Patent Application
20070071505
This application claims the benefit under 35 U.S.C. § 119(a) of Korean Patent Application No. 10-2005-0089510, filed on Sep. 26, 2005, in the Korean Intellectual Property Office, the entire disclosure of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an electrophotographic development apparatus and a development method therefor. More particularly, the present invention relates to a hybrid development apparatus using a magnetic carrier and a non-magnetic toner and a development method therefor.
2. Description of the Related Art
Development methods for image-forming apparatuses using an electrophotographic technique such as copy machines, printers, facsimiles, and multifunction machines are roughly classified into a two-component development method, a one-component development method, and a hybrid development method. In the two-component development method, a toner and a magnetic carrier are used. In the one-component development method, an insulating toner or a conductive toner is used. In the hybrid development method, a non-magnetic toner is charged using a magnetic carrier, only charged toners are attached onto a development roller, and the charged toners on the development roller are transferred onto an electrostatic latent image formed on an image receptor and develop the electrostatic latent image.
The two-component development method has advantages of having good charging properties of the toner. In addition, the lifetime of the toner can be prolonged, and an image can be uniformly obtained. On the other hand, a development apparatus using this method is large and complex, and there are problems of dispersion of a toner, attachment of a carrier onto a latent image, and deterioration in durability of a carrier.
In the one-component development method, the development apparatus is compact and dot-reproducibility thereof is excellent. However, there are problems in that durability is low due to deterioration in the quality of a development roller and a charging roller, the price of consumable parts is high because the entire development apparatus must be replaced when the toner is used up, and a selective development is carried out. During the selective development, a toner having a predetermined weight and electric charge is attached from the development roller to the electrostatic latent image. If the selective development is continuously carried out, a toner having less than the predetermined weight and electric charge cannot be used in a development process, which leads to a decrease in a toner usage rate.
In the hybrid development method, the dot-reproducibility is excellent, the lifetime of the apparatus can be prolonged, and a high speed image forming can be obtained. However, if insufficient amount of toners are supplied to the development roller or toners remaining on the development roller after a development is not sufficiently removed, a development ghost can occur. A mechanism by which of the development ghost occurs will now be described with reference to
Accordingly, there is a need for an improved hybrid development apparatus and method that prevents development ghost during printing.
An aspect of exemplary embodiments of the present invention is to address at least the above problems and/or disadvantages and to provide at least the advantages described below. Accordingly, an aspect of exemplary embodiments of the present invention is to provide a simple hybrid development apparatus that can prevent formation of a development ghost, print an image uniformly when printing is continuously performed, and stably print high quality images, and a development method therefor.
According to an aspect of exemplary embodiments of the present invention, there is provided a hybrid development apparatus which forms a magnetic brush of non-magnetic toner and magnetic carriers on the outer circumference of a magnetic roller, supplies the non-magnetic toner to a donor roller, and develops the toner onto an image receptor. The hybrid development apparatus includes a collecting roller which faces the donor roller and the magnetic roller and is disposed on a downstream side of a development area where the donor roller and the image receptor face each other, with respect to the direction of rotation of the donor roller; and a power supply which supplies a supply bias voltage, a development bias voltage, and a collecting bias voltage to the magnetic roller, the donor roller, and the collecting roller, respectively. The supply bias voltage, the development bias voltage, and the collecting bias voltage are tri-level bias voltages having the same voltage duties of the maximum, medium, and minimum voltages, and the phases of the supply bias voltage, the development bias voltage, and the collecting bias voltage are different by 120 degrees in this order.
According to another aspect of exemplary embodiments of the present invention, there is provided a hybrid development method, in which a donor roller is provided which faces an image receptor, a magnetic roller is provided which forms a magnetic brush of a non-magnetic toner and a magnetic carrier on the outer circumference thereof by a magnetic force and is disposed on an upstream side of a development area where the donor roller and the image receptor face each other, with respect to the direction of rotation of the donor roller, and a collecting roller is provided which faces the donor roller and the magnetic roller and is disposed on a downstream of the development area with respect to the direction of rotation of the donor roller. A supply electric field is formed that transfers a toner from the magnetic roller to the development roller in a supply area where the magnetic roller and the donor roller face each other, a development electric field is formed that develops the toner from the donor roller to an electrostatic latent image on the image receptor in the development area, a first electric field is formed that transfers the toner from the donor roller to the collecting roller in a first collecting area where the donor roller and the collecting roller face each other, and a second collecting electric field is formed that transfers the toner from the collecting roller to the magnetic roller in a second collecting area where the collecting roller and the magnetic roller face each other, by applying a supply bias voltage, a development bias voltage, and a collecting bias voltage to the magnetic roller, the donor roller, and the collecting roller, respectively.
