Development device and image forming apparatus

A development device includes a development case, a first agitating/conveying member and a second agitating/conveying member. The first agitating/conveying member is arranged below the second agitating/conveying member to convey the developer in a first direction. The second agitating/conveying member conveys the developer in a second direction as an opposite direction to the first direction to supply the developer to the developer carrier. The development case includes a first conveyance chamber, a second conveyance chamber, a first communicating portion communicating end parts of the first conveyance chamber and second conveyance chamber in the first direction, and a second communicating portion communicating end parts of the first conveyance chamber and second conveyance chamber in the second direction. The developer carrier has a first ferromagnetic area having magnetic force stronger than another area of the developer carrier, in which the first ferromagnetic area corresponds to the first communicating portion.

INCORPORATION BY REFERENCE

This application is based on and claims the benefit of priority from Japanese Patent application No. 2013-212580 filed on Oct. 10, 2013, the entire contents of which are incorporated herein by reference.

BACKGROUND

The present disclosure relates to a development device including an agitating/conveying member agitating/conveying two-component developer and an image forming apparatus including the development device.

In a development device visualizing an electrostatic latent image formed on a photosensitive drum to a toner image by using two-component developer consisting of a toner and a carrier, an agitating/conveying member agitating, frictionally charging and conveying the toner and carrier is provided.

Recently, a demand for space saving of an image forming apparatus is risen, and moreover, in a color multifunction peripheral and a color printer in a tandem type arranging a plurality of development devices in parallel, it is necessary to miniaturize the development device and to narrow a distance between the photosensitive drums. Thereupon, there is a development device having two agitating/conveying members disposed vertically to narrow the distance between the photosensitive drums.

In a case where the agitating/conveying members are disposed vertically, the developer is circulated between an upper conveyance chamber having an upper agitating/conveying member and a lower conveyance chamber having a lower agitating/conveying member. When the developer is drawn up from the lower conveyance chamber to the upper conveyance chamber, it is necessary to move the developer against gravity. As a feeding member drawing up the developer, a magnet roller connected coaxially to a developer carrier may be applied.

However, in a case where the magnet roller is connected coaxially to the developer carrier, a length in an axial direction of the developer carrier is lengthened and the development device is enlarged. Further, due to a complicated structure connecting the developer carrier and feeding member, cost increase is brought.

In a case where the agitating/conveying members are respectively arranged in the upper and lower conveyance chambers, a developer amount fed to the developer carrier is decreased in a communicating portion between the upper conveyance chamber and lower conveyance chamber. As a result, there are problems that a toner amount becomes insufficient and image density is lowered.

Because of this, the development device may be configured so that the agitating/conveying member and developer carrier is lengthened more than the photosensitive drum and image forming is carried out at a center part of the developer carrier except for the communicating portion. However, a length of the development device in an axial direction of the photosensitive drum is lengthened and the development device is enlarged.

SUMMARY

In accordance with an embodiment of the present disclosure, a development device includes a development case containing two-component developer consisting of a carrier and a toner, a first agitating/conveying member and a second agitating/conveying member agitating and conveying the developer in the development case and a developer carrier carrying the developer supplied from the second agitating/conveying member by magnetic force. The first agitating/conveying member is arranged below the second agitating/conveying member to convey the developer in a first direction as one direction of the axial directions of the developer carrier. The second agitating/conveying member conveys the developer in a second direction as an opposite direction to the first direction to supply the developer to the developer carrier. The development case has a first conveyance chamber in which the first agitating/conveying member is arranged, a second conveyance chamber in which the second agitating/conveying member is arranged, a partition part partitioning into the first conveyance chamber and second conveyance chamber, a first communicating portion communicating end parts of the first conveyance chamber and second conveyance chamber in the first direction, and a second communicating portion communicating end parts of the first conveyance chamber and second conveyance chamber in the second direction. The developer carrier has a first ferromagnetic area having magnetic force stronger than another area of the developer carrier, in which the first ferromagnetic area corresponds to the first communicating portion.

