1. Field of the Invention
The disclosures herein relate to an image forming apparatus having a developing device configured to develop an image by attaching a toner hopping on a surface of a toner carrier to a latent image formed on a latent image carrier.
2. Description of the Related Art
Japanese Patent Application Publication No. 2010-60918 (hereinafter called “Patent Document 1”) discloses an image forming apparatus of this kind. The developing device of the image forming apparatus disclosed in Patent Document 1 includes a rotatable cylindrical toner carrier roller. The cylindrical toner carrier roller includes long and slim electrodes elongated in a rotational axis direction arranged at predetermined pitches. Alternating electric fields are formed between the adjacently arranged long and slim electrodes on the surface of the cylindrical toner carrier roller. The toner may hop from directly above one of the adjacently arranged electrodes to the other, or vice versa based on directional changes of the alternating electric fields. The toner is then carried to a developing region facing the latent image carrier with a rotational movement of the toner carrier roller while reciprocally hopping between the adjacent electrodes. In the developing region, the toner hops from the surface of the toner carrier roller toward and neat to the latent image carrier and then is attracted by the electric fields formed by the electrostatic latent image. The toner attracted to the electrostatic latent image is attached to the latent image accordingly. The latent image is thus developed by the attachment of the toner.
An image forming apparatus of another kind is also generally known in the art. In such image forming apparatus, the toner is not simply carried by a surface movement of the toner carrier roller while reciprocally hopping between the electrodes but the hopping toner on the surface of toner carrier roller itself moves in a predetermined direction by the hopping behavior. For example, in the image forming apparatus having the toner carrier roller on which three electrodes A, B and C phases are repeatedly arranged in this order, the toner is transferred toward the developing region by allowing the toner to sequentially hop from the A phase electrode to the B phase electrode, the B phase electrode to the C phase electrode, the C phase electrode to the A phase electrode, and the like on the surface of the toner carrier roller.
With these kinds of image forming apparatuses utilizing the hopping toner for the development (hereinafter called a “hopping type developing system”), the low voltage development may be achieved to an extent which may not be achieved by the conventional one-component developing system or two-component developing system. For example, the toner may be selectively attached to the electrostatic latent image having a potential difference of several dozen fractional V between the latent image formed region and a peripheral non-image forming region.
However, if the electrostatic charge of the toner on the surface of the toner carrier roller is lowered, the toner exhibits insufficient hopping on the surface of the toner carrier roller, which may result in development degradation.
The image forming apparatus disclosed in Patent Document 1 is provided with a cleaner device, and the toner exhibiting inferior hopping behavior due to the lowered the electrostatic charge is caused to hop from the surface of the toner carrier roller onto the photoreceptor surface such that the toner is discharged from the surface of the toner carrier roller, and the cleaner device collects the discharged toner from the photoreceptor surface. After the toner is removed from the toner carrier roller, new toner having appropriate electrostatic charge is supplied on the surface of the toner carrier roller. Accordingly, the latent image is developed by attaching the toner exhibiting excellent hopping behavior on the toner carrier roller to a latent image formed on the photoreceptor. Thus, the occurrence of the development degradation may be reduced.
In the image forming apparatus disclosed in Patent Document 1, when the toner having a low electrostatic charge is discharged from the surface of the toner carrier roller, the toner is caused to hop from the surface of the toner carrier roller to the photoreceptor surface by applying alternating voltages having an amplitude greater than that for the developing process and having differing phases to the adjacent first and second electrodes while the toner is removed by the cleaner device. Accordingly, when the alternating voltages having the amplitude relatively greater than that for the developing process are applied to the first and the second electrodes of the toner carrier roller, the toner having the lowered electrostatic charge may hop to the photoreceptor to some extent.
However, if the potential difference between the first electrode and the second electrode is too large, the insulator between the first and the second electrodes may be broken due to current leakage having occurred between the first and the second electrodes. Further, if the alternating voltages having the potential difference that may induce no insulator breakage are applied to the first and the second electrodes while the surface of the toner carrier roller is being cleaned, the electric fields sufficiently large to cause the toner having the drastically lowered electrostatic charge to hop from the toner carrier roller to the photoreceptor may not be generated. In this case, the toner having the drastically lowered electrostatic charge may remain on the surface of the toner carrier roller without hopping from the toner carrier roller to the photoreceptor.
It is a general object of at least one embodiment of the present invention to provide an image forming apparatus capable of discharging the toner having the drastically lowered electrostatic charge from the toner carrier roller onto the latent image carrier while suppressing inducement of insulator breakage that substantially eliminates one or more problems caused by the limitations and disadvantages of the related art.
