Patent Publication Number: US-6044237-A

Title: Developing apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a developing apparatus used in an image forming apparatus of electrophotographic or electrostatic recording type as a copying machine, a printer and the like and adapted to develop an electrostatic latent image on an image bearing member. 
     2. Related Background Art 
     In image forming apparatuses of electrophotographic or electrostatic recording type, an electrostatic latent image on an image bearing member has been developed by a developing apparatus containing a developing agent. 
     In the past, as shown in FIG. 14A, in order to prevent magnetic toner from leaking through a gap between a developing frame 12 containing the magnetic toner and a developing roller 9c for supplying the magnetic toner contained in the developing frame 12 to an electrophotographic photosensitive drum, as a sealing means for sealing gaps between the developing frame 12 and the developing roller 9c at both longitudinal ends of the developing roller 9c, elastic members 51 made of felt, rubber or the like have been used. 
     At a lower part of the developing roller 9c, sealing has been effected by abutting a sheet member 52 provided on the developing frame 12 against the lower part of the developing roller 9c along a longitudinal direction of the developing roller. Further, both longitudinal ends of the sheet member 52 have been pinched between the elastic members 51 and the developing roller 9c to prevent the magnetic toner from leaking through both longitudinal ends. 
     Alternatively, as shown in FIG. 14B, at both longitudinal ends of the developing roller 9c, sealing (for magnetic toner) has been effected by magnetic forces of magnets 63 disposed around peripheral surfaces of the both longitudinal ends of the developing roller 9c with small gaps &#34;g&#34; therebetween. 
     However, in the above-mentioned examples, as shown in FIG. 14A, when the elastic members 51 made of felt, rubber or the like are used as the sealing means between both longitudinal ends of the developing roller 9c and developing frame 12, since the both longitudinal ends of the sheet member 52 are pinched between the elastic members 51 and the developing roller 9c, both longitudinal ends of sheet member 52 abut against both longitudinal ends of the developing roller 9c without any gap. Thus, there is an advantage that the magnetic toner can surely be prevented from leaking through both longitudinal ends, but, in such an arrangement, an assembling operation is troublesome, and, since both longitudinal ends of the developing roller 9c are elastically urged by the elastic members 51, when the developing roller 9c is rotated, great load is generated to increase the rotational torque of the developing roller 9c. 
     On the other hand, as shown in FIG. 14B, when the magnets 63 are used as the sealing means between the both longitudinal ends of the developing roller 9c and the developing frame 12, since the magnets 63 do not abut against the developing roller 9c, the assembling operation becomes easy and the rotational torque of the developing roller 9c can be reduced. However, since there are small gaps g between the developing roller 9c and the magnets 63, the magnetic toner remains at opposed portions between the both longitudinal ends of the developing roller 9c and the magnets 63, with the result that the magnetic toner may be accumulated on the ends of the sheet member 52 abutting against the lower part of the developing roller 9c. In such a case, as shown in FIG. 14B, the accumulated magnetic toner forcibly urges the sheet member 52 downwardly to form gaps &#34;h&#34; between the developing roller 9c and the sheet member 52, with the result that the magnetic toner may leak through the gaps h. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a developing apparatus in which magnetic end sealing can be effected. 
     Another object of the present invention is to provide a developing apparatus in which a developing agent can be prevented from leaking through a gap between a developing agent bearing member and a developing container. 
     A further object of the present invention is to provide a developing apparatus comprising a developing container for containing a magnetic developing agent, a developing agent bearing member provided on an opening portion of the developing container and adapted to bear and convey the magnetic developing agent, a sheet member elastically biased against the developing agent bearing member along a longitudinal direction of the developing agent bearing member to close a gap between the developing agent bearing member and the developing container, a magnetic sealing member provided at an end of the developing agent bearing member with a gap between to form a magnetic seal, and an elastic member for urging the sheet member toward the developing agent bearing member. 
