JPH10115984A - Developing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a developing device suitable for a digital image forming device capable of holding a stable image quality being free from the dispersion in the image density of dots or in size by obtaining stable toner stuck quantity even in the case of occurrence of the change of developing potential or the like. SOLUTION: In the developing device developing the electrostatic latent image on a photoreceptor drum 1 by regulating the thickness of layer of the two component developer 3 on a developing sleeve 4 with a doctor 6, and transporting the developer 3 to a developing area, developer activation means activating a movement of the developer 3 on the developing area, for regulating the layer thickness of the developer on the developing sleeve 4 by the doctor 6 so that the developer 3 allowed to pass through the developing area per unit time contains a specific quantity of the toner, and so that almost of the toner in the developer on the developing sleeve 4 allowed to pass through the developing area is adopted for developing the toner stick expected part on the latent image on the photoreceptor drum 1. As the developer activating means for instance, plural magnetic poles are arranged on a position close to the developing area of the magnet roller 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device used for an image forming apparatus such as a copying machine, a facsimile, a printer, etc., and more particularly, to a developing device containing a toner and a carrier carried on the surface of a developer carrying member. The present invention relates to a developing device that develops a latent image on an image carrier by transporting the latent image to a development area facing the image carrier.

[0002]

2. Description of the Related Art Most of electronic data used in recent data processing is digital data, and an image forming apparatus is not a digital image data but a digital type which forms an image based on digital image data instead of analog image data. An image forming apparatus has become necessary. In image formation using this digital image data, due to the nature of the data,
Pixel size and the like are not continuous but discrete (stepwise). In particular, in view of the size of image data, the strength against noise, and the like, each pixel is controlled in two steps, that is, each pixel is controlled by binary whether or not there is a dot having a fixed image density and size. Are preferred.

As a developing device of a conventional image forming apparatus, a two-component developing type developing device using a developer containing a toner and a carrier is known. Image formation based on image data is also performed.

[0004]

However, when a conventional two-component developing type developing device is used, the amount of toner attached changes due to a change in the developing potential and the like, so that each pixel is constituted. It was difficult to keep the dot image density and size constant. In particular, when the development efficiency is increased, the amount of change in the amount of toner attached to a change in the development potential tends to be large. Densities and sizes varied, making it more difficult to maintain stable image quality.

The present invention has been made in view of the above problems, and an object of the present invention is to obtain a stable amount of toner adherence even when the development potential or the like fluctuates.
An object of the present invention is to provide a developing device suitable for a digital image forming apparatus, which can maintain stable image quality without variation in dot image density and size.

[0006]

In order to achieve the above object, according to the first aspect of the present invention, a developer containing a toner and a magnetic carrier carried on the surface of a developer carrier is brought into contact with an image carrier. In the developing device that develops the latent image on the image carrier by being transported to the development area, the developer passing through the development area per unit time contains a certain amount of toner,
When the portion of the latent image formed on the image carrier to which the toner is to be attached passes through the development area, most of the toner in the developer on the developer carrier passing through the development area is It is characterized in that it is configured to be used for development of the toner-attached portion.

In the developing device of the first aspect, the developer containing a fixed amount of toner passes through the developing area. When the portion of the latent image formed on the image carrier to which the toner is to be attached passes through the developing area, most of the toner in the developer on the developer carrier passing through the developing area contains the toner. By being used for development of the portion where the toner is to be adhered, a constant amount of toner always adheres to the portion where the toner is to be attached, even if the development potentials of the portions where the toner is to be attached differ.

According to a second aspect of the present invention, in the developing device according to the first aspect, the developing device further includes a developer regulating member that regulates a layer thickness of the developer on the developer carrier conveyed to the developing region. The developer regulating member regulates the layer thickness of the developer on the developer carrier so that the developer passing through per unit time contains a certain amount of toner, and the developer passing through the development area As most of the toner in the developer on the agent carrier is used for developing the toner-attached portion,
A developer activating means for activating the movement of the developer in the developing area is provided.

In the developing device according to the second aspect, the developer containing a certain amount of toner regulated by the developer regulating member passes through the developing area. Then, by activating the movement of the developer in the developing area by the developer activating means, when the portion where the toner to be attached of the latent image formed on the image carrier is passing through the developing area, the developing area is activated. Most of the toner in the developer on the developer carrier that is passing therethrough is used for developing the portion where the toner is to be attached. Thus, even when the developing potentials of the toner adhering portions differ from each other, a fixed amount of toner always adheres to the toner adhering portions.

