Developing device

A developing device includes an accommodating casing, a rotatable developer carrying member, a regulating portion, a magnetic flux generating portion including a first magnetic pole and a second magnetic pole which have the same polarity, and a cover portion provided downstream of the developing region and upstream of a maximum magnetic flux density position of the second magnetic pole with respect to a rotational direction of the developer carrying member. The cover portion is disposed between the casing and the developer carrying member. As measured in the rotational axis direction, a dimension of the cover portion at an upstream end with respect to the rotational direction is smaller than a dimension of the cover portion in at least a region positioned downstream of the upstream end with respect to the rotational direction.

FIELD OF THE INVENTION AND RELATED ART

The present invention relates to a developing device including a developer carrying member rotatable while carrying a developer, and relates to an image forming apparatus, including the developing device, such as a copying machine, a printer, a facsimile machine or a multi-function machine having a plurality of functions of these machines.

An image forming apparatus of an electrophotographic type or an electrostatic recording type includes a developing device for developing an electrostatic latent image, with a developer such as toner, formed on a photosensitive drum as an image bearing member. The developing device includes a developing sleeve as a developer carrying member rotatable while carrying a developer and supplies, to the photosensitive drum, the developer carried on the developing sleeve.

In the case of such a developing device, there is a liability that air flows into a developing container constituting the developing device due to rotation of the developing sleeve and atmospheric pressure in the developing container increases and thus the developer in the developing container is scattered to an outside of the developing container. For this reason, a constitution in which an inner cover is provided between an outer cover of the developing container and the developing sleeve and the air flowing from between the developing sleeve and the inner cover into the developing container is discharged through between the inner cover and the outer cover has been proposed (Japanese Laid-Open Patent Application (JP-A) 2015-72331).

However, in the case of the constitution disclosed in JP-A 2015-72331, there is a liability that the air containing the developer is discharged, to the outside of the developing container, from an inflow path, between the pressure and the inner cover, for permitting flowing of the air into the developing container. Particularly, the developer scattered from both end portions of the developing container with respect to an axial direction (rotational axis direction) of the developer carrying member is liable to flow into a periphery of the developing container, so that, there is a possibility that scattering of the developer cannot be sufficiently suppressed.

SUMMARY OF THE INVENTION

A principal object of the present invention is to provide a developing device capable of sufficiently suppressing scattering of a developer from both end portions of a developing container with respect to a rotational axis direction of a developer carrying member.

According to an aspect of the present invention, there is provided a developing device comprising: an accommodating casing configured to accommodate a developer; a rotatable developer carrying member provided in the accommodating casing and configured to develop, in a developing region, an electrostatic latent image formed on an image bearing member; a regulating portion provided below the developer carrying member with respect to a vertical direction and configured to regulate an amount of the developer on the developer carrying member; a magnetic flux generating portion provided inside the developer carrying member and including a first magnetic pole provided downstream of the developing region with respect to a rotational direction of the developer carrying member and a second magnetic pole which is provided adjacently downstream of the first magnetic pole with respect to the rotational direction and which has a polarity identical to a polarity of the first magnetic pole; and a cover portion provided downstream of the developing region and upstream of a maximum magnetic flux density position of the second magnetic pole with respect to the rotational direction, the cover portion being disposed between the casing and the developer carrying member over a rotational axis direction of the developer carrying member with a gap between itself and the casing and with a gap between itself and the developer carrying member, wherein as measured in the rotational axis direction, a dimension of the cover portion at an upstream end with respect to the rotational direction is smaller than a dimension of the cover portion in at least a region positioned downstream of the upstream end with respect to the rotational direction.

DESCRIPTION OF EMBODIMENTS

First Embodiment

The First Embodiment will be described with reference toFIGS. 1 to 7. First, a general structure of an image forming apparatus in this embodiment will be described usingFIGS. 1 and 2.

An image forming apparatus100in this embodiment is a tandem(-type) full-color printer of an electrophotographic type, in which four image forming portions PY, PM, PC and PK each including a photosensitive drum1as an image bearing member are provided. The image forming apparatus100forms a toner image (image) on a recording material depending on an image signal from a host device such as an original reading device (not shown) connected with an apparatus main assembly100A or a personal computer communicatably connected with the apparatus main assembly100A. As the recording material, a sheet material such as a sheet, a plastic film or a cloth can be cited. Further, the image forming portions PY, PM, PC and PK form toner images of yellow, magenta, cyan and black, respectively.

The four image forming portions PY, PM, PC and PK provided in the image forming apparatus100have the substantially same constitution except that colors of developers are different from each other. Accordingly, the image forming portion PY will be described as a representative and other image forming portions will be omitted from description.

As shown inFIG. 2, at the image forming portion PY, a cylindrical photosensitive member as the image bearing member, i.e., the photosensitive drum1is provided. The photosensitive drum1is rotationally driven in an arrow direction in the figure. At a periphery of the photosensitive drum1, a charging roller2as a charging means, a developing device4, a primary transfer roller52as a transfer means, and a cleaning device as a cleaning means are provided. Below the photosensitive drum1in the figure, an exposure device (a laser scanner in this embodiment)3as an exposure means is provided.

Above the respective image forming portions inFIG. 1, a transfer device5is provided. In the transfer device5, an endless intermediary transfer belt51as an intermediary transfer member is stretched by a plurality of rollers and is constituted so as to be circulated (rotated) in an arrow direction. The intermediary transfer belt51carries and feeds the toner images which are primary-transferred on the intermediary transfer belt51as described later. At a position opposing an inner secondary transfer roller53, of the rollers stretching the intermediary transfer belt51, while sandwiching the intermediary transfer belt51between itself and the inner secondary transfer roller53, an outer secondary transfer roller54as a secondary transfer means is provided and constitutes a secondary transfer portion T2for transferring the toner images from the intermediary transfer belt51onto the recording material. A fixing device6is provided downstream of the secondary transfer portion T2with respect to a recording material feeding direction.

At a lower portion of the image forming apparatus100, a cassette9in which the recording material S is accommodated. The recording material S fed from the cassette9is fed toward a registration roller pair92by a feeding roller pair91. A leading end of the recording material S abuts against the registration roller pair92which is in a rest state, and forms a loop, so that oblique movement of the recording material S is corrected. Thereafter, rotation of the registration roller pair92is started in synchronism with the toner images on the intermediary transfer belt51, so that the recording material S is fed to the secondary transfer portion T2.

A process of forming, for example, a four-color-based full-color image by the image forming apparatus100constituted as described above will be described. First, when an image forming operation is started, a surface of a rotating photosensitive drum1is electrically charged uniformly by the charging roller2. Then, the photosensitive drum1is exposed to laser light, corresponding to an image signal, emitted from the exposure device3. As a result, an electrostatic latent image corresponding to the image signal is formed on the photosensitive drum1. The electrostatic latent image on the photosensitive drum1is visualized by toner as the developer accommodated in the developing device4and is formed in a visible image (toner image).

The toner image formed on the photosensitive drum1is primary-transferred onto the intermediary transfer belt51at a primary transfer portion T1(FIG. 2) constituted between the photosensitive drum1and a primary transfer roller52provided while sandwiching the intermediary transfer belt51between itself and the photosensitive drum1. At this time, to the primary transfer roller52, a primary transfer bias is applied. Toner (transfer residual toner) remaining on the surface of the photosensitive drum1after the primary transfer is removed by the cleaning device7.

Such an operation is successively performed at the respective image forming portions for yellow, magenta, cyan and black, so that the four color toner images are superposed on the intermediary transfer belt51. Thereafter, in synchronism with timing of toner image formation, the recording material S accommodated in the cassette9is fed to the secondary transfer portion T2. Then, by applying a secondary transfer bias to the outer secondary transfer roller54, the four color toner images are secondary-transferred altogether from the intermediary transfer belt51onto the recording material S. Toner remaining on the intermediary transfer belt51without being completely transferred onto the recording material S at the secondary transfer portion T2is removed by an intermediary transfer belt cleaner55.

