Patent Application
20120241083
The present invention relates to a potential sensor (an electric-potential sensor), an electrophotographic image forming apparatus including the potential sensor, and a manufacturing method of the potential sensor. As the image forming apparatus, it is possible to use apparatuses for forming an image through electrophotography, such as a copying machine, a printer, a facsimile machine, a multi-function machine having a plurality of functions of these machines, and the like.
In the electrophotographic image forming apparatus, a toner image is formed through a series of steps of electric charging, light exposure, development, and transfer. In order to realize high image quality in the apparatus, it is important to electrically charge a surface of a photosensitive member uniformly by a charger in an electrically charging step.
For that reason, a technique in which a surface potential of the photosensitive member electrically charged by the charger is detected and a charging condition by the charger is corrected so that the surface potential is a proper value has been conventionally employed. Further, a technique in which the photosensitive member is idled for a predetermined time in the case where judgment that a desired electrophotographic image is not formed (i.e., an electrophotographic image on the photosensitive member is disturbed due to ambient moisture is made on the basis of a result of the detection of the surface potential of the photosensitive member has also been proposed.
For example, in an apparatus described in Japanese Laid-Open Patent Application (JP-A) Hei 11-183542, a potential sensor includes an elongated curved electrode of which surface is opposed to the photosensitive member with a gap of 10 to 100 μm at an opposing portion and an electrophotographic image on the photosensitive member passing through the opposing portion is by the potential sensor with a dot-size resolution. The potential sensor detects potential distribution of a predetermined electrophotographic image formed on the photosensitive member so that the electrophotographic image has a predetermined line width and is parallel to the electrode surface and then outputs an output voltage corresponding to a differential waveform of the electrophotographic image potential distribution.
In this case, the potential sensor is disposed in non-contact with the photosensitive member, so that when the photosensitive member causes eccentricity (off-center), the gap between the potential sensor and the photosensitive member fluctuates. As a result, it is difficult to detect the surface potential of the photosensitive member with high accuracy.
In an apparatus described in JP-A 2004-77125, a potential sensor for detecting a surface potential (surface defect) of a photosensitive member with a dot-size resolution in a state in which an outer surface of an insulative film which covers a periphery of a curved surface of a wire electrode is brought into contact with the photosensitive member is used.
In this case, the potential sensor is disposed in contact with the photosensitive member, so that it is possible to detect the surface potential of the photosensitive member with high accuracy.
However, an SN ratio of an output signal of the potential sensor has been largely lowered in some cases by radiation noise from image forming equipment (e.g., a developing device or a charger) disposed in the neighborhood of the potential sensor.
In these cases, the output signal is influenced by the radiation noise to largely fluctuate, so that accuracy of detection of the surface of the photosensitive member is lowered. As a result, optimization of the surface potential of the photosensitive member with high accuracy on the basis of the output of the potential sensor cannot be realized.
A principal object of the present invention is to provide a potential sensor capable of improving potential detection accuracy.
Another object of the present invention is to provide an image forming apparatus including the potential sensor and a manufacturing method of the potential sensor.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.
a), 10(b) and 10(c) are explanatory views of electrode patterns.
a) and 13(b) are explanatory views of an effect of noise suppression.
a) to 14(f) are explanatory views of a manufacturing method of the potential sensor.
a) to 15(f) are explanatory views of another manufacturing method of the potential sensor.
a) and 16(b) are explanatory views of examples of a detection electrode.
Hereinbelow, embodiments of the present invention will be described with reference to the drawings. The present invention can also be carried out in other embodiments in which a part or all of constitutions of the following embodiments are replaced by alternative constitutions so long as at least one surface of a potential sensor except for an end of the potential sensor is covered with an electroconductive material.
In First Embodiment, an image forming apparatus in which a toner image is directly transferred from a photosensitive drum onto a recording material in a sheet-fed manner but the present invention can also be carried out by an image forming apparatus using an intermediary transfer belt and an image forming apparatus using a recording material conveying belt.
Incidentally, general matters regarding the image forming apparatus and the potential sensor which are described in JP-A 2002-40876, JP-A Hei 11-183542, and JP-A 2004-77125 are omitted from illustration, thus being omitted from redundant explanation.
Referring to
Around the photosensitive drum 1 as an example of a photosensitive member, a charging roller 2, an exposure device 3, a developing device 4, a transfer roller 5, a cleaning device 6, and a potential sensor 30 are disposed.
In this embodiment, as the charging roller (device) 2 which is a charging means, a roller which comes in contact with the photosensitive drum 1 and is rotated by rotation of the photosensitive drum is used in a state in which an oscillating voltage in the form of a DC voltage biased with an AC voltage is applied from a power source P3 to the charging roller 2. The charging roller 2 electrically charges the photosensitive drum 1 to a uniform dark portion potential VD of a negative polarity.
As the exposure device 3 which is an exposure means, a semiconductor laser for irradiating the photosensitive drum 1 electrically charged to the dark portion potential VD to a laser beam (wavelength λ=780 nm) is used. The semiconductor laser is used for scanning exposure of the photosensitive drum 1, so that an electric potential of an exposed portion is lowered to a light portion potential VL to form an electrophotographic image for an image.
The developing device 4 which is an example of a developing means develops the electrophotographic image formed on the photosensitive drum 1 with negatively charged toner to form a toner image. The developing device 4 carries the toner on a developing sleeve 4s rotating about a fixed magnetic pole 4m to slide on the photosensitive drum 1. By applying an oscillating voltage in the form of a developing voltage Vdc biased with an AC voltage from a power source D4 to the developing sleeve 4s, the toner is transferred onto a potential of the photosensitive drum 1 having the light portion potential VL, so that the electrode is reversely developed.
The transfer roller 5 which is an example of a transfer means forms the transfer portion T1, in contact with the photosensitive drum 1, where the recording material P is to be nip-conveyed. The negatively charged toner image carried on the photosensitive drum 1 is transferred onto the nip-conveyed recording material P by application of a DC voltage from a power source D1 to the transfer roller 5.