According to a third aspect of the present invention, in the developing device according to the second aspect, a plurality of magnetic poles are arranged at positions close to the developing area as the developer activating means.

In the developing device according to the third aspect, the magnetic carrier of the developer passing through the developing region is caused to rotate by a magnetic field formed by a plurality of magnetic poles arranged at positions close to the developing region. By the rotation of the magnetic carrier, the toner is easily released from the magnetic carrier, and is used for developing the toner-attached portion on the image carrier up to the toner adhered to the back side of the magnetic carrier when viewed from the image carrier. To do.

According to a fourth aspect of the present invention, in the developing device according to the second aspect, a rotating magnet is provided at a position close to the developing area as the developer activating means. .

According to the fourth aspect of the present invention, the magnetic field formed in the developing area by the magnet driven to rotate activates the movement of the magnetic carrier of the developer passing through the developing area. By activating the movement of the magnetic carrier in this way,
The toner is easily released from the magnetic carrier, and the toner adhered to the back side of the magnetic carrier when viewed from the image carrier,
It is used for developing a portion where toner is to be attached on the image carrier.

According to a fifth aspect of the present invention, in the developing device of the second aspect, as the developer activating means, an electromagnet to which a current containing an AC component is supplied is provided at a position close to the developing area.

In the developing device according to the fifth aspect, by supplying a current including an AC component to an electromagnet provided in a position close to the developing region, a magnetic field whose intensity fluctuates is formed in the developing region. The movement of the magnetic carrier of the developer passing therethrough is activated. By energizing the movement of the magnetic carrier in this manner, the toner is easily released from the magnetic carrier, and the toner adhered to the back of the magnetic carrier from the image carrier is scheduled to adhere to the toner on the image carrier. To use for the development of the part.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a developing device used in an electrophotographic image forming apparatus will be described below. FIG. 1 is a partial cross-sectional view illustrating a schematic configuration of a developing device according to the present embodiment. The developing device is provided on a side of a cylindrical photosensitive drum 1 used as an image carrier of a copying machine, and has a support case 2 having an opening formed toward the photosensitive drum 1. A developing sleeve 4 serving as a developer carrier for carrying on its surface a developer 3 composed of toner and a magnetic carrier (hereinafter, simply referred to as a “carrier”) having an exposed portion, and fixedly arranged on a shaft 5 a inside the developing sleeve 4. A DC developing bias voltage is applied to a magnet roller 5 composed of a group of fixed magnets, a doctor 6 as a developer regulating member for regulating the layer thickness of the developer 3 carried and conveyed on the developing sleeve 4, and a developing sleeve 4. A power supply 7 to be applied is provided. The polarity of the magnetic pole on the surface of the magnet roller 5 is shown inside the developing sleeve 4 in FIG. The support case 2 forms a developer accommodating portion A for accommodating the developer.
The upper end portion is a doctor supporting portion 2a for supporting the doctor 6.

Further, in this embodiment, in order to favorably activate the movement of the developer 3 due to a magnetic field fluctuation described later, 3 kG
A magnetic carrier having a magnetic susceptibility of at least 1 emu / g or more under an Auss magnetic field was used. More preferably 5e
A magnetic carrier having a magnetic susceptibility of not less than mu / g and not more than 10 emu / g is preferable. The volume average particle diameter of the toner used in the exemplary embodiment was about 7.5 μm, and the volume average particle diameter of the magnetic carrier was about 30 to 100 μm.

Further, as shown in FIG. 1, the developing sleeve 4 and the photosensitive drum 1 are rotated so that their surfaces move in the same direction in the developing area. The ratio of the linear velocity Vs of the developing sleeve 4 to the linear velocity Vp of the photosensitive drum 1 (Vs
/ Vp) is set to an optimum value according to the development conditions, and in this embodiment, Vs / Vp = 2.

The photosensitive drum 1 and the developing sleeve 4 may be in contact with each other in the developing area or may be opposed without contact, but it is preferable to make light contact.

