Developing device and image forming apparatus which can detect a concentration of a developer

A developing device includes: a developer carrier; a first housing chamber; a second housing chamber; a first inflow portion; a first conveying member; a second conveying member; and a concentration detecting member.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 U.S.C. 119 from Japanese Patent Application No. 2007-241671 filed Sep. 19, 2007.

BACKGROUND

Technical Field

The present invention relates to a developing device and an image forming apparatus.

SUMMARY

A technical problem to be solved by the invention is to maintain the inflow amount in a first inflow portion which allows a developer to flow upward in the gravitational direction, and the accuracy of detection of the concentration of the developer in a concentration detecting portion in which the developer is stirred in a circumferential direction, and stagnation of the developer easily occurs, in the case where the developer stagnates.

According to an aspect of the present invention, a developing device including: a developer carrier that is rotated while holding a developer on a surface; a first housing chamber that houses the developer to be supplied to the developer carrier; a second housing chamber that has a bottom face that is provided beneath a bottom face of the first housing chamber in a gravitational direction; a first inflow portion that allows the developer to flow from the second housing chamber into the first housing chamber; a first conveying member that is provided in the first housing chamber, and that conveys the developer in the first housing chamber; a second conveying member that is provided in the second housing chamber, and that conveys the developer in the second housing chamber in a second conveying direction directed toward the developer housing chamber; and a concentration detecting member that is provided in the bottom face of the second housing chamber on an upstream side of the first inflow portion in the second conveying direction, and that detects a concentration of the developer housed in the second housing chamber, wherein the second conveying member includes: a stirring member that is provided at a region opposed to the concentration detecting member, and that stirs the developer in a circumferential direction of the stirring member by making a first conveying force in the circumferential direction greater than a second conveying force in an axial direction of the stirring member, the second housing chamber includes: an inner wall face that is positioned in a region opposed to the first inflow portion, and that is formed into a shape extending along an outer shape of the second conveying member; and a recess that is provided in an inner wall face of a region opposed to the concentration detecting member, and in which a sectional area of the region opposed to the concentration detecting member and perpendicular to the second conveying direction is larger than a sectional area of the region opposed to the first inflow portion and perpendicular to the second conveying direction.

DETAILED DESCRIPTION

Next, examples which are exemplary embodiments of the invention will be described with reference to the accompanying drawings. However, the invention is not restricted to the following examples.

In order to facilitate the understanding of the following description, the front and rear directions in the drawings are indicated as X-axis directions, the right and left directions are indicated as Y-axis directions, and the upper and lower directions are indicated as Z-axis directions. The directions or sides indicated by the arrows X, −X, Y, −Y, Z, and −Z are the front, rear, right, left, upper, and lower directions, or the front, rear, right, left, upper, and lower sides, respectively.

In the figures, the symbol in which “●” is written in “603” indicates the arrow which is directed from the rear of the sheet to the front, and that in which “×” is written in “◯” indicates the arrow which is directed from the front of the sheet to the rear.

In the following description with reference to the drawings, illustrations of members other than those which are necessary in description are suitably omitted for the sake of easy understanding.

FIG. 1is a diagram illustrating the whole of an image forming apparatus of Example 1 of the invention.

Referring toFIG. 1, the image forming apparatus U comprises an automatic document conveying device U1, and an image forming apparatus body U2which supports the device, and which has a transparent document reading face PG in the upper end.

The automatic document conveying device U1has: a document feeding portion TG1in which plural documents Gi to be copied are housed in a stacked manner; and a document discharging portion TG2to which the documents Gi fed from the document feeding portion TG1and passed through a document reading position on the document reading face PG are discharged.

The image forming apparatus body U2has an operation portion U1through which the user inputs an operation command signal such as the start of an image forming operation, an exposing optical system A, etc.

Reflected light from a document which is conveyed on the document reading face PG by the automatic document conveying device U1, or that which is manually placed on the document reading face PG is passed through the exposing optical system A and converted by a solid-state imaging element CCD to electric signals of red R, green G, and blue B.

An image information converting portion IPS converts the electric signals of RGB to image information of black K, yellow Y, magenta M, and cyan C supplied from the solid-state imaging element CCD, temporarily stores the image information, and supplies the image information at a predetermined timing as image information for forming latent images, to a latent-image forming device driving circuit DL.

In the case where the document image is a single-color image or a so-called monochromatic image, only image information of black K is supplied to the latent-image forming device driving circuit DL.