Then, the recording material S is fed to the fixing device6as a fixing means. In the fixing device6, a fixing roller61including a heat source such as a halogen heater and a pressing roller62are provided, and a fixing nip is formed by the fixing roller61and the pressing roller62. The recording material S on which the toner recording materials are transferred is passed through the fixing nip, so that the recording material S is heated and pressed. Then, the toners on the recording material S are melted and mixed with each other and are fixed as a full-color image on the recording material S. Thereafter, the recording material S is discharged onto a discharging tray102by a discharging roller101. As a result, a series of image forming process operations is ended.

Incidentally, the image forming apparatus100in this embodiment is also capable of forming a single-color image, such as a back (monochromatic) image, or a multi-color image by using the image forming portion(s) for a desired single color or for some colors of the four colors.

A detailed structure of the developing device4will be described usingFIGS. 3 and 4. The developing device4includes a developing container41for accommodating non-magnetic toner and a magnetic carrier and includes a developing sleeve44as a developer carrying member rotating while carrying the developer accommodated in the developing container41. In the developing container41, feeding screws43aand43bas developer feeding members for circulating the developer in the developing container41while stirring and feeding the developer in the developing container41are provided. The developing sleeve44is capable of feeding the developer to an opposing region opposing the photosensitive drum1. Inside the developing sleeve44, a magnet44aas a maximum flux generating means including a plurality of magnetic poles with respect to a circumferential direction is non-rotatably provided. Further, a developing blade42as a regulating member forms a thin layer of the developer on a surface of the developing sleeve44. InFIG. 4and the like, a longitudinal direction, i.e., a rotational axis direction (axial direction) of the developing sleeve44is represented as a widthwise direction W.

Inside the developing container41, a substantially central portion thereof is partitioned into left and right portions with respect to a horizontal direction, i.e., into a stirring chamber41band a developing chamber41aby a partition wall41cextending in a direction perpendicular to the surface of the drawing sheet ofFIG. 3, and the developer is accommodated in the developing chamber41aand the stirring chamber41b. In the developing chamber41aand the stirring chamber41b, the feeding screws43aand43bare disposed, respectively. At end portions of the partition wall41cwith respect to a longitudinal direction (i.e., at end portions of the developing sleeve44with respect to a rotational axis direction, end portions with respect to the widthwise direction W inFIG. 4), delivering portions41dand41efor permitting passing of the developer between the developing chamber41aand the stirring chamber41bare provided.

Each of the feeding screws43aand43bis formed by providing a helical blade as a feeding portion around a shaft (rotation shaft) of a magnetic material. Further, the feeding screw43bis provided, in addition to the helical blade, with stirring ribs43b1each having a predetermined width with respect to a developer feeding direction so as to project from the shaft in a radial direction of the shaft. The stirring ribs43b1stir the developer with rotation of the shaft.

The feeding screw43ais disposed at a bottom portion of the developing chamber41aalong the rotational axis direction of the developing sleeve44, and feeds the developer to the developing sleeve44while feeding the developer in the developing chamber41aalong an axial direction by rotating the rotation shaft by an unshown motor. The developer which is carried on the developing sleeve44and of which toner is consumed in a developing step is collected in the developing chamber41a.

The feeding screw43bis disposed at a bottom portion of the stirring chamber41balong the rotational axis direction of the developing sleeve44, and feeds the developer in the stirring chamber41balong an axial direction in a direction opposite to the developer feeding direction of the feeding screw43a. The developer is fed by the feeding screws43aand43bin this manner, and is circulated in the developing container41through the delivering portions41dand41e.

At an upstream end portion of the stirring chamber41bwith respect to the developer feeding direction of the feeding screw43b, a developer supply opening46permits supply of the developer containing the toner into the developing container41. The developer supply opening46is connected with a supplying and feeding portion83of a developer supplying device80shown inFIG. 5and described later. Accordingly, a developer for supply is supplied from the developer supplying device80into the stirring chamber41bthrough the supplying and feeding portion83and the developer supply opening46. The feeding screw43bfeeds the developer supplied through the developer supply46and the developer which has already been in the stirring chamber41bwhile stirring these developers, so that a toner content (concentration) is uniformized.

Accordingly, by feeding forces of the feeding screws43aand43b, the developer in the developing chamber41ain which the toner is consumed in the developing step and thus the toner content is lowered is moved into the stirring chamber41bthrough one delivering portion41d(left (W1) side ofFIG. 4). Then, the developer moved in the stirring chamber41bis fed while being stirred with the supplied developer and is moved into the developing chamber41athough the other delivering portion41e(right (W2) side ofFIG. 4).

As shown inFIG. 3, the developing chamber41aof the developing container41is provided with an opening41hat a position corresponding to an opposing region (developing region) A opposing the photosensitive drum1, and in this opening41h, the developing sleeve44is rotatably provided so as to be partially exposed in a direction of the photosensitive drum1. On the other hand, the magnet44aincorporated in the developing sleeve44is non-rotationally fixed. Such a developing sleeve44is rotated by an unshown motor, and is capable of feeding the developer to the opposing region A, and feeds the developer to the photosensitive drum1in the opposing region A. In this embodiment, the developing sleeve44is formed, in a cylindrical shape, of a non-maximum material such as aluminum or stainless steel. The developing sleeve44rotates from below toward above with respect to a direction of gravitation in the opposing region A, i.e., rotates in a counterclockwise direction ofFIG. 3.

In a side upstream of the opening41hwith respect to the rotation direction of the developing sleeve44, the developing blade42as a regulating member for regulating an amount of the developer carried on the developing sleeve44is fixed to the developing container41. In this embodiment, the developing sleeve44rotates in the opposing region A from below toward above with respect to the direction of gravitation, and therefore, the developing blade42is positioned below the opposing region A with respect to the direction of gravitation.

The magnet44aincludes5magnetic poles in total consisting of a plurality of magnetic poles S1, S2, S3, N1and N2with respect to a circumferential direction and is formed in a roller shape. The developer in the developing chamber41ais supplied to the developing sleeve44by the feeding screw43a, and the developer supplied to the developing sleeve44is carried in a predetermined amount on the developing sleeve44by a magnetic field generated by an attracting magnetic pole S2of the magnet44a, and forms a developer accumulating portion.

The developer on the developing sleeve44passes through the developer accumulating portion by rotation of the developing sleeve44and is erected by a regulating magnetic pole N1, and a layer thickness thereof is regulated by the developing blade42opposing the regulating magnetic pole N1. Then, the developer subjected to the layer thickness regulation is fed to the opposing region A opposing the photosensitive drum1and is erected by a developing magnetic pole Sl, and forms a magnetic chain. This magnetic chain contacts the photosensitive drum1rotating in the same direction as the rotational direction of the developing sleeve44in the opposing region A, so that the electrostatic latent image is developed into the toner image with the charged toner.

Thereafter, the developer on the developing sleeve44is fed into the developing container41by the rotation of the developing sleeve44while attraction of the developer to the surface of the developing sleeve44is maintained by a feeding magnetic pole N2. Then, the developer carried on the developing sleeve44is peeled off the surface of the developing sleeve44by a peeling magnetic pole S3and is collected in the developing chamber41aof the developing container41.

In the developing container41, as shown inFIG. 4, an inductance sensor45as a toner content sensor for detecting a toner content in the developing container41is provided. In this embodiment, the inductance sensor45is provided downstream of the stirring chamber41bwith respect to the developer feeding direction.

The developer supplying device80will be described usingFIG. 5. The developer supplying device80includes an accommodating container8for accommodating the developer for supply and includes a supplying mechanism81and a supplying and feeding portion83. The accommodating container8has a constitution such that a helical groove is provided on an inner wall of a cylindrical container, so that a feeding force feeds the developer in a longitudinal direction (rotational axis direction) by rotation of the accommodating container8itself. The accommodating container8is connected with the supplying mechanism81at a downstream end portion thereof with respect to the developer feeding direction. The supplying mechanism81includes a pump portion81afor discharging the developer, fed from the accommodating container8, through a discharge opening82. The pump portion81ais formed in a bellow shape and changes in volume by being rotationally driven, so that air pressure generates and thus the developer fed from the accommodating container8is discharged through the discharge opening82.

