The present invention relates to an image forming apparatus, having a function of forming an image on a recording material of, e.g., a sheet or the like, such as a copying machine, a printer or a facsimile machine.
The image forming apparatus of an electrophotographic type in which a charging member is contacted to a photosensitive member to uniformly charge the photosensitive member and then an electrostatic image is formed on the charged photosensitive member by exposure has been conventionally known.
In a general image forming process in the electrophotographic type, the electrostatic image formed on the photosensitive drum is developed with a toner into a toner image and the thus-obtained toner image is transferred onto the recording material and is fixed on the recording material by heat and pressure, so that a print is outputted.
Here, when a voltage is applied to the charging member, electric discharge is generated at both sides of a portion where a contact member is contacted to an object to be discharged, such as the photosensitive member or an intermediary transfer member. When the electric discharge is generated in the air, an electric discharge product such as a nitrogen oxide is generated from the air, so that the generated electric discharge product is deposited on the photosensitive member.
Recently, in order to extend a lifetime, the photosensitive member having a surface layer with high hardness is used. The surface of the photosensitive member with high hardness is not readily abraded and therefore the electric discharge product has been unable to be sufficiently removed by a cleaning member such as a cleaning blade.
The electric discharge product which has not been sufficiently removed by the cleaning member causes, when it absorbs moisture in the air, image defect which is called image flow. For that reason, in the case where the high-hardness photosensitive member is used, it would be considered that the electric discharge product is removed by incorporating organic fine particles as abrasives into a developer (Japanese Laid-Open Patent Application Hei 1-113780).
By employing the above constitution, even in the case where the photosensitive member has the high hardness, the photosensitive member is sufficiently abraded by the abrasives incorporated in the developer, so that an effect such that the occurrence of the image flow is suppressed can be obtained.
However, even when abrasive particles for improving an abrasive force for the photosensitive member are contained in the developer, in the case where the abrasive particles are not supplied to the photosensitive member (e.g., in a period in which the developer is filled in an empty developing device), the present inventor noticed that the image flow cannot be sufficiently suppressed.
A conventional process cartridge or the like including the developing device or integrally including the developing device and the photosensitive member is shipped in a state in which at least a developing sleeve is not coated with the developer in order to prevent the developer (toner) from leaking out during conveyance. Specifically, the inside of a developing container is empty or the developing container is sealed with a film so as to prevent the toner contained in therein from leaking out. Thus, in the case where the developing device is provided in an apparatus main assembly in the state in which the developing sleeve is not coated with the developer, a series of operations for feeding the toner to the developing container, coating the developing sleeve with the toner and initializing various sensors on the basis of a proportion between the toner and a carrier of the developer in an initial state (these operations are referred to as a development initializing operation) is performed.
In such a period of the development initializing operation, the abrasives cannot be supplied to the photosensitive member sufficiently and therefore it is difficult to sufficiently remove the electric discharge product deposited on the photosensitive member.
According to an aspect of the present invention, there is provided an image forming apparatus comprising: a photosensitive member; a charging device for electrically charging the photosensitive member; a developing device for developing an electrostatic image formed on the photosensitive member, wherein the developing device includes a carrying member for carrying and conveying the toner to a position where the toner opposes the photosensitive member, and includes a screw, which is rotated by receiving a driving force from a driving source common to the screw and the carrying member, for feeding the toner; a transfer device for transferring a toner image formed on the photosensitive member; an exposure device, provided downstream of the transfer device and upstream of the charging device with respect to a rotational direction of the photosensitive member, for lowering a potential of the photosensitive member by exposing the photosensitive member to light; and a controller for effecting, in a period in which the screw is rotated to supply the toner to a portion of the carrying member where the toner is not carried, such a control that the toner is not moved from the carrying member to the photosensitive member by electrically charging the photosensitive member by the charging device and that an exposure amount of the photosensitive member by the exposure device is smaller than that during image formation.
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.
Hereinbelow, the image forming apparatus according to the present invention will be described with reference to the drawings.
The image forming apparatus includes an image output portion 1P. The image output portion 1P roughly includes an image forming portion 10 (10a, 10b, 10c, 10d), a sheet feeding unit 20, an intermediary transfer unit 30, a fixing unit 40, and a control unit 37. The image forming portion 10 includes four stations P (Pa, Pb, Pc and Pd) which are disposed side by side and have the same constitution.
