Developing apparatus and image forming apparatus

The image forming apparatus includes a developing chamber an agitating chamber, a first conveying screw which is arranged in the developing chamber and coveys developer from one end to the other end of the first chamber, a second conveying screw which is arranged in the agitating chamber and conveys developer from one end to the other end of the second chamber, a developing sleeve which bears developer supplied from the developing chamber and conveys the developer to the agitating chamber via a developing area opposed to a photosensitive drum, motors, which drive the developing sleeve, the first conveying screw and the second conveying screw, and a controller which controls drive of the developing sleeve and the second conveying screw so that trigger timing of drive stopping of at least the second conveying screw is to be later than trigger timing of drive stopping of the developing sleeve.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a developing apparatus used in an image forming apparatus with an electrophotographic system or an electrostatic recording system, such as a copying machine, which visualizes an electrostatic image formed on an image bearing member by fixing developer thereto and an image forming apparatus having the developing apparatus.

2. Description of the Related Art

Recently, for an image forming apparatus with an electrophotographic system, such as a copying machine and a printer, there has been a strong demand for downsizing the apparatus main body in order to save space. In particular, for an image forming apparatus of a full-color mode, the demand for downsizing is growing since a plurality of developing apparatuses are mounted. An invention of a developing apparatus which fulfills such a demand has been disclosed in Japanese Patent Application Laid-open (JP-A) No. 5-333691.

The developing apparatus disclosed in JP-A No. 5-333691 includes a developing chamber for supplying developer to a developing sleeve and an agitating chamber for collecting the developer after developing into a developer container. The developing chamber and the agitating chamber are arranged up and down. Such arrangement is described with reference toFIG. 2in this application.

The developing apparatus1inFIG. 2has a feature that two conveying screws5,6as developer circulation unit are arranged up and down. The developing apparatus1has the developer container2for accommodating the developer. An opening portion2ais formed at a part of the developer container2opposed to a photosensitive drum10. A developing sleeve8as a developer bearing member is provided at the opening portion2a.

Further, a partition wall7extending toward the opening portion2ais formed at an inner wall of the developer container2. The partition wall7partitions the developing chamber3and the agitating chamber4. The developing chamber3is arranged at the upper side in the developer container2and the agitating chamber4is arranged at the lower side in the developer container2. A first conveying screw5and a second conveying screw6are provided respectively in the developing chamber3and the agitating chamber4as the circulation unit for circulating the developer within the developer container2while agitating and conveying the developer. The first conveying screw5conveys the developer in the developing chamber3to the developing sleeve8. The second conveying screw6uniforms toner density of the developer by agitating and conveying toner which is supplied to the upstream side of the second conveying screw6in the agitating chamber4from a toner supplying port (not illustrated) with the developer which is previously contained in the agitating chamber4.

With the developing apparatus1of such a vertical agitation type, the occupying space in the horizontal direction is saved since the developing chamber3and the agitating chamber4are vertically lined. Accordingly, for example, downsizing in the horizontal direction can be achieved even with a color image forming apparatus of a tandem type having a plurality of developing apparatuses1mounted in parallel in the horizontal direction.

In the developing apparatus1of the vertical agitation type, the developer is drawn to the developing sleeve8with a magnetic pole N1of a magnet roller8aas magnetic field generating unit which is provided non-rotatably at the inside of the developing sleeve8, as indicated by arrow a inFIG. 2. In this case, the magnetic pole N1is arranged within the developer container2.

When the developing sleeve8is rotated, the developer is conveyed from the inside to the outside of the developer container2by being sequentially conveyed to a magnetic pole S1and then to a magnetic pole N2which is at a part of the developer sleeve8exposed to the photosensitive drum10side. Then, the developer arrives at a developing area having a magnetic pole S2which is opposed to the developing sleeve8and the photoconductive drum10. At the midway of conveying the developer, the thickness of the developer is magnetically regulated in cooperation with a developer regulating edge9as a developer regulating member and the magnetic pole S1which is arranged to be opposed thereto. Thus, the layer of the developer is thinned and an electrostatic image is developed at the developing area.

The remaining developer without being used for the developing at the developing area is conveyed into the developer container2with a magnetic pole N3which is arranged at the downstream side of the developing area in the rotation direction of the developing sleeve8. The developer is removed from the developing sleeve8by a repulsing magnetic field of the same polarity magnetic poles N1, N3which are adjacently arranged at the inner side of the developer container2. Then, the developer is collected into the agitating chamber4which is defined at the lower part in the developer container2.

In this case, the developer is not collected into the developing chamber in accordance with the rotation of the developing sleeve8unlike a developing apparatus of the horizontal agitation type. As indicated by arrow c inFIG. 2, the developer is collected into the agitating chamber4which is defined vertically below the developing chamber3. Thus, the only developer which is sufficiently agitated in the agitating chamber4invariably exists in the developer container2. In this manner, the developing sleeve8is invariably provided with the developer of uniformed density so that steady images without unevenness and darkness difference in the thrust direction can be obtained.

