Patent Publication Number: US-7711303-B2

Title: Variable tension belt type fusing unit usable with image forming apparatus and driving method thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit under 35 U.S.C. § 119 of Korean Patent Application No. 2005-64180, filed on Jul. 15, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present general inventive concept relates to a fusing unit usable with an electrophotographic image forming apparatus which fuses an image onto a recording medium, such as a paper, in which a toner image is transferred, by applying heat and pressure, and more particularly, to a belt type fusing unit which includes a main roller and a fusing belt to rotate in contact with a portion of an outer circumferential surface of the main roller, wherein the fusing belt has a tension portion and a non-tension portion. 
   2. Description of the Related Art 
   Common image forming apparatuses, such as a laser beam printer, an LED printer, a digital copy machine, and a facsimile, transfer an image onto a paper as a visible image in response to a digital signal input from a computer or a scanner. 
   Electrophotographic image forming apparatuses form an electrostatic latent image corresponding to a desired image onto an outer circumferential surface of a photoconductor by exposing light to the outer circumferential surface of the photoconductor in response to a digital signal corresponding to the desired image to be printed using a predetermined pattern, develop the electrostatic latent image using a power type toner, transfer the developed image onto a paper directly or via a transfer medium, and perform a fusing process thereon. 
   As mentioned above, the electrophotographic image forming apparatus includes a fusing unit which fuses a toner image (i.e., the developed image) transferred onto the paper by applying heat and pressure. A conventional fusing unit used in the electrophotographic image forming apparatus includes a roller type fusing unit and a belt type fusing unit. Compared to the roller type fusing unit, the belt type fusing unit can ensure a long nip section, so that a fusing temperature can be lowered. In addition, since a belt having a small heat capacity is used, a heat transfer efficiency can be improved. 
   In the belt type fusing unit, the belt is pressurized towards a main roller to apply a tension to the belt. Since the belt is made of a material having a form of a thin film and is continuously subjected to a tension stress in a high temperature environment, deformation of the belt frequently occurs. In addition, a lifespan of the belt is severely reduced due to the high temperature environment and the tension. Additionally, if slipping or meandering occurs when a predetermined tension is applied, it is difficult to control the applied tension or to fix the slipping or meandering. 
   SUMMARY OF THE INVENTION 
   The present general inventive concept provides a variable tension belt type fusing unit in which a fusing belt is divided into a tension portion having a nip section required to fuse a toner image and a non-tension portion, wherein a tension is applied to the fusing belt only within the tension portion, and the tension of the tension portion is released during a power saving mode, thereby increasing a lifespan of the fusing belt and improving a stability of the fusing belt traveling, and a driving method thereof. 
   Additional aspects and advantages of the present general inventive concept 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 general inventive concept. 
   The foregoing and/or other aspects of the present general inventive concept may be achieved by providing a variable tension type belt fusing unit including a main roller, a pair of belt driving rollers which is disposed near an outer circumferential surface of the main roller and is disposed towards the main roller, and a fusing belt to travel by the pair of belt driving rollers in a travel direction and having a nip portion and a non-tension portion, the nip portion being biased or pressurized towards the main roller by applying a tension and disposed at one side of the pair of belt driving rollers and the non-tension portion being provided at the other side of the pair of belt driving rollers such that at least one of the pair of belt driving rollers being independently and temporarily driven to apply or release the tension to the nip portion. 
   The at least one of the pair of belt driving rollers may temporarily and relatively rotate in the traveling direction with respect to the main roller to apply or release the tension in the nip portion . 
   The pair of belt driving rollers comprises a preceding roller to temporarily and reversely rotate with respect to the main roller. 
   The pair of belt driving rollers may temporarily rotate in opposite directions to release the tension from the nip portion. 
   At least one of the pair of belt driving rollers temporarily may move in a direction that narrows a distance between the pair of belt driving rollers. 
   The variable tension type belt fusing unit may further comprise a pinch roller engaged with one of the pair of belt driving rollers to drive the fusing belt. 
