Heat roller for fixing apparatus

Abstract

A heat roller for a fixing apparatus includes a conductive cylindrical roller body, and a resistance heater installed in the roller body. Caps at each end of the heat roller have electrodes for supplying a current to the resistance heater. A fastening means confines at least one cap to prevent the cap from being axially separated from the roller body and to substantially prevent the cap from being idled in the roller body.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit under 35 U.S.C. §119(a) of Korean Patent Application No. 2005-54781, filed on Jun. 24, 2005, the entire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a fixing apparatus for an image forming apparatus. More particularly, the present invention relates to a heat roller for a fixing apparatus provided with a key capable of substantially preventing the heat roller from slipping at a roller cap.

2. Description of the Related Art

An image forming apparatus, such as a laser printer, a duplicator and other similar apparatuses, prints a desired image on a recording medium through processes of charging, exposing, transferring and fixing. Among these processes, the fixing process is a process of fixing a toner image transferred to the recording medium by applying heat and pressure, and is generally performed by a fixing apparatus including a pair of rollers.

One of the pair of rollers of the fixing apparatus is a pressure roller and the other roller is a heat roller. FIG. 1 illustrates a structure of a conventional heat roller. Because the heat roller 10 shown in FIG. 1 has a heat source, the heat roller 10 requires a rotating power supply unit for supplying an external power to the heat source. In the conventional heat roller, the rotating power supply unit includes electrodes 13a and 14a installed at an end cap 13 and a gear cap 14, respectively, assembled to both ends of a heat roller body 11. Connection terminals 15 electrically connect the heat source to the electrodes 13a and 14a. When the gear cap 14 and the end cap 13 are loosely fastened to the heat roller, the caps 13 and 14, especially, the gear cap 14 may become unfastened, thereby resulting in twisting and disconnecting of the connecting terminals 15 from the heat roller. Therefore, the caps 13 and 14 should be securely fastened.

FIG. 2 is an exploded perspective view of a gear cap part of a heat roller of FIG. 1. As shown in FIG. 2, the gear cap 14 generally has a screw part 14b that is securely fastened to a screwed hole part 11b formed at the roller body 11. While not shown, the end cap 13 is also fastened by a screw means.

Although the gear cap and the roller body in the heat roller of the fixing apparatus are fastened to each other, when they are backlashed the gear cap may be separated from the roller body so that the connecting terminals 15 for connecting the electrodes 13a and 14a and a resistance heater 12 may be twisted to cause disconnection. Moreover, because the roller body of the heat roller has a thickness of about 1 mm and thus a small thread height of about 0.35 mm, therefore, when the roller is subjected to a strong rotational torque, the threads may be broken to make the gear cap skid to cause disconnection, thereby resulting in bad contact of the terminal, sparks and other detrimental results.

Korean Patent Registration No. 452874 discloses a heat roller of a fixing apparatus for fastening a gear cap and a roller body using a separate fastening means, without forming threads at the gear cap.

FIGS. 3 and 4 illustrate the heat roller of Korean Patent Registration No. 452874. FIG. 3 is an exploded perspective view and FIG. 4 is a cross-sectional view thereof. Referring to FIGS. 3 and 4, a gear cap 24 is fastened to an end of a roller body of a heat roller 20 using a fixing ring 30 and a hooking projection 32a. A groove 24b in the gear cap 24 receives the fixing ring 30. The fixing ring 30 confines the gear cap 24 to the roller body 21 to prevent axial separation, and the hooking projection 32a is inserted into a hooking groove 31a to confine the gear cap 24 to the roller body 21 to prevent idling when the end 31 of the roller body 21 is received in the recess 32 in the gear cap 24.

The fastening structure of the gear cap 24 has a good coherence in comparison with the conventional thread fastening structure. However, as shown in FIGS. 3 and 4, because the roller body 21 has an annular groove 21b into which the fixing ring 30 can be inserted, the roller body may have a low strength due to the annular grooves formed at both ends of the roller body 21. Even though the smaller the thickness of the roller body, the shorter the time required to reach a print temperature, that is, a first print out time (FPOT), there is a limit to how much the thickness of the roller body may be reduced due to the above reasons.

Accordingly, a need exists for a fixing apparatus for an image forming apparatus in which a heat roller has an improved cap connection.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a heat roller for a fixing apparatus capable of maintaining secure engagement of a roller body and caps using a new fastening means, without forming screw threads or screw grooves at the roller body.

