Patent Application
20070071507
1. Field of the Invention
The present invention relates to a developing device used in an image forming device such as a copying machine, a printer, and a facsimile machine employing an electro-photographic system, and relates to an image forming device.
2. Description of Related Art
The developing roller 101 comprises: a non-rotary magnet roller 100 provided with magnetic N-poles and magnetic S-poles disposed alternately at a plurality of positions in the circumferential direction; and a nonmagnetic sleeve 106 fitted to the outside of the magnet roller 100 in a freely rotatable manner. One end portion of the reflux plate 103 is disposed in the vicinity of the outer periphery of the stirring roller 105, while the opposite side of said one end portion is disposed in the vicinity of the outer periphery of the developing roller 101. The control member 102 is disposed in the vicinity of the outer periphery of the developing roller 101 in the downstream side (left-hand side in the figure) of the transfer direction relative to the opposite side of said one end portion of the reflux plate 103.
In the developing device constructed as described above, carrier (magnetic powder) and toner of the binary developer stored in the case 104 are stirred by rotation (in the counterclockwise direction in the figure) of the stirring roller 105, and the toner adheres to the periphery surface of the carrier. Further, when the sleeve 106 of the developing roller 101 rotates (counterclockwise in the figure), the developer is transferred toward a gap between the developing roller 101 and the control member 102, so that the transferring amount to the electrostatic latent image is controlled by the control member 102. The developer having passed through the gap is transferred to the electrostatic latent image, while excess developer resulting from control by the control member 102 stagnates in the space between the control member 102 and the reflux plate 103. When the stagnated amount increases, the developer is flowed toward the reflux plate 103, then guided by the reflux plate 103, and thereby flowed back to the stirring roller 105.
As described above, the developer circulates inside the case 104 via the control member 102, the reflux plate 103, and the like. Nevertheless, for example, when the developer deposits on the reflux plate 103 so that the reflux of the developer is blocked, a problem arises that smooth circulation of the developer is prevented. When smooth circulation of the developer is prevented, adverse influences are caused such as unstable image quality.
The present invention has been devised in view of this situation. An object of the present invention is to provide a developing device in which arrangement of one end portion of a reflux plate is optimized in the vicinity of the outer periphery of a stirring roller so that reflux of developer is stabilized.
Another object of the present invention is to provide a developing device in which arrangement of one end portion of a reflux plate is optimized in the vicinity of the outer periphery of a stirring roller so that the rate of circulation of developer is enhanced.
Yet another object of the present invention is to provide a developing device in which the inclination angle of a reflux plate is optimized so that reflux of developer is stabilized.
Further, another object of the present invention is to provide a developing device in which arrangement of one end portion of a reflux plate is optimized in the vicinity of the outer periphery of a stirring roller so that mixing of flowed-back developer and supplied developer is improved.
Further, another object of the present invention is to provide a developing device in which small-grain diameter developer is used so that image quality is improved.
Further, another object of the present invention is to provide an image forming device in which image quality of an image formed on a sheet is stabilized.
A developing device according to the present invention is a developing device comprising: a stirring roller having stirring blades for stirring a developer; a developing roller for transferring the developer to an electrostatic latent image; a control member for controlling the amount of developer transferred to the electrostatic latent image by said developing roller; and a reflux plate for flowing back excess developer by controlling of said control member to said stirring roller; wherein one end portion of said reflux plate is disposed in the vicinity of the outer periphery of said stirring roller, and part of the developer stirred by said stirring roller flies toward said reflux plate, and is characterized in that said one end portion of said reflux plate is disposed at a position remote from said stirring roller over a distance greater than the maximum fly distance of the developer provided by rotation of said stirring roller.
A developing device according to the present invention is characterized in that said one end portion of said reflux plate is disposed above in the vertical direction of said stirring roller, and said maximum fly distance is the maximum fly distance in the vertical direction.