Each of the units of the image forming apparatus will be described more specifically. At each station P, a drum-like electrophotographic photosensitive member (photosensitive drum) 11 (11a, 11b, 11c, 11d) as an image bearing member is shaft-supported at its center and is rotationally driven in a direction indicated by an arrow. Oppositely to an outer peripheral surface of the photosensitive member 11 (11a, 11b, 11c, 11d), along the rotational direction of the photosensitive member, a primary charger 12 (12a, 12b, 12c, 12d), a laser scanner unit 13 (13a, 13b, 13c, 13d) and a developing device 14 (14a, 14b, 14c, 14d) are disposed. In this embodiment, as the developing device 14 which is a developing means, the developing device 14a is representatively shown in
In this embodiment, as the developer, a two-component developer containing a non-magnetic toner and a magnetic carrier is used. Further, as a characteristic of a color toner (non-magnetic toner particles), it is preferable that a weight-average particle size is 5-8 μm for forming a good image. When the weight-average particle size is within this range, a sufficient resolution property is provided, so that a clear and high-quality image can be formed and a deposition force and an agglomeration force become smaller than an electrostatic force, thus reducing a degree of various troubles.
In this embodiment, primary transfer rollers 12a-12d as a primary charging member constituting the primary charger which is a charging means provide electric charges having uniform charge amount to the surface of the photosensitive drums 11a-11d. Then, by the laser scanner units 13a-13d which are an information writing means, the photosensitive members 11a-11d are exposed to a light beam such as a laser beam modulated correspondingly to a recording image signal, so that an electrostatic latent image is formed on each of the photosensitive drums 11a-11d.
Further, the developers (toners) of four colors of yellow, cyan, magenta and black are supplied to the electrostatic latent images by the developing devices 14a-14d containing the developers, respectively, so that the electrostatic latent images are visualized. The resultant developer images, i.e., the toner images are transferred onto an intermediary transfer belt 31, which is a transfer-receiving material, in image transfer areas Ta, Tb, Tc and Td. Downstream of the image transfer areas Ta, Tb, Tc and Td, toners remaining on the photosensitive drums 11a-11d without being transferred onto a recording material S are scraped off by cleaning devices 15a, 15b, 15c and 15d, so that the respective drum surfaces are cleaned.
By the above-described process, image forming operations with the respective toners are successively performed.
As each of the photosensitive drums 11a-11d, a negatively chargeable OPC photosensitive drum was used. Specifically, as a photosensitive member layer, a negatively chargeable organic semiconductor layer (OPC layer) obtained by laminating a 29 μm-thick CTL layer (carrier transporting layer), in which hydrazone resin is mixed, on a CGL layer (carrier generating layer) of an azo pigment is used.
Next, the cleaning device 15 (15a, 15b, 15c, 15d) as a cleaning means will be described.
As the cleaning device 15 (15a-15d), a counter blade type cleaning device is used and a free length of a cleaning blade 16 (16a-16d) is 8 mm. The cleaning blade 16 is an elastic blade principally comprising urethane resin and is contacted to the photosensitive drum 11 with a linear pressure of about 35 g/cm.
In this embodiment, the above-described photosensitive drum 11, primary charger 12, developing device 14 and cleaning device 15 are integrally assembled into a unit to constitute a process cartridge, which is detachably mountable to an image forming apparatus main assembly. However, the present invention is not limited to this constitution.
The sheet-feeding unit 20 includes cassettes 21a and 21b for accommodating the recording material S, a manual feeding tray 27, and pick-up rollers 22a, 22b and 26 for feeding the recording material S one by one from the cassettes 21a and 21b and the manual feeding tray 27. Further, the unit 20 includes sheet-feeding roller pairs 23 and a sheet feeding guide 24 which are used for conveying the recording material S, fed from each of the pick-up rollers 22a, 22b and 26, to registration rollers 25a and 25b. The registration rollers 25a and 25b are rollers for sensing the recording material S to a secondary transfer area Te in synchronism with image formation timing of the image forming portion.
