Abstract:
A fusing apparatus and method for an image forming apparatus is disclosed. The apparatus and method comprise a heating roller rotatably mounted in a support frame, a pressing roller for rotating in contact with the heating roller, and defining a predetermined nip area by contact with the heating roller, a hinge bracket mounted in the support frame, and supporting either the pressing roller or the heating roller so that either roller rotates in contact with the other roller, first and second elastic members facing each other with the hinge bracket interposed therebetween, and elastically pushing the hinge bracket respectively, and a guide member for guiding movement of the hinge bracket while supporting the respective first and second elastic members, wherein the first and the second elastic members compress and expand reciprocally.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit under 35 U.S.C. § 119(a) of Korean Application No. 2003-66169, filed Sep. 24, 2003, in the Korean Intellectual Property Office, the entire contents of which is incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a fusing apparatus and method. More particularly, the present invention relates to a fusing apparatus and method for an image forming apparatus, which fuses a toner image into a printing paper with predetermined temperature and pressure.  
         [0004]     2. Description of the Related Art  
         [0005]     A general electrophotography image forming apparatus such as a copier, and a laser printer uses an electrophotography developing method. In an electrophotography image forming apparatus, a photoconductive drum is electrified by an adjacent electrifying unit. A surface of the electrified photoconductive drum is exposed to a laser which is emitted from a laser scanning unit. Accordingly, an electrostatic latent image is formed in a pattern corresponding to a desired image. A developing apparatus supplies a toner to the photoconductive drum, and develops the electrostatic latent image on the photoconductive drum into a visible powdery toner image. When a printing paper passes between the photoconductive drum and the transfer roller which rotates in contact with the photoconductive drum, the toner image on the photoconductive drum is transferred to the printing paper. Thus, while the printing paper with the toner image transferred thereon is passing through a fusing apparatus, the toner image is fused by high temperature and pressure. The printing paper passed through the fusing apparatus is discharged.  
         [0006]     The fusing apparatus comprises a pressing roller and a heating roller which rotate facing each other.  FIG. 1  illustrates a fusing apparatus which is disclosed in Japanese Patent No. 2002-139948. Referring to  FIG. 1 , the fusing apparatus comprises a heating roller  12  having a heater  11 , and a pressing roller  13  rotating in contact with the heating roller  12 . The heating roller  12  is rotatably mounted in a support frame  10 , and the pressing roller  13  is rotatably mounted in a hinge frame  14  which rotates about a hinge shaft  14   a . The hinge frame  14  is pushed toward the heating roller  12  by a spring  15  such that a predetermined nip is formed between the heating roller  12  and the pressing roller  13  contacting the heating roller  12 . By turning an operation lever  16  mounted in the support frame  10 , the hinge frame  14  can be forcibly lowered or raised, thereby varying the compression of the spring  15 . Thus, the nip between the rollers  12  and  13  can be controlled. Therefore, in case of printing on a thick paper such as an envelope, a user can lift the operation lever  16  to lower the hinge frame  14 , as shown in  FIG. 1 . Accordingly, the nip between the rollers  12  and  13  is reduced, and the envelope is prevented from crumpling.  
         [0007]     When using a normal printing paper having a standard thickness such as A4 paper, the user lowers the operation lever  16  to lift the hinge frame  14 . Then, the nip between the rollers  12  and  13  increases.  
