JP3818824B2 - Electrophotographic developing method and apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
According to the present invention, a plurality of development units are arranged facing each other around the image carrier, and the development is selectively performed by forming and releasing magnetic spikes on the toner carrier of each development unit with a time difference. The present invention relates to a developing method and apparatus for electrophotography in which, when forming or releasing magnetic spikes in a color electrophotographic apparatus or the like, contamination with toner or contamination due to carrier pulling does not occur.
[0002]
[Prior art]
As disclosed in Japanese Patent Application Laid-Open No. 11-249424, the applicant of the present application can develop each color by arranging a plurality of development units facing the periphery of the image carrier and selectively switching each development unit. A developing apparatus for color electrophotography as described above is proposed. However, in such a developing apparatus, when the developing unit is switched, fogging by toner or contamination due to carrier pulling may occur.
[0003]
Hereinafter, a configuration of an electrophotographic apparatus in which a plurality of developing units disclosed in JP-A-11-249424 and the like are arranged around an image carrier and development is performed by switching the developing units will be described. To clarify.
3 is a cross-sectional view of the conventional electrophotographic apparatus as described above, FIG. 4 is a cross-sectional view of one developing unit 4 in the vicinity of the developing position of the image carrier 1, and FIGS. It is explanatory drawing at the time of a stop.
[0004]
In FIG. 3, 1 is an image carrier, 2 is an optical scanning unit, 3 is a charger, and 4 to 7 are development units including a developer container. These development units are sequentially switched so that each color can be developed. Has been made. 8 is a recording medium, 9 is a recording medium conveying device, 12 is an intermediate transfer member, 13 is a secondary transfer roller, 14 is a fixing device, and at the time of printing, the image carrier 1 is first charged by the charger 3 for each color. The image scanned by the optical scanning unit 2 is formed on the image carrier 1 to form an electrostatic latent image. Then, each developing unit 4 to 7 develops the image and transfers the image to the intermediate transfer body 12. Then, the image is transferred to a recording medium 8 conveyed from a paper feed cassette (not shown) by a secondary transfer roller 13 and heated by a fixing device 14.・ Pressurize, fix and discharge.
[0005]
FIG. 4 is a cross-sectional view showing a mechanism for switching each development unit between a development state and a non-development state in the vicinity of the development position of the image carrier 1 of the development unit 4, and 21 in the figure is attached to the N and S poles. A toner carrier 22 including a fixed magnet roller 20 having a magnetized permanent magnet is disposed upstream of the developing position A of the toner carrier 21 in the rotation direction, and has an S pole that can rotate around a central axis 23a. This is a fixed sleeve in which a movable magnet 23 is provided. In the above description, the movable magnet 23 has a fan shape in cross section, but the same effect can be obtained even in a rod shape.
[0006]
In the developing unit configured as described above, when developing, the movable magnet 23 is stopped at a position that does not affect the magnetic force of the fixed magnet roller 20 as shown in FIG. At the closest contact point between the fixed sleeve 22 and the fixed sleeve 22, the magnetic lines of force are directed from the first pole (S pole) to the second pole (N pole) of the toner carrier 21, and outside the magnet from the second pole (N pole) to the first pole. It occurs toward the pole (S pole) and forms a closed loop.
[0007]
Further, the third pole (N pole) and the first pole (S pole) arranged opposite to the development position A are magnetic lines of force in the magnet from the first pole (S pole) to the third pole (N pole). ), The outside of the magnet is generated from the third pole (N pole) to the first pole (S pole) to form a closed ring. The developer is carried on the toner carrier 21 along these lines of magnetic force, and the thickness of the developer is regulated at the portion in contact with the peripheral surface of the fixed sleeve 22. Then, it is carried to the development position A, and the latent image on the image carrier 1 is developed. (Hereinafter, the state of the developing unit in FIG. 4A is called heading)
[0008]
When the development is stopped from such a development state, the movable magnet 23 is rotated in the direction opposite to the rotation direction of the toner carrier 21 as shown in FIG. 5, and the toner carrier 21 is rotated as shown in FIG. Move to the nearest contact point (layer thickness regulation position). This rotates the movable magnet 23 in the same direction as the rotation direction of the toner carrier 21 as shown in FIG. 6, Fukukyoku the main pole (S pole) opposite ends of the movable magnet 23 (N _A pole, and N _B There is electrode), when the movable magnet 23 comes close to the vicinity of the layer thickness regulating position, N _a pole and once the developer 24a lifted by the first pole (S pole) magnetic force lines between the rotating and moving magnet 23 side sleeve 21 It is because it will be divided into the side.