A developing device according to the present invention is a developing device comprising: a stirring roller having stirring blades for stirring a developer; a developing roller for transferring the developer to an electrostatic latent image; a control member for controlling the amount of developer transferred to the electrostatic latent image by said developing roller; and a reflux plate for flowing back excess developer by controlling of said control member to said stirring roller; wherein one end portion of said reflux plate is disposed in the vicinity of the outer periphery of said stirring roller, and is characterized in that said one end portion of said reflux plate is disposed within a predetermined range from a position where a plane passing through the rotation center axis of said stirring roller and crossing said reflux plate at right angles intersects said reflux plate.
A developing device according to the present invention is characterized in that said one end portion of said reflux plate is disposed at a position where a plane passing through the rotation center axis of said stirring roller and crossing said reflux plate at right angles intersects said reflux plate.
A developing device according to the present invention is characterized in that an inclination angle of said reflux plate is larger than an angle of repose.
A developing device according to the present invention is characterized by further comprising a developer supplying portion from which the developer is supplied, wherein said stirring roller is disposed between said developer supplying portion and said developing roller, and said one end portion of said reflux plate is disposed in the vicinity of the outer periphery on said developer supplying portion side of said stirring roller.
A developing device according to the present invention is characterized in that said stirring roller stirs the developer containing magnetic powder having an average grain diameter of 65 μm or smaller and toner having an average grain diameter of 7.5 μm or smaller.
An image forming device according to the present invention is characterized by comprising a developing device according to above mentioned invention for developing an electrostatic latent, and an image forming unit for forming on a sheet an image developed by said developing device.
In the present invention, in a developing device in which one end portion of a reflux plate is disposed in the vicinity of the outer periphery of a stirring roller having stirring blades and in which part of the developer stirred by the stirring roller flies toward the reflux plate, said one end portion of the reflux plate is disposed at a position remote from the stirring roller over a distance greater than the maximum fly distance of the developer provided by rotation of the stirring roller. Thus, even when the developer stirred by the stirring roller flies toward the reflux plate, since said one end portion of the reflux plate is remote from the stirring roller over a distance greater than the maximum fly distance of the developer, the developer does not reach said one end portion, and hence deposition of the developer is prevented.
In the present invention, one end portion of the reflux plate is disposed above in the vertical direction of the stirring roller having stirring blades, while said one end portion of the reflux plate is disposed at a position remote from the stirring roller over a distance greater than the maximum fly distance of the developer in the vertical direction. Thus, even when the developer stirred by the stirring roller flies toward the reflux plate, since said one end portion of the reflux plate is remote from the stirring roller over a distance greater than the maximum fly distance of the developer in the vertical direction, the developer does not reach said one end portion, and hence deposition of the developer is prevented.
In the present invention, in a developing device in which one end portion of a reflux plate is disposed in the vicinity of the outer periphery of a stirring roller, said one end portion of the reflux plate is disposed within a predetermined range from a position where a plane passing through the rotation center axis of the stirring roller and crossing the reflux plate at right angles intersects the reflux plate. Thus, since the amount of developer transferred to a control member for controlling the transferring amount to an electrostatic latent image increases when said one end portion of the reflux plate approaches the position where the plane passing through the rotation center axis of the stirring roller crosses the reflux plate at right angles, the rate of circulation of the developer can be made to be larger.
In the present invention, one end portion of the reflux plate is disposed at a position where a plane passing through the rotation center axis of the stirring roller and crossing the reflux plate at right angles intersects the reflux plate. Thus, since the amount of developer transferred to a control member for controlling the transferring amount to an electrostatic latent image increases when said one end portion of the reflux plate approaches the position where the plane passing through the rotation center axis of the stirring roller crosses the reflux plate at right angles, the rate of circulation of the developer can approach the maximum.
In the present invention, an inclination angle of the reflux plate is set larger than an angle of repose at which accumulated developer remains stable without collapsing. Then, since the inclination angle is larger than the angle of repose, the developer is prevented from stably depositing on the reflux plate, and hence reflux of the developer is stabilized.
