Belt type fixing apparatus and image forming apparatus having the same

A belt type fixing apparatus includes a fixing belt, a fixing roller disposed to face the fixing belt, a nip forming member that is disposed inside the fixing belt and presses the fixing belt to the fixing roller to form a fixing nip, first and second regulating surfaces that are provided at opposite ends of the nip forming member and restrict an axial movement of the fixing belt, and first and second guide surfaces that are provided inside the fixing belt and guide rotation of the fixing belt. The first regulating surface and the second regulating surface include at least one regulating step portion which is not in contact with one end of the fixing belt, respectively. The first guide surface and the second guide surface include at least one guide step portion which is not in contact with an inner surface of the fixing belt, and the at least one regulating step portion and the guide step portion are formed to be staggered from each other.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority benefit of Korean Patent Application No. 10-2016-0090896 filed on Jul. 18, 2016, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND

The disclosure relates to a fixing apparatus for an image forming apparatus. More particularly, the disclosure relates to a belt type fixing apparatus and an image forming apparatus having the same.

2. Description of the Related Art

Generally, an electrophotographic image forming apparatus such as a laser printer forms a developer image corresponding to print data on a printing medium, and uses a fixing apparatus to permanently fix the developer image on the printing medium by applying predetermined heat and pressure to the developer image.

The fixing apparatus may include a pair of rollers, that is, a heating roller that generates a predetermined heat to be applied to the printing medium and a fixing roller that applies a predetermined pressure to the printing medium.

In recent years, in image forming apparatuses capable of high-speed printing, a belt type fixing apparatus using a fixing belt, which is an endless belt, is widely used instead of the heating roller.

As illustrated inFIG. 1, a conventional belt type fixing apparatus guides the rotation of a fixing belt210by using guide bushes200provided at the opposite ends of the fixing belt210. A first surface201of the guide bush200restricts an axial movement of the fixing belt210, and a second surface203of the guide bush200supports the rotation of the fixing belt210inside the fixing belt210. The first surface201and the second surface203of the guide bush200are formed to be perpendicular to each other.

At this time, at a connecting portion205between the first surface201and the second surface203of the guide bush200forming the right angle, there exists a tool shape (or tool trace) which is generated when the guide bush200is machined. For example, as illustrated inFIG. 2, a round having a predetermined curvature is formed at the connecting portion205between the first surface201and the second surface203of the guide bush200.

While the fixing belt210rotates, the fixing belt210receives an axial force B. Then, as illustrated inFIG. 3, the fixing belt210is moved in the axial direction along the second surface203by the axial force B, so that one end210aof the fixing belt210climbs up along the round shape205formed between the first surface201and the second surface203. Then, the one end210aof the fixing belt210receives a force that acts from the inside of the fixing belt210to the outside to cause the one end210aof the fixing belt210to be spread out. Accordingly, when the fixing belt210repeatedly rotates along the guide bush200, the one end210aof the fixing belt210is cracked and broken.

Accordingly, the development of a belt type fixing apparatus capable of suppressing fatigue cracks at opposite ends of the fixing belt210has been demanded.

SUMMARY

The disclosure has been developed in order to overcome the above drawbacks and other problems associated with the conventional arrangement. An aspect of the disclosure relates to a belt type fixing apparatus that can minimize occurrence of cracks at opposite ends of a fixing belt and an image forming apparatus having the same.

According to an aspect of the disclosure, a belt type fixing apparatus may include a fixing belt, a fixing roller disposed to face the fixing belt, a nip forming member that is disposed inside the fixing belt and presses the fixing belt to the fixing roller to form a fixing nip, first and second regulating surfaces that are provided at opposite ends of the nip forming member and restrict an axial movement of the fixing belt, and first and second guide surfaces that are provided inside the fixing belt and guide rotation of the fixing belt. The first regulating surface and the second regulating surface may include at least one regulating step portion which is not in contact with one end of the fixing belt, respectively. The first guide surface and the second guide surface may include at least one guide step portion which is not in contact with an inner surface of the fixing belt. The at least one regulating step portion and the guide step portion may be formed to be staggered from each other.

The first regulating surface and the first guide surface may be formed integrally with a first guide bush which is provided at the one end of the fixing belt, and the second regulating surface and the second guide surface may be formed integrally with a second guide bush which is provided at another end of the fixing belt.

An entire portion of each of the first and second guide surfaces may be substantially perpendicular to each of the first and second regulating surfaces in an axial direction of the fixing belt, and at least portion of each of opposite ends of a bottom surface of the fixing belt that is in contact with the opposite ends of the fixing belt contacting the first and second regulating surfaces may be in contact with each of the first and second guide surfaces.

The first regulating surface and the second regulating surface may include at least one sub-regulating surface that is in contact with the one end of the fixing belt, respectively, the first guide surface and the second guide surface may include at least one sub-guide surface that is in contact with the inner surface of the fixing belt, and the at least one sub-regulating surface and the at least one sub-guide surface may be staggered so as not to intersect each other.

The first regulating surface and the second regulating surface may include an entrance end where the fixing belt enters, respectively, and an angle between the entrance end and a tangent line of the fixing belt at a point where the fixing belt enters the entrance end may be in a range of about 85 degrees to about 95 degrees.

