Device for feeding developing powder in an image forming apparatus

Abstract: A device for feeding developing powder is intended to be mounted to an image forming apparatus and is constructed to have a feeding bath (20) and a carrying mechanism (21). The feeding bath is mounted to one side of a developing bath (2). The carrying mechanism serves to carry the developing powder guided from one side of the developing bath to the other side. The carrying mechanism (21) is constructed to have a carrying screw (22) and a stirring member (23). The carrying screw is actuated for carrying the developing powder longitudinally from one side to the other side. The stirring member serves to feed the developing powder circumeferentially.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for uniformly feeding developing powder in a developing unit provided in an image forming apparatus of an electronic photography type. 2. Description of the Related Art The inventor of the present application knows a developing unit provided in an image forming apparatus, which unit is constructed to have a developing bath provided with a magnet roller, a stirring roller, an agitator, a flow plate, a toner density sensor and a doctor, and a toner hopper mounted on the developing bath and provided with a toner feeding roller and toner carrying screws. In the known developing unit, to charge the developing powder in the developing bath, the toner hopper is removed from the developing bath so as to make an opening of the developing bath exposed toward the outside. Then, the developing powder is supplied into the developing powder through the opening from a sac or bottle storing the developing powder. At this time, the sac or bottle is horizontally moved above the opening so that the developing powder is uniformly fed into the developing bath. In this construction, however, to exchange the developing powder, it is necessary to take the operations of removing the toner hopper from the developing bath and directing the developing bath reversely for exhausting the waste developing powder. Those operations result in soiling the user's hands. When feeding the developing powder, the developing powder is required to uniformly and longitudinally drop to the developing bath through the opening. As a technique for longitudinally and uniformly dropping the developing powder, there is known a construction wherein a developing powder feeder and a developing powder cartridge of the same longitudinal length as the width of the developing unit are provided above the developing unit and the developing powder is allowed to be fed longitudinally by opening the shutter of the feeder. The above known construction, however, requires the main body of an image forming apparatus to have an area for mounting the cartridge for storing new developing powder. This results in changing the dispositions of the other components, thereby making the main body of the image forming apparatus bulkier. Dokument GB-A-2 199 265 discloses a developing device for an image forming apparatus, comprising a carrying means, disposed in the developing unit, for carrying the developing powder fed from a first side to a second side in the longitudinal direction of the carrying means on which second side it is removed by a stirring member. The purpose thereof is to prevent accumulations of the developing powder at the second side. The developing powder recovered from a developing roller and conveyed by a separator and a guideplate is fed to said first side of the carrying means. SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a developing powder feeding device which is capable of uniformly feeding developing powder in a developing unit along a longitudinal length without having to take large space in the main body of an the image forming apparatus. The object of the invention is accomplished by a developing unit provided in an image forming apparatus having a cylindrical photoreceptor on which a latent image is to be formed and extending parallel to and closely adjacent to the photoreceptor for supplying developing powder onto the photoreceptor to develop the latent image, said developing unit having a first side and a second side in a longitudinal direction thereof, comprising: a feeding unit for feeding fresh developing powder into the developing unit from outside of the first side of the developing unit; a carrying means disposed in said developing unit for carrying said developing powder in said developing unit so as to keep a level of the developing powder uniform in the longitudinal direction, including a carrying screw disposed in the longitudinal direction of said developing unit for carrying said developing powder from the first side to the second side of the developing unit and a rotary cylindrically-shaped stirring member disposed at the second side of the developing unit for removing said developing powder at the second side of the developing unit; and a carrying bath formed to surround said carrying screw and being provided with an opening progressively increased from the first side to the second side of the developing unit. A carrying path may be formed to surround the carrying screw and provided with an opening progressively increased from one side of the other side. The feeding unit may be located on the side of the front door provided in a main body of the image forming apparatus. In the operation of the developing unit according to the invention, when the developing powder is fed from the feeding unit, the carrying screw serves to carry the developing powder from one side to the other side for the purpose of feeding the developing powder in the developing unit. The developing powder carried to the other side is diffused radially by the stirring body so as to keep the level of the developing powder D uniform. If the carrying path is formed to surround the carrying screw and is provided with an opening progressively increased from one side of the other side, the developing powder carried by the carrying screw is transferred from one side to the other side inside of the carrying path. The amount of the developing powder overflown out of the