     The other objects and features of the present invention will be apparent from the following detailed explanation of the invention referring to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of an image forming apparatus according to the present invention; 
     FIG. 2 is an explanatory sectional view showing a construction of the image forming apparatus according to the present invention; 
     FIG. 3 is an explanatory sectional view showing a process cartridge according to the present invention; 
     FIG. 4 is a partial enlarged view showing a developing apparatus according to a first embodiment of the present invention; 
     FIG. 5 is a perspective view showing a developing roller and magnetic sealing members; 
     FIG. 6 is a front view of the developing apparatus according to the first embodiment of the present invention; 
     FIG. 7 is a partial enlarged view showing the developing apparatus according to the first embodiment of the present invention; 
     FIG. 8 is a partial enlarged view showing a developing apparatus according to a second embodiment of the present invention; 
     FIG. 9 is a front view of the developing apparatus according to the second embodiment of the present invention; 
     FIG. 10 is a partial enlarged view showing the developing apparatus according to the second embodiment of the present invention; 
     FIG. 11 is a partial enlarged view showing a developing apparatus according to a third embodiment of the present invention; 
     FIG. 12 is a front view of the developing apparatus according to the third embodiment of the present invention; 
     FIG. 13 is a partial enlarged view showing the developing apparatus according to the third embodiment of the present invention; and 
     FIGS. 14A and 14B are views for explaining problems generated at ends of a developing apparatus. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The present invention will now be explained in connection with embodiments thereof with reference to the accompanying drawings. 
     FIG. 1 is a perspective view of an image forming apparatus using a developing apparatus according to the present invention, FIG. 2 is a sectional view of the apparatus shown in FIG. 1, FIG. 3 is a sectional view of a process cartridge which can detachably be mounted to the apparatus shown in FIGS. 1 and 2, FIG. 4 is a partial enlarged sectional view of a developing apparatus according to an embodiment of the present invention, FIG. 5 is a partial perspective view of the developing apparatus of FIG. 4, FIG. 6 is a front view of the developing apparatus of FIG. 4, and FIG. 7 is a partial enlarged view of the developing apparatus of FIG. 4, looked at from the above. 
     In FIGS. 1 and 2, an image forming apparatus A serves to form an image on a recording medium 2 (made of paper sheet, synthetic resin or cloth) by using an electrophotographic image forming process. A toner image is formed on an electrophotographic photosensitive drum 7. 
     More specifically, after a surface of the photosensitive drum 7 is charged by a charge roller (charge means) 8, a laser beam corresponding to image information and emitted from an optical system (optical means) 1 is illuminated onto the photosensitive drum 7, thereby forming an electrostatic latent image corresponding to the image information. 
     The electrostatic latent image is developed by a developing means 9 to form a toner image. In synchronism with the formation of the toner image, the recording medium 2 is supplied from a sheet supply cassette 3a by means of a pick-up roller 3b, pairs of convey rollers 3c, 3d and a pair of regist rollers 3e in a reversing fashion. 
     Then, the toner image formed on the photosensitive drum 7 contained within a process cartridge B is transferred onto the recording medium 2 by applying voltage to a transfer roller (transfer means) 4. Thereafter, the recording medium 2 to which the toner image was transferred is sent to a fixing means 5 through a convey guide 3f. The fixing means 5 comprises a drive roller 5c and a fixing roller 5b containing a heater 5a therein. By applying heat and pressure to the recording medium 2 passing through the fixing means, the transferred toner image is permanently fixed to the recording medium. 
     Then, the recording medium 2 is conveyed by pairs of discharge rollers 3g, 3h, 3i through a reverse path 3j to discharge the recording medium 2 onto a discharge tray 6 in a face-down fashion. The discharge tray 6 is formed on an upper surface of the image forming apparatus A. Incidentally, by driving a rockable flapper 3k, the recording medium 2 can be discharged out of the apparatus by means of a pair of discharge rollers 3m in a face-up fashion without passing through the reverse path 3j. 
     In the illustrated embodiment, the pick-up roller 3b, pairs of convey rollers 3c, 3d, pair of regist rollers 3e, convey guide 3f, pair of discharge rollers 3g, 3h, 3i and pair of discharge rollers 3m constitute a convey means 3. 
     On the other hand, as shown in FIG. 3, in the process cartridge B, while the photosensitive drum 7 provided at its surface with a photosensitive layer is being rotated, the surface of the photosensitive drum is uniformly charged by applying a voltage to the charge roller 8 contacted with the photosensitive drum 7. Incidentally, the charge roller 8 is rotatingly driven by rotation of the photosensitive drum 7. 
     Then, the laser beam corresponding to the image information and emitted from the optical system 1 is illuminated onto the photosensitive drum 7 through an exposure opening 1e to form the electrostatic latent image. Incidentally, the optical system 1 includes a laser diode 1a, a polygon mirror 1b, a lens 1c and a reflection mirror 1d. 
