JP2011118080A - Developing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developer circulation type developing device configured such that the amount of developer to be supplied to a developer carrier is equalized over the entire developer carrying area of the developer carrier without increasing developer regulating energy in a developer regulating member, thereby image failure of a toner image to be developed is suppressed to that extent. <P>SOLUTION: The developing device equalizes the amount of developer to be supplied to the developer carrier without increasing developer regulating energy in the developer regulating member. An image forming apparatus includes the same. In the developing device, a low magnetic flux density area LBr is provided to a magnetic material portion (conveyance pole m2) extending from the catch pole of the magnetic material incorporated in the developer carrier to the regulation pole thereof. The LBr is provided at the arrangement pitch (pt) of an integral multiple (including a substantially integral multiple) of the screw blade pitch of a screw conveying member used for supplying the developer to the developer carrier. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a combination machine combining two or more of these, and particularly relates to a developing device used in the image forming apparatus.

  Image forming apparatuses such as copiers, printers, facsimile machines, or a combination machine combining two or more of these include electrostatic recording type image forming apparatuses, but electrophotographic type image forming apparatuses are widely used. ing. In an electrophotographic image forming apparatus, the surface of an electrostatic latent image carrier such as a photosensitive member is charged by a charging device, and image exposure is performed on the charging area from an exposure device to form an electrostatic latent image. Generally, an electrostatic latent image is developed by a developing device to form a toner image, and the toner image can be transferred to a transfer target.

  Here, the “transfer object” is generally a recording medium such as recording paper in a monochrome image forming apparatus. In a color image forming apparatus or the like, a toner image on an electrostatic latent image carrier is primarily transferred. When the intermediate transfer member is used, it can be said that both the intermediate transfer member and the recording medium on which the toner image is secondarily transferred from the intermediate transfer member are transferred members.

  In any of the methods, various types of developing devices used in the image forming apparatus are known, and the image to be formed is formed on the electrostatic latent image carrier of the image forming apparatus. A developer carrying member for applying toner to the electrostatic latent image according to the above, a first carrying member that is provided on the developer carrying member and conveys the developer in the rotational axis direction by being driven to rotate. A second conveying member that conveys the developer in the direction of the rotation axis when rotated and in a direction opposite to the first conveying member, and circulates the developer between the first and second conveying members. The developer can be supplied from the first conveying member to the developer carrying member, and the amount of the developer can be regulated by the developer regulating member facing the developer carrying member to be used for developing the electrostatic latent image. There is a device.

  In this type of developing device, the developer is allowed to move from the developer feeding side end of the second conveying member to the developer feeding side end of the first conveying member and the developer sending side end of the first conveying member. The developer is circulated by the first and second conveying members while allowing the developer to move from the first conveying member to the developer feeding side end of the second conveying member, and the developer is supplied from the first conveying member to the developer carrying member. To do.

Hereinafter, this type of developing device may be referred to as a “developer circulation type developing device”.
A typical one of the first and second transport members is a screw transport member in which screw blades (spiral blades) are formed on the rotating shaft.

  On the other hand, as a developer to be used, a so-called one-component developer mainly composed of toner and a so-called two-component developer mainly composed of toner and carrier are known.

  The developer circulation type developing device is employed even when a one-component developer is used, but is suitable when a two-component developer is used. Since the two-component developer mixes and stirs toner and carrier and charges the toner for development, the developer circulation type developing device that can also stir the developer is a developing device that uses a two-component developer. It can be said that it is suitable.

  For example, Japanese Patent Application Laid-Open No. 2005-91854 describes a developer circulation type developing device that employs a two-component developer mainly composed of toner and a magnetic carrier. In the developing device described in the publication, magnetic field generating means having a developer loosening effect is provided on a screw-type second conveying member in order to smoothly stir and mix the toner and the carrier.

JP 2005-91854 A

  However, regardless of whether a one-component developer or a two-component developer is used, a developer circulation type developing device adopting a screw conveying member as a first conveying member that supplies the developer to the developer carrying member. Therefore, the height of the developer surface in the developing device varies according to the shape of the first screw conveying member, and the developer surface as a whole appears uneven, and is supplied to the developer carrying member accordingly. The amount of developer to be developed is not uniform in each part of the developer carrying member, and there is unevenness. Consequently, the uneven supply of the developer amount causes image defects such as a density defect of a toner image to be developed and formed.

  For such a problem, the developer supply amount to the screw conveying member is increased, and more specifically, for example, in each part of the developer carrying region of the developer carrying body on the basis of a place where the developer supply amount is small. The excess developer may be supplied to the first screw conveying member so that the necessary developer amount is supplied, and the fluctuation of the developer surface due to the shape of the screw conveying member may be dealt with. If an excessive amount of developer is supplied in addition to the amount originally required for development on the top, when the amount of the developer supplied from the first screw conveying member to the developer carrying member is regulated by the developer regulating member, the amount of regulation energy that is large Therefore, the driving torque (developing device driving torque) of the developer carrier and the like is increased, and the stress applied to the developer is increased and the developer is deteriorated. No longer, both undesirable.

  Accordingly, the present invention provides a developer circulation type developing device, in which the amount of developer supplied to the developer carrying member is reduced without causing an increase in developer regulating energy in the developer regulating member. It is a first object to provide a developing device that can be uniform over the entire carrying region, and thus can suppress the occurrence of image defects for the toner image that is developed and formed.

