This application claims priority under 35 U.S.C. §119 from Korean Patent Application No. 10-2012-0041146, filed on Apr. 19, 2012, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field
The present general inventive concept relates to a developing device using a dual-component developer including toner and a magnetic carrier, and an image forming apparatus using the developing device.
2. Description of the Related Art
In an electrophotographic image forming apparatus, light that is modulated to correspond to image information is emitted to a photoconductor to form an electrostatic latent image on a surface of the photoconductor, toner is supplied to the electrostatic latent image to develop the electrostatic latent image into a visible toner image, and then the visible toner image is transferred and fused onto a recording medium, thereby printing an image on the recording medium.
An image forming method of an electrophotographic image forming apparatus may be classified into a mono-component development method using a mono-component developer including toner, or a dual-component development method using a dual-component developer including toner and a carrier in which only the toner is used for development on a photoconductor.
In an image forming apparatus using a dual-component development method, a thickness of a developer attached to an outer circumferential surface of a developing roller is regulated by a first regulation member that is spaced apart by a predetermined distance from the outer circumferential surface of the developing roller. In order to obtain a high-quality printed image, a thickness of a developer layer supplied to a development area where the developing roller and a photoconductor face needs to be uniform. If the thickness of the developer layer is not uniform, image density irregularity or toner scattering may occur.
The present general inventive concept provides a developing device that ensures high image quality by forming a uniform developer layer in a longitudinal direction of a development member, and an image forming apparatus using the developing device.
Additional features and utilities of the present general inventive concept will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the general inventive concept.
The foregoing and/or other features and utilities of the present general inventive concept may be achieved by providing a developing device to perform development by supplying toner in a developer in which the toner and a carrier are mixed to an electrostatic latent image formed on an image bearing member, the developing device including a development member to attach the developer to an outer circumferential surface of the development member and supply the toner to the image bearing member, a first regulation member that includes a first regulating portion to form a first doctor gap between the outer circumferential surface of the development member and the first regulating portion, and a second regulation member disposed on an upstream side of the first regulation member in a rotational direction of the development member and includes a second regulating portion to form second doctor gaps between the outer circumferential surface of the development member and the second regulating portion, wherein the second doctor gaps at a central portion and both end portions in a longitudinal direction of the development member are different from each other.
The second doctor gaps at the both end portions may be less than the second doctor gap at the central portion.
The first regulating portion and the second regulating portion may face a same magnetic pole of the development member.
The second doctor gaps may be greater than the first doctor gap.
A difference between the second doctor gap at the central portion and the second doctor gaps at the both end portions may be equal to or less than 1 mm.
The second doctor gaps at the both end portions may range from about 0.5 mm to about 2.0 mm.
The foregoing and/or other features and utilities of the present general inventive concept may also be achieved by providing a developing device to perform development by supplying toner of a developer in which the toner and a carrier are mixed to an electrostatic latent image formed on an image bearing member, the developing device including a development member to attach a developer to an outer circumferential surface of the development member and supply the toner to the image bearing member, a first regulating portion to form a first doctor gap between the outer circumferential surface of the development member and the first regulating portion, and a second regulating portion disposed on an upstream side of the first regulating portion in a rotational direction of the development member to form different pressures of the developer at both end portions and a central portion in a longitudinal direction of the development member.
The second regulation member may form the different pressures such that the pressure of the developer at the both end portions is higher than the pressure of the developer at the central portion.
The second regulating portion may form second doctor gaps between the outer circumferential surface of the development member and the second regulating portion, wherein the second doctor gaps at the both end portions is less than the second doctor gap at the central portion.
A difference between the second doctor gap at the central portion and the second doctor gap at the both end portions may be equal to or less than 1 mm.
The second doctor gap at the both end portions may range from about 0.5 mm to about 2.0 mm.
The foregoing and/or other features and utilities of the present general inventive concept may also be achieved by providing an electrophotographic image forming apparatus using a developer in which toner and a carrier are mixed, the electrophotographic image forming apparatus including an image bearing member on which an electrostatic latent image is formed and a developing device to perform development by supplying toner of a developer in which the toner and a carrier are mixed to an electrostatic latent image formed on an image bearing member, the developing device including a development member to attach a developer to an outer circumferential surface of the development member and supply the toner to the image bearing member, a first regulating portion to form a first doctor gap between the outer circumferential surface of the development member and the first regulating portion, and a second regulating portion disposed on an upstream side of the first regulating portion in a rotational direction of the development member to form different pressures of the developer at both end portions and a central portion in a longitudinal direction of the development member.
The second doctor gaps at the both end portions may be less than the second doctor gap at the central portion.
The first regulating portion and the second regulating portion may face a same magnetic pole of the development member.
The second doctor gaps may be greater than the first doctor gap.