According to another aspect of the disclosure, a belt type fixing apparatus may include a fixing belt, a fixing roller provided to face the fixing belt, a nip forming member that is provided inside the fixing belt and presses the fixing belt to the fixing roller to form a fixing nip, first and second regulating surfaces that are provided at opposite ends of the nip forming member and restrict an axial movement of the fixing belt, and first and second guide surfaces that are provided inside the fixing belt and guide rotation of the fixing belt. The first regulating surface may be provided on a first guide bush disposed at one end of the fixing belt and the second regulating surface may be provided on a second guide bush disposed at another end of the fixing belt. The first guide surface and the second guide surface may be formed adjacent to the first guide bush and the second guide bush on opposite sides of the nip forming member.

The nip forming member may include a plurality of guide ribs formed in a longitudinal direction, and the first guide surface and the second guide surface may be formed by two guide ribs provided at the opposite ends of the plurality of guide ribs.

Other objects, advantages and salient features of the disclosure will become apparent from the following detailed description, which, taken in conjunction with the annexed drawings, discloses preferred embodiments.

DETAILED DESCRIPTION

Reference will now be made in detail to example embodiments which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. The embodiments are described below to explain the disclosure by referring to the figures. Throughout the drawings, like reference numerals will be understood to refer to like parts, components and structures.

Hereinafter, certain exemplary embodiments of the disclosure will be described in detail with reference to the accompanying drawings.

The matters defined herein, such as a detailed construction and elements thereof, are provided to assist in a comprehensive understanding of this description. Thus, it is apparent that exemplary embodiments may be carried out without those defined matters. Also, well-known functions or constructions are omitted to provide a clear and concise description of exemplary embodiments. Further, dimensions of various elements in the accompanying drawings may be arbitrarily increased or decreased for assisting in a comprehensive understanding.

FIG. 4is a perspective view illustrating a belt type fixing apparatus according to an embodiment of the disclosure.FIG. 5is an exploded perspective view illustrating the belt type fixing apparatus ofFIG. 4, andFIG. 6is a cross-sectional view illustrating the belt type fixing apparatus ofFIG. 4taken along a line6-6.

Referring toFIGS. 4, 5, and 6, a belt type fixing apparatus1according to an embodiment of the disclosure may include a fixing roller10, a fixing belt20, a nip forming member30, a pair of regulating surfaces40, and a pair of guide surfaces50.

The fixing roller10is to apply a predetermined pressure to a printing medium P, and is formed in a roller shape. The fixing roller10may include a shaft11formed of a metallic material such as aluminum or steel and an elastic layer13elastically deformed to form a fixing nip N with the fixing belt20. The elastic layer13is generally formed of silicon rubber. The fixing roller10is rotatably supported by a pair of supporting brackets90. The pair of supporting brackets90are provided with bearings91capable of supporting the shaft11.

Although not illustrated inFIGS. 4 to 6, the fixing roller10is configured to rotate by receiving power from a driving source such as a motor. The structure in which the fixing roller10is rotated by the driving source is the same as or similar to the driving structure of the conventional fixing roller; therefore, a detailed description thereof is omitted.

The fixing belt20is to apply predetermined heat to the printing medium P, and is formed of a substantially cylindrical endless belt. The fixing belt20is heated by a heat source in the same manner as a heating roller according to the prior art, thereby transferring heat to the printing medium P passing through the fixing nip N. Accordingly, the fixing belt20is disposed to face the fixing roller10, and forms the fixing nip N through which the printing medium P passes with the fixing roller10. When the fixing roller10rotates, the fixing belt20is rotated by a friction force between the fixing belt20and the fixing roller10. The axial length of the fixing belt20may be longer than the axial length of the fixing roller10.

The fixing belt20may be formed in a variety of structures. For example, the fixing belt20may be composed of a single layer formed of a metal sleeve, a heat-resistant resin film or the like. Alternatively, the fixing belt20may be composed of a base layer formed of a metal sleeve, a heat-resistant resin film or the like, and release layers formed on opposite side surfaces of the base layer. At this time, the release layer may be formed only on one surface facing the fixing roller10. Alternatively, the fixing belt20may include an elastic layer provided between the base layer and the release layer. The fixing belt20may be the same as or similar to the fixing belt used in the conventional belt type fixing apparatus; therefore, a detailed description of the structure of the fixing belt20is omitted.

The nip forming member30is provided inside the fixing belt20, and supports an inner surface of the fixing belt20so that the fixing belt20is in contact with the fixing roller10to form the fixing nip N. The nip forming member30has a length longer than the length of the fixing roller10. In detail, the nip forming member30may include a guiding member31that is in contact with the inner surface of the fixing belt20to guide and press the fixing belt20, and a supporting member32that is disposed on an upper side of the guiding member31and supports the guiding member31.

The guiding member31is in contact with the inner surface of the fixing belt20to form the fixing nip N, and guides the fixing belt20so that the fixing belt20can move smoothly in the vicinity of the fixing nip N. The guiding member31may be formed in a channel shape whose cross-section has a substantially U shape with a flat bottom, and the supporting member32is provided inside the guiding member31. A plurality of guide ribs may be provided in the longitudinal direction on both side surfaces of the guiding member31.

