Patent Application
20050185981
1. Field of the Invention
The present invention generally relates to an electrophotographic image-forming apparatus such as a printer and a facsimile machine.
2. Description of the Related Art
A conventional electrophotographic image-forming apparatus is of the configuration as shown in
However, the sealing members 9 pressed against the longitudinal end portions of the developing roller 4 are not sufficient and some toner still leaks. If the sealing member 9 is firmly pressed against the developing roller 4 prevents the toner leakage but the friction between the developing roller 4 and sealing members 9 increases. Thus, the force that presses the sealing members 9 should be limited.
An object of the invention is to prevent toner from leaking from a developing unit.
Another object of the invention is to provide a configuration of a developing apparatus in which a developing roller is in contact with a photoconductive drum to apply a substantially uniform pressure across the length of the photoconductive drum.
Still another object of the invention is to provide a configuration of a developing apparatus in which the toner is pushed back toward the middle portion of the developing roller, thereby preventing toner leakage.
Yet another object of the invention is to provide a configuration of a developing apparatus in which a sealing member is pressed against the surface of the end portion of the resilient layer of the developing roller, thereby preventing toner leakage.
A developing apparatus includes a developing roller that rotates on a shaft and applies developer to an electrostatic latent image formed on a photoconductive body to develop the electrostatic latent image into a visible image. A resilient layer covers an outer circumferential surface of the developing roller. The resilient layer being in contact with the sealing member, wherein said resilient layer has a diameter that becomes larger nearer a longitudinal end of the developing roller.
The diameter has a maximum value and a minimum value. The difference between the maximum value and the minimum value is such that 10 μm<ΔΦ<300 μm, where <ΔΦ is the difference between the maximum value and the minimum value.
The average diameter of particles of the developer is such that ΔΦ>(50/Ψ)+5 μm, where ΔΦ is an average diameter of the particles of the developer.
The resilient layer has a resin coating formed on it.
The resin coating has a thickness such that 2 μm<t<100 μm where t is the thickness.
The resilient layer has an outer diameter that becomes larger nearer a longitudinal end of the resilient layer.
The resilient layer has a first diameter at a longitudinal middle portion of said resilient layer and a second diameter at a longitudinal end of said resilient layer, the first diameter and the second diameter are related such that Φend<Φmid where Φmid is the first diameter and Φend is the second diameter.
The resilient layer has a first diameter at a longitudinal middle portion and a second diameter at a point between the longitudinal middle portion and a longitudinal end, the second diameter being a smallest diameter across a length of said resilient layer, wherein the first diameter and the second diameter are such that 10 μm<(Φmid−ΦA)<500 μm, where Φmid is the first diameter in μm and ΦA is the second diameter in μm.
The longitudinal end has a surface that lies in a plane at an angle other than 90 degrees with an axis of rotation of the developing roller.
The resilient layer has an outer surface that extends to continuously become further away from an axis of rotation of the developing roller with decreasing distance from a longitudinal end of the developing roller.
The resilient layer has an outer surface that extends to become further away from a rotational axis of the developing roller the axis nearer a longitudinal end of said resilient layer, the outer surface becoming further away from the rotational axis stepwise.
The resilient layer has an outer surface that becomes continuously further away from a rotational axis of the developing roller nearer a longitudinal end of said resilient layer.
The developing apparatus further includes a sealing member disposed to press a circumferential surface of the developing roller to seal the developer.
The developing apparatus further includes a sealing member (9A, 9A1) disposed to press a surface of a longitudinal end of the developing roller to seal the developer.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limiting the present invention, and wherein:
{Construction}
Referring to
The longitudinal end portions of the developing roller 4 have a diameter that becomes larger nearer the longitudinal ends. It is to be noted that the diameter does not change linearly but exponentially. The sealing members 9 are in contact with the circumferential surface of the longitudinal end portions. The geometry of the longitudinal end portions may be shaped using a metal mold and is then subjected to polishing for a final shape. Alternatively, the developing roller may be molded or extruded, and the developing roller 4 may then be polished into a desired final shape.