Here, as described above, the “developer circulation type developing device” forms a toner image by developing an electrostatic latent image formed on an electrostatic latent image carrier in an image forming apparatus using a developer. A developing device for
A rotationally driveable developer carrier for applying toner to the electrostatic latent image;
A first screw conveying member that is erected on the developer carrier and is driven to rotate to convey the developer in the direction of the rotation axis;
A second screw conveying member that conveys the developer in the direction of the rotation axis by being rotationally driven and in a direction opposite to the first screw conveying member;
While the developer is circulated by the first and second screw conveying members, the developer is supplied from the first screw conveying member to the developer carrying member, and the developer amount is regulated by the developer regulating member facing the developer carrying member. The developing device can be used for developing the electrostatic latent image.

  The present invention also provides an image forming apparatus capable of forming an electrostatic latent image corresponding to a target image on an electrostatic latent image carrier and developing the electrostatic latent image with a developing device to form a toner image. In at least one developing device, the amount of developer supplied to the developer carrying member is uniform over the entire developer carrying region of the developer carrying member without causing an increase in developer regulating energy in the developer regulating member. Therefore, a second problem is to provide an image forming apparatus that can form a good image.

  In order to solve the first problem, the present invention provides the following developing device and also provides the next image forming apparatus to solve the second problem.

(1) Developing device A developing device for forming a toner image by developing an electrostatic latent image formed on an electrostatic latent image carrier in an image forming apparatus using a developer,
A rotationally driveable developer carrier for applying toner to the electrostatic latent image;
A first screw conveying member that is erected on the developer carrier and is driven to rotate to convey the developer in the direction of the rotation axis;
A second screw conveying member that conveys the developer in the direction of the rotation axis by being rotationally driven and in a direction opposite to the first screw conveying member;
While the developer is circulated by the first and second screw conveying members, the developer is supplied from the first screw conveying member to the developer carrying member, and the amount of the developer is regulated by the developer regulating member facing the developer carrying member. A developing device that can be used for developing an electrostatic latent image,
A magnetic developer is used as the developer, and the developer carrier has a built-in magnetic field generator. The magnetic field generator has a catch electrode for adsorbing the developer onto the developer carrier and the developer regulating member. And a magnetic pole that faces the control pole in the direction of rotation of the developer carrier. In the longitudinal direction of the magnetic field generator parallel to the direction, with a low magnetic flux density peak interval that is an integral multiple of the screw blade pitch of the first screw conveying member, and gradually decreasing from the upstream side to the downstream side in the developer carrying member rotation direction. A developing device formed to be.

(2) Image forming apparatus An image forming apparatus capable of forming an electrostatic latent image corresponding to a target image on an electrostatic latent image carrier and developing the electrostatic latent image with a developing device to form a toner image. An image forming apparatus in which at least one developing device is a developing device according to the present invention.

According to the developing device of the present invention, a magnetic developer is employed as the developer, and a low magnetic flux density region is formed in a portion from the catch pole to the regulation pole of the magnetic field generator in the developer carrier.
Accordingly, the developer is transported from the region corresponding to the catch electrode to the region corresponding to the regulation electrode, and the developer transport direction (hereinafter referred to as “conventional transport direction”) when there is no such low magnetic flux density region. In some cases, the conveying force component is also applied in the direction crossing (also in the longitudinal direction of the magnetic field generator). As a result, the developer is conveyed toward the regulating member while spreading in an oblique direction with respect to the conventional conveyance direction.

  Further, since the low magnetic flux density region is formed so as to gradually become smaller from the upstream side toward the downstream side in the developer carrying member rotation direction, as the developer is conveyed, the low magnetic flux density region is in a direction crossing the conventional conveying direction. The conveying force component is gradually reduced.

  As a result, uneven developer supply amount on the developer carrier due to the shape of the screw conveying member in the catch electrode corresponding region (in other words, uneven adsorption by the catch electrode) is a process in which the developer reaches the developer regulating member. Reduced.

  In addition, the low magnetic flux density region of the magnetic field generator is formed in the longitudinal direction of the magnetic field generator parallel to the rotational axis direction of the screw conveying member at low magnetic flux density peak intervals that are an integral multiple of the screw blade pitch of the first screw conveying member. ing. The “integer multiple” includes not only “just an integral multiple” but also “substantially an integral multiple”.

  As described above, since the low magnetic flux density region of the magnetic field generator is formed with a low magnetic flux density peak interval that is an integral multiple (including “substantially an integral multiple”) of the screw blade pitch of the first screw conveying member. The amount of developer reaching the region corresponding to the region is made uniform, the difference in developer height between the low magnetic flux density regions is suppressed, and the developer supply to the developer carrier due to the shape of the screw conveying member accordingly Unevenness is reduced.

  As a result, the amount of developer supplied to the screw conveying member is not added to the original amount of developer required for electrostatic latent image development, but is supplied onto the developer carrier. The amount of developer to be applied is made uniform in each part of the developer carrying region of the developer carrying member, and the occurrence of image defects such as a decrease in image density due to uneven developer supply amount can be suppressed.

  In addition, since it is not necessary to add excessive developer as described above, the regulation energy for regulating the amount of developer by the developer regulating member can be suppressed to a small level, and as a result, the developer carrier and the like are driven. Torque (developing device driving torque) can be kept small, and stress applied to the developer can be suppressed to suppress developer deterioration.

  In the image forming apparatus according to the present invention, since the developing device according to the present invention is adopted as at least one developing device, the developer regulating energy in the developer regulating member is increased in at least one developing device. Without incurring, the amount of developer supplied to the developer carrying member can be made uniform over the entire developer carrying region of the developer carrying member, and as a result, a better image can be formed.

