JP4943239B2 - Developing device and image forming apparatus - Google Patents

Description

  The present invention relates to a developing device of an image forming apparatus such as an electrophotographic copying apparatus, a facsimile machine, and a printer, and more particularly to a configuration of a developer agitating / conveying means for agitating and conveying a developer.

  Conventionally, as a developing device of an image forming apparatus adopting a magnetic brush developing method using a two-component developer, a developer carrying is carried on the side of the developer carrying body arranged close to the image carrying body and facing the image carrying body. Two screw-like developer agitating / conveying means arranged in parallel with the body are provided, the toner is replenished on the developer agitating / conveying means, and the toner and the carrier are agitated by the rotation of the developer agitating / conveying means. A method of conveying the developed developer to a developer carrying member is generally employed.

  However, the screw-like developer agitating and conveying means has a high developer conveying efficiency, but the agitating efficiency is low, so the toner cannot be sufficiently charged, and the charging of the toner is caused by the friction between the developers in the doctor section. The current situation depends on this, but in this configuration, there is a problem that the coat film of the carrier is scraped or the additive is buried in the toner due to a strong stress in the doctor portion. This problem is solved by the fact that the replenished toner is sufficiently agitated and charged before being conveyed to the developer carrying member.

  Therefore, in order to improve the stirring efficiency, a plurality of screw-like developer stirring and conveying means arranged in the vertical direction is provided on the side of the developer carrying member facing the image carrier, and the developer is conveyed in the vertical direction. A developing device configured to be able to sufficiently stir the developer is disclosed in, for example, “Patent Document 1”. Further, for example, “Patent Document 2” discloses a developing device that transports and mixes a developer from the bottom to the top by revolving a screw-like developer stirring and conveying means provided in the developer supply section.

Japanese Patent Publication No. 4-62389 Japanese Patent Laid-Open No. 7-134481

  However, in the technique disclosed in “Patent Document 1”, if the developer agitating / conveying means is arranged vertically, the developer is conveyed against the gravity, so that the conveyance efficiency is significantly reduced. Although it is possible to increase the transport amount by increasing the number of rotations of the screw or increasing the outer diameter, increasing the number of rotations is not preferable because the stress applied to the developer increases, and the outer diameter of the screw is not preferable. If the thickness is increased, the conveyance efficiency is improved, but the stirring efficiency is lowered. In order to ensure both the conveyance efficiency and the stirring efficiency, it is necessary to arrange a large number of screws arranged in a line along the longitudinal direction of the developer carrier so that the developer is vertically stirred and conveyed. Inevitable. Furthermore, when the fluidity changes due to environmental fluctuations, developer deterioration, etc., there is a problem that the amount of conveyance greatly fluctuates and the developer supply becomes unstable.

  Even in the technique disclosed in “Patent Document 2”, since a very large space is required to revolve the screw, it is not versatile because it prevents downsizing of the apparatus. As described above, the configuration using the screw as the developer agitating / conveying means is simple and inexpensive, but has a number of problems in achieving both the conveyance efficiency and the agitation efficiency and reducing the size of the apparatus. .

  The present invention solves the above-mentioned problems, and by uniformly stirring and mixing while reducing the stress applied to the developer, it is possible to give a sufficient charge amount to the developer, and a stable amount of developer. An object of the present invention is to provide a developing device provided with a developer agitating / conveying means capable of conveying the developer.

Invention of claim 1, wherein the developer carrying member, while stirring the developer possess a developer stirring and conveying means for transporting said developer carrying member, said developer stirring and conveying means developer in the developing apparatus have a rotatable vertical screw member which is inclined relative to a horizontal axis so as to transport the lower upward, the developer agitation conveyance means, to the longitudinal screw member the developer from the developer carrier A rotatable first horizontal screw member that conveys toward the developer, and a rotatable second horizontal screw member that conveys the developer from the vertical screw member toward the developer carrying member. The vertical screw member and the first horizontal screw member and the first horizontal screw member are positioned on substantially the same plane and the angle formed by the rotary shafts along the developer transport direction is an acute angle. Screw member is placed And wherein the are.

According to a second aspect of the present invention, in the developing device according to the first aspect, the angle is 60 degrees or more .

According to a third aspect of the present invention, there is provided the developing device according to the first or second aspect , further comprising a casing that encloses the developer carrying member and the developer agitating / conveying means, and the casing encloses the vertical screw member. It has the cylindrical shape part to do.