Meanwhile, the image forming apparatus is required to be capable of accepting various media. For example, the process speed can be set variously and is set slow in the case of a thick sheet. At that time, when the developer conveyance capacity of the second conveying screw6is set smaller than that of the developing sleeve8, the developer is accumulated at the upstream side of the second conveying screw6and the circulation of the developer becomes out of balance. For this reason, the developing sleeve8and the second conveying screw6are independently driven and set to be at the appropriate rotation speed for each process speed so as to prevent the developer circulation from being out of balance at any process speed.

However, with the configuration of the developing apparatus1of the vertical agitation type in JP-A No. 5-333691, the following problem remains with the developer conveyance.

There is a difference between inertia forces of the developing sleeve8and the second conveying screw6. Accordingly, there arises a difference between a stop turnaround time until the rotation of the developing sleeve8is stopped based on a drive stop trigger signal and a stop turnaround time until the rotation of the second conveying screw6is stopped based on a drive stop trigger signal.

Here, it is assumed that a motor11of the developing sleeve8and a motor12of the second conveying screw6simultaneously receives the drive stop trigger signal. In this case, due to the difference of the stop turnaround times, the developing sleeve8is rotated longer than the second conveying screw6, for example. Accordingly, there may be a case that the developer is excessively conveyed from the developing chamber3to the agitating chamber4via the developing sleeve8. In the case that redundant rotation of the developing sleeve8is repeated corresponding to repeating of the drive start and the drive stop of the developing sleeve8and the second conveying screw6, the developer circulation becomes out of balance. Then, there is a risk that, in the end, the developer overflows from the developing apparatus1.

The present invention provides a developing apparatus which is capable of suppressing overflowing of developer from the developing apparatus due to imbalance of developer circulation even with difference between stop turnaround times caused by difference between inertia forces of the developer bearing member and a conveying member.

SUMMARY OF THE INVENTION

The present invention provides an image forming apparatus which includes: a first chamber which is capable of accommodating developer; a second chamber which is capable of accommodating developer and forms a circulation passage in communication with the first chamber; a first conveying member which is arranged in the first chamber and conveys developer from one end to the other end of the first chamber; a second conveying member which is arranged in the second chamber and conveys developer from one end to the other end of the second chamber; a developer bearing member which bears developer supplied from the first chamber and conveys the developer to the second chamber via a developing position opposed to an image bearing member; a drive mechanism which drives the developer bearing member, the first conveying member and the second conveying member; and a controller which controls drive of the drive mechanism so that stop timing of drive input for the developer bearing member is to be earlier than stop timing of drive input for the second conveying member in a case of stopping drive of the developer bearing member in accordance with image forming completion.

DESCRIPTION OF THE EMBODIMENTS

First Embodiment

FIG. 1is a sectional view which illustrates the configuration of an image forming apparatus100including a developing apparatus1according to a first embodiment of the present invention. First, the general configuration and operation of the image forming apparatus100is described with reference toFIG. 1. In the following, the image forming apparatus100is described as a full-color image forming apparatus as an example.

As illustrated inFIG. 1, each of a station Y, a station M, a station C and a station K has almost the same configuration and forms an image of a color of respective yellow (Y), magenta (M), cyan (C) and black (K) in a full-color image. Each station Y, M, C, K is respectively provided with each developing apparatus1Y,1M,1C,1K. In the following description, the developing apparatus1commonly denotes the developing apparatuses1Y,1M,1C,1K of each the station Y, M, C, K.

Further, each station Y, M, C, K is respectively provided with a photosensitive drum10Y,10M,10C,10K as an image bearing member. In the following description, the photosensitive drum10commonly denotes the photosensitive drums10Y,10M,10C,10K of each the station Y, M, C, K. The photosensitive drum10is rotatably arranged and evenly charged by a primary charger21. Then, the electrostatic image is formed by exposing with light modulated in accordance with information signals by a light emitting element22such as laser.

Here, each station Y, M, C, K is respectively provided with a primary charger21Y,21M,21C,21K. The primary charger21commonly denotes the four chargers. Further, each station Y, M, C, K is respectively provided with a light emitting element22Y,22M,22C,22K. The light emitting element22denotes the four emitting elements.

The electrostatic image is visualized as a developed image (hereinafter, called a toner image) with the later-mentioned processes by the developing apparatus1. Meanwhile, a transfer sheet27as a recording material is conveyed to a transfer charger23by a transfer sheet conveying member24. The above-mentioned toner image is transferred on the transfer sheet27for each station by the transfer charger23. Subsequently, a permanent image can be obtained by being fixed by a fixing device25.

Remaining toner on the photosensitive drum10after the transfer is removed by a cleaning device26. The toner in the consumed developer for the image forming is replenished from a toner supplying tank20.

Here, each station Y, M, C, K is respectively provided with a cleaning device26Y,26M,26C,26K. The cleaning device26commonly denotes the four cleaning devices26. Further, each station Y, M, C, K is respectively provided with a toner supplying tank20Y,20M,20C,20K. The toner supplying tank20commonly denotes the four toner supplying tanks. Furthermore, each station Y, M, C, K is respectively provided with a transfer charger23Y,23M,23C,23K. The transfer charger23commonly denotes the four transfer chargers.