To the discharge opening82, an upstream end portion of the supplying and feeding portion83is connected, and a lower end portion of the supplying and feeding portion83is connected to a developer supply opening46of the developing device4. That is, the developer supplying and feeding portion83communicates the discharge opening82and the developer supply opening46with each other. Accordingly, the developer discharged through the discharge opening82by the pump portion81apasses through the developer supplying and feeding portion83and is supplied into the developing container41of the developing device4.

In the above-described developing device4, the developer supply opening46is provided upstream of the stirring chamber41bwith respect to the developer feeding direction and outside a circulating path, of the developer, formed by the developing chamber41a(FIG. 4) and the stirring chamber41b. Specifically, the developer supply opening46is provided upstream of one delivering portion41dwith respect to the developer feeding direction of the stirring chamber41b. Accordingly, in the neighborhood of the developer supply opening46, the developer in the developer circulating path little exists, and the developer for supply only passes.

Such supply by the developer supplying device80is carried out by automatic toner replenisher (ATR) control. This ATR control is such that an operation of the developer supplying device80is controlled depending on an image ratio during image formation, the toner content detected by the inductance sensor45, and a density detection result of a patch image by a density sensor103(FIG. 1) for detecting a density of the toner, and thus the developer is supplied (replenished) to the developing device4.

The density sensor103is, as shown inFIG. 1, provided downstream of the most downstream image forming portion PY and upstream of the secondary transfer portion T2with respect to the rotational direction of the intermediary transfer belt51so as to oppose the intermediary transfer belt51. In control using the density sensor103, for example, at timing such as the time of a start of an image forming job or every image formation of a predetermined print number, a toner image for control (patch image) is transferred onto the intermediary transfer belt51and the density of the patch image is detected by the density sensor103. Then, on the basis of this detection result, supply control of the developer by the developer supplying device80is carried out.

Incidentally, the constitution of supplying the developer to the developing device4is not limited to such a constitution, but a conventionally known constitution may also be employed.

Here, scattering of the developer generating from the developing device4will be described. First, as regards the image forming apparatus, not only speed-up and image quality improvement of an output image but also simplification of maintenance are required. As one of methods of the simplification of maintenance, a lowering in degree of contamination of the inside of the image forming apparatus with the developer can be cited. When the inside of the image forming apparatus is contaminated with the developer, an image defect such as contamination of the output image generates, and a cleaning operation is required at the time of exchange of the developing device, the photosensitive drum or the like in some cases. Further, in the case where the developer is deposited on respective driving during systems such as gears, there is a liability that a slip generates in the driving systems.

As one cause of the above-described contamination of the inside of the image forming apparatus with the developer, scattering of the developer from the inside of the developing device can be cited. For example, in the case of a two-component developer, usually, inside the developing device, the toner and the carrier are triboelectrically charged with each other, and therefore, the toner and the carrier are attracted to each other by an electrostatic force. However, there is a liability that due to some impact (shock), scattering of the developer such that this attraction is released (eliminated) and the toner liberated from the carrier is discharged together with air from the inside of the developing device.

A specific example of the scattering of the developer will be described using a developing device400in a comparison example shown inFIG. 6. The developing device400has the same constitution as that of the above-described developing device4except that a constitution of a developing container401is different from the constitution of the above-described developing container41. For this reason, the same constituent elements will be described by adding the same reference numerals or symbols. To the developing device400, similarly as in the case of the above-described developing device4, the supplying and feeding portion83of the developer supplying device80is connected.

The developing container401includes an upper cover402for covering a portion above the developing sleeve44. Further, between the upper cover402and the developing sleeve44, a flow path of air flowing into the developing container401by rotation of the developing sleeve44is formed. This flow path opens at a position opposing the photosensitive drum1, so that the scattering of the developer from the inside of the developing device principally generates from this flow path. This is because on a side opposite from this flow path (on a lower side ofFIG. 6), the developing blade42is close to and opposes the developing sleeve44. That is, at this position, a state in which a layer thickness of the developer carried on the developing sleeve44is regulated by the developing blade42is formed, so that the air does not readily flow out from a gap between the developing sleeve44and the developing blade42.

Here, the scattering of the developer refers to the developer such as liberated toner or the like generating in the developing container401by stirring and feeding of the developer or by supply of the developer passes through an opening of the flow path and is discharged to an outside of the developing container401and is not completely collected in the developing container401.

First, toner liberation will be described. The toner and the carrier which are accommodated in the developing container401are triboelectrically charged with each other in the stirring chamber41band the developing chamber41aand are attracted to each other by an electrostatic attraction (deposition) force generated due to the triboelectric charge and by a non-electrostatic attraction force generated due to a surface property or the like. When an impact or a shearing force is exerted on the toner deposited on the carrier, the toner is peeled off the carrier and thus is liberated from the carrier in the developing container401. As the impact or the shearing force at this time, behavior of the developer during feeding of the developer by the developing sleeve44is cited.

The developer forms, on the developing sleeve44, a magnetic chain which is a chain-like structure along magnetic lines of force of inside magnetic poles. This magnetic chain raises formed with respect to the rotational direction immediately in front of the magnetic pole and falls formed with respect to the rotational direction when the magnetic chain passes through the magnetic pole. In this case, the rotational direction of the magnetic chain is the same as the rotational direction of the developing sleeve44. By an impact and a centrifugal force when the magnetic chain falls, the toner is peeled off the carrier. This causes toner liberation.

The magnetic pole largely contributing to the toner liberation when the developer is fed by the developing sleeve44is the peeling magnetic pole S3generating a repulsive magnetic field between itself and the attracting magnetic pole S2. At this peeling magnetic pole S3, in order to peel the developer off the developing sleeve44, a magnetic force in a direction opposite to the rotational direction of the developing sleeve44is applied by the magnetic pole, so that a speed of the fed developer is lowered and thus the developer is stagnated. At this time, a length of the magnetic chain increases, and therefore, there is a tendency that the impact and the centrifugal force when the magnetic chain falls become large and thus a toner liberation amount increases.

Further, also the developer rose into the air before being sufficiently stirred when the developer is supplied from the developer supplying device80to the developer supply opening46causes the liberated toner in the developing container401. The toner supplied to the developer supply opening46is fed while being stirred with the developer which has already existed in the stirring chamber41b. At this time, in a mixing region of the developer for supply and the already-existing developer, a mixing ratio between the toner and the developer temporarily increases. In the case where the mixing ratio between the toner and the developer is high, a charge amount of the toner lowers, so that an electrostatic depositing force between the toner and the carrier lowers. The toner which is not completely mixed with the developer is liberated as it is or by the impact by the feeding screws43aand43bduring stirring and feeding of the developer, so that the liberated toner rises into the air in the developing container401.

Further, in the case where the developer device80from which the developer is discharged by the air pressure generated by the pump81ais used, the air pressure is transmitted through the supplying and feeding portion83, so that the air flows into the developing container401through the developer supply opening46in some cases. At this time, an air stream flowing into the developing container401raises, into the air in the developing container401, the liberated toner at a portion where the mixing ratio between the developer and the toner in the neighborhood of the developer supply opening46is high. Further, the air pressure transmission to the developing container401causes unsteady rise of the atmospheric pressure from the developer supply opening46to the stirring chamber41b. This rise of the atmospheric pressure causes the flowing of the liberated toner to the outside of the developing container401as described later. Particularly, such inflow of the air by the supply of the developer constitutes one of factors of the scattering of the developer at an end portion, including the developer supply opening46, with respect to a longitudinal direction of the developing container401(the rotational axis direction of the developing sleeve44).

Next, usingFIG. 8, the air stream inside and in the neighborhood of the developing device400will be described. The air stream is generated in the neighborhood of the developing device400by the developing sleeve44and the photosensitive drum1in the following manner. First, by the rotation of the developing sleeve44and behavior of the magnetic chain on the magnetic pole, the air stream is generated in the substantially same direction as the rotational direction of the developing sleeve44. This air stream generated in the substantially same direction as the rotational direction of the developing sleeve44takes the air into the developing container401through a communication opening between the inside and the outside of the developing container401. Further, the air flows into the developing container401also by the supply of the developer.