The supporting member32reinforces the guiding member31so as to minimize the bending deformation of the guiding member31. The supporting member32may be formed in a channel shape whose cross-section has a substantially U shape with a flat bottom, and is disposed inside the guiding member31. The supporting member32may be formed in a structure having a large cross-sectional moment of inertial such as an I-beam, an H-beam, etc., in addition to the U shape having a flat bottom.

As illustrated inFIG. 6, the bottom surface of the nip forming member30, that is, the bottom surface31a of the guiding member31is in contact with the inner surface of the fixing belt20, and an upper portion of the fixing roller10that is in contact with a portion of the fixing belt20supported by the bottom surface31a of the guiding member31forms the fixing nip N. Accordingly, when the fixing roller10rotates, the fixing belt20is rotated by friction with the fixing roller10.

Opposite ends of the guiding member31are supported by the pair of supporting brackets90. The pair of supporting brackets90are fixed to a frame of an image forming apparatus that is not illustrated. The pair of supporting brackets90are provided with a pair of guide bushes60and60′. The pair of guide bushes60and60′ are inserted into guide grooves92provided in the pair of supporting brackets90, and can slide up and down along the side walls92aof the guide groove92. Accordingly, opposite side surfaces of each of the guide bushes60and60′ are provided with insertion slots65in the longitudinal direction. When the side walls92aof the guide groove92of each of the supporting brackets90are inserted into the insertion slots65provided in the opposite side walls92aof each of the guide bushes60and60′, the guide bushes60and60′ may slide up and down with respect to the supporting brackets90. In other words, the side walls92aof the guide groove92of the supporting bracket90may function as a guide rail for guiding the movement of the guide bushes60and60′.

A pressing member94for pressing the guide bush60and60′ is provided on one surface of the supporting bracket90. The pressing member94may include a pressing link94arotatably disposed in the supporting bracket90and a coil spring94bconnected to the pressing link94a. The pressing link94ais provided to be in contact with the top of each of the guide bushes60and60′. One end of the coil spring94bis fixed to the pressing link94a, and the other end of the coil spring94bis fixed to the frame (not illustrated) of the image forming apparatus, thereby applying a force pulling the pressing link94adownward. Accordingly, when the coil spring94bapplies the force pulling the pressing link94adownward, the guide bushes60and60′ are urged in a downward direction. When the guide bushes60and60′ are urged downward, the guiding member31is also urged in the downward direction so that the fixing nip N is formed between the fixing belt20and the fixing roller10.

The pair of regulating surfaces40and40′, that is, a first regulating surface40and a second regulating surface40′ are provided at the opposite ends of the fixing belt20, and restrict axial movement of the fixing belt20. A pair of guide surfaces50and50′, that is, a first guide surface50and a second guide surface50′ are provided to abut or contact with the pair of regulating surfaces40and40′, and support inner surfaces of the opposite end portions of the fixing belt20so that the fixing belt20can rotate. In other words, the first and second guide surfaces50and50′ are provided inside the fixing belt20and are formed to guide the rotation of the fixing belt20.

The pair of regulating surfaces40and40′ and the pair of guide surfaces50and50′ are provided to be perpendicular to each other. In detail, the first regulating surface40is provided at one end of the fixing belt20to be perpendicular to the first guide surface50, and the second regulating surface40′ is provided at the other end of the fixing belt20to be perpendicular to the second guide surface50′.

The first guide surface50is provided in the axial direction of the fixing belt20such that the entire surface of the first guide surface50is perpendicular to the first regulating surface40. In other words, the entire width of the first guide surface50is formed to be perpendicular to the first regulating surface40. Accordingly, unlike the guide bush200(seeFIG. 1) according to the prior art, there is no round shape205at a portion where the first regulating surface40and the first guide surface50are connected or contacted with each other. Accordingly, in the belt type fixing apparatus1according to an embodiment of the disclosure, even when the fixing belt20moves in the axial direction to be close to the first regulating surface40, the force that causes the end portion of the fixing belt20to be spread like a morning glory is not applied to the fixing belt20.

Further, the first guide surface50is provided to be able to contact and support at least a portion of the edge of the bottom surface of the fixing belt20connected to one end of the fixing belt20which is in contact with or adjacent to the first regulating surface40.

The second regulating surface40′ and the second guide surface50′ may be formed in the same manner as the first regulating surface40and the first guide surface50as described above; therefore, detailed descriptions thereof are omitted.

The first and second regulating surfaces40and40′ and the first and second guide surfaces50and50′ as described above may be formed in a variety of manners.

For example, the regulating surfaces40and40′ and the guide surfaces50and50′ may be provided in a single guide bush60and60′. In detail, the first regulating surface40and the first guide surface50may be provided integrally with a first guide bush60disposed at one end of the fixing belt20, and the second regulating surface40′ and the second guide surface50′ may be provided integrally with a second guide bush60′ disposed at the other end of the fixing belt20.

In the following description, the first and second regulating surfaces40and40′ are collectively referred to as a regulating surface40, and the first and second guide surfaces50and50′ are collectively referred to as a guide surface50. Also, the first and second guide bushes60and60′ are collectively referred to as a guide bush60. However, if necessary, the first and second regulating surfaces40and40′, the first and second guide surfaces50and50′, and the first and second guide bushes60and60′ may be used separately.

Hereinafter, a guide bush provided with a regulating surface and a guide surface usable in a belt type fixing apparatus according to an embodiment of the disclosure will be described in detail with reference toFIG. 7.

