Developing apparatus

Abstract: A developing apparatus comprises a hopper (2) in which a developer is stored; an electrostatic latent image carrier (13) to which the developer is supplied; a supply roller (4) disposed to the hopper for supplying the developer stored in the hopper; and a developing roller (6) disposed to the hopper and contacting the supply roller for supply the toner supplied from the supply roller to the electrostatic latent image carrier. A developing blade (8) is brought into contact with the developing roller under pressure for thinning the developer laid on the developing roller, and a restriction member (20) is provided midway in a route through which the developer is delivered from the hopper to the supply roller for restricting the amount of the developer to be delivered to the supply roller.

Description: The present invention relates to a developing apparatus to be employed in an electronic photograph recorder or an electrostatic duplicator, and the like, particularly to the developing apparatus for supplying a developer from a supply roller to a developing roller and further delivering to an electrostatic latent image carrier, thereby subjecting the latent image to development. There are various conventional methods for delivering a toner as a developer to an electric latent image carrier in an electronic photograph recorder and the like, e.g. as disclosed in Japanese Patent Laid-Open Publication No. 63-231469 which employs a developing roller alone as the toner delivering means. There is a method employing, in addition to the developing roller, a delivering roller wherein the toner is first delivered to the developing roller and thereafter to the electrostatic latent image carrier. In the latter developing apparatus, a supply roller for delivering the toner is normally disposed substantially under a toner hopper storing the toner therein and the toner dropped from the toner hopper is supplied to a developing roller. A developing blade contacts the developing roller and restricts the thickness of the toner attached and laid on the surface of the developing roller. The developing blade is brought into contact with the developing roller under pressure by a spring. The toner layer restricted in its thickness is delivered to the electrostatic latent image carrier by the rotation of the developing roller per se, hence the latent image is developed. Since the supply roller supplies the toner dropped thereon from the toner hopper and accumulated thereon, the amount of toner to be supplied to the developing roller is large and the layer on the developing roller composed of a large amount of the toner is thinned by the developing blade. The toner stopped by the developing blade is residual in a residual portion disposed at the front of the delivering direction. In the course of developing process, the toner in the reservoir is increased and fully occupies the entire space of the reservoir. Further supply of the toner into the space of the reservoir occupied by the toner permits the developing blade to push up from the surface of the developing roller against the resilient force of the spring due to the pressure of the toner. Consequently, there is a space between the surface of the developing roller and the tip end of the developing blade and there is likelihood that the layer of the toner restricted by the developing blade becomes thick. Furthermore, there is a likelihood that the toner is solidified by the pressure to form particles of the toner having large diameters which are delivered to the developing point. For these reasons, there occurred such problems that the substrate on which the image is developed is contaminated and the suitable resolution can not be obtained and the like if the layer of the toner after restriction becomes thick, the surplus toner is absorbed by the electrostatic latent image carrier at the developing time. FR-A-2 602 597 discloses a developing apparatus according to the preamble of claim 1. The opening of its hopper is provided with a control member for controlling the opening width. EP-A-0 270 104 discloses a developing apparatus where a partition plate 41 with an opening portion 42 is part of the hopper; this opening defines the portion of the hopper which is open towards the supply roller and the developing roller. The problem to be solved in view of this prior art is to provide a simple means which at the same time is capable of restricting the amount of toner to be supplied from the supply roller and of avoiding clogging of toner on the surface of the supply roller. According to this invention, this object is solved by the characterizing features of claim 1. The lower row of through holes or slits or gaps scrapes the toner clogged on the surface of the supply roller 4, while the upper row or the upper rows of through holes or slits or gaps restrict the amount of toner delivered to the supply roller and keep it at a predetermined amount. With the arrangement set forth above, the amount of the developer to be supplied to the supply roller is restricted and the amount of the developer to be supplied to the developing roller is restricted by the provision of the restriction member in said route through which the toner is supplied from the hopper to the supply roller. Accordingly, the toner is not filled in full in the reservoir disposed at the front of the developing blade for thinning the toner on the developing roller hence, no pressure is