   The foregoing and/or other aspects of the present general inventive concept may also be achieved by providing a driving method of a variable tension type belt fusing unit including a main roller, a pair of belt driving rollers which is disposed near an outer circumferential surface of the main roller and is pressurized towards the main roller, and a fusing belt to travel between the pair of belt driving rollers and the main roller, the method comprising applying a tension to a nip portion of the fusing belt by the pair of belt driving rollers in a printing mode, maintaining the tension in the nip portion during the printing mode, while the fusing belt travels, and releasing the tension in the nip portion by the pair of belt driving rollers when the printing mode is completed or a stand-by mode. 
   The applying of the tension may comprise rotating independently at least one roller of the pair of belt driving rollers in a direction away from the nip portion in the printing mode, the maintaining of the tension may comprise rotating the main roller and the pair of belt driving rollers to be engaged with each other to have a same travel speed at each surface facing each other during the printing mode, and the releasing of the tension may comprise rotating independently at least one of the pair of belt driving rollers towards the nip portion when the printing mode is completed. 
   The applying of the tension and the releasing of the tension may comprise rotating independently only a preceding roller of the pair of belt driving rollers when the variable tension type belt fusing unit is in the printing mode and the stand-by mode, respectively. 
   The applying of the tension and the releasing of the tension may comprise simultaneously rotating the pair of belt driving rollers in opposite directions in the stand-by mode. 
   The applying of the tension may comprise independently moving at least one of the pair of belt driving rollers in a direction that widens a distance between the pair of belt driving rollers when the variable tension type belt fusing unit is in the printing mode, the maintaining of the tension may comprise rotating the main roller and the pair of belt driving rollers engaged with each other to have the same travel speed at each surface facing each other during the printing mode, and the releasing of the tension comprises moving at least one roller of the pair of belt driving rollers in a direction that narrows the distance between the pair of belt driving rollers when the printing mode is terminated. 
   The foregoing and/or other aspects of the present general inventive concept may also be achieved by providing an image forming apparatus, comprising a main roller, a fusing belt, and a pair of belt driving rollers disposed inside the fusing belt to rotate the fusing belt to form a nip portion of the fusing belt between the pair of the belt driving rollers to face a portion of the main roller, one of the pair of belt driving rollers moving according to first and second manners with respect to the other one of the belt driving rollers such that tension is applied to or released from a nip portion of the fusing belt. 
   The foregoing and/or other aspects of the present general inventive concept may also be achieved by providing an image forming apparatus, including a main roller, a pair of belt driving rollers, and a fusing belt having a nip portion disposed between the pair of the belt driving rollers and wound around a portion of the main roller and a non-nip portion disposed between the pair of belt driving belt and opposite to the main roller with respect to the nip portion, the nip portion having a first length in a printing mode and a second length longer than the first length in a stand-by mode according to a movement of one of the pair of the belt driving rollers with respect to the other one of the pair of the belt driving rollers. 
   The foregoing and/or other aspects of the present general inventive concept may also be achieved by providing an image forming apparatus, including a main roller, a pair of belt driving rollers, and a fusing belt having a nip portion disposed between the pair of the belt driving rollers and wound around a portion of the main roller, and a non-nip portion disposed between the pair of belt driving belt and opposite to the main roller with respect to the nip portion, the nip portion having a first length shorter than a distance between rotational axes of the pair of the belt driving rollers in a circumferential direction of the main roller in the printing mode to push a printing medium against the portion of the main roller, and a second length longer than the distance between the rotational axes of the pair of the belt driving rollers in a circumferential direction of the main roller in the printing mode to push a printing medium against the portion of the main roller. 
