Patent Grant
9500991
Field of the Invention
The present invention relates to a developing apparatus including a discharge outlet configured to discharge developer from a developing container.
Description of the Related Art
There has been widely used a developing apparatus configured to circulate two-component developer as a mixture of magnetic carrier and nonmagnetic toner while agitating and conveying the two-component developer by using a pair of conveying screws interposing a partition wall therebetween and arranged along a longitudinal direction of a developing container.
In the above-mentioned developing apparatus, fresh nonmagnetic toner is supplied with consumption in the nonmagnetic toner. However, it is known that, if old magnetic carrier continues to be circulated in the developing container, charging performance of the magnetic carrier to the nonmagnetic toner is gradually reduced. Accordingly, also as the control of the magnetic carrier in the developing container, there has been adopted control of maintaining constant charging performance of the magnetic carrier in the developing container in such a manner that the old magnetic carrier is discharged little by little and a fresh magnetic carrier is supplied by an amount corresponding to the discharge amount.
Japanese Patent Application Laid-Open No. 2002-72686 (Patent Literature 1) discloses a developing apparatus in which two-component developer for replenishment with an appropriate mix of the magnetic carrier and the nonmagnetic toner is supplied into the developing apparatus along with image formation, and thus the old magnetic carrier in the developing container is renewed little by little. Here, with reference to
The conveying screw 46 comprising a main spiral portion and a sub-spiral portion 50 connected to a downstream side of the main spiral portion. The main spiral portion conveys the two-component developer in a circulating direction and sends the two-component developer to the discharge opening 53. The sub-spiral portion 50 conveys the developer by the rotation in a direction opposite to a conveying direction of the main spiral portion. The sub-spiral portion 50 forces back most of the two-component developer that is conveyed by the main spiral portion to move toward the discharge opening 53 so that the sub-spiral portion 50 prevents the two-component developer from being excessively discharged through the discharge opening 53.
For the conveying screw disclosed in Patent Literature 1, an amount of the two-component developer falling into the discharge opening is fluctuated depending on a rotation angle of the sub-spiral portion. This is because a larger amount of the two-component developer falls into the discharge opening at a rotation position at which a root of the screw exposed at an end of the sub-spiral portion is faced upward than at a rotation position at which the root of the screw is faced downward. This phenomenon may cause an unstable discharge amount.
In view of the above, the configuration as described in Japanese Patent Application Laid-Open No. 2010-256701 (Patent Literature 2) is disclosed. Patent Literature 2 proposes, as illustrated in
However, the configuration disclosed in Patent Literature 2 has the following problem. That is, though discharge of the developer is essentially required to be stopped in a case where the amount of the developer in the developing container is reduced, the developer is discharged more than necessary. As a result, the developer in the developing apparatus is extremely reduced so that a quality of an output product may be degraded.
The above-mentioned problem results from the following phenomenon. That is, at a joining portion joining the sub-spiral portion 50 and the disk portion 51 together, a thickness of a blade of the sub-spiral portion 50 and a thickness of the disk portion 51 are added in the conveying direction. Accordingly, apparently, there is a portion having a locally increased blade thickness. At the portion having the locally increased blade thickness, an excessive amount of the developer is thrown up toward a developer discharge outlet, and hence discharge of the developer is not stopped.
The reason will be described below. A small amount of the developer present between an outermost circumferential surface of the sub-spiral portion 50 and an inner surface of the developing container is conveyed in a circumferential direction by the rotation of the conveying screw 46. Similarly, a small amount of the developer present between an outermost circumferential surface of the disk portion 51 and the inner surface of the developing container is also continuously conveyed in the circumferential direction by the rotation of the conveying screw 46. The developer is conveyed in the circumferential direction of the conveying screw 46 by a frictional force generated between the outermost circumferential surface of the sub-spiral portion 50 and the developer and a frictional force generated between the outermost circumferential surface of the disk portion 51 and the developer. Accordingly, in a case where the conveying screw 46 includes a portion in which the area of the outermost circumferential surface of the blade portion of the conveying screw 46 is locally increased, a force of conveying the developer in the circumferential direction is increased at this portion of the conveying screw 46, and thus the developer is thrown up at a position at which the developer is moved away from an inner wall of the developing container. A part of the thrown-up developer climbs over the disk portion 51 and falls toward a discharge screw 49, and hence discharge of the developer is accelerated.