In the developing sleeve 4, a surface layer 4b made of an elastic material is formed on a base 4a made of a non-magnetic rigid material. The developer 3 is carried on the surface layer 4b of the developing sleeve 4. The material of the base 4a is A
1 or non-magnetic SUS can be used.
Sponge rubber is preferable as the material of b. A developer is carried on the surface layer 4b of the developing sleeve 4. The surface of the surface layer 4b of the developing sleeve 4 has a surface roughness R such that it has a concave portion in which a part of the carrier of the developer is buried.
z (for example, 10 to 10 in the same order as the average particle size of the carrier)
(Several tens of μm). More specifically, when a sponge is used as the material of the surface layer 4b, a single-cell foam type in which the average diameter of the cells of the sponge is equal to or less than the average particle diameter of the carrier is preferable. When a non-foamed rubber is used, it is preferable that the average interval between the convex portions in the axial direction of the developing sleeve 4 is equal to or less than the average particle size of the carrier. A particle size equal to or less than the particle size is preferred.

By using the developing sleeve 4 in which the surface layer 4b is made of an elastic material as described above, a predetermined level of the developer thin layer can be easily obtained by compressing the surface layer 4b of the developing sleeve 4. Further, it is possible to prevent a large stress from being applied to the developer 3 and prevent the toner from sticking to the doctor 6. Further, the developing sleeve 4
The thin developer layer is conveyed to the development area, and the thin developer layer is stably pressed against the surface of the photosensitive drum 1 (rigid body) carrying the electrostatic latent image, thereby developing the image faithfully to the electrostatic latent image. Can be performed without unevenness.

FIG. 2 is an enlarged view showing a schematic configuration around the doctor 6 in the developing device of this embodiment. In the present embodiment, the doctor 6 is elastically pressed against the developing sleeve 4 in order to form a thin developer layer having a thickness of three times or less the average particle diameter of the carrier on the developing sleeve 4. . FIG.
, The stepped screw 8 penetrates the elongated hole 6a formed in the doctor 6 and is attached to the doctor support portion 2a of the support case, so that the doctor 6 is positioned inside the doctor support portion 2a in the vertical direction (the direction of arrow B in the drawing). ) Can be moved. A spring 9 is mounted between the upper end surface of the doctor 6 and the inner wall surface of the doctor support 2a in a compressed state.
The doctor 6 is pressed against the developing sleeve 4 by the elastic repulsive force of the doctor. Even when the doctor 6 is brought into contact with the surface of the developing sleeve 4 when the initial setting of the doctor 6 is performed without the developer, the surface roughness of the developing sleeve 4 has the same roughness as the particle size of the magnetic carrier. If so, the developer 3 enters under the doctor 6 and a uniform thin layer can be formed. Although the thickness and uniformity of the thin layer change depending on the surface roughness of the developing sleeve 4, if the surface of the developing sleeve 4 is too smooth, it is difficult to form a uniform thin layer.
If the surface is too rough, the layer thickness will be large, so that a surface roughness equivalent to the carrier particle size is preferable. The pressure of the doctor 6 on the developing sleeve 4 can be adjusted by changing the degree of compression of the spring 13 with a doctor pressure adjusting screw 10 attached to the doctor support 2a so as to contact the upper end of the spring 9.

Since the doctor 6 is movable in the vertical direction as described above, even if an excessive force is applied to the doctor 6, the force can be absorbed by the spring 9. In addition,
An elastic body such as rubber may be used instead of the spring 9 made of wire or the like.

As shown in a modification of FIG. 3, the leaf spring-shaped doctor 6 may be configured to be pressed against the developing sleeve 4 by utilizing the elastic force of the doctor itself. Also in the case of this configuration, an effect is obtained that a uniform thin layer can be formed, as in the configuration of FIG. Also in the configuration of this modified example, if the pressing force of the doctor 6 against the developing sleeve 4 is adjusted by changing the amount of protrusion of the doctor 6, the layer thickness of the developer thin layer formed on the developing sleeve 4 is controlled. be able to.