The recording material P is taken out from a cassette 20 and is separated one by one by a separation roller 21. The separated recording material P is conveyed from a conveying roller 22 to a registration roller 23 to be placed in a stand-by state. The registration roller 23 sends the recording material P to the transfer portion T1 with timing synchronized with the toner image carried on the photosensitive drum 1.
The cleaning device 6 removes untransferred residual toner from the surface of the photosensitive drum 1 having passed through the transfer portion T1 by rubbing the photosensitive drum 1 with a cleaning blade 6b. The cleaning device 6 evaporates water content deposited on the surface of the photosensitive drum 1 by rubbing the rotating photosensitive drum 1 with the cleaning blade 6b during image formation to cause frictional heating. For this reason, when the rotation of the photosensitive drum 1 is continued, a surface resistance of the photosensitive drum 1 is gradually restored with removal of the water content through the rubbing.
The potential sensor 30 is disposed in contact with the photosensitive drum 1 at a position between an exposure position of the exposure device 3 and a developing position of the developing device 4 and detects a predetermined electrophotographic image formed during non-image formation.
The photosensitive drum 1 is an electrophotographic photosensitive member which includes an electroconductive cylindrical base portion of aluminum and at least a surface layer, of a photosensitive layer disposed on the surface of the base portion, formed of a cured compound by polymerization or cross-linking and is rotatably by a main assembly of the image forming apparatus. Incidentally, as the photosensitive layer, it is also possible to use an amorphous silicon organic optical semiconductor.
As shown in
In the case of the photosensitive drum 1 having high hardness, an abrasion speed of the photosensitive layer 1b is 1.4 or less of a conventional abrasion speed. For this reason, the photosensitive drum 1 which has conventionally reached the end of a lifetime thereof at the time of image formation on 30,000 to 70,000 sheets of plain paper can be subjected to continuous image formation until the number of sheets reaches 120,000 to 300,000 sheets.
In another aspect, with respect to the high-hardness photosensitive drum 1, an electric discharge product which has been removed with surface abrasion remains on the surface of the photosensitive drum 1 in a larger amount, so that image deletion due to the electric discharge product is more liable to occur.
In this embodiment, a charging type using the charging roller is employed but the present invention is similarly applicable to chargers of other types using a corona charger, an injection charger, and the like.
The charging roller 2 is prepared by providing an elastic layer 2b of a rubber elastic material on a round bar 2b of an electroconductive supporting member (formed of a metal material of iron, copper, stainless steel, aluminum, nickel, or the like). Electroconductivity is imparted to the elastic layer 2b. The elastic layer 2b may preferably have a thickness in the range of 1-500 mm.
As a method of imparting the electroconductivity to the elastic layer 2b, it is possible to employ a method in which an electroconductive agent having an electron conduction mechanism such as carbon black, graphite, or electroconductive metal oxide is added in the rubber elastic material. Further, it is also possible to add an electroconductive agent having an ion conduction mechanism such as an alkali metal salt or a quaternary ammonium salt. By foaming the rubber elastic material to which the electroconductivity is imparted, the elastic layer 2b may preferably be adjusted to have an electric resistance of less than 1×1010Ω×cm.
As a specific elastic material for the elastic layer 2b, it is possible to use natural rubber: synthetic rubbers such as natural rubber, ethylene-propylene-diene-methylene (EPDM), styrene-butadiene rubber (SBR), silicone rubber, urethane rubber, epichlorohydrin rubber, isoprene rubber (IR), butadiene rubber (BR), nitrile-butadiene rubber (NBR), and chloroprene rubber (CR); and resin materials such as polyamide resin, polyurethane resin, and silicone resin.
The charging roller 2 is formed in an outer diameter of 16 mm and when the oscillating voltage is applied from the power source D3 to the charging roller 2, the surface of the photosensitive drum 1 is electrically charged to a predetermined potential by the charging roller 2. As the voltage to be applied to the charging roller 2, the oscillating voltage in the form of the DC voltage biased with the AC voltage may preferably be used. The oscillating voltage referred to herein is a voltage having a voltage value periodically changing with time and the AC voltage may desirably have a peak-to-peak voltage which is two times or move an electric discharge start voltage at the time when only the DC voltage is applied to the charging roller 2. As a waveform of the AC voltage, it is possible to use not only a sine wave but also a rectangular wave, a triangular wave, and a pulse wave. However, from the viewpoint of a lowering in charging noise, the sine wave containing no harmonic component may preferably be used.
The power source (charging bias application means) D3 effects constant voltage control such that an AC voltage is output at a frequency of 1.8 kHz to provide a total current of 2000 μA. The DC voltage to be biased with the AC voltage is set at a constant charging target voltage (the dark portion potential=700 V). That is, the DC voltage VD applied to the charging roller 2 is transferred onto the surface of the photosensitive drum 1 with the electric discharge with respect to both directions by the AC voltage.
In this embodiment, as the developing means for developing the electrophotographic image formed on the photosensitive drum 1, a developing device using a one component developing system is employed.
The developing sleeve 4s and the photosensitive drum 1 are disposed so as to keep a constant gap of 0.3 mm along a longitudinal direction of the photosensitive drum 1. As the toner, negatively chargeable one component magnetic toner is used and is subjected to jumping reverse development by application of a rectangular waveform-oscillating voltage to the developing sleeve 4s.
To the developing sleeve 4s, from the power source D4, the oscillating voltage in the form of a negative DC voltage (Vdc=−350 V) biased with an AC voltage (peak-to-peak voltage Vpp=1.2 kV) is applied. The magnetic toner carried on the surface of the developing sleeve 4s is conveyed to the developing position, where the toner is urged by the DC voltage Vdc to be transferred from the developing sleeve 4s onto the electrophotographic image on the photosensitive drum 1 in a process of reciprocation between the photosensitive drum 1 and the developing sleeve 4s in response to the AC voltage.