The latent-image forming device driving circuit DL has driving circuits (not shown) for the respective colors Y, M, C, and K, and supplies signals corresponding to the input image information at predetermined timings, to latent-image forming devices LHy, LHm, LHc, LHk which are disposed for the respective colors.

FIG. 2is an enlarged view illustrating main portions of the image forming apparatus of Example 1.

Visible-image forming devices Uy, Um, Uc, Uk which are placed in a middle portion in the gravitational direction of the image forming apparatus U form visible images of the colors Y, M, C, and K, respectively.

Latent-image writing beams Ly, Lm, Lc, and Lk of Y, M, C, and K emitted from latent-image writing light sources of the latent-image forming devices LHy to LHk impinge on rotary image carriers PRy, PRm, PRc, PRk, respectively. In Example 1, the latent-image forming devices LHy to LHk are configured by so-called LED arrays, respectively.

The image forming apparatus Uy for Y has the rotary image carrier PRy, a charging device CRy, the latent-image forming device LHy, a developing device Gy, a transferring device T1y, and an image-carrier cleaner CLy. In Example 1, the image carrier PRy, the charging device CRy, and the image-carrier cleaner CLy are configured by an image carrier unit which is integrally attachable to and detachable from the image forming apparatus body U2.

The visible-image forming devices Um, Uc, Uk are configured in a similar manner as the visible-image forming device Uy for Y.

Referring toFIGS. 1 and 2, the image carriers PRy, PRm, PRc, PRk are charged by the respective charger devices CRy, CRm, CRc, CRk, and, at image writing stations Q1y, Q1m, Q1c, Q1k, electrostatic latent images are formed in their surfaces by the latent-image writing beams Ly, Lm, Lc, Lk. In developing regions Q2y, Q2m, Q2c, Q2k, the electrostatic latent images in the surfaces of the image carriers PRy, PRm, PRc, PRk are developed into toner images which are examples of visible images by developers held by developing rolls R0y, R0m, R0c, R0kwhich are examples of developer carriers of the developing devices Gy, Gm, Gc, Gk.

The developed toner images are conveyed to primary transferring regions Q3y, Q3m, Q3c, Q3kwhich are contacted with an intermediate transfer belt B that is an example of an intermediate transferring member. At a predetermined timing, a power source circuit E which is controlled by a controller C applies a primary transfer voltage in which the polarity is opposite to the charging polarity of the toner, to primary transferring devices T1y, T1m, T1c, T1kplaced on the rear face side of the intermediate transfer belt B in the primary transferring regions Q3y, Q3m, Q3c, Q3k.

The toner images on the image carriers PRy to PRk are primarily transferred to the intermediate transfer belt B by the primary transferring devices T1y, T1m, T1c, T1k. Residuals and adhesions on the surfaces of the image carriers PRy, PRm, PRc, PRk after the primary transfer are cleaned by the image-carrier cleaners CLy, CLm, CLc, CLk. The surfaces of the image carriers PRy, PRm, PRc, PRk which have been cleaned are again charged by the charging devices CRy, CRm, CRc, CRk.

A belt module BM which is an example of an intermediate transferring device, and which is vertically movable and forward extractable is placed above the image carriers PRy to PRk. The belt module BM has: the intermediate transfer belt B; a belt driving roll Rd which is an example of an intermediate-transferring member driving member; a tension roll Rt which is an example of an intermediate-transferring member stretching member; a walking roll Rw which is an example of a meandering preventing member; an idler roll Rf which is an example of a driven member; a backup roll T2awhich is an example of a secondary-transfer region opposing member; and the primary transferring devices T1y, T1m, T1c, T1k. The intermediate transfer belt B is supported in a rotary movable manner by the belt supporting rolls Rd, Rt, Rw, Rf, T2awhich are examples of an intermediate-transferring member support member configured by the rolls Rd, Rt, Rw, Rf, T2a.

A secondary transfer roll T2bwhich is an example of a secondary transfer member is placed while opposing to the surface of the intermediate transfer belt B contacted with the backup roll T2a. A secondary transferring device T2is configured by the rolls T2a, T2b. A secondary transferring region Q4is formed in a region where the secondary transferring device T2band the intermediate transfer belt B are opposed to each other.

The single- or multi-color toner images which are sequentially stackingly transferred onto the intermediate transfer belt B by the primary transferring devices T1y, T1m, T1c, T1kin the primary transferring regions Q3y, Q3m, Q3c, Q3kare conveyed to the secondary transferring region Q4.