Here, an image forming portion for forming an image on a sheet is configured to include the above-mentioned photosensitive drum10and the developing apparatus1.

The present embodiment adopts the method to transfer from the photosensitive drums10M,10C,10Y,10K as the image bearing members directly to the transfer sheet27which is conveyed to the transfer sheet conveying member24. However, it is not limited to this method.

The developing apparatus1is also applicable to an image forming apparatus which is configured to include an intermediate transfer member instead of the transfer sheet conveying member24and to secondarily transfer a mixed toner image of every color on the transfer sheet27after a toner image of each color is primarily transferred to the intermediate transfer member respectively from the photosensitive drum10of each color.

FIG. 2is an enlarged sectional view which illustrates the configuration of the photosensitive drum10and the developing apparatus1according to the first embodiment of the present invention. As illustrated inFIG. 2, the developing apparatus1has the developer container2capable of accommodating the developer T (for example, two-component developer) which includes nonmagnetic toner and magnetic carrier. The opening portion2ais formed at apart of the developer container2opposed to the photosensitive drum10. The developer regulating edge9as the developer regulating member is attached to an end part of the opening portion2a. The developing sleeve8as a developer bearing member is rotatably arranged at a position surrounded by a top end9aof the developer regulating edge9and the opening portion2a. The developing sleeve8, having the top end9aand the opening portion2aas the boundary, is arranged so that a part thereof is exposed to the photosensitive drum10side and another part thereof is to be inside the developer container2.

The developing sleeve8is arranged to be opposed to the photosensitive drum10. The developing sleeve8bears the developer T in the developing chamber3and conveyed to the photosensitive drum10. The developing sleeve8conveys the developer T to the agitating chamber4via the developing area opposed to the photosensitive drum10while bearing the developer T supplied from the developing chamber3.

A partition wall7is formed at an approximate center part of the inside of the developer container2. The partition wall7partitions, within the developer container2, a developing chamber3as a first chamber capable of accommodating the developer T for developing therewith and an agitating chamber4as a second chamber for forming a circulation passage in communication with the developing chamber3and for agitating the developer T while being capable of accommodating the developer T. The developing chamber3is defined at the upper side in the developer container2. The agitating chamber4is defined at the lower side in the developer container2. Namely, the agitating chamber4is arranged below the developing chamber3in the gravitational direction. The developer T is accommodated in the developer container2having the developing chamber3and the agitating chamber4which are arranged up and down.

The first conveying screw5as the first conveying member which agitates the developer T in the developing chamber3and conveys to the developing sleeve8is arranged within the developing chamber3. The second conveying screw6as the second conveying member which agitates the developer T in the agitating chamber4and conveys to the developing chamber3when the developer T remained at the developing sleeve8is collected into the agitating chamber4is arranged within the agitating chamber4. The first conveying screw5or the second conveying screw6functions as the circulation unit for circulating the developer T within the developer container2.

Here, the developing sleeve8is configured with a nonmagnetic unit. The magnet roller8aas the magnetic field generating unit is arranged non-rotatably at the inside of the developing sleeve8. The magnet roller8aincludes a magnetic pole S2as the developing pole and magnetic poles S1, N1, N2, N3for conveying the developer T. The magnetic pole N3and the magnetic pole N1having the same polarity are arranged at the inner side of the developer container2being adjacent each other. Accordingly, the repulsing magnetic field is formed between the magnetic pole N3and the magnetic pole N1, so that a barrier for the developer T is formed. Therefore, the developer T is removed from the developing sleeve8at the agitating chamber4.

The developing sleeve8is connected to a motor11as the first motor as being a drive mechanism. The second conveying screw6is connected to the motor12as the second motor as being a drive mechanism. The first conveying screw5is connected to the motor as the third motor13as being a drive mechanism. The motors11to13are connected to a controller30as a control portion. Since the motor11, the motor12and the motor13are capable of being independently controlled, the developing sleeve8, the second conveying screw6and the first conveying screw5are capable of being independently driven.

In order to suppress accumulation of the developer at a communicating portion71, which is described later withFIG. 3, for drawing the developer from the agitating chamber4to the developing chamber3, the controller30is capable of adjusting the drive order of the developing sleeve8, the second conveying screw6and the first conveying screw5. InFIG. 3, when the developer is drawn through the communicating portion71with the drive of the second conveying screw6after the first conveying screw5is stopped, the developer overflows at the vicinity of the communicating portion71. In addition, when the developer is added to the communicating portion71with the drive of the developing sleeve8after the first conveying screw5and the second conveying screw6are stopped, the communicating portion71is further overflowed.

In order to suppress such a phenomenon, the controller30is capable of storing data of a first stop turnaround time from transmitting of a first drive stop trigger signal for stopping the drive of the developing sleeve8until the stopping of the drive of the developing sleeve8. Further, the controller30is capable of storing data of a second stop turnaround time from transmitting a second stop trigger signal for stopping the drive of the second conveying screw6until the stopping of the second conveying screw6. Furthermore, the controller30is capable of storing data of a third stop turnaround time from transmitting a third drive stop trigger signal for stopping the drive of the first conveying screw5until the stopping of the first conveying screw5.