  A transport pole for transporting the developer adsorbed on the developer carrier by the catch pole to a region corresponding to the regulation pole as a magnetic field generator portion from the catch pole to the regulation pole where the low magnetic flux density region is formed. Can be illustrated.

  In the developing device according to the present invention, the first screw conveying member supplies the developer carrying member between the first screw conveying member and the developer carrying member along the rotation axis direction of the screw conveying member. The auxiliary supply members may be sequentially arranged to change the moving direction of the developer to be divided (sprayed so as to be divided). In that case, the arrangement pitch may be an integral multiple of the screw blade pitch of the first screw conveying member. The “integer multiple” includes not only “just an integral multiple” but also “substantially an integral multiple”.

  By providing such a supply auxiliary member, the amount of developer reaching each low magnetic flux density region of the magnetic field generator can be made constant regardless of the rotational phase of the screw conveying member, and thereby the amount of developer Is promoted.

  In any case, in the developing device according to the present invention, the developer carrying member may be in the form of a belt, but as a representative example, a rotationally driveable developing roller incorporating the magnetic field generator can be mentioned. .

  The developer employed in the developing device according to the present invention is a magnetic developer. For example, a so-called one-component developer mainly composed of a magnetic toner, or a so-called two-component developer mainly composed of a toner and a magnetic carrier. An agent can be mentioned.

  According to the present invention, there is provided a developer circulation type developing device in which the amount of developer supplied to the developer carrying member is increased without causing an increase in developer regulating energy in the developer regulating member. It is possible to provide a developing device that can be uniform over the entire carrying region, and thus can suppress the occurrence of image defects for the toner image to be developed and formed accordingly.

  Further, according to the present invention, there is provided an image forming apparatus capable of forming an electrostatic latent image corresponding to a target image on an electrostatic latent image carrier and developing the electrostatic latent image with a developing device to form a toner image. In at least one developing device, the amount of developer supplied to the developer carrying member is uniform over the entire developer carrying region of the developer carrying member without causing an increase in developer regulating energy in the developer regulating member. Therefore, it is possible to provide an image forming apparatus capable of forming a good image.

1 is a diagram schematically illustrating a configuration of an example of an image forming apparatus according to the present invention. FIG. 2 is a diagram illustrating an outline of a cross-sectional structure of a developing device in the image forming apparatus of FIG. 1. FIG. 3A is a diagram showing the relationship between the developing roller and the magnetic field generator (magnet body) etc. of the developing device of FIG. 2 and the positional relationship between the developing roller and the photosensitive member, and FIG. It is a perspective view which shows D cut surface of the axial end part of a body (magnet body). FIG. 3 is a schematic view of the developing device of FIG. 2 as viewed from the left side in FIG. 2 and with a case lid removed. FIG. 3 is a schematic view of the developing device shown in FIG. 2 as viewed from above in FIG. 2 and omitting a case lid and a developer regulating member. It is a perspective view of a magnetic field generator (magnet body) (illustration of a low magnetic flux density region is omitted). It is a one part perspective view of the magnetic pole part in a magnetic field generator (magnet body). It is a figure which shows the positional relationship of each position of the magnetic pole part of a magnetic field generator (magnet body), and a photoconductor. FIG. 9A is a perspective view of a part of the transport pole in which a low magnetic flux density region is formed, and FIG. 9B is a cut end view at a low magnetic flux density peak position in the low magnetic flux density region. It is a figure which shows the position of each part of a conveyance pole. It is a figure which shows magnetic flux density distribution in the magnet body circumferential direction in each position of the longitudinal direction of a conveyance pole. It is a figure which shows magnetic flux density distribution in the magnet body longitudinal direction in each position of the magnet body circumferential direction of a conveyance pole. The developer supplied from the first conveying member due to the low magnetic flux density region in the conveying pole, in the process of being conveyed by the conveying pole from the catch pole corresponding area to the regulating electrode corresponding area in a quantitative manner It is a figure which shows a mode that it equalizes in a support body longitudinal direction. FIG. 14A shows the developer on the developer carrier when the low magnetic flux density region arrangement pitch of the conveying poles is an integral multiple (including the case of substantially an integral multiple) of the screw blade pitch of the first conveying member. FIG. 14B is a diagram showing a state of uneven distribution of the amount of developer on the developer carrying member when the amount is not so. The upper drawing of FIG. 15 shows the developer transport amount on the developing roller after the amount is regulated by the developer regulating member without increasing the amount of developer supplied to the developer regulating region, according to the developing device of the present invention. The lower drawing of FIG. 15 shows that the developer regulating energy by the developer regulating member can be suppressed to be small according to the developing device according to the present invention. . FIG. 16A is a view showing another example of the developing device according to the present invention, and FIG. 16B is a perspective view of a developer supply auxiliary member that is used in the developing device and has a developer scattering effect. is there. In the developing device provided with the auxiliary member shown in FIG. 16, the developer that is supplied from the first conveying member and has a quantity of uneven screw blade pitch is developed by both the auxiliary member and the low magnetic flux density region in the conveying pole. It is a figure which shows a mode that it equalizes in a support body longitudinal direction. When a conveyance pole is made into the conventional conveyance pole without a low magnetic flux density area, it is a figure which shows a mode that the screw blade pitch nonuniformity of a 1st screw conveyance member of a developer amount is produced in a developer carrier longitudinal direction.

Hereinafter, an example of an image forming apparatus according to the present invention and a developing device used therein will be described with reference to the drawings.
FIG. 1 shows an outline of the configuration of an example PR of an image forming apparatus. The image forming apparatus PR is a tandem type full color printer.