[0009]
That is, in this way the developer is divided, the developer of the rotary sleeve 21 side will be recovered but, N _A pole developer of the movable magnet 23 will remain, unstable, flying over the rotating sleeve 21 It is easy to go to and the developer cannot be cut off reliably.
[0010]
However, rotating the movable magnet 23 in a direction opposite to the rotation direction of the toner carrier 21 as shown in FIG. 5, Fukukyoku first movable magnet 23 (N _A pole) and the second pole of the fixed magnet 20 (N pole) When the magnetic shield is made, and further rotating, an attractive magnetic field is generated between the main pole (S pole) of the movable magnet 23 and the second pole (N pole) of the fixed magnet 20, and the developer has both poles. Restrained between. When the movable magnet 23 comes to the layer thickness regulation position, the developer on the toner carrier 21 is a magnetic shield by a repulsive magnetic field formed by the south pole of the movable magnet 23 and the first pole of the toner carrier 21. The boundary is separated from the development position A side to the inner side than the layer thickness regulation position. (Hereinafter, the state of the developing unit in FIG.
[0011]
Therefore, the developer on the developing position A side is collected in the developing unit 4 by the rotation of the toner carrier 21. Thus, the shield magnetic force and the binding magnetic force block the magnetic lines of force between the second pole and the first pole of the toner carrier 21, so that no magnetic field lines pass between the second pole and the first pole, and the developer carries the toner. It stops in the state of FIG. 4 (C) without being conveyed on the body. That, or performed by rotating the movable magnet 23 in a direction opposite to the rotation direction of the toner carrier 21, an unstable state developer remaining in N _A pole portion, flying over the rotating sleeve 21, developing It is possible to prevent the agent from being reliably shut off, and to prevent the developer from being mixed into another developing unit and to disturb the toner image on the photoreceptor.
[0012]
When the movable magnet 23 is moved from the state shown in FIG. 4C to the state shown in FIG. 4A to start development, the developer does not lift up as described above regardless of the direction of rotation. By rotating in the same direction as when development is stopped, that is, in the direction opposite to the rotation direction of the toner carrier 21, first, the main pole (S pole) of the movable magnet 23 and the second pole (N pole) of the fixed magnet 20 are used. Since the binding magnetic force disappears and then the shielding magnetic force disappears, the magnetic force that sequentially restrains the developer in the developer transport direction disappears, and the developer carrying force of the rotating sleeve 21 is recovered smoothly.
[0013]
Also, the mechanism for rotating the movable magnet 23 must be complicated when rotating reversely at the stop and start of development, and the mechanism rotating in one direction can be simplified.
[0014]
However, in switching between the development state and the non-development state in the conventional electrophotographic apparatus configured as described above, for example, the movable magnet 23 is moved from the state shown in FIG. 4C to the state shown in FIG. When starting, if developing DC bias and AC bias are applied as they are, fogging by reverse charge toner occurs, or the layer thickness is still unstable at the moment when the developer contacts the image carrier. It may be worn or carrier pulling may occur. This is the same when the movable magnet 23 is moved from the state shown in FIG. 4A to the state shown in FIG. 4C to stop development, and it is necessary to prevent these phenomena.