FIG. 4 is an enlarged view showing a schematic configuration around the developing area in the developing device of this embodiment. In the present embodiment, the developer in the developing area is used so that most of the toner of the developer 3 transported to the developing area is used for developing the toner-attached portion (character portion) of the electrostatic latent image on the photosensitive drum. Developer activating means for activating the movement of the developer. As shown in FIG. 4, the developer activating means in the present embodiment has a plurality of magnetic poles alternately arranged on the surface of the magnet roller 5 facing the developing area, with S poles and N poles. By arranging a plurality of magnetic poles in such a manner as to face the development region, as shown in FIGS. 5A to 5C, the magnetic carrier 3a of the developer passing through the development region is changed according to the magnetic field change. Due to the rotational movement, the kinetic energy makes it easier for the toner to be released from the magnetic carrier 3a, thereby improving the developing ability. Further, the developer activating means shown in FIG. 4 does not require an extra mechanical configuration, and thus has an advantage that the cost can be reduced.

In the developing device having the above structure, the developer 3 on the developing sleeve 4 is conveyed with the rotation of the sleeve 4 in the direction of the arrow, and is regulated by the doctor 6 to be about three times or less the average particle diameter of the carrier. It is thinned. The thinned developer 3 is conveyed to a development area facing the photosensitive drum 1 rotating in the direction of the arrow. In the developing area, almost all of the toner in the developer is applied to the electrostatic latent image formed on the photosensitive drum 1 while the magnetic brush made of the developer 3 on the developing sleeve 4 is in contact with the surface of the photosensitive drum 1. Is supplied, and the electrostatic latent image is visualized.

As described above, according to the present embodiment, most of the toner in the developer 3 conveyed to the developing area is used for developing the portion where the toner is to be attached on the photosensitive drum 1 so that Since a fixed amount of toner can be always adhered, a stable amount of toner can be obtained even when the development potential or the like fluctuates as shown by the characteristic line in FIG. In particular, the developing device according to the present embodiment is suitable as a developing device for a digital image forming apparatus. The characteristic lines b and c in FIG. 6 show the relationship between the developing potential and the amount of toner adhered to the conventional developing device as a comparative example. Here, the characteristic line c
Indicates a case where the developing ability is increased as compared with the characteristic line b.

In particular, according to the present embodiment, the magnetic carrier 3 of the developer 3 passing through the developing region has a simple and inexpensive configuration in which a plurality of magnetic poles are arranged at positions close to the developing region.
a is rotated to facilitate release of the toner from the magnetic carrier, and the toner adhering to the back side of the magnetic carrier 3a as viewed from the photosensitive drum 1 is used for developing the portion of the photosensitive drum 1 where the toner is to be attached. Can be.

In the above embodiment, a plurality of magnetic poles are arranged at a position close to the developing area. However, instead of this configuration, as shown in FIG. The magnet 11 may be provided at a position close to and opposed to the developing area with the developing sleeve 4 interposed therebetween. In the case of this configuration, the magnetic field changes even in the developing area formed by the magnet 11 that is driven by rotation, so that the movement of the magnetic carrier of the developer 3 passing through the developing area is activated, and the toner is easily released from the magnetic carrier. The toner attached to the back side of the magnetic carrier 3a when viewed from the body drum 1
It can be used for the development of the portion where the toner is to be attached. In particular, by using the rotating magnet 11 serving as the developer activating means also as the main developing pole, a strong magnetic force for securely carrying the magnetic carrier on the developing sleeve 4 can be secured.

As shown in FIG. 8, an electromagnet 12 that supplies a current containing an AC component to a coil 12b wound around an iron core 12a may be provided at a position close to and opposed to the developing area with the developing sleeve 4 interposed therebetween. . Also in this configuration, the magnetic field changes in the developing region formed by the rotationally driven magnet 11 so that the movement of the magnetic carrier of the developer 3 passing through the developing region is activated, and the toner is easily released from the magnetic carrier. Even the toner adhered to the back side of the magnetic carrier 3a as viewed from the body drum 1 can be used for developing the portion of the photosensitive drum 1 where toner is to be attached. In particular, the electromagnet 12
, The coil 12 of the electromagnet 12
Since the magnitude of the magnetic force can be freely set by adjusting the current supplied to b, the optimum magnetic force can be easily set.