Assuming that the developing container401is a substantially closed space, the air is gas, and therefore, continuity equation is applicable. When a flow rate of the air is v and a density of the air is ρ, there is no source flow of the air in the developing container401, and therefore, the following formula (1) holds
∂ρ/∂t+∇ρv=0   (1)

When a steady state is considered, in respective regions in the developing container401, the density ρ is roughly constant and therefore, the formula (1) can be represented by the following formula (2).
ρ∇v=0   (2)

From this formula (2), a flow rate pv of the air is conserved. In a longitudinal cross-section in the neighborhood of the developing device400, income and expenditure of the flow rate ρv is 0, so that the air is discharged to the outside of the developing sleeve44in the same amount as the flow rate of the air flowing into the developing container401by the developing sleeve44and the supply of the developer. Here, the flow rate of the air flowing into the developing container401through a communication opening, constituted by the upper cover402of the developing container401and by the developing sleeve44, with rotation of the developing sleeve44is Qa (sleeve inflow). Further, the air stream discharged through the communication opening between the inside and the outside of the developing container401passes through the upper cover402side so as to oppose the flow of the air taken through this communication opening. The flow rate of the thus discharged air stream is Qb (sleeve discharge). Further, when the flow rate of the air stream flowing into the developing container401with the supply of the developer to the developing device400is Qd (supply inflow), a relationship of the following formula (3) holds.
Qa+Qd=Qb(3)

The air stream taken by the developing sleeve44and flowing along the developing sleeve44is turned back in the developing container401and then is discharged. At this time, at the developer stagnation portion of the peeling magnetic pole S3, when the air stream including the developer peeled off the developing sleeve44is turned back, the air stream moves toward a discharge direction while containing, in a large amount, the developer such as the liberated toner generated in the developing container401.

A step in which the developer contained in the sleeve discharge air (flow rate Qb) is discharged to the outside of the developing container401is principally constituted by the following three component steps (factors). A first component step (factor) is such that the sleeve discharge air (flow rate Qb) discharged to the outside of the developing device400through the communication opening is directly discharged from a gap between the upper cover402and the photosensitive drum1. A second component step (factor) is such that the sleeve discharge air (flow rate Qb) is mixed, in the neighborhood of the photosensitive drum1, with the developer carried on the developing sleeve44or the developer is transferred, by force of inertia, to an air streaming generated by rotation of the photosensitive drum1and is then discharged while being carried on the air stream g. A third component step (factor) is such that the liberated toner contained in the sleeve discharge air (flow rate Qb) is moved to the air stream g, by the force of inertia, generated by rotation of the photosensitive drum1, and thus is discharged to the outside of the developing container401.

The scattering of the developer is caused by discharge of the developer to the outside of the developer due to at least one factor of the above-described three factors (component steps). Then, the scattered developer contaminates the periphery of the developing device400, an outer wall of the developing container401, the photosensitive drum1, the exposure device3and the transfer device5.

[Structure of Developing Container in this Embodiment]

Therefore, in this embodiment, the developing container41of the developing device4is constituted as follows. A detailed structure of the developing container41in this embodiment will be described usingFIG. 6. A curve C shown at a periphery ofFIG. 6shows a distribution of magnetic flux density of the respective magnetic poles. Further, a rotational direction of the developing sleeve44is R. Of the respective magnetic poles of the magnet44a, a peeling magnetic pole S3corresponds to a first magnetic pole, and an attracting magnetic pole S2corresponds to a second magnetic pole. The peeling magnetic pole S3is provided downstream of the opposing region A with respect to the rotational direction R and peels the developer carried on the developing sleeve44. The attracting magnetic pole S2is provided adjacently downstream of the peeling magnetic pole S3with respect to the rotational direction R and has the same polarity as that of the peeling magnetic pole S3, and scoops up the developer in the developing container41onto the developing sleeve44. InFIG. 6, positions of the respective magnetic poles are represented by rectilinear lines showing peak positions of the magnetic flux density of the five magnetic poles.

The developing container41in this embodiment includes an upper cover41ffor covering the developing sleeve44on a side downstream of the opposing region A with respect to the rotational direction R of the developing sleeve44. The upper cover41fincludes an outer cover47as a first covering portion and an inner cover48as a second covering portion. The outer cover47is disposed on a side downstream of the opposing region A with respect to the rotational direction R and covers the developing sleeve44with a gap.

The inner cover48is disposed between the outer cover47and the developing sleeve44so as to provide a gap between itself and the outer cover47and a gap between itself and the developing sleeve44and covers the developing sleeve44.

A downstream end48bof the inner cover48with respect to the rotational direction R is positioned downstream of a position of an upstream minimum M1of a pair of minimum M1and M2, with respect to the rotational direction R, in terms of an absolute value of a magnetic flux density distribution of the peeling magnetic pole S3. The rotational direction downstream end48bof the inner cover48may preferably be positioned at a peak position of the magnetic flux density of the peeling magnetic pole S3or positioned downstream of the peak position with respect to the rotational direction R. By disposing the position of the downstream end48bof the inner cover48with respect to the rotational direction R at a position satisfying these conditions, a range in which the peeling magnetic pole S3is covered with the inner cover48can be broadened.

However, the rotational direction downstream end48bof the inner cover48may preferably be in a position of the horizontal plane H passing through the center O of the developing sleeve44or be positioned upstream of the position of the horizontal plane H with respect to the rotational direction R. This is because when the rotational direction downstream end48bof the inner cover48is positioned further downstream of this position, the developer peeled off the developing sleeve44is not readily taken in the developing chamber41a.

[Characteristic Structure in this Embodiment]

A characteristic structure of the developing device4in this embodiment will be described usingFIGS. 4 and 7. First, a gap between the inner cover48and the developing sleeve44is referred to as first gap (gap) F1. A gap between the inner cover48and the outer cover47is referred to as a second gap (flow path, gap) F2. A gap between the photosensitive drum1and an opposing end portion47a, of the outer cover47, opposing the photosensitive drum1is referred to as a third gap F3. The developing container41includes a pair of side walls49(FIG. 4) provided at each of both end portions with respect to the widthwise direction W of the developing sleeve44between the outer cover47and the inner cover48. Each of the side walls49blocks a space between the outer cover47and the inner cover48and forms the second gap F2as a flow path along the rotational direction R in cooperation with the outer cover47and the inner cover48.

The second gap F2includes an inlet port (first opening)11through which the air flows in and an outlet port (second opening)12through which the air flows out. The inlet port11is an opening formed by the inner cover47, the outer cover48and an end portion, of each of the pair of side walls49, on a downstream side with respect to the rotational direction R. The outlet port12is an opening formed by the inner cover47, the outer cover48and an end portion, of each of the pair of side walls49, on an upstream side with respect to the rotational direction R.

As shown inFIG. 4, the inner cover48has widths L1and L2satisfying a relationship of L1<L2at the inlet port11and the outlet port12, respectively, with respect to the axis direction (rotational axis direction), so that the outlet port12is narrower in width than the inlet port11with respect to the widthwise direction W. Further, the width of the second gap F2with respect to the widthwise direction W gradually decreases from the inlet port11side toward the outlet port12side.

The both end portions of the inlet port11with respect to the widthwise direction W are positioned outside, with respect to the widthwise direction W, a coated region (developer carrying region) B1in which the developing sleeve44is capable of carrying the developer. The coated region B1is an image formable region which is subjected to a surface-roughening treatment so that the developer can be carried. The width L1of the inlet port11is broader than the coated region B1. Further, the both end portions of the outlet port12with respect to the widthwise direction W are positioned inside the coated region B1with respect to the widthwise direction W. That is, the width L2of the outlet port12is narrower than the coated region B1.

Here, a distance (shortest distance) between the outer cover47and the inner cover48at the inlet port11is referred to as a height H1, and a distance (shortest distance) between the outer cover47and the inner cover48at the outlet port12is referred to as a height H2(FIG. 6). In this case, the respective heights H1and H2satisfy a relationship of H1<H2, so that the shortest distance between the outer cover47and the inner cover48gradually increases from the inlet port11toward the outlet port12. That is, the outlet port12is broader than the inlet port11with respect to not only a direction perpendicular to the widthwise direction W but also a radial direction of the developing sleeve44.