         [0008]     However, using a conventional structure as described, the fusing nip between the rollers by the pressure on the rollers can be set to only two degrees. Therefore, it is inconvenient to use since papers of various thickness cannot be accommodated.  
         [0009]     In addition, since the pressing roller is made of a silicone gum of a high coefficient of thermal expansion, or a foaming silicone gum, the shape of the pressing roller varies according to the degree of heat. Therefore, the fusing nip changes during a printing job. However, because the conventional fusing apparatus has only two modes for the fusing nip, the fusing apparatus can not adaptively cope with the various changes of the fusing nip. Further, when the pressure increases, the printing paper often crumples. In contrast, when the pressure decreases, the fusing performance is deteriorated.  
       SUMMARY OF THE INVENTION  
       [0010]     The present invention has been made to overcome the above-mentioned problems of the prior art. Accordingly, it is an aspect of the present invention to provide a fusing apparatus and method for an image forming apparatus, which has an improved structure so that a fusing nip between rollers can be maintained regularly.  
         [0011]     In order to achieve the above-described aspects of the present invention, there is provided a fusing apparatus and method for an image forming apparatus. The apparatus and method comprise a heating roller rotatably mounted in a support frame, a pressing roller for rotating in contact with the heating roller, and defining a predetermined nip area by contact with the heating roller, a hinge bracket mounted in the support frame, and supporting either the pressing roller or the heating roller so that either roller rotates in contact with the other roller, first and second elastic members facing each other with the hinge bracket interposed therebetween, and elastically pushing the hinge bracket respectively, and a guide member guiding movement of the hinge bracket while supporting the respective first and second elastic members, wherein the first and the second elastic members compress and expand reciprocally.  
         [0012]     One end of the hinge bracket is rotatably connected to the support frame, and the other end is movably connected to the guide member to rotatably support the pressing roller.  
         [0013]     The hinge bracket comprises a shaft hole corresponding to a hinge shaft at one end, and a guide hole at the opposite end in which a guide member is slidably disposed.  
         [0014]     The hinge bracket comprises an arcuate bearing part disposed between the shaft hole and the guide hole to rotatably support the pressing roller.  
         [0015]     The pressing roller is disposed above the heating roller, and the hinge bracket is disposed above the pressing roller and rotatably supports the pressing roller in contact with the heating roller.  
         [0016]     The first elastic member elastically pushes the hinge bracket down toward the heating roller, and the second elastic member elastically pushes the hinge bracket upward away from the heating roller.  
         [0017]     The guide member comprises a bolt fastened to the support frame through the guide hole.  
         [0018]     The first and the second elastic members are supported in a compressed state, while being disposed around the bolt with the guide hole positioned therebetween.  
         [0019]     The first and the second elastic members comprise compression coil springs, and have the same elastic force. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]     These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where:  
         [0021]      FIG. 1  is a diagram illustrating a conventional fusing apparatus of an image forming apparatus;  
         [0022]      FIG. 2  is a diagram illustrating a sectional view of a fusing apparatus of an image forming apparatus according to an embodiment of the present invention;  
         [0023]      FIG. 3  is a diagram illustrating a degree of freedom for a force operated on a hinge bracket of the fusing apparatus of  FIG. 2 ; and  
         [0024]      FIG. 4  is a diagram illustrating a sectional view of a pressing roller thermally expanded from a state of  FIG. 2 . 
     
