The present application is based on and claims priority from Japanese Patent Application No. 2007-130588, filed on May 16, 2007 in the Japan Patent Office, the entire contents of which are hereby incorporated herein by reference.
1. Field of the Invention
Exemplary aspects of the present invention relate to a development device and an image forming apparatus, and more particularly, to a development device and an image forming apparatus for forming a high quality image without uneven image density.
2. Description of the Related Art
A related-art image forming apparatus, such as a copier, a facsimile machine, a printer, a plotter, or a multifunction printer having at least one of copying, printing, scanning, plotter, and facsimile functions, forms a toner image on a recording medium (e.g., a sheet) according to image data by electrophotography. For example, a charging device charges a surface of a latent image carrier. An optical writer emits a light beam onto the charged surface of the latent image carrier to form an electrostatic latent image on the latent image carrier according to the image data. A development device develops the electrostatic latent image with a developer (e.g., toner) to form a toner image on the latent image carrier. The toner image is transferred from the latent image carrier onto a sheet. A fixing device applies heat and pressure to the sheet bearing the toner image to fix the toner image on the sheet. Thus, the toner image is formed on the sheet.
Recently, in order to satisfy an increasing demand for full color image formation, an image forming apparatus may include a plurality of development devices to form toner images in colors different from each other. The toner images are superimposed on a latent image carrier to form a color toner image thereon.
One example of a related-art image forming apparatus includes development devices using a toner cloud development method. The development devices do not contact a latent image carrier and form a toner cloud between the latent image carrier and development rollers included in the development devices due to an effect of an alternating current electrical field generated by an alternating current voltage source. Toner particles in the toner cloud may be attracted to a latent image formed on the latent image carrier and used for development of the latent image. For example, while the latent image carrier bearing the latent image rotates, the development devices adhere toner particles in different colors, respectively, to the latent image on the latent image carrier. In other words, a toner image in one color may be superimposed on another toner image in a different color, thereby forming a full color toner image.
Another example of a related-art image forming apparatus includes a development device using an effect of an electrical field curtain. Such development device also does not contact a latent image carrier and forms the electrical field curtain between the latent image carrier and a development roller included in the development device by application of an alternating current voltage to electrodes. The electrical field curtain may convey toner particles to the latent image carrier so as to form a toner image thereon.
However, due to the alternating current electrical field formed between the latent image carrier and the development device, some toner particles may be removed from the toner image formed on the latent image carrier and return to an inside of the development device, resulting in a faulty image. In addition, the toner particles may be mixed with another toner particles in a different color.
Therefore, in order to form a high-quality full color toner image, there is a need for a technology to form a toner cloud without generating an alternating current electrical field between a latent image carrier and a development device.
This specification describes a development device according to exemplary embodiments of the present invention. In one exemplary embodiment of the present invention, the development device includes a toner carrier, a toner supplier, and a surface electrical potential controller. The toner carrier is configured to oppose the latent image carrier and carry toner particles to be adhered to a latent image formed on the latent image carrier. The toner supplier is configured to supply the toner particles to the toner carrier and have a time constant τ1 of a surface electrical potential change of a surface of the toner carrier. The surface electrical potential controller is configured to control a surface electrical potential of the toner carrier and have a time constant τ2 of a surface electrical potential change of the surface of the toner carrier. The time constant τ2 is smaller than the time constant τ1. The toner carrier includes a plurality of electrodes and a voltage supplier. The plurality of electrodes are provided aligned in parallel on the surface of the toner carrier in a predetermined direction and electrically insulated from each other. The voltage supplier is configured to supply the plurality of electrodes with a voltage so as to periodically switch electrical fields between each electrode of the plurality of electrodes to cause the toner particles carried on the surface of the toner carrier to form a cloud while hopping on the surface of the toner carrier.
This specification further describes a development device according to exemplary embodiments of the present invention. In one exemplary embodiment of the present invention, the development device includes a toner carrier, a toner supplier, a toner collector, and a surface electrical potential controller. The toner carrier is configured to oppose the latent image carrier and carry toner particles to be adhered to a latent image formed on the latent image carrier. The toner supplier is configured to supply the toner particles to the toner carrier. The toner collector is configured to collect the toner particles from the toner carrier. The surface electrical potential controller is configured to control a surface electrical potential of the toner carrier and supplied with a bias. The toner carrier includes a plurality of electrodes and a voltage supplier. The plurality of electrodes are provided aligned in parallel on the surface of the toner carrier in a predetermined direction and electrically insulated from each other, and supplied with a bias having an average electrical potential substantially equal to an average electrical potential of the bias applied to the surface electrical potential controller. The voltage supplier is configured to supply the plurality of electrodes with a voltage so as to periodically switch electrical fields between each electrode of the plurality of electrodes to cause the toner particles carried on the surface of the toner carrier to form a cloud while hopping on the surface of the toner carrier.