   The foregoing and/or other aspects of the present general inventive concept may also be achieved by providing an image forming apparatus, including a main roller, a pair of belt driving rollers, and a fusing belt having a nip portion disposed between the pair of the belt driving rollers and wound around a portion of the main roller and a non-nip portion disposed between the pair of belt driving belt and opposite to the main roller with respect to the nip portion, the nip portion having a length in a stand-by mode, and the length of the nip portion becoming shorter than the length according to a movement of at least one of the pair of belt driving rollers with respect to the other one of the pair of the belt driving rollers when the stand-by mode is changed to the printing mode. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and/or other aspects and advantages of the present general inventive concept will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
       FIG. 1  is a schematic side view illustrating a variable tension belt type fusing unit according to an embodiment of the present general inventive concept; 
       FIGS. 2A and 2B  are views illustrating a driving method of the fusing unit of  FIG. 1  according to an embodiment of the present general inventive concept; 
       FIGS. 3A and 3B  are views illustrating a driving method of a fusing unit according to another embodiment of the present general inventive concept; 
       FIGS. 4A and 4B  are views illustrating a driving method of a fusing unit according to another embodiment of the present general inventive concept; 
       FIGS. 5A and 5B  are views illustrating a driving method of the fusing unit of  FIG. 1  according to yet another embodiment of the present general inventive concept; and 
       FIG. 6  is a view illustrating an image forming apparatus having a variable tension belt type fusing unit according to an embodiment of the present general inventive concept. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Reference will now be made in detail to the embodiments of the present general inventive concept, 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 general inventive concept by referring to the figures. 
     FIG. 1  is a schematic side view illustrating a variable tension belt type fusing unit according to an embodiment of the present general inventive concept. The variable type fusing unit may be usable with an image forming apparatus and may include a main roller  11  and a pair of belt driving rollers, such as a preceding roller  12  and an accompanying roller  13 . The main roller  11  may have a relatively larger diameter than the pair of belt driving rollers. 
   A fusing belt  20  forming an infinite loop is wound around the preceding and accompanying rollers  12  and  13  which are respectively pressurized towards the main roller  11  by a predetermined pressure so that the fusing belt  20  is pushed against an outer circumferential surface of the main roller  11 . The fusing belt  20  includes a nip portion  201  and a non-tension portion  202 . The nip portion  201  is disposed around the main roller  11 , and the non-tension portion  202  is disposed away from the main roller  11  with respect to the nip portion  201 . If a tension is applied to the nip portion  201  of the fusing belt  20  between the two rollers  12  and  13 , the nip portion  201  is adhered onto or disposed to be in contact with the outer circumferential surface of the main roller  11  due to the predetermined pressure according to a strength of the tension. The non-tension portion  202  loosely travels. Due to a force exerted on the fusing belt  20  and the main roller  11  by the belt driving rollers, a friction force is ensured between the pair of belt driving rollers and the fusing belt  20  such that the tension is applied to the nip portion  201 . 
   A heat source of the variable tension belt type fusing unit to apply heat on a toner image may be provided in various forms, such as a halogen lamp, a resistance heating element, and an induction heating element. The heat source may be selectively disposed at a portion A in the main roller  11 , a portion B in the loop of the fusing belt  20 , a portion C in the preceding roller  12 , or a portion D in the accompanying roller  13 . 
   The variable tension belt type fusing unit of the present embodiment has a driving force transfer structure in which the main roller  11 , the preceding roller  12 , and the accompanying roller  13  can rotate together when the variable tension belt type fusing unit operates. In the driving force transfer structure (not shown), at least one of the preceding roller  12  and the accompanying roller  13  is independently and temporarily drivable. Here, a travel direction of the fusing belt  20  during the operation of the variable tension belt type fusing unit is considered as a reference of forward and reverse directions. The fusion belt  20  may rotate along a traveling direction as illustrated in  FIG. 1 . At least one of the preceding roller  12  and the accompanying roller  13  can be temporarily released from an engaging state with the main roller  11  to be independently driven. Accordingly, the preceding roller  12  independently rotates with respect to the accompanying roller  13  and/or the main roller  11 , the preceding roller  12  and the accompanying roller  13  rotates in opposite directions while the main roller does not rotate, or the axis of the preceding roller  12  or the accompanying roller  13  may be moved, so that the tension is applied to and released from the nip portion  201  of the fusing belt  20 . 