In the above embodiment, the developing device using the thin-layer contact developing system of the two-component developer containing the toner and the carrier has been described. However, the present invention is also applied to the developing device employing the non-contact developing system. Applicable. Further, the present invention can be applied to a case where a DC developing bias voltage is applied and a case where an AC developing bias voltage on which a DC voltage is superimposed is applied, regardless of the type of the developing bias. (Hereinafter, margin)

[0032]

According to the first, second, third, fourth or fifth aspect of the present invention, most of a certain amount of toner in the developer passing through the developing area is scheduled to adhere to the latent image on the image carrier. When the toner is used for the development of the portion, a fixed amount of toner is always adhered to the portion where the toner is to be adhered, so that a stable amount of toner adhesion can be obtained even when the development potential or the like fluctuates. Therefore, there is an effect that it is possible to provide a developing device suitable for a digital image forming apparatus capable of maintaining stable image quality without variation in dot image density and size.

In particular, according to the third aspect of the present invention, the magnetic carrier of the developer passing through the developing region is rotated by a simple and inexpensive configuration in which a plurality of magnetic poles are arranged at positions close to the developing region, and the toner is Is easily released from the magnetic carrier, and the toner adhering to the back side of the magnetic carrier when viewed from the image carrier is used for developing the toner adhering portion on the image carrier. There is an effect that the toner can be attached.

In particular, according to the invention of claim 4 or 5, the movement of the magnetic carrier of the developer passing through the developing area is activated, and the toner is easily released from the magnetic carrier.
Since the toner adhering to the back side of the magnetic carrier when viewed from the image carrier is used for developing the toner adhering portion on the image carrier, a constant amount of toner can always be adhered to the toner adhering portion. effective.

In particular, according to the fourth aspect of the present invention, by using the rotating magnet as a developing main pole, it is possible to secure a strong magnetic force for securely supporting the magnetic carrier on the developer carrier. There is.

In particular, according to the fifth aspect of the present invention, since the electromagnet is used, the magnitude of the magnetic force can be freely set by adjusting the current supplied to the electromagnet. There is an effect that it can be set.

[Brief description of the drawings]

FIG. 1 is a front sectional view showing a schematic configuration of a developing device according to an embodiment of the present invention.

FIG. 2 is an enlarged view showing a schematic configuration around a doctor of the developing device.

FIG. 3 is an enlarged view showing a schematic configuration around a doctor of a developing device according to a modification.

FIG. 4 is an enlarged view showing a schematic configuration around a developing area of the developing device according to the embodiment.

FIGS. 5A to 5C are explanatory views showing a rotational movement of a magnetic carrier in a developing region.

FIG. 6 is a characteristic diagram showing a relationship between a development potential and a toner adhesion amount.

FIG. 7 is an enlarged view showing a schematic configuration around a developing area of a developing device according to a modification.

FIG. 8 is an enlarged view showing a schematic configuration around a developing area of a developing device according to another modification.

[Explanation of symbols]

 Reference Signs List 1 photosensitive drum 2 support case 2a doctor support part 3 developer 3a magnetic carrier 4 developing sleeve 4a base 4b surface layer 5 magnet roller 6 doctor 6a long hole 7 power supply 8 stepped screw 9 spring 10 doctor pressure adjusting screw 11 magnet 12 electromagnet

Claims (5)

[Claims] 1. A latent image on an image carrier is developed by transporting a developer containing a toner and a magnetic carrier carried on the surface of the developer carrier to a development area facing the image carrier. In the developing device, when the developer passing through the developing area per unit time contains a certain amount of toner, and the toner adhering portion of the latent image formed on the image carrier is passing through the developing area, A developing device wherein most of the toner in the developer on the developer carrier passing through the developing area is used for developing the portion where the toner is to be attached. 2. The developing device according to claim 1, further comprising a developer regulating member for regulating a layer thickness of the developer on the developer carrier conveyed to the developing area, wherein the developer passes through the developing area per unit time. The developer regulating member regulates the layer thickness of the developer on the developer carrier so that the developer contains a certain amount of toner. A developing device provided with developer activating means for activating the movement of the developer in the developing area so that most of the toner in the developer is used for developing the toner-attached portion. 3. The developing device according to claim 2, wherein a plurality of magnetic poles are arranged at positions close to said developing area as said developer activating means. 4. A developing device according to claim 2, wherein a rotating magnet is provided at a position close to said developing area as said developer activating means. 5. The developing device according to claim 2, wherein an electromagnet to which a current containing an alternating current component is supplied is provided at a position close to said developing region as said developer activating means.