     The electrostatic latent image is developed by the developing means 9 with magnetic toner. The developing means 9 serves to develop the electrostatic latent image formed on the photosensitive drum 7 by supplying the magnetic toner to a developing area of the photosensitive drum 7. 
     In the developing means 9, the magnetic toner contained within a toner container 11a is sent to a developing roller 9c by rotating a toner feed member 9b. By rotating the developing roller 9c containing a fixed magnet therein and by applying frictional charges to the toner by means of a developing blade 9d, a magnetic toner layer is formed on the developing roller 9c, thereby supplying the magnetic toner to the developing area of the photosensitive drum 7. 
     By transferring the magnetic toner onto the electrostatic latent image on the photosensitive drum 7, the electrostatic latent image is visualized as the toner image. The developing blade 9d serves to regulate an amount of the magnetic toner around the developing roller 9c and to apply the frictional charges to the toner. A toner agitating member 9e for circulating the magnetic toner within a developing chamber is disposed in the vicinity of the developing roller 9c. 
     After the toner image formed on the photosensitive drum 7 is transferred to the recording medium 2 by applying voltage having polarity opposite to that of the toner image to the transfer roller 4, residual toner remaining on the photosensitive drum 7 is removed by a cleaning means 10. In the cleaning means 10, the residual toner remaining on the photosensitive drum 7 is scraped by an elastic cleaning blade 10a and the scraped toner is collected into a waste toner reservoir 10b. 
     The process cartridge B is formed by joining a toner frame 11 having the toner container 11a containing the magnetic toner to the developing frame 12 for holding the developing means 9 such as the developing roller 9c and the like and by joining a cleaning frame 13 (to which the photosensitive drum 7, the cleaning means 10 such as the elastic cleaning blade 10a and the like and the charge roller 8 are attached) to the joined frames 11, 12. The process cartridge B can detachably be mounted to the image forming apparatus A by the operator. 
     The process cartridge B is provided with the exposure opening 1e through which the laser beam corresponding to the image information is illuminated onto the photosensitive drum 7 and a transfer opening 13a through which the photosensitive drum 7 is opposed to the recording medium 2. More specifically, the exposure opening 1e is formed in the cleaning frame 13 and the transfer opening 13a is formed between the developing frame 12 and the cleaning frame 13. 
     Next, a first embodiment of the magnetic toner sealing means around the developing roller 9c will be fully explained with reference to FIGS. 4 to 7. In FIGS. 4 to 7, magnetic seal members 14 for preventing the magnetic toner from leaking through both longitudinal ends of developing roller 9c are provided at the both longitudinal ends of the developing roller. Each magnetic seal member 14 is attached to the developing frame 12 with a small gap g between the seal member and the peripheral surface of the developing roller 9c. 
     Further, each magnetic seal member 14 is formed by joining a magnetic plate (magnetic member) 14b to an outer surface of a magnet 14a along the longitudinal direction of the developing roller 9c. 
     Now, explaining each magnetic seal member 14 in more detail, in each magnetic seal member 14, the magnet 14a (one of constructural elements) is formed from an injection-molded part having a width of 3 to 4 mm and having nylon binder including magnetic powder of Nd-Fe-B, and the magnetic plate 14b (the other constructural element) is formed from iron material having a thickness of 1 mm. 
     The magnetic plate 14b is joined to the magnet 14a by insert molding. However, the magnetic plate may be joined to the magnet by a both-face adhesive tape or a magnetic force alone. The small gap &#34;g&#34; between the developing roller 9c and the magnetic seal member 14 is 0.1 to 0.9 mm. In this case, magnetic flux density of the surface of the developing roller 9c given by the magnetic force of the magnetic seal member 14 is about 1000 to 2000 Gauss (Gs). 
     Regarding a positional relation between the magnet 14a and the magnetic plate 14b of the magnetic seal member 14, the magnet 14a is disposed inside along the longitudinal direction of the developing roller 9c, and the magnetic plate 14b is disposed outside of the magnet. 
     As another sealing means, an elastic sheet 15 made of sheet material such as PET (polyethylene terephthalate) or urethane is attached to the developing frame 12 along the longitudinal direction of the developing roller 9c and is urged against a lower part of the developing roller 9c by its own elasticity. 