[0015]
In order to improve this, for example, in Japanese Patent Laid-Open No. 8-171269, a plurality of developing units are configured to be rotatable by a revolver mechanism or the like, and a desired developing unit is moved to a developing position so that a direct current component and an alternating current are obtained. In an electrophotographic apparatus in which a developing bias composed of components is applied and the developer is allowed to fly onto the image carrier to develop the latent image, the developer on the developing roller is moved to the image carrier by the movement of the developing unit. A color electrophotographic apparatus provided with means for turning on and off a developing AC bias used for image formation at the time of contact and separation, and changing a DC bias voltage so that an electric field is difficult to move the developer to the image carrier. It is shown.
[0016]
[Problems to be solved by the invention]
However, as described above, configuring a plurality of development units to be rotatable requires a complicated mechanism, which increases the size and cost of the apparatus, and requires waiting until the development unit reaches the development position. It becomes a factor that hinders the speeding up. In addition, unlike the case where the developing unit is rotated and positioned at the developing position as described above, in the electrophotographic developing unit described in FIGS. 3 and 4, the toner carrier is always opposed to the image carrier, If the developer is not cut off reliably, an accident may occur in which the toner enters another developing unit. However, when the AC bias is simply turned on and off as in the apparatus of JP-A-8-171269, fogging due to reverse charge toner occurs, fogging or carrier pulling at the moment when the developer contacts the image carrier. Occurrence and the like cannot be prevented, and therefore, an accident in which toner is mixed into another developing unit cannot be prevented.
[0017]
Therefore, in the present invention, in the developing method and apparatus for electrophotography in which development from a plurality of developing units arranged facing the image carrier can be selectively switched to develop each color, it occurs when the developing unit is switched. The challenge is to prevent fogging and carrier pulling.
[0018]
[Means for Solving the Problems]
In order to solve the above problem, the invention described in claim 1 is a method invention,
A plurality of developing units for each color arranged face-to-face on the image carrier is formed by using magnetic lines acting on the toner carrier to form (ear) and release magnetic ears at the developing position of the toner carrier. An electrophotographic developing method in which a switching mechanism is disposed upstream of the developing position in the rotation direction of the toner carrier, and a plurality of colors are developed while sequentially developing each color with a time difference. ,
At the start of development of each of the toner carriers, a first step of applying a surface potential to the image carrier while maintaining the line of magnetic force of the switching mechanism in a heading release state, the toner carrier having the same polarity as the surface potential a second step of applying a low DC bias of the third step of performing transition to the ears out state of the magnetic chain by switching the magnetic field lines acting direction of the switching mechanism from ear out the released state of the magnetic chain, AC bias developing The fourth step of applying the color is sequentially performed to perform development for each color.
[0019]
The invention according to claim 1 is a case of starting development, but at the end of development, as described in claim 2,
Upon completion of the development, the rear end of the latent image on the image bearing member of the fourth releasing the application of the developing AC bias after passing through the developing position step, the magnetic chain by switching the magnetic field lines acting direction of the switching mechanism In the order of the third step of shifting from the formation state to the release state of the magnetic spike, the second step of releasing the application of the DC bias, and the first step of releasing the application of the surface potential of the image carrier. The development bias is released and the development is terminated.
[0020]
The invention according to claim 3, which is an apparatus invention for carrying out the method invention according to claim 1,
A development bias power source in which an alternating current bias is superimposed on a direct current bias; a toner carrier that is connected to the development bias power source and guides toner to a development position of the image carrier;
A heading switching mechanism that uses magnetic lines of force acting on the toner carrier to switch between the formation (heading) state of the magnetic head at the development position of the toner carrier of the developing unit and the heading release state; In the electrophotographic developing apparatus in which the heading switching mechanism is arranged on the upstream side of the developing position in the rotation direction of the toner carrier, the direction of the magnetic force lines of the switching mechanism is maintained in the heading release state at the start of development. After applying a surface potential to the image carrier, a DC bias having the same polarity as that of the surface potential is applied to the toner carrier, and then the direction of the magnetic line of force of the heading switching mechanism is switched to change the ear of the magnetic head. A development bias control mechanism is provided that shifts from the ejection state to the release state and then applies a development AC bias.