The intermediary transfer unit 30 will be described in detail.
As a material for the intermediary transfer belt 31, it is possible to use, e.g., PET (polyethylene terephthalate) and PVdF (polyvinylidene fluoride). The intermediary transfer belt 31 is stretched and extended around a driving roller 32 for transmitting a driving force of the intermediary transfer belt 31, a tension roller 33 for applying proper tension to the intermediary transfer belt 31 by urging of springs (not shown), and a follower roller 34 which opposes the secondary transfer area Te via the belt. The intermediary transfer belt 31 is circulated and moved in an arrow B direction in
In the primary transfer areas Ta-Td in which the photosensitive drums 11a-11d and the intermediary transfer belt 31 oppose each other, primary transfer rollers 35 (35a, 35b, 35c, 35d) are disposed on the back surface of the intermediary transfer belt 31. The secondary transfer roller 36 is disposed oppositely to the follower roller 34 to form the secondary transfer area Te in a nip belt itself and the intermediary transfer belt 31.
The secondary transfer roller 36 is urged against the intermediary transfer belt 31 under a proper pressure. Further, in the rotational direction of the intermediary transfer belt 31, downstream of the secondary transfer area Te, a brush roller (not shown) for cleaning an image forming surface of the intermediary transfer belt 31 and a residual toner box (not shown) for containing residual toner are provided. Further, on the intermediary transfer belt 31, a cleaning device 100 for removing secondary transfer residual toner is provided.
The fixing unit 40 includes a fixing roller 41a provided with a heat source such as a halogen heater inside the fixing roller 41a and includes a pressing roller 41b to be pressed by the fixing roller 41a. The pressuring roller 41b may also contain the heat source. The fixing unit 40 further includes a guide 43 for guiding the recording material S into a nip between the rollers 41a and 41b, and inner sheet discharging rollers 44 and outer sheet discharging rollers 45 for guiding the recording material S, discharged from the rollers 41a and 41b, to the outside of the image forming apparatus.
The control unit 37 is constituted by a control board for controlling operations of mechanisms in the above-described respective units and by a motor drive board (not shown) and the like and includes a control means (CPU) 301 (
As the intermediary transfer belt 31, a 100 μm-thick polyimide film is used, and in this embodiment the case where an urethane sponge roller is used as the primary transfer roller 35 (15a-35d) provided at the primary transfer portion will be described.
In the image forming apparatus used in this embodiment, a peripheral speed of the intermediary transfer belt 31 is 300 mm/sec and a width of each of the primary transfer portions with respect to the thrust direction is 330 mm. The toner on the photosensitive member 11 has a charge retaining amount of 30 μC/g and a current of 40 μA is applied to a core metal of the primary transfer roller 35 during the primary transfer. This applied current amount may desirably be changed depending on a change in toner charge retaining amount or the like caused due to a change in environment but the above value is a proper current value set in a normal environment (23° C./60% RH).
Next, the charging roller 12 which is the charging member will be described.
A roller surface layer of the charging roller 12 is formed of 1-2 mm thick electroconductive rubber in which an electroconductive material such as carbon black is dispersed and mixed, and is controlled so that a resistance value thereof is 105 to 107 ohm·cm in order to prevent charging non-uniformity during the image formation. Further, the charging roller 12 is of a contact type in which it is contactable to the photosensitive drum 11 without creating a gap by utilizing its elasticity, and charges the photosensitive drum 11 at a low voltage. Or, on a surface of an electroconductive support, ABS resin which contains an ion conductive polymeric compound such as polyetherester amide and is controlled so as to have a resistance value of 105 to 107 ohm·cm is coated in a thickness of 0.5 to 1 mm by injection molding to form a resistance adjustment layer. On the surface of the resistance adjustment layer, a protective layer of a thermoplastic resin composition containing electroconductive fine particles of tin oxide or the like dispersed therein is formed. As the electroconductive support to which a charging voltage is to be applied, a metal shaft member is used. The metal shaft member is constituted by integrally molding a shaft-supporting portion, a voltage-applying shaft-supporting portion, and a coating portion providing an outer diameter of 14 mm. On the peripheral surface of the coating layer, the resistance adjustment layer, of the ABS resin (thermoplastic resin) containing the ion conductive polymeric compound such as polyetherester amide, adjusted to have a volume resistivity of 105 to 107 ohm·cm is coated in the thickness of 0.5 to 1 mm by the injection molding.