FIG. 7is a perspective view illustrating an example of a guide bush used in a belt type fixing apparatus according to an embodiment of the disclosure.

Referring toFIG. 7, a guide bush60may include a fixed body62and a rotary support part61. The fixed body62is formed to be slidable up and down with respect to the supporting bracket90of the fixing apparatus. The fixed body62is formed in a substantially octagonal shape, the rotary support part61is provided on the front surface of the fixed body62, and the insertion slots65into which the opposite side walls92aof the supporting bracket90are inserted are formed on opposite side surfaces of the fixed body62.

The front surface of the fixed body62is provided with the regulating surface40for restricting the axial movement of the fixing belt20. The regulating surface40may include at least one regulating step portion41with which one end of the fixing belt20is not in contact. Since the regulating step portion41is formed to be lower in height than the regulating surface40, when one end of the fixing belt20is in contact with the regulating surface40, the regulating step portion41is not in contact with the one end of the fixing belt20. In other words, the fixed body62is formed so that the entire front surface40does not restrict the one end of the fixing belt20but only a portion of the front surface40restricts the one end of the fixing belt20.

Also, the regulating surface40may include at least one sub-regulating surface43in contact with the one end of the fixing belt20. Accordingly, the regulating surface40may include at least one sub-regulating surface43and at least one regulating step portion41that are formed alternately. When the one end of the fixing belt20is in contact with the regulating surface40, the sub-regulating surface43is in contact with the one end of the fixing belt20, and the regulating step portion41is not in contact with the one end of the fixing belt20.

A portion41a of the regulating step portion41connected to the sub-regulating surface43is formed to be inclined upward in the rotational direction of the fixing belt20. Accordingly, when the fixing belt20rotates, the one end of the fixing belt20may easily enter the sub-regulating surface43of the guide bush60.

The rotary support part61extends perpendicularly from the front surface of the fixed body62, and supports the fixing belt20to rotate. The rotary support part61may be formed in a variety of shapes as long as it can support the rotation of the fixing belt20. InFIG. 7, the rotary support part61formed in an arc shape or an arch shape for providing a space below the rotary support part61is illustrated. Accordingly, a predetermined space is provided below the rotary support part61. Further, the rotary support part61may be formed in an arc shape that is larger or smaller than a semi-circle. In the embodiment, the rotary support part61is formed in an arc shape substantially larger than the semi-circle. The guide surface50is formed on the top surface of the rotary support part61.

The guide surface50may include at least one guide step portion51that is not in contact with the inner surface of the fixing belt20. The guide step portion51is formed to be lower in height than the guide surface50, and when the inner surface of the fixing belt20is in contact with the guide surface50, the guide step portion51is not in contact with the inner surface of the fixing belt20. In other words, the guide surface50is formed so that the entire portion of the guide surface50does not support the inner surface of the fixing belt20but only a portion of the guide surface50supports the inner surface of the fixing belt20. Since a point where the portion of the guide surface50that supports the inner surface of the fixing belt20meets the front surface of the fixed body62is positioned at the inner side than the point where the regulating surface40meets the guide surface50, the one end of the fixing belt20is not in contact with the point where the portion of the guide surface50supporting the inner surface of the fixing belt20meets the front surface of the fixed body62.

Further, the guide surface50may include at least one sub-guide surface53in contact with the inner surface of the fixing belt20. Accordingly, the guide surface50may include at least one sub-guide surface53and at least one guide step portion51that are formed alternately. When the inner surface of the fixing belt20is in contact with the guide surface50, the sub-guide surface53is in contact with the inner surface of the fixing belt20, and the guide step portion51is not in contact with the inner surface of the fixing belt20.

Further, the at least one guide step portion51and the at least one regulating step portion41are formed to be staggered from each other. In other words, the at least one sub-guide surface53and the at least one sub-regulating surface43are provided to be staggered from each other. Accordingly, the at least one sub-regulating surface43and the at least one sub-guide surface53do not intersect each other, the at least one sub-regulating surface43intersects with the at least one guide step portion51, and the at least one sub-guide surface53intersects with the at least one regulating step portion41.

For example, referring toFIG. 7, the guide surface50may include three sub-guide surfaces53and two guide step portions51provided therebetween. Also, the regulating surface40may include two sub-regulating surfaces43and three regulating step portions41. One regulating step portion41is provided between the two sub-regulating surface43, and two regulating step portions41are provided outside the two sub-regulating surfaces43. Accordingly, the three sub-guide surfaces53are formed to intersect at right angles with the three regulating step portions41, respectively. Accordingly, a rounded tool shape is formed at each portion where the three sub-guide surfaces53and the three regulating step portions41are connected. However, since the height of the regulating step portion41is lower than that of the sub-regulating surface43, the connecting portion between the sub-guide surface53and the regulating step portion41is located inside than the sub-regulating surface43. Accordingly, when the fixing belt20guided by the three sub-guide surface53moves in the axial direction, the one end of the fixing belt20is in contact with only the sub-regulating surface43and is not in contact with the round shape of the connecting portion of the sub-guide surface53.