In addition, the controller30is capable of transmitting the first drive stop trigger signal to the developing sleeve8for triggering the drive stop of the developing sleeve8based on the data of the first stop turnaround time. Further, the controller30is capable of transmitting the second drive stop trigger signal to the second conveying screw6for triggering the drive stop of the second conveying screw6based on the data of the second stop turnaround time. Furthermore, the controller30is capable of transmitting the third drive stop trigger signal to the first conveying screw5for triggering the drive stop of the first conveying screw5based on the data of the third stop turnaround time.

The above-mentioned drive stop trigger signals are transmitted in the following order. First, the controller30transmits the first drive stop trigger signal to the developing sleeve8based on the data of the first stop turnaround time. Then, the controller30transmits the second drive stop trigger signal to the second conveying screw6based on the data of the second stop turnaround time. Subsequently, the controller30transmits the third drive stop trigger signal to the first conveying screw5based on the data of the third stop turnaround time.

Accordingly, based on the first stop turnaround time, the second stop turnaround time and the third stop turnaround time, the controller30stops the drive of the second conveying screw6after the drive of the developing sleeve8is stopped, and then, the controller30stops the drive of the first conveying screw5. Instead, the drives of the developing sleeve8, the second conveying screw6and the first conveying screw5may be simultaneously stopped based on the data of the first stop turnaround time, the second stop turnaround time and the third stop turnaround time.

FIG. 3is a sectional view which illustrates the configuration of the developing apparatus1. As illustrated inFIG. 3, a rotation shaft5aof the first conveying screw5is arranged to be approximately parallel to the rotation center8bof the developing sleeve8(i.e., the approximate developing width direction) at the bottom of the developing chamber3. When the first conveying screw5is rotated, the developer T in the developing chamber3is conveyed in one direction (i.e., from the left to the right inFIG. 3) along the rotation shaft5aof the first conveying screw5. The first conveying screw5is formed to be a screw configuration including the rotation shaft5aformed of ferromagnetic material and a blade member5bformed of nonmagnetic material arranged to be spiral-shaped around the rotation shaft5a.

Further, as illustrated inFIG. 3, a rotation shaft6aof the second conveying screw6is arranged to be approximately parallel to the rotation center8bof the developing sleeve8and the rotation shaft5aof the first conveying screw5(i.e., the approximate developing width direction) at the bottom of the agitating chamber4. When the second conveying screw6is rotated in the same direction as the first conveying screw5, the developer T in the agitating chamber4is conveyed in the other direction (i.e., from the right to the left inFIG. 3) along the rotation shaft6aof the second conveying screw6. The second conveying screw6is formed to be a screw configuration including the rotation shaft6aformed of ferromagnetic material and a blade member6bformed of nonmagnetic material arranged to be spiral-shaped around the rotation shaft6a.

Further, as illustrated inFIG. 3, the communicating portion71and a communicating portion72are formed as the opening portions at the partition wall7formed between the developing chamber3and the agitating chamber4at both ends in the direction along the rotation center8bof the developing sleeve8. Then, when the developer T is conveyed with the rotation of the first conveying screw5and the second conveying screw6, the developer T is circulated between the developing chamber3and the agitating chamber4through the opening portions (i.e., the communicating portions71,72) at both ends of the partition wall7.

As clearly seen fromFIGS. 2 and 3, the developing chamber3is arranged at the vertical upside and the agitating chamber4is arranged at the vertical downside. Regarding movement from the developing chamber3to the agitating chamber4, the developer T is moved from the upside to the downside though the communicating portion72, as indicated by arrow e. Regarding movement from the agitating chamber4to the developing chamber3, the developer T is moved from the downside to the upside through the communicating portion71, as indicated by arrow f. Specifically, regarding the movement from the agitating chamber4to the developing chamber3, the developer T is passed by being pressed up from the downside to the upside with the pressure of the developer T accumulated at the end.

Here, the developer T is prone to be accumulated at the vicinity of the communicating portion71in the agitating chamber4for passing to the developing chamber3from the agitating chamber4, as illustrated inFIG. 3. Accordingly, the developer T is prone to overflow at the vicinity of the communicating portion71.

Additionally, the overflowing proneness of the developer T at the vicinity of the communicating portion71is described in the following. As illustrated inFIG. 3, in the developing apparatus1of the vertical agitation type, the developer T flows in the direction indicated by arrows e, f. The developer T is passed to the developing chamber3from the agitating chamber4through the communicating portion71out of the openings of the communicating portions71,72arranged at both ends in the axis direction of the partition wall7which partitions the developing chamber3and the agitating chamber4.

Here, not all of the developer T arrives at the downstream end of the first conveying screw5at the developing chamber3. There exists some components supplied to the developing sleeve8on the midway (seeFIG. 2) and collected into the agitating chamber4after passing through the developing area. The passing of the developer T to the developing sleeve8is performed almost all over the developing sleeve8in the thrust direction. Therefore, the amount of the developer T conveyed by the first conveying screw5within the developing chamber3tends to be gradually decreased toward the downstream end from the upstream end in the conveying direction.