In accordance with an embodiment of the present disclosure, an image forming apparatus includes a development device. The development device has a development case containing two-component developer consisting of a carrier and a toner, a first agitating/conveying member and a second agitating/conveying member agitating and conveying the developer in the development case and a developer carrier carrying the developer supplied from the second agitating/conveying member by magnetic force. The first agitating/conveying member is arranged below the second agitating/conveying member to convey the developer in a first direction as one direction of the axial directions of the developer carrier. The second agitating/conveying member conveys the developer in a second direction as an opposite direction to the first direction to supply the developer to the developer carrier. The development case has a first conveyance chamber in which the first agitating/conveying member is arranged, a second conveyance chamber in which the second agitating/conveying member is arranged, a partition part partitioning into the first conveyance chamber and second conveyance chamber, a first communicating portion communicating end parts of the first conveyance chamber and second conveyance chamber in the first direction, and a second communicating portion communicating end parts of the first conveyance chamber and second conveyance chamber in the second direction. The developer carrier has a first ferromagnetic area having magnetic force stronger than another area of the developer carrier, in which the first ferromagnetic area corresponds to the first communicating portion.

DETAILED DESCRIPTION

In the following, with reference the drawings, a development device and an image forming apparatus according to an embodiment of the present disclosure will be described.

First, with reference toFIG. 1, an entire structure of a color printer1as the image forming apparatus will be described.FIG. 1is a schematic diagram schematically showing the structure of the color printer in accordance with the embodiment of the present disclosure. In the following description, the left-hand side ofFIG. 1indicates the front side of the printer1and orthogonal directions to forward and backward directions as viewed from the front side indicate left and right directions.

The color printer1includes a box-formed printer main body2. In a lower part of the printer main body2, a sheet feeding cartridge3storing sheets (not shown) is installed and, in an upper end of the printer main body2, an ejected sheet tray4is provided.

In an upper part of the printer main body2, an intermediate transferring belt5is disposed around a plurality of rollers. Below the intermediate transferring belt5, an exposure device6composed of a laser scanning unit (LSU) is arranged. At a lower side of the intermediate transferring belt5, a plurality of image forming parts7are installed for respective colors of yellow (Y), magenta (M), cyan (C) and black (B). In each image forming part7, a photosensitive drum10is rotatably attached by a support axis10a. As the photosensitive drum10, a photoconductor made of amorphous silicon (a-Si) or an organic photoconductor (OPC) may be applied. Around the photosensitive drum10, a charger11, a development device12, a first transferring part13, a cleaning device14and a static eliminator15are located along the rotation direction (refer to an arrow inFIG. 1) of the photosensitive drum10. Above each development device12, a developer container16is arranged.

At the rear side in the printer main body2, a conveying path20for the sheet is positioned. At an upstream end of the conveying path20, a sheet feeding part21is positioned. At an intermediate stream part of the conveying path20, a second transferring part22is positioned at the rear end of the intermediate transferring belt5. At a downstream part of the conveying path20, a fixing part23is positioned. At a downstream end of the conveying path20, an ejection port24is positioned.

Next, the operation of forming an image by the color printer1having such a configuration will be described.

When the power is supplied to the color printer1, various parameters are initialized and initial determination, such as temperature determination of the fixing part23, is carried out. Subsequently, in the color printer1, when image data is inputted and a printing start is directed from a computer or the like connected with the color printer1, image forming operation is carried out as follows.

First, the surface of the photosensitive drum10is electric-charged by the charger11. Then, exposure corresponding to the image data to the photosensitive drum10is carried out by a laser light (refer to an arrow P) from the exposure device6, thereby forming an electrostatic latent image on the surface of the photosensitive drum10. The electrostatic latent image is developed to a toner image having a correspondent color in the development device12. The toner image is first-transferred onto the surface of the intermediate transferring belt5in the first transferring part13. The above-mentioned operation is repeated in order by the respective image forming parts7, thereby forming the toner image having full color onto the intermediate transferring belt5. Incidentally, toner remained on the photosensitive drum10is removed by the cleaning device14and residual electric charge is eliminated by the static eliminator15.