A heat roller for a fixing apparatus includes a conductive cylindrical roller body, a resistance heater installed in the roller body, and caps connected to both ends of the roller body and respectively having electrodes for supplying current to the resistance heater. Fastening means confine at least one cap so that the cap is prevented from being axially separated from the roller body and from being idled at the roller body.

The fastening means may include a fastening part projecting from a gear cap to be inserted into the roller body and having a fastening groove with a predetermined depth on the outer surface of the roller body. A spring key is inserted in the fastening groove and has a plurality of protrusions on its outer surface.

The fastening groove may be an annular groove or a polygonal groove, such as a hexagonal or octagonal groove.

The spring key is preferably formed as a semi-circular resilient key having an inner surface consisting of a plurality of planes. More preferably, the spring key is formed as two keys installed opposite to each other in one cap.

Preferably, the cap has an inner cap installed therein. The cap and the inner cap are fastened to each other by a fastening member, such as a screw, a bolt or similar fastener.

A bearing may be installed at an outer surface of the roller body.

Other objects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features of the present invention will be described in reference to certain exemplary embodiments thereof with reference to the attached drawings, in which:

FIG. 1 is an elevational view in cross section of a conventional heat roller for a fixing apparatus;

FIG. 2 is an exploded perspective view of a gear cap of the heat roller of FIG. 1;

FIG. 3 is an exploded perspective view of a gear cap of another conventional heat roller;

FIG. 4 is an elevational view in cross section of the gear cap of FIG. 3;

FIG. 5 is an exploded perspective view of a gear cap of a heat roller in accordance with an exemplary embodiment of the present invention; and

FIG. 6 is a partially cut-away perspective view of the assembled heat roller of FIG. 5.

Throughout the drawings, the same drawing reference numerals will be understood to refer to the same elements, features, and structures.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

The present invention is described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown.

FIG. 5 is an exploded perspective view of a gear cap of a heat roller in accordance with an exemplary embodiment of the present invention. FIG. 6 is a partially cut-away perspective view of the assembled heat roller of FIG. 5.

Referring to FIGS. 5 and 6, a heat roller 100 according to an exemplary embodiment of the present invention includes a conductive cylindrical roller body 111, a resistance heater 112 installed in the roller body, and caps 114 respectively connected to both ends of the roller body and having electrodes for supplying a current to the resistance heater. Fastening means 120 confine at least one cap to prevent the cap from axially separating from the roller body and to substantially prevent the cap from idling at the roller body.

The fastening means 120 includes a fastening part 122 projecting from the cap 114 to be inserted into the roller body 111 and having a fastening groove 124 of predetermined depth formed at its outer surface. A spring key 121 is inserted in the fastening groove 124.

The fastening means 120 may confine a gear cap 114, an end cap, or may be used at both ends to confine the gear and end caps. Securing the end cap is substantially similar to securing the gear cap 114, accordingly the end cap is not shown.

The fastening groove 124 may be an annular groove, or a polygonal groove, such as a hexagonal or octagonal groove.

The spring key 121 has a plurality of protrusions 125 at its outer edge. An inner surface of the spring key 121 has an annular shape or a polygonal shape, such as a hexagonal or octagonal shape. Preferably, the inner surface has a plurality of planes 123. The protrusions 125 may have various shapes, such as a triangular shape, a tooth shape, or the like. Preferably, the protrusions have a substantially triangular shape. The spring key 121 is preferably formed to have a semi-circular shape. In an exemplary implementation, as shown in FIG. 5, the spring key is formed as two keys installed opposite to each other in one cap. The spring key is preferably formed of a resilient material, such as steel, steel alloy, or stainless steel.

Preferably, the cap 114 has an inner cap 115 installed therein. The cap 114 and the inner cap 115 are fastened to each other by fastening member 117, such as a screw, a bolt or other suitable fastener. As shown in FIGS. 5 and 6, the fastening member includes a bolt 117a inserted from one side of the cap 111 and a nut 117b disposed on an opposite side of inner cap 115, thereby securing the cap 114 and the inner cap 115. An insulating material 114b is provided on a side surface of the cap 114 when the cap 114 is fastened to the roller body 111. The electrode 114a is then installed on the insulating material 114b.

A bearing 116 may be installed at a periphery of the roller body 111.

Because the heat roller 100 having the above fastening structure includes the roller body 111 securely fastened by the spring key 121, the heat roller is not separated in an axial direction of the roller as well as not being idled in a rotational direction.