In the present invention, the stirring roller is disposed between the developer supplying portion and the developing roller, while one end portion of the reflux plate is disposed in the vicinity of the outer periphery on the developer supplying portion side of the stirring roller. Thus, since excess developer is flowed back from the reflux plate to the developer supplying portion side of the stirring roller, and mixing of the developer having been flowed back and the developer supplied from the developer supplying portion can be improved.
In the present invention, small-grain diameter developer containing magnetic powder having an average grain diameter of 65 μm or smaller and toner having an average grain diameter of 7.5 μm or smaller is stirred by the stirring roller. When the small-grain diameter developer is used, image quality is improved. Nevertheless, developer of small grain diameter aggregates easily and has a tendency that its fluidity becomes poor and hence causes instability in the circulation. However, in the present invention, as described above, the developer is prevented from depositing on the reflux plate, or alternatively the rate of circulation of the developer is improved, yet alternatively, mixing of the developer is improved. Thus, even when such small-grain diameter developer is used, circulation of the developer is stabilized.
In the present invention, a developing device according to the present invention described above develops an electrostatic latent image. Then, an image forming unit forms the developed image onto a sheet. In the developing device of the present invention, circulation of the developer is stabilized as described above, so that image quality formed on the sheet can be stabilized.
According to the present invention, one end portion of the reflux plate is disposed at a position remote from the stirring roller over a distance greater than the maximum fly distance of the developer provided by rotation of the stirring roller, so that the developer does not reach said one end portion, and hence deposition of the developer is prevented. This prevention of deposition of the developer stabilizes the reflux of the developer.
According to the present invention, one end portion of the reflux plate is disposed at a position which is located above in the vertical direction and which is remote from the stirring roller over a distance greater than the maximum fly distance of the developer in the vertical direction, so that the developer does not reach said one end portion, and hence deposition of the developer is prevented. This prevention of deposition of the developer stabilizes the reflux of the developer.
According to the present invention, one end portion of the reflux plate is disposed within a predetermined range from a position where a plane passing through the rotation center axis of the stirring roller and crossing the reflux plate at right angles intersects the reflux plate, so that the amount of developer transferred to the control member increases, and hence the rate of circulation of the developer can be made to be larger.
According to the present invention, one end portion of the reflux plate is disposed at a position where a plane passing through the rotation center axis of the stirring roller and crossing the reflux plate at right angles intersects the reflux plate, so that the amount of developer transferred to the control member reaches the maximum, and the rate of circulation of the developer reaches the maximum.
According to the present invention, the inclination angle of the reflux plate is made to be larger than the angle of repose, so that the developer can not deposit stably on the reflux plate, and hence the circulation of the developer is stabilized.
According to the present invention, one end portion of the reflux plate is disposed on the developer supplying portion side of the stirring roller, so that excess developer is flowed back to the developer supplying portion side of the stirring roller. Thus, the mixing of the developer having been flowed back and the developer supplied from the developer supplying portion can be improved. This improvement in the mixing of the developer stabilizes image quality.
According to the present invention, by using small-grain diameter developer, image quality is improved. Further, even when such small-grain diameter developer is used, circulation of the developer can be stabilized as described above.
According to the present invention, a developing device in which circulation of the developer can be stabilized as described above is used, so that image quality of an image formed on a sheet can be stabilized.
The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings.
The present invention is described below in detail with reference to the drawings showing embodiments.
The case 1 has an approximate prism shape provided with an opening portion 1a located at a position facing the periphery surface of the photosensitive drum 2. A developer supplying portion 1b is opened on the opposite side to the opening portion 1a. The developing roller 3 and the control member 4 are disposed at positions facing the opening portion 1a inside the case 1. The stirring roller 7 is disposed at a position facing the developer supplying portion 1b. Further, a transfer roller 8 for transferring to the stirring roller 7 the developer (toner) supplied from the developer supplying portion 1b into the case 1 is disposed between the developer supplying portion 1b and the stirring roller 7. The stirring roller 7 and the transfer roller 8 rotate counterclockwise.
