Image forming apparatus and image forming system with cartridge capacity dependent transport force

An image forming apparatus includes: a cartridge installing section in which a first cartridge and a second cartridge are selectively installable; and a controller. The first cartridge includes: a first case configured to contain a first developer; a first developing roller; and a first transport member configured to transport the first developer toward the first developing roller. The second cartridge includes: a second case configured to contain a second developer, an amount of the second developer being greater than an amount of the first developer; a second developing roller; and a second transport member configured to transport the second developer toward the second developing roller. The controller is configured to control a drive source to drive one of the first transport member and the second transport member.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority from Japanese Patent Application No. 2013-236687, filed on Nov. 15, 2013, the disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND

1. Field of the Invention

The present invention relates to an image forming apparatus and an image forming system to which one of a first cartridge containing a developer, and a second cartridge containing the developer more than the first cartridge is selectively installable.

2. Description of the Related Art

Conventionally, there is known an image forming apparatus configured such that one of two types of cartridges, which contain different amounts of a developer when the cartridges are unused, is selectively installable. In particular, one of a small capacity cartridge and a large capacity cartridge containing the developer more than the small capacity cartridge is selectively installable (see Japanese Patent Application Laid-open No. 2011-186880, for example). Further, in such an image forming apparatus, each of the cartridges includes a casing containing the developer, a developing roller supported by the casing, an agitator configured to transport the developer in the casing toward the developing roller, and a supply roller configured to supply the developing roller with the developer transported by the agitator.

SUMMARY

However, because the large capacity cartridge contains large amount of the developer, it is usable for a longer period of time than the small capacity cartridge. Therefore, in the large capacity cartridge, it is feared that the developer leaks because, for example, the developing roller is scraped away by the developer present on a seal member.

Accordingly, it is an object of the present teaching to provide an image forming apparatus and an image forming system which are capable of restraining leakage of the developer from the large capacity cartridge.

According to a first aspect of the present teaching, there is provided an image forming apparatus including: a cartridge installing section in which a first cartridge and a second cartridge are selectively installable, the first cartridge including: a first case configured to contain a first developer; a first developing roller; and a first transport member configured to transport the first developer toward the first developing roller, and the second cartridge including: a second case configured to contain a second developer, an amount of the second developer being greater than an amount of the first developer; a second developing roller; and a second transport member configured to transport the second developer toward the second developing roller; and a controller configured to: determine whether the first cartridge is installed in the cartridge installing section or the second cartridge is installed in the cartridge installing section; control a drive source to drive the first transport member to transport the first developer by first transport force, in a case that the controller determines that the first cartridge is installed in the cartridge installing section; and control the drive source to drive the second transport member to transport the second developer by second transport force which is smaller than the first transport force, in a case that the controller determines that the second cartridge is installed in the cartridge installing section.

According to the image forming apparatus having such a configuration as described above, an amount of the second developer transported by the second transport member toward the second developing roller is smaller than an amount of the first developer transported by the first transport member toward the first developing roller. By virtue of this, in the second cartridge usable for a longer period of time than the first cartridge, even if the second developing roller is scraped away by the second developer, for example, it is still possible to restrain leakage of the second developer.

According to a second aspect of the present teaching, there is provided an image forming system including: a first cartridge including: a first case configured to contain a first developer; a first developing roller; and a first transport member configured to transport the first developer in the first case toward the first developing roller by first transport force; a second cartridge including: a second case configured to contain a second developer, an amount of the second developer being greater than an amount of the first developer in the first case; a second developing roller; and a second transport member configured to transport the second developer in the second case toward the second developing roller by second transport force which is smaller than the first transport force; and an image forming apparatus including a cartridge installing section in which the first cartridge and the second cartridge are selectively installable.

According to an image forming system having such a configuration as described above, an amount of the second developer transported by the second transport member toward the second developing roller is smaller than an amount of the first developer transported by the first transport member toward the first developing roller. By virtue of this, in the second cartridge usable for a longer period of time than the first cartridge, even if the second developing roller is scraped away by the second developer, for example, it is still possible to restrain leakage of the second developer.

DESCRIPTION OF THE EMBODIMENTS

Hereinbelow, a first embodiment of the present teaching will be explained in detail while referring to the accompanying drawings as appropriate. In the following description, first, a brief explanation will be made on an overall configuration of a laser printer1as an example of an image forming apparatus included in an image forming system. Next, an explanation will be made on details of the characteristic parts of the present teaching.