That is, a developer throwing-up phenomenon due to the joining portion joining the sub-spiral portion 50 and the disk portion 51 occurs. The throwing-up phenomenon occurs as long as the developer is present in a slight gap between a bottom surface of the developing container and the joining portion joining the sub-spiral portion 50 and the disk portion 51 even when only a small amount of the developer is present on an upstream side in a direction of conveying the developer by the sub-spiral portion 50. Thus, though discharge of the developer is essentially required to be stopped in a case where the amount of the developer in the developing container is reduced, the developer is discharged more than necessary. As a result, the developer is extremely reduced so that the quality of an output product may be degraded.
The present invention has been made under such circumstances. The present invention provides a developing apparatus configured to discharge a surplus of developer through a discharge outlet, and also to suppress the developer throwing-up phenomenon due to a conveying portion and a disk portion provided in a path for discharging the developer toward the discharge outlet.
In order to solve the above-mentioned problem, according to an embodiment of the present invention, there is provided a developing apparatus, comprising:
a developer carrying member configured to carry developer;
a containing portion configured to contain the developer to be carried by the developer carrying member;
a discharge outlet through which a surplus of the developer in the containing portion is to be discharged;
a first conveying portion, provided in the containing portion so as to be rotatable, configured to convey the developer;
a second conveying portion provided downstream of the first conveying portion in a conveying direction of the first conveying portion so as to be rotatable together with the first conveying portion, the second conveying portion including a spiral blade portion configured to convey the developer in a conveying direction opposite to the conveying direction of the first conveying portion;
a disk portion provided upstream of the second conveying portion in the conveying direction of the second conveying portion so as to be rotatable together with the second conveying portion, the disk portion being formed to project radially-outwardly from a whole circumference of a rotary shaft; and
a third conveying portion provided upstream of the disk portion in the conveying direction of the second conveying portion so as to be rotatable together with the second conveying portion, the third conveying portion being configured to convey the developer that climbs over the disk portion, toward the discharge outlet,
wherein an upstream end of the spiral blade portion of the second conveying portion in the conveying direction of the second conveying portion and the disk portion are arranged with an interval therebetween.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Now, the embodiments of the present invention will be described in detail with reference to the drawings. The present invention may be similarly carried out in various types of image forming apparatus using a common developing apparatus. The present invention may be carried out regardless of types of the image forming apparatus, such as an intermediate transfer type, a recording material conveyance type, a tandem type, a single-drum type, a full-color type, and a monochrome type.
In the embodiment, only a substantial part for formation and transfer of a toner image will be described. By adding necessary apparatus, equipment, and housing structure, the present invention may be carried out for various applications such as a printer, various printing machines, a copying machine, a facsimile, and a multifunction peripheral.
Note that, general matters of the image forming apparatus disclosed in Patent Literature 1 are not shown, and redundant description thereof is omitted.
<Image Forming Apparatus>
As illustrated in
In the image forming portion Pa, a yellow toner image is formed on a photosensitive drum 1a and is then primarily transferred onto the intermediate transfer belt 10. In the image forming portion Pb, a magenta toner image is formed on a photosensitive drum 1b and is then primarily transferred to be superimposed on the yellow toner image of the intermediate transfer belt 10. In the image forming portions Pc and Pd, a cyan toner image and a black toner image are formed on photosensitive drums 1c and 1d, respectively, and are also primarily transferred sequentially onto the intermediate transfer belt 10 in a superimposed manner.
Four color toner images primarily transferred onto the intermediate transfer belt 10 are conveyed to a secondary transfer portion T2 and, collectively and secondarily transferred onto a recording material P.
In a case of a simplex mode in which an image is formed on one surface of the recording material P, the recording material P on which the four color toner images have been secondarily transferred is heated and pressurized by a fixing device 15 to have the toner image fixed onto a surface of the recording material P, and is then delivered through delivery rollers 16 onto an upper tray 17.
In a case of a duplex mode in which images are formed on both surfaces of the recording material P, a front surface and a rear surface of the recording material P having the image formed on the front surface of the recording material P is reversed through a duplex path (not shown), and is conveyed again to the secondary transfer portion T2. The recording material P, which has undergone a back surface recording in the same manner as the image forming process of the front surface recording, is delivered through the delivery rollers 16 onto the upper tray 17.
