheet supply cassette 101 disposed at a lower part thereof, and a manual sheet supply portion 102 disposed at a front side thereof. Since the constitutions of the developing portion 110 and the fixing portion 120 are identical to those of the developing portion 13 and the fixing portion 18 as described in FIG. 1 above, respectively, a detailed description thereof will be omitted.
The printer body 100 is also provided with first, second and third sheet feeding rollers 131, 132 and 133 successively disposed to direct a sheet, after being passed through the fixing portion 120, to a stacking surface 103 provided on an upper portion of the printer body 100. Each of the sheet feeding rollers 131, 132 and 133 is driven to rotate by a predetermined driving source, and to forcibly feed the sheet. In other words, after passing through the fixing portion 120, the sheet passes through the first and second sheet feeding rollers 131 and 132 to be discharged to the stacking surface 103 by the third sheet feeding roller 133. Furthermore, the second and third sheet feeding rollers 132 and 133 may rotate reversely, in order to reverse the sheet passed out of the first sheet feeding roller 131. The reversed sheet is directed to a duplex feeding path 104, and supplied to the developing portion 110 again.
The sheet feeding rollers 131, 132 and 133 contact the first, second and third idle rollers 151, 152 and 153 to rotate, respectively. That is, the idle rollers 151, 152 and 153 contact the sheet feeding rollers 131, 132 and 133, respectively, at a predetermined pressure to rotate in order to feed the sheet. The first and third idle rollers 151 and 153 are disposed at the printer body 100, while the second idle roller 152 is rotatably disposed at the rear cover 140.
The rear cover 140 is provided with supporting projections 142 having supporting slits 142a to movably support the idle roller 152. Thus, a rotation shaft of the idle roller 152 is fitted in the supporting slits 142a to enable the idler roller 152 to move. As shown in FIG. 4, a torsion spring 154 is interposed between a main panel 141 of the rear cover and the idle roller 152. The torsion spring 154 compresses the idle roller 152 elastically toward the second sheet feeding roller 132 to generate a predetermined friction force between the second sheet feeding roller 132 and the idle roller 152.
Furthermore, the rear cover 140 is provided with a plurality of sheet guide ribs 143 on an inner side of the main panel 141. The plurality of guide ribs 143 are disposed at a predetermined spacing. Guide surfaces of the guide ribs 143 are rounded to form curved surfaces so that the sheet is guided in a vertical direction. The rear cover 140 may pivot on a hinge shaft 144 at a predetermined angle, and preferably may be opened at an angle of 45° to 60°.
Meanwhile, when a special sheet like an envelope or an OHP film is printed, jams, curls, etc., are very likely to occur if the special sheet is discharged passed the second and third sheet feeding rollers 132 and 133. Therefore, by opening the rear cover 140, the special sheet may be stacked on the guide ribs 143 of the rear cover 140 right after passing the first sheet feeding roller 131. Thus, the rear cover 140 must be configured to open at a predetermined angle.
The supplementary guide member 160 is provided to prevent the special sheet from running into the idle roller 152 when the special sheet is stacked on the opened rear cover 140. The supplementary guide member 160 is positioned below the idle roller 152. Moreover, the supplementary guide member 160 is interposed between guide ribs 143 of the rear cover 140, and is pivotably fitted in and supported by supporting holes 143a formed in the guide ribs 143.
Referring to FIG. 5, the supplementary guide member 160 includes a plate-shaped body 161 to face the main panel 141 of the rear cover 140, a pair of wings 162 extended from both edges of the plate-shaped body 161 in a vertical direction, and rotation shafts 163 to coaxially protrude from outer sides of the pair of wings 162. The wings 162 are aligned with the guide ribs 143, and function to guide the discharged special sheet. The rotation shafts 163 are eccentrically positioned relative to a center of an entire length of the supplementary guide member 160. That is, the rotation shafts 163 are eccentrically positioned above the center of a vertical length of the supplementary guide member 160. Therefore, a center of gravity of the supplementary guide member 160 is located in a lower portion of the supplementary guide member from the rotation shafts 163. Accordingly, when the rear cover 140 is pivoted at an angle as shown in FIG. 6, the supplementary guide member 160 is pivoted clockwise due to its own weight on the rotation shafts 163. Accordingly, the supplementary guide member 160 changes its position so that its upper end protrudes higher than the guide rib 143, and therefore higher than the idle roller 152 relative to a surface of the main panel 141.
Furthermore, each of the rotation shafts 163 is provided on both ends thereof with latching projections 163a to protrude crosswise and preferably at an angle of 90° with respect to an axial direction of the rotation shaft 163. The latching projections 163a prevent separation of the rotation shaft 163 from the supporting holes 143a of the guide ribs 143. Therefore, the supporting holes 143a formed in the guide ribs 143 are not circular-shaped, but have shapes corresponding to those of the rotation shafts 163 and the latching projections 163a, as shown in FIG. 7.
Hereinafter, an operation of the image forming apparatus of the present invention will be described below.
As shown FIG. 2, the rear cover 140 maintains an upright position when it is not open. Here, the supplementary guide member 160 also maintains an upright position due to its own weight. Therefore, the upper end of the supplementary guide member 160 does not protrude beyond the idle roller 152 relative to the guide rib 143, and thus maintains a position at least parallel to the sheet guide surface of the guide rib 143. Here, none of the special sheets are printed. Accordingly, an ordinary printed sheet, after passing through the fixing portion 120, is guided by the first, second and third sheet feeding rollers 131, 132 and 133 successively, and is finally discharged to the upper portion of the printer body 100.
Furthermore, to print on both sides of a sheet, as soon as a trailing edge of the sheet passes through the first sheet feeding roller 131, the second and third sheet feeding rollers 132 and 133 reverse their rotating direction, so that the sheet is directed to the duplex feeding path 104 and then fed to the developing portion 110 again.
When a special sheet such as an envelope or an OHP film is printed, the rear cover 140 is pivoted as shown in FIG. 6, so that a side of the printer body 100 in which the rear cover 140 is positioned, is opened. Here, the rear cover 140 is opened at an angle from about 45° to 60°. As the rear cover 140 is opened to change its position, the supplementary guide member 160 is pivoted due to its own weight on the rotation shaft 163. Therefore, as shown in FIG. 6, the lower end of the supplementary guide member 160 hangs down and the upper end thereof protrudes upward. Then, the upper end of the supplementary guide member 160 protrudes beyond the guide surface of the guide rib 143, and thus the upper end of the supplementary guide member 160 is extended as far as or farther than the idle roller 152.
As printing is performed under the above-described conditions, the special sheet, after passing the first sheet feeding roller 131, is directly fed to an inner surface of the rear cover 140 outside of the printer body 100. A leading edge of the special sheet being discharged by the first sheet feeding roller 131 contacts the guide surface of the supplementary guide member 160 to be guided pass the supplementary guide member as it passes the idle roller 152, thereby being stacked on the rear cover 140. Therefore, as the discharged special sheet does not run into the idle roller 152 as in the prior art, the possibility of the special sheet being stacked in a non-aligned and irregular state is minimized.
As described above, according to the image forming apparatus of the present invention, a sheet discharge path is shortened by opening the rear cover during printing of a special sheet so that the special sheet or a plurality of special sheets are smoothly stacked. Moreover, as the supplementary guide member provided on the rear cover changes its position when the rear cover is open, a discharged special sheet is prevented from running into the idle roller, so that smooth stacking is accomplished.
Although a few preferred embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.