Further, the following explanation will be made with such directions as based on a user using the laser printer1. That is, inFIG. 1, the right side is referred to as “front side”, the left side is referred to as “rear side”, the far side in a direction perpendicular to the page is referred to as “right side”, and the near side in the direction perpendicular to the page is referred to as “left side”. Further, the up-down direction of the figure is referred to as “up-down direction”.

As shown inFIG. 1, the laser printer1is provided with a feeder section4for feeding sheet3into an apparatus main body2, an image forming section5for forming an image on the sheet3, etc.

The feeder section4has a publicly known configuration and is primarily provided with a feed tray6, a sheet pressing plate7, and a sheet transporting mechanism9. Then, in the feeder section4, the sheet3in the feed tray6is introduced by the sheet pressing plate7to the sheet transporting mechanism9arranged above the sheet pressing plate7, and then transported by the sheet transporting mechanism9to the image forming section5.

The image forming section5is provided with a scanner unit8, a process cartridge17, a fixing section18, etc.

The scanner unit8is provided with a laser light emitting section, a polygonal mirror, a lens, a reflecting mirror, etc., all of which are not shown. From the scanner unit8, a laser beam passes through the path indicated by a chain line in each drawing so as to irradiate the surface of a photosensitive drum27by way of rapid scanning.

The process cartridge17is installable in a cartridge installing section2B provided in the apparatus main body2by appropriately opening a front cover2A of the apparatus main body2on the near side. The process cartridge17is constructed primarily of a developing cartridge28and a drum unit51.

The developing cartridge28is installed to be either fittable into and removable from the cartridge installing section2B of the apparatus main body2via the drum unit51or fittable to and removable from the drum unit51fixed on the apparatus main body2. The developing cartridge28is primarily provided with a developing roller31, a layer thickness restriction blade32, a supply roller33, and a case34adapted to contain a positively charged toner T as an example of developer.

The case34has a toner container35adapted to internally contain the toner T, and supports the developing roller31, the layer thickness restriction blade32and the supply roller33at the rear side of the toner container35. Further, an agitator36is provided in the toner container35.

The agitator36has a shaft portion361rotatably supported by the case34, and an agitating blade362fixed on the shaft portion361to be rotatable integrally with the shaft portion361. The agitator36is configured such that the agitating blade362rotates inside the toner container35while sliding along the inner surface of the toner container35, along with clockwise rotation of the shaft portion361according toFIG. 1. On this occasion, because the toner T inside the toner container35is transported by a transport surface363oriented to the downstream side in the rotation direction of the agitating blade362, the toner T inside the toner container35is agitated by the agitator36while being supplied to the supply roller33arranged at the rear side thereof.

The developing roller31is capable of holding the toner T on its surface. The layer thickness restriction blade32is such a member whose leading end is provided to contact with the surface of the developing roller31as to restrict the thickness of the toner T on the developing roller31.

The supply roller33is a member capable of transporting, toward the developing roller31, the toner T in the case34supplied by the agitator36. The supply roller33is arranged in a position obliquely below the developing roller31to face the developing roller31, and provided to be rotatable while in contact with the developing roller31.

The supply roller33has a cylindrical supply roller body331extending in an axial direction of the developing roller31, that is, in a left-right direction, and a supply roller shaft portion332inserted into the supply roller body331to be rotatable integrally with the supply roller body331. Further, the supply roller body331is formed of, for example, a urethane sponge or the like. Further, the supply roller shaft portion332is formed of a metal.

In the developing cartridge28, the toner T contained in the toner container35is first agitated by the agitator36and then fed to the developing roller31by the supply roller33, where the toner T is positively charged through friction between the supply roller33and the developing roller31. Along with the rotation of the developing roller31, the toner T fed onto the developing roller31comes between the layer thickness restriction blade32and the developing roller31, and is held on the developing roller31as a thin layer of a certain thickness while being further charged through friction.

The drum unit51is primarily provided with the photosensitive drum27which is publicly known, a scorotron charger29, and a transfer roller30. Thereby, inside the drum unit51, the surface of the photosensitive drum27is uniformly charged positively by the scorotron charger29, and thereafter exposed by way of the rapid scanning of the laser beam from the scanner unit8. By virtue of this, the potential of the exposed portion decreases, thereby forming an electrostatic latent image based on some image data.

Next, due to the rotation of the developing roller31, the toner T held on the developing roller31is supplied to the electrostatic latent image formed on the surface of the photosensitive drum27, so as to form a toner image on the surface of the photosensitive drum27. Thereafter, the sheet3is transported therethrough between the photosensitive drum27and the transfer roller30whereby the toner image carried by the surface of the photosensitive drum27is transferred to the sheet3.