   The fusing belt  20  is made of a film material in a shape of a closed loop, and may be made of a laminated film, which is composed of a heat proof resin, a metal thin plate, or a plurality of layers, and the laminated film may include a metal layer. In order to reduce time for receiving a tension stress compared to a conventional belt type fusing unit in a high temperature environment, various materials can be selected. 
   The driving force transfer structure to temporary and independently drive a roller can be implemented by selecting and combining elements to transfer and to block a driving force to the roller. As an example, in one embodiment of the driving force transfer structure, the preceding roller  12  may be independently and temporarily driven by providing a clutch at a rotation axis of the preceding roller  12 . The driving force transfer structure may be provided in various forms by selecting and combining elements to transfer the driving force. 
     FIGS. 2A and 2B  are views illustrating a driving method of the variable tension belt type fusing unit according to the first embodiment of  FIG. 1 . Like reference numerals as illustrated in  FIG. 1  denote like elements or parts of  FIGS. 2A and 2B , and identical descriptions may be omitted in order to avoid unnecessary repetition with respect to all drawings described hereinafter. 
   When the variable tension belt type fusing unit operates, the preceding roller  12  independently rotates in the forward direction corresponding to the traveling direction of the fusing belt  20  as shown in  FIG. 2A . Since the accompanying roller  13  rotates according to a rotation of the preceding roller  12 , the tension is applied to the nip portion  201 . 
   In order to apply a proper tension to the nip portion  201 , a proper amount of deformation may be determined based on a tension test for the fusing belt  20  and then the preceding roller  12  may be rotated to generate the tension, or the tension may be determined from a targeted pressure between the fusing belt  20  and the main roller  11  and then the preceding roller  12  may be rotated by a torque corresponding to the targeted pressure. 
   During the operation of the variable tension belt type fusing unit, the main roller  11  and the preceding and accompanying rollers  12  and  13  maintain the tension in the nip portion  201  while being engaged with each other to travel at the same speed at respective facing surfaces (or contact areas). 
   When the operation of the variable tension belt type fusing unit is completed, the preceding roller  12  independently rotates in the reverse direction as illustrated in  FIG. 2B . That is, the preceding roller  12  reversely rotates and loosens the fusion belt  20  to form a non-nip portion  201 ′. The second nip portion  201 ′ of  FIG. 2B  is longer than the nip portion  201  of  FIG. 2A  that is subjected to the tension, and a second non-tension portion  202 ′ may be shorter than the non-tension portion  202  corresponding to the nip portion  201 . When the tension in the nip portion  201  is released to show the non-nip portion  201 ′ of  FIG. 2B , the variable tension belt type fusing unit is in a power save mode (or a stand-by mode). 
   The nip portion and non-nip portion  201  and  201 ′ include first portions disposed between the main roller  11  and the preceding roller  12  and the accompanying roller  13 , respectively, and spaced apart from the main roller  11  by a first distance or in contact with the main roller  11 , and a second portion between the first portions to be spaced from the main roller  11  by a second distance and a third distance according to a printing operation mode and a stand-by mode, respectively. The second portion is apart from the main roller  11  by the third distance greater than the second distance in the stand-by mode by a movement of at least one of the preceding roller  12  and the accompanying roller  13 . That is, the preceding roller  12  moves or rotates in the forward direction with respect to the accompanying roller  13  in the printing mode, the tension is applied to the nip portion  201  of the fusing belt  20  to rotate the fusing belt  20  in the traveling direction, and the preceding roller  12  moves or rotates in the reverse direction with respect to the accompanying roller  13  in the stand-by mode or when the printing mode is completed, the tension is leased from the nip portion  201  of the fusing belt  20  to rotate a portion of the fusing belt  20  in a direction opposite to the traveling direction, so that the second non-nip portion  201 ′ is formed. 
     FIGS. 3A and 3B  are views illustrating a driving method of the variable tension belt type fusing unit of  FIG. 1 . The variable tension belt type fusing unit and the driving method of  FIGS. 3A and 3B  are similar to the embodiment of  FIGS. 2A and 2B . However, a pinch roller  121  to generate a friction force with the fusing belt  20  and the preceding roller  12  is further provided. The pinch roller  121  provided to be pressurized towards the preceding roller  12  may rotate together with the preceding roller  12 , the fusing belt  20  is disposed therebetween, and the pinch roller  121  ensures a stable traveling of the fusing belt  20 . 