This specification further describes an image forming apparatus according to exemplary embodiments of the present invention. In one exemplary embodiment of the present invention, the image forming apparatus includes a latent image carrier and a development device. The latent image carrier is configured to carry a latent image. The development device is configured to develop the latent image carried by the latent image carrier and includes a toner carrier, a toner supplier, and a surface electrical potential controller. The toner carrier is configured to oppose the latent image carrier and carry toner particles to be adhered to a latent image formed on the latent image carrier. The toner supplier is configured to supply the toner particles to the toner carrier and have a time constant τ1 of a surface electrical potential change of a surface of the toner carrier. The surface electrical potential controller is configured to control a surface electrical potential of the toner carrier and have a time constant τ2 of an electrical potential change of the surface of the toner carrier. The time constant τ2 is smaller than the time constant τ1. The toner carrier includes a plurality of electrodes and a voltage supplier. The plurality of electrodes are provided aligned in parallel on the surface of the toner carrier in a predetermined direction and electrically insulated from each other. The voltage supplier is configured to supply the plurality of electrodes with a voltage so as to periodically switch electrical fields between each electrode of the plurality of electrodes to cause the toner particles carried on the surface of the toner carrier to form a cloud while hopping on the surface of the toner carrier.
A more complete appreciation of the invention and the many attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:
In describing exemplary embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this specification is not intended to be limited to the specific terminology so selected, and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner and achieve a similar result.
Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, in particular to
The image forming apparatus 100 includes a photoconductor 50, a plurality of rollers 51, 52, 53, and 54, development devices 30M, 30C, 30Y, and 30K, chargers 56M, 56C, 56Y, and 56K, primary transfer rollers 55M, 55C, 55Y, and 55K, a registration roller pair 58, a secondary transfer roller 59, and a fixing device 60. The development devices 30M, 30C, 30Y, and 30K include casings 31M, 31C, 31Y, and 31K, agitators 32M, 32C, 32Y, and 32K, flare rollers 33M, 33C, 33Y, and 33K, supply rollers 34M, 34C, 34Y, and 34K, toner thickness controllers 35M, 35C, 35Y, and 35K, sealing members 36M, 36C, 36Y, and 36K, collecting rollers 37M, 37C, 37Y, and 37K, and flickers 38M, 38C, 38Y, and 38K, respectively.
The image forming apparatus 100 may be a copier, a facsimile machine, a printer, a plotter, a multifunction printer having at least one of copying, printing, scanning, plotter, and facsimile functions, or the like. According to this non-limiting exemplary embodiment, the image forming apparatus 100 forms a full color toner image by superimposing magenta, cyan, yellow, and black toner images on each other on the photoconductor 50. However, the image forming apparatus 100 is not limited to the full color image forming apparatus and may form a color and/or monochrome image with other structure.
The photoconductor 50, having an endless belt shape and serving as a latent image carrier, is looped over the plurality of rollers 51, 52, 53, and 54, and driven to rotate by a driver (not shown).
The development devices 30M, 30C, 30Y, and 30K oppose the photoconductor 50 and form magenta, cyan, yellow, and black toner images, respectively.
When the photoconductor 50 is uniformly charged by the charger 56M and exposed to a light beam 57M modulated from magenta image data by a writer (not shown), serving as an exposure device, an electrostatic latent image is formed on the photoconductor 50. The development device 30M develops the electrostatic latent image to form a magenta toner image. After the primary transfer roller 55M transfers the magenta toner image onto the photoconductor 50, a discharger (not shown) discharges the photoconductor 50 to prepare for subsequent image formation.
Thereafter, when the photoconductor 50 is uniformly charged by the charger 56C and exposed to a light beam 57C modulated from cyan image data by the writer, an electrostatic latent image is formed on the photoconductor 50. The development device 30C develops the electrostatic latent image to form a cyan toner image to be superimposed on the magenta toner image. After the primary transfer roller 55C transfers the cyan toner image onto the photoconductor 50, the discharger discharges the photoconductor 50 to prepare for subsequent image formation.
Thereafter, when the photoconductor 50 is uniformly charged by the charger 56Y and exposed to a light beam 57Y modulated from yellow image data by the writer, an electrostatic latent image is formed on the photoconductor 50. The development device 30Y develops the electrostatic latent image to form a yellow toner image to be superimposed on the magenta toner image and the cyan toner image. After the primary transfer roller 55Y transfers the yellow toner image onto the photoconductor 50, the discharger discharges the photoconductor 50 to prepare for subsequent image formation.
Thereafter, when the photoconductor 50 is uniformly charged by the charger 56K and exposed to a light beam 57K modulated from black image data by the writer, an electrostatic latent image is formed on the photoconductor 50. The development device 30K develops the electrostatic latent image to form a black toner image to be superimposed on the magenta toner image, the cyan toner image, and the yellow toner image. The primary transfer roller 55K transfers the black toner image onto the photoconductor 50, thereby forming a full color toner image.
After a feeding device (not shown) feeds a recoding medium P (e.g., a recording sheet), the recording medium P is aligned by the registration roller pair 58 and conveyed to a secondary transfer portion at a predetermined timing. When the secondary transfer roller 59 is supplied with a transfer bias from a power supply, the secondary transfer roller 59 transfers the full color toner image formed on the photoconductor 50 onto the recording medium P.
After the fixing device 60 fixes the full color toner image on the recording medium P, the recording medium P bearing the fixed full color toner image is discharged to an outside of the image forming apparatus 100. After the full color toner image is transferred to the recording medium P, a cleaner (not shown) removes residual toner, and the like, remaining on the photoconductor 50.