According to another aspect of exemplary embodiments of the present invention, there is provided a hybrid development method for a hybrid development apparatus having a donor roller which faces an image receptor, a magnetic roller which forms a magnetic brush of a non-magnetic toner and a magnetic carrier on the outer circumference thereof by a magnetic force and is disposed on an upstream side of a development area where the donor roller and the image receptor face each other, with respect to the direction of rotation of the donor roller, and a collecting roller which is disposed on a downstream side of the development area with respect to the direction of rotation of the donor roller. The hybrid development method includes the collecting roller disposed in opposite to the donor roller and the magnetic roller; the non-magnetic toner supplied from the magnetic roller to the donor roller; and toner remaining on the donor roller collected after passing through the development area among the toner supplied to the donor roller, onto the magnetic roller via the collecting roller.
In the aforementioned aspect of exemplary embodiments of the present invention, the collecting roller may come in contact with the donor roller.
In an exemplary implementation, the collecting roller may rotate in a forward direction with respect to the donor roller.
In another exemplary implementation, the minimum, medium, and maximum voltages of the supply bias voltage, the development bias voltage, and the collecting bias voltage may be the same.
In still another exemplary implementation, the maximum, medium, and minimum voltages of the supply bias voltage, the development bias voltage, and the collecting bias voltage are determined such that a voltage difference of a reverse electric field formed on the development area, a first collecting area where the donor roller and the collecting roller face each other, and a second collecting area where the collecting roller and the magnetic roller face each other is less than a threshold electric potential difference, at which the toner is transferred, in the development area and the first and second collecting areas.
Other objects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention.
The above and other objects, features and advantages of certain exemplary embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings in which:
FIGS. 1(a) and 1(b) are views illustrating a development ghost generation process;
FIGS. 8(a)-8(c) are views illustrating a change in a toner layer on the surface of a donor roller; and
Throughout the drawings, the same drawing reference numerals will be understood to refer to the same elements, features, and structures.
The matters defined in the description such as a detailed construction and elements are provided to assist in a comprehensive understanding of the embodiments of the invention. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. Also, descriptions of well-known functions and constructions are omitted for clarity and conciseness.
A developer 6 stores a non-magnetic toner and a magnetic carrier. The carrier is a magnetic powder type. The stirrer 4 stirs the carrier and the toner to frictionally charge the toner. The toner is not particularly limited, and either a negative or positive charged toner is acceptable.
The donor roller 1 faces the image receptor 10. In case of a contact type development apparatus, the donor roller 1 comes in contact with the image receptor 10 by applying predetermined pressure, whereas in case of a non-contact type development apparatus, the donor roller 1 is separated from the image receptor 10 by a development gap G. The development gap G is approximately 150 to 400 μm, preferably 200 to 300 μm. If the development gap G is less than 150 μm, image fading occurs, and if the development gap G is greater than 400 μm, the toner cannot be readily transferred to the image receptor 10, and thus a sufficient image density cannot be obtained, which leads to a selective development.
The magnetic roller 2 is disposed on an upstream side of a development area where the donor roller 1 and the image receptor 10 face each other, with respect to the direction of rotation of the donor roller 1. Although not shown, the magnetic roller 2 includes a rotating sleeve and a magnet disposed in the sleeve. The surface roughness of the sleeve is approximately 3 to 9 μm. The carrier is attached to the outer circumference of the magnetic roller 2 by the magnetic force of the magnet, and the toner is attached to the carrier by the electrostatic force. Then, a magnetic brush (see
A power supply 30 applies a supply bias voltage V1 to the magnetic roller 2 for supplying the toner onto the donor roller 1 and a development bias voltage V2 to the donor roller 1 for developing the toner onto the image receptor 10. The toner is transferred from the magnetic roller 2 to the donor roller 1 in response to the supply bias voltage V1, and a toner layer is formed on the outer circumference of the donor roller 1. While passing the development area, the toner is attached onto the electrostatic latent image formed on the image receptor 10, and a toner image is formed on the image receptor 10. The toner image is transferred onto a paper P passing a transfer nip where a transfer unit 23 and the image receptor 10 face each other, and is fixed onto the paper P by heat and pressure 25. Thereby, printing is completed. A cleaning blade 24 removes a toner remaining on the image receptor 10 after the transfer of toner is terminated.
As shown in
Where the toner is simply collected from the donor roller 1 to the collecting roller 3, for example, in case of a negatively charged toner, the relationship among the collecting bias voltage V3, the development bias voltage V2, and the supply bias voltage V1 may be V3>V2>V1. In case of a positively charged toner, the relationship may be V3<V2<V1. However, in this case, since the collected toner may be continuously attached onto the collecting roller 3, the capability of collecting toner via the collecting roller 3 and the collecting bias voltage V3 may deteriorate. In addition, the toner attached onto the collecting roller 3 may be attached again onto the donor roller 1.