## Claims

1. An image forming apparatus, comprising:
a printer body having a developing portion and a fixing portion therein; 
a plurality of sheet feeding rollers successively disposed along a sheet discharge path and driven to discharge a sheet passing through the fixing portion to an upper portion of the printer body; 
a rear cover provided on a side of the printer body to open and close, and having guide ribs to guide the sheet passed through the fixing portion; 
an idle roller movably disposed at the rear cover to rotate in contact with one of the sheet feeding rollers to feed the sheet; and 
a supplementary guide member pivotably disposed at the rear cover below the idle roller, to change a position thereof when the rear cover is open to prevent the sheet being discharged directly to the guide ribs from running into the idle roller.

2. The image forming apparatus according to claim 1, wherein the supplementary guide member is rotatably fitted into supporting holes formed in the guide ribs and is supported by the supporting holes to pivot due to a weight thereof when the position of the rear cover changes.

3. The image forming apparatus according to claim 1, wherein the supplementary guide member is supported rotatably on the guide ribs, and is arranged so that a center of gravity of the supplementary guide member is positioned below a center of rotation thereof, the supplementary guide member being rotated by the weight thereof when the position of the rear cover changes, so that an upper end of the supplementary guide member is moved to a position that extends as far as or farther than the idle roller relative to a surface of a main panel of the rear cover.

4. The image forming apparatus according to claim 1, wherein the supplementary guide member comprises:
a plate-shaped body to face a main panel of the rear cover; 
a pair of wings to extend vertically from both edges of the plate-shaped body and aligned with the guide ribs to guide the discharged sheet; and 
a rotation shaft to protrude from both sides of the wings and rotatably coupled to the guide ribs.

5. The image forming apparatus according to claim 4, wherein the rotation shaft comprises:
a latching projection formed on an end of the rotation shaft to protrude crosswise at an angle of 90° with respect to an axial direction of the rotation shaft to prevent a disengagement of the rotation shaft from the guide ribs.

6. The image forming apparatus according to claim 5, further comprising:
supporting holes formed on the guide ribs to have a shape to correspond to a shape of the rotation shaft and the latching projection, so that the rotation shaft and the latching projection pass through the supporting holes.

7. The image forming apparatus according to claim 1, wherein the rear cover comprises:
a plurality of supporting projections, each having supporting slits to movably support the idle roller.

8. The image forming apparatus according to claim 7, wherein the idle roller comprises:
a rotation shaft to fit into the supporting slits and enable the idle roller to move.

9. The image forming apparatus according to claim 8, further comprising:
a torsion spring interposed between a main panel of the rear cover and the idle roller, to compress the idle roller elastically toward the one of the sheet feeding rollers so as to generate a predetermined friction force between the one of the sheet feeding rollers and the idle roller.

10. The image forming apparatus according to claim 1, wherein the guide ribs are disposed at a predetermined spacing on a main panel of the rear cover.

11. The image forming apparatus according to claim 10, wherein the guide ribs are provided with guide surfaces which are curved so that the sheet is guided in a vertical direction.

12. The image forming apparatus according to claim 1, wherein the rear cover is opened from the printer body and pivots on a hinge shaft at an angle of about 45° to 60°.

13. The image forming apparatus according to claim 4, wherein the rotation shaft is positioned above a center of a vertical length of the supplementary guide member.

14. An image forming apparatus having a printer body, comprising:
a rear cover provided on a side of the printer body to open and close, and having a plurality of guide ribs to guide a sheet passed through a portion of the printer body; 
an idle roller movably disposed at the rear cover to rotate as the sheet is discharged in a direction of the guide ribs; and 
a supplementary guide member pivotably disposed at the rear cover below the idle roller, to change a position thereof when the rear cover is open, preventing the sheet being discharged directly to the guide ribs from running into the idle roller.