given to the developing blade. As a result, the layer of the toner on the developing roller is appropriately thinned by the developing blade, which results in eliminating the contamination of the substrate of the printing medium and obtaining the suitable resolution. The above and other objects, features and advantages of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a cross sectional view of a developing apparatus according to a first embodiment of the present invention; Fig. 2 is a perspective view of a toner delivery restriction plate employed in the first embodiment of the present invention; Fig. 3 is a cross sectional view showing the operation of the first embodiment; Fig. 4 is a perspective view showing a toner delivery restriction plate employed in a second embodiment of the present invention; Fig. 5 is a view showing the operation of scraping a toner according to the second embodiment; Fig. 6 is a perspective view of a toner delivery restriction plate according to a modified embodiment of the present invention; and Fig. 7 is as enlarged side view of Fig. 6. DESCRIPTION OF THE PREFERRED EMBODIMENT First Embodiment (Fig. 1 to 3) A developing apparatus according to a first embodiment will be described with reference to Figs. 1 to 3. A developing apparatus for supplying a developer to an electrostatic latent image carrier and developing thereof comprises a toner cartridge 1 for containing a toner 1a as the developer, a toner hopper 2 formed under the toner cartridge 1 for storing or stagnating the toner 1a fallen from the toner cartridge 1, a stirring shaft 3 in the toner hopper 2 for stirring the toner 1a stagnant in the toner hopper 2, a supply roller 4 rotatably provided in the lower portion aslant the stirring shaft 3 for delivering and supplying the toner 1a, a toner delivery restriction plate 20 provided between the toner hopper 2 and the supply roller 4 for restricting the amount of supply of the toner. The toner cartridge 1 is provided with a shutter 1b provided thereunder and an opening 1c to allow the toner 1a to fall downward therethrough by opening the shutter 1b. The stirring shaft 3 is rotated in the direction of the arrow A for stirring the toner stagnant in the toner hopper 2. The supply roller 4 is made of foaming materials such as urethane and the like and conductive. The supply roller 4 has a central shaft 5 made of a metal to which a predetermined bias current is applied, not shown. The toner delivery restriction plate 20 is fixed to a frame 21. The toner delivery restriction plate 20 has a length substantially same as that of the axial length of the supply roller 4 as shown in Fig. 2 and is bent in a doglegged shape in cross section. A part of the plate 20 covers the supply roller 4 and has a plurality of through holes 22. The toner in the toner hopper 2 can reach the supply roller 4 through the plurality of through holes 22. The toner delivery restriction plate 20 is made of a metal but may be made of a resin. The through holes 22 are spaced substantially in the same intervals in the axial direction of the supply roller 4. The through holes 22 on the first row are staggered with those of the second row in the direction crossing the axial direction of the supply roller 4. The intervals of the through holes 22 adjacent to each other on the first row are same as those of the through holes 24 adjacent to each other on the second row. With such an arrangement, the toner 1a in the hopper 2 can be supplied uniformly in the axial direction of the supply roller 4 for the entire length thereof. Although the shape of the through holes 22 is oval according to the present invention, it is not limited thereto but may be circular or rectangular. The number of the through holes 22 are not necessary to be plural but may be one as a slit extending along the supply roller 4. According to the present embodiment, the toner delivery restriction plate 20 contacts the supply roller 4 but the toner delivery restriction plate 20 does not always contact the supply roller 4. The developing apparatus further comprises a developing roller 6 rotatably fixed to the developing apparatus by driving means, not shown, a developing blade 8 disposed over and contacting the developing roller 6 for thinning a toner layer formed around the developing roller 6, a toner reservoir 18 provided at the space defined at the right side of the developing balde 8 for reserving the toner which can not pass through the interval between the developing blade 8 and the developing roller 6, a sensitive drum 13 as an electrostatic latent image carrier rotatably fixed to driving means, not shown and disposed at left side of the developing roller 6, a first charger 15 substantially over the sensitive drum 13 for charging the surface of the sensitive drum 13 and a cleaning portion 16 disposed at the left side of the sensitive drum 13 provided with a cleaning blade 17 for scraping the toner residual on the surface of the sensitive drum 13 after tansferring the image on the substrate of the printing medium. There is provided a partition plate 12 contacting the developing roller 6 at the bottom of the developing roller 6 for preventing the toner from scattering outside the developing apparatus. The developing roller 6 is formed of a conductive and elastic rubber and the like and has a central metal shaft to which a bias voltage is applied. The supply roller 4 and the developing roller 6 respectively serve to deliver the toner