When the developing roller 4 is driven to rotate counterclockwise, the developing blade 6 forms a layer of toner having a uniform thickness on the developing roller 4. The layer of toner is strongly attracted by the Coulomb force to the developing roller 4 and will not leak to the outside environment. The toner-supplying roller 5 scrapes the toner off the developing roller 4 as well as supplying fresh toner to the developing roller 4. The electrostatic force no longer affects residual toner scraped by the toner-supplying roller 5. Thus, the sealing member 9 is effective in preventing the scraped toner from leaking to the outside environment. The diameter of the developing roller 4 near its longitudinal end portions becomes larger nearer the longitudinal ends of the developing roller 4. Thus, the sealing member 9 does not exert a pressing force that is uniformly distributed across the length of the developing roller 4 but a pressing force that becomes larger nearer the longitudinal ends. This profile of distribution of the pressing force is effective in preventing the toner from leaking toward the longitudinal ends of the developing roller 4.
The pressing force exerted by the sealing member 9 on the developing roller 4 is proportional to the ΔΦ. For ΔΦ smaller than 10 μm, the pressing force is distributed relatively uniformly and is therefore not effective in blocking the leakage of the toner. For ΔΦ larger than 300 μm, a gap is created between the developing roller 4 and the sealing member 9, so that the toner accumulates between the developing roller 4 and the sealing member 9 to cause “filming.” The filming of toner scratches the developing roller 4 to cause grooves in the developing roller 4 through which the toner leaks. The smaller the particle diameter of toner is, the larger the ΔΦ should be, so that the particle diameter and the ΔΦ are inversely proportional. In other words, there is a relation that ΔΦ>(a/Ψ)+b (a and b are fixed values). The values of a and b can be calculated from the data listed in Table 1. The values of Ψ and ΔΦ that provide the advantages listed in Table 1 are put into Equation ΔΦ>(a/Ψ)+b. In other words, (Ψ, ΔΦ)=(4, 20), (6, 15), (8, 15), and (10, 10) are put into Equation ΔΦ>(a/Ψ)+b, thereby calculating the values of a and b. The thus calculated values of a and b are 50 and 5, respectively. The data in Table 1 reveal that toner will not leak if ΔΦ>(50/Ψ)+5 μm.
Δ: leakage is serious toward the end of lifetime of the developing roller.
Because the longitudinal end of the developing roller 4B has not the largest diameter, the pressing force exerted by the sealing member 9 is concentrated on the largest diameter portion, so that the developing roller 4B is subjected to serious wear. If the sealing member 9 is disposed in such a way that the largest diameter portion is closer to the longitudinally middle portion of the developing roller 4B than the mid point in the width of the sealing member 9, the effective areas for sealing become smaller. If the diameter of the developing roller 4 is formed to have a diameter that rapidly changes, then a gap will be created between the developing roller 4B and the sealing member 9. This gap allows the toner to be deposited on the developing roller 4B to cause filming, the filming of toner scratching the developing roller 4B. Thus, the diameter of the developing roller should not change rapidly. For developing rollers 4A and 4C, the diameter is a maximum at the longitudinal ends and therefore the pressing force will decrease. The pressing force acts toward the longitudinal ends of the developing roller, so that the wear of the developing rollers in
The developing rollers 4A-4C allow the sealing members 9 to be pressed against the developing roller in a limited area without increasing the pressing force. In addition, the shape of the end portions of the developing rollers 4A-4C creates a force tending to push the toner toward the longitudinally middle portions of the developing rollers. Thus, the toner will not migrate toward the longitudinal end portions, firmly sealing the toner which would otherwise adhere to the drive gears to cause an increase in drive torque. Further, the toner is prevented from falling on the recording medium and therefore does not cause soiling of the recording medium.
An electrophotographic image forming apparatus according to a second embodiment has the same configuration as the first embodiment.