opening of the carrying path is progressively increased from one side to the other side. Hence, the developing powder is not shifted to one side. No special stirring work is required for uniformly feeding the developing powder. If the feeding unit is located on the side of the front door provided in a main body of the image forming apparatus, the feeding unit is disposed not above the developing unit but on the one side of the developing unit. This disposition makes it possible to save the space of the main body of the image forming apparatus. Further objects and advantages of the present invention will be apparent from the following description of the preferred embodiments of the invention as illustrated in the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a sectional side view showing a developing powder feeding device according to a first embodiment of the invention; Fig. 2 is a sectional view showing the developing powder feeding device shown in Fig. 1; Fig. 3 is a sectional view showing an agitator included in the feeding device; Fig. 4 is a perspective view showing a main body of an image forming apparatus with a front door being opened; Fig. 5 is a sectional side view showing a developing powder feeding device according to a second embodiment of the present invention; and Fig. 6 is a sectional view showing the developing powder feeding device shown in Fig. 5. DESCRIPTION OF THE PREFERRED EMBODIMENTS The description will be directed to a developing unit according to a first embodiment of the present invention as referring to Figs. 1 to 4. As shown in Fig. 2, a developing powder feeding device, which is arranged in the vicinity of a photosensitive drum 1, is provided with a developing unit 2 and a toner hopper 3 on the developing unit 2. In the unit there is provided a magnet roller 4, a stirring roller 5, a flow plate 7, a toner density sensor 8 and a doctor 9. In the toner hopper 3 there is provided a toner feeding roller 10 and a toner carrying screw 11. The toner hopper 3 is fixed on the developing unit by mechanical screws 12 from the front side and the rear side. As shown in Figs. 1 and 2, the feeding device provided in an image forming apparatus has a developing powder feeding unit 20 and a carrying means 21. The feeding unit 20 serves to feed the developing powder D into a developing unit 2. The carrying means 21 serves to carry the developing powder inside of the developing unit 2. The carrying means 21 is composed of a carrying screw 22 and a stirring member 23. The carrying screw 22 carries the developing powder D from one side to the other side of the developing unit 2 in the longitudinal direction. Herein, one side means the side closer to the front door of the image forming apparatus and the other side means the opposite side thereto. The stirring member 23 circumferentially stirs the developing powder at the other side. As shown in Fig.2, the carrying means 21 is located immediately below an opening 2a of the developing unit 2 and obliquely upward of said stirring roller 5. As shown in Fig. 1, at one side of the carrying means 21, the carrying screw 22 is inserted into the inside of a cylinder 24 projected on the developing unit 2. The carrying screw 22 is constructed to have a rotary shaft 25 and a spiral plate 26 fitted on the rotary shaft 25. The stirring member 23 is composed of an agitator whose sectional form is as shown in Fig. 3. The stirring member 23 is mounted on the other side of the rotary shaft 25. Both ends of the rotary shaft 25 are rotatably supported by the developing unit 2 and the cylinder 24, respectively. In addition, the stirring member 23 may be such as an impeller. Below the stirring roller 5 of the developing unit 2, there is located an exhausting screw 27 for exhausting the waste developing powder D out of the developing unit 2. Like the carrying mechanism 21, the exhausting screw 27 is at one side, inserted into the inside of a cylinder 28 projected on the developing unit 2. The feeding unit 20 is located on the one side of the developing unit. As shown in Fig. 4, it is found when a front door 30 provided on the main body 15 of the image forming apparatus is opened. It means that on the front side of the main body 15, the sufficient space can be taken. Hence, this space gives so much freedom in designing the apparatus that the feeding unit 20 may be located therein. The feeding unit 20 is linked to the cylinder 24. A shutter (not shown) is provided between the feeding unit 20 and the cylinder 24 so that the shutter may open or close the path for achieving the communication therebetween if any. Like the feeding unit 20, a waste vessel 31 is located on the one side of the main body and is connected to the cylinder 28. The waste vessel 31 may be easily removed from the main body 15 of the image forming apparatus. The carrying mechanism 21 and the exhausting screw 27 are rotated by a driving unit such as a motor (not shown) located on the other side of the main body 15. The carrying means 21 is activated for stirring toner and developing powder D not only during the supply of the developing powder D but also during the image-forming operation. On the other hand, the exhausting screw 27 is activated only when exhausting the developing powder to vessel 31. In the foregoing construction to exchange the waste developing powder D with new, one the exhausting screw 27 is rotated by the driving unit (not shown) so as to move the waste developing powder D in the A direction. Then, the developing powder D drops out of the opening of the cylinder 28 and is guided to the waste vessel 31. To feed the new developing powder D, the carrying mechanism 21 is driven. As such, the shutter is opened so that the developing powder D may flow from the feeding unit 20 into the cylinder 24. Then, the developing powder D is carried in the B direction by the carrying screw 22. At the other side the developing powder D is stirred by the stirring roller 5 so as to uniformly charge the powder D in the developing unit 2. The carrying screw 22 is used for carrying the developing powder D from the one side to the other side and provides excellent carrying