Further, the widths L1and L2and the heights H1and H2satisfy a relationship of L1×H1=L2×H2, so that an area of the inlet port11and an area of the outlet port12are equal to each other. In this embodiment, in the second gap F2, an area of a cross-section perpendicular to a flowing direction of communicating air (gas) is made constant. In this embodiment, the inlet port11is positioned downstream of a position of an upstream minimum M1of a pair of minimums M1and M2with respect to the rotational direction R in terms of an absolute value of a magnetic flux density distribution of the peeling magnetic pole S3. Further, the inlet port11is positioned at a peak position of the magnetic flux density of the peeling magnetic pole S3or downstream of the peak position with respect to the rotational direction R is positioned upstream of the attracting magnetic pole S2with respect to the rotational direction R.

Air streams generated by the rotation of the developing sleeve44and the photosensitive drum1will be described. In the neighborhood of the developing sleeve44, an air stream a generates with the rotation of the developing sleeve44, and flows into the developing container41through the first gap F1. By this flow of the air into the developing container41, an internal pressure of the developing container41increases, so that the air is discharged from a discharging path. Here, in a constitution in which the inner cover48is not provided, scattering (scattered) toner generating in the developing container41is directly discharged to the outside air by an air stream b through the first gap F1. As described above, in the neighborhood of the peeling magnetic pole S3, a toner liberation amount increases, and therefore, liberated toner is scattered to an outside of the developing container41by the air stream b.

On the other hand, in this embodiment, by providing the second gap F2as the discharging path between the outer cover47and the inner cover48, an air stream d generates from an inside of the developing container41toward the second gap F2, and an air stream e generates as a discharging air stream in the second gap F2. As a result, the air stream e as the discharging air stream does not generate in the first gap F1, and therefore, the air in the developing container41can be discharged without being passed through the neighborhood of the peeling magnetic pole S3, so that a degree of toner scattering can be reduced. Incidentally, in some cases, the toner in a small amount passes through a path of the air stream e and is discharged to the outside of the developing container41through the outlet port12, but most of the toner is deposited on the opposing photosensitive drum1and is collected by the cleaning device7, and therefore, does not contaminate a periphery of the developing device4.

Here, there is a liability that the toner discharged from the both end portions, with respect to the rotational direction R, at the opening41hof the developing device4is scattered to the outside of the end portions with respect to the widthwise direction W of the photosensitive drum1by the air stream with respect to the widthwise direction W of the developing sleeve44can causes contamination of the periphery of the developing device4. Further, as described above, by the flow of the air from the supplying and feeding portion83of the developer supplying device80, compared with the central portion, the air stream entering the inlet port11at the both end portions of the developing container41contains the toner in a large amount.

On the other hand, the widths L1and L2of the inlet port11and the outlet port12, respectively, are L1>L2and thus the width gradually decreases from the inlet port11toward the outlet port12. For this reason, the toner flows from the both end portions of the developing container41through the inlet port11into the second gap F2and passes through the second gap F2by the air stream e, and is sent to the central portion toward the outlet port12. Then, the toner is not discharged through the both end portions of the developing container41, so that the contamination of the periphery of the developing device4with the scattering toner can be suppressed.

In order to discharge the air stream with no pressure loss in the air stream e, a cross-sectional area of the second gap F is always made the same (L1×H1=L2×H2). Further, in the case where the width L1of the inlet port11is smaller than the coated region B1of the developing sleeve44and the both end portions of the inner cover48with respect to the widthwise direction W do not oppose ends of the coated region B1, the air stream b generates in the coated region B1. As a result, the generation of the air stream b causes the toner scattering from the end portions of the developing container41, and therefore, the width L1of the inlet port11may preferably be made broader than the coated region B1.

As described above, according to the developing device4in this embodiment, the outlet port12of the second gap F2is made narrower than the inlet port11with respect to the widthwise direction W. For this reason, the air discharged from the inside of the developing container41through the outlet port12is discharged toward a portion excluding the end portions of the developing sleeve44. As a result, discharge of the air, discharged from the inside of the developing container41, toward the end portions of the developing sleeve44can be avoided, so that developer scattering from the end portions of the developing container41with respect to the widthwise direction W of the developing sleeve44can be sufficiently suppressed. Further, even if the developer is scattered, a scattering amount is small, and therefore, even when the developer is deposited on the image, a deposition amount is to the extent such that the deposited toner cannot be visually recognized, so that a lowering in image quality can be suppressed. In this embodiment, a constitution in which an air path was formed in a space sandwiched between the outer cover47and the inner cover48was employed. A constitution in which at that time, walls are provided on both sides, with respect to the longitudinal direction of the developing sleeve44, of the space sandwiched between the outer cover47and the inner cover48and thus a closed space defined by the walls, the outer cover47and the inner cover48is formed may also be employed. Or, a constitution in which the walls are not provided on the both sides and a space sandwiched by the outer cover47and the inner cover48is formed may also be employed.

Further, according to the developing device4in this embodiment, the area of the inlet port11and the area of the outlet port12are equal to each other, and in the second gap F2, the area of the cross-section perpendicular to the flowing direction of the communicating air is constant. For this reason, the pressure loss of the air circulating in the second gap F2can be made very small, so that there is no generation of the air stream b discharged through the first gap F1and thus the contamination of the periphery of the developing device4with the scattering toner can be suppressed.

Further, according to the developing device4in this embodiment, the end portions of the inlet port11with respect to the widthwise direction W are positioned outside the coated region B1with respect to the widthwise direction W. For this reason, compared with the case where the end portions of the inlet port11with respect to the widthwise direction W are positioned inside the coated region B1with respect to the widthwise direction W, the generation of the air stream b in the coated region B1can be suppressed, so that the contamination of the periphery of the developing device4with the scattering toner can be suppressed.

Further, according to the developing device4in this embodiment, the end portions of the outlet port12with respect to the widthwise direction W are positioned inside the coated region B1with respect to the widthwise direction W. For this reason, compared with the case where the end portions of the outlet port12with respect to the widthwise direction W are positioned outside the coated region B1with respect to the widthwise direction W, the scattering of the toner to the outside of the end portions of the photosensitive drum1with respect to the widthwise direction W by the air stream in the widthwise direction W of the developing device4can be suppressed.

Further, as described above, the toner is liberated in a large amount when the magnetic chain falls down at the peeling magnetic pole S3, and therefore, the thus generating liberated toner is contained in a large amount in the air stream e in the first gap F1. According to the developing device4in this embodiment, the downstream end48bof the inner cover48is positioned downstream of the position of the upstream minimum M1of the magnetic flux density distribution of the peeling magnetic pole S3with respect to the rotational direction R, so that at least a part of the peeling magnetic pole S3can be covered with the inner cover48. Particularly, in this embodiment, the downstream end48bof the inner cover48is positioned downstream of the peak position of the peeling magnetic pole S3with respect to the rotational direction R, and therefore, when the magnetic chain falls down at the peeling magnetic pole S3, most of a region where the liberated toner generates can be covered with the inner cover48.

In order to confirm an effect of this embodiment, an experiment in which the toner scattering amount was compared between a constitution of a comparison example and the constitution of this embodiment will be described. When a toner supplying operation for supplying the toner to each of developing devices was performed, measurement of an amount of the toner scattering from the neighborhood of an opening of a developing container and check of contamination of a periphery of each of the developing devices with the toner were carried out. First, an outline of a toner scattering amount measuring method employed in this experiment will be described with reference toFIG. 7. Incidentally, an apparatus used in the experiment is prepared by assembling the photosensitive drum, the developing device and other constituent members, excluding the exposure device, disposed at the periphery of the photosensitive drum into a unit. In the experiment, similarly as during normal image formation, in a state in which the rotation of the photosensitive drum, the drive of the charging device and the developing device and the bias application are carried out, the toner scattering amount was measured in the following manner.

