Patent Description:
In the following description, with reference to the drawings, the same reference numbers are assigned to the same components or to similar components having the same function, and overlapping description is omitted.

The present disclosure provides a developing device for use with a two-component developer according to claim <NUM>. The device includes among other features an air flow passage extending from inside of the developing device and directed upstream, in a rotation direction of the developer roller, of a position at which the developer roller and a photosensitive body are closest, through at least one of non-image forming regions located at both longitudinal ends of an image forming region of the developer roller. This example developing device can circulate air through the flow passage between the inside and the outside of the developing device, thereby suppressing increase in the internal pressure of the developing device, while suppressing new introduction of air from the outside into the developing device and, as a result, can alleviate scattering of toner within a printer, excessive discharge of the developer from a developer replenishing device as described further below, and the aforementioned effects stemming from these.

In an example developing device, the flow passage extends toward upstream, in the rotation direction of the developer roller (e.g. relative to the rotation direction of the developer roller), of the position at which the photosensitive body and the developer roller are closest, and downstream, in the rotation direction of the developer roller, of the layer regulating member. This example developing device can circulate air between the inside and the outside of the developing device, through the flow passage extending toward the side which is upstream, in the rotation direction of the developer roller, of the position at which the photosensitive body and the developer roller are closest, and which is downstream, in the rotation direction of the developer roller, of the layer regulating member, such that the developer on the developer roller can capture and collect splashed toner.

In an example developing device, a first seal member adjacent to or in contact with the developer on the developer roller is disposed upstream, in the rotation direction of the developer roller, of the position at which the photosensitive body and the developer roller are closest, and downstream of the layer regulating member in the rotation direction of the developer roller. This example developing device can define the flow passage for air by the first seal member, the developer roller and the layer regulating member, thereby enabling to perform the circulation of air and the capturing of toner more efficiently.

In an example developing device having disposed therein the first seal member, at least one or more magnetic poles of the developer roller may be disposed in a range which is upstream, in the rotation direction of the developer roller, of the first seal member, and which is downstream, in the rotation direction of the developer roller, of the layer regulating member. In this example developing device, as the developer on the developer roller has a maximum height at the center of the magnetic pole of the developer roller in a direction normal to the surface of the developer roller and is tilted at front or rear thereof toward the tangential directions of the developer roller, capturing of splashed toner by the developer can be made more efficiently by disposing the magnetic pole in the region of the developer roller opposing the first seal member.

In another example developing device, a second seal member is adjacent to or in contact with the developer on the developer roller, and is disposed in a developer container at a side downstream, in the rotation direction of the developer roller, of the position at which the photosensitive body and the developer roller are closest. This example developing device can suppress scattering of the toner by preventing with the second seal member leakage of air through a gap between the developer container and the developer roller, and can also facilitate flow of air through the flow passage by enhancing the airtightness of the developing device.

In an example developing device, an air vent with a filter is disposed in the developer container. In this example developing device, as the air vent with the filter is disposed in the developer container, pressure loss may be made in addition to the flow passage, so as to achieve a further decrease in the internal pressure.

In an example developing device, the air vent may be positioned downstream, in the rotation direction of the developer roller, of a position at which the developer roller and the developer container are closest, and upstream of the layer regulating member in the rotation direction of the developer roller. As this example developing device is substantially airtight, pressure tends to increase in an internal region of the developing device between the position at which the developer roller and the developer container are closest and the position of the layer regulating member disposed downstream in the rotation direction of the developer roller. Accordingly, the air vent disposed in this region can effectively decrease the internal pressure of the region.

In an example developing device, the portion of the flow passage disposed inside the developing device is located downstream, in the rotation direction of the developer roller, of the position at which the developer roller and the developer container are closest, and upstream of the layer regulating member in the rotation direction of the developer roller. As this example developing device is substantially airtight and pressure tends to increase in the internal region of the developing device between the position at which the developer roller and the developer container are closest and the position of the layer regulating member disposed downstream in the rotation direction of the developer roller, increase in the internal pressure of the developing device can be effectively suppressed by adapting this region to discharge air.

In an example developing device, in the non-image forming regions located at both longitudinal ends of the image forming region of the developer roller, the flow passage is formed with an opening to fluidly communicate with an interior of the developer container, and the flow passage extends from the inside of the developing device to the outside of the developing device through the opening. In this example developing device, with the opening formed in the flow passage, clogging of the flow passage by the toner or carrier entrained in the air passing through the flow passage can be prevented.