[0021]
Further, at the end of development, as described in claim 4,
When the development bias control mechanism has finished development, after the trailing edge of the latent image on the image carrier has passed the development position and after the application of the development AC bias in the magnetic spike formation state, by switching the magnetic field lines of the switching mechanism from the formation state of the magnetic chain out to the release state of the magnetic chain, that it has to perform application release of the surface potential of the image carrier after application release DC bias of said toner carrying member Features.
[0022]
By carrying out the electrophotographic development method in this order and constructing the electrophotographic development apparatus, it is possible to prevent fogging due to reverse charge toner by first applying a DC bias after applying the surface potential, By applying an AC bias after formation (heading) , fogging and carrier pulling caused by unstable developer layer thickness can be prevented.
[0023]
Further, the heading switching mechanism for switching between formation and release of magnetic ears, as described in claim 5,
The heading switching mechanism is characterized in that the heading switching mechanism is composed of a movable magnet that is movable so that a magnetic line of force selectively acts on a magnetic head formation position and a magnetic head formation release position.
[0024]
By configuring the heading switching mechanism in this manner, magnetic heads can be reliably formed and released, and a plurality of development units are arranged around the image carrier to selectively use them. can do. Therefore, the apparatus is not enlarged or complicated using a revolver mechanism or the like as in the conventional apparatus, and further, it is not a factor that impedes speeding up, and the electrophotographic apparatus can be configured at low cost.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be exemplarily described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention only to specific examples unless otherwise specified. Only.
[0026]
FIGS. 1 and 2 are timing charts for explaining an electrophotographic developing method and apparatus according to the present invention, and a diagram showing the state of the developing unit. FIG. 1 is at the start of development, and FIG. 2 is also at the end of development. is there. In the figure, the same components as those in FIGS. 3 and 4 are given the same reference numerals. 1, in the timing chart of FIG. 2, (1) the surface potential of the image carrier 1, (2) a DC bias application conditions of the preparative toner carrying member 21, (3) to the photosensitive drum 1 in the developer (4) is a state of application of an AC bias to the toner carrier 21, (5) is a description of the state of the developer in the developing unit, and (a) to (f) are toner carriers in the respective states. 21 is a diagram showing the state of the movable magnet 23 and the toner 24, AC is an AC bias power source, and DC is a DC bias power source.
[0027]
In the timing chart of FIG. 1 showing the state at the start of development, the movable magnet 23 is attached to the toner carrier 21 as shown in FIG. 1A, which is the same state as FIG. Nearest contact (development position A) . Therefore, a magnetic shield is formed by a repulsive magnetic field between the S pole of the movable magnet 23 and the first pole of the toner carrier 21, and the attractive magnetic field from the S pole of the movable magnet 23 to the second pole of the toner carrier 21 is generated. At the same time, the developer inside the position closest to the movable magnet 23 and the toner carrier 21 is restrained between the two poles. For this reason, the shield magnetic force and the binding magnetic force block the magnetic lines of force between the second pole and the first pole of the toner carrier 21, so that the magnetic lines of force do not pass between the second pole and the first pole. Is stopped without being transported (head cut state).
[0028]
In this state, the surface potential (1), the DC bias (2), and the AC bias (4) are not applied. When the order of development by this development unit comes, a surface potential of +420 V, for example, is first applied to the image carrier 1 as shown in FIG. 1 (1) by a development bias control mechanism (not shown). However, if heading is performed only by applying a surface potential, fogging due to the reverse charge toner occurs, or carrier pulling occurs in the case of two-component development.
[0029]
Therefore, as shown in FIG. 1 (2), after application of the surface potential, a DC bias of, for example, + 250V is applied from the DC bias power source DC by an unillustrated development bias control mechanism before heading at an appropriate time. To do. If the potential difference between the surface potential of the image carrier and the DC bias of the toner carrier is changed from 170 V to 180 V in this way, fogging and carrier pulling can be prevented.