Incidentally, the oscillating voltage referred to herein is a voltage having a voltage value which periodically changes with time. As the waveform of the AC voltage, it is possible to use not only the rectangular wave but also the sine wave, the triangular wave, and the pulse wave. However, from the view point of cost advances and shape factor, the rectangular wave may preferably be employed.
As shown in
The potential sensor 30 is caused to slide on the photosensitive drum 1 by being obliquely inclined at a thin plate-like side surface portion so that the potential sensor 30 is supported in a cantilever-like manner by a main assembly of the image forming apparatus so as to project toward a rotational direction of the photosensitive drum 1 at the curved end surface. The potential sensor 30 contacts the photosensitive drum 1 at the thin plate-like curved surface portion, so that a contact pressure thereof with respect to the photosensitive drum 1 is set by a bending reaction force of the thin plate-like side surface portion inclined at a predetermined inclination angle. The potential sensor 30 contacts the photosensitive drum 1 at the outer side surface of an insulative film layer, having a thickness of 25 μm, covering the surface of the electrode, so that an opposing distance between the electrode surface and the photosensitive drum 1 surface is set at 25 μm.
A contact line along which the potential sensor 30 contacts the photosensitive drum 1 is positioned in parallel to a rectilinear line crossing the surface of the photosensitive drum 1 in an axial direction (generating line of the curved surface). For this reason, an electrophotographic image 1s formed on the photosensitive drum 1 with respect to a main scan direction passes through the contact line substantially at one time.
The insulative film 31 of the potential sensor 30 is folded with a predetermined curvature so as to form the curved surface contactable to the photosensitive drum 1. A thin film electrode layer 32 is formed in a thin film pattern to constitute a detection electrode portion 32a, at the curved surface, adhesively contacting the inner side surface of the film 31 in a folding area. A center layer 33 is provided so that mutually opposing detection electrode portions do not contact each other during the folding, i.e., cause no electrical short circuit. That is, the center layer 33 is an insulative cover layer laminated on the thin film electrode layer 32 provided on the film 31 so as to cover the thin film electrode layer 32. The thin film electrode layer 32 includes a connecting wiring portion 32b fixed to the inner surface of the film 31 while being extended continuously from the detection electrode portion 32a so that the thin film electrode layer 32 is electrically connectable with a signal processing portion 120 on a side opposite from the folding area of the film 31.
As shown in
The film 31 is required to possess elasticity to some extent in order to cause bending deformation in direct contact with the photosensitive drum 1 and thus may preferably be formed of a material having Young's modulus of 0.001 to 10 GPa. The Young's modulus was obtained based on JIS-Z 1702 by simultaneously calculating strength and elongation through measurement of a test piece of 10 mm in width and 50 mm in length at a tension speed of 20 mm/min. by a testing machine (“TENSILON”, mfd. by Toyo Boldwin Co., Ltd.). When the Young's modulus is less than 0.001 Gpa, the resultant film is excessively soft, so that the film cannot satisfactorily contact the photosensitive drum 1. On the other hand, when the Young's modulus is more than 10 Gpa, the resultant film is excessively hard, so that the film damages the photosensitive drum 1. For a material satisfying such a physical property, a polyester film or a polyimide film is most suitable.
The width (L2) of the potential sensor 30 may preferably be 1 to 320 mm, further preferably 2 to 10 mm. Below 1 mm, there is a possibility that the potential sensor 30 is broken from a view point of strength to fail to detect a signal. On the other hand, above 320 mm, the potential sensor 30 is excessively long to cause deformation or the like, thus causing signal non-uniformity.
The length (L3) of the potential sensor 30 may preferably be 1 to 50 mm. Below 1 mm, it is difficult to build a circuit and there is a possibility that the photosensitive drum 1 contacts a supporting structure of the potential sensor 30 due to eccentric rotation or the like of the photosensitive drum 1. Above 50 mm, the potential sensor 30 is large in size as a whole, thus causing breakage thereof in the image forming apparatus.
Inside the film 31, the thin film electrode layer 32 as the electroconductive member is located. A material for the thin film electrode layer 32 may preferably be electroconductive in order to detect induction current of the photosensitive drum 1 and may preferably have an electrical resistivity (JIS K-6911, at room temperature of 20° C.) of 1×10−6 to 2×10−4Ω×cm. The electrical resistivity may further preferably be 1×10−6 to 3×10−6Ω×cm. As a specific material, silver, copper, gold, aluminum, tungsten, iron, tin, lead, titanium, platinum, and the like may preferably be used. Of these materials, silver having a low electrical resistivity may particularly preferably be used.
When the electrical resistivity is lower than 1×10−6Ω×cm, it is generally difficult to obtain such a material under present circumstances. Further, the material shows excessively high electroconductivity, so that the potential sensor is liable to detect other noises. On the other hand, when the electrical resistivity is higher than 2×104Ω×cm, a signal sensitivity is somewhat worsen. The thin film electrode layer 32 may preferably have a thickness of 0.5 to 50 μm. Below 0.5 μm, the thickness of the film 31 is required to be made small. When the thickness of the film 31 is made small, sensitivity is excessively increased, so that the potential sensor detects an excess electrical noise. On the other hand, above 50 μm, the sensitivity is lowered, so that the potential sensor cannot detect the image deletion with high accuracy.
The potential sensor 30 contacts the photosensitive drum 1 at the outer curved surface of the film 31, so that the opposing distance between the detect electrode portion 32a and the photosensitive drum 1 surface is kept at a constant level. The opposing distance, i.e., the thickness of the film 31 may preferably be 5 to 100 μm, more preferably 15 to 50 μm. Below 5 μm, a signal strength of the detection electrode portion 32a is excessively increased, so that the potential sensor 30 is liable to detect noise due to surface oscillation of the photosensitive drum 1. Above 50 μm, the signal strength is decreased, so that the potential sensor 30 cannot detect the signal satisfactorily.