The fixing section18has a publicly known configuration, and includes a heating roller41and a pressing roller42. Thereby, in the fixing section18, the toner T transferred onto the sheet3is fixed by heat while the sheet3is passing between the heating roller41and the pressing roller42. Further, the sheet3finished with the heat fixing by the fixing section18is sent out by a discharge roller45onto a discharge tray46.

As shown inFIGS. 1 and 2, the image forming system according to the first embodiment is configured such that any one of two types of developing cartridges28with toner containers35different in capacity is selectively installable in the cartridge installing section2B of the laser printer1, that is, in particular, a small capacity cartridge28L as an example of the first cartridge, and a large capacity cartridge28H as an example of the second cartridge containing the toner T more than the small capacity cartridge28L.

In the following explanation, the developing roller31, the supply roller33, the case34, and the agitator36, which are included in the small capacity cartridge28L, will also be referred to as first developing roller31L, first supply roller33L (an example of the first transport member), first case34L, and first agitator36L, respectively. The toner container35in the first case34L will also be referred to as first toner container35L. Further, the developing roller31, the supply roller33, the case34, and the agitator36, which are included in the large capacity cartridge28H, will also be referred to as second developing roller31H, second supply roller33H (an example of the second transport member), second case34H, and second agitator36H, respectively. The toner container35in the second case34H will also be referred to as second toner container35H.

Further, in the first embodiment, the small capacity cartridge28L and the large capacity cartridge28H are different only in the capacity of the toner container35and in the amount of the toner T contained in the toner container35when the small capacity cartridge28L and the large capacity cartridge28H are unused, but identical in configuration with the other members.

That is, the first developing roller31L, the first supply roller33L and the first agitator36L included in the small capacity cartridge28L are identical in configuration with the second developing roller31H, the second supply roller33H and the second agitator36H included in the large capacity cartridge28H, respectively. Further, in order for the second toner container35H of the large capacity cartridge28H to be larger in capacity than the first toner container35L of the small capacity cartridge28L, such a portion in the second case34H as to define the second toner container35H is formed to be larger than such a portion in the first case34L as to define the first toner container35L. Further, in a state that the large capacity cartridge28H and the small capacity cartridge28L are unused, the second toner container35H in the second case34H contains more of the toner T than the first toner container35L in the first case34L.

Further, as shown inFIGS. 3 and 8, a drive device110, a bias application section120, and a specification detection device130are provided in the cartridge installing section2B of the laser printer1. Further, a controller140is provided inside the apparatus main body2of the laser printer1.

The drive device110is constructed from a plurality of gears and a drive motor which are not shown. Further, when the developing cartridge28is installed into the cartridge installing section2B, a gear of the drive device110engages with an input gear11provided in the developing cartridge28such that a drive force is transmitted from the drive motor to the input gear11via each of the gears.

Further, the developing cartridge28is provided with a gear row10which includes the input gear11mentioned above, a developing roller gear14which rotates integrally with the developing roller31, a supply roller gear15which rotates integrally with the supply roller33, an intermediate gear16, and an agitator gear19which rotates integrally with the agitator36. Each of the developing roller gear14, the supply roller gear15and the intermediate gear16engages with the input gear11, while the agitator gear19engages with the intermediate gear16. Further, in the first embodiment, the gear row10included in the small capacity cartridge28L is identical in configuration with the gear row10included in the large capacity cartridge28H.

The bias application section120is configured to apply a predetermined bias to the developing roller31and the supply roller33of the developing cartridge28installed in the cartridge installing section2B, such that the toner T on the supply roller33is transported to the developing roller31.

The specification detection device130is a sensor having a publicly known configuration. The specification detection device130is configured to detect a detection target portion150included in the developing cartridge28when the developing cartridge28is installed in the cartridge installing section2B. In particular, the detection target portion150has a different configuration between the small capacity cartridge28L and the large capacity cartridge28H. Further, the specification detection device130is configured to output a different signal to the controller140between having detected the detection target portion150provided in the small capacity cartridge28L and having detected the detection target portion150provided in the large capacity cartridge28H.

For example, the detection target portion150is configured to move along with the rotation of the gear row10when the drive force is inputted to the gear row10. The detection target portion150provided in the small capacity cartridge28L is different in movement amount from the detection target portion150provided in the large capacity cartridge28H, and the specification detection device130is configured to output a signal based on the movement amount of the detection target portion150.

As shown inFIGS. 3 and 8, the controller140is capable of controlling the drive device110and the bias application section120. The controller140is configured to determine whether the small capacity cartridge28L is installed in the cartridge installing section2B or the large capacity cartridge28H is installed in the cartridge installing section2B, based on the signal inputted from the specification detection device130. The controller140is configured to drive the first supply roller33L to transport the toner T by first transport force in the case of determining that the small capacity cartridge28L is installed, and to drive the second supply roller33H to transport the toner T by second transport force smaller than the first transport force in the case of determining that the large capacity cartridge28H is installed.