According to this exemplary embodiment, the magenta, cyan, yellow, and black toner images may be superimposed on each other onto a single photoconductor, that is, the photoconductor 50 to form the full color toner image on the photoconductor 50. Therefore, compared to a tandem type image forming apparatus in which magenta, cyan, yellow, and black toner images are formed on four photoconductors, respectively, the magenta, cyan, yellow, and black toner images may be superimposed on the photoconductor 50 more precisely without being shifted from each other. Thus, the image forming apparatus 100 may form a high-quality full color toner image.
Moreover, according to this exemplary embodiment, the flare rollers 33M, 33C, 33Y, and 33K do not contact the photoconductor 50, preventing wear of the photoconductor 50 and thereby providing improved durability of the photoconductor 50. Further, no alternating current electrical field is formed in a vicinity of each development area of the photoconductor 50. Thus, a subsequent development process does not mechanically and electrically affect a toner image already formed on the photoconductor 50, preventing scavenging, color mixing, or the like, and thereby enabling formation of a high-quality image stably over a long period of time. In other words, the development devices 30M, 30C, 30Y, and 30K develop the electrostatic latent image on the photoconductor 50 without contacting the photoconductor 50, and a direct current electric field generates near the electrostatic latent image. Accordingly, the magenta, cyan, yellow, and black toner images may be superimposed on the photoconductor 50, forming a high-quality full color image without image shift with a simple structure.
Referring to
When aluminum is evaporated onto the glass substrate 1, the electrode pattern 2 including the plurality of electrodes 21, 22, 23, . . . 2n arranged at a pitch p μm in a direction of movement of the photoconductor 50 (depicted in
As illustrated in
This formation of the flare when the substrate 4 faces the photoconductor 50, serving as a latent image carrier, may cause the toner particles to adhere to the latent image formed on the photoconductor 50 and develop the latent image. Such development method is called a “flare development”, and a roller shaped toner carrier (e.g., the flare rollers 33M, 33C, 33Y, and 33K depicted in
Referring to
The casing 31K stores a developer (e.g., toner). The agitator 32K agitates the toner in the casing 31K. The flare roller 33K, serving as a toner carrier, opposes the photoconductor 50 (depicted in
As illustrated in
The common electrode 33A is circumferentially provided in one end of the flare roller 33K in an axial direction of the flare roller 33K and supplies the plurality of electrodes 20A with a voltage of a phase A, while the common electrode 33B is circumferentially provided in another end of the flare roller 33K in the axial direction of the flare roller 33K and supplies the plurality of electrodes 20B with a voltage of a phase B opposite to the phase A. As illustrated in
As illustrated in
The electrodes 20A and 20B are provided at a predetermined distance on the supporting substrate 4K, and the surface protection layer 3K is formed thereover and includes an organic or inorganic insulating material.
Lines extending from the respective electrodes 20A and 20B represent conductive lines for supplying the respective electrodes 20A and 20B with a voltage. A black circle portion of the respective lines in which the respective lines overlap each other is electrically connected, while the other portions are electrically insulated.
Therefore, driving voltages of two different phases (e.g., phases A and B) are applied by a power supply of the development device 30K (depicted in
As illustrated in
The flare roller 33K is driven to rotate, with one end of a rotation axis of the flare roller 33K being connected to an odd number electrode (e.g., the common electrode 33A), while another end thereof being connected to an even number electrode (e.g., the common electrode 33B).
Therefore, the toner particles supplied to the flare roller 33K from the supply roller 34K (depicted in
By contrast, when the toner particles do not transfer to the photoconductor 50, the flare roller 33K conveys them to an area facing the collecting roller 37K (depicted in
The supporting substrate 4K (depicted in
The electrodes 20A and 20B each is formed by forming a conductive material such as Al (aluminum), Ni—Cr (nickel-chromium), and the like with a thickness of from about 0.1 μm to about 10 μm, and more preferably from about 0.5 μm to about 2.0 μm on the supporting substrate 4K, and formed into a desired shape in a pattern by using a photolithographic technique.
As illustrated in
P=R+L (1)
When the toner particles remain in a gap between the electrodes 20A and 20B, an electrical field in a substantially horizontal direction moves the toner particles to the adjacent electrodes 20A and 20B on the supporting substrate 4K. By contrast, most of the toner particles being on the electrodes 20A and 20B may fly to separate from a surface of the supporting substrate 4K at an initial velocity having at least a vertical component.
In particular, since the toner particles being around an edge surface of the electrodes 20A and 20B jump over the adjacent electrodes 20A and 20B, when the electrode width L is large, the increasing amount of the toner particles being on the electrodes 20A and 20B may move for a long distance. However, when the electrode width L is too large, an electrical field strength around a center of the electrodes 20A and 20B may decrease, thereby the toner particles may adhere to the electrodes 20A and 20B, resulting in reduction of hopping efficiency.
According to this exemplary embodiment, the toner particles may efficiently hop on the flare roller 33K at a decreased voltage when the electrodes 20A and 20B of the flare roller 33K have an appropriate width for toner particles to hop.
