Patent Application
20080080906
Basically, this developing device 1 is mainly composed of a housing 10 functioning as a case, a developing roller 20 functioning as a developer carry member, a trimming plate 30 functioning as a layer regulate member, and two screw augers 41, 42 each functioning as a developer stir/carry member. In
The housing 10 is structured as follows: that is, in the portion of the housing 10 providing its end portion that is opposed to the developing area D of the sensitive drum 3, there is opened up an opening 12 to which the developing roller 20 is in part exposed; and, in the portion of the housing 10 extending over the end portion thereof that is opposite to the opening 12, there is formed a developer storage portion 13 for storing the two-component developer 2 therein. The developer storage portion 13 includes two parallel arranged developer circulate/carry passages 13b and 13c which communicate with each other at the two end portions thereof and are separated in the central portions thereof by a partition wall 13a.
The developing roller 20 includes a cylindrical-shaped sleeve 21 which can be rotated in such a manner that it is exposed in part to the vicinity of the opening 12 of the housing 10, and a magnet roller 22 having two or more magnetic poles disposed in the internal space of the sleeve 21 at a given angle, while the positions of the sleeve 21 and magnet roller 22 are respectively fixed. Also, the developing roller 20 (specifically, the sleeve 21 thereof) can be driven and rotated when power is applied thereto from a rotation drive device (not shown), and, to the developing roller 20, there is applied from a developing bias power supply (not shown) a given developing bias which is used to form a developing electric field between the sensitive drum 3 and developing roller 20. As the developing bias, for example, there is applied a direct current on which an alternating current component is superimposed. By the way, the developing device 1 is set in such a manner that a clearance (d: see
The sleeve 21 is formed in a cylindrical shape having almost the same width (length) as an image formation effective area of the sensitive drum 3 in the axial direction thereof, and the sleeve 21 is made of nonmagnetic material (for example, stainless steel, or aluminum). Also, the magnet roller 22 includes five magnetic poles S1, S2, S3, N1 and N2 which are disposed properly on its roller shaft 22a so as to cooperate together in forming such a normal direction magnetic flux density distribution as shown by a dotted line in
The trimming plate 30 is formed in a plate shape having almost the same length as the developing effective area of the sleeve 21 in the axial direction and is made of nonmagnetic material (for example, stainless steel). As the trimming plate, there may also be used other member, for example, a member which is structured such that magnetic material is bonded to the nonmagnetic material thereof. And, the trimming plate 30 is fixed to the portion of the housing 10 on the opening 12 side by installing means such as a screw in such a manner that the leading end portion 30a thereof is opposed to the surface of the surface of the developing roller 20 (sleeve 21) while having a clearance (γ: see
The screw augers 41, 42 are rotation members which are structured such that the vane portions 41b, 42b thereof for stirring and carrying the two-component developer 2 are wound spirally on their associated rotation shaft portions 41a, 42a at a given pitch. The screw augers 41, 42 are respectively mounted within the two developer circulate/carry passages 13b, 13c formed in the developer storage portion 13 of the housing 10 in such a manner that they can be rotated in a given direction to circulate and carry the developer 3 existing in the two carry passages in a given direction.
Also, in the present developing device 1, as shown in
The projecting portion 15 is formed in the opposed portion 14 of the housing 10, more specifically, at least in the portion of the opposed portion 14 that extends from the developing magnetic pole S1 of the magnet roller 22 in the rotation direction A of the sleeve 21 to the developer peel-off magnetic pole S2 and corresponds to an area E having a normal direction magnetic flux density of 20 mT or less. In the present embodiment, since one area E having a normal direction magnetic flux density of 20 mT or less exists between the post-development carry magnetic pole N1 and developer peel-off magnetic pole S2, the formation position of the projecting portion 15 is set in this area E. Reference sign Mo, which is shown by a one-dot chain line in
Also, the projecting portion 15 is formed such that, as shown in
The projecting portion 15 according to the present embodiment is formed such that, in the projecting corner portion (15aa: see
As described above, according to the present projecting portion 15, its end portion 15a, where the clearance α between the projecting portion 15 and the outer peripheral surface of the sleeve 21 is the minimum value, is formed such that it exists at least within the area E which provides the normal direction magnetic flux density of 20 mT or less. Also, the projecting portion 15 is formed integrally with the housing 10 (at least the opposed portion 14 of the housing 10). However, the projecting portion 15 may also be provided separately from the housing 10 and, after then, the projecting portion 15 may be mounted onto the opposed portion 14.
