Abstract:
A developing unit of an image forming apparatus which can maintain a regular developing gap without a separate pressing member. The developing unit comprises a photoconductive drum which is rotatable, a developing roller rotating in association with the photoconductive drum and attaching a toner to the photoconductive drum, a toner supplying roller for supplying the toner to the developing roller, a first support body for rotatably supporting the photoconductive drum, and an idle gear being mounted in the first support body so that the centers of the idle gear, the photoconductive drum and the developing roller are arranged to form a triangle. In such an arrangement, a force is created and exerted upon the rollers to determine a position of the developing roller with respect to the photoconductive drum.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority under 35 U.S.C. §119 to an application entitled “Developing Unit” filed in the Korean Intellectual Property Office on Jul. 14, 2003 and assigned Serial No. 2003-47913, the entire content of which is incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a developing unit of an image forming apparatus, and more particularly, to a non-contact type developing unit of an image forming apparatus using a single-component nonmagnetic toner.  
         [0004]     2. Description of the Related Art  
         [0005]     In a non-contact developing unit using a single-component nonmagnetic toner, it is typically required to maintain a regular gap (hereinafter, called ‘developing gap’) between a photoconductive drum and a developing roller. In addition, the developing roller is typically driven by a driving force transmitted from a photoconductive drum gear of the photoconductive drum to a developing roller gear of the developing roller. At this point, a developing gap irregularity is often caused by a repulsive force generated in a pressure angle α direction, as shown in FIGS.  1  to  3 . Such an irregular developing gap has a severe influence on the image quality, and therefore, close maintenance of the regular developing gap is required.  
         [0006]     One conventional way of maintaining the regular developing gap is by a developing unit as shown in  FIG. 1 .  
         [0007]     According to  FIG. 1 , an example of a conventional developing unit  1  comprises a photoconductive part  20  and a developing part  40 . The photoconductive part  20  includes a first support body  10 , an electrifying roller  11  provided in the first support body, a photoconductive drum  12 , a cleaning blade  13  and a waste toner tub  14 . The developing part  40  includes a second support body  30 , a developing roller  31  provided in the second support body  30 , a controlling blade  32 , a toner supplying roller  33  and a toner  34 . The developing unit  1  further comprises a positioning member  50  which is included in the developing part  40  and rotatably supported by the photoconductive part  20  to determine a position of the developing roller  31  with respect to the photoconductive drum  12 .  
         [0008]     The above-structured developing unit  1  develops an electrostatic latent image on the photoconductive drum  12  as described in greater detail below. A driving force is transmitted from a main body of the image forming apparatus to the photoconductive drum gear (not shown) of the photoconductive drum  12 , and transmitted from the photoconductive drum gear to the developing roller gear (not shown) of the developing roller  31 . Also, the driving force is transmitted to a gear (not shown) of the toner supplying roller  33  via an idle gear (not shown), and thereby the photoconductive drum  12 , the developing roller  31 , and the toner supplying roller  33  are rotatably driven. Thus the electrostatic latent image is developed.  
         [0009]     Here, in order to prevent the developing gap irregularity by the repulsive force generated in the pressure angle α occurring in the driving force transmitting process, the rotation point  51  of the positioning member  50  is placed on the pressure angle α vector, as shown in  FIG. 1 , thereby pressing the developing roller  31  to the photoconductive drum  12 .  
         [0010]     However, the conventional method of maintaining the developing gap by controlling only the rotation point  51  of the positioning member  50  has a difficulty in managing parts, since to function properly, the parts should be fabricated with high precision for providing the regular developing gap. In particular, a compact-sized developing unit is difficult to realize due to restrictions in determining the rotation point  51 .  
         [0011]      FIG. 2  is a sectional view illustrating another conventional method for maintaining the regular developing gap. In referring to the elements having the same structure and operation as shown in  FIG. 1 , the elements will be cited by the same reference numerals and detailed description thereof will be omitted.  
         [0012]     According to  FIG. 2 , in a developing unit  2 , a rotation point  51 A of a positioning member  50 A is placed in a predetermined range β and a moment  91  is applied to press the developing roller  31  against the photoconductive drum  12  using a separate pressing member (not shown) to prevent the developing gap irregularity from occurring by the repulsive force generated in the pressure angle α of the gear during the transmission of the driving force.  