On the other hand, the sheet fed from the sheet feeding cartridge3or a manual bypass tray (not shown) by the sheet feeding part21is conveyed to the second transferring part22in a suitable timing for the above-mentioned image forming operation. Then, in the second transferring part22, the toner image having full color on the intermediate transferring belt5is second-transferred onto the sheet. The sheet with the second-transferred toner image is conveyed to a downstream side on the conveying path20to enter the fixing part23, and then, the toner image is fixed on the sheet in the fixing part23. The sheet with the fixed toner image is ejected from the ejection port24onto the ejected sheet tray4.

Next, with reference toFIGS. 2 and 3, the development device12will be described.FIG. 2is a lateral sectional view showing the development device andFIG. 3is a sectional view showing the development device, as viewed of from the back side of the printer. The development device12includes a development case30, an agitating/conveying member40and a developing roller50(a developer carrier).

The development case30is a case in which the agitating/conveying member40and developing roller50are supported and a developer (two-component developer consisting of a carrier and a toner) is stored. The development case30is a box-formed member having a vertically long side face shape and having a length roughly equal to a length in an axial direction of the photosensitive drum10. At the back side of a top face of the development case30, an opening30afacing to a front lower side of the photosensitive drum10is formed so as to extend in the axial direction of the photosensitive drum10. On a lower edge of the opening30a, a regulating blade31regulating an amount of the developer is attached.

The inside of the development case30is partitioned into a first conveyance chamber35at the lower side and a second conveyance chamber36at the upper side by a partition board33(a partition part) arranged roughly horizontally. The first conveyance chamber35has a rectangular shape in the side view. The second conveyance chamber36is formed in an inverted trapezoid shape being approximately double a height of the first conveyance chamber35and having a width wider toward the upper side in the side view.

As shown inFIG. 3, at both left and right sides of the partition board33, a first communicating portion37and a second communicating portion38communicating the first conveyance chamber35and second conveyance chamber36are provided. Incidentally, becauseFIG. 3shows the development device12as viewed from the back side of the printer1, the left-hand side and right-hand side ofFIG. 3indicate the inverse of the left and right directions of the printer.

The first communicating portion37has a width W1 of approximately 8% of the length of the photosensitive drum10, e.g. the width of 20 mm. The second communicating portion38has a width W2 of approximately 8% of the length of the photosensitive drum10, e.g. the width of 20 mm.

The agitating/conveying member40is configured to agitate, to frictionally charge and to convey the developer, simultaneously. The agitating/conveying member40includes a first spiral41and a second spiral42.

The first spiral41is a screw conveyor having a length roughly equal to the length in the axial direction of the photosensitive drum10. The first spiral41has a rotating shaft41a, a spiral blade41bformed in a dextrorse spiral shape at a constant pitch in an axial direction of the rotating shaft41aand a drawing-up blade41cformed in a left end of the rotating shaft41a. The drawing-up blade41chas four rectangular thin plates and the respective thin plates are radially extended from the rotating shaft41aat equal central angles.

The first spiral41is positioned at the roughly center of the first conveyance chamber35of the development case30and both ends of the rotating shaft41aare rotatably supported in the development case30.

The second spiral42is a screw conveyor having a length roughly equal to the length in the axial direction of the photosensitive drum10. The second spiral42has a rotating shaft42aand a spiral blade42bformed in a sinistrorse spiral shape at a constant pitch in an axial direction of the rotating shaft42a. The pitch of the spiral blade42bof the second spiral42is narrower than the pitch of the spiral blade41bof the first spiral41.