Since the electrical field strength is determined based on a relation between a distance and an applied voltage, the smaller the electrode gap R is, the larger the electrical field strength is, so that the toner particles may obtain an initial velocity of hopping. However, when the toner particles move from the electrode 20A to the electrode 20B, or from the electrode 20B to the electrode 20A, a movement distance of the toner particles may be shortened. Accordingly, a period of hopping time may be shortened unless a drive frequency increases. However, according to this exemplary embodiment, the toner particles may be efficiently conveyed and may hop on the flare roller 33K at a decreased voltage when the electrode gap R of the flare roller 33K is appropriate for the toner particles to hop on the flare roller 33K.
In addition, a thickness of the surface protection layer 3K over the surfaces of the electrodes 20A and 20B may also affect the electrical field strength of the surface of the electrodes 20A and 20B, and in particular, the thickness thereof may substantially affect a line of electric force of a vertical component and the toner hopping efficiency.
That is, by appropriately setting the electrode width L, the electrode gap R, and the thickness of the surface protection layer 3K, the toner particles may efficiently hop on the flare roller 33K at a decreased voltage.
According to this exemplary embodiment, the electrode width L may be not smaller than one time and not larger than 20 times an average particle size of the toner particles. The electrode distance R may be not smaller than one time and not larger than 20 times the average particle size of the toner particles.
Referring to
According to this exemplary embodiment, the driving waveforms of the voltages applied to the electrodes 20A and 20B include a rectangular wave alternately turned by 180 degrees, that is, a rectangular wave in which adjacent phases are shifted from each other by 180 degrees, as illustrated in
In addition, the voltage applied to the electrodes 20A and 20B of the flare roller 33K may not have a rectangular wave, but may have a driving waveform such as a triangular wave, or the like, having a time constant. Alternatively, when a sine wave corresponding to the time constant is used as the driving waveform, the toner particles may substantially hop on the flare roller 33K.
The surface protection layer 3K (depicted in
SiO2, or the like, may be coated with an organic material such as a polycarbonate, and the like, or may be coated with a zirconia or a material generally used for coating a carrier of a two-component developer such as a silicon series resin or the like. The surface protection layer 3K may be appropriately selected based on an insulation property, durability, a manufacturing method of the flare roller 33K, and a relation with the toner in triboelectric series.
In order to use the development device 30K in the image forming apparatus 100 (depicted in
There are some methods for manufacturing the flare roller 33K.
One of the manufacturing methods is forming a flexible electrode pattern and wrapping it around a holding drum to provide the flare roller 33K.
In order to form a substrate having a flexible fine pitch thin layer electrode, for example, a polyimide base film with a thickness of from about 20 μm to about 100 μm is provided as a base material (e.g., the supporting substrate 4K depicted in
Specifically, the evaporation method may include a sputtering method, an ion plating method, a CVD method, and an ion beam method. For example, when the electrode is formed by the sputtering method, a Cr (chromium) film may be provided in order to improve adhesiveness to the polyimide, or plasma processing or primer processing may improve the adhesiveness.
Other than the evaporation method, an electrodeposition method may provide the thin layer electrode. An electrode is formed on the polyimide base material by electroless plating. After the electrode is sequentially soaked in tin chloride, palladium chloride, and nickel chloride, so as to form a base electrode, it is subjected to electroplating to form a Ni film with a thickness of from about 1 μm to about 3 μm by using the roll-to-roll manufacturing machine.
After the thin film electrode undergoes resist coating, patterning, and etching, the electrodes 20A and 20B are formed. Photolithographic processing and etching processing may precisely form the thin film electrode with a thickness of from about 0.1 μm to about 3 μm having a width or a pitch of a fine pattern electrode of from about 5 μm to about dozens of μm.
Subsequently, SiO2, BaTiO2, TiO2, or the like, with a thickness of from about 0.5 μm to about 2 μm is formed as the surface protection layer 3K by the sputtering method, or the like. Alternatively, a roll coater or other coating machines may apply a coat of P1 (polyimide) with a thickness of from about 2 μm to about 5 μm as the surface protection layer 3K and the surface protection layer is baked. When another layer is needed on the polyimide layer, SiO2 or other inorganic film with a thickness of from about 0.1 μm to about 0.5 μm may be provided on an uppermost surface by the sputtering method, and the like. In addition, an organic material such as a polycarbonate, and the like may be applied to the surface protection layer 3K including SiO2, BaTiO2, and TiO2. Alternatively, a zirconia or a material generally used for coating a carrier of a two-component developer such as a silicon series resin, or the like may be used.
The above-described flexible substrate may be attached to a cylindrical drum or may form a partially curved surface.
As another example, after provision of a polyimide base film with a thickness of from about 20 μm to about 100 μm as a base material (e.g., the supporting substrate 4K), a metal material such as Cu, SUS, or the like, with a thickness of from about 10 μm to about 20 μm may be provided thereon as an electrode material. Thereafter, the roll coater applies a coat of a polyimide with a thickness of from about 20 μm to about 100 μm to the metal material. After being baked, the metal material is patterned into a shape of an electrode by photolithographic processing and etching processing, and a polyimide is coated over an electrode surface to serve as a protection layer. The electrode surface is planarized when it has irregularities due to the thickness of the electrode of from about 20 μm to about 100 μm.