  The printer PR has an endless intermediate transfer belt 7 wound around a driving roller 71 and a roller 72 facing the driving roller 71. The transfer belt 7 is rotated in the counterclockwise direction (arrow direction in the figure) CCW by a driving roller 71 driven by a belt driving unit (not shown).

  A cleaning device 73 that cleans secondary transfer residual toner and the like on the transfer belt 7 faces the roller 72, and a secondary transfer roller 8 faces the drive roller 71. The toner or the like collected by the cleaning device 73 is sent to a waste container by a conveying means (not shown).

  The secondary transfer roller 8 is pressed against a portion of the intermediate transfer belt 7 supported by the driving roller 71 by a pressing unit (not shown), forms a nip portion with the intermediate transfer belt 7, and rotates the intermediate transfer belt 7. It can be rotated following the movement of the recording medium S fed to the nip portion or driven by a drive unit (not shown). A secondary transfer bias can be applied to the secondary transfer roller 8 from a power supply (not shown).

  A fixing device FX is disposed above the intermediate transfer belt 7 and the secondary transfer roller 8, a timing roller pair TR is disposed below, and a recording medium S such as recording paper is accommodated below the fixing device FX. The recording medium storage cassette 9 is disposed.

The fixing device FX includes a fixing heating roller incorporating a heat source such as a halogen lamp heater and a pressure roller pressed against the fixing heating roller.
The recording medium S accommodated in the recording medium accommodation cassette 9 can be pulled out one by one by the medium supply roller 91 and supplied to the timing roller pair TR.

  Between the rollers 71 and 72 around which the intermediate transfer belt 7 is wound, the yellow image forming unit Y, the magenta image forming unit M, and the cyan image forming unit C are arranged along the transfer belt 7 from the roller 72 toward the roller 71. And the black image forming portion K are arranged in this order.

  Each of the image forming units Y, M, C, and K includes a drum-type photosensitive member 1 as an electrostatic latent image carrier, and a charger 2, an exposure device 3, a developing device 4 and the like around the photosensitive member. The cleaning devices 6 are arranged in this order.

  A primary transfer roller 5 is disposed opposite to the photoreceptor 1 of each image forming unit with a belt 7 therebetween. The primary transfer roller 5 is pressed in the direction of the photosensitive member 1 by a pressing unit (not shown), contacts the belt 7 and is driven to rotate, and can bring the belt 7 into contact with the photosensitive member 1.

  A primary transfer bias for primary transfer of the toner image formed on the photoreceptor 1 to the belt 7 can be applied to the primary transfer roller 5 from a power supply (not shown).

  The exposure device 3 can perform image exposure by dot (point) exposure on the photosensitive member 1 by blinking of a laser beam in accordance with image information provided from a personal computer (not shown), an image reading device, or the like.

  The photoconductor 1 in each image forming unit is a negatively chargeable photoconductor here, and can be driven to rotate clockwise in the drawing by a photoconductor drive motor (not shown).

  The charger 2 in each image forming unit is a scorotron charger in this example, and a charging voltage is applied from a power supply (not shown) at a predetermined timing. The charger 2 may be one using a charging roller.

  The developing device 4 in each image forming unit develops an electrostatic latent image formed on the photoreceptor 1 from a power supply (not shown) using a so-called two-component developer mainly composed of a magnetic carrier and a non-magnetic toner. Reversal development can be performed by a developer carrier 41 in the form of a roller to which a bias is applied. The developing device 4 will be further described later.

According to this printer, an image can be formed using one or more of Y, M, C, and K image forming units.
Taking a case where a full color image is formed using all of the image forming portions Y, M, C, and K as an example, first, a yellow toner image is formed in the yellow image forming portion Y, and this is formed on the transfer belt 7 as a primary. Transcript.

  That is, in the yellow image forming portion Y, the photosensitive member 1 is rotated in the clockwise direction in the drawing, and the surface is uniformly charged to a predetermined potential by the charger 2, and the yellow region for the yellow image is transferred from the exposure device 3 to the charged area. Image exposure is performed, and a yellow electrostatic latent image is formed on the photoreceptor 1. This electrostatic latent image is developed by a developer carrier 41 to which a developing bias of the developing device 4 having yellow toner is applied, and becomes a visible yellow toner image. The yellow toner image is primarily transferred onto the transfer belt 7 by the primary transfer roller 5. At this time, a primary transfer bias is applied to the primary transfer roller 5 from a power supply (not shown).

  Similarly, a magenta toner image is formed in the magenta image forming unit M and transferred to the transfer belt 7. A cyan toner image is formed in the cyan image forming unit C and transferred to the transfer belt 7. In the black image forming unit K. A black toner image is formed and transferred to the transfer belt 7.

Yellow, magenta, cyan, and black toner images are formed at a timing when these toner images are transferred onto the intermediate transfer belt 7 in an overlapping manner.
Thus, the multiple toner image formed on the transfer belt 7 moves toward the secondary transfer roller 8 by the rotation of the transfer belt 7.

  On the other hand, the recording medium S is pulled out from the recording medium accommodating cassette 9 by the medium supply roller 91 and is supplied to the timing roller pair TR and is on standby.

  Thus, the recording medium S waiting at the timing roller pair TR is supplied to the nip portion between the transfer belt 7 and the secondary transfer roller 8 in accordance with the multiple toner image sent by the intermediate transfer belt 7. . The multiple toner image is secondarily transferred onto the recording medium S by a secondary transfer roller 8 to which a secondary transfer bias is applied from a power supply (not shown).