In one embodiment, there is provided an image forming apparatus that includes a latent image carrier configured to carry a latent image; a latent image writer configured to write the latent image on the latent image carrier; a developing unit including a toner carrier configured to carry toner, the toner carrier including a first electrode and a second electrode arranged along a surface thereof, the first electrode and the second electrode being insulated from each other via an insulator member, and a voltage applying unit configured to apply voltages to the first electrode and the second electrode such that first electric fields formed by a potential difference between the first electrode and the second electrode cause the toner to hop from the toner carrier to the latent image carrier to attach the hopping toner to the latent image formed on the latent image carrier to develop a toner image on the latent image carrier; and a transfer unit configured to transfer the toner image developed on the latent image carrier to a transferring member. In the image forming apparatus, when alternating voltages having a same phase and a same amplitude and capable of forming second electric fields between the latent image carrier and the toner carrier to cause the toner to hop from the toner carrier toward the latent image carrier are applied to the first electrode and the second electrode in a toner discharge mode, the toner is discharged from the toner carrier to the latent image carrier in the toner discharge mode.
Other objects and further features of embodiments will be apparent from the following detailed description when read in conjunction with the accompanying drawings, in which:
In the following, embodiments of the present invention will be described with reference to the accompanying drawings.
An electrophotographic image forming apparatus according to a first embodiment is described. A configuration and operations of the image forming apparatus according to the first embodiment are described.
As illustrated in
Further, in
Moreover, the image forming apparatus according to the first embodiment further includes a temperature sensor 76 as a temperature detector configured to detect the temperature inside the image forming apparatus, a humidity sensor 77 as a humidity detector configured to detect humidity inside the image forming apparatus, a transfer roller 73 as a transfer unit configured to transfer an image from the photoreceptor 1 onto a recording material, and a cleaner device 74 as a cleaning unit configured to clean the surface of the photoreceptor 1. In addition, the image forming apparatus according to the first embodiment further includes not-illustrated paper feeder and fixing device parts. Note that hereinafter, generically, the process units 6M, 6C, 6Y and 6Bk may be called “process unit 6”, the developing devices 4M, 4C, 4Y and 4Bk may be called “developing device 4”, the chargers 2M, 2C, 2Y and 2Bk may be called “charger 2”, and the exposure beams Lm, Lc, Ly and Lbk may be called “exposure beam L” for convenience in illustration.
The photoreceptor 1 is rotatably driven in a direction illustrated by an arrow in
Next, the photoreceptor 1 is uniformly charged by the cyan charger 2C of the cyan process unit 6C, and subsequently exposed with the exposure beam Lc that is modulated based on cyan image data by the optical writer 3 so as to form a cyan electrostatic latent image. The electrostatic latent image is then developed by the cyan developing device 4C so as to form a cyan toner image superimposed over the magenta toner image. Thereafter, the not-illustrated static eliminator discharges the photoreceptor 1.
Further, the photoreceptor 1 is uniformly charged by the yellow charger 2Y of the yellow process unit 6Y, and subsequently exposed with the exposure beam Ly that is modulated based on yellow image data by the optical writer 3 so as to form a yellow electrostatic latent image. The electrostatic latent image is then developed by the yellow developing device 4Y so as to form a yellow toner image superimposed over the cyan and magenta toner images. Thereafter, the not-illustrated static eliminator discharges the photoreceptor 1.
Finally, the photoreceptor 1 is uniformly charged by the black charger 2Bk of the black process unit 6Bk, and subsequently exposed with the exposure beam Lbk that is modulated based on black image data by the optical writer 3 so as to form a black electrostatic latent image. The electrostatic latent image is then developed by the black developing device 4Bk so as to form a black toner image superimposed over the yellow, cyan and magenta toner images.
Meanwhile, the recording material such as a recording sheet is fed by the paper feeder (not illustrated), on which a full-color image formed on the surface of the photoreceptor 1 is transferred by the transfer roller 73 utilized as the transfer unit configured to apply a transfer bias to the recording material. The full-color image formed on the recording material is then fixed by the fixing device (not illustrated) and the recording material on which the full-color image is fixed is then discharged from the image forming apparatus. After having transferred the full-color image to the recording material, residual toner and the like remaining on the surface of the photoreceptor 1 are removed by the cleaner device 74 utilized as the cleaning unit.
In the image forming apparatus having the above configuration, since the four color images are recorded on the surface of the same photoreceptor 1, positional deviations in superimposing the four color images scarcely occur, compared to a generally used tandem type image forming apparatus including four photoreceptors from which different color images are superimposed to form a full-color image.
Note that the configuration of the image forming apparatus according to the first embodiment may be applied to the general tandem type image forming apparatus or to other types of the image forming apparatus.
Next, the developing device 4 utilizing the hopping type developing system adopted by the image forming apparatus according to the first embodiment is described.
Note that the developing devices 4M, 4C, 4Y and 4Bk have the same configurations and exhibit the same operations except that they contain toner of different colors, and thus the generic term “developing device 4” is used in the following illustration when appropriate.