For example, by spin-coating a polyimide series material or a polyurethane series material having a viscosity of from about 50 cps to about 10,000 cps, or more preferably from about 100 cps to about 300 cps and leaving it alone, surface tension of the material may smooth the irregularities on the substrate, thereby planarizing the uppermost surface of the flexible substrate.
As another example of an enhanced flexible substrate, after a metal material such as SUS, Al, and the like, having a thickness of from about 20 μm to about 30 μm is provided as a base material, the roll coater applies a coat of a diluted polyimide material with a thickness of about 5 μm to a surface of the base material as an insulation layer for insulating an electrode from the base material. For example, the polyimide material is pre-baked at about 150 degrees centigrade for about 30 minutes and post-baked at about 350 degrees centigrade for about 60 minutes, so as to form a thin polyimide film. Thus, the supporting substrate 4K is formed.
After being subjected to plasma processing and primer processing in order to improve adhesive force, Ni—Cr with a thickness of from about 0.1 μm to about 0.2 μm, serving as a thin electrode layer, is evaporated, so as to form a fine pattern electrode having a thickness of about dozens of μm by photolithographic processing and etching processing. Thereafter, as the surface protection layer 3K, SiO2, BaTiO2, TiO2, or the like, with a thickness of from about 0.5 μm to about 1 μm is formed by the sputtering method, thereby obtaining a flexible substrate.
An organic material such as polycarbonate and the like may be applied to the surface protection layer including SiO2, BaTiO2, TiO2, or the like. Alternatively, a zirconia or a material generally used for coating a carrier of a two-component developer such as a silicon series resin, or the like may be used.
Referring to
As illustrated in
As illustrated in
As illustrated in
As illustrated in
As illustrated in
As yet another method for manufacturing the flare roller 33K, an electrode is printed and plated by screen printing and ink-jet printing using a conductive ink, and a non-electrode portion of the plated electrode is removed by laser processing.
It is to be noted that the method for manufacturing the flare roller 33K including the electrode pattern and the surface protection layer 3K is not limited to the above. The electrode material may include silver and copper.
Electrical capacitance measured between a connecting terminal (e.g., the common electrode 33A depicted in
The toner particles may have an average particle size of from about 3 μm to about 12 μm. An amount of silica added to the toner may be preferably in a range of from about 1 parts by weight to about 5 parts by weight, such that an electrical charge is properly applied to the toner particles, that is, the toner may be supplied with a sufficient amount of electrical charge to hop on the flare roller 33K, but may not be supplied with an amount of electrical charge large enough to adhere to the flare roller 33K.
Referring to
A first experiment is performed as follows. Toner particles have a volume average particle size of 6 μm.
As illustrated in
As the toner particles are supplied to the flare roller 33K, they are charged by friction. The rotation of the flare roller 33K conveys the toner particles to the toner thickness controller 35K, which includes an insulating rubber blade, for controlling an amount of toner supplied to the flare roller 33K.
After the amount of toner is controlled, the toner particles are uniformly supplied to the flare roller 33K while hopping and conveyed to a development area, so as to develop an electrostatic latent image formed on the photoconductor 50 (depicted in
The collecting roller 37K, serving as a toner collector and a surface electrical potential controller, includes a compressible sponge and is pressed against the flare roller 33K up to a depth of 0.5 mm into the sponge. Toner particles that are not used in development are collected by the collecting roller 37K after passing through the development area and temporarily returned to the toner accommodation part of the casing 31K. Since the hopping toner particles have substantially decreased adhesive force, the collecting roller 37K is able to sufficiently collect the toner particles even when the collecting roller 37K is pressed slightly against the flare roller 33K. The collected toner particles are then mixed with other toner particles and subsequently again supplied to the flare roller 33K. It is to be noted that the collecting roller 37K is supplied with −200 V, which is equal to Vave, an average value of a bias applied to the flare roller 33K.
The flare roller 33K has a linear velocity of 300 mm/s, and the supply roller 34K has a linear velocity of 200 mm/s moving in a direction opposite to the flare roller 33K. The flare roller 33K is supplied with a rectangular-wave voltage with a frequency f of 1 kHz and a Vpp (peak to peak voltage) of 200 V, such that the phase A and the phase B are out of phase with each other by 180 degrees as illustrated in
The supply roller 34K is supplied with a DC (direct current) of −450 V and obtains a supply potential of 250 V.
Table 1 shows experimental conditions 1 to 6 of a type, a time constant τ1, depression in mm of the supply roller 34K serving as a toner supplier, and a diameter thereof, and a type, a time constant τ2, depression of the collecting roller 37K serving as a surface electrical potential controller and a toner collector, and a diameter thereof.
A high resistance roller has a resistance of 108Ω, and a low resistance roller has a resistance of 106Ω.
It is to be noted that resistances of the supply roller 34K and the collecting roller 37K are measured when they are supplied with a DC of −100 V and a load of 500 g on one side thereof, and placed on a metal roller with a diameter of 30 mm rotated at a speed of 30 rpm.