A difference between the second doctor gap at the central portion and the second doctor gaps at the both end portions may be equal to or less than 1 mm.
The second doctor gaps at the both end portions may range from about 0.5 mm to about 2.0 mm.
The foregoing and/or other features and utilities of the present general inventive concept may also be achieved by providing a developing device to supply toner in a developer to a photosensitive drum to form an image on a printing medium, the developing device including a developing roller having an outer circumferential surface to attach the developer thereto and to supply the toner to the photosensitive drum, a first regulation member to form a first doctor gap with the outer circumferential surface of the developing roller, and a second regulation member disposed upstream of the first regulation member to form second doctor gaps with the outer circumferential surface of the developing roller that are larger than the first doctor gap, at least one of the second doctor gaps being different in size than the remaining second doctor gaps.
The second regulating member may uniformly distribute pressure and density of the developer along a length of the outer circumferential surface of developing roller.
The second regulating member may include a central portion to form the at least one of the second doctor gaps to be larger in size than the remaining second doctor gaps.
The central portion may be longer than a width of the printing medium.
The second doctor gaps may have different sizes.
The above and other features and utilities of the present general inventive concept will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:
Reference will now be made in detail to the embodiments of the present general inventive concept, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present general inventive concept while referring to the figures.
A photosensitive drum 10, which is an image bearing member on which an electrostatic latent image is formed, is obtained by forming a photosensitive layer with photoconductivity on an outer circumferential surface of a cylindrical metal pipe. Instead of the photosensitive drum 10, a photosensitive belt obtained by forming a photosensitive layer on an outer surface of a belt that circulates may be used.
A charger 40 charges a surface of the photosensitive drum 10 to a uniform charge potential. The charger 40 may be, for example, a corona charger that charges the surface of the photosensitive drum 10 by causing a corona discharge by applying a bias voltage between a plate electrode 41 and a wire electrode 42, but is not limited thereto. To perform uniform charging, the image forming apparatus may further include a grid electrode 43. Further in the charger 40, a charging roller (not illustrated) that rotates while contacting the photosensitive drum 10 and allows a charge bias voltage to be applied thereto, may be used.
An exposure unit 50 forms an electrostatic latent image on the photosensitive drum 10 by emitting light corresponding to image information to a surface of the photosensitive drum 10, which has been charged. The exposure unit 50 may include a laser scanning unit (LSU) that reflects light emitted from a laser diode (not illustrated) to the photosensitive drum 10 in a main scanning direction by using a polygon mirror (not illustrated), but the present embodiment is not limited thereto.
As illustrated in
A transfer roller 60 is a transfer unit that transfers the toner image formed on the photosensitive drum 10 to a recording medium P. The transfer roller 60 forms a transfer nip by facing the photosensitive drum 10, and a transfer bias voltage is applied to the transfer roller 60. Due to a transfer electric field formed between the photosensitive drum 10 and the transfer roller 60 due to the transfer bias voltage, the toner image developed on the surface of the photosensitive drum 10 is transferred to a recording medium P. Instead of the transfer roller 60, a corona transfer unit using a corona discharge may be used. After the transfer of the toner image to the recording medium P is completed, a portion of the toner remaining on the surface of the photosensitive drum 10 is removed by using a cleaning blade 70.
The toner image transferred to the recording medium P is attached to the recording medium P due to an electrostatic force. A fusing unit 80 fuses the toner image onto the recording medium P by using heat and pressure.
As the toner is delivered to the photosensitive drum 10 from the developing roller 1, the amount of the toner remaining in the first and second areas 110 and 120 is reduced. A toner concentration sensor (not illustrated) to detect a concentration of the toner in the developer may be provided in the developing device 100. The toner concentration sensor may be disposed in, for example, the first area 110. A concentration of the toner may be represented as a ratio of a weight of the toner to a total weight of the developer. The toner concentration sensor may be, for example, a magnetic sensor to directly or indirectly detect a concentration of the toner by measuring an intensity of a magnetic force due to the magnetic carrier within the developer. When the magnetic carrier is greater than the toner in a detection area, an intensity of a magnetic force detected by the magnetic sensor in the detection area is increased, and when the toner is greater than the magnetic carrier in the detection area, an intensity of a magnetic force detected by the magnetic sensor in the detection area is reduced. The magnetic sensor may detect a concentration of the toner by using a relationship between the intensity of the magnetic field detected and the concentration of the toner. Alternatively, the toner concentration sensor may be a capacitive sensor to detect a concentration of the toner by using a difference between dielectric indices of the carrier and the toner. When the concentration of the toner detected by the toner concentration sensor is less than a standard toner concentration, toner may be added to the toner in the developing device 100. For example, toner may be added to the first area 110 from, for example, a toner container (not illustrated). As such, the concentration of the toner in the developing device 100 may be maintained constant. The toner container may be integrally formed with the developing device 100. Alternatively, the toner container may be separated from the developing device 100, and may be individually replaced. The standard toner concentration may be set to, for example, about 7%, but the present embodiment is not limited thereto.