It is basically desirable that the thin film electrode layer 32 is prepared by changing a state of the above-described electroconductive material into an ink state (a paste state) and then subjecting a resultant electroconductive paste to pattern printing in a developed (extended) shape on the flat surface by using a printing method described below. To the electroconductive paste, it is possible to appropriately add a solvent, an antifoaming agent, an anti-setting agent, a dispersing agent, a coupling agent, a resistance-adjusting agent, and the like, as desired or in a commonly used range.
As the result, it is possible to select a solvent which does not react with thermosetting resin and is capable of dissolving a chelate-forming substance, oxygen acid capable of forming a complex with the chelate-forming substance, partial ester of the oxygen acid, or partial amide of the oxygen acid. For example, it is possible to use ethyl cellosolve, methyl cellosolve, butyl cellosolve, ethyl cellosolve acetate, methyl cellosolve acetate, butyl cellosolve acetate, ethyl carbitol, methyl carbitol, butyl carbitol, ethyl carbitol acetate, methyl carbitol acetate, butyl carbitol acetate, and the like.
As the coupling agent, it is possible to appropriately add a coupling agent, such as silane-based coupling agent, which is effective in electroconductivity within a range not deteriorating a pot life of the electroconductive paste. Preferred species of the coupling agent may include, e.g., γ-glycidoxypropyltrimethylsilane, γ-glycidoxypropyl-methyldiethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, N-(β-aminoethyl)-γ-aminopropylmethyldimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, γ-aminopropyltriethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, and the like. These coupling agents have volatility and safety such a requirement that they have low reactivity with the thermosetting resin. An amount of addition of the coupling agent may appropriately be determined depending on an amount of electroconductive powder to be contained in the electroconductive paste and is determined, in consideration of adhesiveness or the like, in a range of 1 to 10 wt. parts per 100 wt. parts of the electroconductive powder.
As the resistance-adjusting agent, it is possible to use metal oxides such as colloidal silica, titanium oxide, zinc oxide, and alumina; inorganic fine powder of silicon carbide, calcium carbonate, barium carbonate, calcium silicate, and the like; beads of polymers such as PMMA, polyethylene, nylon, silicone resin, phenolic resin, benzoquinamine resin, polyester, and the like; organic fine powder of fluorine-containing resin materials such as polytetrafluoroethylene and polyvinylidene fluoride; and fine powder of carbon black, acetylene black, channel black, aniline black, and the like. The resistance-adjusting agent may appropriately be added depending on a necessary resistance value.
Next, an example of a preparation method (manufacturing method) of the electroconductive paste will be described. Basically, the above-described electroconductive powder of the electroconductive material is a base material. To the base material, principal constituent components including the thermosetting resin, alkoxy group-containing modified silicone resin, the chelate-forming substance, and the oxygen acid or the partial ester or partial amide of the oxygen acid are added. Further, as desired, additives such as the coupling agent and the solvent are added. To the resultant mixture, shearing stress is applied so as to uniformly knead the mixture, so that the electroconductive paste is prepared. In a method of applying the shearing stress, e.g., an ordinarily used kneading device such as a kneader, a three-roll mill can be used. Particularly, as the kneading device, it is possible to suitably use a stone mill or stirring deaerator which permits kneading in a closed system and of a rotation-revolution combined use type (e.g., “MS-SNB-2000”, mfd. by Matsuo Sangyo Co., Ltd.). The kneading may preferably be performed so that oxidation of the electroconductive powder does not proceed excessively.
As a manner of adding the various constituent components, it is possible to add all the components at one time. However, in order to ensure processing (treatment) of the electroconductive powder with the chelate-forming substance, first, the electroconductive powder may preferably be subjected to the processing with the chelate-forming substance in advance by adding the electroconductive powder into a solution of the chelate-forming substance in the solvent. The electroconductive paste may preferably be prepared by dividing the manufacturing method into a step of effecting the processing with the chelate-forming substance and a step of kneading the electroconductive powder processed with the chelate-forming substance with the thermosetting resin, a resin component such as the alkoxy group—containing modified silicone resin, and other additives to prepare a paste. In this case, during the step of effecting the processing with the chelate-forming substance, the oxygen acid or its partial ester or partial amide may further preferably be added in order to deactivate an excessive chelate-forming substance. Thus, by using a two-stage mixing step constituted by a first step and a second step, intended processing is performed in each of the steps, so that the resultant electroconductive paste is further stabilized with respect to an electroconductive performance and a storage property.
In the first step, the solvent is added to the electroconductive powder (e.g., copper powder) and the chelate-forming substance (e.g., 2,2′-bipyridyl), followed by high-speed stirring. At this time, eluted metal ions form a chelate with the chelate-forming substance, so that the color of the dispersion liquid is changed to blue.
To the dispersion liquid, the oxygen acid or its partial ester or partial amide is added in a predetermined amount so as to be uniformly mixed, so that the chelate-forming substance remaining after acting on the copper powder to form the chelate in the first step is deactivated. In the resultant liquid, copper ions derived from a natural oxide film at the copper powder surface are subjected to the chelate formation to be dissolved in the solvent and the electroconductive powder itself is dispersed in the solvent to result in a dispersion liquid. At the same time, other additives, which do not inhibit the above-described chelate forming process and are preferably dissolved in the solvent, such as the anti-setting agent and the dispersing agent can also be added.
In the second step, the thermosetting resin (e.g., resol-type phenolic resin) and the alkoxy group-containing modified silicone resin are added and stirred. At this time, the copper chelate is incorporated into the phenolic resin used as the thermosetting resin to be changed in color to black. Further, as desired, the additives such as the coupling agent, the antifoaming agent, and an additional solvent are added and then a resultant mixture is kneaded by the above-described kneading device to complete the copper paste.
By the division into the above-described two steps, it is possible to process the electroconductive powder with the chelate-forming substance with reliability to further improve the electroconductive performance. Further, it is possible to prolong the pot life, shelf life, and the like. Incidentally, for the purpose of adjusting a viscosity, a volatile component, and the like of the electroconductive paste, it is also possible to add a further solvent.