to the developing portion by the rotation thereof. The developing blade 8 comprises a rubber portion 9 contacting the developing roller 6 and a metal portion 10 fixing the rubber portion 9 thereto. A given pressing force is generated in the developing blade 8 when it is pressed by the spring 11 toward the developing roller 6. The developing apparatus having the arrangement set forth above is operated as follows. In Fig. 3, when the power is ON, the stirring shaft 3, the supply roller 4 and the developing roller 6 are respectively rotated by the driving means, not shown, in the directions of the arrows A, B and C. When the shutter 1b is turned, the toner 1a is dropped from the opening 1c of the toner cartridge 1 and joins residual developer at the toner hopper 2. The toner 1a enters into the reservoir 18 and is accumulated on the toner delivery restriction plate 20. The amount of the toner entered from the toner hopper 2 is kept at a predetermined amount. However, the amount of the toner supplied from the supply roller 4 is restricted by the toner delivery restriction plate 20. According to the present embodiment, the size and the numbers of the through holes 22 as illustrated in Fig. 2 are set to the extent that the amount of the toner passing the through holes 22 is slightly greater than the amount of the toner which is restricted by the developing blade 8. The toner 1a passed the toner delivery restriction plate 20 and attached to the supply roller 4 is delivered to the toner reservoir 18. The amount of the toner 1a supplied afresh from the hopper 2 to the toner reservoir 18 is substantially same as that passed the toner delivery restriction plate 20. The toner 1a attached to the surface of the developing roller 6 in the toner reservoir 18 is delivered to the position where the developing roller 6 contacts the developing blade 8 by the rotation of the developing roller 6 per se. The toner laid over the developing roller 6 is thinned to a predetermined thickness, e.g. to several ten microns by the developing blade 8. Inasmuch as the amount of the toner in the toner reservoir 18 is kept substantially constant, the toner reservoir 18 is not filled by the toner, hence it does not affect the thinning operation by the developing blade 8. The toner 1a is charged by the developing blade 8. The thus thinned charged toner is subjected to the development of the elecrostatic latent image at the portion contacting the sensitive drum 13. The toner which is not subjected to the development among those attached to the developing roller 6 and residual on the developing roller 6 is rotated by the rotation of the developing roller 6 in the direction of the arrow C and reaches the portion contacting the supply roller 4. As mentioned above, the supply roller 4 is the roller like a sponge and has a plurality of minute convex and concave portions at the surface thereof. The suppy roller also functions to scrape the toner residual on the developing roller by contacting the developing roller 6 and rotating. Inasmuch as there is provided a toner delivery restriction plate 20 as set forth above according to the present invention, the amount of the toner is restricted so that the toner layer on the developing roller 6 can be thinned appropriately by the developing blade. Second Embodiment (Figs. 4 and 5) A developing apparatus according to a second embodiment will be described with reference to Figs. 4 and 5. In Fig. 4, a toner delivery restriction plate 30 according to the second embodiment is formed to extend so as to cover the supply roller 4 in the entire length thereof. There are provided rectangular slits at the portion covering the supply roller 4 along the axial direction of the supply roller 4. Among the slits, the slits 31a in the first row 31 and the slits 32a in the second row function respectively to supply the toner in the toner hopper 2 to the supply roller 4 as the supply slits whereas the slits 33a in the third row 33 function to scrape the toner attached to the supply roller as the scraping slits. This is described more in detail with reference to Fig. 5. In Fig. 5, the surface of the supply roller 4 has a plurality of minute convex and concave portions. The toner delivery restriction plate 30 contacts the surface of the supply roller 4. Suppose that the toner is filled in the toner hopper 2 positioned substantially over the toner delivery restriction plate 30. The toner passed the slits 31a in the first row 31 and the toner passed the slits 32a of the second row 32 are moved toward the supply roller 4. The size and the numbers of the slits 31a of the first row 31 and the slits 32a of the second row 32 are determined in the given values so that the amount of the toner to be supplied to the supply roller 4 is optimum. The upper ends 33b of the slits 33a in the third row is brought into contact with the supply roller 4 under pressure. The supply roller 4, as set forth above, functions to scrape the toner residual on the developing roller 6 but the same roller 4 is likely to be clogged at the surface thereof due to the repetitive delivering operation of the toner. When the surface of the supply roller is clogged the function to scrape the toner residual on the developing roller 6 is not fully carried out. Since the upper ends 33b of the slits 33a of the toner delivery restriction plate 30 is brought into contact with the supply roller 4 under pressure and the supply roller 4 is rotated in the direction