Next, the constitution, around the photosensitive drum 11, which constitutes the image forming portion 10 in this embodiment and the process cartridge will be described with reference to
The optical charge-removing means 112a in the present invention is roughly constituted by the following two members.
1. Light-emitting source: “LED lamp” 503 provided to the image forming apparatus main assembly.
2. Light irradiating member: “Rod-like light guide” 501 provided in the process cartridge constituting each station P.
Here, the LED lamp 503 and the rod-like light guide 501 will be further described.
First, the light guide LED lamp 503 as the light-emitting source functions as a light source of the optical charge-removing means 112a and is provided outside an image forming apparatus side plate (image forming apparatus main assembly). Further, the LED lamp 503 is disposed outside a charge-removing width (area) on the photosensitive drum with respect to a longitudinal direction. That is, the LED lamp 503 exposes the light guide 501 to light from a direction C parallel (or non-parallel) to the longitudinal direction of the light guide 501 (or the photosensitive drum 11a). Further, a light-blocking measure (not shown) is also taken so that an end portion of the photosensitive drum 11a is unnecessarily exposed to the light from the LED lamp 503.
Next, the rod-like light guide 501 will be described with respect to a material, a shape, a function and an arrangement.
As a material for the light guide 501, a resin material excellent in light transmittance, such as acrylic resin, polycarbonate or polystyrene, or glass is used. A shape of the light guide 501 is shown in
At a portion where the light guide surface opposes the photosensitive drum 11a, a plurality of V-shaped cuts 502 for forming projection/recess portion as a reflection means are provided. The number of the cuts 502 may be any number and can also be one. Further, the shape of the projection/recess portion is not necessarily V-shape but may also be other shapes such as U-shape and I-shape.
As shown in
Further, in this embodiment, the light guide 501 is spaced from the photosensitive drum 11a with a spacing distance of 4 mm and is disposed oppositely to the photosensitive drum 11a with respect to the longitudinal direction in order to remove the electric charges on the photosensitive drum 11a after the transfer step.
Next, with reference to
As in this embodiment, in the case where the member of a “light guide type” is used as the light irradiating member for the photosensitive drum 11a, compared with a “chip array type” in which a plurality of, e.g., LEDs are arranged, a ripple (degree of variation) of the light quantity on the photosensitive drum is small, so that the electric charges can be uniformly removed.
Incidentally, the LED lamp 503 in this embodiment is provided at a position opposing one end surface of the light guide 501 but may also be provided at two positions opposing both end surfaces of the light guide 501 in, e.g., the case where the light quantity is insufficient. In that case, the cuts of the light guide are made deepest (largest) at its central portion so that a light quantity distribution becomes uniform in the charge-removing area on the photosensitive drum.
As described above, by providing the optical charge-removing means 112a as in this embodiment, image disadvantages, such as a lateral stripe and a positive ghost, generated in a halftone image were prevented relatively inexpensively without impairing a design latitude of the image forming apparatus main assembly, so that it became possible to obtain a good image.
In this embodiment, in order to reflect the light emitted from the LED lamp 503 onto the surface of the photosensitive drum 11a, a reflection surface as a reflection film which is a reflection means is provided on the light guide surface by using paint (or resin) of a color (white, silver or the like) which is high in reflectance.
In this embodiment, the example in which the light guide 501 is provided to the process cartridge is described but the present invention is not limited to such an example. That is, the constitution of the process cartridge may also be such that the light guide 501 is not provided but may be provided to the image forming apparatus main assembly side. As a result, it is possible to reduce a cost of the process cartridge.
Next, the photosensitive drum 11a used in this embodiment will be described. Other photosensitive drums 11b to 11d also have the same constitution.
As shown in
The undercoat layer B is formed for improving an adhesive property of the photosensitive layer, improving a coating property of the photosensitive layer, protecting the support, coating a defect on the support, improving a charge injection property from the support, or protecting the photosensitive layer from electrical breakdown.