Further, a magnetic permeability sensor 9 for detecting the concentration of the toner inside the case 1 is provided under the stirring roller 7. When the toner amount stirred by the stirring roller 7 goes below an appropriate value, the toner is supplied from the developer supplying portion 1b on the basis of the detected value of the magnetic permeability sensor 9.
The developing roller 3 comprises: a magnet roller 31 of multi-electrode magnetization in which magnetic poles N1, N2, N3 and magnetic poles S1, S2, S3, S4 each composed of a bar magnet having a rectangular cross section are disposed in a radial manner at a plurality of positions in the circumferential direction; and a nonmagnetic sleeve 32 fitted to the outside of the magnet roller 31. The magnet roller 31 does not rotate, whereas the sleeve 32 is configured so at to rotate counterclockwise. Both ends of the magnet roller 31 are supported by both side walls of the case 1 in a non-rotary manner, and the magnetic pole N1 is disposed at a position facing the periphery surface of the photosensitive drum 2, while the magnetic pole N2 is disposed at a position facing the second gap G2. Each of the magnetic poles N1 and N2 has the center of magnetic pole (pole center axis P1 or P2) at the center of the width dimension in the circumferential direction of the developing roller 3.
The magnetic pole N1 facing the periphery surface of the photosensitive drum 2 is disposed in such a manner that the pole center axis P1 is displaced by 3° toward the upstream side (the magnetic pole S1 side) of the developer transferring direction relative to a straight line passing through the center axis O1 of the photosensitive drum 2 and the center axis O2 of the developing roller 3. The displacement amount of the pole center axis P1 is measured with a measuring instrument. This measuring instrument has, for example, a magnetic needle that rotates about the center axis O1 of the photosensitive drum 2, so that the displacement amount is detected on the basis of the rotation angle of the magnetic needle. Further, the control member 4, on which a cover body 10 is mounted, is disposed between the magnetic poles S1 and N2 in the inner side of the opening portion 1a of the case 1. Here, the control member 4 and the scraping member 5 are formed by metal plates such as aluminum or stainless steel.
The control member 4 performs main electrostatic charging of the developer under controlling the transferring amount of the developer at midway to the developing roller 3. The control member 4 consists of a nonmagnetic metal plate having a rectangular cross section, and periphery surface thereof faces the periphery surface of the developing roller 3 with spacing of the first gap G1. The control member 4 and the scraping member 5 are composed, for example, of similar materials such as to have approximately the same coefficient of linear expansion. Thus, even when curvature displacement occurs in the control member 4 and the scraping member 5 owing to a temperature change, variation of the first and the second gaps G1 and G2 can be limited at minimum.
The scraping member 5 scrapes the developer so as to perform preliminary electrostatic charging of the developer under controlling the transferring amount (the layer thickness) of the developer transferred to the first gap G1 at midway to the developing roller 3. The scraping member 5 is formed integrally with the nonmagnetic reflux plate 6. The reflux plate 6 is located from the above portion of the developing roller 3 (the upper end portion, hereafter) to the above portion of the stirring roller 7 (the lower end portion, hereafter) in an inclined manner such that the developing roller 3 side (the upper end portion) becomes high. An end portion on the developing roller 3 side of the reflux plate 6 is folded back toward the developing roller 3 side, so that a folded piece 6a is formed, and the folded piece 6a is made to be the scraping member 5.
Prior to transfer the developer to the first gap G1, the scraping member 5 scrapes the developer and thereby performs preliminary electrostatic charging of the developer. Thus, when the developer is binary developer, a repulsive face acts between respective parts of excess developer generated by the control member 4, and thereby prevents the excessive developer parts from combining with each other. This achieves smooth circulation of the developer. Further, since the scraping member 5 and the reflux plate 6 are integrated with each other, they reinforce each other so that displacement of the scraping member 5 in the expanding direction of the gap caused by a drag generating when the developer is scraped can be reduced. In the example of
The second gap G2, the first gap G1 (mm), and the width dimension Dm (mm) of the magnetic pole N2 are set up such that the following relation should hold.