On the other hand, the amount of the developer T conveyed by the second conveying screw6within the agitating chamber4tends to be gradually increased toward the downstream end from the upstream end in the conveying direction. Namely, unevenness of the distribution of the developer T is highly caused within the developing apparatus101as illustrated inFIG. 3. In light of the configuration ofFIG. 2in such a situation, in the case that the developing sleeve8is still rotated after the second conveying screw6is stopped, the amount of the developer Tin the agitating chamber4is further increased. Then, the amount of the developer T is particularly increased at the downstream side in the agitating chamber4. Accordingly, it becomes difficult to collect the developer T from the developing sleeve8to the agitating chamber4at the vicinity of the communicating portion (also called drawing portion)71. In this case, the developer T flows on the developing sleeve8and overflowing is caused. Accordingly, it becomes even more difficult to collect the developer T from the developing sleeve8to the agitating chamber4. The developer T which is not collected flows on the developing sleeve8and leaking is caused.

Here, the drive stop timing of the first conveying screw5is set to be later than or equal to the drive stop timing of the second conveying screw6in consideration with the pressure applied to the developer at the communicating portion (i.e., the drawing portion)71. Assuming that the rotation of the second conveying screw6in the agitating chamber4is stopped after the rotation of the first conveying screw5in the developing chamber3is stopped, the pressure of the developer is increased at the communicating portion71by the rotation of the second conveying screw6and the developer is deteriorated. The above-mentioned operation is for suppressing such deterioration.

FIG. 4is a flowchart which describes control processes of the controller30. As described inFIG. 4, the controller30starts the operation in step S1(hereinafter, the step is denoted by S). The controller30transmits the first drive stop trigger signal for triggering stopping of the drive of the developing sleeve8to the motor11in S2. Then, the controller30transmits the second drive trigger signal for triggering stopping of the drive of the second conveying screw6to the motor12in S3. Subsequently, the controller30transmits the third drive stop trigger signal for triggering stopping of the drive of the first conveying screw5to the motor13in S4.

The controller30detects the stopping of the rotation of the developing sleeve8based on a signal received from a rotation detecting sensor (not illustrated) of the developing sleeve8in S5. Then, the controller30detects the stopping of the second conveying screw6based on a signal of a rotation detecting sensor (not illustrated) of the second conveying screw6in S6. Subsequently, the controller30detects the stopping of the rotation of the first conveying screw5based on a signal received from a rotation sensor (not illustrated) of the first conveying screw5in S7. Then, the controller30ends the operation in S8.

Further, as mentioned above, the simultaneous stopping of the developing sleeve8, the second conveying screw6and the first conveying screw5may be detected in S9with rotation detecting sensors (not illustrated) after the controller30transmits the third drive stop trigger signal to the motor13in S4.

Here, as mentioned above, the stop timings of the developing sleeve8, the second conveying screw6and the first conveying screw5may be transposed within a predetermined time range after the controller30transmits the third drive stop trigger signal to the motor13in S4.

FIGS. 5A,5B and5C are graphs which illustrate a situation of sequential stopping of the developing sleeve8, the second conveying screw6and the first conveying screw5while the respective drive stop trigger signals are transmitted with respectively shifted drive timings. As illustrated inFIGS. 5A,5B and5C, by previously shifting the drive stop timings with consideration of the difference among the inertia forces of the developing sleeve8, the second conveying screw6and the first conveying screw5, the circulation balance of the developer T can be maintained appropriately based on the actual stop turnaround times.

As illustrated inFIG. 5A, for example, the developing sleeve8is switched from ON (as indicated “ON” in the figures) to OFF (as indicated “OFF” in the figures) at time tA. Then, actually, the developing sleeve8is stopped at t1. Meanwhile, as illustrated inFIG. 5B, for example, the second conveying screw6is switched from ON to OFF at time tB. Then, actually, the second conveying screw6is stopped at t2. Further, as illustrated inFIG. 5C, for example, the first conveying screw5is switched from ON to OFF at time tC. Then, actually, the first conveying screw5is stopped at t3. InFIGS. 5A,5B and5C, time lapses in the order of tA, tB, tC, t1, t2and t3. Further, the relation of the stop turnaround times is as the expression of “the first stop turnaround time (t1−tA)>the second stop turnaround time (t2−tB)÷the third stop turnaround time (t3−tC)”. The controller30sequentially triggers the stopping of rotation of the developing sleeve8, the second conveying screw6and the first conveying screw5based the stop turnaround times, so that the stopping of rotation can be reliably actualized in the order of the developing sleeve8, the second conveying screw6and the first conveying screw5.

FIGS. 6A,6B and6C are graphs which illustrate a situation of simultaneous stopping of the developing sleeve8, the second conveying screw6and the first conveying screw5while the respective drive stop trigger signals are transmitted with respectively shifted drive timings. As illustrated inFIGS. 6A,6B and6C, by previously shifting the drive stop timings in consideration of the difference among the inertia forces of the developing sleeve8, the second conveying screw6and the first conveying screw5, the circulation balance of the developer T can be maintained appropriately based on the actual stop turnaround times, as well.