Three pairs of right and left guide rails GR which are examples of a guiding member are disposed below the visible-image forming devices Uy to Uk. Sheet feeding trays TR1to TR3which are examples of a sheet feeding container are supported by the guide rails GR so as to be movable in the front and rear directions. Recording sheets S which are examples of media housed in the sheet feeding trays TR1to TR3are taken out by a pickup roll Rp which is an example of a medium taking out member, and separated one by one by a separating roll Rs which is an example a medium separating member. Then, the recording sheet is conveyed by plural conveying rolls Ra which are examples of a medium conveying member, along a sheet conveying path SH which is an example a medium conveying path, and sent to a registration roll Rr which is an example a transfer-region conveyance timing adjusting member, and which is disposed on the upstream side of the secondary transferring region Q4in the sheet conveying direction. A sheet conveying device (SH+Ra+Rr) is configured by the sheet conveying path SH, the sheet conveying rolls Ra, the registration roll Rr, etc.

The registration roll Rr conveys the recording sheet S to the secondary transferring region Q4in timing with the conveyance of the toner image formed on the intermediate transfer belt B to the secondary transferring region Q4. When the recording sheet S is passed through the secondary transferring region Q4, the backup roll T2ais grounded, and the power source circuit E which is controlled by the controller C applies a secondary transfer voltage which is opposite to the charging polarity of the toner, to the secondary transferring device T2b. At this time, the toner image on the intermediate transfer belt B is transferred to the recording sheet S by the secondary transferring device T2.

After the secondary transfer, the intermediate transfer belt B is cleaned by a belt cleaner CLb which is an example of an intermediate-transferring member cleaner.

The recording sheet S onto which the toner image has been secondarily transferred is conveyed to a fixing region Q5which is a press contact region between a heating roll Fh that is an example of a heating fixing member of a fixing device F, and a pressuring roll Fp that is an example of a pressuring fixing member, and subjected to heating fixation when passed through the fixing region. The recording sheet S which has undergone heating fixation is discharged to a discharge tray TRh which is an example of a medium discharging portion, from a discharging roller Rh which is an example of a medium discharging member.

A release agent which improves the property of releasing of the recording sheet S from the heating roll is applied to the surface of the heating roll Fh by a release-agent applying device Fa.

Developer cartridges Ky, Km, Kc, Kk which are examples of developer replenishment containers respectively housing developers of yellow Y, magenta M, cyan C, and black K are arranged above the belt module BM. The developers housed in the developer cartridges Ky, Km, Kc, Kk are replenished to the developing devices Gy, Gm, Gc, Gk in accordance with consumptions of the developers of the developing devices Gy, Gm, Gc, Gk, through developer replenishment paths which will be described later. In Example 1, each developer is configured by a two-component developer containing a magnetic carrier, and a toner to which an external additive is added.

Referring toFIG. 1, the image forming apparatus U has an upper frame UF and a lower frame LF. The upper frame UF supports the visible-image forming devices Uy to Uk and the components which are placed above the visible-image forming devices Uy to Uk, i.e., the belt module BM, etc.

The lower frame LF supports the guide rails GR supporting the sheet feeding trays TR1to TR3, the sheet feeding members which feed sheets from the trays TR1to TR3, i.e., the pickup roll Rp, the separating roll Rs, the sheet conveying rolls Ra, etc.

(Description of Developing Device)

FIG. 3is a view illustrating the developing device of Example 1 of the invention,FIG. 3Ais a partial section perspective view showing main portions in a state where a developing container cover is removed away,FIG. 3Bis a view illustrating a first conveying member, andFIG. 3Cis a view illustrating a second conveying member.

FIG. 4is a section view taken along the line IV-IV inFIG. 3A.

FIG. 5is a section view taken along the line V-V inFIG. 3A.

Next, the developing devices Gy, Gm, Gc, Gk of Example 1 of the invention will be described. Since the developing devices Gy, Gm, Gc, Gk for the respective colors are configured in the same manner, only the developing device Gy for Y color will be described, and detailed description of the developing devices Gm, Gc, Gk for the other colors will be omitted.

Referring toFIGS. 2 to 5, the developing device Gy which is placed while opposing the image carrier PRy has a developing container V which houses a two-component developer containing a toner and a carrier. The developing container V has: a developing container body1; and the developing container cover2which is an example of a lid member, and which closes the upper end of the developing container body1as shown inFIG. 2; and a developer supply/discharge tube3which is an example of a developer supply/discharge member, and which is coupled to the front end of the developing container body1as shown inFIG. 4.