In table 1, type A represents a high resistance sponge roller, type B represents a low resistance sponge roller, type C represents a medium resistance fur brush roller, and type D represents a conducting blade.
A description is now given of a method of measurement of the time constant τ1 of the supply roller 34 injecting an electrical charge to the flare roller 33K and a method of measurement of the time constant τ2 of the collecting roller 37K changing an electrical charge of the flare roller 33K.
Under conditions of an amount of depression, a number of rotations, and the like equivalent to conditions under which the development device 33K is used in the image forming apparatus 100 (depicted in
When the flare roller 33K and the supply roller 34K are supplied with a flare bias and a supply bias, respectively, and rotate for 90 seconds, an electrical potential behavior on a surface of the flare roller 33K is measured by an electrostatic voltmeter. Three biases, that is, DC biases of −250 V, 0 V, and +250 V, are applied, although the number of biases may be reduced since the time constants are substantially identical.
However, the electrical potential behavior when the supply bias is 0 V needs to be examined. This is because the electrical potential may vary due to factors other than charge injection, and thus the time constant needs to be obtained from the electrical potential behavior from which the behavior when the supply bias is 0 V is eliminated.
As a result, an electrical potential profile like that illustrated in
A surface potential of the flare roller 33K may be obtained by a following formula (2):
where “Rsup” represents a resistance of the supply roller 34K (depicted in
A time constant τ may be obtained by a following formula (3):
τ=RsupC (3)
The obtained time constant τ indicates a charge injection characteristic represented by the graph in
Similarly, the time constant τ2 of the collecting roller 37K (depicted in
As a result, as illustrated in table 1, the time constant τ1 of the supply roller 34K is 14, and the time constant τ2 of the collecting roller 37K is 1.5, which satisfies a relation of τ1>τ2.
Under the above conditions, when the flare roller 33K of the development device 30K (depicted in
Since the cloud potential is kept constant, a potential difference between the cloud potential and a latent image potential on the photoconductor 50K (depicted in
That is, when a rate of a decrease in the surface potential of the flare roller 33K by the supply roller 34K is larger than a rate of an increase in the surface potential of the flare roller 33K by the collecting roller 37K (τ1>τ2), the potential difference between the cloud potential and the latent image potential on the photoconductor 50K may be kept constant.
A description is now given of a second experiment. Condition 2 in table 1 shows that a sponge roller with a diameter of 10 mm is used as the supply roller 34K, and a sponge roller with a diameter of 14 mm including a material equivalent to that of the above sponge roller is used as the collecting roller 37K. When both sponge rollers are pressed with equal force against the flare roller 33K, one of the rollers having a smaller diameter than another one has a smaller nip portion contacting the flare roller 33K than another one has, and therefore, the time constant τ1 of charge injection becomes larger than the time constant τ2, thereby satisfying the relation of τ1>τ2. Thus, even when the flare roller 33K continuously rotates, an amount of toner adhered to the flare roller 33K and an amount of charged toner after the toner thickness is controlled are kept constant. In addition, a cloud potential of the flare roller 33K is kept constant after one rotation of the flare roller 33K. Therefore, a potential difference between the cloud potential and a latent image potential on the photoconductor 50K may be kept constant, thereby enabling formation of a high quality image having a stable image density without background fouling.
A description is now given of a third experiment. Condition 3 in table 1 shows that the collecting roller 37K is pressed against the flare roller 33K up to a depth of 1.0 mm, and a width of a nip between the collecting roller 37K and the flare roller 33K is larger than a width of a nip between the supply roller 34K and the flare roller 33K.
Therefore, charge injection per rotation of the flare roller 33K takes a long time, thereby reducing the time constant τ2, satisfying the relation of τ1>τ2. Thus, even when the flare roller 33K continuously rotates, an amount of toner adhered to the flare roller 33K and an amount of charged toner after the toner thickness is controlled are kept constant. In addition, a cloud potential of the flare roller 33K is kept constant after one rotation of the flare roller 33K. Therefore, a potential difference between the cloud potential and a latent image potential on the photoconductor 50K may be kept constant, thereby enabling formation of a high quality image having a stable image density without background fouling.
As shown in table 1, when a fourth experiment is performed using a fur brush as the collecting roller 37K instead of the sponge roller used as the supply roller 34K and the collecting roller 37K in the first, second, and third experiments, the relation of τ1>τ2 is satisfied, thereby achieving sufficient potential control.
Alternatively, even when a fur brush is used as the supply roller 34K in a fifth experiment, the relation of τ1>τ2 is satisfied, thereby achieving sufficient potential control.
A description is now given of a first comparison in which the supply roller 34K is replaced by the collecting roller 37K. FIG. 13 is a graph illustrating a relation between a rotation time of the flare roller 33K (depicted in
In addition, since an electrical potential for toner supply substantially decreases from an initial potential, a sufficient amount of toner may not be supplied to the flare roller 33K.
Consequently, although a desired image may be formed immediately after the flare roller 33K starts rotating since the surface potential of the flare roller 33K is 0, when the surface potential negatively increases (e.g., when the surface potential decreases below 0), the development potential, which is a difference between the surface potential of the flare roller 33K and the latent image potential of the photoconductor 50, increases, resulting in a faulty image with increased image density. This is because the flare roller 33K lacks potential control.