In particular, the controller140controls the drive device110to input the same drive force to the input gear11of each of the cartridges28L and28H, and to rotate, respectively at the same rotation speed, either the first developing roller31L, first supply roller33L and first agitator36L of the small capacity cartridge28L or the second developing roller31H, second supply roller33H and second agitator36H of the large capacity cartridge28H.

Then, the controller140determines whether the small capacity cartridge28L is installed in the cartridge installing section2B or the large capacity cartridge28H is installed in the cartridge installing section2B, based on the signal inputted from the specification detection device130. (Step S100inFIG. 9) In the case of determining that the small capacity cartridge28L is installed (Step S100: SMALL inFIG. 9), as shown inFIG. 4, the controller140is configured to apply a first bias V1to the first developing roller31L and the first supply roller33L by controlling the bias application section120to set the first developing roller31L to a first electric potential and to set the first supply roller33L to a second electric potential (Step S200inFIG. 9). Further, if a pulverized toner is used as the toner T, then the toner T may deteriorate when used continuously, thereby causing an increase in a transporting amount of the toner T from the first developing roller31L to the photosensitive drum27. Therefore, in the first embodiment, the first electric potential for the first developing roller31L is set to be constant until the printed pages from the point of installing the pristine small capacity cartridge28L (with zero printed pages), that is, the accumulated printed pages, exceed a predetermined number, and to decrease gradually after the accumulated printed pages exceed the predetermined number. Further, the second electric potential for the first supply roller33L is set to be higher than the first electric potential for the first developing roller31L so that the first bias V1is constant.

In the case of determining that the large capacity cartridge28H is installed (Step S100: LARGE inFIG. 9), the controller140is configured to apply a second bias V2to the second developing roller31H and the second supply roller33H, by controlling the bias application section120to set the second developing roller31H to a third electric potential and to set the second supply roller33H to a fourth electric potential (Step S300inFIG. 9). Further, the third electric potential for the second developing roller31H is equal to the first electric potential for the first developing roller31L. Further, the fourth electric potential for the second supply roller33H is set to be higher than the third electric potential for the second developing roller31H, so that the second bias V2is constant.

Further, the magnitude (absolute value) of the second bias V2is set to be smaller than the magnitude (absolute value) of the first bias V1. That is, in a case that the accumulated printed pages are the same, the fourth potential for the second supply roller33H is set to be lower than the second potential for the first supply roller33L.

Now, an explanation will be made on the function and effect of the image forming system configured as described above. If the small capacity cartridge28L is installed into the cartridge installing section2B, then the first developing roller31L and the first supply roller33L rotate in a state that the first bias V1is applied to the first developing roller31L and the first supply roller33L.

On the other hand, if the large capacity cartridge28H is installed into the cartridge installing section2B, then the second developing roller31H and the second supply roller33H rotate in a state that the second bias V2, which is smaller than the first bias V1, is applied to the second developing roller31H and the second supply roller33H.

On this occasion, because the magnitude of the second bias V2is smaller than the magnitude of the first bias V1, the toner T which is transported from the second supply roller33H to the second developing roller31H is less in amount than the toner T which is transported from the first supply roller33L to the first developing roller31L.

That is, in the large capacity cartridge28H, the second supply roller33H supplies the second developing roller31H with less of the toner T. Hence, even though the large capacity cartridge28H is usable for a longer period of time than the small capacity cartridge28L, it is still possible to restrain leakage of the toner T.

In the first embodiment described above, the controller140is configured to set the second transport force of the second supply roller33H to be smaller than the first transport force of the first supply roller33L by changing the bias applied to the developing roller31and the supply roller33, between the case of installing the small capacity cartridge28L and the case of installing the large capacity cartridge28H. However, the present teaching is not limited to this configuration. For example, it is also possible to apply a constant bias to the developing roller31and the supply roller33, and to change the rotation speeds of the first supply roller33L and the second supply roller33H.

In particular, the drive device110may have a first drive motor adapted to drive the input gear11, and a second drive motor different from the first drive motor. Further, the supply roller gear15is configured not to engage with the input gear11, and the drive force is transmitted thereto from the second drive motor.