Referring toFIGS. 2 to 5, the developing container body1has inside it: a developing roll chamber4which is an example of a developer carrier housing portion; a first stirring chamber6which is an example of a first developer housing chamber, and which is adjacent to the developing roll chamber4; and a second stirring chamber7which is an example of a second developer housing chamber, and which is placed adjacently to a right lower portion of the first stirring chamber6in order to reduce the lateral and vertical dimensions of the developing container V. The developing roll R0which is an example of a developer carrier is housed in the developing roll chamber4. A layer thickness regulating member8for regulating the thickness of the developer on the surface of the developing roll R0is disposed on the upstream side in the rotation direction of the developing roll R0.

Referring toFIGS. 4 and 5, in both front and rear end portions of the developing container V, a butting member Va or a so-called tracking member for setting the distance between the developing roll R0and the image carrier PRy to a predetermined value is supported at a position opposed to the image carrier PRy.

Referring toFIG. 3, a supply/discharge chamber6ainside the developer supply/discharge tube3is connected to the front side of the first stirring chamber6, and a replenishment chamber7ainside the developer supply/discharge tube3is connected to the front side of the second stirring chamber7. Referring toFIG. 3, a developer replenishment port3ato which the developer of the developer cartridge Ky, Km, Kc, Kk is replenished is formed in the upper face of a front end portion (+X end portion) of the supply/discharge chamber6a. A developer discharge port3bwhich is an example of a developer discharging portion is formed in the lower face of a rear portion of the supply/discharge chamber6a, and a waste developer which is discharged and dropped through the developer discharge port3bis recovered into a developer recovery container which is not shown.

In the developing container body1, as shown inFIG. 3, a partition wall9is formed between the first stirring chamber6and the second stirring chamber7except the both end portions. Referring toFIGS. 3 and 4, the first stirring chamber6and the second stirring chamber7communicate with each other through an upward inflow portion E1which is an example of a first inflow portion, and which is placed in the rear end portion, and a downward inflow portion E2which is an example of a second inflow portion, and which is placed in the front side, so that the developer can circulate. An opening forming member11in which an opening for adjusting the inflow amount is formed is attached to the downward inflow portion E2.

In the developer supply/discharge tube3, a partition wall12is formed between the supply/discharge chamber6aand the replenishment chamber7a. As shown inFIG. 3, therefore, the supply/discharge chamber6aand the replenishment chamber7acommunicate with each other through a replenishment inflow portion E3which is an example of a third inflow portion, so that the developer can flow from the supply/discharge chamber6ato the replenishment chamber7a.

A circulation stirring chamber6and7is configured by the first stirring chamber6and the second stirring chamber7.

Referring toFIGS. 3 to 5, a supply auger21which is an example of a supplying member, and which conveys the developer while stirring the developer to supply the developer to the developing roll R0is placed in the first stirring chamber6.

Referring toFIGS. 3A and 3B, the supply auger21has: a first rotation shaft22which extends in the axial direction of the developing roll R0; and a first conveying vane23which is spiral, and which is supported on the outer circumference of the first rotation shaft22. The first conveying vane23has: a replenishment reverse conveying vane23awhich is placed correspondingly with the front end portion of the supply/discharge chamber6a; a discharge conveying vane23bwhich is an example of a fourth conveying member, and which is placed correspondingly with the middle and rear portions of the supply/discharge chamber6a; a circulation reverse conveying vane23cwhich is an example of a reverse conveying portion and a third conveying member, and which is placed correspondingly with a range from the rear end portion of the supply/discharge chamber6ato the front side of the downward inflow portion E2; and a first main stirring conveying vane23dwhich is an example of a first conveying member, and which is placed correspondingly with a range from the downward inflow portion E2to the rear end of the first stirring chamber6.

In Example 1, the vanes23ato23dare formed into a spiral shape, and the distance by which the developer is moved by one rotation of the first main stirring conveying vane23d, i.e., the distance or pitch of vanes which are adjacent to each other in the axial direction is set to be larger than the pitches of the conveying vanes23ato23c. In Example 1, the first rotation shaft22and the first conveying vane23of the supply auger21are integrally formed by a resin. Alternatively, the shaft and the conveying vane may be separately formed and then combined to each other. In Example 1, the vanes23ato23dare disposed on the single first rotation shaft22. The invention is not restricted to this configuration. For example, combinations of the replenishment reverse conveying vane23aand its rotation shaft, the discharge conveying vane23band its rotation shaft, the circulation reverse conveying vane23cand its rotation shaft, and the first main stirring conveying vane23dand its rotation shaft may be configured separately from each other.