In a region excluding both longitudinal end of the developing device4with respect to the widthwise direction W, the toner in the developing device4is passed by the air stream g, through the third gap F3between the photosensitive drum1and the opposing end portion47a, of the outer cover47, opposing the photosensitive drum1and is scattered to the outside of the developing device4. Therefore, the central portion and the end portions of the third gap F3with respect to the widthwise direction W is selectively irradiated with line laser beam (light) so as to be perpendicular to the developing sleeve44and the photosensitive drum1. The line laser beam is a laser beam (light) which is emitted in a line shape with a certain line width and which forms a sector-shaped two-dimensional plane optical path. The line laser beam is usually prepared by scattering a dot laser beam in a certain direction by a cylindrical lens or a rod lens. The scattering toner flying on the optical path of the line laser beam scatters the laser light (beam). For that reason, from a direction substantially perpendicular to an irradiation direction of the line laser beam, a laser irradiation range is observed through a high-speed camera or the like, whereby it is possible to measure the number of particles and a locus of the scattering toner present in the laser irradiation range.

As regards the line laser beam, a YAG laser (“DPGL-5W”, manufactured by Japan Laser Corp.) was used as a light source. Further, an optical system using a cylindrical lens (attached to the product) was adjusted so that a line width was 0.5 mm in the third gap F3and then an object was irradiated with the line laser beam. For observation, a high-speed camera (“SA-3”, manufactured by PHOTORON Ltd.) was used. Further, in order to permit observation of the scattering toner on the line laser beam, a shooting condition (frame rate and exposure time) and the optical system (such as the lens) of the high-speed camera were selected.

The number of scattering (scattered) toner particles, obtained by the above-described method, passing through each of the central portion and the end portion of the third gap F3with respect to the widthwise direction W was converted into a scattering toner (particle) number corresponding to that per A4-sized sheet (210 mm×297 mm).

The above-described developing device4in First Embodiment was used, and a constitution satisfying L1>L2was employed. In this embodiment, L1=320 mm, L2=290 mm, H1=2.9 mm and H2=3.2 mm were set.

Comparison Example 1

A conventional developing device400shown inFIG. 8was used. As shown inFIG. 8, the developing device400does not include the inner cover.

Comparison Example 2

In the above-described developing device4in the First Embodiment, a constitution satisfying L1=L2was employed. In this comparison example, L1=320 mm, L2=320 mm, H1=2.9 mm and H2=2.9 mm were set.

In the above-described conditions, experiments were conducted, and results thereof were compared with each other. Other constitutions are common to Embodiment 1 and Comparison Examples 1 and 2. The results of the experiments are shown inFIG. 12. In Comparison Example 2, compared with Comparison Example 1, the scattering (scattered) toner particle number corresponding to an output time of a single A4-sized sheet in a range of 0.5 mm width decreases, but a scattering suppressing effect at the end portion is small compared with that at the central portion. In Embodiment 1, compared with Comparison Example 2, the scattering toner particle number at the end portion is decreased, so that scattering suppressing power was largely improved. Accordingly, it was confirmed that compared with Comparison Examples 1 and 2, the constitution of Embodiment 1 was effective in reducing the degree of the toner scattering.

Second Embodiment

Next, Second Embodiment of the present invention will be described while making reference toFIG. 9. In this embodiment, the constitution is different from the constitution of the First Embodiment in that the second gap F2includes a same width portion F2aand a gradually narrowing (decreasing) portion F2b. However, other constitutions are similar to those in the First Embodiment, and therefore, are represented by the same reference numerals or symbols and will be omitted from detailed description.

As shown inFIG. 9, the same width portion F2ais formed so that a width thereof with respect to the widthwise direction W is a certain width from the inlet port11toward an upstream side with respect to the rotational direction by a predetermined length. The gradually narrowing portion F2bis formed so that a width thereof with respect to the widthwise direction W gradually decreases in width with respect to the widthwise direction W from the same width portion F2atoward the outlet port12. As a result, the width of the inner cover48with respect to the widthwise direction W of the developing sleeve44maintains the width L2from the inlet port11toward the outlet port12until an intermediary portion and gradually decreases from the intermediary portion to the outlet port12. Further, also in this embodiment, the distance between the inner cover47and the outer cover48is different depending on a position so that the cross-sectional area of the second gap F2is always the same, so that the width L1of the inlet port11is broader than the coated region B1. Further, also in this embodiment, the inner cover48covers the neighborhood of the peeling magnetic pole S3in an entire region of the coated region B1and thus does not generate the discharging air stream b (FIG. 7) in the first gap F1.

Also according to the developing device4in this embodiment, the outlet port12of the second gap F2is made narrower than the inlet port11with respect to the widthwise direction W. For this reason, the air discharged from the inside of the developing container41through the outlet port12is discharged toward a portion excluding the end portions of the developing sleeve44. As a result, discharge of the air, discharged from the inside of the developing container41, toward the end portions of the developing sleeve44can be avoided, so that developer scattering from the end portions of the developing container41with respect to the widthwise direction W of the developing sleeve44can be sufficiently suppressed. Further, even if the developer is scattered, a scattering amount is small, and therefore, even when the developer is deposited on the image, a deposition amount is to the extent such that the deposited toner cannot be visually recognized, so that a lowering in image quality can be suppressed.

Further, according to the developing device4in this embodiment, the same width portion F2ahaving a certain width with respect to the widthwise direction W from the inlet port11toward the upstream side by a predetermined length is provided. For this reason, compared with the case where the same width portion F2ais not provided and the width of the inner cover48gradually decreases from the inlet port11toward the outlet port12, an area in which the end portions of the coated region B1of the developing sleeve44with respect to the widthwise direction is covered with the inner cover48increases. As a result, the generation of the air stream b in the coated region B1can be more effectively suppressed, so that the contamination of the periphery of the developing device4with the scattering toner can be suppressed.

The above-described developing device4in the Second Embodiment was used, and a constitution satisfying L1>L2was employed. An experiment similar to that of Embodiment 1 was conducted. In this embodiment, L1=320 mm, L2=290 mm, H1=2.9 mm and H2=3.2 mm were set.

A result of the experiment is shown inFIG. 12. In Embodiment 2, compared with Embodiment 1, a scattering suppressing effect was further improved. This would be considered because in Embodiment 2, the same width portion F2ais provided and therefore the area in which the end portions of the coated region B1of the developing sleeve44with respect to the widthwise direction W increases and thus the generation of the air stream b in the coated region B1is more effectively suppressed. Accordingly, it was confirmed that the constitution of Embodiment 2 was effective in reducing the degree of the toner scattering similarly as in Embodiment 1.

Third Embodiment

Next, Third Embodiment of the present invention will be described while making reference toFIGS. 10 and 11. In this embodiment, the constitution is different from the constitution of the First Embodiment in that the outlet port12does not oppose the photosensitive drum1but opposes a neighborhood of an uppermost portion (top) of the developing sleeve44. However, other constitutions are similar to those in the First Embodiment, and therefore, are represented by the same reference numerals or symbols and will be omitted from detailed description.

As shown inFIGS. 10 and 11, the outer cover47is formed by being bent toward the photosensitive drum1so as to cover the developing sleeve44from an upper end of a side wall41gof the developing container41on a side opposite from the photosensitive drum1with respect to the developing sleeve44.

The outer cover47includes a first opposing portion47bprovided in the photosensitive drum1side, a second opposing portion47cprovided on the side wall41gside, and a continuous portion47dconnecting the first opposing portion47band the second opposing portion47c.

The first opposing portion47bopposes the developing sleeve44in a side upstream, with respect to the rotational direction R of the developing sleeve44, of a part (the continuous portion47d) opposing the rotational direction upstream end48aof the inner cover48. The second opposing portion47copposes an intermediary portion between the upstream end48aand the downstream end48bof the inner cover48with respect to the rotational direction R.

The second opposing portion47cis disposed outside the first opposing portion47bwith respect to a radial direction of the developing sleeve44since the inner cover48is disposed between itself and the developing sleeve44. For this reason, the continuous portion47dconnecting the upstream end of the second opposing portion47cwith respect to the rotational direction R and the downstream end of the first opposing portion47bwith respect to the rotational direction R is provided. The continuous portion47dis formed so as to be bent toward the developing sleeve44side from the upstream end of the second opposing portion47cwith respect to the rotational direction R. Further, the continuous portion47dopposes the upstream end48aof the inner cover48with respect to the rotational direction R with the second gap F22with respect to the rotational direction R. That is, the inner cover48is formed so that the upstream end48athereof with respect to the rotational direction R opposes a part of the outer cover47through the second gap22with respect to the rotational direction R.