G1<G2≦0.8×Dm
For example, preferably, the first gap G1 is made to be 0.5 mm, while the second gap G2 is made to be 2.3 mm or 3.2 mm. Since the magnetic pole N2 is disposed in the vicinity of the scraping member 5 while the width dimension Dm of the magnetic pole N2 satisfies G1<G2<0.8×Dm, the magnetic flux density can be enhanced in the vicinity of the scraping member 5. Accordingly, preliminary charging can be efficiently performed. Further, the width dimension Dm of the magnetic pole N2 is made to be 4 mm as described above. However, this width dimension may be an appropriate dimension.
Further, the first gap G1, the second gap G2, the amount of developer M1 (g/s/cm) transferred from the first gap G1, and the amount of developer M2 (g/s/cm) to be transferred to the second gap G2 are set up such that the following relation should hold.
M2>(M1/G1)G2
Here, M1 and M2 are based on the passing amount for 10 seconds in a portion where a length dimension of 5 cm in the longitudinal direction (center axis direction of the developing roller 3) of the control member 4 and the scraping member 5. (M1/G1) is the passing amount (g) per unit length of the gap G1. By establishing (M2/G2)>(M1/G1), the control member 4 stably scrapes and contacts with the developer, so that the circulation amount by the preliminary electrostatic charging can be increased.
In the vicinity of the control member 4 disposed inside the case 1, a first developer stagnation suppressing member 12 is provided for suppressing the stagnation of excess developer whose transferring is controlled by the control member 4. Further, in the vicinity of the scraping member 5, a second developer stagnation suppressing member 13 is attached for suppressing the stagnation of the developer to be transferred to the second gap G2.
The first developer stagnation suppressing member 12, and the second developer stagnation suppressing member 13 consist of nonmagnetic materials such as metal or synthetic resin having a length corresponding to that of the developing roller 3. The first developer stagnation suppressing member 12 is disposed between the upper end portion of the reflux plate 6 and the upper wall of the case 1 remote from the reflux plate 6, and flows back excess developer smoothly to the reflux plate 6. Further, under surface of the first developer stagnation suppressing member 12, a plurality of protruding portions 12a that contact with the upper surface of the reflux plate 6 protrude with spacing in the longitudinal direction. Upward bending of the reflux plate 6 is regulated by the protruding portions 12a. As such, since the protruding portions 12a contact with the reflux plate 6 and thereby suppress the displacement of the scraping member 5, displacement of the scraping member 5 in the expanding direction of the gap caused by a drag generating when the developer is scraped can be reduced. Here, the first developer stagnation suppressing member 12 shown in
The second developer stagnation suppressing member 13 extends from the upper end portion of the reflux plate 6 along the under surface of the reflux plate 6, and thereby transfers the developer smoothly to the second gap G2. Here, the second developer stagnation suppressing member 13 may be integrated with the reflux plate 6.
The inclination angle of the reflux plate 6 is larger than a angle of repose at which accumulated developer remains stable without collapsing.
Further, an end portion (the lower end portion) on the stirring roller 7 side of the reflux plate 6 is disposed within a predetermined range from a position where a plane passing through the rotation center axis O3 of the stirring roller 7 and crossing the reflux plate 6 at right angles intersects the reflux plate 6.
In the examples of
In the example of
Further, the lower end portion of the reflux plate 6 is disposed in the vicinity of the outer periphery of the stirring roller 7. Thus, part of the developer stirred by the stirring roller 7 flies toward the reflux plate 6. Here, in
Further, as shown in
The support members 11 and 11 consist of flat plates, and, in the respective center portions thereof, through holes 11a and 11a having a large diameter are bored into which center shaft end portions 3a and 3a of the developing roller 3 are fitted into, respectively. Further, in the support members 11 and 11, small-diameter through holes 11b and 11b facing a plurality of screw holes 12b and 12b bored at both end portions of the first developer stagnation suppressing member 12 attached to the control member 4, and small-diameter through holes 11c and 11c facing a plurality of screw holes 13a and 13a bored at both end portions of the second developer stagnation suppressing member 13 attached to the scraping member 5 and the reflux plate 6.