     FIGS. 4A and 4B  are views illustrating a driving method of the variable tension belt type fusing unit of  FIG. 1 . According to the present embodiment, when the variable tension belt type fusing unit completes the operation as illustrated in  FIG. 4A , a preceding roller  14  reversely rotates while an accompanying roller  15  forwardly rotates, so that a nip portion  201  is loosened to form a non-nip portion  201 ′ as illustrated in  FIG. 4B . At this time, a length of the second non-tension portion  202 ′ is shortened compared to that of the non-tension portion  202 . However, the tension is not applied to the second non-tension portion  202 ′ according to the reverse rotation of the preceding roller  14 . 
     FIGS. 5A and 5B  are views illustrating a driving method of a variable tension belt type fusing unit according to yet another embodiment of the present general inventive concept. According to the present embodiment, a preceding roller  16  is provided to be temporarily displaceable with respect to the accompanying roller  13  and the main roller  11 . When the variable tension belt type fusing unit completes the operation, as illustrated in  FIG. 5B , the preceding roller  16  may be moved towards the accompanying roller  13  along the outer circumferential surface of the main roller  11  to loosen the fusion belt  20  to form a non-nip section  201 ′. 
   Accordingly, in various embodiments of a variable tension belt type fusing unit usable with an image forming apparatus and a driving method thereof according to the present general inventive concept, a fusing belt is divided into a tension portion having a nip portion close to a main roller to fuse an image on a recording medium and a non-tension portion, a tension is applied to the fusing belt only within the tension portion in a printing operation mode, and the tension of the tension portion is released during a power saving mode which is a non-printing operation mode, so that the lifespan of the fusing belt increases. In addition, when the fusing belt is meandered or slipped, the tension is temporarily released and then is reapplied, thereby improving the stability of traveling of the fusing belt. 
   When the image forming apparatus is turned on and the variable tension belt type fusing unit is prepared for an operation, a pair of belt driving rollers is released from an engaging condition with a main roller and the pair of belt driving rollers apply a tension by pulling the nip section. When the tension is applied to the nip section of the fusing belt, the nip section is adhered towards the main roller by applying a predetermined pressure. During the operation of the variable tension belt type fusing unit, the pair of rollers and the main roller are engaged with each other and maintain the tension in the nip section. A paper on which a toner image is transferred is fed while being engaged to the nip section between the main roller and the fusing belt. At this time, the toner image transferred onto the paper is melt by the heat source, and the melted toner image is pressurized and adhered onto the paper by the pressure between the main roller and the fusing belt. When the operation of the variable tension belt type fusing unit is completed, the pair of belt driving rollers operates in an opposite way with respect to when the variable tension belt type fusing unit is prepared for the operation and thereby releases the tension in the nip section. Thus, the variable tension belt type fusing unit according to various embodiments of the present general inventive concept can minimize the time for applying the tension to the fusing belt, increase the lifespan of the fusing belt, and prevent problems of slipping or meandering caused by deformation of the fusing belt. 
     FIG. 6  is a view illustrating an image forming apparatus  100  having the variable tension belt type fusing unit of  FIG. 1  according to an embodiment of the present general inventive concept. Referring to  FIGS. 1 and 6 , a sheet of paper  300  is fed through a nip between the main roller  11  and the nip portion  201  of the fusing belt  20 . A toner image  301  on the sheet of paper  300  is fixed thereon due to heat and pressure applied while the sheet of paper  300  passes through the nip along the nip portion  201 . The operations of the pair of belt driving rollers  12  and  13  are similar to the operations described in  FIGS. 2-5B  in order to control tension of the fusing belt  20  and a distance between the main roller  11  and the fusing belt  20 . 
   Although a few embodiments of the present general inventive concept have been shown and described, it will 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 general inventive concept, the scope of which is defined in the appended claims and their equivalents.