In the neighborhood of the developing sleeve44, with the rotation of the developing sleeve44, the air streams a and c generate in the first gaps F11and F12, respectively, and flow into the developing container41. By the flow of the air rate the developing container41, the internal pressure of the developing container41increases, so that the air is discharged through a discharging path. In this embodiment, similarly as in the First Embodiment, the air stream d generates from the inside of the developing container41toward the second gaps (flow paths) F21and F22between the outer cover47and the inner cover48, so that the air streams e and f generate as discharging air streams in the second gaps F21and F22, respectively. The air stream f merges with the first gap F11between the developing sleeve44and the outer cover47in the neighborhood of the uppermost portion of the developing sleeve44, and then is discharged to the outside of the developing container41through the air streams b and g.

Further, as shown inFIG. 11, the widths L1and L2of the inlet port11and the outlet port12, respectively, are such that the width of the inner cover48gradually decrease so that L1>L2is satisfied. For this reason, the air streams e and f from the end portions of the inlet port11with respect to the widthwise direction W are moved toward the central portion, so that the degree of the toner scattering from the opening41hof the developing sleeve44at the end portions can be reduced.

Also according to the developing device4in this embodiment, the outlet port12of the second gap F22is made narrower than the inlet port11with respect to the widthwise direction W. For this reason, the air discharged from the inside of the developing container41through the outlet port12is discharged toward a portion excluding the end portions of the developing sleeve44. As a result, discharge of the air, discharged from the inside of the developing container41, toward the end portions of the developing sleeve44can be avoided, so that developer scattering from the end portions of the developing container41with respect to the widthwise direction W of the developing sleeve44can be sufficiently suppressed. Further, even if the developer is scattered, a scattering amount is small, and therefore, even when the developer is deposited on the image, a deposition amount is to the extent such that the deposited toner cannot be visually recognized, so that a lowering in image quality can be suppressed. In this embodiment, a constitution in which the air streams were formed in the space sandwiched between the outer cover47and the inner cover48was described. A constitution in which at that time, walls are provided on both sides, with respect to the longitudinal direction of the developing sleeve44, of the space sandwiched between the outer cover47and the inner cover48and thus a closed space defined by the walls, the outer cover47and the inner cover48is formed may also be employed. Or, a constitution in which the walls are not provided on the both sides and a space sandwiched by the outer cover47and the inner cover48is formed may also be employed.

Further, according to the developing device4in this embodiment, the upstream end48aof the inner cover48with respect to the rotational direction R opposes the continuous portion47dof the outer cover47through the second gap F22with respect to the rotational direction R. For this reason, the air stream e passing through the second gap F21merges with the air stream b in the first gap F11through the second gap F22. At this time, the air stream f flowing through the second gap F22constitutes the air curtain, and thus the air stream containing the liberated toner in a large amount is not readily discharged from the first gap F11, so that the scattering of the developer can be suppressed.

Incidentally, in the above-described embodiments, as the constitution of the developing devices, the constitution using the two-component developer containing the toner and the carrier were described. However, even in the case of using a one-component developer containing toner having a magnetic property, the present invention is applicable even when a constitution including the above-described peeling magnetic pole S3is employed. Further, the constitutions of the above-described embodiments can be carried out by being appropriately combined with each other. For example, the constitutions of the Second and Third Embodiments may also be combined with each other.

Fourth Embodiment

Next, a Fourth Embodiment of the present invention will be described while making reference toFIGS. 7 and 13. However, other constitutions are similar to those in the First Embodiment, and therefore, are represented by the same reference numerals or symbols and will be omitted from detailed description.

First, a gap between the inner cover48and the developing sleeve44is referred to as a first gap (gap) F1. A gap between the inner cover48and the outer cover47is referred to as a second gap (flow path, gap) F2. A gap between the photosensitive drum1and an opposing end portion47a, of the outer cover47, opposing the photosensitive drum1is referred to as a third gap F3. The developing container41includes a pair of side walls49provided at each of both end portions with respect to the widthwise direction W of the developing sleeve44between the outer cover47and the inner cover48. Each of the side walls49blocks a space between the outer cover47and the inner cover48and forms the second gap F2as a flow path along the rotational direction R in cooperation with the outer cover47and the inner cover48.

The second gap F2includes an inlet port (opening)11through which the air flows in and an outlet port12through which the air flows out. The inlet port11is an opening formed by the inner cover47, the outer cover48and an end portion, of each of the pair of side walls49, on a downstream side with respect to the rotational direction R. The outlet port12is an opening formed by the inner cover47, the outer cover48and an end portion, of each of the pair of side walls49, on an upstream side with respect to the rotational direction R.

In this embodiment, the inlet port11includes a central region B2and end regions B3. That is, at least a part of the second gap F2includes the end regions B3positioned on the both end sides of the developing sleeve44and includes the central region B2positioned in the central side of the developing sleeve44with respect to the widthwise direction W. Each of the end regions B3is formed so as to be narrower than the central region B2with respect to a direction perpendicular to the flowing direction of the communicating (circulating) air and perpendicular to the widthwise direction W in the second gap F2. That is, in the case where the distance between the outer cover47and the inner cover48is a height H, a height H2(shortest distance) in the central region B2and a height H3(shortest distance) in the end regions B3satisfy a relationship of H2>H3.

Further, a shape of the inlet port11and a shape of the outlet port12are the same. Further, in the second gap F2, an area of a cross-section perpendicular to a flowing direction of the communicating air is made constant. In this embodiment, the surface of the inner cover48on the second gap F2side is constituted by a single curved surface which has a rectilinear shape with respect to the widthwise direction W. Further, the surface of the outer cover47on the second gap F2side is constituted by two rectilinear surfaces (bent surface) such that a central portion thereof projects upward and includes a top47pand that each of end portions thereof inclines downward.

As a result, the height H increases toward the central region B2of the second gap F2, so that the pressure loss of the communicating air decreases. As a result, when the air taken in the developing container41by the rotation of the developing sleeve44is discharged from the second gap F2, the air in the end regions B3is concentrated at the central region B2((b) ofFIG. 13). As a result, the degree of end portion scattering of the toner can be suppressed while discharging the air in the developing container41by the air stream taken in the developing container41. In this embodiment, the inlet port11is positioned downstream of a position of an upstream minimum M1of a pair of minimums M1and M2with respect to the rotational direction R in terms of an absolute value of a magnetic flux density distribution of the peeling magnetic pole S3. Further, the inlet port11is positioned at a peak position of the magnetic flux density of the peeling magnetic pole S3or downstream of the peak position with respect to the rotational direction R is positioned upstream of the attracting magnetic pole S2with respect to the rotational direction R.

Air streams generated by the rotation of the developing sleeve44and the photosensitive drum1will be described. In the neighborhood of the developing sleeve44, an air stream a generates with the rotation of the developing sleeve44, and flows into the developing container41through the first gap F1. By this flow of the air into the developing container41, an internal pressure of the developing container41increases, so that the air is discharged from a discharging path. Here, in a constitution in which the inner cover48is not provided, scattering (scattered) toner generating in the developing container41is directly discharged to the outside air by an air stream b through the first gap F1. As described above, in the neighborhood of the peeling magnetic pole S3, a toner liberation amount increases, and therefore, liberated toner is scattered to an outside of the developing container41by the air stream b.

On the other hand, in this embodiment, by providing the second gap F2as the discharging path between the outer cover47and the inner cover48, an air stream d generates from an inside of the developing container41toward the second gap F2, and an air stream e generates as a discharging air stream in the second gap F2. As a result, the air stream e as the discharging air stream does not generate in the first gap F1, and therefore, the air in the developing container41can be discharged without being passed through the neighborhood of the peeling magnetic pole S3, so that a degree of toner scattering can be reduced. Incidentally, in some cases, the toner in a small amount passes through a path of the air stream e and is discharged to the outside of the developing container41through the outlet port12, but most of the toner is deposited on the opposing photosensitive drum1and is collected by the cleaning device7, and therefore, does not contaminate a periphery of the developing device4.