Referring toFIGS. 3A and 3C, a stir auger26which is an example of a stirring member, and which conveys the developer while stirring the developer is placed in the second stirring chamber7. The stir auger26has: a second rotation shaft27which extends in the axial direction of the developing roll R0; and a second conveying vane28which is spiral, and which is supported on the outer circumference of the second rotation shaft27. The second conveying vane28has: a replenishment conveying vane28awhich is placed correspondingly with the replenishment chamber7a; a second main stirring conveying vane28bwhich is placed correspondingly with a range from the downward inflow portion E2to the front side of the upward inflow portion E1; and a reverse conveying vane28cwhich is placed in the rear end portion of the second stirring chamber7.

In Example 1, the vanes28ato28care formed into a spiral shape, and the pitch of the second main stirring conveying vane28bis set to be larger than the pitches of the conveying vanes28a,28c. In the region where the second main stirring conveying vane28bis disposed, as shown inFIG. 3, plural flat plate-like stirring members28dare supported at predetermined intervals on the second rotation shaft27. Referring toFIG. 3C, on the left side of the reverse conveying vane28c, a stirring paddle28ewhich is an example of a stirring portion is supported on the second rotation shaft27. The stirring members28dand the stirring paddle28eare formed so that the conveying force in the circumferential direction of the second rotation shaft27is greater than that in the axial direction. In Example 1, particularly, the stirring members28dand the stirring paddle28eare configured by plate-like members which extend along the second rotation shaft27, and exert substantially no conveying force in the axial direction.

In Example 1, also the stir auger26is integrally formed similarly with the supply auger21. In Example 1, the vanes28ato28care disposed on the single second rotation shaft27. The invention is not restricted to this configuration. For example, combinations of the replenishment conveying vane28aand its rotation shaft, the second main stirring conveying vane28band its rotation shaft, and the reverse conveying vane28cand its rotation shaft may be configured separately from each other.

When the conveying members21,26are rotated, the developer which is replenished from the developer replenishment port3ais caused to flow into the replenishment inflow portion E3by the replenishment reverse conveying vane23aand the discharge conveying vane23b, and then conveyed to the replenishment chamber7a. The developer which is conveyed to the replenishment chamber7ais conveyed by the replenishment conveying vane28to the second stirring chamber7in the developing container body1, and further conveyed in a second developer conveying direction Ya by the second main stirring conveying vane28b. The developer which is conveyed to the upward inflow portion E1is caused to stagnate by the second main stirring conveying vane28band the reverse conveying vane28cwhich conveys the developer in the direction opposite to the second developer conveying direction, to increase the amount of the developer, and then flows into the first stirring chamber6which is situated in the upward oblique side.

The developer which flows into the first stirring chamber6is conveyed by the first main stirring conveying vane23din a first developer conveying direction Yb opposite to the second developer conveying direction Ya. The developer which is conveyed in the first stirring chamber6is caused by a magnetic force to adhere to the surface of the developing roll R0during the conveyance, and is then used in developing. The developer which is conveyed to the downward inflow portion E2is caused to stagnate in the downward inflow portion E2by the circulation reverse conveying vane23cwhich tries to convey the developer in the direction opposite to the first developer conveying direction Yb, and then caused by the gravity to flow into the second stirring chamber7through the downward inflow portion E2. As a result, the developer in the stirring chambers6,7is circulated and conveyed while being stirred by the conveying members21,26.

When the amount of the developer in the downward inflow portion E2is increased, there is a case where a part of the developer cannot be conveyed in the opposite direction by the circulation reverse conveying vane23c, and flows to the discharge conveying vane23bon the side of the supply/discharge chamber6a. In this case, the developer which flows to the side of the discharge conveying vane23bwith passing over the circulation reverse conveying vane23cis conveyed to the developer discharge port3bby the discharge conveying vane23bto be discharged.

FIG. 6is a view illustrating the developing device of Example 1,FIG. 6Ais a view showing a state where the developing container cover is opened, andFIG. 6Bis a section view taken along the line VIB-VIB inFIG. 5.

FIG. 7is an enlarged perspective view of main portions of a rear end portion of the developing container cover in Example 1.

FIG. 8is a side view as seen from the direction of the arrow VIII inFIG. 7.

FIG. 9is an enlarged view of main portions of a region in the vicinity of the conveying member of the developing container V in Example 1.

InFIG. 6, the illustration of the developing roll is omitted.

Referring toFIGS. 3,5, and6, as an example of a developer detecting member, a concentration detecting member31for detecting the concentration of the developer housed in the second stirring chamber7is placed in the bottom face of the second stirring chamber7on the upstream side of the upward inflow portion E1in the second developer conveying direction. The concentration detecting member31is configured by a so-called magnetic sensor which is conventionally known, and detects the rate of the toner with respect to the total amount of the toner and the carrier. The concentration detecting member is placed in a state where a sensing surface31ais directed toward the second stirring chamber.