  Thereafter, the recording medium S is passed through the fixing device FX, where the multiple toner images are fixed on the recording medium S under heat and pressure. The recording medium S is continuously discharged to the discharge tray DT by the discharge roller pair DR.

  In the primary transfer of the toner image to the belt 7, transfer residual toner or the like remaining on the photoreceptor 1 is cleaned by the cleaning device 6, and secondary transfer residual toner or the like remaining on the belt 7 by the secondary transfer is cleaned by the cleaning device 73. It is cleaned with. Each of these cleaned and removed toners is sent to a waste container by a conveying means (not shown).

  Although the image is formed as described above, the developing device 4 using the two-component developer will be further described. The developing device 4 is shown in FIGS. 2 to 5 and the like, and is an example of the developing device according to the present invention.

  FIG. 2 schematically shows a cross-sectional structure of the developing device 4. FIG. 3A shows the relationship between the developer carrier 41 and the magnetic field generator 42 of the developing device 4 and the positional relationship between the developer carrier 41 and the photosensitive member 1. FIG. 3B is a perspective view showing a D-cut surface Dc of one end 421 of the shaft 420 of the magnetic field generator 42.

  4 is a schematic view of the developing device 4 as viewed from the left side in FIG. 2 and the case lid 40L is removed. FIG. 5 is a schematic view of the developing device 4 as viewed from above in FIG. FIG. 4 is a schematic view showing 40L and a developer regulating member 43 omitted.

  The developing device 4 includes a developing carrier 41 that can be rotated and a magnetic field generator (hereinafter, also referred to as “magnet body”) 42 that is fixedly disposed inside the developing carrier 41. Here, the developer carrier 41 is in the form of a hollow roller with a circular cross section formed of a non-magnetic material, and is externally fitted to the magnet body 42. As shown in FIG. 3A, the left and right bearing portions b1, It is rotatably supported by the magnet body 42 via b2, and can be rotated in the clockwise direction CW in FIG. 2 from one of the left side and the right side. Here, the magnet body 42 is generally formed in a roller shape.

  The developing roller 41 has a disc-like end member e1 fitted to the left end 411 in FIG. 3A and a disc-like end member fitted to the right end 412 in FIG. e2. The magnet body 42 has a shaft portion 420. One end portion 421 of the magnet body 42 protrudes from the left end of the magnet body to the outside of the developing roller 41, and the other end portion 422 protrudes short to the opposite side.

  The shaft end portion 421 of the magnet body 42 protruding from the developing roller 41 is supported by the developing device case 40 (see FIG. 2), and thus the magnet body 42 is a fixedly arranged magnet body that takes a fixed position with respect to the developing device case 40. It has become.

  A recess is formed as a paragraph on the inner surface side of the left end member e1 of the developing roller 41. The left bearing portion b <b> 1 is fitted in the recess and is fitted on the shaft end portion 421 of the magnet body 42. A recess is also formed as a paragraph on the inner surface side of the right end member e2 of the developing roller 41. The right bearing portion b <b> 2 is fitted in the recess and is fitted on the shaft end portion 422 of the magnet body 42.

In this way, the developing roller 41 is externally fitted to the magnet body 42 and is rotatable on the magnet body via the left and right bearing portions b1 and b2.
A recess is also formed as a paragraph on the outer surface side of the left end member e1 of the developing roller 41. A seal ring sr is fitted in the recess and is fitted on the shaft end 421 of the magnet body 42.

  A shaft portion 410 for rotationally driving the developing roller 41 protrudes integrally from an end member e2 on the right side of the developing roller 41, and the shaft portion is rotatably supported on the developing device case 40 by a bearing portion (not shown). A driving gear G (see FIGS. 4 and 5 to be described later) is fitted to the end protruding outside the case 40. When the driving gear G is driven by a developing device driving unit (not shown), the developing roller 41 is rotationally driven in the clockwise direction CW in FIG.

  The magnet body 42 is in the form of a roller as a whole, and when the developing roller 41 is rotationally driven around the magnet body 42, a magnetic brush (developer spike) made of a developer used in the developing device 4 is a developing roller. It has N poles and S poles alternately along the circumferential direction of the magnet body so as to be formed on the peripheral surface of 41. The magnet body 42 will be further described later.

  In the development area Da, the magnetic brush arrives at the gap (development gap) Dg between the photosensitive member 1 and the developing roller 41, and the electrostatic latent image on the photosensitive member 1 is developed to form a visible toner image. . This toner image is transferred from the photoreceptor 1 to a transfer target (here, belt 7).

Here, the development gap Dg in the development region is ensured as follows.
As shown in FIG. 3A, the shaft end portion 421 of the magnet body 42 is fitted and supported by a shaft portion positioning device PS1 provided on a member (not shown) that supports the photosensitive member 1, and the developing roller. The drive shaft portion 410 of 41 is fitted and supported in a shaft portion positioning device PS2 provided on a member (not shown) that supports the photosensitive member 1. Thus, the developing roller 41 is fixedly provided at a fixed position with respect to the photosensitive member 1 and faces the photosensitive member 1 with a predetermined developing gap Dg.

  In FIG. 3A, the shaft portion positioning device PS1 is shown in a simplified manner. However, as shown in FIG. 3B, the device PS1 has a part of the shaft end portion 421 having a D-shaped cross section. A so-called D-cut surface Dc is formed by flat cutting parallel to the center line of the shaft portion 420 so as to form a shape, and a positioning spring is brought into contact with the D-cut surface Dc.