As illustrated inFIG. 6A, for example, the developing sleeve8is switched from ON (as indicated “ON” in the figures) to OFF (as indicated “OFF” in the figures) at time tA. Then, actually, the developing sleeve8is stopped at t1. Meanwhile, as illustrated inFIG. 6B, for example, the second conveying screw6is switched from ON to OFF at time tB. Then, actually, the second conveying screw6is stopped at t1. Further, as illustrated inFIG. 6C, for example, the first conveying screw5is switched from ON to OFF at time tC. Then, actually, the first conveying screw5is stopped at t1. InFIGS. 6A,6B and6C, time lapses in the order of tA, tB, tCand t1. Further, the relation of the stop turnaround times is as the expression of “the first stop turnaround time (t1−tA)>the second stop turnaround time (t1−tB)≈the third stop turnaround time (t1−tC)”. The controller30sequentially triggers the stopping of rotation of the developing sleeve8, the second conveying screw6and the first conveying screw5based the stop turnaround times, so that the simultaneous stopping of rotation of the developing sleeve8, the second conveying screw6and the first conveying screw5can be reliably actualized.

Here, inFIGS. 5 and 6, it is assumed that the drive stop trigger signals for the developing sleeve8, the second conveying screw6and the first conveying screw5are transmitted at the same timing. In this case, since there is a difference among the inertia forces of the developing sleeve8, the second conveying screw6and the first conveying screw5, there arises a difference among the stop turnaround times from the transmitting of the drive stop trigger signal to the actual stopping of drive. As a result, the developing sleeve8is still rotated after the first conveying screw5and the second conveying screw6are stopped. This is a drawback of the related art.

In this example, in particular, when the drive of the second conveying screw6is stopped earlier than that of the developing sleeve8, the developer T collected from the developing sleeve8into the agitating chamber4is accumulated at the upstream side of the second conveying screw6in the agitating chamber4. Since the second conveying screw6is previously stopped, the accumulated developer T remains accumulated without being conveyed. Then, when the starting and stopping of the drive of the developing sleeve8and the second conveying screw6are repeated, there arises a risk that the circulation of the developer T becomes out of balance to cause overflowing of the developer T at the vicinity of the communicating portion71where the developer T is prone to be accumulated.

Next, the operation of the developing apparatus1is described with reference toFIG. 2. The developer T is drawn to the developing sleeve8by the magnetic pole N1. When the developing sleeve8is rotated, the developer T is magnetically regulated by the developer regulating edge9and conveyed sequentially to the magnetic pole S1and the magnetic pole N2. Then, the developer T arrives at the developing area having the magnetic pole S2therein. The remaining developer T without being consumed for the developing at the developing area is conveyed into the developer container2by the magnetic pole N3. The developer T is removed from the developing sleeve8by the repulsing magnetic field of the adjacent magnetic poles N1, N3and collected into the agitating chamber4.

The controller30previously stores the first stop turnaround time from the transmitting of the first drive stop trigger signal for stopping the drive of the developing sleeve8until the stopping of the drive of the developing sleeve8. Further, the controller30stores the second stop turnaround time from the transmitting of the second drive stop trigger signal for stopping the drive of the second conveying screw6until the stopping of the drive of the second conveying screw6. Furthermore, the controller30stores the third stop turnaround time from the transmitting of the first drive stop trigger signal for stopping the drive of the first conveying screw5until the stopping of the drive of the first conveying screw5.

The controller30controls the developing sleeve8to be stopped after the first stop turnaround time lapses from the transmitting of the first drive stop trigger signal. Further, the controller30controls the second conveying screw6to be stopped after the second stop turnaround time lapses from the transmitting of the second drive stop trigger signal. After calculating the stop timing with the first stop turnaround time and the second stop turnaround time, the controller30stops the drive of the developing sleeve8earlier than that of the second conveying screw6. The second conveying screw6may still be driven at the time when the developing sleeve8is stopped. Since the developer T is agitated and conveyed to the developing chamber3with the drive of the second conveying screw6, the developer T is not excessively accumulated at the upstream side of the second conveying screw6in the agitating chamber4.

Further, the controller30controls the second conveying screw6to be stopped after the second stop turnaround time lapses from the transmitting of the second drive stop trigger signal. Furthermore, the controller30controls the first conveying screw5to be stopped after the third stop turnaround time lapses from the transmitting of the third stop trigger signal. With the second stop turnaround time and the third stop turnaround time, the controller30stops the drive of the second conveying screw6to be earlier than that of the first conveying screw5. The first conveying screw5may be still rotated at the time when the second conveying screw6is stopped. Thus, the developer T is not excessively accumulated in the developing chamber3, in particular, at the communicating portion71.

With the configuration of the developing apparatus1, the timing for triggering the drive stop of the developing sleeve8is to be earlier than that of the second conveying screw6. Accordingly, compared to the related art of simultaneous drive stop timing of the developing sleeve8and the second conveying screw6, the drive stop timing of the developing sleeve8is advanced. In the related art, the developing sleeve8remains driven after the second conveying screw6is stopped due to the inertia force difference and the like and the phenomenon of overflowing of the developer in the developing apparatus may occur. However, such a phenomenon can be suppressed. Thus, even though there is a difference between the stop turnaround times due to the inertia force difference between the developing sleeve8and the second conveying screw6, it can be suppressed that the developer T overflows from the developing apparatus1with the imbalance of the developer circulation. In the meantime, the developer T is effectively collected from the developing sleeve8.