To compare performance of the heat roller 100 according to an exemplary embodiment of the present invention and the conventional heat roller 10 (FIG. 1), a gear chuck for chucking the cap was manufactured to perform a torque test of each heat roller.

As a result of the torque test, while the threads of the conventional heat roller broke to make the roller idle, resulting in disconnection at a torque of 30˜35 kg-cm, the heat roller according to an exemplary embodiment of the present invention was not idled at a torque of 163˜167 kg-cm.

As shown by the foregoing test results, the heat roller for a fixing apparatus according to an exemplary embodiment of the present invention is capable of more securely fastening the roller body to the caps using a novel fastening means and therefore increasing lifespan of the heat roller because there is no disconnection of a coil and no spark between the electrodes. Furthermore, because the heat roller for a fixing apparatus according to an exemplary embodiment of the present invention does not use a screw means, it is possible to reduce manufacturing costs of the roller body and a first print out time (FPOT) by decreasing a thickness of the roller body in comparison with the conventional art.

Although the present invention has been described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that a variety of modifications and variations may be made to the present invention without departing from the spirit or scope of the present invention defined in the appended claims, and their equivalents.

Claims

1. A heat roller for a fixing apparatus, comprising:

a conductive cylindrical roller body;

a resistance heater installed in the roller body;

a cap connected to one end of the roller body and respectively having an electrode for supplying a current to the resistance heater; and

fastening means for confining the cap to prevent the cap from axially being separated from the roller body and to substantially prevent the cap from being idled at the roller body.

2. The heat roller for a fixing apparatus according to claim 1, wherein the fastening means includes

a fastening part projecting from the cap and having a fastening groove on the outer surface of the fastening part; and

a spring key disposed in the fastening groove and having a plurality of protrusions extending outwardly from an outer edge thereof.

3. The heat roller for a fixing apparatus according to claim 1, wherein

the fastening means confines a gear cap.

4. The heat roller for a fixing apparatus according to claim 1, wherein

the fastening means confines an end cap.

5. The heat roller for a fixing apparatus according to claim 2, wherein

the fastening groove is an annular groove.

6. The heat roller for a fixing apparatus according to claim 2, wherein

the fastening groove has a substantially polygonal shape.

7. The heat roller for a fixing apparatus according to claim 2, wherein

the spring key is formed as a semi-circular resilient key.

8. The heat roller for a fixing apparatus according to claim 2, wherein

the spring key has an inner surface having a plurality of planes.

9. The heat roller for a fixing apparatus according to claim 2, wherein

the spring key is formed as two keys installed opposite to each other in the cap.

10. The heat roller for a fixing apparatus according to claim 1, wherein

the cap has an inner cap installed therein.

11. The heat roller for a fixing apparatus according to claim 1, wherein

a bearing is disposed on an outer surface of the roller body.

12. The heat roller for a fixing apparatus according to claim 10, wherein

the cap and the inner cap are fastened to each other by a fastening member.

13. The heat roller for a fixing apparatus according to claim 2, wherein

the plurality of protrusions have a substantially triangular shape.

14. The heat roller for a fixing apparatus according to claim 12, wherein

an insulating member is disposed between the electrode and the fastening member.

15. A heat roller for a fixing apparatus, comprising:

a conductive cylindrical roller body;

a resistance heater installed in the roller body;

a first cap connected to a first end of the roller body;

a second cap connected to a second end of the roller body;

first and second electrodes disposed at first and second caps, respectively, for supplying a current to the resistance heater; and

first and second fastening means for confining the first and second caps to prevent the fist and second caps from axially being separated from the roller body and to substantially prevent the first and second caps from being idled at the roller body.

16. The heat roller for a fixing apparatus according to claim 15, wherein each of the first and second fastening means includes

a fastening part projecting from the cap and having a fastening groove on the outer surface of the fastening part; and

a spring key disposed in the fastening groove and having a plurality of protrusions extending outwardly from an outer edge thereof.

17. The heat roller for a fixing apparatus according to claim 16, wherein

the plurality of protrusions have a substantially triangular shape.

18. The heat roller for a fixing apparatus according to claim 16, wherein

the spring key is formed as a semi-circular resilient key.

19. The heat roller for a fixing apparatus according to claim 16, wherein

the spring key is formed as two keys installed opposite to each other in the cap.

20. The heat roller for a fixing apparatus according to claim 15, wherein

each of the first and second caps has an inner cap secured thereto by a fastening member.