A description is now given of a second comparison.
The conducting blade 39K, serving as a surface electrical potential controller, is provided downstream from a development area and upstream from a toner supply area in the direction of rotation of the flare roller 33K, and supplied with a bias.
Since the conducting blade 39K has a blade shape, there is insufficient width of a nip between the conducting blade 39K and the flare roller 33K. Thus, a potential injection time is substantially shorter than the time of potential injection by the supply roller 34K, so that the conducting blade 39K may not sufficiently discharge the injected electrical charge to control the surface potential of the flare roller 33K.
However, the flare roller 33K and the collecting roller 37K may be supplied with a voltage of a polarity (e.g., a negative polarity) identical to that of the toner particles, and the flare roller 33K may have a larger electrical potential absolute value than that of the collecting roller 37K. For example, when the flare roller 33K has a potential VF of −200 V, and the collecting roller 37K has a potential VR of −100 V (|VF|>|VR|), the toner particles may be attracted to the collecting roller 37K.
Therefore, since a rate of toner collection from the flare roller 33K by the collecting roller 37K may increase, so as to change the surface potential of the flare roller 33K, the surface potential of the flare roller 33K may be controlled (e.g., discharged), thereby increasing an effect of discharging the flare roller 33K.
A description is now given of the fourth experiment using the rectangular wave (depicted in
Since a duty ratio of the rectangular wave voltage is 50%, the average value Vave of the bias applied to the flare roller 33K (depicted in
Alternatively, when the average value Vave of the bias applied to the flare roller 33K is not identical to the offset voltage VO since the duty ratio is not 50%, or the like, the collecting roller 37K (depicted in
The supply roller 34K and the collecting roller 37K include a sponge roller with a resistance of from 105Ω to 107Ω.
It is to be noted that resistances of the supply roller 34K and the collecting roller 37K are measured when the supply roller 34K and the collecting roller 37K are supplied with a DC of −100 V and a load of 500 g on one side thereof, and placed on a metal roller with a diameter of 30 mm rotated at a rotation speed of 30 rpm.
Under the above conditions, when the flare roller 33K of the development device 30K (depicted in
In addition, as illustrated in
A description is now given of a comparison to the fourth experiment. Under conditions similar to the conditions for the fourth experiment, when the flare roller 33K is supplied with a bias equivalent to that applied to the flare roller 33K in the first experiment, and the collecting roller 37K, serving as a surface electrical potential controller, is supplied with a voltage of −400 V, the cloud potential continues to decrease for about 20 seconds after the flare roller 33K starts rotating, as illustrated in
In addition, since an electrical potential for toner supply substantially decreases from an initial potential, a sufficient amount of toner may not be supplied to the flare roller 33K.
Consequently, although a desired image may be formed immediately after the flare roller 33K starts rotating since the surface potential of the flare roller 33K is 0, when the surface potential negatively increases (e.g., when the surface potential decreases below 0), the development potential, which is a difference between the surface potential of the flare roller 33K and the latent image potential of the photoconductor 50, increases, resulting in a faulty image with increased image density.
A description is now given of a fifth experiment using the rectangular wave (depicted in
Therefore, when one of the electrodes of two phases is constantly supplied with an even voltage while the other one is supplied with a rectangular wave voltage, the toner particles may hop on the flare roller 33K. Accordingly, since one of the biases applied to the flare roller 33K is a DC bias, one power supply system for generating a pulse may be reduced, resulting in a cost reduction of the power source.
The supply roller 34K is supplied with a DC bias of VO.
Therefore, since an average value of the bias applied to the supply roller 34K is equal to an average value of the bias applied to the flare roller 33K, the surface potential of the flare roller 33K may be kept constant, so that the cloud potential is kept constant even when the flare roller 33K continuously rotates, thereby enabling formation of a high-quality image without uneven image density.
A description is now given of a sixth experiment using the rectangular wave (depicted in
Also, the supply roller 34K is supplied with a rectangular wave bias of an average value VO of −300 V, a frequency f2 of 500 Hz, and a peak-to-peak voltage V2 of 400 V.
Under the above conditions, when the flare roller 33K continuously rotates, a cloud potential of the flare roller 33K is kept constant, thereby enabling formation of a high-quality image without uneven image density.
A description is now given of a seventh experiment. The flare roller 33K is supplied with a flare bias having a driving waveform identical to the driving waveform used in the sixth experiment, and the supply roller 34K is supplied with a bias having a waveform equal to a waveform of the rectangular wave bias (e.g., phase A or phase B) applied to the flare roller 33K.
Under the above conditions, when the flare roller 33K continuously rotates, a cloud potential of the flare roller 33K is kept constant, thereby enabling formation of a high-quality image without uneven image density.
A description is now given of an eighth experiment using the rectangular wave (depicted in
The supply roller 34K is supplied with a rectangular wave bias equal to the rectangular wave bias applied to one electrode of one phase on one side of the flare roller 33K.
Under the above conditions, when the flare roller 33K continuously rotates, a cloud potential of the flare roller 33K is kept constant, thereby enabling formation of a high-quality image without uneven image density.