As a method for setting the developing gap between the photosensitive member 1 and the developing roller 41, a roller may be employed in addition to the shaft positioning devices PS1 and PS2 as described above.
For example, a roller having a diameter twice as large as the developing gap Dg from the developing roller 41 is fitted to the shaft portion of the developing roller, and the entire developing device is biased toward the photosensitive member, or the developing roller 41 is biased toward the photosensitive member 1. Thus, the developing gap Dg may be obtained by bringing the roller into contact with the peripheral surface of the photoreceptor 1.

  In addition to the developing roller 41 described above, the developing device 4 also includes a first screw conveying member 44 and a second screw conveying member 45 that supply the developer to the developing roller 41 while stirring and circulating. The first screw conveying member 44 has a rotating blade 441 around a screw blade 442, and the screw conveying member 45 has a rotating shaft 451 around a screw blade 452.

  A partition wall 46 is provided between the screw conveying members 44 and 45. 4 and 5, the partition wall 46 has a developer circulation opening h1 at one end (only the position is shown in FIGS. 4 and 5), and a developer circulation opening h2 at the other end. Is formed.

  The screw conveying members 44 and 45 are rotationally driven by a drive motor (not shown) (which may be the developing roller drive motor), so that the developer circulates in the developing device 4. The developer in the developing device 4 is conveyed to the right side in FIGS. 4 and 5 while the carrier and toner are agitated by the second screw conveying member 45, and is pushed out from the partition opening h2 to the first screw conveying member 44 side. 4 and 5, the developer is supplied to each part of the developing roller 41 while being agitated by the conveying member 44.

  The developing roller 41 supplied with the developer from the screw conveying member 44 carries a magnetic brush made of a developer containing a magnetic carrier and toner on the peripheral surface of the roller by the action of the internal magnet body 42, and is on the photoreceptor 1. The electrostatic latent image can be conveyed to a developing area Da for developing. Further, during the developer conveyance, the amount of developer conveyed to the development area Da (the height of the magnetic brush head) is regulated to a predetermined value by the developer regulating member (developer spike height regulating member) 43. .

  The developer transported to the delivery end side by the screw transport member 44 without being subjected to development moves from the partition wall opening h1 to the screw transport member 45 side. In this way, the developer circulates in the developing device 4.

  As shown in FIGS. 4 and 5, a toner replenishment supply screw 441 is coaxially connected to the screw conveying member 44 from its delivery end side, and is predetermined from a toner replenishment hopper (not shown) to the toner replenishment port TS. The replenished toner supplied at the same timing is sent to the partition opening h1, mixed with the developer already in the apparatus 4, and used for development.

The magnet body 42 will be further described.
FIG. 6 is a perspective view of the magnet body 42 with the illustration of a low magnetic flux density region to be described later omitted.
FIG. 7 is a perspective view of a part of one magnetic pole portion in the magnet body 42.
FIG. 8 is a diagram showing the positional relationship between the positions of the magnetic pole portions m1 to m5 of the magnet body 42 and the photosensitive member 1.

  As shown in FIGS. 2 and 6, the magnet body 42 is formed by circularly arranging magnetic pole portions (magnets having the same polarity on the surface) m 1 to 5 having a fan-shaped cross section perpendicular to the developing roller rotation axis direction. Therefore, it is configured as a roller as a whole. As a magnetic pole portion, a catch pole m1, a transport pole m2, a regulation pole m3, a development pole m4, and a peeling pole m5 that also serves as a sealing pole are provided.

  As shown in FIG. 7, each magnetic pole portion has a fan-shaped center angle θ, a thickness t (however, the transport pole m2 has a low magnetic flux density region with a small thickness as described later), and an axial length L. The sector center angle θ is determined according to the magnetic pole portion.

  The catch pole m1 is a magnetic pole portion that attracts the developer supplied from the first screw conveying member 44 onto the development roller 41, and the regulation pole m3 is at a predetermined gap with respect to the development roller 41 as shown in FIG. This is a magnetic pole portion corresponding to the developer amount restriction region where the developer restriction member 43 is facing.

  The transport pole m2 is a magnetic pole portion for transporting the developer adsorbed on the developing roller 41 by the catch pole m1 to the developer regulating area corresponding to the developer regulating pole m3 as the developing roller 41 rotates. The development pole m4 is a magnetic pole portion corresponding to the development area Da for developing the electrostatic latent image on the photoreceptor 1.

  The peeling pole m5 is a magnetic pole portion that peels and drops the developer that is not consumed in the developing area Da and returns to the developing device along with the rotation of the developing roller 41 from the developing roller 41 by a repulsive magnetic force with the catch pole m1. The peeling electrode m5 also serves as a sealing electrode that suppresses external leakage of the developer.

  The position of each magnetic pole portion in the magnet body 42 in the state where the developing device 4 is set in the printer PR is a perpendicular line (magnet) standing on the surface Dc at the center ce in the circumferential direction of the shaft portion of the D cut surface Dc in FIG. The center angle position corresponding to the center angle amount to reach the magnetic flux density peak of the magnetic pole portion with the same position as the radial line of the body) as the reference position.

  An angle of −30 ° to −45 ° shown in FIG. 10 to be described later, a horizontal axis angle in FIG. 11 to be described later, and an angle of −25 ° to −45 ° in FIG. 12 are the centers on the D-cut surface Dc. With the radial line passing ce as the reference position (0 °), the counterclockwise (counterclockwise) center angle position in FIG. 8 is a plus side angle, and the clockwise (clockwise) center angle position is a minus side angle. Appears.