At this time, the number of the at least one regulating step portion41may be formed to be larger than that of the at least one guide step portion51. In other words, the number of the at least one sub-guide surface53may be formed to be larger than the number of the at least one sub-regulating surface43. Since the guide bush60as illustrated inFIG. 7is provided with two sub-regulating surfaces43and three sub-guide surfaces53, the number of the sub-guide surfaces53is one more than the number of the sub-regulating surfaces43.

FIG. 8is a partial perspective view illustrating a state in which the guide bush ofFIG. 7guides the fixing belt, andFIG. 9is a view illustrating a state in which the guide bush ofFIG. 7guides the fixing belt.

As illustrated inFIGS. 8 and 9, when the fixing belt20rotates, the inner surface adjacent to one end20aof the fixing belt20is supported by the three sub-guide surfaces53, and the one end20aof the fixing belt20is restricted by the two sub-regulating surfaces43. At this time, since the sub-regulating surface43protrudes toward the guide surface50more than the connecting portion between the sub-guide surface53and the regulating step portion41, the one end20aof the fixing belt20is not in contact with the connecting portion between the guide surface50and the regulating surface40. Also, when the one end20aof the fixing belt20is in contact with the sub-regulating surface43, the one end20aof the fixing belt20is not in contact with the regulating step portion41. Accordingly, the one end20aof the fixing belt20does not receive the force acting from the inside to the outside by the round shape of the connecting portion.

In the above description, the guide surface50includes three sub-guide surfaces53, and the regulating surface40includes two sub-regulating surfaces43. However, the number of the sub-guide surfaces53constituting the guide surface50and the number of the sub-regulating surfaces43constituting the regulating surface40are not limited thereto. For example, the regulating surface40may include one sub-regulating surface43or three or more sub-regulating surfaces43, and the guide surface50may include one sub-guide surface53or four or more sub-guide surfaces53.

Hereinafter, as another example of the guide bush, with reference toFIGS. 10 to 12, a guide bush60awill be described in which the guide surface50includes two sub-guide surfaces53, and the regulating surface40includes one sub-regulating surface43.

FIG. 10is a perspective view illustrating another example of a guide bush used in a belt type fixing apparatus according to an embodiment of the disclosure.FIG. 11is a partial perspective view illustrating a state in which the guide bush ofFIG. 10guides the fixing belt, andFIG. 12is a view illustrating a state in which the guide bush ofFIG. 10guides the fixing belt.

Referring toFIG. 10, the guide surface50may include two sub-guide surfaces53and one guide step portion51provided between the two sub-guide surfaces53. Also, the regulating surface40may include one sub-regulating surface43and two regulating step portions41. The two regulating step portions41are provided on opposite sides of the one sub-regulating surface43. Accordingly, the two sub-guide surfaces53are formed to intersect at right angles with the two regulating step portions41, respectively. Accordingly, a rounded tool shape is formed at each connecting portion where the two sub-guide surfaces53and the two regulating step portions41are connected. At this time, since the regulating step portion41is lower than the sub-regulating surface43, the connecting portion between the sub-guide surface53and the regulating step portion41is located inside than the sub-regulating surface43. Accordingly, when the fixing belt20guided by the two sub-guide surfaces53moves in the axial direction, the one end of the fixing belt20is only in contact with the sub-regulating surface43, and does not move along the round shape of the connecting portion between the sub-guide surface53and the regulating step portion41.

In detail, as illustrated inFIGS. 11 and 12, when the fixing belt20rotates, the inner surface adjacent to the one end20aof the fixing belt20is supported by the two sub-guide surfaces53, and the one end20aof the fixing belt20is restricted by the one sub-regulating surface43. At this time, since the sub-regulating surface43protrudes toward the guide surface50more than the connecting portion between the sub-guide surface53and the regulating step portion41, the one end20aof the fixing belt20is not in contact with the connecting portion. Accordingly, the one end20aof the fixing belt20does not receive the force acting from the inside to the outside by the round shape of the connecting portion, so that cracking of the one end20aof the fixing belt20may be prevented.

FIG. 13is a front view illustrating another example of a guide bush used in a belt type fixing apparatus according to an embodiment of the disclosure.

Referring toFIG. 13, a guide bush60bmay include a guide surface50provided with four sub-guide surfaces53and three guide step portions51, and a regulating surface40provided with three sub-regulating surfaces43and four regulating step portions41. At this time, since connecting portions between the four sub-guide surfaces53and the four regulating step portions41are positioned behind the three sub-regulating surfaces43, when the fixing belt20rotates along the guide surface50of the guide bush60b, one end of the fixing belt20is not in contact with the connecting portions between the sub-guide surfaces53and the regulating step portions41.

The above-described guide bush60may be formed of a material having high heat resistance. For example, the guide bush60may be formed of poly phenylene sulfide (PPS) or the like.

The heat source70is provided inside the fixing belt20, and generates heat to heat the fixing belt20to the fixing temperature. As illustrated inFIG. 6, the heat source70is disposed on the bottom surface of the nip forming member30to directly heat the fixing belt20. As the heat source70, a ceramic heater or the like may be used. An electric wire for supplying electricity is connected to the heat source70. However, the electric wire connected to the heat source70is omitted for the convenience of illustration. The heat source70may use a heat source used in a conventional fixing apparatus; therefore, a detailed description thereof is omitted.