Here, there is a liability that the toner discharged from the both end portions, with respect to the rotational direction R, at the opening41hof the developing device4is scattered to the outside of the end portions with respect to the widthwise direction W of the photosensitive drum1by the air stream with respect to the widthwise direction W of the developing sleeve44can causes contamination of the periphery of the developing device4. Further, as described above, by the flow of the air from the supplying and feeding portion83of the developer supplying device80, compared with the central portion, the air stream entering the inlet port11at the both end portions of the developing container41contains the toner in a large amount.

On the other hand, in this embodiment, each of the end regions B3is formed so as to narrower than the central region B2with respect to the direction perpendicular to the flowing direction of the communicating air in the second gap F2and perpendicular to the widthwise direction W. As a result, while discharging the air in the developing container41by the air stream taken in the developing container41, the scattering of the developer from the end portions of the developing sleeve44of the developing container41with respect to the widthwise direction W can be sufficiently suppressed and thus the contamination of the periphery of the developing device4with the scattering toner can be suppressed.

Further, in the case where each of the end regions B3is closer to the central portion side than ends of the coated region B1of the developing sleeve44are and the both end portions of the inner cover48with respect to the widthwise direction W does not oppose the ends of the coated region B1, the air stream b generates in the coated region B1. As a result, the generation of the air stream b causes the toner scattering from the end portions of the developing container41, and therefore, at least a part of each of the end regions B3may preferably be positioned outside the coated region B1.

Here, the central region B2and the end regions B3will be described using a specific example. Both end portions of the developing sleeve44are sealed. As a sealing constitution for sealing the both end portions of the developing sleeve44, a magnetic sealing constitution for magnetically blocking between the outside and the inside of the developing container41is used.FIG. 14shows an example of the magnetic sealing constitution. The magnetic sealing constitution shown inFIG. 14is such that a magnetic plate13and a magnet sheet14are provided at a sleeve end portion44bof the developing sleeve44which has not been subjected to the surface roughening process, i.e., outside the coated region B1(developer carrying region) with respect to the widthwise W direction of the developing sleeve44.

The magnetic plate13is capable of forming the magnetic chain while covering the developing sleeve44in a non-contact manner in the form along an outer periphery of the developing sleeve44. That is, a magnetic force generates between the magnetic plate13and the magnet44aof the developing sleeve44, so that the developer entering between the magnetic plate13and the developing sleeve44forms the magnetic chain. This magnetic chain blocks (closes) a gap between the magnetic plate13and the developing sleeve44, and prevents leakage of the developer from the sleeve end portion44b. Further, the magnet sheet14is provided outside the magnetic plate13with respect to the rotational axis direction of the developing sleeve44. The magnet sheet14holds, by the magnetic force, the developer leaked through between the magnetic plate13and the developing sleeve44. Thus, by providing the magnetic plate13and the magnet sheet14, the developer leakage from the sleeve end portion44bis suppressed.

The central region B2is formed so that each of both ends thereof is in a position spaced from, e.g., a position of the magnetic plate13toward a central side by 10 mm or more and 30 mm or less. Thus, the end regions B3are capable of covering the both end portions of the coated region B1. In this embodiment, as an example, a longitudinal length of the central region B2was 290 mm-310 mm, and a longitudinal length of each of the end regions B3was 20 mm-40 mm. As a result, a part of each of the end regions B3is positioned outside the coated region B1.

As described above, according to the developing device4of this embodiment, the end regions B3in the second gap F2are narrower than the central region B2with respect to the direction perpendicular to the air flowing direction and perpendicular to the widthwise direction W. For this reason, the pressure loss of the air flowing through the second gap F2is larger in the end regions B3than in the central region B2, so that the air discharged from the inside of the developing container41through the second gap F2flows easier in the central region B2than in the end regions B3. As a result, when the air taken in the developing container41by the rotation of the developing sleeve44passes through the second gap F2, the air in the end regions B3is concentrated at the central region B2. As a result, not only the air from the end portions of the developing sleeve44of the developing container41with respect to the widthwise direction W can be made hard to flow in the second gap F2, but also discharge of the air, discharged from the inside of the developing container41, toward the end portions of the developing sleeve44can be avoided. Therefore, developer scattering from the end portions of the developing container41with respect to the widthwise direction W of the developing sleeve44can be sufficiently suppressed. Further, even if the developer is scattered, a scattering amount is small, and therefore, even when the developer is deposited on the image, a deposition amount is to the extent such that the deposited toner cannot be visually recognized, so that a lowering in image quality can be suppressed.

Further, according to the developing device4in this embodiment, the area of the inlet port11and the area of the outlet port12are equal to each other, and in the second gap F2, the area of the cross-section perpendicular to the flowing direction of the communicating air is constant. For this reason, the pressure loss of the air circulating in an entirety of the second gap F2can be made very small, so that there is no generation of the air stream b discharged through the first gap F1and thus the contamination of the periphery of the developing device4with the scattering toner can be suppressed.

Further, according to the developing device4in this embodiment, at least a part of each of the end regions B3is positioned outside the coated region B1with respect to the widthwise direction W. For this reason, compared with the case where the entire region of the end regions B3is positioned inside the coated region B1with respect to the widthwise direction W, the generation of the air stream b in the coated region B1can be suppressed, so that the contamination of the periphery of the developing device4with the scattering toner can be suppressed.

Further, according to the developing device4in this embodiment, the end portions of the outlet port12with respect to the widthwise direction W are positioned inside the coated region B1with respect to the widthwise direction W. For this reason, compared with the case where the end portions of the outlet port12with respect to the widthwise direction W are positioned outside the coated region B1with respect to the widthwise direction W, the scattering of the toner to the outside of the end portions of the photosensitive drum1with respect to the widthwise direction W by the air stream in the widthwise direction W of the developing device4can be suppressed.

Further, as described above, the toner is liberated in a large amount when the magnetic chain falls down at the peeling magnetic pole S3, and therefore, the thus generating liberated toner is contained in a large amount in the air stream e in the first gap F1. According to the developing device4in this embodiment, the downstream end48bof the inner cover48is positioned downstream of the position of the upstream minimum M1of the magnetic flux density distribution of the peeling magnetic pole S3with respect to the rotational direction R, so that at least a part of the peeling magnetic pole S3can be covered with the inner cover48. Particularly, in this embodiment, the downstream end48bof the inner cover48is positioned downstream of the peak position of the peeling magnetic pole S3with respect to the rotational direction R, and therefore, when the magnetic chain falls down at the peeling magnetic pole S3, most of a region where the liberated toner generates can be covered with the inner cover48. Incidentally, in the above description, the present invention is applied to the developing device having the constitution ofFIG. 7, but is also applicable to the developing device having the constitution ofFIG. 10.

Other Embodiments

In the above-described Fourth Embodiment, as regards the cross-sectional shape of the second gap F2, the case where the surface of the outer cover47on the second gap F2side is constituted by the two rectilinear surfaces (bent surface) such that the central portion thereof projects upward and includes the top47pand that each of the end portions thereof inclines downward was described, but the present invention is not limited thereto. For example, as shown in part (a) ofFIG. 15, the cross-sectional shape may also be such that the height of each of the end portions is substantially the same and the height of the central portion is substantially the same or, as shown in part (b) ofFIG. 15, the cross-sectional shape may also be such that the height of each of the end portions is substantially the same and the central region B2includes a top47pat a center thereof with respect to the widthwise direction W. Further, in the above-described embodiments, the case where the surface of the inner cover48on the second gap F2side is the single rectilinear surface was described, but the present invention is not limited thereto. Also the surface of the inner cover48on the second gap F2side, similarly as in the case of the surface of the outer cover47on the second gap F2side, may also have various shapes other than the rectilinear shape.

Further, the present invention is also applicable to, other than the constitution in which in the developing chamber41a, the supply of the developer to the developing sleeve44and collection of the developer from the developing sleeve44are carried out as described above. For example, with reference toFIG. 3, even a constitution such that the developer is supplied from the developing chamber41ato the developing sleeve44and the developer peeled off the developing device44is collected by the stirring chamber41bis employed, the present invention is applicable thereto.

This application claims the benefit of Japanese Patent Applications Nos. 2017-068772 filed on Mar. 30, 2017 and 2017-068780 filed on Mar. 30, 2017, which are hereby incorporated by reference herein in their entirety.