The present disclosure also provides a method for suppressing internal pressure of an example developing device for use with a two-component developer according to claim <NUM>. In the method, among other features, an air flow passage is disposed to extend from inside of the developing device and directed toward upstream, in a rotation direction of the developer roller, of a position at which the developer roller and a photosensitive body are closest, through at least one of non-image forming regions located at both longitudinal ends of an image forming region of the developer roller. This example method can circulate air through the flow passage between the inside and the outside of the developing device, thereby suppressing increase in the internal pressure of the developing device, while suppressing new introduction of air from the outside into the developing device and, as a result, can alleviate scattering of toner within a printer, excessive discharge of the developer from a developer replenishing device, and the aforementioned effects stemming from these.

In an example method, the flow passage extends toward upstream, in the rotation direction of the developer roller, of the position at which the photosensitive body and the developer roller are closest, and downstream of the layer regulating member in the rotation direction of the developer roller. This example method allows to circulate air between the inside and the outside of the developing device, through the flow passage extending toward the side which is upstream, in the rotation direction of the developer roller, of the position at which the photosensitive body and the developer roller are closest, and which is downstream, in the rotation direction of the developer roller, of the layer regulating member, such that the developer on the developer roller can capture and collect splashed toner.

In an example method, a first seal member adjacent to or in contact with the developer on the developer roller is disposed upstream, in the rotation direction of the developer roller, of the position at which the photosensitive body and the developer roller are closest, and downstream of the layer regulating member in the rotation direction of the developer roller. This example method can define the flow passage for air by the first seal member, the developer roller and the layer regulating member, thereby enabling to perform the circulation of air and the capturing of toner more efficiently.

In an example method having disposed therein the first seal member is provided, at least one or more magnetic poles of the developer roller are disposed in a range which is upstream, in the rotation direction of the developer roller, of the first seal member, and which is downstream, in the rotation direction of the developer roller, of the layer regulating member. As the developer on the developer roller has a maximum height at the center of the magnetic pole of the developer roller in a direction normal to the surface of the developer roller and is tilted at a front or a rear thereof toward the tangential directions of the developer roller, this example method enables to capture splashed toner by the developer more efficiently by disposing the magnetic pole in the region of the developer roller opposing the first seal member.

In an example method, a second seal member is adjacent to or in contact with the developer on the developer roller, and is disposed in a developer container at a side downstream, in the rotation direction of the developer roller, of the position at which the photosensitive body and the developer roller are closest. This example method can suppress scattering of the toner by preventing with the second seal member, leakage of air through a gap between the developer container and the developer roller, and can also facilitate flow of air through the flow passage by enhancing the airtightness of the developing device.

In an example method, an air vent with a filter is disposed in the developer container, and the air vent is positioned downstream, in the rotation direction of the developer roller, of a position at which the developer roller and the developer container are closest, and upstream of the layer regulating member in the rotation direction of the developer roller. As the example developing device is substantially airtight and pressure tends to increase in an internal region of the developing device between the position at which the developer roller and the developer container are closest and the position of the layer regulating member disposed downstream in the rotation direction of the developer roller, this example method can effectively decrease the internal pressure of the region by disposing the air vent in this region.

In an example method, in the non-image forming regions located at both longitudinal ends of the image forming region of the developer roller, the flow passage is formed with an opening to fluidly communicate with an interior of the developer container, and the flow passage extends from the inside of the developing device to the outside of the developing device through the opening. In this example method, clogging of the flow passage by the toner or carrier entrained in the air passing through the flow passage can be prevented by forming the opening in the flow passage.

<FIG> schematically shows an example of an image forming apparatus <NUM> which may employ an example developing device. As shown in <FIG>, the image forming apparatus <NUM> is an apparatus to form color images using toner cartridges N of magenta, yellow, cyan and black colors. The image forming apparatus <NUM> forms an image on a paper sheet (recording medium) P.

The image forming apparatus <NUM> is provided, for example, with a recording medium conveyance unit <NUM> for conveying a paper sheet P, developing devices <NUM> for developing an electrostatic latent image, a transfer unit <NUM> for secondarily transferring the toner image to the paper sheet P, photosensitive bodies <NUM> that are electrostatic latent image carriers, on circumferential surfaces of which images are formed, and a fixation unit <NUM> for fixing the toner image onto the paper sheet P.