A separation roller 21 separates one by one the recording materials P fed out from a recording material cassette 20, and feeds the recording material P to registration rollers 22. The registration rollers 22 in a stop state receive the recording material P so as to put the recording material P on standby, and convey the recording material P into the secondary transfer portion T2 in synchronization with timing of the toner image transferred on the intermediate transfer belt 10.
The fixing device 15 brings a pressure roller 15b into pressure contact with a fixing roller 15a including a heater, to form a heating nip. While nipped and conveyed in the heating nip, the recording material P is heated and pressurized. Thus, the toner image is fused, and a full-color image is fixed onto the surface of the recording material P.
The image forming portions Pa, Pb, Pc, and Pd have substantially the same structure except that developing apparatus 4a, 4b, 4c, and 4d use different color toners of yellow, magenta, cyan, and black, respectively. The image forming portion Pa will be described below, and the other image forming portions Pb, Pc, and Pd are described by replacing the suffix of the reference symbol “a” in the description with “b”, “c”, and “d”.
The image forming portion Pa includes a charging roller 2a, an exposure device 3, the developing apparatus 4a, a primary transfer roller 5a, and a cleaning apparatus 6a, which are arranged around the photosensitive drum 1a.
The photosensitive drum 1a has a photosensitive layer having a negative charge polarity, which is formed on an outer circumferential surface of an aluminum cylinder, and rotates at a process speed switchable in a plurality of steps. An oscillation voltage of an AC voltage superimposed on a DC voltage is applied to the charging roller 2a. Then, the charging roller 2a is rotated in association with the rotation of the photosensitive drum 1a so as to uniformly charge the surface of the photosensitive drum 1a to a negative potential.
The exposure device 3 scans a laser beam, ON-OFF modulated in accordance with scan line image data expanded from a yellow color separation image, by a rotary mirror to write the electrostatic image on the surface of the charged photosensitive drum 1a. The developing apparatus 4a agitates and charges two-component developer, causes a developing sleeve 43 to carry the two-component developer in a magnetic brush state, and rubs the photosensitive drum 1a. An oscillation voltage of an AC voltage superimposed on a DC voltage is applied to the developing sleeve 43, and thus the nonmagnetic toner charged to a negative polarity is moved to the electrostatic image (exposed portion) having a positive polarity relative to the developing sleeve 43. Thus, the electrostatic image is reversely developed.
The primary transfer roller 5a presses an inner surface of the intermediate transfer belt 10 so as to form a primary transfer portion between the photosensitive drum 1a and the intermediate transfer belt 10. A positive DC voltage is applied to the primary transfer roller 5a to primarily transfer a negative toner image borne on the photosensitive drum 1a onto the intermediate transfer belt 10 passing through the primary transfer portion.
The intermediate transfer belt 10 is passed over and supported by a tension roller 12, a driving roller 11, and a stretching roller 13, and is driven by the driving roller 11 to rotate in a direction indicated by an arrow R2. A secondary transfer roller 14 abuts on the intermediate transfer belt 10 having the inner surface stretched by the stretching roller 13 connected to a ground potential, to form the secondary transfer portion T2. A positive DC voltage is applied to the secondary transfer roller 14 to secondarily transfer the toner image borne on the intermediate transfer belt 10 onto the recording material P.
<Developing Apparatus>
As illustrated in
The developing apparatus 4a has an automatic developer discharging function of maintaining a constant amount of the two-component developer in the developing container 42 even when a rotation speed of a conveying screw 46 is switched over.
As illustrated in
A pair of conveying screws 45, 46 is arranged with the partition wall 47 being interposed between the pair of conveying screws 45, 46. The conveying screws 45, are set to convey the two-component developer in opposite directions, respectively. The conveying screw 46 agitates and conveys the two-component developer in a direction indicated by an arrow D1, and the conveying screw 45 agitates and conveys the two-component developer in a direction indicated by an arrow D2. Thus, the two-component developer circulates in the developing container 42.