         [0013]     The above conventional method maintains the regular developing gap of the developing roller  31  with respect to the photoconductive drum  12  by using the moment  91  obtained via a pressing member as well as controlling the rotation point  51 A of the positioning member  50 A. However, there are still problems, such as variation of a driving load according to toner quantity and usage. It is also difficult to plan for the pressing member considering both a tolerance of part size and assembly deviation. Therefore even in this approach, it is difficult to maintain a certain quality.  
         [0014]      FIG. 3  is a sectional view of a developing unit for illustrating yet another conventional method of maintaining the regular developing gap. Again, the elements of the same structure of  FIGS. 1 and 2  will be referred by the same reference numerals, and the description thereof are omitted.  
         [0015]     Referring to  FIG. 3 , in a developing unit  3 , a positioning member  50 B is provided in a gravity-direction positioning member  15  which is mounted in the first support body  10  of the photoconductive part  20  to determine a first gravity-direction position. A member  60  is mounted in the main body of the image forming apparatus to determine a second gravity-direction position of the developing part  40 .  
         [0016]     In the above developing unit  3 , to prevent the developing gap irregularity due to the repulsive force generated in a direction of the pressure angle α of the gear, positions of the positioning member  50 B and the developing roller  31  are determined during transfer of the driving force. Specifically, the position of the positioning member  50 B for determining the first gravity-direction position of the developing part  40  from the gravity-direction positioning member  15 , and the developing roller  31  with respect to the photoconductive drum  12  to the second gravity-direction positioning member  60 , are both determined during transfer of the driving force. Then, the moment  92  is applied to press the developing roller  31  against the photoconductive drum  12  using the separate pressing member (not shown).  
         [0017]     However, the above method for maintaining the regular developing gap has similar problems as the developing unit  2  of  FIG. 2 , that is, it is difficult to design the pressing member while considering the variations of a driving load according to quantity and usage of the toner  34 , including both parts size deviation and an assembly deviation. It is also hard to maintain quality of the pressing member at a certain level.  
         [0018]     Accordingly, a need exists for a non-contact type developing unit of an image forming apparatus using a simple component to address the problems described above.  
       SUMMARY OF THE INVENTION  
       [0019]     It is, therefore, an object of the present invention to overcome the above-mentioned problems of the prior art. An aspect of the present invention is to provide a developing unit capable of maintaining a regular developing gap without requiring a separate pressing member.  
         [0020]     Another aspect of the present invention is to provide a compact-sized developing unit.  
         [0021]     In order to achieve the above-described aspects of the present invention, a developing unit is provided comprising a photoconductive drum, a developing roller, a toner supplying roller, a first support body, and an idle gear.  
         [0022]     The photoconductive drum is rotatable. The developing roller rotates in association with the photoconductive drum and attaches a toner to the photoconductive drum. The toner supplying roller supplies the toner to the developing roller. The first support body rotatably supports the photoconductive drum and the idle gear is also mounted in the first support body so that the centers of the idle gear, the photoconductive drum and the developing roller are arranged to form a triangle, so that a rotation driving force of the developing roller is transmitted to the toner supplying roller.  
         [0023]     Accordingly, as a photoconductive drum gear, a developing roller gear, and the idle gear are driven, the centers of which are also arranged to form a triangle, the developing roller is applied with a force directed toward the photoconductive drum, and is thereby pressed against the photoconductive drum without requiring a pressing member.  
         [0024]     According to a first embodiment of the present invention, the developing unit comprises a second support body for rotatably supporting the developing roller, and a positioning member is mounted in the second support body to determine a position of the developing roller with respect to the photoconductive drum and with an end thereof rotatably supported by the first support body. The rotation center of the positioning member is on a line labeled “G” connecting the centers of the idle gear and the developing roller.  
         [0025]     Also in the first embodiment of the present invention, the second support body includes a developing chamber and a toner receptacle which are separate from each other. The toner receptacle is fixed to the first support body, and the developing chamber is rotatably supported in the first support body by the position determining member.  