As shown in
The formation of a developed electrode pattern can be effected by a general printing method such as a silk-screen printing method, a gravure printing method, a screen printing method, a method using a gravure plate, reverse-roll coating, sheet-fed printing, or offset printing.
Further, it is also possible to form the electrode pattern by a method in which masking is effected at a portion other than the electrode on the surface of the film 31 and thereon the electroconductive paste is applied or printed at the entire surface and is dried, followed by removal of the masking portion.
Further, it is also possible to employ a method in which masking of the electrode pattern is effected after the entire surface printing and then a portion which has not been subjected to the masking is removed by etching treatment to impart a desired shape to the electroconductive paste pattern.
Further, the thin film electrode layer 32 may also be formed by forming a thin metal film, through vacuum vapor deposition or sputtering, on the film on which a mask provided with an opening corresponding to the detection electrode portion 32a and the connecting wiring portion 32b is superposed.
Further, the detect electrode portion 32a and the connecting wiring portion 32b may also be formed into a pattern by forming a resist pattern on a thin metal film which has been formed on the entire surface of the film 31 through the vacuum vapor deposition or the sputtering and then by etching the resist pattern.
Further, as in the case of preparing a flexible printed board, the electrode pattern may also be formed by forming a resist pattern through projection exposure of a circuit pattern onto a resist layer on a thin metal film and then by subjecting the resist pattern to etching treatment.
As shown in
For noise suppression, the shielding layers 37a and 37b are formed in a thin film through the above-described printing method by using the above-described electroconductive paste in an area except for the end portion (an area contactable to the photosensitive drum 1) of the potential sensor 30. As the electroconductive material for the thin film formation, there is no problem when the electroconductive material usable for the above-described thin film electrode layer 32 is employed. It is also possible to form the shielding layers 37a and 37b by using the above-described other materials for the thin film and the above-described other pattern forming methods. It is also possible to use a method in which masking is effected at a predetermined portion and the entire portion is soaked in the electroconductive paste and then is dried, followed by removal of the masking portion. It is also possible to coat both sides by the vacuum vapor deposition or the sputtering. Further, it is also possible to employ a method in which the material for the shielding layer is formed in a metal foil in advance and then coats the entire surface except for the end portion.
In this case, attention should be given to a manner of covering both (front and back) surfaces of the potential sensor 30. In a state of contact of the potential sensor 30 with the photosensitive drum 1, it is important to provide an uncovered portion, at which the photosensitive drum 1 is not covered with the shielding layer on the basis of a contact position, in a small area.
With respect to this uncovered portion, it was found that, as shown in
D2≧6/D1 . . . (15 mm≦D1≦120 mm)
Therefore, when the end side of the potential sensor 30 is covered with the shielding layers 37a and 37b in a large amount, noise is lowered, so that sensitivity is improved. However, when the end side of the potential sensor 30 is covered with the shielding layers 37a and 37b in an excessively large amount, the electric discharge is caused to occur between the photosensitive drum 1 and the shielding layers 37a and 37b to cause leakage of electric charges of the electrophotographic image, so that an output signal itself is impaired. For that reason, for leakage prevention, it is preferable that at least the above-described range of D2 is not covered with the shielding layers 37a and 37b.
Further, heights H1 and H2 from the photosensitive drum 1 to the lower edges of the shielding layers 37a and 37b are also important. The heights H1 and H2 may preferably be 5 to 5000 μm. When the heights H1 and H2 are lower than 5 μm, slight leakage of current is caused to occur by vertical vibration of the end of the potential sensor 30 due to the eccentric rotation of the photosensitive drum 1, so that the detection cannot be effected. When the heights H1 and H2 are higher than 5000 μm, a shielding effect necessary for the detection electrode portion 32a is insufficient, so that noise of the output signal is increased and thus it is difficult to accurately detect the electrophotographic image.
Basically, the shielding layers 37a and 37b may preferably cover most of the cured end surface except for the contact area of the end of the potential sensor 30. As a result, the shielding layer 37a extending toward a downstream side with respect to the rotational direction of the photosensitive drum 1 covers the curved end surface in a larger amount than that of the shielding layer 37b extending toward an opposite side.
The shielding layers 37a and 37b may preferably have a film (layer) thickness of 0.1 to 1000 μm. Below 0.1 μm, the shielding layers 37a and 37b cannot follow bending of the thin plate portion of the potential sensor 30 contacting the photosensitive drum 1 to be liable to cause crack or the like, so that disconnection or the like occurs. On the other hand, above 100 μm, the edges of the shielding layers 37a and 37b come near to the photosensitive drum 1, so that the electrode is liable to be leaked.
As an angle at which the end of the potential sensor 30 contacts the photosensitive drum 1, in order that the end of the potential sensor 30 can follow the surface vibration of the photosensitive drum 1 by being brought into oblique contact with the photosensitive drum 1, a contact angle α formed between a direction normal to a rotation center of the photosensitive drum 1 and a direction of a center line of the potential sensor 30 extending to the contact point of the potential sensor 30 with the photosensitive drum 1 may preferably be 5 to 80 degrees. When the contact angle α is less than 5 degrees, followability with respect to the surface vibration of the photosensitive drum 1 is worsen, so that the signal is liable to be unstable. When the contact angle α is more than 80 degrees, the potential sensor 30 is liable to tangentially contact the photosensitive drum 1, so that the detection cannot be effected satisfactorily also in this case. This is because the potential sensor 30 can detect a stable signal by ensuring the above-described heights H1 and H2 from the photosensitive drum 1 to the lower edges of the shielding layers 37a and 37b.
A linear pressure of the potential sensor 30 with respect to the photosensitive drum 1 may preferably be 0.01 mg/mm to 10 g/mm. When the linear is less than 0.01 mg/mm, the potential sensor 30 is in a substantially non-contact state with the photosensitive drum 1, so that signal stability is insufficient. When the linear pressure is larger than 10 g/mm, there is a possibility that the potential sensor 30 damages the photosensitive drum 1.