efficiency. The extension of the carrying screw 22 to the tip of the rotary shaft 25 will result in constantly moving the developing powder D in the B direction, thereby making the height of the developing powder D in the developing unit 2 irregular, which makes the toner density variable. Hence, the resulting copying image may be degraded. To prevent the disadvantageous phenomenon, the stirring member 23 is provided on the other side. This stirring member 23 provides no capability of carrying the developing powder in the B direction but a more excellent capability of stirring the developing powder radially compared to carrying screw 22. Hence, the developing powder D is carried toward the other side by the carrying screw 22 and is diffused radially by means of the stirring member 23 for the purpose of keeping the density of the developing powder D uniform in the developing unit 2. As described above, the developing powder D fed from the other side of the developing unit is allowed to be uniformly fed from the one side to the other side within the developing unit 2 without having to soil the user's hands. Further, the developing powder feeding unit 20 is not located above the developing unit but on the one side of the developing unit. Hence, it is possible to effectively use the space of the main body 15, resulting in making it possible to reduce the image forming apparatus in size. In turn, the description will be directed to the developing unit according to a second embodiment of the invention as referring to Figs. 5 and 6. In the first embodiment, the developing powder D being fed from the feeding unit 20 is gradually carried from the one side of the developing unit 2 to the other side. Since not all developing powder D is carried, more of the developing powder D is left around the one-side part than at the remaining part. That is, the distribution of the developing powder in the developing unit 2 is formed like a mountain whose tip is shifted to the one side. Hence, the density of the developing powder D is higher around the entry part and gradually becomes lower toward the other side. The irregular density of the developing powder D may give rise to an uneven-density image. To make the density even, it is necessary to stir the developing powder D again. Only the carrying screw 22, however, cannot achieve the efficient re-stirring operation. To make the density even, as shown in Figs. 5 and 6, the developing unit according to the second embodiment is constructed so that the carrying screw 22 is provided with a carrying path 32 surrounding the carrying screw 22. The carrying path 32 has an opening 33 progressively increasing from the one side to the other side. The carrying path 32 is formed around the carrying screw 22 like a U character in a manner that the opening 33 may be directed upward. The wall of the carrying path 32 opposite to the rotating direction of the carrying screw 22 is made gradually lower from the one side to the other side. The foregoing construction makes it possible to rapidly move the developing powder D from the one side to the other side within the carrying path 32 by means of the carrying screw 22. The amount of the developing powder D overflown out of the opening 33 of the carrying path 32 is gradually increased from the one side to the other side. Hence, the developing powder D is not shifted locally on the one side. As such, no special stirring work is required for uniformly feeding the developing powder D. Many widely different embodiments of the present invention may be constructed without departing from the spirit and scope of the present invention. It should be understood that the present invention is not limited to the specific embodiments described in the specification, except as defined in the appended claims.

Claims: A developing unit (2) provided in an image forming apparatus having a cylindrical photoreceptor (1) on which a latent image is to be formed and extending parallel to and closely adjacent to the photoreceptor for supplying developing powder onto the photoreceptor to develop the latent image, said developing unit having a first side and a second side in a longitudinal direction thereof, comprising: a feeding unit (20) for feeding fresh developing powder into the developing unit from outside of the first side of the developing unit: a carrying means (21) disposed in said developing unit for carrying said developing powder in said developing unit so as to keep a level of the developing powder uniform in the longitudinal direction, including a carrying screw (22) disposed in the longitudinal direction of said developing unit for carrying said developing powder from the first side to the second side of the developing unit and a rotary cylindrically-shaped stirring member (23) disposed at the second side of the developing unit for removing said developing powder at the second side of the developing unit: and a carrying bath (32) formed to surround said carrying screw and being provided with an opening (33) progressively increased from the first side to the second side of the developing unit. A developing unit as claimed in claim 1, wherein said feeding unit is located on a main body of the image forming apparatus so as to be close to the front door (30) provided in the main body. A developing unit as claimed in claim 1, wherein said carrying means is located immediately below an opening (2a) of said developing unit through which opening fresh toner can be fed. A developing unit as claimed in claim 1, wherein at the first side of the developing unit said carrying screw is inserted into a cylinder (24) projected on the developing unit and said feeding unit is connected with said cylinder through a shutter. A developing unit as claimed in claim 5, wherein said carrying screw includes a rotary shaft (25) and a spiral plate (26) fitted on the rotary shaft, and wherein said stirring member is composed of an agitator and mounted on said rotary shaft on the second side of the developing unit.

Inventors: AIMOTO TOYOKA, AIMOTO, TOYOKA
Applicants: SHARP KK, SHARP KABUSHIKI KAISHA
Application year: 1992
Main classification: G03G15
IPC codes: G03G15