         [0026]     Further, according to first embodiment of the present invention, the developing unit comprises a gap maintaining member for maintaining a distance between axes of the photoconductive drum and the developing roller.  
         [0027]     The gap maintaining member comprises a gap maintaining block in the first support body to support an axis of the developing roller at a side of the axis. Alternatively, the gap maintaining member may comprise a gap maintaining ring at one end or both ends of the developing roller in contact with the outer circumference of the photoconductive drum.  
         [0028]     Additionally, the developing unit comprises a gravity-direction positioning member for determining a gravity-direction position of the second support body.  
         [0029]     The gravity-direction positioning member comprises a first member mounted in the first support body to support an axis of the developing roller at a lower part thereof, and a second member mounted in the main body of the image forming apparatus to support the second support body. Here, the first member is an axis support block, and the second member is a roller.  
         [0030]     According to a second embodiment of the present invention, a developing unit comprises a photoconductive drum which is rotatable, a developing roller rotating in association with the photoconductive drum and attaching a toner to the photoconductive drum, a toner supplying roller for supplying the toner to the developing roller, a first support body for rotatably supporting the photoconductive drum, a second support body for rotatably supporting the developing roller, a third support body mounted on both sides of the first and the second support bodies, respectively, to connect the first and the second support bodies, and an idle gear mounted in the third support body so that centers of the idle gear, the photoconductive drum and the developing roller are arranged to form a triangle. In such an arrangement, a rotation driving force of the developing roller is transmitted to the toner supplying roller.  
         [0031]     Further, the developing unit according to the embodiments of the present invention comprises a positioning member being supported in the second support body with an end thereof being rotatably supported by the third support body to determine a position of the developing roller with respect to the photoconductive drum. A rotation center of the positioning member is on a line G connecting centers of the idle gear and the developing roller. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0032]     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:  
         [0033]      FIG. 1  is a sectional view of an exemplary conventional developing unit;  
         [0034]      FIG. 2  is a sectional view of another exemplary conventional developing unit;  
         [0035]      FIG. 3  is a sectional view of yet another exemplary conventional developing unit;  
         [0036]      FIG. 4  is a sectional view of an example developing unit according to a first embodiment of the present invention;  
         [0037]      FIG. 5  is a sectional view of an example developing unit according to a second embodiment of the present invention;  
         [0038]      FIG. 6  is a sectional view of an example developing unit according to a third embodiment of the present invention;  
         [0039]      FIG. 7  is a sectional view of an example developing unit according to a fourth embodiment of the present invention;  
         [0040]      FIG. 8  is a schematic view of an example photoconductive part showing the arrangement of an idle gear which is a main element of the embodiment of the present invention of  FIGS. 4 through 7 ;  
         [0041]     FIGS.  9  to  12  are drawings for illustrating a principle for maintaining a regular developing gap of the developing unit according to the embodiments of the present invention;  
         [0042]      FIG. 13  is a sectional view of an example developing unit according to a fifth embodiment of the present invention; and  
         [0043]      FIG. 14  is an exploded perspective view of a third support body of the developing unit of  FIG. 13 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0044]     Hereinafter, preferred embodiments of a developing unit according to the present invention will be described in detail with reference to the accompanying drawings.  
         [0045]      FIG. 4  is a sectional view of an example developing unit according to a first embodiment of the present invention, and  FIG. 8  is a schematic view of a photoconductive part. A reference numeral  100  refers to a photoconductive part,  200  is a developing part, and  300  is a position determining member.  
         [0046]     As shown in  FIGS. 4 and 8 , the photoconductive part  100  comprises a first support body  110 , an electrifying roller  120  provided in the first support body, a photoconductive drum  130 , a cleaning blade  140  and a waste toner tub  150 .  
         [0047]     The photoconductive drum  130  is rotatably mounted in the first support body  110  by an axis  131  in the center thereof. Also, the photoconductive drum  130  comprises a photoconductive drum gear  132  for transmitting the rotation driving force to a developing roller  220  which is described in greater detail below.  
         [0048]     Further, according to the present invention, an idle gear  160  is rotatably mounted at a predetermined position in the first support body  110  by an axis  161 . Regarding this, a detailed description is provided below.  