The second spiral42is positioned at a lower part in the second conveyance chamber36of the development case30so as to be above or right above the first spiral41. Both ends of the rotating shaft42aof the second spiral42are rotatably supported in the development case30.

The developing roller50is configured to carry the developer by magnetic force and supply the developer on the surface of the photosensitive drum10. The developing roller50is a columnar member having a length roughly equal to the length in the axial direction of the photosensitive drum10. The developing roller50has a cylindrical sleeve51and a magnet roller52inserted into the sleeve51. The developing roller50has the diameter of 16 mm.

The sleeve51is a cylindrical member made of non-magnetic material. To the sleeve51, a developing bias taken by superposing direct voltage with alternating voltage is applied.

The magnet roller52is a columnar magnet and is magnetized with predetermined magnetic poles along a circumferential direction to have a main magnetic pole N1, a conveying magnetic pole S1, a separating magnetic pole N2, drawing-up magnetic pole N3and a regulating magnetic pole S2in a counter clockwise direction as viewed from the right side (refer toFIG. 2).

The main magnetic pole N1is a magnetic pole used for supplying the developer on the photosensitive drum10and has magnetic flux density of 100 mT (Wb/m2). Between the main magnetic pole N1and conveying magnetic pole S1and between the conveying magnetic pole S1and separating magnetic pole N2, magnetic fields are generated to convey the developer from the main magnetic pole N1to the separating magnetic pole N2. Because the separating magnetic pole N2and drawing-up magnetic pole N3are same pole, no magnetic field is generated between the separating magnetic pole N2and drawing-up magnetic pole N3, and therefore, the developer is not supported on the surface of the sleeve51, but falls. The drawing-up magnetic pole N3is a magnetic pole used for drawing up the developer and has magnetic flux density of 45 mT. The regulating magnetic pole S2is a magnetic pole used for regulating the amount of the drawn-up developer and has magnetic flux density of 60 mT.

As shown inFIG. 3, in the drawing-up magnetic pole N3of the magnet roller52above the first communicating portion37, a first ferromagnetic area52ahaving magnetic flux density (magnetic force) higher than another area is provided. The first ferromagnetic area52ahas the magnetic flux density higher than the other area by 10 mT, e.g. the magnetic flux density of 55 mT. Incidentally, the first ferromagnetic area52ahas the maximum magnetic flux density of 60-70 mT (i.e. 20% to 50% higher than the other area).

The inner end of the first ferromagnetic area52ais extended inwardly (in the direction toward the center) than the inner end (the end in the direction toward the center) of the first communicating portion37and reaches above the partition board33. An extending distance D1of the first ferromagnetic area52afrom the inner end of the first communicating portion37is set to preferably 5-50% of the width W1 of the first communicating portion37, more preferably approximately 25%. For example, the first ferromagnetic area52ahas a width W3 of 25 mm and the extending distance D1is 5 mm if the width W1 of the first communicating portion37is 20 mm.

As away of providing the first ferromagnetic area52a, a way of strongly magnetizing a relevant area of the magnetic roller52, a way of forming a piece with high magnetic flux density in advance and fitting the piece to a relevant area of the magnetic roller52or another way may be applied

The developing roller50is positioned obliquely above the second spiral42in an upper part of in the second conveyance chamber36of the development case30. The sleeve51of the developing roller50is rotatably supported in the development case30and the magnet roller52is inserted into the sleeve51and unrotatably fixed. The magnet roller52is positioned so that the main magnetic pole N1faces to the photosensitive drum10through the opening30aof the development case30, the drawing-up magnetic pole N3faces to the second spiral42and the regulating magnetic pole S2faces to the regulating blade31.

The rotating shaft41aof the first spiral41, the rotating shaft42aof the second spiral42and the sleeve51of the developing roller50are driven by a driving mechanism (not shown) composed of a drive source, such as a motor, a deceleration device, gears and others arranged outside the development case30to rotate in the counter clockwise direction as viewed from the right side.