     Both longitudinal ends of the elastic sheet 15 are overlapped with the magnetic seal members 14 along the longitudinal direction of the developing roller 9c so that both ends of the elastic sheet 15 are positioned within the small gaps g between the magnetic seal members 14 and the developing roller 9c. 
     In a longitudinal direction of the developing frame 12, rubber sponge members (elastic members) 16 for aiding abutment between the elastic sheet 15 and the developing roller 9c are provided on the developing frame 12 below the elastic sheet 15 and inside of the magnetic seal members 14. Each rubber sponge member 16 is formed from soft urethane foam having 30 to 150 cells/25 mm and having a thickness of 3 to 7 mm. In a condition that the developing roller 9c is attached to the developing frame 12, the rubber sponge members 16 are compressed by an amount of 0 to 4 mm. 
     With the arrangement as mentioned above, both longitudinal ends of the elastic sheet 15 are always urged against the developing roller 9c by the rubber sponge members 16. Thus, even when the magnetic seal members 14 (not contacted with the developing roller) effective as the magnetic toner sealing means for the ends of the developing roller 9c are used, both longitudinal ends of the elastic sheet 15 are stably urged against the developing roller 9c without separating from the developing roller by the magnetic toner existing within the small gap &#34;g&#34; between the magnetic seal members 14 and the developing roller 9c, thereby preventing the leakage of the magnetic toner. 
     Next, a second embodiment of the present invention will be explained with reference to FIGS. 8 to 10. FIG. 8 is a partial enlarged view showing a developing apparatus according to the second embodiment of the present invention, FIG. 9 is a front view of the developing apparatus according to the second embodiment of the present invention, and FIG. 10 is a partial enlarged view showing the developing apparatus according to the second embodiment of the present invention. Incidentally, elements the same as those in the first embodiment are designated by the same reference numerals and explanation thereof will be omitted. 
     In the second embodiment, in a longitudinal direction of the developing frame 12, elastic sheet members (elastic members) 21 for aiding abutment between the elastic sheet 15 and the developing roller 9c are provided on the developing frame 12 below the elastic sheet 15 and inside of the magnetic seal members 14. The elastic sheet members are formed from PET (polyethylene terephthalate), urethane rubber, stainless steel or bronze phosphide. 
     With this arrangement, both longitudinal ends of the elastic sheet 15 are always urged against the developing roller 9c by the elastic sheet members 21. Thus, even when the magnetic seal members 14 (not contacted with the developing roller) effective as the magnetic toner sealing means for the ends of the developing roller 9c are used, both longitudinal ends of the elastic sheet 15 are stably urged against the developing roller 9c without separating from the developing roller by the magnetic toner existing within the small gaps &#34;g&#34; between the magnetic seal members 14 and the developing roller 9c, thereby preventing the leakage of the magnetic toner. 
     Next, a third embodiment of the present invention will be explained with reference to FIGS. 11 to 13. FIG. 11 is a partial enlarged view showing a developing apparatus according to the third embodiment of the present invention, FIG. 12 is a front view of the developing apparatus according to the third embodiment of the present invention, and FIG. 13 is a partial enlarged view showing the developing apparatus according to the third embodiment of the present invention. Incidentally, elements the same as those in the first embodiment are designated by the same reference numerals and explanation thereof will be omitted. 
     In the third embodiment, in a longitudinal direction of the developing frame 12, rubber sponge members (elastic members) 31 for aiding abutment between the elastic sheet 15 and the developing roller 9c are provided on the developing frame 12 below the elastic sheet 15 and within the magnetic seal members 14. The rubber sponge members 31 are made of the same material as those of the rubber sponge members 16 in the first embodiment. 
     With this arrangement, both longitudinal ends of the elastic sheet 15 are always urged against the developing roller 9c by the rubber sponge members 31. Thus, even when the magnetic seal members 14 (not contacted with the developing roller) effective as the magnetic toner sealing means for the ends of the developing roller 9c are used, the both longitudinal ends of the elastic sheet 15 are stably urged against the developing roller 9c without separating from the developing roller by the magnetic toner existing within the small gaps &#34;g&#34; between the magnetic seal members 14 and the developing roller 9c, thereby preventing the leakage of the magnetic toner. 
     While the present invention was explained with reference to the illustrated embodiments, the present invention is not limited to such embodiments, but, various alterations and modifications can be made within the scope of the invention.