In the case of determining that the small capacity cartridge28L is installed, the controller140controls the drive device110to drive the first drive motor such that the first developing roller31L may rotate at a predetermined rotation speed and, meanwhile, to drive the second drive motor such that the first supply roller33L may rotate at a first rotation speed. On the other hand, in the case of determining that the large capacity cartridge28H is installed, the controller140controls the drive device110to drive the first drive motor such that the second developing roller31H may rotate at the same predetermined rotation speed as that of the first developing roller31L and, meanwhile, to drive the second drive motor such that the second supply roller33H may rotate at a second rotation speed slower than the first rotation speed.

On the other hand, the controller140is configured to apply the same bias to the developing roller31and the supply roller33, between the case of installing the small capacity cartridge28L and the case of installing the large capacity cartridge28H. That is, the first bias V1and the second bias V2are set to be the same value.

Being configured as described above, in the large capacity cartridge28H, the second supply roller33H rotates slowly against the second developing roller31H. Therefore, the second supply roller33H supplies the second developing roller31H with less of the toner T. By virtue of this, even though the large capacity cartridge28H is usable for a longer period of time than the small capacity cartridge28L, it is still possible to restrain leakage of the toner T.

Further, while the rotation speed of the first supply roller33L (an example of the first transport member) and the rotation speed of the second supply roller33H (an example of the second transport member) are changed in such a modification as described above, the present teaching is not limited to this method. For example, it is also possible to change the rotation speed of the first agitator36L (an example of the first transport member) and the rotation speed of the second agitator36H (an example of the second transport member).

In particular, the gear row10may be configured not to have the intermediate gear16, and thus the drive force is not transmitted from the first drive motor to the agitator gear19. Instead, the drive force is transmitted from the second drive motor to the agitator gear19. Further, in such a modification, the supply roller gear15engages with the input gear11.

In the case of determining that the small capacity cartridge28L is installed, the controller140drives the second drive motor such that the first agitator36L may rotate at a first rotation speed, whereas in the case of determining that the large capacity cartridge28H is installed, the controller140drives the second drive motor such that the second agitator36H may rotate at a second rotation speed slower than the first rotation speed.

In the case of being configured as described above, in the large capacity cartridge28H, the second agitator36H transports less of the toner T toward the second developing roller31H. Therefore, even though the large capacity cartridge28H is usable for a longer period of time than the small capacity cartridge28L, it is still possible to restrain leakage of the toner T.

Next, a second embodiment of the present teaching will be explained in detail while referring to the accompanying drawings as appropriate. In the second embodiment, the configurations of the small capacity cartridge28L and the large capacity cartridge28H are partially changed so as to change the transport force of the first supply roller33L when the small capacity cartridge28L is installed and the transport force of the second supply roller33H when the large capacity cartridge28H is installed. Further, in the second embodiment, the same reference signs are assigned to the components identical or similar to those in the first embodiment described above, and any explanation therefor will be omitted.

As shown inFIG. 5A, the small capacity cartridge28L includes a first gear row10L on the left lateral side. The first gear row10L is configured to have a first input gear11L, a first developing roller gear14L, a first supply roller gear15L as an example of the first transport member gear, a first intermediate gear16L, and a first agitator gear19L. Further, inFIG. 5A, each gear is shown in the form of a pitch circle.

The first input gear11L is rotatably supported by the first case34L, and the drive force from the drive device110is inputted thereto if the small capacity cartridge28L is installed in the cartridge installing section2B of the laser printer1. The first input gear11L has a first large diameter gear portion12L, and a first small diameter gear portion13L smaller in diameter than the first large diameter gear portion12L. Further, the first large diameter gear portion12L and the first small diameter gear portion13L are configured to rotate integrally.

The first developing roller gear14L is fixed on a shaft portion of the first developing roller31L to rotate integrally with the first developing roller31L. The first developing roller gear14L engages with the first large diameter gear portion12L of the first input gear11L.

The first supply roller gear15L is fixed on the supply roller shaft portion332of the first supply roller33L to rotate integrally with the first supply roller33L. The first supply roller gear15L engages with the first small diameter gear portion13L of the first input gear11L.

The first intermediate gear16L is rotatably supported by the first case34L in a position between the first input gear11L and the first agitator gear19L. The first intermediate gear16L has a first large diameter portion17L, and a first small diameter portion18L smaller in diameter than the first large diameter portion17L, where the first large diameter portion17L and the first small diameter portion18L are integrally rotatable. Further, the first large diameter portion17L engages with the first small diameter gear portion13L of the first input gear11L.

The first agitator gear19L is fixed on the shaft portion361of the agitator36to rotate integrally with the agitator36. The first agitator gear19L engages with the first small diameter portion18L of the first intermediate gear16L.

As shown inFIG. 5B, the large capacity cartridge28H includes a second gear row10H on the left lateral side. The second gear row10H is configured to have a second input gear11H, a second developing roller gear14H, a second supply roller gear15H as an example of the second transport member gear, a second intermediate gear16H, and a second agitator gear19H.