In the development apparatus according to an exemplary embodiment of the present invention, the toner on the donor roller 1 is collected onto the collecting roller 3, and also the collected toner is transferred onto the magnetic roller 2 again. As shown in
According to an exemplary embodiment of the present invention, operations of a development method for the aforementioned development apparatus are as follows. Hereinafter, it is assumed that the toner is negatively charged.
The magnetic roller 2, the donor roller 1, and the collecting roller 3 face each other as shown in
In an area where the magnetic roller 2 and the donor roller 1 face each other, as shown in
A development electric field created by electric potentials of the image and non-image portions of the image receptor 10 acts on the development area. In the case of the negatively charged toner, the electric potential in the image portion is greater than the electric potential in the non-image portion. According to the development electric field, the toner passes across the development gap G, is developed onto the image portion of the electrostatic latent image formed on the image receptor 10, and the toner image is formed onto the image receptor 10. The toner layer on the surface of the donor roller 1 facing a first collecting area where the donor roller 1 and the collecting roller 3 face each other is not uniform as shown in
In the first collecting area, as shown in
In a second collecting area where the collecting roller 3 and the magnetic roller 2 face each other, as shown in
The collecting roller 3 preferably rotates in a forward direction with respect to the donor roller 1. The forward direction refers to the case when the surface of the collecting roller 3 and the surface of the donor roller 1 are transferred in the same direction in the area where the donor roller 1 and the collecting roller 3 face each other. If the collecting roller 3 rotates in a reverse direction with respect to the donor roller 1, the collected toner on the collecting roller 3 may be attached again onto the surface of the donor roller 1 by passing through the first collecting area.
Referring to
If a potential difference of the reverse electric field is less than a threshold potential difference, the toner is not transferred. Although the potential difference of the reverse electric field is greater than the threshold potential difference, if the difference is substantially small, a movement of the toner by the reverse electric field is also substantially small. The threshold potential difference is determined by various factors such as the charging quantity and mass of the toner, and the resistance and permittivity of each roller. When determining the maximum voltages V1max, V2max and V3max, the medium voltages V1mid, V2mid and V3mid, and the minimum voltages V1min, V2min and V3min of the supply bias voltage V1, the development bias voltage V2, and the collecting bias voltage V3, the difference between the electric potential difference of the reverse electric field and the threshold potential difference is preferably determined to be as small as possible so that the amount of toner transferred during the formation of a reverse electric field can be reduced. More preferably, when determining the maximum voltages V1max, V2max and V3max, the medium voltages V1mid, V2mid and V3mid, and the minimum voltages V1min, V2min and V3min of the supply bias voltage V1, the electric potential difference of the reverse electric field is determined to be smaller than the threshold potential difference so that the toner is not transferred at all when the reverse electric field is created, except for the case of the reversely charged toner. The toner can be effectively transferred in the desired direction in the supply area and the first and second areas.
In an exemplary embodiment of the present invention, a bias voltage, in which the potential difference between the maximum voltage and the minimum voltage is 1.2 KV, frequency is 2.0 KHz, and the potential difference between the minimum voltage and the medium voltage is 0.6 KV, may be transformed to generate the supply bias voltage V1, the development bias voltage V2, and the collecting bias voltage V3 having a phase difference of 120 degrees with respect to each other. The supply bias voltage V1, the development bias voltage V2, and the collecting bias voltage V3 are applied to the magnetic roller 2, the donor roller 1, and the collecting roller 3, respectively. Thus, the power supply 30 may be less expensive if the bias voltages are the same except for their phases, since they can be obtained by changing only their phases using one power source.
Although in the above description, a monochrome development apparatus and a development method therefor have been described, the development apparatus and the development method therefor according to exemplary embodiments of the present invention can be applied to a single-pass type color development apparatus having a tandem configuration and a multi-pass type color development apparatus in which a single image receptor is repeatedly developed and sequentially transferred to a intermediary transfer unit.
Accordingly, a hybrid development apparatus and a development method therefor of the present invention have the following advantages.
First, a toner remaining on a donor roller after developing is collected onto the collecting roller and the collected toner is transferred onto a magnetic roller, so that a development ghost can be prevented from appearing and printing quality is constant during continuous printing.
Second, deterioration of toner collecting capability due to toner dispersion can be prevented by contacting a collecting roller with the donor roller.
Third, the collected toner can be prevented from attaching onto the donor roller by passing through a first collecting area by rotating the collecting roller in a forward direction with respect to the donor roller.
Fourth, a chip power supply can be used since the minimum, medium, and maximum levels, of a supply bias voltage, a development bias voltage, and a collecting bias voltage are the same.
While the present invention has been particularly shown and described with reference to certain exemplary embodiments thereof, it would be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the appended claims and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2005-0089510 | Sep 2005 | KR | national |