In the above description, the heat source70is provided on the bottom surface of the nip forming member30to directly heat the fixing belt20. However, the heat source70may be disposed above the nip forming member30to heat the fixing belt20by radiation. For example, a halogen lamp may be provided as the heat source70above the nip forming member30so that the halogen lamp radiates heat onto the inner surface of the fixing belt20.

In the above description, the guide surface50and the regulating surface40for guiding the rotation of the fixing belt20are integrally formed on the guide bush60, but the guide surface50and the regulating surface40may be formed as separate parts.

Hereinafter, a case where the guide surface and the regulating surface are formed as separate parts will be described with reference toFIGS. 14 to 17.

FIG. 14is a perspective view illustrating a state in which a nip forming member and a guide bush of a belt type fixing apparatus according to an embodiment of the disclosure are assembled.FIG. 15is a perspective view illustrating a state in which a nip forming member and a guide bush of a belt type fixing apparatus according to an embodiment of the disclosure are separated from each other.FIG. 16is a cross-sectional view illustrating a state in which the guide bush and the nip forming apparatus ofFIG. 14guide the fixing belt.

Referring toFIGS. 14 to 16, a front surface of each of a pair of guide bushes600provided at opposite ends of a nip forming member300forms a regulating surface40for restricting axial movement of the fixing belt20, and a pair of guide surfaces310for guiding rotation of the fixing belt20are provided at portions of the nip forming member300adjacent to the front surfaces of the pair of guide bushes600.

In detail, a first regulating surface40is provided in a first guide bush600disposed at one end of the fixing belt20to restrict the axial movement of the fixing belt20, and a second regulating surface (not illustrated) is provided in a second guide bush (not illustrated) disposed at the other end of the fixing belt20to restrict the axial movement of the fixing belt20. In other words, the front surface of the first guide bush600provided in the vicinity of one end of the nip forming member300that is disposed inside the fixing belt20forms the first regulating surface40, and the front surface of the second guide bush (not illustrated) provided in the vicinity of the other end of the nip forming member300forms the second regulating surface.

The pair of guide surfaces310for supporting the inner surfaces of the opposite ends of the fixing belt20, that is, a first guide surface310and a second guide surface are provided in the nip forming member300. In detail, the first guide surface310is provided adjacent to the first guide bush600disposed at one side of the nip forming member300, and the second guide surface is provided adjacent to the second guide bush disposed at the other side of the nip forming member300. The first and second guide surfaces310may be formed by two guide ribs320-1which are provided near the opposite ends of the nip forming member300among a plurality of guide ribs320provided in the nip forming member300.

For example, referring toFIG. 14, a guiding member301of the nip forming member300may include the plurality of guide ribs320formed in the longitudinal direction. The plurality of guide ribs320support the inner surface of the fixing belt20so that the fixing belt20can smoothly rotate. The guide surface310may be formed on each of the two guide ribs320-1that are provided at both ends of the plurality of guide ribs320and support the inner surfaces of the opposite ends of the fixing belt20. In other words, a first guide surface310may be formed on the first guide rib320-1for supporting the inner surface adjacent to the first guide bush600, and a second guide surface may be formed on the second guide rib (not illustrated) adjacent to the second guide bush (not illustrated). The first guide surface310may be formed by the top surface of the first guide rib320-1in contact with the inner surface of the one end of the fixing belt20, and the second guide surface may be formed by the top surface of the second guide rib in contact with the inner surface of the other end of the fixing belt20. Accordingly, the first guide surface310may support the inner surface of the fixing belt20in contact with the one end of the fixing belt20, and the second guide surface may support the inner surface of the fixing belt20in contact with the other end of the fixing belt20.

The first guide bush600is provided in the guide member301so that the front surface of the first guide bush600is in contact with or adjacent to the side surface of the first guide rib320-1and is perpendicular to the top surface of the first guide rib320-1, that is, the first guide surface310. Further, the second guide surface is provided in the guide member301so that the front surface of the second guide bush is in contact with or adjacent to the side surface of the second guide rib and is perpendicular to the top surface of the second guide rib, that is, the second guide surface.

Referring toFIG. 14, each of the plurality of guide ribs320provided in the guide member301may include two sub-guide ribs321and322facing each other in the width direction of the guide member301. In detail, the guide rib320may include an entry side sub guide rib321extending from an entry end of the guide member301into which the fixing belt20enters the fixing nip N and an exit side sub guide rib322extending from an exit end of the guide member301through which the fixing belt20exits the fixing nip N, the above-described first guide rib320-1may be formed by connecting the two sub-guide ribs321and322provided at the one end of the guide member301. Also, the second guide rib may be formed by connecting two sub-guide ribs provided at the other end of the guide member301. At this time, the first guide surface310of the first guide rib320-1and the second guide surface of the second guide rib may be formed in an arch shape corresponding to the shape of the fixing belt20.

Further, the width W1of each of the two guide ribs320-1provided at both ends of the plurality of guide ribs320provided in the guide member301, that is, the first guide rib320-1and the second guide rib may be formed wider than the width W2of each of the remaining guide ribs320located between the first guide rib320-1and the second guide rib. When increasing the widths W1of the first guide rib320-1and the second guide rib, the opposite end portions of the fixing belt20may be stably supported so that the opposite ends of the fixing belt20may be prevented from being wrinkled or damaged by external force.

On the other hand, the first guide bush600and the second guide bush may be detachably provided in the nip forming member300.