Referring toFIGS. 4 to 8, the developing container cover2which covers the upper face of the developing container V has: a second upper wall face2aof the second stirring chamber7which is formed into an arcuate shape extending along the outer shape of the stir auger26; a partition groove portion2binto which the partition wall9is fitted, thereby separating the first stirring chamber6and the second stirring chamber7from each other; and a first upper wall face2cwhich constitutes the upper wall faces of the first stirring chamber6and the developing roll chamber4.

Referring toFIGS. 6 to 8, in a sectional-area expanded region A1which is set so as to include a region opposed to the concentration detecting member31in the second upper wall face2a, as an example of a recess for expanding the sectional area, a cutaway portion2dwhich constitutes the upper wall face of the second stirring chamber7in the sectional-area expanded region A1is formed into a shape in which the second upper wall face2ais partly cut away. In Example 1, the sectional area of the second stirring chamber7in the sectional-area expanded region A1where the cutaway portion2dshown inFIG. 5is disposed is set so as to be larger than that of the second stirring chamber7in the upward inflow portion E1in which the upper portion is closed by the upper wall face2aextending along the outer shape of the stir auger26shown inFIG. 4.

Referring toFIGS. 6 to 9, a conveying member proximity region A2extending in the axial direction of the stir auger26is set in the vicinity of the concentration detecting member31, and a semi-arcuate raised bottom portion32is formed in the second stirring chamber7so as to extend along the bottom and side faces. As shown inFIG. 5, in the conveying member proximity region A2, therefore, the raised bottom portion32causes the distance between the bottom face and the second rotation shaft27of the stir auger26to be shorter than that in the upward inflow portion E1shown inFIG. 4, so that the outer circumference of the stir auger26is close to the bottom face and the gap is narrowed. In the sectional-area expanded region A1, the total sectional area which is obtained after it is increased by the cutaway portion2dand decreased by the raised bottom portion32and the stirring paddle28eis set so as to be larger than the sectional area of the second stirring chamber7other than the cutaway portion2d, such as that of the second stirring chamber7of an inflow portion corresponding region E1acorresponding to the upward inflow portion E1, i.e., the circular sectional area extending along the outer shape of the stir auger26.

The stirring paddle28eof the stir auger26is placed in the vicinity of the concentration detecting member31to stir the developer in the vicinity of the concentration detecting member31, thereby reducing the conveying speed of the developer. In Example 1, the stirring paddle28eis not placed between the downstream side of the sectional-area expanded region A1in the second developer conveying direction and the upward inflow portion E1.

Referring toFIG. 6, in the developing devices Gy of Example 1, the width L1of the stirring paddle28ein the second developer conveying direction is set so as to be included within the width L2of the conveying member proximity region A2. That is, the downstream end portion of the conveying member proximity region A2in the second developer conveying direction Ya is placed on the downstream side of the downstream end portion of the stirring paddle28e.

As shown inFIG. 6B, in the second developer conveying direction Ya, the downstream end of the sectional-area expanded region A1is placed on the downstream side of the downstream end portion of the stirring paddle28e. The downstream end of the sectional-area expanded region A1is set to be located closer to an end portion of the downstream end of the stirring paddle28ethan the downstream end of the conveying member proximity region A2, i.e., on the upstream side of the downstream end of the conveying member proximity region A2. The upstream end of the sectional-area expanded region A1is set to be located on the upstream side of the upstream end of the stirring paddle28ein the second developer conveying direction.

On the upstream side of the stirring paddle28ein the second developer conveying direction Ya, the stirring members28dwhich are an example of a second stirring member are placed. The downstream end of the extreme downstream one of the stirring members28din the second developer conveying direction Ya is placed on the upstream side of the upstream end of the sectional-area expanded region A1.

Function of Example 1

In the image forming apparatus U of Example 1 having the above-described configuration, the developer to be used in developing in the developing device Gy to Gk is conveyed while being stirred in the developing container V. In the upward inflow portion E1, in order to allow the developer to efficiently flow from the second stirring chamber7in the lower side to the first stirring chamber6in the upper side, the upper wall face2aof the second stirring chamber7has the shape which extends along the outer shape of the stir auger26. The increasing/decreasing amount of the developer existing in the upward inflow portion E1is smaller than that of the developer in the developing device Gy to Gk. Even when the amount of the developer in the developing device Gy to Gk is reduced, therefore, the developer efficiently flows into the first stirring chamber6.