Further, with the configuration of the developing apparatus1, the timing for triggering the drive stop of the second conveying screw6is to be earlier than that of the first conveying screw5. Accordingly, compared to the related art of simultaneous drive stop timing of the second conveying screw6and the first conveying screw5, the drive stop timing of the second conveying screw6is advanced. In the related art, the second conveying screw6remains driven after the first conveying screw5is stopped due to the inertia force difference and the like and the phenomenon of overflowing of the developer in the developing apparatus may occur. However, such a phenomenon can be suppressed. Thus, even though there is a difference between the stop turnaround times due to the inertia force difference between the second conveying screw6and the first conveying screw5, it can be suppressed that the developer T overflows from the developing apparatus1with the imbalance of the developer circulation. In the meantime, the developer T is effectively collected from the developing sleeve8.

As above-mentioned, when the drive of the developing sleeve8and the second conveying screw6is to be stopped, there is difference between the inertia forces thereof. Accordingly, in the related art, there is a case that the developing sleeve8remains rotated even after the second conveying screw6is stopped and that the developing sleeve8moves the developer T from the developing sleeve8into the agitating chamber4. Thus, there is a case that the circulation of the developer T becomes out of balance and the developer T overflows from the developing apparatus.

With the configuration of the developing apparatus1, since the developing chamber3and the agitating chamber4are arranged up and down, the occupying space in the horizontal direction can be saved. For example, downsizing can be achieved even with a color image forming apparatus of a tandem type including a plurality of developing apparatuses1to be mounted in parallel in the horizontal direction.

Further, with the configuration of the developing apparatus1, the drive of the second conveying screw6is stopped when or after the drive of the developing sleeve8is stopped based on the stop turnaround time data. Accordingly, even when the stop turnaround time is varied corresponding to variation of torque applied to the developing sleeve8and the second conveying screw6with usage time, the circulation balance of the developer T is appropriately maintained.

FIG. 7is an enlarged sectional view which illustrates the configuration of the photosensitive drum10and the developing apparatus1according to a modification of the first embodiment of the present invention. In the above-mentioned embodiment, the developing sleeve8and the second conveying screw6can be driven independently. However, not limited to this, it is also possible that the developing sleeve8and the second conveying screw6are driven with a single drive mechanism112and are capable of being switched between ON and OFF with a clutch, as illustrated inFIG. 7.

Here, in the present embodiment, the required time for the drive stopping of the developing sleeve8which is driven at the same speed as the second conveying member in the normal image forming is longer than the required time for the drive stopping of the second conveying screw6in the state that the developer T is accommodated in the developing apparatus1. However, the present invention is also applicable to the case that the required time for the drive stopping of the developing sleeve8which is driven at the same speed as in the normal image forming is shorter than the required time for the drive stopping of the second conveying screw6which is driven at the same speed as in the image forming in the state that the developer T is accommodated in the developing apparatus1.

In the present embodiment, the stop turnaround time is varied in accordance with usage time even without the inertia difference among the developing sleeve8, the second conveying screw6and the first conveying screw5. When the present invention is applied to such a case, the above-mentioned developer overflowing can be suppressed by setting the stop timing of the drive input for the developing sleeve8to be earlier than that for the second conveying screw6.

Here, the present embodiment is described with the case that the difference between the stop timing of the drive input for the developing sleeve8and the stop timing of the drive input for the second conveying screw6is invariable, as an example. However, it is also possible that the difference is varied in accordance with usage time. For example, in the case that usage time of the developer in the developing chamber3is increased, the required time for stopping the screw prone to be shortened due to increase of agglomeration degree of the developer. Therefore, the difference between the stop timing of the drive input for the developing sleeve8and that for the second conveying screw6may be prolonged in accordance with usage time. With this configuration, the rotation time of the developing sleeve8after the rotation of the second conveying screw6is stopped can be suppressed or the rotation of the developing sleeve8can be stopped before the rotation of the second conveying screw6is stopped. In this manner, the developer overflowing can be suppressed.

Second Embodiment

FIG. 8is an enlarged sectional view which illustrates the configuration of the photosensitive drum10and a developing apparatus101according to a second embodiment of the present invention.FIG. 9is a sectional view which illustrates the configuration of the developing apparatus101. The same numeral is given to the similar part to the photosensitive drum10and the developing apparatus1of the first embodiment and the description will not be repeated. In the following, description will be made only for the distinctive configuration of the developing apparatus101according to the second embodiment. The developing apparatus101differs from the developing apparatus1in that a developing chamber103is arranged below the partition wall7in the developer container2and an agitating chamber104is arranged above the partition wall7in the developer container2. Then, a first conveying screw105is arranged within the developing chamber103and a second conveying screw106is arranged within the agitating chamber104.

