BRIEF DESCRIPTION OF THE DRAWINGS
A better understanding of the present invention will become apparent from the following detailed description of example embodiments and the claims when read in connection with the accompanying drawings, all forming a part of the disclosure of this invention. While the following written and illustrated disclosure focuses on disclosing example embodiments of the invention, it should be clearly understood that the same is by way of illustration and example only and that the invention is not limited thereto. The spirit and scope of the present invention are limited only by the terms of the appended claims. The following represents brief descriptions of the drawings, wherein:
FIG. 1 is a perspective view of a typical belt type image fixing unit;
FIG. 2 is a cross-sectional view of a structure of a nip of the image fixing unit shown in FIG. 1;
FIG. 3 is an end view of a structure of a guide roller of the image fixing unit shown in FIG.
FIG. 4 is a perspective view of a structure of an image fixing unit for use in an image forming apparatus according to an embodiment of the present invention;
FIG. 5 is an enlarged cut away view of a bushing, which is a main part of the image fixing unit, shown in FIG. 4, according to an embodiment of the present invention;
FIGS. 6A through 6D and 8 are views of various examples of shapes of a protrusion shown in FIG. 5 according to an embodiment of the present invention;
FIG. 7A is a friction torque versus contact area graph of a belt and a bushing according to an embodiment of the present invention;
FIG. 7B is a graph showing the relationship between the radius of curvature of a protrusion and an incidence of damage to a belt; and
FIG. 9 is a view showing a structure of an image fixing unit for use in an image forming apparatus according to another embodiment of the present invention.
DETAILED DESCRIPTION OF THE EMBODIMENTS
Reference will now be made in detail to the present embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures.
FIG. 4 is a perspective view of a structure of an image fixing unit for use in an image forming apparatus according to an embodiment of the present invention. As previously discussed, the image forming apparatus can be a laser beam printer, a photo-copier, a facsimile machine or a multi-functional product.
Referring to FIG. 4, the image fixing unit has a belt type structure, and includes a heat roller 300 in which a heater (not shown) is mounted and a circulating belt 200, which is cyclically rotated, while forming a long nip N when engaged with the heat roller 300. A printable medium 1, such as a paper, to which a toner image is transferred onto by a developing unit (not shown), receives heat due to a high temperature of the heat roller 300 simultaneously with undergoing a high pressure from the circulating belt 200 when passing through the nip N. As a result, the toner image is completely fused by heat and pressure.
Guide rollers 110 and 120 support the circulating belt 200 to stably rotate, while maintaining a tight tension, and bushings 100 of the guide rollers 110 and 120 have a structure which reduces friction with the circulating belt 200. Each of the bushings 100 is not a rotary component which rotates together with the circulating belt 200. Rather, each of the bushings 100 is a fixed component for preventing the circulating belt 200 from meandering by means of a regulating portion 100a while supporting the rotation of bodies 111 and 121 of the guide rollers 110 and 120. Therefore, in the embodiments of present embodiment, to minimize friction by reducing a contact area between the circulating belt 200 and the guide rollers 110 and 120, a plurality of protrusions 101 having a dome shape are formed on a surface of the bushing 100 contacting the circulating belt 200 as shown in FIGS. 4 and 5. That is, a plurality of protrusions 101 are formed on the contact surface between the circulating belt 200 and the bushings 100, so that the circulating belt 200 passes, while touching the protrusions 101. Therefore, a contact area is greatly reduced in comparison to the case without the protrusions 101, and thus a friction is significantly reduced. Also, the protrusions 101 are not aligned in lines in a shaft direction of the guide rollers 110 and 120, but are disposed in a zigzag pattern. Accordingly, the circulating belt 200 can rotate more smoothly over the protrusions 101 formed in a zigzag pattern, although it makes point contact with the protrusions 101.
Therefore, both end portions of the circulating belt 200 contact very small areas of tops of the protrusions 101, thereby reducing a friction between the circulating belt 200 and the bushing 100, and thus reducing a wearing amount of the circulating belt 200 and a driving torque required to drive the image fixing device.