The developing device 4 includes a toner carrier roller 41 utilized as a toner carrier, a toner supply roller 42 utilized as a toner supply member configured to supply toner to the toner carrier roller 41, a regulator blade 43 utilized as a toner regulator member configured to regulate a thickness of a toner layer, an entrance sealer 44, a first transfer screw 45 configured to be rotationally driven in a clockwise direction in
At the toner supply position, the surface of the toner supply roller 42 and the outer circumferential surface of the toner carrier roller 41 move in opposite directions (counter directions) to each other. Note that the toner supply roller 42 and toner carrier roller 41 rotate in the same direction as illustrated in
As illustrated in
The toner supplied on the surface of the toner carrier roller 41 is transferred by the regulator blade 43 to the regulating part along with the movement the rotationally driven toner carrier roller 41 such that the regulator blade 43 regulates the amount of toner on the surface of the toner carrier roller 41. At this moment, the toner is charged to the normal charging polarity due to friction against the regulator blade 43 or the outer circumferential surface of the toner carrier roller 41. The charged toner having passed through the regulating part of the regulator blade 43 is then transferred from the toner supply position to the developing region along with the rotational movement of the toner carrier roller 41 while hopping on the surface of the toner carrier roller 41 for a later described reason. The toner transferred to the developing region is attached to the electrostatic latent image on the surface of the photoreceptor 1 due to the development field generated between the toner carrier roller 41 and the electrostatic latent image on the photoreceptor 1. The development of an image is thus conducted. The hopping toner not utilized for the development of the image is further transferred to the toner supply position along with the rotational movement of the toner carrier roller 41. The unutilized hopping toner is rubbed off (removed) from the toner carrier roller 41 by the toner supply roller 42 before being placed in the toner supply position. The removed toner is then returned into the casing of the developing device 4 for later reuse.
Note that the toner carried on the toner carrier roller 41 is hopping when microscopically viewed, but looks like flares when macroscopically viewed. In this embodiment, the toner in such a condition is called the “toner flaring”. Further, the developing system utilizing the toner flaring is called a “flaring developing” system. Note that the term “flare” derives from a solar flare since the macroscopically viewed hopping toner is analogous to the solar flare.
Next, the configuration of the toner carrier roller 41 utilized in the first embodiment is specifically described.
As illustrated in
The first electrode 53 is a metallic roller formed of a conductive material such as stainless steel (SUS) or aluminum in a cylindrical shape. Note that the first electrode 53 also serves as a substrate of the toner carrier roller 41. The first electrode 53 may also be formed of a conductive metallic layer made of aluminum or copper on a surface of a resin roller made of polyacetal (POM) or polycarbonate (PC). The method for forming such a conductive layer may include metallic plating, vapor deposition, and adhering metallic film on the surface of the roller.
The outer circumferential surface of the first electrode 53 is covered with the insulator layer 55. In the first embodiment, the insulator layer 55 is made of polycarbonate, melamine alkyd, or the like. Further, in the first embodiment, the thickness of the insulator layer 55 is preferably in a range of 3 to 50 μm. The insulator layer 55 having the thickness less than 3 μm may not sufficiently maintain the insulating property between the first electrode 53 and the second electrode 54, which may result in the current leakage between the first electrode 53 and the second electrode 54. On the other hand, the insulator layer 55 having the thickness greater than 50 μm may inhibit the electric fields formed between the first electrode 53 and the second electrode 54 from being formed outside the surface layer 56, which may not allow strong hopping electric fields to be formed outside the surface layer 56.
Note that the “hopping electric fields” indicate the electric fields formed between the first electrode 53 and the second electrode 54 which cause the toner to hop or exhibit hopping behavior between the two electrodes.
In the first embodiment, the insulator layer 55 formed of melamine resin has a thickness of 20 μm. The insulator layer 55 may be formed by spraying or dipping such that the insulator layer 55 is formed with a uniform thickness on the first electrode 53.
The second electrode 54 is formed over the insulator layer 55. In the first embodiment, the second electrode 54 is made of metal such as aluminum, copper or silver. Various methods may be employed for forming the comb-like (ladder-like) second electrode 54. For example, the comb-like (ladder-like) second electrode 54 may be formed by forming a metallic film on the insulator layer 55 by plating or vacuum deposition and then forming the metallic film in the comb-like (ladder-like) shape by the photoresist etching. Alternatively, the comb-like (ladder-like) second electrode 54 may be formed by attaching conductive paste on the insulator layer 55 by inkjet printing or screen printing.