Next, an action of the development device12having the above-mentioned configuration will be described. When the driving mechanism is activated, in the first conveyance chamber35, the rotation shaft41aof the first spiral41is rotated, and accordingly, the developer D in the first conveyance chamber35is conveyed in a first direction A1 (one direction of the axial directions of the developer carrier) from the second communicating portion38to the first communicating portion37by the spiral blade41b.

Since the pitch of the spiral blade42bof the second spiral42is narrower than the pitch of the spiral blade41bof the first spiral41, in a case where the first spiral41and second spiral42are rotated at same rotation speed, a conveying speed by the first spiral41is faster than a conveying speed by the second spiral42. Therefore, in the first conveyance chamber35, much developers D are accumulated at a downstream portion in the first direction A1.

The developer D is conveyed to the downstream of the first conveyance chamber35and then drawn up to the second conveyance chamber36via the first communicating portion37by the drawing-up blade41c. Since, at the downstream of the first conveyance chamber35, the developers D are densely accumulated mentioned above and the developer D is conveyed by the rotation of the first spiral41without interruption, it is possible to securely draw up the developer D to the second conveying chamber36by the drawing-up blade41c.

In the second conveyance chamber36, the rotating shaft42aof the second spiral42is rotated and the drawn-up developer D is conveyed in a second direction A2 from the first communicating portion37to the second communicating portion38by the spiral blade42b. During this conveying, the developer D is drawn up to the drawing-up magnetic pole N3of the developing roller50(refer toFIG. 2) to make a magnetic brush on the surface of the sleeve51.

The magnetic brush is regulated to a predetermined height when passing between the regulating magnetic pole S2and regulating blade31. Subsequently, when the magnetic brush reaches the main magnetic pole N1, the magnetic brush is erected along lines of magnetic force toward the surface of the photosensitive drum10to come into contact with the surface of the photosensitive drum10. At this time, according to a difference between an electrical potential of the electrostatic latent image formed on the photosensitive drum10and an electrical potential of the developing bias applied to the sleeve51, the toner is supplied to the electrostatic latent image and the electrostatic latent image is visualized by the toner.

The developer D passed through the main magnetic pole N1is conveyed from the conveying magnetic pole S1to the separating magnetic pole N2, and then, dropped out from the surface of the sleeve51in an area where magnetic force between the separating magnetic pole N2and drawing-up magnetic pole N3is not generated. The dropped-out developer D falls to the lower part of the second conveyance chamber36along an inner wall of the development case30.

The developer D containing the fallen developer conveyed to the downstream in the second direction A2 in the second conveyance chamber36passes through the second communicating portion38and falls to the first conveyance chamber35. Thus, the developer D is agitated while circulating between the first conveyance chamber35and second conveyance chamber36(refer to a void arrow inFIG. 3) through the first communication portion37communicating end parts of the first conveyance chamber35and second conveyance chamber36in the first direction A1 and the second communication portion38communicating end parts of the first conveyance chamber35and second conveyance chamber36in the second direction A2.

As described above, in accordance with the development device12according to the embodiment of the present disclosure, since the first ferromagnetic area52ais provided in the drawing-up magnetic pole N3of the magnetic roller52above the first communicating portion37, the drawing-up magnetic pole N3can hold much developers D on the surface of the sleeve51and convey much developers D to the regulating magnetic pole S2. As a result, since density of the developers D in a space above the first communicating portion37is lowered, it is possible to smoothly draw up the developer D in the first conveyance chamber35through the first communicating portion37to the second conveyance chamber36. Therefore, even if the first spiral41and second spiral42are disposed vertically, the amount of the developer supplied to the developing roller50in the first communicating portion37is increased, and accordingly, it is possible to solve insufficient of image density of a portion corresponding to the first communicating portion37.