At this time, through the opening portion 47a provided on the side of the sub-spiral portion, the two-component developer is smoothly delivered from the conveying screw 46 as an example of a first conveying member to the conveying screw 45 as an example of a second conveying member. Furthermore, through the opening portion 47b provided on the side opposite to the sub-spiral portion, the two-component developer is smoothly delivered from the conveying screw 45 as the example of the second conveying member to the conveying screw 46 as the example of the first conveying member.
A return screw 50 is connected to a downstream side of the conveying screw 46 in a conveying direction of the two-component developer by the conveying screw 46. The return screw 50 conveys the two-component developer so as to force back the two-component developer from an outside of a circulation path of the two-component developer into the circulation path. The opening portion 47a is provided at a position opposed to a joint between a main spiral portion (46m:
As illustrated in
A length, a diameter, and a pitch of the return screw 50 are changed as appropriate depending on the configuration of the developing apparatus 4a, a discharging condition, an amount of the two-component developer in the developing container 42, and a target discharge amount. For example, when the length of the return screw 50 is extremely large, discharge of the two-component developer is suppressed more than necessary, with the result that reduction in charging performance of the two-component developer in the developing container 42 is progressed. Conversely, when the length of the return screw 50 is extremely small, the two-component developer is discharged more than necessary, and the amount of the two-component developer in the developing container 42 is insufficient so that the development may be failed.
According to the embodiment, the disk-like collar portion 51 as an example of a disk portion configured to cover the discharge opening 53 is provided on the most upstream side of the return screw 50 in the conveying direction of the return screw 50. The collar portion 51 is formed to project radially-outwardly from a whole circumference of a rotary shaft.
The collar portion 51 reduces a difference in inertial force of the two-component developer that is conveyed toward the discharge opening 53 by a difference in conveying performance between the main spiral portion and the return screw 50 of the conveying screw 46. The collar portion 51 prevents the two-component developer from falling from a discontinuity of the conveying blade of the return screw 50 into the discharge opening 53 to stabilize the discharge amount of the two-component developer. The collar portion 51 covers an end of the return screw 50 opposed to the discharge opening 53, and thus does not expose a root of the screw to the discharge opening 53. By use of the return screw provided with the collar portion 51, a necessary discharge amount is secured even when the rotation speed of the conveying screw 46 is switched over to a lower speed. Even when the rotation speed of the conveying screw 46 is switched over to a higher speed, the discharge amount of the two-component developer is not abruptly increased.
A discharge screw 49 connected to the return screw 50 is extended through a center of the discharge opening 53. When the developer is supplied so as to compensate the toner consumed with the image formation, an amount of the developer in the developing container is increased because of the supply of fresh carrier. The discharge screw 49 discharges a surplus of the developer that is newly increased by the supply. Specifically, the discharge screw 49 conveys the surplus of the developer that climbs over the collar portion 51 and falls onto the discharge screw 49, through the discharge opening 53. Then, the discharge screw 49 conveys the developer to a developer discharge outlet 48 to discharge the developer out of the developing apparatus 4a.
As illustrated in
<Supply Control of Two-Component Developer for Replenishment>
As illustrated in
A supply amount of the two-component developer for replenishment is approximately determined based on the number of revolutions of the supplying screw 32 of the supplying mechanism 31. A control portion 30 controls ON/OFF of rotation and the rotation speed of the supplying screw 32, and supplies the two-component developer for replenishment so that a toner density of the two-component developer contained in the developing container 42 is maintained constant.
At this time, the amount of the two-component developer in the developing container 42 is gradually increased with the image formation. The nonmagnetic toner is consumed with the image formation, but the magnetic carrier is not consumed to remain and keep circulating in the developing container 42. Thus, the amount of the two-component developer in the developing container 42 is increased. In a case where the amount of the two-component developer is increased, the developer climbs over the return screw 50 and the collar portion 51 illustrated in
In this way, the consumed nonmagnetic toner is supplied with the two-component developer for replenishment, and at the same time, the two-component developer in the developing container 42 containing an excessive amount of the magnetic carrier is discharged little by little. The two-component developer is renewed automatically and gradually so that the amount of the two-component developer in the developing container 42 is maintained constant, and thus the automatic developer discharging function is realized.
Next, a structure configured to suppress the throwing-up of the developer in a vicinity of the disk portion according to the first embodiment will be described in detail.