On the undercoat layer B, the photosensitive layer is formed. As in this embodiment, in the case where the photosensitive member is of a functionally-separated type in which the charge (carrier) generating layer C and the charge (carrier) transporting layer D are function-separated and laminated, the charge generating layer C and the charge transporting layer D are laminated on the undercoat layer B in this order. The constitution of such a photosensitive member is well known by a person skilled in the art and therefore further detailed description will be omitted.
(Image Flow Phenomenon (Problem) to be Solved by the Present Invention)
Here, generating factors of the image flow and image blur will be described.
The surface layer (i.e., the protective layer) E of the photosensitive drum in
However, the generation of the abrasion or the damage of the photosensitive drum can be prevented but on the other hand, in the case where the electric discharge product such as NOx or ozone is deposited on the photosensitive drum surface, the electric discharge product cannot be satisfactorily removed by the cleaning blade 16. For that reason, there is the disadvantage such that the image defect such as the image flow of the image blur is liable to be caused. That is, of the electric discharge product, NOx reacts with the moisture in the air to generate nitric acid and also reacts with metal to generate metal nitrate. When the thus-generated nitric acid or metal nitrate is formed in a thin film on the image bearing member surface, by a moisture-absorbing action of these nitric acid and metal nitrate, a resistance value of the image bearing member surface is lowered. As a result, the electrostatic latent image formed on the photosensitive drum which is the image bearing member is broken and therefore particularly in a high-humidity environment, an abnormal image such that the image flows is generated.
As described above, by modification of the electric discharge product, the generated nitric acid or metal nitrate is formed in the thin layer on the photosensitive member surface and therefore it is very difficult to remove only the thin film deposited on the surface layer E of the photosensitive drum 11 by the friction with the cleaning blade 16. In order to remove only the thin film by the friction with the cleaning blade 16, there is a need to abrade off the entire surface layer of the photosensitive drum. Accordingly, hardening of the protective layer E and the suppression of the image flow by the abrasion (friction) with the cleaning blade 16 provide a trade-off relationship.
Therefore, in this embodiment, the image flow is suppressed by a method other than the method in which the phenomenon of the image flow or the image blur is suppressed by the cleaning blade 16.
Here, a relationship between the generation of the electric discharge product and a charging factor will be described.
Rank 1: level at which the occurrence of the image flow is not observed.
Rank 2: level at which density non-uniformity on a halftone image is generated in a drum period.
Rank 3: level at which a thin line disappears on a lattice image.
Rank 4: level at which a character is extended.
Rank 5: level at which a character is not printed at all.
The charging type is roughly classified into two types depending on a biasing method. That is, there are so-called a DC charging type in which a DC bias is applied to the contact type charging member and so-called an AC charging type in which the DC bias is superposed with an AC bias.
As shown in the graph of
That is, the image flow occurrence level by the charging DC component and that by the charging AC component are substantially equivalent to each other. For that reason, in the case of the AC charging, in which the DC component is biased with the AC component, which is the charging type inconformity with a high image quality used in this embodiment, deposition of the electric discharge product in an amount which is about two times that in the case of the DC charging is promoted. Therefore, the result such that the image flow occurrence level is correspondingly worsen is obtained (
Next, a block circuit of a charging bias application system in this embodiment will be described.
As a representative example, when the station Pa is described,
A control circuit 103 has a function of controlling the power source S1 so that either one or both (the superposition voltage) of the DC voltage and the AC voltage and applied to the charge roller 12a by turning the DC power source 101 or/and the AC power source 102 of the charging bias source S1 on or off. Further, the control circuit 103 also has a function of controlling the DC voltage value applied from the DC power source 101 to the charging roller 12a and the peak-to-peak voltage value of the AC voltage applied from the AC power source 102 to the charge roller 12a. An AC current value measurement circuit 104 as a means for measuring a value of AC current passing through the charging roller 12a via the photosensitive member 11a is disposed. From this circuit 104, AC current value information measured by the control circuit 103 is inputted. An environment sensor 105 as an environment detection means for detecting an environment in which the image forming apparatus 100 is provided. To the control circuit 103, detected environmental information is inputted from the environment sensor 105.