Next, description will be given below of the operation of the present developing device 1.
When the image forming apparatus of an electrophotographic system incorporating the developing device 1 therein is in a mode for forming an image, firstly, the developing roller 20 and augers 41, 42 start to rotate and, at the same time, a developing bias voltage is applied to the developing roller 20. Thus, the two-component developer 2 stored in the developer storage portion 13 of the housing 10 is circulated and carried within the circulation passage of the developer storage portion 13 while it is being stirred up by the rotating augers 41, 42. In this operation, the toner of the two-component developer 2 is fully stirred with carriers, whereby the toner is frictionally charged and is also stuck on the surface of the carriers electrostatically.
Then, part of the two-component developer 2, which is carried by the auger 41 situated near to the developing roller 20, is held by the magnetic force of the developing roller 20. That is, on the surface of the rotating sleeve 21 of the developing roller 20, there are held a large number of chain-like connected magnetic carriers with the toner stuck thereon by the magnetic forces of the magnetic poles S3, N2 of the magnet roller 22 in a state where the magnetic carriers with the toner stuck thereon form a magnetic brush. Next, when the two-component developer 2 held by the sleeve 21 passes through a given clearance (γ) formed between the sleeve 21 and trimming plate 30 while the developer 2 is being carried with the rotation of the sleeve 21, the passing state of the two-component developer 2 is regulated, whereby the layer thickness (the magnetic brush height) of the two-component developer 2 is turned into a substantially even thickness.
After then, the two-component developer 2, the layer thickness of which is regulated in this manner, is carried to the developing area D disposed opposed to the sensitive drum 3 with the rotation of the sleeve 21 of the developing roller 20. Next, the two-component developer 2 carried to the developing area D is made to pass in a state where the leading end portion of the magnetic brush formed by the magnetic force of the developing magnetic pole S1 is contacted with the outer peripheral surface of the sensitive drum 3; and, in such passage of the two-component developer 2, owing to a developing (alternating) electric field formed between the developing roller 20 and sensitive drum 3 by a developing bias voltage applied to the developing roller 20, only the toner of the two-component developer 2 is electrostatically stuck onto an electrostatic latent image on the sensitive drum 3. Thus, the development of the electrostatic image is carried out by the developing device 1.
Also, the two-component developer 2 on the developing roller 20 after it has passed through the developing area D is then carried while it is held on the sleeve 21 by the magnetic force of the post-development carry magnetic pole N1 and, after then, when it passes through between the developer peel-off magnetic poles S2 and S3, in principle, it is peeled off from the sleeve 21 due to a repelling magnetic force (magnetic field) formed by the developer peel-off magnetic poles S2 and S3 having the same polarity, and is then returned into the housing 10. The thus peeled and returned developer 2 is stirred again within the developer storage portion 13 of the housing 10. On the other hand, onto the developing roller 20 from which such developer has been peeled off, there is supplemented again the two-component developer 2 stirred within the developer storage portion 13 according to the above-mentioned principle, whereby the two-component developer 2 is supplied to and held by the developing roller 20.
And, in the present developing device 1, the two-component developer 2 held by the sleeve 21 of the developing roller 20 after having passed through the developing area D, when it passes with the rotation of the sleeve 21 in such a manner that it is opposed to the opposed portion 14 of the housing 10, is held in the following state.
Firstly, the two-component developer 2 on the sleeve 21, as shown in
Next, the developer 2 forming the magnetic brush 2a, when it passes the area E where the normal direction magnetic flux density between the post-development carry magnetic pole N1 and developer peel-off magnetic pole S2 is 20 mT or less, forms a magnetic brush 2b the rising head height of which decreases gradually as the magnetic flux density decreases; and, especially, when the developer 2 passes through the point (Mo) having a magnetic flux density of 0 mT, the developer 2 moves in a state where the magnetic brush 2b provides the lowest height (h).
In this case, since the two-component developer 2 on the sleeve 21 passes through the area E the magnetic force of which is weaker than its front and rear areas, the height of the magnetic brush is lowered; and, at the time when the magnetic brush 2a provides the lowest height (h), the developer 2 passes through (the corner portion 15aa of) the end portion 15a of the projecting portion 15 of the opposed portion 14 of the housing 10 where the clearance (α) between the projecting portion 15 and the sleeve 21 is set for the narrowest value (α min).
The two-component developer 2 on the sleeve 21 after having passed through the projecting portion 15 receives the magnetic force of the developer peel-off magnetic pole S2 as it approaches the developer peel-off magnetic pole S2, and moves while forming again an angularly rising magnetic brush 2c.