  It should be noted here that a portion of the magnet body 42 from the catch pole m1 to the regulation pole m3 (in this example, the carry pole m2) has a predetermined pitch along the longitudinal direction of the carry pole as shown in FIG. The point is that a low magnetic flux density region LBr having a low magnetic flux density in the normal direction with respect to the circumferential surface of the transport pole is formed at pt.

  In this example, as shown in FIG. 9A, each of the low magnetic flux density regions LBr is scraped down by the width w in the portion m21 adjacent to the catch pole m1 by the substantially transport pole thickness t. As shown also in (B), the thickness gradually increases and the width decreases toward the regulation pole m3 (from the upstream side to the downstream side in the developing roller rotation direction CW), and a part adjacent to the regulation pole m3 When viewed from the normal direction, m22 is formed in a triangular shape as a whole so that the thickness is the original thickness t and the width is 0 at m22.

  The arrangement pitch in the longitudinal direction of the conveyance pole of the low magnetic flux density region LBr (in this example, the arrangement pitch of the low magnetic flux density peak) pt is an integral multiple (may be substantially an integral multiple) of the pitch of the screw blades 442 of the first screw conveyance member 44. To do.

Specific examples of the transport electrode m2 include the following.
Polarity: S pole Fan-shaped center angle θ: Approximately 60 °
Conveyance pole longitudinal length L: 312 mm
Thickness of portion excluding low magnetic flux density region: 4mm
Maximum surface magnetic flux density: 70 mT,
Low magnetic flux density region LBr: The arrangement pitch pt is the same as the pitch of the screw blades 442 of the conveying member 44 and is 25 mm.
Maximum width w15mm,

In FIG. 10, (1) is the center position of the low magnetic flux density region LBr, and (2), (3), (4) and (5) are 3 mm, 6 mm, 9 mm and 12 mm in the longitudinal direction from the center position (1). Indicates the position.
Further, −30 ° to −45 ° indicate angular positions clockwise (clockwise in FIG. 8) from the radial reference line perpendicular to the D-cut surface.

  According to such conveyance pole conditions, the magnetic flux density in the circumferential direction of the magnet body at each of the parts (1) to (4) of the conveyance pole m2 is as shown in FIG. It can be seen that the magnetic flux density is reduced by adjusting the thickness.

  Further, according to such a transport pole condition, the magnetic flux density distribution at each of the above-mentioned (1) to (5) in the longitudinal direction of the magnet body is approximately as shown in FIG.

  According to the developing device 4 described above, the low magnetic flux density region LBr is formed at an integral multiple pitch (same pitch as the screw blade pitch in the above example) of the pitch of the screw blades 442 in the longitudinal direction of the transport pole m2 of the magnet body 42. Is formed.

  If such a low magnetic flux density region is not provided, as shown in FIG. 18, the unevenness of the screw blade pitch of the first screw conveying member of the developer amount occurs in the longitudinal direction of the developing roller.

  However, in the developing device 4, as shown in FIG. 13, the developer Dp is transported from the region corresponding to the catch pole m1 to the region corresponding to the regulation pole m3, which is held on the developing roller 41 by the magnetic force of the magnet body 42. In the process, a conveying force component is applied also in the direction crossing the conventional developer conveying direction (in the longitudinal direction of the magnet body 42) when there is no such low magnetic flux density region LBr. As a result, the developer Dp is transported toward the regulating member while spreading in an oblique direction with respect to the conventional transport direction.

  Further, since the low magnetic flux density region LBr is formed so as to gradually decrease from the upstream side to the downstream side in the rotation direction of the developing roller 41, as the developer is transported, the low magnetic flux density region LBr extends in the direction crossing the conventional transport direction. The conveying force component is gradually reduced.

  As a result, the developer supply amount unevenness on the developing roller 41 due to the shape of the first screw conveying member 44 in the catch pole m1 corresponding region (in other words, the suction unevenness due to the catch pole m1) reaches the developing roller 41. Is reduced in the process of

  Further, the low magnetic flux density region LBr of the magnet body 42 is an integral multiple of the pitch of the screw blades 442 of the first screw conveying member 44 in the longitudinal direction of the magnet body parallel to the rotation axis direction of the first screw conveying member 44 (the above-mentioned In the example, it is formed with a low magnetic flux density peak interval pt of the same pitch as the screw blade pitch.

  Therefore, the amount of developer reaching the region corresponding to each low magnetic flux density region LBr is made uniform, the difference in developer height between the low magnetic flux density regions is suppressed, and the development due to the shape of the screw conveying member 44 is correspondingly reduced. Unevenness in supplying the developer to the roller 41 is reduced.

  FIG. 14A shows a developing roller when the arrangement pitch pt of the low magnetic flux density region LBr of the conveyance pole m2 is an integral multiple of the pitch of the screw blades 442 of the first conveyance member 44 (same as the blade pitch in the illustrated example). 41 shows how the amount of developer is made uniform on 41. FIG. 14B shows a state in which the developer amount distribution on the developing roller 41 becomes non-uniform when the arrangement pitch of the low magnetic flux density region LBr is not an integral multiple of the pitch of the screw blades 442. Yes.

  Further, according to the developing device 4, it is assumed that the amount of developer supplied to the screw conveying member 44 is obtained by adding an excessive amount to the original amount of developer required for developing the electrostatic latent image on the photoreceptor 1. Needless to say, the amount of developer on the developing roller 41 is made uniform in each part of the developer carrying region of the developing roller, and the occurrence of image defects such as a decrease in image density due to uneven developer supply amount can be suppressed.