The developing roller 1 is a development member that supplies the toner to the surface of the photosensitive drum 10. The developing roller 1 is disposed to face the photosensitive drum 10. The developing roller 1 may be spaced apart by a development gap from the photosensitive drum 10. The development gap refers to an interval between an outer circumferential surface of the photosensitive drum 10 and an outer circumferential surface of the developing roller 1. The development gap may be set to range from about tens of microns to about several hundreds of microns.
In the second area 120, the carrier is attached to the outer circumferential surface of the developing roller 1 due to a magnetic force of the magnet 12, and the toner is attached to the carrier due to an electrostatic force. Then, a developer layer including the carrier and the toner is formed on the outer circumferential surface of the developing roller 1. A first regulation member 2 regulates a thickness of the developer layer to a predetermined thickness. In general, the first regulation member 2 may be called a doctor blade. The first regulation member 2 includes a first regulating portion 21. There is an interval, that is, a first doctor gap DG, between the first regulating portion 21 and the outer circumferential surface of the developing roller 1. The first doctor gap DG may be set to range from about 0.3 mm to about 1.5 mm.
The magnet 12 may include a plurality of magnetic poles. The plurality of magnetic poles may include a main pole S1 that faces the photosensitive drum 10, and a carrying pole N1, a separation pole S2, a reception pole S3, and a regulation pole N2 which are sequentially arranged from the main pole S1 in a rotational direction of the sleeve 11. The developer in the second area 120 carried by the second agitator 4 is adhered to the outer circumferential surface of the sleeve 11 due to a magnetic force of the reception pole S3. In detail, the carrier is attached to the outer circumferential surface of the sleeve 11 due to the magnetic force of the reception pole S3, and the toner is attached to the magnetic carrier by an electrostatic force. Accordingly, the developer layer is formed on the outer circumferential surface of the sleeve 11. As the sleeve 11 rotates, the developer layer is sequentially delivered from the regulation pole N2, to the main pole S1, the carrying pole N1, and the separation pole S2. The developer at the separation pole S2 is separated from the sleeve 11, retrieved to the second area, and circulated along the first area 110 and the second area 120 by the first agitator 3 and the second agitator 4, respectively.
A process of circulating the developer throughout the developing device 100 will be explained in detail. The developer layer formed on the outer circumferential surface of the sleeve 11 due to the magnetic force of the reception pole S3 is carried to the regulation pole N2 as the sleeve 11 rotates. The first regulation member 2 is disposed to face the regulation pole N2. As the sleeve 11 rotates, the developer layer passes through the first doctor gap DG, so that a thickness of the developer layer is regulated. Accordingly, a portion of the developer layer having a predetermined thickness passes through the first doctor gap DG and a remaining portion of the developer layer is blocked by the first regulation member 2 and is retrieved to the second area 120. The developer layer whose thickness has been regulated is delivered to the main pole S1 as the sleeve 11 rotates. The main pole S1 is located at a development area where the sleeve 11 and the photosensitive drum 10 face each other. In the development area, due to a development bias voltage applied to the sleeve 11, the toner of the developer layer formed on the surface of the sleeve 11 passes through the development gap and is attached to the electrostatic latent image formed on the surface of the photosensitive drum 10. After passing through the development area, a portion of the developer layer remaining on the outer circumferential surface of the sleeve 11 passes through the carrier pole N1, is delivered to the separation pole S2, is separated from the outer circumferential surface of the sleeve 11 at the separation pole S2, and is retrieved to the second area 120.
A process of forming an image by using the developing device 100 constructed as described above will be explained briefly. When a charge bias voltage is applied to the charger 40, the surface of the photosensitive drum 10 is charged to a uniform potential. The exposure unit 50 forms an electrostatic latent image by emitting light corresponding to image information to the surface of the photosensitive drum 10. When a development bias voltage is applied to the developing roller 1 and a development electric field is formed between the developing roller 1 and the photosensitive drum 10, the toner is moved from a developer layer formed on the surface of the developing roller 1 to the surface of the photosensitive drum 10 to develop the electrostatic latent image. A toner image is formed on the surface of the photosensitive drum 10. The recording medium P is fed from a paper feeding unit (not illustrated) to the transfer nip where the photosensitive drum 10 and the transfer roller 60 face each other. Due to a transfer electric field formed due to the transfer bias voltage, the toner image is moved from the surface of the photosensitive drum 10 to the recording medium P and is attached to the recording medium P. When the recording medium P passes through the fusing unit 80, the toner image is fused onto the recording medium P due to heat and pressure, thereby completing image printing. The cleaning blade 70 contacts the surface of the photosensitive drum 10, and removes a portion of the toner remaining on the surface of the photosensitive drum 10 after the transferring.