Thus, the two-component developer 2 held on the sleeve 21 after having passed through the developing area D, when it passes through the point (Mo) which belongs to the area E having a normal direction magnetic flux density of 20 mT or less and has a magnetic flux density of 0 mT, passes through (the corner portion 15aa) of the end portion 15a of the projecting portion 15 where the minimum clearance α between the sleeve 21 and projecting portion 15 is set substantially equal to the magnetic brush height h. Especially, the height h of the magnetic brush 2b when the developer 2 passes through the area E having a normal direction magnetic flux density of 20 mT or less hardly depends on variations (increase and decrease) in the developer carry amount by the sleeve 21 and can be thereby easily held constant.
Therefore, between the end portion 15a of the projecting portion 15 of the opposed portion 14 of the housing 10 and the magnetic brush 2b on the sleeve 21 passing through such end portion 15a, an unnecessary gap is prevented against occurrence. That is, a space between the end portion 15a of the projecting portion 15 and the outer peripheral surface of the sleeve 21 is maintained in a stably closed state by the magnetic brush 2b. As a result of this, the developer (especially, toner) 2 existing within the housing 10 can be prevented from being discharged and flown out to the outside from the opening 12 of the housing 10 through an air gap which could be otherwise formed between the end portion 15a of the projecting portion 15 and magnetic brush 2b.
Also, the projecting portion 15, as shown in
Further, the projecting portion 15, as shown in
In addition, since the projecting portion 15, as shown in
That is, when the developer carry amount increases, the height of the magnetic brush on the sleeve 21 increases generally, which can give rise to a phenomenon (a so called inverted fall phenomenon) that the upper end portion of the magnetic brush 2e portion of the magnetic brush 2c formed by the magnetic force of the developer peel-off magnetic pole S2 just after the developer has passed through the projecting portion 15 can be curved and fallen on the upstream side of the rotation direction of the sleeve 21. However, even when such inverted fall phenomenon occurs, the inversely fallen portion of the magnetic brush 2e is contacted with the stepped surface of the end portion 15e of the projecting portion 15, while the stepped surface extends substantially parallel to a virtual line going outward in the diameter direction of the magnet member. As result of this, the steep stepped surface of the end portion 15a of the projecting portion 15 is closed by the magnetic brush portion which has fallen onto and contacted with such stepped surface, thereby preventing an unnecessary clearance from occurring between the projecting portion 15 and magnetic brush (2b). This prevents the occurrence of an air stream which flows toward the outside from the interior of the housing 10 through such clearance, thereby being able to prevent the developer from gushing and flying out on such air stream to the outside.
Also, since the projecting portion 15 is formed such that its portion 15a having the minimum clearance (α min) is situated at the opposite position substantially opposed to the trimming plate 30 with the sleeve 21 between them, there can be obtained the following operation effects. That is, firstly, when the sleeve 21 passes through the position opposed to the trimming plate 30, owing to the dense existence of the developer 2 in the clearance between the sleeve 21 and the leading end portion 30a of the trimming plate 30, the sleeve 21 is allowed to rotate stably in a state where it is slightly pushed up in the opposite direction to the trimming plate 30. Thanks to this, in the developing time, the sleeve 21 can rotate stably in a state where the variations of the position thereof are controlled properly, whereby the dimensional variations of the minimum clearance (α min) of the sleeve 21 with respect to the end portion 15a of the projecting portion 15 can be restricted properly. As a result of this, the occurrence of the unnecessary gap between the end portion 1Sa of the projecting portion 15 and magnetic brush 2b can be prevented further positively, thereby being able to prevent the flying of the developer further firmly.
Now, description will be given below of tests that have been conducted using the present developing device.
<Test 1>
In the test 1, using the developing device 1 (example of the invention) including the projecting portion 15 according to the above-mentioned embodiment and other developing devices (comparison examples 1 to 3) respectively excluding the projecting portion 15, the occurring states of the flying (toner cloud) of the developer when an image is formed using the respective developing devices are checked.