As shown in
a) and 13(b) show results of comparison of detected signals of electrophotographic images when images of
As shown in
With a smaller amplitude NL of the noise signal, even a slight peak voltage can be detected accurately. On the other hand, when the noise signal amplitude NL is large, the peak voltage is buried in noise to be less readable, so that it is difficult to discriminate the peak voltage. Absolute values of the output voltage are not limited to those in
a) to 14(b) are explanatory views of a manufacturing method of the potential sensor, and
The potential sensor manufacturing method shown in
As shown in
On the film 31 and the thin film electrode layer 32, a cover layer 33 is provided. The cover layer 33 is constituted by an adhesive layer 34, a film layer 35, and an adhesive layer 36. First, as shown in
Thereafter, as shown in
As shown in
Each of the thicknesses of the film 31 and the film 35 may be 5 to 100 μm, preferably 15 to 50 μm. Below 5 μm, strength of the thin plate-like portion of the potential sensor 30 is weakened and thus the thin plate-like portion is broken, so that sensitivity non-uniformity of the potential sensor 30 is caused to occur. Above 50 μm, the strength of the thin plate-like portion is excessively increased, so that the thin plate-like portion damages the photosensitive drum 1.
As an adhesive used for the adhesive layers 34 an 36, a general-purpose adhesive may preferably be used. Specific examples thereof may include adhesives of vinyl chloride type, vinylidene chloride type, natural rubber type, polyacrylate type, synthetic rubber type, acrylic type, acryl/styrene modified type, styrene-butadiene rubber type, isoprene rubber type, neoprene rubber type, neoprene-phenol type, butadiene rubber type, cured acrylic type, polyurethane type, and the like. The material for the adhesive layers 34 and 36 can be arbitrarily selected from these adhesives. The thickness of each of the adhesive layers 34 and 36 may preferably be 5 to 100 μm. Below 5 μm, an adhesive strength is lowered, so that a gap is liable to occur above 100 μm, rigidity is excessively increased, so that there is a possibility of damage to the photosensitive drum 1.
The potential sensor manufacturing method shown in
As shown in
As shown in
As shown in
The potential sensor 30 in this embodiment is configured to detect the surface potential of the photosensitive member on the basis of current induced in the thin film electrode layer.
In this case, there is a possibility of a lowering in S/N ratio of a detected signal due to radiation noise.
Therefore, as described above, the potential sensor 30 in this embodiment is covered with the shielding layer. During normal image formation, normal development cannot be effected when the application of the oscillating voltage to the developing sleeve 4s is terminated, so that the application of the oscillating voltage is not interrupted until the image formation is completed. However, when the test electrophotographic image 1s is detected by the potential sensor 30 provided with no shielding layer 37a in a state in which the oscillating voltage is applied to the developing sleeve 4s, high-frequency noise at high level appears in an output waveform measured by the oscilloscope. This is because radio wave noise generates due to an influence of an AC voltage component contained in the oscillating voltage and therefore the potential sensor 30 constitutes an antenna to detect the noise. For this reason, the shielding layer 37a is disposed and is connected to ground potential so as to keep the surface potential of the potential sensor 30 at the ground potential, so that an unnecessary AC voltage is prevented from being induced in the thin film electrode layer 32.
Incidentally, in this embodiment, high-frequency noise from the charging roller also influences the S/N ratio of the detected signal. For this reason, in order to prevent the S/N ratio of the detected signal from being lowered, the above-described shielding layer 37b is a very effective means.
As shown in
By the rotation of the photosensitive drum 1, the test electrophotographic image 1s including portions with the dark portion potential VD and portions with the light portion potential VL passes through the potential sensor 30. At this time, the detection electrode portion 32a opposes the photosensitive drum 1 with a constant distance, so that a voltage signal depending on a change in surface potential of the photosensitive drum 1 is detected by the detection electrode portion 32a.
In a process in which the test electrophotographic image 1s comes near to the potential sensor 30, induced current flows from the detection electrode portion 32a, so that a voltage signal of a positive polarity is output. Thereafter, in a process in which the test electrophotographic image 1s has passed through the potential sensor 30 and moves away from the potential sensor 30, the induced current enters the detect electrode portion 32a, so that a voltage signal of a negative polarity is output. In this manner, an output waveform corresponding to differential waveform of potential distribution of the test electrophotographic image 1s is output from the potential sensor 30 (
The potential sensor 30 outputs peaks of the output voltage at rising edge and falling edge of the potential distribution of the test electrophotographic image 1s. Positive and negative peak values of the output voltage corresponds to slopes of the edges of the potential distribution of the test electrophotographic image 1s. The control portion 110 determines the image deletion state on the photosensitive drum 1 without forming the toner image by measuring the peak values of the output voltage at the time when the potential sensor 30 detects the test electrophotographic image 1s.
The control portion 110 obtains the output of the potential sensor 30 through a signal processing circuit 120. The output voltage of the potential sensor 30 is amplified by an amplifying circuit 121 and then is converted into a digital value by an AD converter circuit 122 to be input into the control portion 110. The control portion 110 compares the measured peak voltage value with a reference value of the peak voltage measured in a low-temperature/low-humidity (L/L) environment in a state in which the photosensitive drum 1 is in a fresh photosensitive drum.
Specifically, the signal processing circuit amplifies the voltage signal of the potential sensor 30 by the amplifying circuit 121 and outputs an analog voltage signal corresponding to the differential waveform of the potential distribution of the test electrophotographic image 1s as shown at (a). The analog processing circuit 122 detects positive and negative peak voltages VP1 and VP2 of the amplified analog voltage signal and converts the peak voltages PV1 and PV2 into digital peak voltages (A/D conversion). The resultant data is sent to the control portion 110 by output circuits 123 and 124. The control portion 110 obtains the positive and negative peak voltages VP1 and VP2 and then judges the slope of the edge of the potential distribution of the test electrophotographic image 1s.