[0030]
Normally, an AC bias is also applied here. However, when the developer first contacts the image carrier 1, the developer layer thickness is unstable. If an AC bias is applied in this state, it is covered or carrier pulling occurs. . Therefore, after a DC bias is applied, a developing bias control mechanism (not shown) waits for a suitable time to move the movable magnet 23 of the fixed sleeve 22 in the direction opposite to the rotational direction of the rotary sleeve 21 as indicated by the arrow 25 in FIG. To a position that does not affect the magnetic force of the fixed magnet roller 20. Then, at the closest contact point between the toner carrier 21 and the fixed sleeve 22, the magnetic lines of force are directed from the first pole (S pole) of the toner carrier 21 to the second pole (N pole) inside the magnet and to the second pole (N pole) outside the magnet. From the pole) to the first pole (S pole), forming a closed ring.
[0031]
Further, the third pole (N pole) and the first pole (S pole) arranged opposite to the development position A are magnetic lines of force in the magnet from the first pole (S pole) to the third pole (N pole). ), The outside of the magnet is generated from the third pole (N pole) to the first pole (S pole) to form a closed ring. Therefore, the developer is carried on the toner carrier 21 along these lines of magnetic force, the layer thickness is regulated at the portion in contact with the peripheral surface of the fixed sleeve 22, and then the first pole is generated by the conveying force due to the rotation of the toner carrier 21. To the developing position A (heading state).
[0032]
When the developer comes into contact with the image carrier 1 as shown in FIG. 1 (3) and the developer layer thickness is stabilized as shown in FIG. 1 (c), the developer bias control mechanism (not shown) causes the developer layer shown in FIG. As in 4), an AC bias power source AC is applied for development, for example, an AC bias having a peak-to-peak voltage Vp-p of 1.2 KV, and development starts.
[0033]
As described above, when a developing bias is applied in the order of surface potential application, DC bias application, developer contact, and AC bias application by a developing bias control mechanism (not shown), the above-described reverse charge toner fog, carrier, Pulling can be prevented.
[0034]
This is exactly the same when the development shown in FIG. 2 is completed. When the development of the rear end of the image on the image carrier 1 is completed, first, as shown in FIG. Then, the application of the AC bias for development is canceled to stop the development, and then the movable magnet 23 is rotated in the direction opposite to the rotation direction of the rotary sleeve 21 as indicated by an arrow 26 in FIG. The body 21 is moved near the nearest point of contact. Then, the developer on the developing position A side is collected in the developing unit 4 by the rotation of the toner carrier 21 as described in FIG. However, during this recovery, the developer layer thickness becomes unstable, and as described above, there is a possibility of covering or carrier pulling, so that the application of the DC bias is canceled on the image carrier 1 side on the toner carrier 21. This is performed after the toner runs out, and after the timing of (2) in FIG. 2, that is, after the state shown in (f) is reached.
[0035]
Then, when the surface potential of the image carrier 1 is finally released, the developing operation is completed, the surface potential is applied to the image carrier 1 for the next image, and the next developing unit has been described above. Do the same operation as.
[0036]
As described above, when the timing of surface potential application, DC bias application, heading developer contact, and AC bias application is controlled by a development bias control mechanism (not shown), fogging or carrier pulling due to the reverse charge toner as described above may occur. Can be prevented.
[0037]
【The invention's effect】
As described above, the electrophotographic development method is carried out in the order as described in claims 1 to 4 and the electrophotographic development apparatus is constructed. Fog due to the charge toner can be prevented, and by applying an AC bias after the formation of the magnetic spike, fogging and carrier pulling caused by unstable developer layer thickness can be prevented.
[0038]
In addition, if the heading changeover mechanism (development unit magnetic head formation and release mechanism) is configured as described in claim 5, magnetic ears can be formed and released reliably, and a plurality of around the image carrier can be formed. Development units can be arranged to selectively use them. Therefore, the apparatus is not enlarged or complicated by using a revolver mechanism or the like as in the conventional apparatus, and further, it is not a factor that impedes speeding up, and the electrophotographic apparatus can be configured at low cost.