The recording medium conveyance unit <NUM> conveys a paper sheet P to be formed with an image along a conveyance path R1. The paper sheet P is stacked and contained in a cassette K, picked up by paper feed rollers 15a-15d and conveyed. The recording medium conveyance unit <NUM> conveys the paper sheet P to a secondary transfer region R2 through the conveyance path R1 in such a timing that a toner image to be transferred to the paper sheet P arrives at the secondary transfer region R2.

Four developing devices <NUM> are provided, for example, for the respective colors. Each of the example developing devices <NUM> is provided with a developer roller <NUM> for carrying toner to the photosensitive body <NUM>. In the developing device <NUM>, toner and carrier are adjusted to have a desired mixing ratio. The toner is uniformly dispersed to prepare a developer imparted with an optimal amount of charge. The developer is carried by the developer roller <NUM>. As the developer roller <NUM> rotates to carry the developer to a region opposing the photosensitive body <NUM>, toner is moved out of the developer carried on the developer roller <NUM> and onto an electrostatic latent image formed on a circumferential surface of the photosensitive body <NUM> to develop the electrostatic latent image.

The transfer unit <NUM> carries the toner image formed with the developing device <NUM> to the secondary transfer region R2 where the toner image is secondarily transferred to the paper sheet P. The transfer unit <NUM> is provided with a transfer belt <NUM>, support rollers 31a, 31b, 31c and 31d for supporting the transfer belt <NUM>, primary transfer rollers <NUM> for holding the transfer belt <NUM> with the photosensitive bodies <NUM>, and a secondary transfer roller <NUM> for holding the transfer belt with the support roller 31d.

The transfer belt <NUM> is an endless belt circularly moved by the support rollers 31a, 31b, 31c and 31d. The primary transfer rollers <NUM> are disposed to press the photosensitive bodies <NUM> from the inside of the transfer belt <NUM>. The secondary transfer roller <NUM> is disposed to press the support roller 31d from the outside of the transfer belt <NUM>.

Four photosensitive bodies <NUM> are provided for the respective colors. Each of the photosensitive bodies <NUM> is provided along the direction of movement of the transfer belt <NUM>. Around the circumference of the photosensitive body <NUM>, the developing device <NUM>, a charge roller <NUM>, an exposure unit <NUM> and a cleaning unit <NUM> are arranged.

The charge roller <NUM> is a charge means for uniformly charging the surface of the photosensitive body <NUM> at a predetermined potential. The charge roller <NUM> is driven to follow the rotation of the photosensitive body <NUM>. The exposure unit <NUM> exposes the surface of the photosensitive body <NUM> charged by the charge roller <NUM> in accordance with an image to be formed on the paper sheet P. The potential of portions of the surface of the photosensitive body <NUM> exposed by the exposure unit <NUM> is thereby changed to form an electrostatic latent image. The four developing devices <NUM> each uses the toner supplied from the toner cartridge N provided opposite to the developing device <NUM> to develop the electrostatic latent image formed on the photosensitive body <NUM> and creates a toner image. The toner cartridges N are respectively filled with magenta, yellow, cyan and black toners. The cleaning unit <NUM> recovers the toner remaining on the photosensitive body <NUM> after the toner image formed on the photosensitive body <NUM> has been primarily transferred onto the transfer belt <NUM>.

The fixation unit <NUM> adheres and fixates onto the paper sheet P the toner image that has been secondarily transferred from the transfer belt <NUM> to the paper sheet P. The fixation unit <NUM> is provided with a heater roller <NUM> for heating the paper sheet P and a pressure roller <NUM> for pressing the heater roller <NUM>. The heater roller <NUM> and the pressure roller <NUM> are formed in cylindrical shapes, and the heater roller <NUM> is internally provided with a heat source such as a halogen lamp. A contact area called a fixation nip is formed between the heater roller <NUM> and the pressure roller <NUM>, and the toner image is fused and fixated onto the paper sheet P while passing the paper sheet P through the fixation nip. After the toner image has been secondarily transferred onto the paper sheet P, the toner remaining on the transfer belt <NUM> is recovered by a belt cleaning device.