An integrating circuit 125 integrates “the analog signal corresponding to the differential waveform of the potential distribution” output from the amplifying circuit 121 and outputs an analog voltage signal corresponding to the potential distribution as shown at (b). An amplitude VP3 of this analog voltage signal is a value reflecting an electrophotographic image contrast of the test electrophotographic image 1s (i.e., the sum of a developing contrast (a difference between Vdc and VL) and a fog-removal voltage (a difference between VD and Vdc) in
Here, the case where the detection electrode portion 32a and the surface of the photosensitive drum 1 are regarded as a capacitor with an opposing electrode distance d and the photosensitive drum 1-side potential is changed is considered. In this case, a voltage V output by the induced current entering and flowing from the detection electrode portion 32a changes depending on the opposing electrode distance d, so that the output voltage of the potential sensor 30 fluctuates by the eccentric rotation of the photosensitive drum 1 and vibration of the potential sensor 30.
V=Q/C=k×Q×d/S (k: constant, d: opposing electrode distance, S: electrode area)
Accordingly, surface amplitude by movement is generated by the eccentric rotation or the like of the photosensitive drum 1, so that the output of the potential sensor 30 is changed by 10% only by fluctuation of 2.5 μm of the opposing electrode distance d of 25 μm.
In this regard, the potential sensor 30 contacts the photosensitive drum 1 at the curved end surface, so that an external mechanism or control for keeping the opposing distance between the detection electrode portion 32a and the photosensitive drum 1 at a constant level is not needed. The opposing distance can be kept at the constant level by the thickness of the film 31 while the curved end surface follows the eccentric rotation of the photosensitive drum 1.
Further, the potential sensor 30 obliquely contacts the surface of the photosensitive drum 1 so that the end thereof projects toward the rotational direction in a plane perpendicular to a widthwise direction of the photosensitive drum 1. By the oblique contact, the potential sensor 30 end is urged upward by a frictional force with respect to the photosensitive drum 1 to be decreased in contact pressure, so that the potential sensor 30 can precisely follow the surface of the photosensitive drum 1 while keeping a stable small contact pressure even when the photosensitive drum 1 causes the eccentric rotation.
As shown in
As shown in
The image deletion is liable to occur after the image forming apparatus is stopped and then is left standing for a long time. For this reason, the image deletion is less liable to occur during a continuous operation of the image forming apparatus 100. This is because a surface temperature of the photosensitive drum 1 is kept at a high level by radiation heat of the fixing device 8 and frictional heat of the cleaning blade 6b during the image formation and therefore the surface of the photosensitive drum 1 is drier than ambient portions due to a temperature difference to suppress adsorption of the water content.
However, when time has elapsed to some extent after the image forming apparatus is stopped, the surface temperature of the photosensitive drum 1 is lowered to the same temperature as the ambient portions. For this reason, the surface of the photosensitive drum 1 is more liable to adsorb the water content than the ambient portions in proportion to enhancement of hygroscopicity and hydrophilicity by the deposition of the electric discharge products.
First, an experiment causing the image deletion in a high-temperature/high-humidity (H/H) environment (30° C./80% RH) by using the photosensitive drum 1 which was made liable to cause the image deletion by being subjected to an image forming test on 100,000 sheets was conducted. By using the photosensitive drum 1 made liable to cause the image deletion, continuous image formation on 10,000 sheets of A4-sized plain paper with landscape feeding was performed in a one-sheet intermittent manner to form 40 lines per sheet of the test electrophotographic image 1s (line width (2 dots): 80 μm) extending in the main scan direction. As shown in
Next, the test electrophotographic image 1s was formed on the photosensitive drum 1 and subjected to image output and at the same time the potential distribution of the test electrophotographic image 1s was measured by using the potential sensor 30. Image deletion states different in level were intentionally generated by changing the temperature and the humidity, the type of the photosensitive drum 1, a rest time, a rest environment, and the like, so that a relationship with a peak value of an output signal of the potential sensor 30 was investigated.
As shown in
As a result, it was confirmed that the degree of the image deletion of the formed image and the peak voltage of the obtained output signal showed high correlativity. Accordingly, by measuring the peak voltage of the detection signal of the test electrophotographic image 1s with the use of the potential sensor 30, it was confirmed that an occurrence of the image deletion was sufficiently predictable.
The control portion 110 as a controller executes a refresh mode for refreshing the photosensitive drum 1 when a slope of a potential of the test electrophotographic image 1s from the light portion potential to the dark portion potential is gentler than a predetermined slope. Further, an execution time of the refresh mode for refreshing the photosensitive drum 1 is prolonged with the potential slope gentler than the predetermined slope.
In the refresh mode, a processing in which the photosensitive drum 1 is idled is performed. During the idling, the photosensitive drum 1 is rubbed with the cleaning blade 6b, so that the water content deposited on the surface of the photosensitive drum 1 is removed. By this removal of the water content, it is possible to avoid the above-described image deletion phenomenon.
Further, it is also possible to employ such a constitution that the refresh mode is executed when the potential slope of the test electrophotographic image 1s from the dark portion potential to the light portion potential is detected and the detected potential slope is gentler than the predetermined slope.
The idling time in the refresh mode is set depending on the peak voltage of the output signal of the potential sensor 30 so that the idling time is set at a larger value with a smaller peak voltage Vp.
Incidentally, as described in JP-A 2002-40876, the surface resistance may be restored by using a heater as a heating device contained in an inner hollow portion of the photosensitive drum. In this case, an energization time of the heater may be set at a larger value with a smaller peak voltage Vp.
In either case, the potential of the test electrophotographic image 1s measured by the potential sensor 30 and a control time for restoring the surface resistance of the photosensitive drum 1 is set depending on a measurement result. Then, with completion of the control for restoring the surface resistance (the refresh mode) for the set time, image formation is started. Incidentally, in the case where the refresh mode is executed during warm-up immediately after a main switch is turned on, a warm-up sequence is completed by stopping the rotation of the photosensitive drum 1 with the completion of the refresh mode.