Further, from the AC current value information inputted from the AC current value measurement circuit 104 and the environmental information inputted from the environment sensor 105, the control circuit 103 has a function of executing a program for operating and determining an appropriate peak-to-peak voltage value of the AC voltage to be applied to the charging roller 12 in the charging step of the printing step.
Here, the development initializing operation in this embodiment will be described. The development initializing operation is carried out when the developing device in an uncoated state is mounted in the image forming apparatus main assembly and a period therefor is longer than a period of a normal pre-multi-rotation step.
The development initializing operation in this embodiment is performed along a flow shown in
As shown in
Here, the pre-multi-rotation operation (S108) normally performed during the turning-on of the main power source of the main assembly is an initial preparatory operation performed in the main assembly until image formation. In general, on the photosensitive drum or the intermediary transfer belt, a patch image is formed with the developer. Then, a density of the patch image is read by a sensor (density sensor 77 shown in
If in the case where the ON signal of the development initializing operation is not provided from the operating panel 303 to the CPU 301, after the main power source is turned on, the control means 301 determines transfer to the above-described normal pre-multi-rotation operation (S108).
Next, the development initializing operation (S103) will be described.
The development initializing operation is an operation normally performed in the case where the developing device is replaced with a new (fresh) developing device when it reaches the end of its lifetime in the main assembly or a trouble is caused, i.e., immediately before the developing device exchange. When the development initializing operation is started (S103), the control means 301 controls a pre-exposure amount of the optical charge-removing means 112 so as to be lower than that during the image formation (S104).
In this embodiment, during the development initializing operation, the CPU 301 of the main assembly performs an operation in which the developing sleeve is coated with the developer to create an image formable state (S105) to judge whether or not the developer is in an initial state. Then, the patch image for density measurement is formed on the intermediary transfer belt so that the density thereof is measurable by the patch density sensor. By measuring the patch image density, whether or not a ratio between the toner and the carrier in the developer (so-called T/D ratio) or a condition of a latent image contrast of the photosensitive drum is required to be changed is judged. In the case where the CPU 301 judges that the change is necessary, correction is made so as to change the T/D ratio from that in the initial state and in addition a condition of charging high voltage setting and developing high voltage setting is changed so as to change the latent image contrast condition. Then, the developer initial state is stored in a memory 302 of the CPU 301.
The operation for coating the developing sleeve with the developer in S105 will be further described.
The developing device is a consumable and is required to be changed to a new developing device some times until the main assembly reaches the end of its lifetime. In general, when the amount of the developer in the developing device is fluctuated or non-uniformity of coating of the developer with respect to a thrust direction is caused by abrasion of the developing sleeve surface, the developing device reaches the end of its lifetime. Then, replacement of each developing device unit or only the developer is made by a service person on a user's premises in many cases. At that time, the developing device unit which is a replacement part is normally sealed so as be suitable for transportation by the service person, i.e., so as to be sealed to prevent drop out of the developing device. Therefore, the service person releases the sealing of the developing device unit on the user's premises and mounts the developing device in the main assembly. However, in this case, the developing sleeve is in a state in which it is substantially not coated with the developer. Therefore, when the developing device is newly mounted, it is required that the developing sleeve and the developing screws in the developing device are driven and rotated for at least several minutes. Further, the developer is not required to be simply present over the inside of the developing device but is required to be triboelectrically charged to some extent so as to be moved onto the latent image portion on the photosensitive drum. For that reason, as described above, a stirring step for several minutes in the developing device is required.
Then, when the above-described development initializing operation is ended (S107), thereafter the control means 301 starts the normal pre-multi-rotation operation (S108). At this time, the control means 301 controls the pre-exposure amount outputted from the optical charge-removing means 112 so that the pre-exposure amount is larger than that during the development initializing operation (S109). Then, after the normal pre-multi-rotation operation is ended (S110), the main assembly is kept in the stand-by state and is controlled so as to await in a copy state enable state (S111).