The example image forming apparatus <NUM> is further provided with discharge rollers <NUM> and <NUM> for discharging the paper sheet P with the fixated toner image to the outside of the apparatus.

A printing operation of the example image forming apparatus <NUM> will be described. When an image signal of a recording image is input to the image forming apparatus <NUM>, the image forming apparatus <NUM> rotates the paper feed rollers 15a-15d to pick up and convey a paper sheet P stacked in the cassette K. Then, the surface of the photosensitive body <NUM> is uniformly charged at a predetermined potential by the charge roller <NUM> (charging). After that, based on the image signal received, an electrostatic latent image is formed by irradiating laser light onto the surface of the photosensitive body <NUM> with the exposure unit <NUM> (exposing).

In the developing device <NUM>, the electrostatic latent image is developed to form a toner image (developing). Thus formed toner image is primarily transferred from the photosensitive body <NUM> to the transfer belt <NUM> in the region at which the photosensitive body <NUM> and the transfer belt <NUM> are opposed, i.e. aligned and facing one another (transferring). The toner images formed on the four photosensitive bodies <NUM> are successively overlaid to form a single overlaid toner image on the transfer belt <NUM>. Then, the overlaid toner image is secondarily transferred onto the paper sheet P conveyed from the recording medium conveyance unit <NUM> in the secondary transfer region R2 at which the support roller 31d and the secondary transfer roller <NUM> are opposed, i.e. aligned and facing one another.

The paper sheet P, with the secondarily transferred overlaid toner image, is conveyed to the fixation unit <NUM>. The overlaid toner image is fused and fixated onto the paper sheet P while the paper sheet P is made to pass under heat and pressure between the heater roller <NUM> and the pressure roller <NUM> (fixating). After that, the paper sheet P is discharged to the outside of the image forming apparatus <NUM> by the discharge rollers <NUM> and <NUM>.

<FIG> is a perspective view showing one example of the developing device <NUM>. The developer roller <NUM> has an image forming region C, on which the developer is adsorbed, and non-image forming regions D, on which no developer is adsorbed, located at both longitudinal ends of the image forming region C. The layer regulating member (hidden behind a protective cover <NUM> and not shown in <FIG>) has a longitudinal length approximately equal to that of the developer roller <NUM> and aligned with the developer roller <NUM> in the longitudinal direction. The protective cover <NUM> has a longitudinal length approximately equal to the longitudinal length of the layer regulating member and aligned with the layer regulating member in the longitudinal direction.

<FIG> is a lateral side view showing an example developing device <NUM>, along with a photosensitive body <NUM>. The photosensitive body <NUM> forms part of a photosensitive device (not shown), but <FIG> shows the photosensitive body <NUM> without other parts of the photosensitive device, for clarity of explanation. The developing device <NUM> includes, for example, a developer container <NUM> for containing a developer (not shown) comprising toner and carrier, mixing and stirring members <NUM>, <NUM> for stirring the developer in the developer container <NUM>, a developer roller <NUM> for magnetically adsorbing the developer stirred and transported by the mixing and stirring members <NUM>, <NUM>, a layer regulating member <NUM> for shaping the developer adsorbed onto the developer roller <NUM> into a thin layer of developer, a protective cover <NUM> for protecting the layer regulating member <NUM>, a seal member <NUM> disposed on the protective cover <NUM> adjacent to or in contact with the developer on the developer roller <NUM>, a seal member <NUM> disposed in the developer container <NUM> adjacent to or in contact with the developer on the developer roller <NUM>, and a flow passage forming member <NUM> for fluidly communicating the interior of the developing device <NUM> with the exterior of the developing device <NUM>. The flow passage forming member <NUM> includes, for example, an inlet 111a located inside the developing device <NUM> (at an inlet position). A symbol A denotes a position at which the developer roller <NUM> and the photosensitive body <NUM> are closest (e.g. a first closest position A), and a symbol B denotes a position at which the developer container <NUM> and the developer roller <NUM> are closest (e.g. a second closest position B). The developing device <NUM> may further include, for example, a developer replenishing device (not shown) for discharging degraded carrier while replenishing lacking carrier, and a toner density sensor (not shown) for detecting a toner density of the developer.