  Since it is not necessary to add an excessive amount of developer as described above, the regulation energy for regulating the amount of developer by the developer regulating member 43 can be suppressed to a small value, and as a result, the driving torque of the developing roller 41 and the like ( (Developing device driving torque) can be kept small, and stress applied to the developer can be suppressed to suppress developer deterioration.

  The upper drawing of FIG. 15 shows the development on the developing roller 41 after the amount is regulated by the developer regulating member 43 without increasing the amount of developer supplied to the developer regulating region, according to the developing device 4 according to the present invention. FIG. 15 shows that the developer transport amount can be set to the target transport amount. According to the developing device 4, the developer regulating energy by the developer regulating member 43 can be kept small. Is shown.

  As a result, the printer PR as a whole can form a better image.

  FIG. 16A shows an example of a schematic configuration of another example of the developing device according to the present invention. In the developing device 400, auxiliary members 100 as illustrated in FIG. 16B are arranged below the developing roller 41 at a predetermined pitch in the longitudinal direction. The other points are the same as those of the developing device 4 described above.

  The auxiliary member 100 divides and changes the moving direction of the developer supplied from the first screw conveying member 44 to the developing roller 41 along the rotation axis direction of the developing roller 41 and the screw conveying member 44 (spreads so as to be divided). ) Supply auxiliary member. The arrangement pitch is an integral multiple (may be substantially an integral multiple) of the screw blade pitch of the screw conveying member 44.

  According to the developing device 400, the developer that is supplied from the first screw conveying member 44 and has a quantity of screw blade pitch unevenness by the auxiliary member 100 and the low magnetic flux density region LBr in the conveying pole m <b> 2 is the length of the developing roller 41. Uniform in the direction. FIG. 17 shows such a state.

  The image forming apparatus described above is a tandem type full-color image forming apparatus. However, the present invention can be applied to other types of color image forming apparatuses such as a so-called four-cycle type, multi-function machines, and the like. Is also applicable.

  INDUSTRIAL APPLICABILITY The present invention can be used to provide a developer circulation type developing device that can equalize the amount of developer supplied to the developer carrying member at each part of the developer carrying member and an image forming apparatus equipped with the developing device.

PR printer (an example of an image forming apparatus)
Y Yellow image forming portion M Magenta image forming portion C Cyan image forming portion K Black image forming portion 1 Photoconductor 2 Charger 3 Image exposure device 4, 400 Developing device 40 Developing device case 41 Roller-shaped developer carrier (developing roller) )
42 Magnetic field generator (magnet)
m1 Catch pole m2 Transport pole LBr Low magnetic flux density region pt Low magnetic flux density region arrangement pitch m3 Restriction pole m4 Development pole m5 Separation pole 43 Developer regulation member 44 First screw transport member 441 Rotating shaft 442 Screw blade 45 Second screw transport Member 451 Rotating shaft 452 Screw blade 46 Partition Dp Developer 100 Supply auxiliary member 5 Primary transfer roller 6 Cleaning device 7 Intermediate transfer belt 71 Driving roller 72 Opposing roller 73 Cleaning device 8 Secondary transfer roller 9 Recording medium supply cassette 91 Recording medium Supply roller TR Timing roller pair FX Fixing device DR Recording medium discharge roller pair DT Recording medium discharge tray S Recording medium

Claims (6)

A developing device for developing a latent electrostatic image formed on a latent electrostatic image bearing member in an image forming apparatus using a developer to form a toner image,
A rotationally driveable developer carrier for applying toner to the electrostatic latent image;
A first screw conveying member that is erected on the developer carrier and is driven to rotate to convey the developer in the direction of the rotation axis;
A second screw conveying member that conveys the developer in the direction of the rotation axis by being rotationally driven and in a direction opposite to the first screw conveying member;
While the developer is circulated by the first and second screw conveying members, the developer is supplied from the first screw conveying member to the developer carrying member, and the amount of the developer is regulated by the developer regulating member facing the developer carrying member. A developing device that can be used for developing an electrostatic latent image,
A magnetic developer is used as the developer, and the developer carrier has a built-in magnetic field generator. The magnetic field generator has a catch electrode for adsorbing the developer on the developer carrier, and the developer regulating member. A developer electrode, and a conveying electrode for conveying the developer adsorbed on the developer carrier by the catch electrode to a region corresponding to the regulation electrode. In the direction of the magnetic field generator portion extending from the catch pole to the regulating pole in the direction, the low magnetic flux density region is an integer of the screw blade pitch of the first screw conveying member in the longitudinal direction of the magnetic field generator parallel to the rotational axis direction of the screw conveying member A developing device characterized in that it is formed so as to gradually decrease from the upstream side to the downstream side in the developer carrying member rotation direction at a double magnetic flux density peak interval.   The developing device according to claim 1, wherein the low magnetic flux density region is formed in the transport pole.   The moving direction of the developer supplied from the first screw conveying member to the developer carrying member is divided between the first screw conveying member and the developer carrying member along the rotation axis direction of the screw conveying member. 3. The developing device according to claim 1, wherein the supply auxiliary members to be changed are sequentially arranged, and the supply auxiliary members are arranged at an arrangement pitch that is an integral multiple of a screw blade pitch of the first screw conveying member.   4. The developing device according to claim 1, wherein the developer carrying member is a rotationally driveable developing roller having the magnetic field generator built therein.   5. The developing device according to claim 1, wherein the magnetic developer is a two-component developer mainly composed of toner and a magnetic carrier.   An image forming apparatus capable of forming an electrostatic latent image corresponding to a target image on an electrostatic latent image carrier and developing the electrostatic latent image with a developing device to form a toner image, at least one developing device An image forming apparatus comprising the developing device according to claim 1.

Images