According to a fourth aspect of the present invention, in the developing device according to the third aspect , the vertical screw member is arranged such that the rotation axis of the vertical screw member is shifted from the center line of the cylindrical portion in a direction away from the developer carrier. and said that you are.

According to a fifth aspect of the present invention, in the developing device according to any one of the first to fourth aspects, the rotational speed of the vertical screw member is variable .

According to a sixth aspect of the present invention, in the developing device according to the fifth aspect , the rotational speed of the vertical screw member is changed in accordance with the fluidity of the developer .

According to a seventh aspect of the invention, in the developing device according to the fifth aspect , the number of rotations of the vertical screw member is changed in accordance with the number of image forming sheets .

According to an eighth aspect of the present invention, in the developing device according to the fifth aspect of the present invention, the developing device further includes a toner replenishing unit that replenishes toner, and the rotational speed of the vertical screw member temporarily after the toner is replenished by the toner replenishing unit It is characterized by increasing .

A ninth aspect of the present invention is an image forming apparatus having the developing device according to any one of the first to eighth aspects .

  According to the present invention, since the rotating shaft of the vertical screw member is inclined with respect to the horizontal axis, the toner and the carrier can be sufficiently agitated, and a developer having a uniform toner density and charge amount is applied to the developing roller. Compared to the case where the rotation axis is arranged vertically, it is possible to secure a sufficient amount of developer transport, and it is better by reliably supplying the developer necessary for development to the developing roller. Image formation can be performed.

  FIG. 1 shows an image forming apparatus employing the first embodiment of the present invention. In FIG. 1, an image forming apparatus 1 has a photosensitive drum 2 inside the apparatus main body, and a charging roller 3 for charging the surface of the photosensitive drum 2 around the photosensitive drum 2 and a uniformly charged photosensitive drum. An exposure device 4 that forms an electrostatic latent image with a laser beam on the surface 2; a developing device 6 that supplies charged toner to the surface of the photosensitive drum 2 to develop the electrostatic latent image into a toner image; and a transfer belt 5a. A transfer device 5 for transferring the toner image formed on the photosensitive drum 2 to the recording paper 9, a cleaning device 7 for removing residual toner remaining on the photosensitive drum 2 after the toner image transfer, and the photosensitive drum 2 A neutralizing device 8 for removing the residual potential is provided.

  In the above configuration, the photosensitive drum 2 whose surface is uniformly charged by the charging roller 3 forms an electrostatic latent image by the exposure device 4, and is developed by the developing device 6 to form a toner image on the surface. . This toner image is transferred by the transfer device 5 to the recording paper 9 fed through the registration roller pair 11 from the paper feeding device 10 provided at the lower part of the apparatus main body, and the recording paper 9 on which the toner image is transferred is fixed. After the toner image is fixed by being sent to the apparatus 12, it is sent to a subsequent process by the paper discharge roller pair 13. After the residual toner is removed by the cleaning device 7, the photosensitive drum 2 is discharged by the charge removing device 8 and used for the next image forming process. In the transfer device 5, the toner remaining on the transfer belt 5a is cleaned by the belt cleaning device 5b.

  FIG. 2 is a schematic view of the developing device 6 which is a characteristic part of the present invention. A developing device 6 containing a two-component developer in which toner and a carrier are mixed includes a developing roller 15 as a developer carrying member, a first screw 16 as a first horizontal screw member, and a second horizontal screw in a casing 14. It has a second screw 17 as a member, a third screw 18 (see FIG. 3) as a vertical screw member, a toner supply port 19 and a toner supply path 20 constituting a toner supply means, a doctor blade 21 and the like. As shown in FIG. 3, the developer in the casing 14 is stirred and conveyed from the developing roller 15 toward the third screw 18 by the rotation of the first screw 16, and from the third screw 18 to the developing roller by the rotation of the second screw 17. Agitated and conveyed toward 15. Part of the developer agitated and conveyed by the second screw 17 is adsorbed to the peripheral surface of the developing roller 15 by a magnetic force, and the thickness thereof is made uniform by the doctor blade 21 and then supplied to the photosensitive drum 2. The electrostatic latent image formed on the body drum 2 is visualized. The developed developer is collected on the first screw 16 and then stirred and conveyed toward the third screw.

  In the above configuration, the third screw 18 is arranged so that the rotation axis thereof is located substantially on the same plane as the rotation axis of the first screw 16, and the third screw 18 further includes the rotation axis and the first screw 16. The third screw 18 is disposed in such a manner that the upper portion of the third screw 18 is inclined toward the second screw 17 with respect to the vertical line so that the rotation axis forms an acute angle along the developer conveyance direction. Moreover, the casing 14 in the site | part which encloses the 3rd screw 18 is formed in the cylindrical shape, and comprises the cylindrical-shaped part 14a. A density sensor 22 that detects the toner density in the developing device 6 is disposed at a position upstream of the toner supply port 19 in the developer transport direction.