Moreover, since the first ferromagnetic area52ais lengthened inwardly than the width of the first communicating portion37, more amount of the developer D can be supplied to the developing roller50in the first communicating portion37. In addition, since the developer D is supplied to the center portion of the second conveyance chamber36, it is possible to smoothly convey the developer from the first communicating portion37to the center portion of the second conveyance chamber36.

Further, since the first ferromagnetic area52ais provided in a part of the developing roller50to increase a drawing-up amount of the developer D, it is unnecessary to lengthen lengths in the axial direction of the developing roller50and agitating/conveying member40to be equal to or more than the length in the axial direction of the photosensitive drum10. In addition, new mechanism increasing the drawing-up amount is not required.

Therefore, it is possible to restrain cost increase by a simplified mechanism and to be prevented from lengthening the size in the forward and backward directions and in the left and right directions of the printer1.

Next, with reference toFIG. 4, the development device12′ according to another embodiment of the present disclosure. Incidentally, inFIG. 4, with respect to same components as the development device according to the above-described embodiment, same reference numerals asFIG. 3are attached to the figure and the detail description is omitted.

In the development device12′, in the drawing-up magnetic pole N3above the second communicating portion38of a magnetic roller52′ of the developing roller50′, a second ferromagnetic area52bhaving magnetic flux density (magnetic force) higher than a center area is provided. The second ferromagnetic area52bhas the magnetic flux density higher than the center area by 10 mT, e.g. the magnetic flux density of 55 mT. Incidentally, the second ferromagnetic area52bhas the maximum magnetic flux density of 60-70 mT (i.e. 20% to 55% higher than the center area).

The inner end of the second ferromagnetic area52bis extended inwardly (in the direction toward the center) than the inner end (the end in the direction toward the center) of the second communicating portion38and reaches above the partition board33. An extending distance D2of the second ferromagnetic area52bfrom the inner end of the second communicating portion38is set to preferably 5-50% of the width W2 of the second communicating portion38, more preferably approximately 25%. For example, the second ferromagnetic area52bhas a width W4 of 25 mm and the extending distance D2is 5 mm if the width W2 of the second communicating portion38is 20 mm.

In accordance with the development device12′ according to the other embodiment, since the second ferromagnetic area52bis provided in the drawing-up magnetic pole N3of the magnetic roller52′ above the second communicating portion38in which the developer D falls from the second conveyance chamber36to the first conveyance chamber35, the developer D hardly falls from the second communicating portion38to the first conveyance chamber35and the drawing-up magnetic pole N3can hold much developers D on the surface of the sleeve51. Therefore, it is possible to solve insufficient of image density of a portion corresponding to the second communicating portion38.

Although it is preferable for solving the insufficient of the image density in the vicinities of both ends of the photosensitive drum10that, as the development device12′ according to the other embodiment, the first ferromagnetic area52aand second ferromagnetic area52bare provided, it is possible to obtain sufficient effect by the first ferromagnetic area52a.

Incidentally, although, in the above-described embodiments of the present disclosure, the first spiral41and second spiral42are disposed vertically, the disposing direction is not restricted by the right vertical direction, but may be an oblique upward direction. The first spiral41and second spiral42may be disposed so as to correspond to a layout and others of the development device.

Although, in the above-described embodiments of the present disclosure, a case where the amount of the developer conveyed by the first spiral41is larger than the amount of the developer conveyed by the second spiral42was described, the amounts of the conveyed developers may be equal.

The embodiments of the present disclosure were described in a case of applying the configuration of the present disclosure to the printer1. On the other hand, in another embodiment, the configuration of the disclosure may be applied to another image forming apparatus, such as a copying machine, a facsimile or a multifunction peripheral, except for the printer1.

While the present disclosure has been described with reference to the particular illustrative embodiments, it is not to be restricted by the embodiments. It is to be appreciated that those skilled in the art can change or modify the embodiments without departing from the scope and spirit of the present disclosure.