In the present embodiment shown in FIG. 5, the protrusions 101 have a dome shape; however, the protrusions 101 can have other shapes as well. For example, protrusions 102 with a cylindrical shaped body having a domed top can be used as shown in FIG. 6A, or protrusions 103 with a rectangular shaped body having a domed top can be used as shown in FIG. 6B. Further, instead of the semicircular dome shape, an elliptical dome shape can be used similarly in protrusions 104 and 105 shown in FIGS. 6C and 6D.
However, in terms of reducing friction, the pattern shown in FIG. 6C, or a dome shape shown in FIGS. 5 through 6B, are more efficient than the pattern shown in FIG. 6D. This is because, as shown in FIG. 6D, when protrusions 105 are elongated in a shaft direction that is perpendicular to a rotating direction of the circulating belt 200, contact areas of tops of the protrusions 105 producing frictions may be significantly enlarged. Therefore, if R1 shown in FIG. 6D indicates a radius of curvature of the protrusion taken along a shaft direction of the guide rollers 110 and 120, and R2 shown in FIG. 6C indicates a radius of curvature of the protrusion taken along a rotation direction, it is advantageous to determine the protrusion shape to satisfy an equation “R1≦R2”. However, when a radius of curvature of the protrusions 101 through 105 becomes too small to decrease a contact area with the circulating belt 200, the protrusions become pointed at the end, and thus may scratch the circulating belt 200. In other words, a friction torque decreases in proportion to a contact area as shown in FIG. 7A, while an incidence of partial damage such a scratch in the circulating belt 200 increases in an inverse proportion to the radius of curvature as shown in FIG. 7B. In particular, when the radius of curvature is below 0.05 mm, an amount of scratching rapidly increases. Accordingly, when a shape of the protrusions 101˜105 is determined to satisfy an equation “0.05 mm≦R1≦R2”, friction can be decreased and scratching can be prevented. Alternatively, as shown in FIG. 8, when a space is formed in a protrusion 106 and a ball 107 is rotatably disposed in the space, the resulting structure serves as a ball bearing, and thus can support more smoothly movement of the circulating belt 200.
The protrusions 101, 102, 103, 104, 105 and 106, as shown in FIG. 4, FIG. 5, FIGS. 6A-6D, and FIG. 8, should be aligned such that tops thereof are as high as the bodies 111 and 121 of the guide rollers 110 and 120.
Turning now to FIG. 9, an image fixing unit for use in an image forming apparatus according to another embodiment of the present invention is illustrated. In the image fixing unit of the current embodiment, a protrusion 108 formed on a bushing 100 of guide rollers 110 and 120 is not formed as a plurality of separated dome shapes. Rather, such a protrusion 108 is formed as a ring shape along an outer circumference of the bushing 100. That is, a circulating belt 200 may be supported by a plurality of small protrusions as in the previous embodiments, shown in FIG. 4, FIG. 5, FIGS. 6A-6D, and FIG. 8, or by the protrusion 108 of a ring shape as the current embodiment. Likewise, a contact area with the circulating belt 200 is decreased in comparison to the bushing 100 without the protrusion 108, thereby reducing wear and tear of the circulating belt 200 and a required drive torque for driving the image fixing unit. In addition, the protrusion 108 should have the same height as the bodies 111 and 121 of the guide rollers 110 and 120 such that the circulating belt 200 rotates smoothly.
Therefore, a contact area between the bushing 100, which is a fixed component, and the circulating belt 200 may decrease, thereby alleviating the problems caused due to friction.
As described above, in the image fixing unit for use in an image forming apparatus of the present invention, the protrusions formed on a surface of the bushing reduces a contact area between the rotating circulating belt and the bushing, which is a fixed component, of the guide rollers, thereby reducing wear and tear of the circulating belt and a drive torque for driving the image fixing device.
While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention. Many modifications, permutations, additions and sub-combinations may be made to adapt the teachings of the present invention to a particular situation without departing from the scope thereof. For example, protrusions can be configured to have different sizes and shapes than that shown in FIG. 5, FIG. 6A-6D and FIG. 8. In addition, the area on which the protrusions are formed can be made larger or smaller than that shown in FIG. 5 to ensure contact with the circulating belt. Accordingly, it is intended, therefore, that the present invention not be limited to the various example embodiments disclosed, but that the present invention includes all embodiments falling within the scope of the appended claims.
Patent Application
20080003026