  With the above-described configuration, the toner accommodated in the toner container (not shown) is little by little through the toner supply path 20 and into the developing device 6 from the toner supply port 19 by the operation of a pump (not shown) constituting the toner supply means. To be replenished. The toner replenishment amount is determined based on the detection result by the density sensor 22. The toner replenished onto the first screw 16 is conveyed to the third screw 18 while being agitated with the developer sent from the developing roller 15 side, and is agitated and conveyed upward by the third screw 18 to be conveyed to the second screw 17. It is conveyed to the upper part on the near side.

  With the above-described configuration, the rotation axis of the third screw 18 is inclined with respect to the horizontal axis, so that the toner and the carrier can be sufficiently stirred, and a developer having a uniform toner density and charge amount is applied to the developing roller. Compared to the case where the rotation axis is arranged vertically, it is possible to secure a sufficient amount of developer transport, and it is better by reliably supplying the developer necessary for development to the developing roller. Image formation can be performed.

  When the developer is transported in the horizontal direction, even if the developer fluidity changes, there is almost no effect on the transport amount, but when the developer is transported in the vertical direction, the developer fluidity changes. The transport amount changes greatly. Accordingly, when the first screw 16 and the second screw 17 and the third screw 18 are connected by a gear, the transport amount of the third screw 18 is transported by the first screw 16 and the second screw 17 due to the change in the fluidity of the developer. There is a concern that the amount of the developer becomes less than the amount, and the developer is not normally circulated. Therefore, in the present embodiment, the third screw 18 is rotated by a dedicated motor 23 and the rotation is controlled independently of the first screw 16 and the second screw 17. With this configuration, even when the developer fluidity changes, the developer conveyance amount can be adjusted by changing the rotation speed of the third screw 18, and development caused by the change in the developer fluidity can be achieved. The clogging of the agent can be prevented.

  Specifically, the torque of the third screw 18 is monitored, and when the output becomes higher than the reference value, it is determined that the amount of developer around the third screw 18 has increased, and the rotational speed is increased. Further, when the image forming operation is repeated, the developer deteriorates due to scraping of the coat film of the carrier and spent toner and additive with respect to the carrier and the fluidity deteriorates. As shown in FIG. 4, it is effective to perform control so that the number of rotations of the third screw 18 increases as the number of formed images increases from the reference value. Further, since the developer fluidity temporarily deteriorates even when the amount of toner replenished is large, the number of rotations of the third screw 18 is increased until the toner is dispersed to some extent after toner replenishment as shown in FIG. Thus, by improving both the agitation property and the conveyance property, the agitation conveyance operation at the time of toner replenishment can be stabilized.

  As shown in this embodiment, when the rotation axis of the first screw 16 and the rotation axis of the third screw 18 are located on substantially the same plane, the rotation speed and / or outer diameter of each screw is different. Therefore, the developer tends to stay in the connecting portion of each screw. However, in this embodiment, as shown in FIG. 6, the angle α formed by the rotation axis of the first screw 16 and the rotation axis of the third screw 18 is an acute angle, and the developer dropped from the third screw 18 is the first screw. 16 will collide with the flow of developer conveyed to the third screw 18. The toner is replenished from the upstream side in the developer conveying direction of the first screw 16, and the replenished toner is conveyed to the third screw 18 in a state where it is hardly mixed with the developer. Agitation and mixing are promoted by the collision of the developer dropped from the top of the screw 18. When the angle α is an obtuse angle, the developer dropped from the third screw 18 does not collide with the flow of the developer conveyed to the third screw 18 by the first screw 16 as shown in FIG. Will occur. Furthermore, in the present embodiment, the developer from the first screw 16 is conveyed slightly above the lowermost part of the third screw 18, so that the developer is prevented from being clogged in the lower part of the third screw 18, and the first screw is prevented. The developer is smoothly transferred from 16 to the third screw 18.

  Next, the principle of stirring and mixing the developer in the present invention will be described. As shown in FIG. 7, the developer in the third screw 18 includes a developer P that rises with the rotation of the screw and a developer Q that descends due to gravity, and the developer flows that move in opposite directions. Stir mixing is promoted. Further, by providing an appropriate gap between the third screw 18 and the cylindrical portion 14a, as a developer flow moving downward from the screw, a flow of the developer Q sliding down on the screw and a cylindrical shape from above the screw are formed. Since two types of flows, that is, the flow of the developer R that jumps out and falls into the gap with the portion 14a, can be created, the stirrability can be further improved.