    
       [0025]     Throughout the drawings, it should be noted that the same or similar elements are denoted by like reference numerals.  
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0026]     Embodiments of a fusing apparatus for an image forming apparatus according to embodiments of the present invention will now be described in detail with reference to the accompanying drawings.  
         [0027]     Referring to  FIG. 2 , a fusing apparatus of an image forming apparatus according to an embodiment of the present invention comprises a heating roller  30  rotatably mounted in a support frame  20 , a pressing roller  40  rotating in contact with the heating roller  30 , a hinge bracket  50  rotatably supporting the pressing roller  40 , first and second elastic members  61  and  63  facing each other with the hinge bracket  50  interposed therebetween, and a guide member  70 .  
         [0028]     A heater  31  is mounted in the heating roller  30 . The heating roller  30  rotates in contact with the pressing roller  40 , fusing an image onto a printing paper passing between the rollers  30  and  40  using a predetermined heat and pressure.  
         [0029]     The pressing roller  40  presses the heating roller  30  with a predetermined pressure, while rotating in contact with the heating roller  30 . The pressing roller  40  has a pressing layer  42  having a predetermined thickness wrapping a shaft  41 . The pressing layer  42  comprises a silicone gum or a foaming silicone gum, and can be thermally expanded by a heat caused by contact with the heating roller  30 .  
         [0030]     When the pressing roller  40  and the heating roller  30  contact each other, a fusing nip is formed between the rollers  30  and  40 . Fusing time, temperature and pressure of the printing paper passing through between the rollers  30  and  40  are determined according to width of the fusing nip.  
         [0031]     Therefore, for varying the fusing nip, the pressing roller  40  is mounted such that it can minutely move up and down on the support frame  20 . One of the pressing roller  40  and the heating roller  30  is rotated by a driving motor (not shown), and the other roller is passively rotated. Preferably, the heating roller  30  is rotated by the driving motor, and the pressing roller  40  is passively rotated. In another embodiment of the present invention, the pressing roller  40  can be rotated by the driving motor, and the heating roller can be passively rotated.  
         [0032]     The shaft  41  of the pressing roller  40 A is rotatably inserted on the bearing  43 . The bearing  43  is supported by the hinge bracket  50 .  
         [0033]     The hinge bracket  50  is rotatably mounted in the support frame  20  to support the pressing roller  40  so that the pressing roller  40  can rotate in contact with the heating roller  30 . The hinge bracket  50  has a shaft hole  52  corresponding to a hinge shaft  51  at one end, and a guide hole  53  at the opposite end, in which the guide member  70  is slidably disposed. The hinge bracket  50  comprises an arcuate bearing part  55 , which supports the bearing  43  of the pressing roller  40 . The bearing part  55  is formed between the shaft hole  52  and the guide hole  53 , that is, approximately in the middle of the hinge bracket  50 , and supports the pressing roller  40  downward. That is, being mounted at an upper part of the pressing roller  40 , the hinge bracket  50  presses the pressing roller  40  toward the heating roller  30  by its own weight.  
         [0034]     The first and the second elastic members  61  and  63  are disposed opposite to each other with respect to the hinge bracket  50  interposed therebetween. The elastic members  61 ,  63  are disposed in a substantially straight line, and preferably are compression coil springs which provide an elastic pressure to the hinge bracket  50  in opposite directions. The elastic members  61  and  63  are hereinafter referred to as first and second compression springs. In an embodiment of the present invention, the first and the second compression springs  61  and  63  are disposed to provide the elastic pressure to the end of the hinge bracket  50  which is farthest side from the hinge shaft  51 . The respective compression springs  61  and  63  are inserted and supported in the guide member  70 . The compression springs  61  and  63  have the same elastic force. Therefore, the elastic force of the compression springs  61  and  63  operating in opposite directions with respect to the hinge bracket  50  is the same.  
         [0035]     The guide member  70  may include a bolt which is screw-coupled with a support block  21  of the support frame  20 . The bolt is engaged with the support block  21 , passing through the guide hole  53  of the hinge bracket  50 , and guides a vertical movement of the hinge bracket  50 . The guide member  70  supports the compression springs  61  and  63  in compression. For this, a diameter of the bolt is smaller than a diameter of the guide hole  53 , and also smaller than an inner diameter of the compression springs  61  and  63 .  
         [0036]     According to the above structure, the first compression spring  61  disposed around the bolt on the upper part of the hinge bracket  50  pushes the hinge bracket  50  toward the heating roller  30 . The second compression spring  63  disposed around the bolt in a compressed state between the hinge bracket  50 . The support block  21  elastically pushes the hinge bracket  50  upward, that is, in a direction moving away from the heating roller  30 .  
         [0037]     The load and deflection of the hinge bracket  50  by the compression springs  61  and  63  can be set up as predetermined values.  
         [0038]     According to the above structure, when the fusing nip increases due to a thermal expansion of the pressing roller  40 , a pressure P on the hinge bracket  50  increases. Then, a compressive force F 1  increases as the first compression spring  61  is compressed. On the contrary, a compressive force F 2  decreases as the second compression spring  63  is expanded. As a result, the pressure between the pressing roller  40  and the heating roller  30  is maintained, and the fusing nip is appropriately adjusted to a normal width. The fusing nip can be uniformly maintained because the hinge bracket  50  compensates for the expansion of the pressing roller  40  by moving upward a predetermined distance.  
         [0039]      FIG. 3  shows a degree of freedom for a force operated on the hinge bracket of the fusing apparatus of the above structure.  
         [0040]     According to the degree of freedom, the sum of the force acting on the hinge bracket  50  along the y-axis is zero. The sum of the rotational moment M about a rotation of the hinge bracket  50  is also zero.  
         [0041]     More specifically, the degree of freedom of  FIG. 3  can be expressed by the following equations.  
         [0042]     Equation 1 
 