FIG. 17is a partial plan view illustrating a nip forming member of a belt type fixing apparatus according to an embodiment of the disclosure.

Referring toFIG. 15, a pair of coupling ribs603facing each other are formed on opposite side surfaces of an opening601provided in the middle of the lower portion of the first guide bush600. Also, referring toFIG. 17, one end of the guide member301of the nip forming member300is provided with a pair of coupling slots303into which the pair of coupling ribs603of the first guide bush600are inserted. Accordingly, when the pair of coupling ribs603of the first guide bush600are inserted into the pair of coupling slots303of the guide member301, the first guide bush600is firmly fixed to the guide member301. Accordingly, movement of the first guide bush600for restricting the axial movement of the fixing belt20with respect to the guide member301may be minimized.

Although not illustrated, the second guide bush also has a pair of coupling ribs like the first guide bush600, and the guide member301is provided with a pair of coupling slots into which the pair of coupling ribs of the second guide bush are inserted. The coupling ribs of the second guide bush and the coupling slots of the guide member301are the same as the coupling ribs603of the first guide bush600and the coupling slots303of the guide member301as described above; therefore, detailed descriptions thereof are omitted.

In the above description, the guide surface310provided in the nip forming member300is formed as a continuous curved surface. However, the structure of the guide surface310is not limited thereto. The guide surface may be formed as separate curved surfaces.

FIG. 18is a view illustrating another example of a guide rib of a nip forming member used in a belt type fixing apparatus according to an embodiment of the disclosure.

For example, as illustrated inFIG. 18, an opening311may be provided at the top of the first guide rib320-1adjacent to the first guide bush600. In detail, the first guide rib320-1may be formed of two cut curved surfaces instead of a continuous curved surface. In other words, the entry side sub guide rib321and the exit side sub guide rib322of the guide rib320-1may be formed not to be connected to each other. Accordingly, the guide surface310′ may be formed as two separate curved surfaces.

On the other hand, the regulating surface400of the guide bush600for restricting the axial movement of the fixing belt20may be formed in a partially cut shape in order to avoid interference with the counterpart part.

FIG. 19is a view illustrating an angle between a fixing belt and an entrance end of a guide bush used in a conventional belt type fixing apparatus.

For example, as illustrated inFIG. 19, the guide bush600is provided with the opening601at the lower portion of the guide bush600to avoid interference with the guide member301. Accordingly, when the fixing belt20rotates, the one end of the fixing belt20enters the regulating surface400of the guide bush600from the opening601, and then comes into contact with the regulating surface400. At this time, a portion of the guide bush600where contact with the fixing belt20starts is provided with an inclined surface611so that the fixing belt20may smoothly enter the regulating surface400.

InFIG. 19, the fixing belt20rotating in the clockwise direction is brought into contact with the regulating surface400through the opening601and the inclined surface611. In other words, the one end of the fixing belt20is brought into contact with the regulating surface400through an entrance end610where the inclined surface611and the regulating surface400abut. When the one end of the fixing belt20passes through the entrance end610, a force F is applied to the fixing belt20. At this time, an angle between the entrance end610and a tangent line of the fixing belt20drawn at a point where the fixing belt20enters the entrance end610is8.

FIG. 20shows the force (i.e., reaction force) applied to the fixing belt20at the time when the fixing belt20passes through the entrance end610of the guide bush600. InFIG. 20, the reaction force F applied to the fixing belt20may be divided into a radial force component F1and a circumferential force component F2. At this time, the larger the radial force component F1is, the more the one end of the fixing belt20spread, so that the fixing belt20may be easily broken. Accordingly, it is desirable to minimize the radial force component F1.

When the fixing belt20begins to contact the regulating surface400at the entrance end610of the guide bush600, the radial force component F1of the force applied to the fixing belt20is zero when the angle θ between the entrance end610and the tangent line of the fixing belt20drawn at the entering point is 90 degrees. That is, F1=0. At this time, F2=F.

Accordingly, as illustrated inFIG. 21, the entrance end610may be formed at an angle of 90 degrees with the tangent line of the fixing belt20. However, the angle θ between the entrance end610of the guide bush600and the tangent line of the fixing belt20may be formed within a range of 90±5 degrees in consideration of the machining tolerance of the parts, the assembly deviation between the parts, and the like. Here,FIG. 21is a view illustrating a force applied to a fixing belt by a guide bush used in a belt type fixing apparatus according to an embodiment of the disclosure.

As another embodiment, as illustrated inFIG. 7, in the case in which the regulating surface400may include a plurality of sub-regulating surfaces43and a plurality of regulating step portions41, when the fixing belt20enters the sub-regulating surface43from the regulating step portion41, a reaction force is applied to the fixing belt20. Accordingly, if the angle θ between an entrance end48connecting the regulating step portion41and the sub-regulating surface43and the tangent line of the fixing belt20is caused to be 90 degrees, the radial force component of the force applied to the fixing belt20may be made zero.

FIG. 22is a view illustrating an angle between a fixing belt and an entrance end of a guide bush used in a belt type fixing apparatus according to an embodiment of the disclosure.