  When the gap described above is extremely small, the density becomes high when the developer slides down along the cylindrical portion 14a, and the developer is easily stressed. When the gap disappears, the developer flows on the screw. It is limited and stirrability is reduced. On the other hand, if the gap is too wide, the amount of developer that falls is reduced and the transport amount is lowered. Therefore, it is important to appropriately form the gap. In the present invention, since the third screw 18 is disposed at an angle α, the amount of developer that falls along the side surface of the cylindrical portion 14a on the developing roller 15 side is large. Therefore, the rotation axis of the third screw 18 is shifted in the direction away from the developing roller 15 from the center line of the cylindrical portion 14a, and a gap B through which a large amount of developer passes is formed larger than the gap A as shown in FIG. By doing so, the stress received by the developer can be reduced and good image formation can be performed.

  Further, as a method of reducing the stress applied to the developer, it is effective to dispose bearings 24 (see FIG. 3) at both ends of the third screw 18. If the third screw 18 is supported in a cantilever manner, the developer moving through the gap is crushed by the cylindrical portion 14a as the screw rotates at a high speed. Can be prevented.

  Next, the inclination angle α of the third screw 18 will be described. As the angle α changes, the developer agitation strength and transport amount change. Generally, as the angle α increases, the developer needs to be transported against gravity, so the transport amount decreases and the stirrability increases. Conversely improves. In order to transport a sufficient amount of developer while securing an appropriate charge amount, the management of the angle α is important.

  When the angle α is 90 degrees, the developer falls from the entire outer periphery of the third screw 18 into the outer gap, so that the agitation is good but the transport amount is insufficient. In particular, when the flowability of the developer changes due to changes in environmental conditions or repeated image formation, the transport amount greatly changes. When the angle α is not less than 45 degrees and less than 90 degrees, the developer does not fall from the outer peripheral surface of the screw but falls along the inner wall of the cylindrical portion 14a. It is hard to drop and the transport amount increases. The developer transport amount can be increased as the angle α is decreased. However, when the angle α is set to 60 degrees or less, the developer has poor fluidity as in the developer indicated by R in FIG. As a result of the developer sliding down along the inner wall of the cylindrical portion 14a sticking to the inner wall to form a wall and hindering the movement of the developer from above to below, the developer flow is shown in FIG. The developer flow that slides along the screw indicated by Q and the developer flow that rises on the screw indicated by symbol P in FIG. 7 become two types, which makes it difficult to stir and mix the developer. Therefore, the angle α is preferably 60 degrees or more and less than 90 degrees, and more preferably 70 degrees or more and less than 80 degrees.

  Mixing of the replenished toner is promoted by mixing the developer falling from the upper side to the lower side and the developer conveyed from the lower side to the upper side. When the angle α is 45 degrees or less, the developer on the screw hardly falls and the ratio of the rising developer becomes extremely larger than the falling developer, so the developer is not sufficiently stirred. Unsuitable.

  Next, a specific example of the embodiment of the present invention will be described. A third screw 18 having a screw diameter of 20 mm, a pitch of 20 mm, a lead angle of 20 degrees, and a length of 90 mm was used, and the charge amount and flow rate when the toner and the carrier were agitated were measured. Actually, the length of stirring by the vertical movement of the developer is 35 mm. The clearance between the cylindrical portion 14a and the outer diameter of the third screw 18 is 1 mm, and the rotation speed of the third screw 18 is 700 r. p. m. It was. Prior to operation, 48 g of carrier and 2 g of toner were charged into the developing device 6.

  Under the above conditions, the motor 23 is operated to rotate the third screw 18, whereby the toner and the carrier are agitated and mixed and discharged from the upper part of the third screw 18. In the above-described configuration, the inclination angle α of the third screw 18 was changed from 45 degrees to 90 degrees, and the variation in toner density and the transport amount of the discharged developer were measured. The variation in toner density was evaluated by sampling six locations from the stirred developer and measuring the standard deviation of the mixture. When the standard deviation is less than 0.5, the evaluation is ○, evaluation of 0.5 or more and less than 0.8 is Δ, and 0.8 or more is ×. FIG. 8 shows the measurement result of the toner density variation, and FIG. 9 shows the measurement result of the transport amount.