The seal member <NUM> may have a longitudinal length approximately equal to the whole length of the developer roller <NUM>, including an image forming region and non-image forming regions at respective ends of the developer roller <NUM> (similarly to the image forming region C and the non-image forming regions D at the respective ends of the developer roller <NUM>, shown in <FIG>), and is disposed such that one edge along the longitudinal length thereof is adjacent to or in contact with the developer on the developer roller <NUM>. Depending on embodiments, the seal member <NUM> may be formed integrally with the protective cover <NUM>, or the seal member <NUM> may be disposed without any protective cover. Alternatively, seal member <NUM> may be provided separately from an existing seal member (not shown) having a longitudinal length approximately equal to the image forming region of the developer roller <NUM> and disposed on the protective cover <NUM> in contact with the photosensitive body <NUM> for preventing a foreign material such as toner scattered, for example, through a gap between the photosensitive body <NUM> and the developer roller <NUM> from contaminating the exposure unit <NUM>.

<FIG> is a perspective view showing part of the developing device <NUM> in a state where the developer roller <NUM>, the mixing and stirring members <NUM>, <NUM>, the layer regulating member <NUM> and the protective cover <NUM> have been removed from the developing device <NUM> shown in <FIG>, in order to show further details of the flow passage forming member <NUM>, and <FIG> is a front view thereof. The flow passage forming member <NUM> is disposed in at least one of the non-image forming regions at the ends of the image forming region of the developer roller <NUM>. Further, the flow passage forming member <NUM> has, in addition to the inlet 111a, an outlet 111b located to channel air outside the developing device <NUM> (at an outlet position), and the inlet 111a and the outlet 111b are fluidly communicated with each other. The outlet 111b may be located, at least in part, outside the developing device <NUM>. As indicated above, the flow passage forming member <NUM> is disposed in at least one of the non-image forming regions at the ends of the image forming region of the developer roller <NUM>, and the layer regulating member <NUM> has, for example, a longitudinal length approximately equal to the whole length of the image forming region. Accordingly, the air discharged from the outlet 111b is not hindered by the layer regulating member <NUM>.

<FIG> is a simplified perspective view showing part of the developing device <NUM> shown in <FIG>, in order to show a direction G in which the air discharged from the at least one of the non-image forming regions at the ends of the image forming region of the developer roller <NUM> flows along the longitudinal direction of the developer roller <NUM> into the image forming region.

Referring back to <FIG>, during the operation of the developing device <NUM>, the developer contained in the developer container <NUM> is stirred and transported by the rotating mixing and stirring members <NUM>, <NUM>, magnetically adsorbed onto the rotating developer roller <NUM>, shaped into a thin layer of developer by the layer regulating member <NUM>, and the toner is adsorbed from the thin layer of developer onto an electrostatic latent image on the rotating photosensitive body <NUM> for developing the electrostatic latent image.

During such operation of the developing device <NUM>, the air external to the developing device <NUM> is taken into the interior of the developing device <NUM> from, for example, a position indicated by a symbol E in <FIG>, through the position B at which the developer container <NUM> and the developer roller <NUM> are closest, by the developer on the developer roller <NUM> rotated in the direction indicated by the solid arrow in the figure. Then the air proceeds to flow from the inlet 111a to the outlet 111b of the flow passage forming member <NUM> through an air flow passage <NUM> (cf. <FIG>), and discharged from the outlet 111b to the exterior of the developing device <NUM>. The air discharged from the outlet 111b flows in a direction indicated by the arrow G in <FIG>, through a passage formed by the developer roller <NUM>, the layer regulating member <NUM>, the protective cover <NUM> and the seal member <NUM>, during which scattered toner entrained in the air stream is adsorbed to the developer on the developing roller <NUM> and collected thereby, and the air is once again taken by the developer into the interior of the developing device <NUM> through the closest positions A, B. A path F of such air circulation is shown in <FIG> by dotted arrows.

For example, the air taken into the interior of the developing device <NUM> flows, from the interior of the developing device <NUM> and through at least one of the non-image forming regions located at the longitudinal ends of the image forming region of the developer roller <NUM>, along an air flow passage directed toward upstream, in the direction of rotation of the developer roller <NUM>, of the closest position A between the developer roller <NUM> and the photosensitive body <NUM>. For example, with reference to <FIG>, the air flow passage <NUM> may extend from inside the developing device <NUM>, at an inlet 111a, and direct an air flow F toward an outlet 111b located upstream, in the rotation direction of the developer roller, of the closest position A between the developer roller and the photosensitive body, through the non-image forming region of the developer roller <NUM>.