In order to obtain a high-quality printed image, a thickness of a developer layer supplied to a development area through the first doctor gap DG has to be uniform in a longitudinal direction of the developing roller 1.
In general, the first regulation member 2 faces the regulation pole N2, and is disposed to maintain constant the first doctor gap DG between the developing roller 1 and the first regulation member 2. As illustrated in
Referring to
A thickness of the developer layer at the development area may be represented by using a weight of the developer per unit area of the outer circumferential surface of the developing roller 1, that is, a developer mass per area (DMA). In order to obtain a high-quality printed image, the DMA may be adjusted to range from, for example, about 20 mg/cm2 to about 90 mg/cm2 by ranging the first doctor gap DG from about 0.25 mm to about 0.7 mm. However, as described above, since the first doctor gap DG formed by the first regulation member 2 is less at the both end portions than at the central portion, the DMA is less at the both end portions than at the central portion of the developing roller 1.
A charge amount is a value measured by using an electric field ratio equation-based charge amount measurement device (made by DIT Co., Ltd.) at 2.8 kV and 2000 rpm for 30 seconds. The DMA is a value measured by using a precise scale by absorbing the developer of a 5×40 mm-area at the central portion of the developing roller 1, and at points 60 mm and 120 mm from the central portion toward the both end portions. The DMA is a value obtained by averaging three measurement values.
Referring to
After sequentially passing through the second doctor gap G and the first doctor gap DG, a packing density (PD) of the developer in the development area is shown in Table 1.
A PD is calculated as follows.
It is found that the PD when the second doctor gap G is 1.5 mm is about 10% higher than the PD when the second doctor gap G is 2.2 mm. A high PD means that a pressure and a density of developer in the development area are high. That is, when the PD is high, this means that a space occupied by the developer in the development area is large and a space occupied by air is small, compared to those when the PD is low. The possibility of toner scattering may be reduced by reducing the space occupied by the air.
From the above test, it is found that the DMA at the both end portions may be adjusted by adjusting the second doctor gap G. That is, irregularity of the DMA due to irregularity of the first doctor gap DG may be solved by making the second doctor gap G at the central portion different from the second doctor gap G at the both end portions.
Since the first doctor gap DG at the both end portions is less than the first doctor gap DG at the central portion, as illustrated in
Referring to
The tests 1, 2, and 3 are obtained when a process speed is 141 mm/sec, but the same result may be obtained even when the process speed is 90 mm/sec or 167 mm/sec.
When the second doctor gaps G1, G2, and G3 are less than the first doctor gap DG, since regulation of the developer layer occurs in the second doctor gaps G1, G2, and G3 and thus the first doctor gap DG becomes meaningless, the second doctor gaps G1, G2, and G3 need to be greater than the first doctor gap DG. Also, a difference between the second doctor gaps G1, G2, and G3 may be less than 1 mm. When the difference between the second doctor gaps G1, G2, and G3 is equal to or greater than 1 mm, a difference in a pressure and a density of the developer between the both end portions and the central portion is increased, thereby leading to a difference in an image density between a central portion and both end portions of a printed image.
The second doctor gaps G1 and G3 may be set to range from about 0.5 mm to about 2.0 mm. When the second doctor gaps G1 and G3 are less than 0.5 mm, a pressure of the developer is increased too much, thereby increasing a driving load of the developing roller 1 and degrading the performance of the developer. Also, when the second doctor gaps G1 and G3 are greater than 2.0 mm, the second doctor gap G2 is increased too much, a pressure and a density of the developer at the central portion are reduced too much, and there occurs irregularity in the amount of the developer in a direction in which the developer is delivered in the second area 120 by the second agitator 4, thereby leading to an image density difference in an inclined pattern, a so-called auger mark.
When a pressure and a density of the developer in boundary areas 53 between the central portion and the both end portions are drastically changed, image density irregularity may occur in the boundary areas 53 between the central portion and the both end portions of the printed image. Hence, as illustrated in
Although the second doctor gaps G1, G2, and G3 of the second regulation member 5 are changed in stepwise manner in
Referring to
Although the second regulation member 5 includes the second regulating portion 51 and the concave portion 52 in
As described above, even when the first doctor gap DG at the both end portions is less than that at the central portion, the developer layer may be formed to a uniform thickness in a longitudinal direction of the developing roller 1 by making a pressure and a density of the developer at the both end portions higher than those at the central portion, and the risk of toner scattering may be reduced by increasing a PD of the developer in the development area and the first regulating portion 21.
Although a few embodiments of the present general inventive concept have been shown and described, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the general inventive concept, the scope of which is defined in the appended claims and their equivalents.
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