In the second gear row10H, the teeth number of the second input gear11H and the teeth number of the second developing roller gear14H are set such that the speed transmission ratio from the second input gear11H to the second developing roller gear14H may be equal to the speed transmission ratio from the first input gear11L to the first developing roller gear14L. Further, the teeth number of the second input gear11H and the teeth number of the second supply roller gear15H are set such that the speed transmission ratio from the second input gear11H to the second supply roller gear15H may be larger than the speed transmission ratio from the first input gear11L to the first supply roller gear15L. Further, the teeth numbers of the second input gear11H, the second intermediate gear16H and the second agitator gear19H are set such that the speed transmission ratio from the second input gear11H to the second agitator gear19H may be equal to the speed transmission ratio from the first input gear11L to the first agitator gear19L. Further, since the speed transmission ratio is obtained by dividing the angular speed of the driving-side gear by the angular speed of the driven-side gear, this speed transmission ratio can be expressed in terms of the teeth numbers of the driving-side gear and the driven-side gear, that is, the speed transmission ratio is obtained by dividing the teeth number of the driven-side gear by the teeth number of the driving-side gear.

The second input gear11H is rotatably supported by the second case34H, and the drive force from the drive device110is inputted thereto if the large capacity cartridge28H is installed in the cartridge installing section2B of the laser printer1. The second input gear11H has a second large diameter gear portion12H, and a second small diameter gear portion13H smaller in diameter than the second large diameter gear portion12H. Further, the second large diameter gear portion12H and the second small diameter gear portion13H are configured to rotate integrally.

The second large diameter gear portion12H has the same configuration and the same teeth number as the first large diameter gear portion12L of the first input gear11L included in the small capacity cartridge28L.

The second developing roller gear14H is fixed on a shaft portion of the second developing roller31H to rotate integrally with the second developing roller31H. The second developing roller gear14H engages with the second large diameter gear portion12H of the second input gear11H. The second developing roller gear14H has the same configuration and the same teeth number as the first developing roller gear14L.

The second supply roller gear15H is fixed on the supply roller shaft portion332of the second supply roller33H to rotate integrally with the second supply roller33H. The second supply roller gear15H engages with the second small diameter gear portion13H of the second input gear11H. Further, the second supply roller gear15H has a larger teeth number than the first supply roller gear15L.

Further, the second small diameter gear portion13H of the second input gear11H engaging with the second supply roller gear15H has a smaller teeth number than the first small diameter gear portion13L.

The second intermediate gear16H is rotatably supported by the second case34H in a position between the second input gear11H and the second agitator gear19H. The second intermediate gear16H has a second large diameter portion17H, and a second small diameter portion18H smaller in diameter than the second large diameter portion17H, where the second large diameter portion17H and the second small diameter portion18H are integrally rotatable. Further, the second large diameter portion17H engages with the second small diameter gear portion13H of the second input gear11H.

With respect to the second intermediate gear16H, the second large diameter portion17H has a larger teeth number than the first large diameter portion17L of the first intermediate gear16L, while the second small diameter portion18H has a larger teeth number than the first small diameter portion18L of the first intermediate gear16L.

The second agitator gear19H is fixed on the shaft portion361of the agitator36to rotate integrally with the agitator36. The second agitator gear19H engages with the second small diameter portion18H of the second intermediate gear16H. Further, the second agitator gear19H has a smaller teeth number than the first agitator gear19L.

Further, in the second embodiment, the controller140controls the bias application section120to apply the same bias to the developing roller31and the supply roller33, in the case of installing the small capacity cartridge28L and in the case of installing the large capacity cartridge28H. That is, the first bias V1and the second bias V2are set to be the same value. Further, the controller140controls the drive device110to input the same drive force to the first input gear11L and the second input gear11H, in the case of installing the small capacity cartridge28L and in the case of installing the large capacity cartridge28H.

In the image forming system configured as described above, if the small capacity cartridge28L is installed in the cartridge installing section2B, then the drive force is inputted to the first input gear11L to start rotating the respective gears constituting the first gear row10L. This leads to the rotations of the first developing roller31L, first supply roller33L and agitator36of the small capacity cartridge28L.

Further, if the large capacity cartridge28H is installed in the cartridge installing section2B, then the drive force is inputted to the second input gear11H to start rotating the respective gears constituting the second gear row10H. This leads to the rotations of the second developing roller31H, second supply roller33H and agitator36of the large capacity cartridge28H.