[Brief description of the drawings]
FIG. 1 is a diagram showing a state and a timing chart at the start of development according to the present invention.
FIG. 2 is a diagram showing a state and a timing chart when development is stopped according to the present invention.
FIG. 3 is a cross-sectional view of an electrophotographic apparatus configured to switch a developing unit by arranging a plurality of developing units around an image carrier.
4 is a cross-sectional view of one developing unit 4 in the vicinity of the developing position of the image carrier 1. FIG.
FIG. 5 is an explanatory diagram when the movable magnet is rotated in the direction opposite to the rotation direction of the rotary sleeve.
FIG. 6 is an explanatory diagram when the movable magnet is rotated in the same direction as the rotation direction of the rotary sleeve.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Image carrier 4, 5, 6, 7 Developing unit 12 Intermediate transfer body 20 Fixed magnet roller 21 Toner carrier 22 Fixed sleeve 23 Movable magnet (heading switching mechanism)
24 Toner AC AC bias power supply DC DC bias power supply

Claims (5)

A plurality of developing units for each color arranged face-to-face on the image carrier is formed by using magnetic lines acting on the toner carrier to form (ear) and release magnetic ears at the developing position of the toner carrier. An electrophotographic developing method in which a switching mechanism is disposed upstream of the developing position in the rotation direction of the toner carrier, and a plurality of colors are developed while sequentially developing each color with a time difference. ,
At the start of development of each of the toner carriers, a first step of applying a surface potential to the image carrier while maintaining the line of magnetic force of the switching mechanism in a heading release state, the toner carrier having the same polarity as the surface potential a second step of applying a low DC bias of the third step of performing transition to the ears out state of the magnetic chain by switching the magnetic field lines acting direction of the switching mechanism from ear out the released state of the magnetic chain, AC bias developing A development method for electrophotography, wherein the development is performed for each color by sequentially performing the fourth step of applying the. Upon completion of the development, the rear end of the latent image on the image bearing member of the fourth releasing the application of the developing AC bias after passing through the developing position step, the magnetic chain by switching the magnetic field lines acting direction of the switching mechanism In the order of the third step of shifting from the formation state to the release state of the magnetic spike, the second step of releasing the application of the DC bias, and the first step of releasing the application of the surface potential of the image carrier. 2. The electrophotographic developing method according to claim 1, wherein the developing bias is released and the developing is terminated. A development bias power source in which an alternating current bias is superimposed on a direct current bias; a toner carrier that is connected to the development bias power source and guides toner to a development position of the image carrier;
A heading switching mechanism that uses magnetic lines of force acting on the toner carrier to switch between the formation (heading) state of the magnetic head at the development position of the toner carrier of the developing unit and the heading release state; In the electrophotographic developing device in which the heading switching mechanism is disposed upstream of the developing position in the rotational direction of the toner carrier,
After applying a surface potential to the image carrier in a state where the direction of magnetic force lines of the switching mechanism is maintained in a heading release state at the start of development, a direct current bias having the same polarity as the surface potential is applied to the toner carrier. After that, it has a developing bias control mechanism for switching the direction of the magnetic line of force of the heading switching mechanism to shift from the heading state of the magnetic head to the released state, and then applying a developing AC bias. An electrophotographic developing apparatus. When the development bias control mechanism has finished development, after the trailing edge of the latent image on the image carrier has passed the development position and after the application of the development AC bias in the magnetic spike formation state, by switching the magnetic field lines acting direction of the switching mechanism from the formation state of the magnetic chain out to the release state of the magnetic chain, and to perform application release of the surface potential of the image carrier after application release DC bias of said toner carrying member The electrophotographic developing device according to claim 3, wherein the developing device is an electrophotographic developing device. 5. The electrophotography according to claim 3, wherein the heading switching mechanism is configured by a movable magnet that is movable so that magnetic lines of force selectively act on a magnetic ear formation position and a magnetic ear formation release position. Development device.

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