As illustrated in
In the longitudinal direction of
Here, the conveying screw 46 rotates clockwise when viewed from the discharge opening 53. The joining portion of the return screw 50 and the collar portion 51 passes the same point once for each revolution period with the rotation of the conveying screw 46. As described above, by the rotation of the return screw 50 and the collar portion 51, the return screw 50 and the collar portion 51 apply a frictional force to a small amount of the developer that is present in a clearance portion H formed between the outermost diameter portion of the return screw 50 and an inner surface of the developing container and between the outermost diameter portion of the collar portion 51 and the inner surface of the developing container. Thus, the small amount of the developer is conveyed by the frictional force.
That is, the above-mentioned frictional force exerted on the developer present in the clearance portion H is in proportion to an axial length (thickness of the blade) of the outermost diameter portion of the blade portion of the return screw 50 and an axial length (thickness of the blade) of the outermost diameter portion of the blade portion of the collar portion 51. As a result, the following phenomenon occurs. The conveying screw 46 rotates clockwise when viewed from the discharge opening 53, and it is assumed that a vertical top position of the clockwise rotation is twelve o'clock. The developer present at a bottom of the zone A is conveyed by the rotation of the conveying screw 46 to a position of nine o'clock along the inner surface of the developing container. However, when the joining portion of the return screw 50 and the collar portion 51, i.e., a portion having a locally increased width (thickness) of the rim of the blade portion in the rotation axis direction passes the position of nine o'clock, a conveying force is increased as compared to a case where other portion than the joining portion passes the position of nine o'clock. Accordingly, after passing the position of nine o'clock, the developer is thrown up vertically upward due to the inertial force. Then, the thrown-up developer falls radially. One part of the thrown-up developer falls to the return screw 50, and another part of the thrown-up developer falls to the discharge screw 49 so as to be discharged.
That is, when the amount of the developer in the developing container 42 is reduced, discharge of the developer is essentially required to be stopped. However, as long as even a small amount of the developer is present in the zone A, the developer is thrown up every time the conveying screw 46 makes one revolution, and thus the developer is conveyed to the developer discharge outlet 48. Accordingly, there has been a problem in that the amount of the developer is extremely reduced.
Accordingly, in the first embodiment, as illustrated in
With this configuration, it is possible to suppress apparent and local increase of the thickness of the rim of the blade portion of the screw due to the joining portion of the blade portion of the return screw 50 and the blade portion of the collar portion 51. As a result, excessive discharge of the developer is suppressed, and thus the amount of the developer can be controlled suitably.
Note that, in the first embodiment, as illustrated in
Note that, as illustrated in
The second embodiment is different from the first embodiment in the following points, but is similar to the first embodiment in the other points. Accordingly, in the following description of the second embodiment, components corresponding to the components of the first embodiment are denoted by the same reference symbols, and detailed description thereof is omitted.
The second embodiment has a feature in that, as illustrated in
In the second embodiment, as illustrated in
In the embodiment, the diameter of the blade portion of the return screw 50 is reduced only at the most upstream end portion of the return screw 50, but the present invention is not limited thereto. The diameter of the blade portion of the return screw 50 may be reduced in the whole region in the longitudinal direction of the return screw 50.
The collar portion 51 only needs to have a circumferential surface at an outer periphery thereof. In addition to the flat-plate-like shape described in the first and second embodiments, the collar portion 51 may have such an appearance that a surface of revolution such as a conical surface and a spherical surface is opposed to the discharge opening.
As illustrated in
According to the present invention, a developing apparatus configured to discharge a surplus of developer through a discharge outlet can suppress a thrown-up developer which might otherwise be caused by a joining portion joining an upstream side of a disk portion and a conveying portion, the disk portion being provided in a path through which the developer is discharged toward the discharge outlet.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2013-136150, filed Jun. 28, 2013, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2013-136150 | Jun 2013 | JP | national |
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| Number | Date | Country |
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| 2001-265098 | Sep 2001 | JP |
| 2002-072686 | Mar 2002 | JP |
| 2009-192701 | Aug 2009 | JP |
| 2010-026292 | Feb 2010 | JP |
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| Entry |
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| Number | Date | Country | |
|---|---|---|---|
| 20150003876 A1 | Jan 2015 | US |