On this occasion, because the speed transmission ratio from the second input gear11H to the second supply roller gear15H is larger than the speed transmission ratio from the first input gear11L to the first supply roller gear15L included in the small capacity cartridge28L, the rotation speed of the second supply roller gear15H is slower than the rotation speed of the first supply roller gear15L. That is, the second supply roller33H of the large capacity cartridge28H has a slower circumferential speed than the first supply roller33L of the small capacity cartridge28L.

On the other hand, because the speed transmission ratio from the second input gear11H to the second developing roller gear14H is equal to the speed transmission ratio from the first input gear11L to the first developing roller gear14L, the rotation speed of the second developing roller gear14H is equal to the rotation speed of the first developing roller gear14L. That is, the second developing roller31H of the large capacity cartridge28H has the same circumferential speed as the first developing roller31L of the small capacity cartridge28L.

Therefore, in the large capacity cartridge28H, the second supply roller33H rotates slowly against the second developing roller31H as compared with the small capacity cartridge28L, and thus the second transport force for the second supply roller33H to transport the toner T is smaller than the first transport force for the first supply roller33L to transport the toner T.

On this occasion, in the large capacity cartridge28H, the second supply roller33H supplies the second developing roller31H with less of the toner T. Therefore, even though the large capacity cartridge28H is usable for a longer period of time than the small capacity cartridge28L, it is still possible to restrain leakage of the toner T.

In the second embodiment described above, by letting the speed transmission ratio from the second input gear11H to the second supply roller gear15H be larger than the speed transmission ratio from the first input gear11L to the first supply roller gear15L, the circumferential speed of the second supply roller33H is caused to be slower than the circumferential speed of the first supply roller33L. However, the configuration for causing the circumferential speed of the second supply roller33H to be slower than the circumferential speed of the first supply roller33L is not limited to this. For example, as shown inFIGS. 6A and 6B, the circumferential speed of the second supply roller33H may also be caused to be slower than the circumferential speed of the first supply roller33L by changing the diameters of the first supply roller33L and the second supply roller33H.

In particular, the second supply roller33H included in the large capacity cartridge28H has a smaller diameter than the first supply roller33L included in the small capacity cartridge28L.

Further, in such a modification, the second input gear11H (the second small diameter gear portion13H) and the second supply roller gear15H are configured such that the speed transmission ratio from the second input gear11H to the second supply roller gear15H may be equal to the speed transmission ratio from the first input gear11L to the first supply roller gear15L. Accordingly, the first supply roller gear15L in the first gear row10L rotates at the same angular speed as the second supply roller gear15H in the second gear row10H.

Being configured as described above, although the first supply roller33L rotates at the same angular speed as the second supply roller33H, due to the different diameters, the second supply roller33H has a slower circumferential speed than the first supply roller33L. By virtue of this, the transport force for the second supply roller33H to transport the toner T to the second developing roller31H becomes smaller than the transport force for the first supply roller33L to transport the toner T to the first developing roller31L.

Further, in order to cause the transport force for the second supply roller33H to transport the toner T to be smaller than the transport force for the first supply roller33L to transport the toner T, the supply roller body331of the second supply roller33H may be configured to have a higher electrical resistance than the supply roller body331of the first supply roller33L. For example, if the supply roller body331is made of urethane foam impregnated with a carbon solvent, then it is possible to change the electrical resistance by changing the amount of the carbon solvent impregnating the urethane foam, between the first supply roller33L and the second supply roller33H. Further, it is also possible to place a resistor between the second supply roller33H, and any electrode supplying electricity to the first supply roller33L or the second supply roller33H.

Further, if the first supply roller33L and the second supply roller33H are configured as described above, then the controller140controls the bias application section120to apply the same electric current to the first supply roller33L and to the second supply roller33H and, meanwhile, to set the first developing roller31L and the second developing roller31H at the same electric potential, in the case of installing the small capacity cartridge28L and in the case of installing the large capacity cartridge28H.

Being configured as described above, because the second supply roller33H has a lower electric potential than the first supply roller33L, the electric potential difference between the second developing roller31H and the second supply roller33H (the second bias V2) is smaller than the electric potential difference between the first developing roller31L and the first supply roller33L (the first bias V1). By virtue of this, the transport force for the second supply roller33H to transport the toner T is smaller than the transport force for the first supply roller33L to transport the toner T.

In the second embodiment described above, the transport force for the second supply roller33H (an example of the second transport member) to transport the toner T is smaller than the transport force for the first supply roller33L (an example of the first transport member) to transport the toner T. However, the present teaching is not limited to this but, for example, the transport force for the second agitator36H (an example of the second transport member) included in the large capacity cartridge28H to transport the toner T may be smaller than the transport force for the first agitator36L (an example of the first transport member) included in the small capacity cartridge28L to transport the toner T.