  As can be seen from FIG. 8, when the angle α is in the range of 60 degrees or more and 90 or less, the variation in the toner density after stirring is a standard deviation of 0.5 or less, and the toner and the carrier are almost uniformly mixed, and the charge amount thereof Was also good. As is clear from FIG. 9, there was a tendency that the conveyance amount increases as the angle α decreases. However, when the angle α is 90 degrees, if the developer is deteriorated by repeating the image forming operation, the amount of conveyance is increased. As a result, an extremely low result was obtained. When the angle α is in the range of 45 degrees or more and 60 or less, when a large amount of toner is replenished, the toner stays at the bottom of the developing device 6 and mixing takes time. When the angle α was 45 degrees or less, only the effect of conveyance was obtained, and the developer could not be mixed uniformly. From the above results, it was found that by setting the angle α to 60 degrees or more and less than 90 degrees, it is possible to simultaneously improve both the stirring property and the transportability.

  In the above-described embodiment, an example in which an electrophotographic copying apparatus is used as the image forming apparatus 1 has been described. However, the image forming apparatus to which the present invention can be applied is not limited thereto, and the present invention is not limited to this. Of course, the present invention can be applied to other image forming apparatuses.

1 is a schematic front view of a main part of an image forming apparatus employing an embodiment of the present invention. 1 is a schematic view of a developing device used in an embodiment of the present invention. It is the schematic explaining the 1st screw used for one embodiment of the present invention, the 2nd screw, and the 3rd screw. It is a diagram which shows the relationship between the number of image formation in one Embodiment of this invention, and the rotation speed of a 3rd screw. FIG. 6 is a diagram showing a relationship between a toner replenishing operation and a third screw rotation speed in an embodiment of the present invention. It is the schematic explaining the relationship between the angle which the rotating shaft of a 1st screw and the rotating shaft of a 3rd screw which are used for one Embodiment of this invention make, and the flow of a developer. It is the schematic explaining the relationship between the clearance gap between the 3rd screw used for one Embodiment of this invention, and a cylindrical shape part, and the flow of a developer. It is a graph which shows the measurement result of the dispersion | variation in a toner density when changing the inclination angle of the 3rd screw in one Embodiment of this invention. It is a diagram which shows the measurement result of the conveyance amount of a developer when changing the inclination-angle of the 3rd screw in one Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 6 Developing apparatus 14 Casing 14a Cylindrical shaped part 15 Developer carrier (developing roller)
16 First horizontal screw member (first screw)
17 Second horizontal screw member (second screw)
18 Vertical screw member (third screw)
α angle

Claims (9)

A developer carrying member, the developer possess a developer stirring and conveying means for transporting the developer carrier while stirring and the developer stirring and conveying means so as to transport upward the developer from the lower in the developing apparatus have a rotatable vertical screw member which is inclined relative to the horizontal axis,
The developer stirring and conveying means includes a rotatable first horizontal screw member that conveys the developer from the developer carrier toward the vertical screw member, and a developer from the vertical screw member to the developer carrier. A rotatable second horizontal screw member that conveys toward the surface, and the rotation shaft of the vertical screw member and the rotation shaft of the first horizontal screw member are positioned on substantially the same plane and along the developer conveyance direction. The developing device is characterized in that the vertical screw member and the first horizontal screw member are arranged so that an angle formed by the rotation shafts is an acute angle . The developing device according to claim 1,
The developing device characterized in that the angle is 60 degrees or more . The developing device according to claim 1 or 2 ,
A developing device comprising a casing enclosing the developer carrying member and the developer agitating / conveying means, and the casing having a cylindrical portion enclosing the vertical screw member . The developing device according to claim 3 .
The developing device according to claim 1, wherein the vertical screw member is arranged such that a rotation axis thereof is shifted from a center line of the cylindrical portion in a direction away from the developer carrying member . In the developing device according to any one of claims 1 to 4 ,
The developing device characterized in that the rotational speed of the vertical screw member is variable . The developing device according to claim 5 , wherein
The developing device according to claim 1, wherein the rotational speed of the vertical screw member is changed in accordance with the fluidity of the developer. The developing device according to claim 5 , wherein
2. A developing apparatus according to claim 1, wherein the number of rotations of the vertical screw member is changed in accordance with the number of image forming sheets . The developing device according to claim 5 , wherein
A developing device comprising toner replenishing means for replenishing toner, wherein the rotational speed of the vertical screw member is temporarily increased immediately after the toner is replenished by the toner replenishing means . An image forming apparatus comprising the developing device according to claim 1 .

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