The concentration of the developer housed in the developing container V is detected by the concentration detecting member31of the second stirring chamber7, and the replenishment of the developer is controlled. In the vicinity of the concentration detecting member31, the developer is stirred by the stirring paddle28e, and the developer in the vicinity of the concentration detecting member31placed in the bottom face is stirred, thereby reducing the stagnation. At this time, the conveying speed of the developer in the axial direction of the stir auger26is lowered. In the case where the total amount of the developer in the developing container V is increased by the timing difference between consumption and replenishment of the developer, in the range where the conveying speed is lowered or the stirring paddle28eis placed, the developer stagnates, but the sectional area is widened by the sectional-area expanded region A1. In the sectional-area expanded region A1where the sectional area is increased, namely, the pressure acting on the developer is not excessively raised, the developer is prevented from being pressed and packed, and the concentration is accurately detected by the concentration detecting member31. Irrespective of the increase/decrease of the total amount of the developer, therefore, the concentration detection is performed stably and accurately as compared with the case where the sectional-area expanded region A1is not disposed and the upper wall face at the position where the concentration detecting member31is disposed is identical with the upper wall face2aof the upward inflow portion E1.

In the image forming apparatus U of Example 1, the raised bottom portion32causes the sensing surface31aof the concentration detecting member31to be placed close to the second rotation shaft27. Namely, the sensing surface31ais placed in or in the vicinity of the flow of the developer which is directly stirred by the second main stirring conveying vane28bof the stir auger26and the stirring paddle28e, and stagnation of the developer on the sensing surface31ahardly occurs, thereby improving the detection accuracy. In the image forming apparatus U of Example 1, therefore, it is possible to cope with both stagnation of the developer on the sensing surface31aand the increase/decrease of the total amount of the developer, and the detection accuracy is improved and stabilized. In the image forming apparatus U of Example 1, moreover, the upstream end of the sectional-area expanded region A1in the second developer conveying direction is set to be on the upstream side of the upstream end of the stirring paddle28e, and, even when the conveying ability is reduced by the stirring paddle28eto cause the developer to stagnate on the upstream side of the stirring paddle28e, an excessive pressure is prevented from being applied. The upstream end of the sectional-area expanded region A1is placed downstream of the downstream end of the extreme downstream one of the stirring members28din the second developer conveying direction Ya, and the sectional-area expanded region A1is placed downstream of the downstream side of the stirring members28dwhere the conveying speed of the developer begins to be lowered. In the sectional-area expanded region A1on the downstream side of the stirring members28d, namely, the conveying speed of the developer is restored, and stagnation of the developer in the sectional-area expanded region A1is reduced.

In the image forming apparatus U of Example 1, the downstream end of the sectional-area expanded region A1is placed on the downstream side of the downstream end portion of the stirring paddle28ein the second developer conveying direction Ya. In the step part of the cutaway portion2din the downstream end of the sectional-area expanded region A1which is placed on the downstream side of the stirring paddle28ewhere the developer begins to stagnate, the conveying speed of the developer is restored, and an influence due to stagnation of the developer is reduced in the step part of the cutaway portion2d.

In the image forming apparatus U of Example 1, the width L1of the stirring paddle28ein the second developer conveying direction is set so as to be included within the width L2of the conveying member proximity region A2, and the downstream end of the conveying member proximity region A2is placed at the position which is on the downstream side of the region where the conveying speed is lowered by the stirring paddle28e, and in which the conveying speed is increased. Namely, the conveying speed is made higher in the downstream end of the conveying member proximity region A2, and stagnation of the developer in the step part of the raised bottom portion32is reduced.

As shown inFIG. 6B, in the second developer conveying direction, the downstream end of the sectional-area expanded region A1is set at a position closer to the downstream end portion of the stirring paddle28ethan to the downstream end of the conveying member proximity region A2, i.e., on the upstream side. In the region which is on the downstream side of the stirring paddle28e, and in which the conveying speed is restored, stagnation of the developer which may possibly occur is prevented from occurring by setting the step part of the downstream end of the sectional-area expanded region A1. When the amount of the developer in the developing device Gy to Gk is increased, particularly, stagnation of the developer which occurs in the step part of the downstream end portion of the raised bottom portion32is effectively reduced by placing the downstream end portion of the sectional-area expanded region A1where the amount of the developer is increased more easily than the other regions, at the upstream side of the step of the downstream end portion of the conveying member proximity region A2corresponding to the raised bottom portion32.