Then, a sequence of the refresh mode will be described.
As shown in
In the case of a normal-temperature/normal-humidity environment (N/N: 23° C./50% RH), the peak voltage of the detection signal of the test electrophotographic image 1s was restored to 85% of the reference value by the idling for 20 sec.
In the case of a normal-temperature/low-humidity environment (N/L: 23° C./5% RH), the water content causing the image deletion is very small in this environment, so that the peak voltage of the detection signal of the test electrophotographic image 1s was 85% or more from the initial stage. For this reason, the execution of the refresh mode in which the photosensitive drum 1 was idled was not needed.
The image deletion is liable to occur immediately after the standing of the image forming apparatus 100 and is less liable to occur during the continuous operation of the image forming apparatus 100. Therefore, as a measuring against the image deletion, a method of executing the refresh mode concentratedly during pre-rotation at the time of actuating the image forming apparatus 100 or pre-rotation, before image formation, at the time of re-actuating the image forming apparatus 100 after stand-by in a sleep mode is effective.
In this embodiment, as described above, a lowing in peak height of 15% on the basis of the reference value of the detection signal is taken was a threshold value for determining whether or not the measure against the image deletion is taken or not.
As shown in
The control portion 110 forms the test electrophotographic image 1s (
The control portion 110 extracts a peak height in a lowest area from the peak height values (S4).
The control portion 110 sends an image formation enabling signal when a peak height of 85 or more of the reference value (i.e., a peak height in a range within 15 or less of the reference value) is detected (S4).
On the other hand, the control portion 110 executes the refresh mode when a peak height of less than 85% is detected (S6). In this refresh mode, as described above, the idling of the photosensitive drum 1 is performed, so that the water content is removed by the rubbing with the cleaning blade.
When the refresh mode is completed, the image formation enabling signal is sent.
According to this control, the state of the image deletion can be converted into a signal by detecting the electrophotographic image, so that the image deletion state can be stably detected with high accuracy. Therefore, it is possible to avoid the occurrence of the image deletion, so that it is possible to present the occurrence of the image defect.
a) and 16(b) are explanatory views of another detection electrode.
As another detection electrode buried in the end portion of the potential sensor 30, a wire type detection electrode described in JP-A Hei 11-183542 and JP-A 2004-77125 is used.
Outside an L-shaped wire 42 shown in
In this case, a wire diameter D4 of the wire 42 used largely affects detection resolving power of the potential sensor 40. Basically, the wire diameter D4 may desirably be small but a thickness D5 of the film 31 is required to be larger with a decreasing wire diameter D4, so that a signal strength is rather lowered. For this reason, there is a lower limit with respect to the wire diameter D4.
The wire diameter D4 may desirably be 1 to 500 μm.
As shown in
Film 31 and center film layer 36: PET (“Lu-mirror”, mfd. by Toray Industries, Inc.), thickness=25 μm, width=2.5 mm, length=45 mm, Young's modulus=2.7 GPa, resistance=1×1015Ω×cm.
Thin film electrode layer 32i silver paste (“K-3424”, mfd. by K.K. Shinto Chemitron), resistance=1.59×10−6Ω×cm.
Electrode pattern: L-shaped pattern of
Adhesive layers 34 and 36: acrylic type adhesive (“Olibain”, mfd. by Toyo Ink Mfg. Co., Ltd.), thickness=20 μm, bar coater application and drying.
Folding back position: 20 mm from the end.
As shown in
As shown in
Onto the photosensitive drum 1, a slight amount of a finger mark (finger oil) was intentionally applied at one position. By using the photosensitive drum 1, in the high-temperature/high-humidity environment (30° C./80% RH), image formation of a line image including 40 lines with a line width of 100 μm and a line interval of 100 μm as shown in
As shown in
Film 31 and center film layer 36: polyimide film (“Kapton”, mfd. by DuPont-Toray Co., Ltd.), thickness=100 μm, width=2.5 mm, length=45 mm, Young's modulus=1.96 GPa, resistance=1×1016Ω×cm.
Thin film electrode layer 32i copper paste (“CUX-R”, mfd. by K.K. Mitsuboshi Belting Ltd.), resistance=1.68×10−6Ω×cm.
As shown in
Trough the steps shown in
The thus-prepared potential sensor 30 was also subjected to the same evaluation as in Embodiment 1.
Onto the photosensitive drum 1, a slight amount of the finger mark (finger oil) was intentionally applied at one position. By using the photosensitive drum 1, in the high-temperature/high-humidity environment (30° C./80% RH), image formation of a horizontal line image with a line width of 100 μm as shown in
The potential sensor 40 using the wire electrode as shown in
Film 31: polyphenylene sulfide film (“Torelina”, mfd. by Toray Industries, Inc.), thickness=100 μm, electric resistance=1×1016Ω×cm, Young's modulus=2.5 GPa.
Wire electrode: Tungsten wire, diameter=50 μm.
As shown in
The photosensitive drum 1 was damaged to leave a scar of about 200 μm in diameter and then was subjected to the same evaluation as in Embodiment 1. The photosensitive drum 1 was subjected to image formation of a horizontal line image with a line width of 100 μm on plain paper as shown in Figure in the low-temperature/low humidity environment (15° C./10% RH). At that time, the resultant image was deleted at a position corresponding to the scar portion to expose the white background. When the finger mark portion was subjected to measurement by the potential sensor 40, a resultant peak voltage value of the output signal was lowered by about 65% compared with the case of image formation before the photosensitive drum 1 was damaged to leave the scar portion.
While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth and this application is intended to cover such modifications or changes as may come within the purpose of the improvements or the scope of the following claims.
This application claims priority from Japanese Patent Application No. 225396/2008 filed Sep. 3, 2008, which is hereby incorporated by reference.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008-225396 | Sep 2008 | JP | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12546214 | Aug 2009 | US |
| Child | 13489585 | US |