Namely, the partition wall7is formed at the approximate center of the inside of the developer container2. The partition wall7partitions, within the developer container2, the developing chamber103as the first chamber capable of accommodating the developer T for developing therewith and the agitating chamber104as the second chamber for forming the circulation passage in communication with the developing chamber103and for agitating the developer T while being capable of accommodating the developer T. The developing chamber103is defined at the lower side in the developer container2. The agitating chamber104is defined at the upper side in the developer container2. Namely, the agitating chamber104is arranged above the developing chamber103in the gravitational direction. The developer T is accommodated in the developer container2having the agitating chamber104and the developing chamber103which are arranged up and down.

The first conveying screw105as the first conveying member which agitates the developer T in the developing chamber103and conveys to the developing sleeve8is arranged in the developing chamber103. The second conveying screw106as the second conveying member which agitates the developer T in the agitating chamber104and conveys to the developing chamber103when the developer T remained at the developing sleeve8is collected into the agitating chamber104is arranged in the agitating chamber104. The first conveying screw105or the second conveying screw106functions as the circulation unit for circulating the developer T within the developer container2. Further, the motor11is connected to the developing sleeve8, the motor13is connected to the first conveying screw105, and the motor12is connected to the second conveying screw106. The motors11to13are connected to the controller30. As illustrated inFIG. 9, the first conveying screw105includes a rotation shaft105aand a blade member105b. The second conveying screw106includes a rotation shaft106aand a blade member106b. Here, the rotation direction of the first conveying screw105is the same direction as that of the second conveying screw6of the first embodiment. Then, the rotation direction of the second conveying screw106is the same direction as that of the first conveying screw5of the first embodiment.

The developing apparatus101is operated as follows. As illustrated inFIG. 8, the photosensitive drum10is rotated counterclockwise as indicated by an arrow. Meanwhile, the developing sleeve8is rotated clockwise. In the developing apparatus101, the toner in the developing chamber103is borne on the developing sleeve8due to the rotation of the first conveying screw105. Subsequently, the toner is transferred to the photosensitive drum10from the developing sleeve8. The remaining toner is conveyed to the agitating chamber104. The toner in the agitating chamber104is conveyed to the developing chamber103through the communicating portion72with the rotation of the second conveying screw106as indicated by arrow g.

In this case, the controller30sequentially transmits the first drive stop trigger signal, the third drive stop trigger signal and the second drive stop trigger signal in such order. Accordingly, the rotation is stopped in the order of the developing sleeve8, the first conveying screw105and the second conveying screw106. In this case as well, the actual order of the stop timings of the developing sleeve8, the second conveying screw106and the first conveying screw105may be transposed within a predetermined time range.

Here, the drive stop timing of the second conveying screw106is set to be earlier than or equal to the drive stop timing of the first conveying screw105in consideration with the pressure applied to the developer at the communicating portion71to be utilized for the drawing in the direction of arrow h. Assuming that the rotation of the first conveying screw105in the developing chamber103is stopped after the rotation of the second conveying screw106in the agitating chamber104, the pressure of the developer is increased at the connecting portion71by the rotation of the second conveying screw6and the developer is deteriorated. The above-mentioned setting is for suppressing such deterioration.

With the configuration of the developing apparatus101, the timing for triggering the drive stop of the developing sleeve8is to be earlier than that of the second conveying screw106. Accordingly, compared to the related art of simultaneous drive stop timing of the developing sleeve8and the second conveying screw106, the drive stop timing of the developing sleeve8is advanced. In the related art, the developing sleeve8remains driven after the second conveying screw106is stopped due to the inertia force difference and the like and the phenomenon of overflowing of the developer in the developing apparatus1may occur. However, such a phenomenon can be suppressed. Thus, even though there is a difference between the stop turnaround times due to the inertia force difference between the developing sleeve8and the second conveying screw106, it can be suppressed that the developer T overflows from the developing apparatus1with the imbalance of the developer circulation. In the meantime, the developer T is effectively collected from the developing sleeve8.

Further, with the configuration of the developing apparatus101, the timing for triggering the drive stop of the second conveying screw106is to be earlier than that of the first conveying screw105. Accordingly, compared to the related art of simultaneous drive stop timings of the second conveying screw106and the first conveying screw105, the drive stop timing of the first conveying screw105can be delayed. In the related art, the second conveying screw106remains driven after the first conveying screw105is stopped due to the inertia force difference and the like and the phenomenon of overflowing of the developer in the developing apparatus1may occur. However, such a phenomenon can be suppressed. Thus, even though there is a difference between the stop turnaround times due to the inertia force difference between the second conveying screw106and the first conveying screw105, it can be suppressed that the developer T overflows from the developing apparatus1with the imbalance of the developer circulation. In the meantime, the developer T is effectively collected from the developing sleeve8.

FIG. 10is an enlarged sectional view which illustrates the configuration of the photosensitive drum10and the developing apparatus101according to a modification of the second embodiment of the present invention. In the above-mentioned embodiment, the second conveying screw106and the first conveying screw105can be driven independently. However, not limited to this, it is also possible that the second conveying screw106and the first conveying screw105are driven with a single drive mechanism112and are capable of being switched between ON and OFF with a clutch, as illustrated inFIG. 10.

This application claims the benefit of Japanese Patent Application No. 2008-271571, filed Oct. 22, 2008, which is hereby incorporated by reference herein in its entirety.