As the developing device 1 according to the example of the invention, there is prepared a developing device which satisfies the following conditions. That is, as the sleeve 21, there is used a sleeve which has a thickness of the order of 0.5 mm and an outside diameter of the order of 18 mm. As the magnet roller 22, there is disposed a developing magnetic pole S1 having an S polarity in such a manner that the peak value (120 mT or more) of the normal direction magnetic flux density can appear at a position which provides an elevation angle of about 15° from the horizontal line (in
Also, the minimum clearance (α min) between the sleeve 21 and end portion 15a existing on the downstream side of the sleeve rotation direction in the projecting portion 15 of the housing 10 is set for about 1.3 mm. The end portion 15b existing on the upstream side of the sleeve rotation direction in the projecting portion 15 is set at the same position as the point where the normal direction magnetic flux density of the carry magnetic pole N1 becomes about one half. And, the clearance β between the sleeve 21 and the opposed position 14 of the housing 10 is set for a value equal to or larger than about 1.5 mm.
On the other hand, as the comparison examples 1˜3, there are prepared developing devices respectively satisfying the same conditions as the developing device according to the example of the invention except that the following conditions are changed. That is, as shown in
And, after the developing device according to the example and the developing devices according to the comparison examples are mounted on printers each of an electrophotographic system respectively, print for the test is carried out individually. In this case, the developing devices are respectively set such that a clearance d between the sleeve 21 and sensitive drum 3 provides about 0.35˜0.50 mm, and the sleeve 21 is rotated at a sufficient velocity to allow the print speed to print 8 sheets/min. for recording paper of a horizontal A4 size (the print velocity is set about double the velocity of the sensitive drum 3 that is about 170 cm/sec.). As the developer 2, there is used a two-component developer containing non-magnetic toner having an average particle diameter of the order of 6 μm and magnetic carriers each having an average particle diameter of the order of 30 μm, with the toner having a density of about 11 wt %. The print for the test is carried out under the condition that test images each having an image density of 16% are successively formed on 1500 sheets of A4-size recording paper under the low-temperature and low-humidity environment of 10° C., 15% RH (the environment where a toner cloud is easy to occur). Also, the print is carried out by setting the developer carry amount of the sleeve 21 for values varied every 50 g/m2 in the range of 250˜650 g/m2. For reference, the developer carry amount, in normal use, is set for values in the range of, for example, 300˜600 g/m2.
As for the occurring state of the toner cloud, after the above-mentioned print for the test is completed, toner, which had stuck to the portion of the housing 10 existing upwardly of the opening 12, is transferred to adhesive tape, the weight of the toner is measured, and the measured weight value is evaluated according to the following reference levels (toner cloud levels). Table 6 shows the evaluation results. In the table 6, together with the evaluation results, there are shown their respective approximate curves. Here, an allowable level may preferably be the level 2 or lower and, more preferably, the allowable level may be the level 1.
Level 1: Toner sticking amount is 0.015 g/m2 or less
Level 2: Toner sticking amount is 0.030 g/m2 or less
Level 3: Toner sticking amount is 0.050 g/m2 or less
Level 4: Toner sticking amount is 0.075 g/m2 or less
Level 5: Toner sticking amount is more than 0.100/m2
<Test 2>
In the test 2, for the embodiment of the invention, there is used a developing device in which the forming position of the projecting portion 15 to be formed in the opposed portion 14 of the housing 10 is changed in the following manner. This developing device is applied to the printer and the occurring state of the flying (toner cloud) of the developer is checked when an image is formed.
To form the projecting portion, as shown in
As the developing devices, there are prepared developing devices having the same conditions as those used in the test 1 except that the condition of the projecting portion is changed in the above-mentioned manner. And, similarly to the test 1, after the respective developing devices are mounted onto their associated printers and print for the test is carried out, the test print is checked for the occurring states of the toner cloud, and the toner cloud occurring states are evaluated respectively. In the present test print, the developer carry amount is set for 450 g/m2.
As regards the projecting portion 15 to be formed in the opposed portion 14 of the housing 10 in the above-mentioned embodiment, it is not limited to the structure shown in the present embodiment but, for example, there may also be employed such structures as shown in
Specifically, as regards a projecting portion 15 shown in
As regards a projecting portion 15 shown in
As regards a projecting portion 15 shown in
Also, when there is used a magnet roller 22 employing a magnetic pole arrangement structure in which there are present two or more areas E each having a normal direction magnetic flux density of 20 mT or less in the opposed portion 14 of the housing 10, a projecting portion 15 to be formed in the opposed portion 14 can be formed such that the projecting portion 15 is contained in at least one of the areas E; and, preferably, the projecting portion 15 may be formed such that it is contained at least in the area E that exists nearest to the opening 12.
The developing devices according to the above-mentioned embodiments of the invention can be applied to a single or multiple color image forming apparatus represented by a printer, a copying machine, a facsimile and the like which use an electrophotographic system or an electrostatic recording system.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-267987 | Sep 2006 | JP | national |