Here, in the development initializing operation (S103), the CPU 301 as the control means judges whether or not the operation instruction is provided from the user through the operating panel 303 but there is the case where the operation is delayed when the operation is performed after the main power source turning on which is timing when the development initializing operation should be performed. That is, there is the case where the normal pre-multi-rotation operation is performed in the main assembly in a state, before the development initializing operation is performed, in which the developing sleeve is not coated with the developer. In this state, as described above, the operation in which the patch image is formed on the intermediary transfer belt with the developer and its density is read by the density sensor and then is judged and controlled as to whether or not the read image density is proper (so-called patch density control) or the like is performed. For that reason, an inconvenience such that the control cannot be effected at a proper density is caused. Therefore, in the main assembly, the control means 301 is required to perform the development initializing operation before the normal pre-multi-rotation operation is started. In order to realize this operation, in general, in a state of the immediately preceding turning-on of the main power source for performing the development initializing operation, the development initializing operation signal is required to be turned on through the operating panel 303.
As shown in
Generally, the idling time may appropriately be 2 to 3 minutes in view of a coating time of the developing sleeve with the developer and a charging time of the developer but in this embodiment the idling time (S105) was 2 minutes. A conventional operation was performed with setting of the pre-exposure: ON with respect to the pre-exposure amount control means 308 during the operations including the idling operation of the developing device, the developer coating onto the developing sleeve and the developer stirring. However, by study of the present inventor, it was found that the image flow is generated on the photosensitive drum when the time of applying the charging high voltage and performing the idling of the photosensitive drum in a state in which the developer is not coated on the developing sleeve. That is, during this time, the developer is in a state in which the amount of the developer transferred onto the photosensitive drum (so-called developer fog) is very small. For that reason, the developer is not sufficiently supplied to the cleaning blade and thus the electric discharge product on the photosensitive drum cannot be satisfactorily removed by the cleaning blade edge portion, so that the image flow is liable to occur.
However, also in this case, the amount of the electric discharge product deposited on the photosensitive drum, i.e., an amount of electric discharge current passing from the charging member to the photosensitive drum is minimized, so that it was substantiated that the occurrence of the image flow can be suppressed.
Then, as shown in
That is, in this embodiment, the image flow suppression is made by only a means for decreasing the pre-exposure light quantity during only the developing device idling operation, in the development initializing operation, which does not have the influence on the image formation to the end. That is, according to the present invention, a particular device is not required during the development initializing operation, so that the occurrence of the image flow can be suppressed by a method which does not adversely affect the image formation at all.
However, in the case where the pre-exposure amount is substantially 0 V and thus the drum surface is little charge-removed, reversely, the drum surface charged to −700 V is changed to about −300 V after passing through the transfer member. The drum surface reaches again the charging member as it is and therefore only the DC current (charging DC current) corresponding to a contrast of 400 V which is a difference between −700 V and −300 V flows, so that a resultant current amount is about 27 μA.
Therefore, during the development initializing operation which does not influence the image formation, particularly with timing when the developer is coated on the developing sleeve and with timing when the developer is stirred, the discharge amount of the DC component from the charging member is controlled so as to be decreased as small as possible. That is, by decreasing the light quantity of the pre-exposure, it became possible to suppress the occurrence of the image flow during the mounting of the developing device.
A relationship between a setting condition of the pre-exposure light quantity during the development initializing operation and a rank of the image flow is shown in Table 1.
According to the study by the present inventor, the occurrence of the image flow, during the development initializing operation, which is the problem to be solved was able to be suppressed only by changing the setting of the pre-exposure light quantity only with the timing when the image formation is not influenced. Further, as described above, according to the present invention, it is possible to suppress the occurrence of the image flow by an inexpensive and space-saving method which does not require the particular device during the development initializing operation and does not have the influence at all during the image formation.
Next, Embodiment 2 of the present invention will be described. An image flow suppressing method in this embodiment will be described with reference to a flow chart of
The control procedure from the turning on of the main power source to the stand-by state is the same as that shown in the flow chart of
As shown in
Generally, the idling time may appropriately be 2 to 3 minutes in view of a coating time of the developing sleeve with the developer and a charging time of the developer but in this embodiment the idling time (S205) was 2 minutes. Further, as shown in
A conventional operation was performed with the same setting as the normal image setting with respect to the charging high voltage and the developing high voltage during the operations including the idling operation of the developing device, the developer coating onto the developing sleeve and the developer stirring. However, by study of the present inventor, it was found that the image flow is generated on the photosensitive drum when the time of applying the charging high voltage and performing the idling of the photosensitive drum in a state in which the developer is not coated on the developing sleeve. That is, during this time, the developer is in a state in which the amount of the developer transferred onto the photosensitive drum (so-called developer fog) is very small. For that reason, the developer is not sufficiently supplied to the cleaning blade and thus the electric discharge product on the photosensitive drum cannot be satisfactorily removed by the cleaning blade edge portion, so that the image flow is liable to occur.