of the arrow B, i.e. in the direction to bring into contact with the upper ends 33b of the slits 33a, the toner clogged on the surface of the supply roller 4 is scraped. At this time, although the toner in the toner hopper is residual on the toner delivery restriction plate 30 and enters into the slits 33a, the density of the toner is relatively low. Whereupon, there is generated a great scraping force in the upper ends 33b of the toner delivery restriction plate 30 when the toner clogged on the surface of the supply roller 4 is scraped because the supply roller 4 is formed of the elastic sponge. The toner clogged on the surface of the supply roller 4 enters into the toner having a low density in the toner hopper. Accordingly, the toner clogged on the surface of the supply roller 4 is scraped by the upper ends 33b so that the clogging problem can be eliminated. The supply roller 4 thus eliminating the clogging problem by the upper ends 33b receives the toner again from the slits 32a and 31a. However, a large amount of the toner supplied afresh is delivered into the developing roller, hence the toner is less residual on the surface of the supply roller 4. Since the toner residual on the developing roller 6 is scraped by the supply roller 4, the scraping operation is carried out favorably. As explained above, the toner delivery restriction plate according to the second embodiment functions to restrict the amount of the toner and to scrape the toner residual on the developing roller by eliminating the clogging problem on the supply roller. Accordingly, there are such effects according to the second embodiment that the thickness of the toner layer on the developing roller can be restricted appropriately and the toner residual on the developing roller can be eliminated so that no undesired images occur at the developing process. Although the invention has been described in the first and the second embodiments, it is to be understood that many variations and changes are possible. For example, the toner delivery restriction plate can be varied as illustrated in Fig. 6. The delivery restriction plate 35 comprises three plates connected with each other with providing predetermined gaps 34 therebetween. As illustrated in Fig. 7, there are provided connecting members 36 for connecting the three plates with each other by providing the predetermined gaps 34 at the both sides and at the central portion of the toner delivery restriction plate 35 alone. With such an arrangement, the toner can pass the gaps 34. The sizes of the gaps 34 are set to the extent that the optimum amount of the toner can pass the gaps. Edge portions 37 of the toner delivery restriction plate 35 as illustrated in Fig. 7 are brought into contact with the supply roller 4 so as to scrape the toner clogged on the surface of the supply roller 4.

Claims: A developing apparatus provided with a hopper (2) in which a developer is stored and an electrostatic latent image carrier (13) to which the developer is supplied, the developing apparatus further comprising: a supply roller (4) disposed adjacent to the hopper for supplying the developer stored in the hopper, the developer being delivered from the hopper to the supply roller along a route; a developing roller (6) disposed adjacent to the hopper and contacting the supply roller for supplying the developer supplied from the supply roller to the electrostatic latent image carrier; a developing blade (8) being brought into contact with the developing roller under pressure for thinning the developer laid on the developing roller; and a restriction member (20,30,35) provided in said route for restricting the amount of the developer to be delivered to the supply roller, said restriction member being in contact with said supply roller; characterized in that said restriction member (20,30,35) is provided with a plurality of rows of through holes (22) or slits (31a,32a,33a) or gaps (34) extending along the entire length of the supply roller in the axial direction thereof, and in that the edge(s) (33b, 37) of the through holes or slits (33a) or gaps (34) of one of said plurality of rows positioned at the downstream of the rotary direction of the supply roller is (are) in contact with the supply roller. A developing apparatus according to Claim 1, wherein the edge(s) (33b, 37) is (are) biased against the supply roller (4). A developing apparatus according to Claim 1 or 2, wherein said restriction member (20,30,35) has a bended configuration. A developing apparatus according to any of Claims 1 to 3, wherein plural through holes (22) are arranged in the axial direction of the supply roller at the same intervals. A developing apparatus according to any of Claims 1 to 3, wherein the restriction member (35) comprises a plurality of plate-like members disposed in the axial direction of the supply roller (4) and connected with each other by gap-setting members (36).

Inventors: KIKUCHI HIROSHI OKI ELECTRIC I, KOGA YOSHITOMI OKI ELECTRIC IN, MOMIYAMA YOSHIHARU OKI ELECTRI, NAKAJIMA SHIGEKI OKI ELECTRIC, OTA YUKIO OKI ELECTRIC INDUSTR, KIKUCHI, HIROSHI, OKI ELECTRIC INDUSTRY CO. LTD., KOGA, YOSHITOMI, OKI ELECTRIC INDUSTRY CO. LTD., MOMIYAMA, YOSHIHARU, OKI ELECTRIC INDUSTRY CO. LTD, NAKAJIMA, SHIGEKI, OKI ELECTRIC INDUSTRY CO. LTD., OTA, YUKIO, OKI ELECTRIC INDUSTRY CO. LTD.
Applicants: OKI ELECTRIC IND CO LTD, OKI ELECTRIC INDUSTRY CO., LTD.
Application year: 1990
Main classification: G03G15
IPC codes: G03G15