As described above, by circulating air through the prescribed flow passage that communicates the interior of the developing device with its exterior, the developing device can suppress an increase in the internal pressure of the developing device while suppressing the introduction of new external air, and can also collect during the course of the circulation scattered toner entrained in the air. Such developing device can reduce contamination inside the printer by scattered toner caused by the air containing toner and discharged, due to increase in the internal pressure, to the exterior of the developing device from a portion of the developing device with low airtightness, as well as degradation of print quality concomitant with the contamination, and can further reduce excessive discharge of the developer from a developer discharge port of the developer replenishing device due to increase in the internal pressure of the developing device, thereby reducing the occurrence of image density unevenness attributable to excessive discharge of the developer, of reduced image density, and of inadequate toner/carrier mixing ratio due to detection error of a toner density sensor. Such occurrences tend to become prominent as the number of rotations of the developer roller increases. In the example developing device described herein, the amount of circulating air increases as the number of rotations of the developer roller increases, and the circulating air has a tendency to prevent the introduction of new external air. Accordingly, an increase in the internal pressure of the developing device can be suppressed.

In some examples, the layer regulating member <NUM> does not extend over the non-image forming regions in the construction described above. In some examples, when the layer regulating member <NUM> or any other component extends over the non-image forming regions, for example (the layer regulating member <NUM> may be disposed to close the outlet 111b of the flow passage forming member <NUM>), the same effect as the aforementioned case can be obtained by forming an opening in that location. <FIG> shows an example of such a case. In this figure, the layer regulating member <NUM> is formed with a cut 104a as the opening, at a location opposing (e.g. facing and/or aligned with) the outlet 111b of the flow passage forming member <NUM> (see <FIG> and <FIG>), so that the air discharged from the outlet 111b is not hindered by the layer regulating member <NUM>.

Further, referring back to <FIG>, for example, when the left-hand portion of the protective cover <NUM> is cut along the dotted line shown therein, the volume of the flow passage formed by the developer roller <NUM>, the layer regulating member <NUM>, the protective cover <NUM> and the seal member <NUM> can be increased, thereby enabling to capture the toner more efficiently. Further, while the flow passage from the interior to the exterior of the developing device <NUM> has been shown to be implemented by the flow passage forming member <NUM>, any gap existing in the vicinity of the image forming regions of the developer roller and communicating from the interior to the exterior of the developing device (for example, an existing gap around a driving mechanism located in the non-image forming regions of the developer roller or in the vicinity thereof), for example, may be utilized as the air flow passage depending on the design of the developing device. Further, with reference to <FIG>, while an increase in the internal pressure of the developing device <NUM> may be suppressed when the seal member <NUM> is disposed without disposing the seal member <NUM>, the disposition of the seal member <NUM> in addition to the seal member <NUM> enables to prevent leakage of the air entraining scattered toner through the gap between the developer container <NUM> and the developer roller <NUM>, and it also enables to enhance the airtightness of the developing device <NUM> so as to facilitate flow of air through the flow passage.

Claim 1:
A developing device (<NUM>, <NUM>) for use with a two-component developer, comprising:
a developer roller (<NUM>, <NUM>) to rotate in a rotation direction, the developer roller (<NUM>, <NUM>) extending longitudinally and having longitudinal ends, the developer roller (<NUM>, <NUM>) having an image forming region located between the longitudinal ends, and a non-image forming region (C) located at at least one of the longitudinal ends;
a photosensitive body (<NUM>) adjacent the developer roller (<NUM>, <NUM>), wherein a closest position (A) is defined where the developer roller (<NUM>, <NUM>) and the photosensitive body (<NUM>) are closest to one another; and
an air flow passage (<NUM>) extending from an inlet (111a) located inside the developing device (<NUM>, <NUM>) to an outlet (111b) located outside the developing device to discharge the air out of the developing device (<NUM>, <NUM>), the air flow passage (<NUM>) to form an air flow directed toward an upstream side, relative to the rotation direction of the developer roller (<NUM>, <NUM>), of the closest position (A) between the developer roller (<NUM>, <NUM>) and the photosensitive body (<NUM>), characterised by the air flow passage (<NUM>) extending through the non-image forming region (D) of the developer roller (<NUM>, <NUM>).