However, also in this case, the amount of the electric discharge product deposited on the photosensitive drum, i.e., an amount of electric discharge current passing from the charging member to the photosensitive drum is minimized, so that it was substantiated that the occurrence of the image flow can be suppressed.
Then, as shown in
That is, in this embodiment, the image flow suppression is made by only a means for setting the charging high voltage and the developing high voltage at low levels during only the developing device idling operation, in the development initializing operation, which does not have the influence on the image formation to the end. Therefore, also in this embodiment, it is possible to achieve a functional effect similar to that in Embodiment 1.
However, in the case where charging high voltage setting is −300 V, only the DC current corresponding to a contrast of 150 V to 200 V which is a difference between −300 V and −50 V to −100 V flows, so that a resultant current amount is about 30 μA.
Therefore, during the development initializing operation which does not influence the image formation, particularly with timing when the developer is coated on the developing sleeve and with timing when the developer is stirred, the discharge amount of the DC component from the charging member is controlled so as to be decreased as small as possible. That is, by decreasing the charging high voltage value (absolute value), it became possible to suppress the occurrence of the image flow during the mounting of the developing device.
A relationship between a setting condition of the charging DC high voltage during the development initializing operation and a rank of the image flow is shown in Table 2.
According to the study by the present inventor, the occurrence of the image flow, during the development initializing operation, which is the problem to be solved was able to be suppressed only by changing the setting of the charging high voltage only with the timing when the image formation is not influenced.
In the above-described embodiments, the present invention is described as the color image forming apparatus of the intermediary transfer type but is not limited thereto.
The present invention is also applicable to, e.g., a color image forming apparatus of a direct transfer type in which the toner images formed on the surfaces of the respective photosensitive drums 11 (11a, 11b, 11c, 11d) are successively and directly transferred onto the recording material which is a transfer-receiving material conveyed to the respective stations P (Pa, Pb, Pc, Pd) by the recording material carrying member. A constitution of such an image forming apparatus is well known by the person skilled in the art and therefore will be omitted from further detailed description.
To such a color image forming apparatus of the direct transfer type, it is possible to apply the constitutions of Embodiments 1 and 2 described above. In the color image forming apparatus of the direct transfer type, the same constitutions as those in Embodiments 1 and 2 are employed, so that a similar functional effect can be achieved.
Incidentally, in the above-described embodiments, the development initializing operation in the case where the developing device is replaced is described but the present invention is not limited thereto. For example, the present invention may also be adopted to the case where the developing device and another process element are assembled into a unit. That is, in an initializing step performed when a unit in a state in which the developer carrying member (developing sleeve) is not coated with the toner is mounted, the control embodiments of the present invention may also be employed.
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. 021579/2011 filed Feb. 3, 2011, which is hereby incorporated by reference.
Number | Date | Country | Kind |
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2011-021579 | Feb 2011 | JP | national |
Number | Name | Date | Kind |
---|---|---|---|
4621920 | Takahashi | Nov 1986 | A |
5130749 | Tanada | Jul 1992 | A |
5794097 | Shinkawa et al. | Aug 1998 | A |
5911097 | Haga et al. | Jun 1999 | A |
6704522 | Sasago et al. | Mar 2004 | B2 |
6970661 | Shoji | Nov 2005 | B2 |
20080113285 | Nakamori et al. | May 2008 | A1 |
Number | Date | Country |
---|---|---|
01024288 | Jan 1989 | JP |
1-113780 | May 1989 | JP |
04060681 | Feb 1992 | JP |
11038740 | Feb 1999 | JP |
2000147967 | May 2000 | JP |
2007034086 | Feb 2007 | JP |
Number | Date | Country | |
---|---|---|---|
20120201561 A1 | Aug 2012 | US |