As illustrated inFIG. 22, when the fixing belt20rotates in the clockwise direction, the fixing belt20enters the first sub-regulating surface43-1through the inclined surface41-1a of the first regulating step portion41-1adjacent to the opening60a. At this time, when the fixing belt20passes through the entrance end48where the first regulating step portion41-1is in contact with the first sub-regulating surface43-1, a force is applied to the fixing belt20, and when the angle θ between the entrance end48and the tangent line of the fixing belt20is 90 degrees, the radial force component applied to the fixing belt20becomes zero. In this case as well, the angle θ between the entrance end48and the tangent line of the fixing belt20may be a range of 90±5 degrees in consideration of the machining tolerance of the parts, the assembly deviation between the parts, and the like.

The inventors measured the number of printing media in which breakage occurred in the fixing belt in accordance with the change in the angle between the entrance end and the tangent line of the fixing belt.

In the case in which the angle between tangent line of the fixing belt and the entrance end was 75 degrees, the flaring of the end of the fixing belt started when approximately 90,000 sheets of the printing media were printed. However, in the case in which the angle between tangent line of the fixing belt and the entrance end was 85 degrees, the end of the fixing belt was not damaged until approximately 170,000 sheets of the printing media were printed.

The conditions of the durability test of the above-described fixing belt are as follows.

One side pressing force of the fixing apparatus; 10 Kgf

Axial diagonal force of the fixing belt (Fz); 500 gf

Inclination angle of the guide bush; 165 degrees

Reaction force applied to the fixing belt; F=Fz×Tan(180°−165°)=133.98 gf

When an angle between a tangent line of the fixing belt and the entrance end is 75 degrees, the radial force component of the reaction force: F1=F×Sin(90°−75°)=45.82 gf

When an angle between a tangent line of the fixing belt and the entrance end is 85 degrees, the radial force component of the reaction force: F1=F×Sin(90°−8°)=11.68 gf

As described above, when the angle between the tangent line of the fixing belt and the entrance end is set to be close to 90 degrees, the force applied to the fixing belt is reduced, so that the lifetime of the fixing belt may be prolonged.

Hereinafter, an image forming apparatus100provided with a belt type fixing apparatus1according to an embodiment of the disclosure will be described with reference toFIG. 23.

FIG. 23is a cross-sectional view schematically illustrating an image forming apparatus including a belt type fixing apparatus according to an embodiment of the disclosure.

Referring toFIG. 23, the image forming apparatus100may include a main body101, a printing medium feeding unit110, an image forming unit120, a belt type fixing apparatus1, and a printing medium discharging unit150.

The main body101forms an appearance of the image forming apparatus100, accommodates the printing medium feeding unit110, the image forming unit120, the belt type fixing apparatus1, and the printing medium discharging unit150therein, and fixes and supports them.

The printing medium feeding unit110is disposed inside the main body101to supply the printing medium P to the image forming unit120, and may include a printing medium feeding cassette111and a pickup roller112. The printing medium feeding cassette111accommodates a predetermined number of printing media, and the pickup roller112picks up the printing medium P accommodated in the printing medium feeding cassette111one by one, and supplies the printing medium P to the image forming unit120.

A plurality of conveying rollers115for conveying the printing medium P picked up by the pickup roller112are provided between the pickup roller112and the image forming unit120.

The image forming unit120forms a predetermined image on the printing medium P supplied from the printing medium feeding unit110, and may include an exposure unit121, a developing cartridge130, and a transfer roller140. The exposure unit121emits a predetermined light corresponding to the print data depending to the printing command. The developing cartridge130may include an image carrier131on which an electrostatic latent image is formed by the light emitted from the exposure unit121, and a developing roller132which is disposed at a side of the image carrier131, and supplies developer to the image carrier120, thereby developing the electrostatic latent image formed on the image carrier131into a developer image. In addition, the developing cartridge130stores a predetermined amount of developer, and may include a developer supply roller133for supplying the developer to the developing roller132, an agitator134for agitating the developer, a cleaning blade135for cleaning the surface of the image carrier131, and the like. The transfer roller140is rotatably disposed to face the image carrier131of the developing cartridge130, and transfers the developer image formed on the image carrier120onto the printing medium P.

The belt type fixing apparatus1fixes the developer image onto the printing medium P by applying heat and pressure while the printing medium P on which the developer image is transferred in the image forming unit120passes through the belt type fixing apparatus1, and may include a fixing roller10and a fixing belt20. The structure and operation of the belt type fixing apparatus1are described above; therefore, a detailed description thereof will not be repeated for the sake of brevity.

The printing medium discharging unit150discharges the printing medium P on which the image is fixed while passing through the belt type fixing apparatus1, to the outside of the image forming apparatus100. The printing medium discharging unit150may include a pair of discharging rollers that face each other and rotate.

As described above, the belt type fixing apparatus1according to one or more embodiments of the disclosure may fix the developer image transferred to the printing medium P onto the printing medium P.

Also, the belt type fixing apparatus according to one or more embodiments of the disclosure does not have a round shape that connects the guide surface and the regulating surface of the guide bush in the regions through which the opposite ends of the fixing belt pass. Therefore, the fatigue cracks at the opposite ends of the fixing belt, which are generated when the fixing belt climbs up the round shape, may be minimized.

While various embodiments of the disclosure have been described, additional variations and modifications of the embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. Therefore, it is intended that the appended claims shall be construed to include both the above embodiments and all such variations and modifications that fall within the spirit and scope of the inventive concepts.