The resin coating 42 has a resin coating having a uniform thickness in the range of 2 to 100 μm. A resin coating 42 having a thickness smaller than 2 μm causes a poor durability. The resin coating 42 is harder than the resilient layer 43 and therefore the change in shape at the longitudinal ends is smaller than the resin coating 42. If the thickness of the resin coating 42 is greater than 100 μm, the change in the diameter of the developing roller 4D is too small near the longitudinal ends, not being effective in preventing toner leakage.
Resin coating is small in surface roughness and viscosity as compared to semiconductive rubber, and therefore resin coating has good sliding ability. Because the resin coating 42 covers the surface of the developing roller 4D, the toner is easy to slip on the resin coating 42. For this reason, the toner-supplying roller 5 can effectively scrape the toner on the developing roller 4D, preventing an “after-image” from occurring. This also prevents filming on the developing roller 4D due to adhesion of toner that would otherwise fail to be scraped by the toner-supplying roller 5. However, the good ability of resin coating to slide reduces the friction between the developing roller 4D and the toner-supplying roller 5. As a result, the toner entered between the developing roller 4D and the sealing member 9 tends to move in an axial direction. Thus, if the pressing force between the developing roller 4D and sealing member 9 is distributed uniformly, the toner is apt to leak from the inside of the developing unit to the outside of the developing unit. However, the diameter of the resilient layer 43, which becomes larger nearer the longitudinal end of the developing roller 4D, exerts a force on the coating 42, the force causing the resin coating 42 to widen outwardly. Therefore, despite the fact that the resin coating 42 is made of a material having a uniform thickness, the developing roller 4D has an overall diameter that becomes large nearer the longitudinal ends. Even if the toner enters between the developing roller 4D and the sealing member 9, the toner is pushed back toward the inner space of the developing unit.
Resin coating is harder than semiconductive rubber, so that the resin coating is difficult to be polished to into a shape such that the diameter becomes larger nearer the longitudinal ends. In the second embodiment, the resilient layer 43 of the developing roller 4D is formed such that the diameter becomes larger nearer the longitudinal ends. Therefore, despite the fact that the resilient layer 43 is covered with the resin coating 42, an area on the developing roller 4D in contact with the sealing member 9 also becomes larger in diameter nearer the longitudinal ends. This provides the developing roller 4D that prevents the toner from leaking to the outside environment and allows the toner to slide thereon.
An electrophotographic image forming apparatus according to a third embodiment is of the same configuration as the first embodiment.
In the first embodiment, the developing rollers 4A, 4B, and 4C are pressed against the photoconductive drum 1 with a certain pressing force. Therefore, the pressing force exerted on the surface of the photoconductive drum 1 by the developing roller is a maximum at the longitudinal ends and a minimum at the longitudinal middle portion. Thus, the efficiency of the toner to be deposited on the photoconductive drum 1 is not uniform along the length of the photoconductive drum 1.
In contrast, the developing roller 4E according to the third embodiment provides a substantially uniform profile of the distribution of pressing force across the entire length of the photoconductive drum 1. For Φmid<Φend, there is no advantage of having a diameter that becomes larger nearer the longitudinal middle. If the developing roller 4E has too large a diameter at the longitudinally middle portion, the pressing force tends to be concentrated to the longitudinal middle. Thus, for the developing roller 4E, when the minimum diameter is ΦA, the diameters Φmid and φA are related preferably such that 10 μm<(Φmid−ΦA)<500 μm.
When the developing roller 4E and the photoconductive drum 1 are in pressure contact with each other, because the pressing force is uniform along the length of the developing roller 4E, the movability of the toner from the developing roller 4E to the photoconductive drum 1 can be uniform across the length of the developing roller 4E. Thus, the density of an image becomes substantially the same across the width of an image formed on the recording medium. Moreover, the pressure acting between the photoconductive drum 1 and the developing roller 4E is not concentrated on the longitudinal end portions, and therefore deteriorated toner will not accumulate in the vicinity of the longitudinal end portions of the developing roller 4E.