         [0049]     The developing part  200  comprises a second support body  210 , a developing roller  220  provided in the second support body  210 , a controlling blade  230 , a toner supplying roller  240 , and a toner  250 .  
         [0050]     The developing roller  220  is rotatably mounted in the second support body  210  by an axis  221  in the center thereof. In addition, the developing roller  220  comprises a developing roller gear  222  engaged with the photoconductive drum gear  132 , and attaches the toner  250  to the photoconductive drum  130  when rotating in association with the photoconductive drum  130 . Further, the developing roller  220  comprises a gap maintaining ring  223  mounted at one end or both ends of the developing roller  220  and contacting an outer circumference of the photoconductive drum  130 . The gap maintaining ring  223  functions as a gap maintaining member for maintaining a distance between axes of the developing roller  220  and the photoconductive drum  130 .  
         [0051]     The toner supplying roller  240  supplies the toner  250  to the developing roller  220 , and is rotatably mounted in the second support body  210  by an axis  241  in the center thereof. Additionally, the toner supplying roller  240  comprises a passive gear  242  engaged with the idle gear  160 .  
         [0052]     The idle gear  160 , added according to one aspect of the present invention, is engaged with the developing gear  222  and the passive gear  242 , and thereby, the rotation driving force of the photoconductive drum  130  is transmitted to the passive gear  242  through the developing roller gear  222  and the idle gear  160 . Here, the idle gear  160  is disposed at a predetermined position in the first support body  110  so that a center thereof  01 , a center  02  of the photoconductive drum gear  132 , and a center  03  of the developing roller gear  222 , are arranged to make up a triangle as shown in  FIG. 9 .  
         [0053]     According to the triangular arrangement of the three gears, a force labeled “F” of  FIG. 9  is generated as the gears drive. Therefore, the developing roller  220  is stably pressed against the photoconductive drum  130  without having to use a pressing member as in the conventional developing unit. Referring to FIGS.  10  to  12 , the above triangle structure is described in detail.  
         [0054]     Referring to  FIG. 10 , when the photoconductive drum gear  132  drives the developing roller gear  222 , a force labeled “F 1 ” is generated in a direction of the pressure angle α of the gear, and thereby the developing roller  220  is pushed from the photoconductive drum  130 . Also, as shown in  FIG. 11 , a force labeled “F 2 ” is generated in a direction of the pressure angle α when the developing roller gear  222  drives the idle gear  160 . Here, if the idle gear  160  is mounted firmly, the developing roller gear  222  is again pushed toward the photoconductive drum  130  by a reaction force labeled “F 2   t ” of F 2  as shown in  FIG. 12 . Accordingly, by the association of the two forces F 1  and F 2   t  of  FIG. 12 , the developing roller gear  222  is stably pressed against the photoconductive drum  130  by the force F, as shown in  FIG. 9 .  
         [0055]     Returning to  FIG. 4 , the positioning member  300  connects the first and the second support bodies  110  and  210 , and supports the second support body  210  rotatably with respect to the first support body  110  to press the developing roller  220  against the photoconductive drum  130 . By this, the position of the developing roller  220  with respect to the photoconductive drum  130  can be kept regular. At this point, the positioning member  300  is mounted in the second support body  210 , and the end thereof is supported by the first support body  110  by a hinge. Here, the center of the hinging movement of the positioning member  300 , that is, the rotation center  310 , lies in a line G which connects the centers of the idle gear  160  and the developing roller  220 .  
         [0056]      FIG. 5  is a sectional view of an example developing unit according to a second embodiment of the present invention. Referring to  FIG. 5 , the developing unit is similarly structured to the first embodiment except wherein the second support body  210 A, which constitutes the developing part  200 , is divided into a developing chamber  211  and a toner receptacle  212 . The toner receptacle  212  is fixed to the first support body  110  in a manner that an upper and a lower fastener pieces  212   a  and  212   b  are fastened by a fastening element of corresponding parts of the first support body  110  which constitutes the photosensitive part  100 . The developing chamber  211  is rotatably mounted on the line G of the first support body  110  by the positioning member  300 . The structure and the operation of the other elements are the same as described in the first embodiment, and therefore, description thereof will be omitted.  