+↑Σ Fy =0 ; −F   1 + F   2 + P−R= 0 
 
         [0043]     Equation 2 
 
+ cccΣM= 0; ( F   1   −F   2 )× L   1   −P×L   2 =0 
 
∴ P= [( F   1   −F   2 )× L   1   ]/L   2  
 
 where, F 1  is a compressive force applied on the hinge bracket  50  by the first compression spring  61 , and F 2  is a force applied on the hinge bracket  50  by the second compression spring  63 . 
 
         [0045]     P is a load transmitted to the hinge bracket  50  through the bearing of the pressing roller  40  and the fusing nip between the pressing roller  40  and the heating roller  30 . R is a reaction force generated at a center of the rotation, that is, the hinge shaft  51  of the hinge bracket  50 .  
         [0046]     The forces F 1  and F 2  operated on the hinge bracket  50  by the first and the second compression springs  61  and  63  are calculated by Equation  3  which expresses relationship between the load applied to the springs  61  and  63  and the deflections which result.  
         [0047]     Equation 3 
 
δ=[(8  nD   3   /Gd   4 )]× P  
 
 where, δ is the compressive displacement, n is the number of turns, d is a wire diameter of a spring coil, D is a mean diameter of a spring coil, G is a shear modulus, and P is the compressive load[N(kgf)]. 
 
         [0049]     In the above structure, as the number of printing paper increases, the pressing roller  40  is thermally expanded by a high temperature. At this time, if the hinge bracket  50  is fixed in position, the pressure P would increase, subsequently increasing the fusing nip. If a thick paper such as an envelope is passed, the paper would crumple more often.  
         [0050]     The embodiments of the present invention resolve the problem mentioned above. Since the hinge bracket  50  is not fixed, but is rotatable about the hinge shaft  51 , when the compressive load[N(kgf)] P is changed, the hinge bracket  50  moves by the reciprocal compression and expansion of the first and the second compression springs  61  and  63 . Accordingly, the fusing nip can be maintained.  
         [0051]     In other words, if the pressure P becomes P+ΔP, the compressive force F 1  of the first compression spring  61  changes to F 1 +ΔF 1 , and the compressive force F 2  of the second compression spring  63  changes to F 2 -ΔF 2 .  
         [0052]     Specifically, if P=6 kgf, F 1 =5 kgf, L 1 =40 mm, and L 2 =20 mm before the pressing roller  40  expands, for instance, the fusing nip is 8 mm.  
         [0053]     After the pressing roller  40  expands, the above values change to P=8 kgf, F 1 =5.5 kgf, and F 2 =1.5 kgf. Accordingly, the fusing nip is maintained as 8 mm.  
         [0054]      FIG. 2  shows the pressing roller  40  before the thermal expansion. A height of the second spring  63 , that is, a height H1 between the hinge bracket  50  and the support block  21  increases to H2 after the pressing roller  40  expands as shown in  FIG. 4  because the compressive force F 1  increases as the pressure P increases, and therefore, the hinge bracket  50  is lifted as the second compression spring  63  expands such that the compressive force F 2  of the second spring  63  accordingly decreases. That is, since the hinge bracket  50  is lifted as much as the expansion of the pressing roller  40 , the fusing nip between the rollers  30  and  40  can be maintained.  
         [0055]     In contrast, when the pressing roller  40  is cooled and contracted, the pressure P decreases, and the compressive force F 1  of the first compression spring  61  decreases, while the compressive force F 2  of the second compression spring  63  increases. Thus, the fusing nip is maintained.  
         [0056]     The fusing nip of the conventional fusing apparatus varies according to the temperature of the pressing roller  40  during the printing job. According to an embodiment of the present invention, the fusing apparatus maintains the spacing of the fusing nip by adaptively varying the fusing nip according to the reciprocal deformation of the first and the second compression springs  61  and  63 .  
         [0057]     Meanwhile, although the present invention has been described above with reference to certain exemplary embodiments where the pressing roller  40  is disposed above the heating roller  30 . The embodiments are shown by way of example, and therefore, the positions of the rollers can be adequately changed to obtain better efficiency.  
         [0058]     With the fusing apparatus of the image forming apparatus according to the embodiments of the present invention, the spacing of the fusing nip can be maintained because the compressive force of the first and the second compression springs varies adaptively.  
         [0059]     Therefore, even when relatively thick paper such as an envelope is used as the printing paper, crumples on the printing paper can be prevented, and a high-quality printed image can be guaranteed.  
         [0060]     In addition, the fusing apparatus is able to handle printing papers of various thicknesses, by maintaining the fusing nip.  
         [0061]     While the invention has been shown and described with reference to certain embodiments thereof, it should be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.