An electrophotographic image forming apparatus according to a fourth embodiment is of the same configuration as the first embodiment.
When the developing roller 4F rotates, the developing roller 4F rubs the sealing member 9. The sealing member 9 exerts a frictional force on the developing roller 4F so that the developing roller 4F is twisted by a torsional force exerted at its longitudinal ends. Because the resilient layer 41 of the developing roller 4F tends to correct the torsion, a force acts on the toner in such a direction as to push the toner toward the longitudinally middle portion of the developing roller 4F. The force that acts on the toner is a maximum at the longitudinal end of the developing roller 4F. This longitudinal end lies in a plane at an angle other than 90 degrees with the rotational axis of the developing roller 4F. Thus, when the developing roller 4F rotates about its rotational axis, the longitudinal ends repeat its reciprocating motion along the rotational axis. This increases the force tending to push back the toner toward the longitudinally middle portion of the developing roller 4F. In other words, a force acting in a direction toward the longitudinally middle portion of the developing roller 4F is greater than a force acting in a direction toward the longitudinal end. Thus, leakage of the toner is effectively prevented.
In the first to fourth embodiments, the developing roller is shaped to have a diameter that becomes larger nearer the longitudinal ends and the Coulomb force attracts the toner to the developing roller, thereby preventing the toner from leaking. However, some of the toner may still leak. In a fifth embodiment, a sealing member 9 is pressed against a resilient layer 45 of a developing roller 4G. Even when the toner layer is formed on the full length of the developing roller 4G, the toner is prevented from leaking to the outside environment.
If the sealing member 9A is to be in direct contact with the photoconductive drum 1, the sealing member 9A is formed to have an area 9A1 that is configured to accommodate the circumferential surface of the photoconductive drum 1. The sealing member 9A has a flat surface that is in contact with the longitudinal end of the resilient layer 45. In order to prevent wear of the sealing member 9A and the resilient layer 45, a thin ring-shaped film 10 may be inserted between the sealing member 9A and the developing roller 4G. The thin ring-shaped film 10 has a thickness of about 10 μm and an outer diameter smaller than that of the longitudinal end of the developing roller 4G.
The resilient layer 45 is formed such that the diameter becomes larger nearer the longitudinal end of the resilient layer 45, starting 15 mm from the longitudinal end. The diameter of the resilient layer 45 is related such that 10 μm<(Φ1−Φ0)<300 μm. The surface of the longitudinal end of the resilient layer 45 of the developing roller 4G lies in a plane substantially perpendicular to the shaft 40. The sealing member 9A may also be applied to the developing roller 4D according to the second embodiment and the developing roller 4E according to the third embodiment.
A frictional force exists between the sealing member 9 and the developing roller G. When the developing roller 4G rotates, the frictional force causes the end portions of the resilient layer 45 to twist. The torsional force acts toward the rotational axis of the developing roller, so that a gap tends to be created between the developing roller 4G and the sealing member 9A. The geometry of the resilient layer 45 is such that the diameter of the resilient layer 45 extends to become away from the rotational axis of the resilient layer toward the longitudinal ends of the resilient layer 45. It is to be noted that the diameter does not change linearly but exponentially. The resilient force acts radially outwardly of the developing roller and is greater than the torsional force acting toward the rotational axis of the developing roller. Thus, a gap is difficult to be created between the developing roller 4G and the sealing member 9A. Because the outer diameter of the thin ring-shaped film 10 is smaller than that Φ1 of the longitudinal end of the developing roller 4G, the thin ring-shaped film 10 is intimate contact with the resilient layer 45. Thus, a gap is not created between the resilient layer 45 of the developing roller 4G and the sealing member 9A and therefore the toner will not leak between the sealing member 9 and the thin ring-shaped film 10.
The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art intended to be included within the scope of the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-047824 | Feb 2004 | JP | national |