         [0057]      FIG. 6  shows an example developing unit according to a third embodiment of the present invention. As shown in  FIG. 6 , the developing unit according to the third embodiment comprises a gap maintaining block  223 A as a gap maintaining member for maintaining a distance between axes of the developing roller  220  with respect to the photoconductive drum  130 . The gap maintaining block  223 A is formed in the first support body  110  to support a side of an axis  221  of the developing roller  220 . The other structure is the same as the first embodiment. Therefore, the same elements will be referred by the same numeral references and the description thereof will be omitted.  
         [0058]      FIG. 7  is an example developing unit according to the fourth embodiment of the present invention. The developing unit of  FIG. 7  comprises a gravity-direction positioning member  400  for determining a gravity-direction position of the second support body  210  which constitutes the developing part  200 . The remaining components of the fourth embodiment have the same structure as the above-described first embodiment, and accordingly, a description will be given hereinafter only regarding the gravity-direction positioning member  400 .  
         [0059]     The gravity-direction positioning member  400  comprises an axis support block  410  as a first member which is mounted in the first support body  110  which constitutes the photoconductive part  100  to support the axis  221  at a lower part of the axis  221  of the developing roller  220 . The gravity-direction positioning member  400  further comprises a roller  420  as a second member which is mounted in the main body of the image forming apparatus to support the second support body  210 . In this embodiment, in a state where a first gravity-direction position of the developing part  200  is determined by the axis support block  410  and the positioning member  300 , and a second gravity-direction position is determined by the roller  420 , the developing roller  220  is pressed against the photoconductive drum  130  by the force F. As noted above, the force F is generated during the transfer of driving forces among the photoconductive drum gear  132 , the developing roller gear  222  and the idle gear  160 . As a result, a stable and regular developing gap can be guaranteed.  
         [0060]      FIGS. 13 and 14  show a sectional view and a perspective view of an example developing unit according to the fifth embodiment of the present invention, respectively.  
         [0061]     As shown in  FIGS. 13 and 14 , the features of the developing unit according to the fifth embodiment, comprise third support bodies  500  and  500 A for connecting the first support body  110 , rotatably supporting the photoconductive drum  130 , with the second support body  210 , rotatably supporting the developing roller  220 . The idle gear  160  is mounted in the third support bodies  500  and  500 A.  
         [0062]     The idle gear  160  is arranged so that the centers of the idle gear  160 , the photoconductive drum  130 , and the developing roller  220  form a triangle, as described above in the other embodiments. The idle gear  160  functions to transmit the rotation driving force of the developing roller  220  to the toner supplying roller  240 .  
         [0063]     In addition, the positioning member  300  is provided for determining the position of the developing roller  220  with respect to photoconductive drum  130 . The positioning member  300  is mounted in the second support body  210 , with an end thereof rotatably supported by the third support bodies  500  and  500 A. The rotation center  310  of the positioning member  300  is on the line G connecting the centers of the idle gear  160  and the developing roller  220 .  
         [0064]     Accordingly, the third support bodies  500  and  500 A further comprise a hinge  510  for rotatably supporting the positioning member  300 , and a drum supporting portion  520  for supporting the axis  131  of the photoconductive drum  130  as shown in  FIG. 14 .  
         [0065]     The structure and the operation of the other elements are substantially the same as the other embodiments described above, and therefore, a detailed description thereof is omitted.  
         [0066]     As described above, the developing unit according to the present invention is capable of stably maintaining a regular developing gap without requiring a pressing member, and can be manufactured having a compact size since the center of rotation of the positioning member can be set up within a relatively wide range.  
         [0067]     That is, according to the embodiments of the present invention, there can be provided an image forming apparatus maintaining a regular developing gap without requiring a pressing member, thereby providing a good-quality image in a simple structure.  
         [0068]     Additionally, since the image forming apparatus can be of a compact size, the handling and maintenance becomes convenient, and accordingly, the product can be very satisfying to the users.  
         [0069]     While the invention has been shown and described with reference to certain preferred embodiments thereof, it will 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.