In particular, the teeth numbers of the second input gear11H (the second small diameter gear portion13H), the second intermediate gear16H and the second agitator gear19H are set such that the speed transmission ratio from the second input gear11H to the second agitator gear19H (an example of the second transport member gear) may be larger than the speed transmission ratio from the first input gear11L to the first agitator gear19L (an example of the first transport member gear).

Being configured as described above, the rotation speed of the second agitator36H when the large capacity cartridge28H is installed becomes slower than the rotation speed of the first agitator36L when the small capacity cartridge28L is installed. That is, the first agitator36L transports the toner T in the first case34L to the first developing roller31L by the first transport force, while the second agitator36H transports the toner T in the second case34H to the second developing roller31H by the second transport force smaller than the first transport force. On this occasion, in the large capacity cartridge28H, the second agitator36H transports less of the toner T toward the second developing roller31H. Therefore, even though the large capacity cartridge28H is usable for a longer period of time than the small capacity cartridge28L, it is still possible to restrain leakage of the toner T.

Further, in order to make the transport force for the second agitator36H included in the large capacity cartridge28H to transport the toner T be smaller than the transport force for the first agitator36L included in the small capacity cartridge28L to transport the toner T, as shown inFIGS. 7A and 7Bfor example, the first agitator36L and the second agitator36H may have different configurations.

In particular, as shown inFIG. 7B, the second agitator36H has an opening portion364, in a second agitating blade362H fixed on the aforementioned shaft portion361(an example of the second rotating shaft), which extends from one end to the other end along the extending direction of the shaft portion361.

On the other hand, as shown inFIG. 7A, the first agitator36L does not have such an opening portion, as that in the second agitating blade362H, in a first agitating blade362L fixed on the aforementioned shaft portion361(an example of the first rotating shaft).

By configuring the first agitating blade362L and the second agitating blade362H as described above, as shown inFIGS. 7A and 7B, a transport surface363H (an example of the second transport surface) of the second agitating blade362H has a smaller area than a transport surface363L (an example of the first transport surface) of the first agitating blade362L. By virtue of this, the second transport force for the second agitator36H to transport the toner T becomes smaller than the first transport force for the first agitator36L to transport the toner T.

Further, the second agitating blade362H may be formed not to have the only one opening portion364as in the modification described above, but to have a plurality of small opening portions364along the extending direction of the shaft portion361.

While some embodiments of the present teaching are explained above, the present teaching is not limited to the embodiments described above. It is possible to change and modify any specific configuration as appropriate without departing from the true spirit and scope of the present teaching. Further, in the following explanation, the same reference signs are assigned to the components identical or similar to those in the embodiments described above, and any explanation therefor will be omitted.

While the second case34H is larger than the first case34L in the above embodiments, the present teaching is not limited to this configuration. For example, provided that the second case34H is as large as the first case34L, by changing the amounts of the toner T to be contained in the first case34L and the second case34H, the second case34H may contain a larger amount of the toner T than the first case34L in a state that the small capacity cartridge28L and the large capacity cartridge28H are unused.

While the developer is a positively charged toner T in the above embodiments, the present teaching is not limited to this application, but may adopt a negatively charged toner T as the developer. In such a case, the controller140is configured to control the bias application section120to apply such a bias to the developing roller31and the supply roller33as to transport the toner T on the supply roller33to the developing roller31by setting the supply roller33at a lower electric potential than the developing roller31.

In the first embodiment, the small capacity cartridge28L and the large capacity cartridge28H are different only in the capacity of the toner container35and in the amount of the toner T contained in the toner container35in the state that the small capacity cartridge28L and the large capacity cartridge28H are unused, but identical in configuration with the other corresponding members (the developing roller31, the supply roller33, etc.). However, those other corresponding members may also differ in configuration. In such cases, the rotation speed of the drive motor controlled by the controller140, as well as the first bias V1and the second bias V2, is set such that the second transport force of the second supply roller33H may be smaller than the first transport force of the first supply roller33L.

In the above embodiments, the developing cartridge28is exemplified as the first cartridge and the second cartridge in two types different in capacity for the toner T. However, the present teaching is not limited to this exemplification. For example, the first cartridge and the second cartridge may be two types of process cartridges which differ in capacity for the toner T and integrate the developing cartridge28and the drum unit51of the above embodiments.

In the above embodiments, the black-and-white laser printer1is exemplified as the image forming apparatus capable of installing only one developing cartridge28. However, the present teaching is not limited to this exemplification. For example, the present teaching may also be applied to color printers capable of installing a plurality of developing cartridges28.