Then, in a state where the center shaft end portions 3a and 3a of the developing roller 3 are fitted into the through holes 11a and 11a, respectively and that the control member 4 and the scraping member 5 are disposed between the support members 11 and 11, male screws such as small screws are screwed and tightened through the through holes 11b and 11c into the screw holes 12b and 13a, so that a unit is formed. This unit can be incorporated into the case 1. The relative positional relation of the developing roller 3, the control member 4, and the reflux plate 6 (scraping member 5) can be accurately maintained, so that the amount of the first and the second gaps can be maintained. Further, the developing roller 3, the control member 4, and the reflux plate 6 (scraping member 5) can be made up in one unit, thereby improving the workability in assembling.
Further, by constituting the shape of the support members 11 and the shape of the case 1 in such a manner that the support members 11 are accurately fitted into and fixed to the case 1, the angle of inclination, the position of the lower end portion, and the like of the reflux plate 6 can be accurately maintained.
Binary developer is stored in the case 1 of the developing device configured as described above. The developer is composed of carrier such as, for example, magnetic powder, and toner. The present embodiment employs developer having a grain diameter smaller than ordinary one. Ordinary carrier has an average grain diameter of 85 μm, whereas the carrier of the present embodiment has an average grain diameter of 65 μm or smaller. Further, ordinary toner has an average grain diameter of 8.5 μm, whereas the toner of the present embodiment has an average grain diameter of 7.5 μm or smaller. When small-grain diameter developer is used, image quality can be improved.
When an electrostatic latent image carried on the photosensitive drum 2 is to be developed, the photosensitive drum 2 rotates clockwise, while the sleeve 32 of the developing roller 3 and the stirring roller 7 rotate counterclockwise. Accordingly, the developer inside the case 1 is transferred by the developing roller 3 to the second gap G2 under being stirred by the stirring roller 7. Then, the developer is controlled its transferring amount (the layer thickness) by the second gap G2, and passes through the second gap G2 under being scraped by the scraping member 5.
The developer to be transferred to the second gap G2 is transferred smoothly to the second gap G2, since its stagnation is suppressed by the second developer stagnation suppressing member 13. The developer having passed through the second gap G2 is transferred to the first gap G1. Since the second gap G2 is set up larger than the first gap G1, excess developer is surely generated by the control member 4. The excess developer is flowed back toward the reflux plate 6 in a state that the stagnation is suppressed by the first developer stagnation suppressing member 12, and is then flowed back to the stirring roller 7 by the reflux plate 6. As a whole, the developer circulates around the reflux plate 6. The angle of inclination and the position of the lower end portion of the reflux plate 6 are configured in such a manner that the reflux should be stabilized and that the transferring amount to the gap G2 should increase, as described above. Thus, circulation of the small-grain diameter developer can be stably performed.
The developing device constituted as described above is attached, for example, to a digital copying machine (image forming device) having an electro-photographic processing unit.
As this invention may be embodied in several forms without departing from the spirit of essential characteristics thereof, the present embodiments are therefore illustrative and not restrictive, since the scope of the invention is defined by the appended claims rather than by the description preceding them, and all changes that fall within metes and bounds of the claims, or equivalence of such metes and bounds there of are therefore intended to be embraced by the claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2003-317506 | Sep 2003 | JP | national |
This application is the national phase under 35 U.S.C. § 371 of PCT International Application No. PCT/JP04/12994 which has an International filing date of Sep. 7, 2004 and designated the United States of America.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP04/12994 | 9/7/2004 | WO | 3/8/2006 |