It is to be noted that although the fourth, fifth, sixth, seventh, and eighth experiments use a sponge roller as the supply roller 34K and the collecting roller 37K, at least one of the supply roller 34K and the collecting roller 37K may be replaced by a fur brush.
Referring to
There are three factors liable to produce fluctuation of the surface potential of the flare roller 33K.
A first factor is an accumulation of an electrical charge by a condenser model.
Specifically, the electrical charge accumulates in a surface protection layer of the flare roller 33K until there is no potential difference between the supply roller 34 and the flare roller 33K, so that the surface potential of the flare roller 33K is saturated.
After a power supply for generating the supply bias and the flare bias is powered off, the flare roller 33K gradually loses the electrical charge. However, since the surface protection layer of the flare roller 33K has a high resistance in order to provide insulation between the electrodes, the accumulated electrical charge is barely discharged. Therefore, a discharge function needs to be provided.
A second factor is a frictional charge between the flare roller 33K and the supply roller 34K.
The result shows that the flare roller 33K is supplied with a voltage of about −40 V due to the frictional charge between the flare roller 33K and the supply roller 34K. A value of a convergence rate is affected by a relation of triboelectric series between the supply roller 34K and the surface protection layer of the flare roller 33K, an amount of depression in the supply roller 34K, and the like.
A third factor is an induction of an electrical charge canceling a negative charge of toner particles.
When the toner particles supplied by the supply roller 34K hop on the flare roller 33K, a positive charge opposite to the negative charge of the toner particles is induced in the surface protection layer of the flare roller 33K. After the toner particles are removed from the flare roller 33K, the surface potential of the flare roller 33K is positively charged. The larger the amount of the negatively charged toner is, the larger the surface potential of the positively charged flare roller 33K becomes.
When the surface of the flare roller 33K is charged by the condenser only, that is, when only the first factor affects the surface potential of the flare roller 33K, the fluctuation of the surface potential of the flare roller 33K by the condenser model may be prevented, if the toner particles are supplied and collected by mechanical scraping without using an electrical field. However, since the second factor and the third factor also affect the surface potential of the flare roller 33K, in order to supply the surface of the flare roller 33K with a constant voltage to convey the toner particles to an area facing the photoconductor 50 (depicted in
The development device 30KB integrates the function of the collecting roller 37K into the supply roller 34K. The agitators 32KA and 32KB rotate in a direction opposite to each other, so that a developer (e.g., the toner) may move to circulate inside the casing 31K.
The development device 30 KB may achieve a surface potential control result similar to that of the above experiments using the development device 30K.
According to the above-described exemplary embodiments, the image forming apparatus 100 (depicted in
Thus,
The development device 30K and the photoconductor 62K, serving as a latent image carrier, are integrated into the process cartridge 63K. The process cartridge 63K, which forms a black toner image, may be detachably attachable to a tandem type image forming apparatus. In this case, the tandem type image forming apparatus may further include process cartridges for forming yellow, cyan, and magenta toner images, respectively. The development device 30K may have a structure identical to that of the development device 30KB (depicted in
As can be appreciated by those skilled in the art, although the present invention has been described above with reference to specific exemplary embodiments the present invention is not limited to the specific embodiments described above, and various modifications and enhancements are possible without departing from the spirit and scope of the invention. It is therefore to be understood that the present invention may be practiced otherwise than as specifically described herein. For example, elements and/or features of different illustrative exemplary embodiments may be combined with each other and/or substituted for each other within the scope of the present invention.
Number | Date | Country | Kind |
---|---|---|---|
2007-130588 | May 2007 | JP | national |
Number | Name | Date | Kind |
---|---|---|---|
6658227 | Oyama et al. | Dec 2003 | B2 |
6901231 | Sakai et al. | May 2005 | B1 |
7024142 | Sakai et al. | Apr 2006 | B2 |
7123864 | Miyaguchi et al. | Oct 2006 | B2 |
7187892 | Horike et al. | Mar 2007 | B2 |
7200352 | Sakai et al. | Apr 2007 | B2 |
7236720 | Nakazato et al. | Jun 2007 | B2 |
7308222 | Nakagawa et al. | Dec 2007 | B2 |
7340204 | Nakazato et al. | Mar 2008 | B2 |
20060216071 | Yamada et al. | Sep 2006 | A1 |
20060251449 | Takahashi et al. | Nov 2006 | A1 |
20070013924 | Sakai et al. | Jan 2007 | A1 |
20070015071 | Tsukamoto et al. | Jan 2007 | A1 |
20070086811 | Tsukamoto et al. | Apr 2007 | A1 |
20070212121 | Takahashi et al. | Sep 2007 | A1 |
20070242985 | Aoki et al. | Oct 2007 | A1 |
Number | Date | Country |
---|---|---|
3-21967 | Jan 1991 | JP |
3-100575 | Apr 1991 | JP |
3-113474 | May 1991 | JP |
9-269661 | Oct 1997 | JP |
2002-341656 | Nov 2002 | JP |
2003-15419 | Jan 2003 | JP |
2003-84560 | Mar 2003 | JP |
2004-286837 | Oct 2004 | JP |
Number | Date | Country | |
---|---|---|---|
20080286015 A1 | Nov 2008 | US |