In the image forming apparatus U of Example 1, the stirring paddle28eand the stirring members28dare not disposed between the downstream side of the sectional-area expanded region A1and the upward inflow portion E1, and stagnation of the developer between the sectional-area expanded region A1and the upward inflow portion E1is reduced. Between the first inflow portion in which the developer must be lifted or upward in the gravitational direction, and the developer easily stagnates, and the region where the stirring members are placed in the opposed region, and the concentration detecting member in which the developer easily stagnates is placed, it is possible to reduce continuous stagnation of the developer which stagnates in the first inflow portion, to the region where the concentration detecting member is placed. Namely, the lifting of the developer is effectively performed by causing the developer to flow from the region which is between the sectional-area expanded region A1and the upward inflow portion E1, and in which little stagnation occurs, into the upward inflow portion E1.

Next, Example 2 of the invention will be described. In the description of Example 2, the components corresponding to those of Example 1 are denoted by the same reference numerals, and their detailed description will be omitted.

Example 2 is configured in the same manner as Example 1 except the following points.

FIG. 10is a view illustrating the developing device of Example 2 corresponding toFIG. 6of Example 1,FIG. 10Ais a view showing a state where the developing container cover is opened, andFIG. 10Bis a section view of main portions.

Referring toFIG. 10, in the developing device Gy of Example 2, in place of the raised bottom portion32, the portion of the conveying member proximity region A2of the second main stirring conveying vane28bis configured by a large vane28fwhich is larger in outer shape than the other portions, and set so as to, during rotation, pass the vicinity of the concentration detecting member31. Also in the developing device Gy of Example 2, in the sectional-area expanded region A1, the total sectional area which is obtained after it is decreased by the large vane28fand the stirring paddle28eand increased by the cutaway portion2dis set so as to be larger than the sectional area of the inflow portion corresponding region E1a.

(Function of Example 2)

In the image forming apparatus of Example 2 having the above-described configuration, stagnation of the developer in the vicinity of the sensing surface31aof the concentration detecting member31is reduced by the large vane28fin the same manner as the raised bottom portion32in Example 1. Even when, in order to reduce stagnation and improve the detection accuracy, the outer shape of the stir auger26is increased, namely, the detection accuracy of the concentration detecting member31due to the increase/decrease of the total amount of the developer can be improved and stabilized.

Although, in the above, the examples of the invention have been described in detail, the invention is not restricted to the examples. Various modifications are enabled within the scope of the spirit of the invention set forth in the claims. Modifications (H01) to (H06) of the invention will be exemplified.

(H01) In the examples, a copier is exemplified as the image forming apparatus. The invention is not restricted to this. The image forming apparatus may be configured as a facsimile apparatus, a printer, or a multifunction machine having all or plural functions of such apparatuses. The image forming apparatus having the image carriers PRy to PRk, developing devices Gy to Gk, and latent-image forming devices LHy to LHk which are used for the four colors has been described. The invention is not restricted to this. The invention can be applied also to a monochrome image forming apparatus, and a rotary type image forming apparatus in which a single image carrier and a single latent-image forming device are used, and four developing devices are rotated to be sequentially opposed to the image carrier.
(H02) In the examples, the downstream end portions of the sectional-area expanded region A1and the conveying member proximity region A2are formed into a step shape. The invention is not restricted to this. The portions may be formed as a continuously changing surface such as an inclined surface which is inclined from the upstream side toward the downstream side, or an arcuate surface. In the case of an inclined surface or the like, a so-called dead space such as a step shape is hardly formed, and stagnation of the developer is reduced further effectively.
(H03) In the examples, the downstream end of the conveying member proximity region is set to be downstream of the downstream end of the sectional-area expanded region A1. The invention is not restricted to this. Their positional relationship may be inverted, or they may be at the same position.
(H04) In the examples, it is preferable to dispose the conveying member proximity region. Alternatively, the region may be omitted.
(H05) In the examples, the conveying speed of the developer is reduced by the stirring paddle28e. The invention is not restricted to the configuration. For example, the conveying speed may be reduced by arbitrary conveying speed reducing means such as increasing the diameter of the second rotation shaft, or changing the inclination angle or pitch of the second main stirring conveying vane28b.
(H06) In the examples, as the stirring member and the second stirring member, the stirring paddle28eand the stirring members28dare exemplified. The stirring members are not restricted to plate-like ones which are shown in the examples, and which extend in the axial direction. A member having a shape in which the conveying force in the circumferential direction is greater than that in the axial direction may be used. For example, a plate-like stirring member which does not extend in the axial direction, and which is slightly inclined may be employed.