The outer circumferential surfaces of the second electrode 54 and the insulator layer 55 are covered with the surface layer 56 having the insulating property. The toner is charged by being frictionally attached to the surface layer 56 while the toner repeatedly exhibits hopping behavior on the surface layer 56. In order to allow the toner to be charged to the normal charging polarity (a minus polarity in this embodiment), silicone, nylon (registered trade mark), urethane, melamine alkyd, polycarbonate and the like may be used as a material for the surface layer 56. In the first embodiment, polycarbonate is used as the material for the surface layer 56. Further, since the surface layer 56 serves as a protector to protect the second electrode 54, the thickness of the surface layer is preferably in a range of 3 to 40 μm. The surface layer 56 having the thickness less than 3 μm may result in breakage due to aging, which may expose the second electrode. As a result, the current may be leaked via the toner carried on the toner carrier roller 41 or other components that may come into contact with the toner carrier roller 41. On the other hand, the insulator layer 55 having the thickness greater than 40 μm may inhibit the electric fields formed between the first electrode 53 and the second electrode 54 from being formed outside the surface layer 56, which may not allow strong hopping electric fields to be formed outside the surface layer 56. In the first embodiment, the surface layer 56 has a thickness of 20 μm. The surface layer may be formed by spraying or dipping in the manner similar to that used for the insulator layer 55.
In the first embodiment, the electric fields formed between the first electrode 53 and the second electrode 54, that is, the electric fields formed over portions of the first electrode 53 that have no facing counterpart portions of the second electrode 54 are formed outside of the surface layer 56, which may cause the toner on the toner carrier roller 41 to exhibit hopping behavior. As a result, the hopping toner may appear to be flared. Note that the toner in a flaring state may also be called the “toner flaring” and the toner in a non-flaring state may also be called the “non-toner flaring”. In this case, the toner on the toner carrier roller 41 may be hopping in a reciprocating manner between portions of the surface layer 56 facing the first electrode 53 via the insulator layer 55 and adjacent portions of the surface layer 56 facing the second electrode 54.
In order to cause the toner to be flared with stability, substantially strong hopping electric fields may need to be formed. It may be necessary to generate a significantly large potential difference between the first electrode 53 and the second electrode 54 for forming such strong hopping electric fields. However, in order to generate such a significantly large potential difference between the first electrode 53 and the second electrode 54, the first electrode 53 may need to be efficiently insulated from the second electrode 54 with stability to prevent the current from leaking via intervals between the first electrode 53 and the second electrode 54.
Note that if two different types of electrodes are concentrically formed in a comb-like (ladder-like) shape on the cylindrical resin substrate as the first electrode and the second electrode, and narrow pointed teeth along one side of the first electrode are alternately arranged between narrow pointed teeth along the other side of the second electrode, the insulating property between the two electrodes may be drastically reduced due to structural defects in forming the electrodes, which may induce the current leakage from the intervals between the two electrodes. More specifically, for example, if the electrodes are formed by etching, portions of the metallic film to be removed may remain, or if the electrodes are formed by inkjet printing or screen printing, the conductive paste may remain between the two electrodes. In either of the above cases, the current leakage may occur between the two electrodes and thus appropriate hopping electric fields may not be formed. Further, in considering the electrode structure of the above two cases, even if two comb-like (ladder-like) electrodes are formed on the resin surface of the roller with high precision, the outer circumferential surfaces of the two comb-like (ladder-like) electrodes are covered with the insulator material in the intervals between the teeth array of the two electrodes. However, since interfaces of the resin surface of the roller and the insulator material are formed between the two electrodes, the current may easily leak through the interfaces. Thus, when a relatively high voltage is applied to the electrodes having this structure, the insulating property between the two electrodes may be drastically degraded.
In the first embodiment, the insulator layer 55 is formed on the first electrode 53, and the comb-like (ladder-like) second electrode 54 is formed on the insulator layer 55. Accordingly, there are no interfaces that may cause the current leakage from the intervals between the two electrodes. Further, in the first embodiment, the conductive material that is a possible factor of the current leakage may hardly intrude in the intervals between the two electrodes in forming the toner carrier roller 41. As described above, in the first embodiment, the first electrode 53 may be effectively insulated from the second electrode 54 with stability. Accordingly, even if a relatively high voltage is applied to the electrodes, the current leakage may be effectively prevented.
Further, the electrode width of the second electrode 54 (i.e., each narrow pointed tooth) is preferably in a range of 10 to 120 μm. The second electrode 54 having the electrode width less than 10 μm may result in the breakage of the electrode due to a too-fine structure. On the other hand, the second electrode 54 having the electrode width greater than 10 μm may result in lowering the voltage applied to part of the second electrode 54 arranged far from the power supply position, which may inhibit stable and effective activation of the toner hopping. In the first embodiment, the power supply position is provided at both ends on the outer circumferential surface of the toner carrier roller 41 in the axial direction. Accordingly, the second electrode 54 having the electrode width greater than 12 μm may result in forming the hopping electric fields in the central portion of the toner carrier roller 41 in the axial direction that are comparatively lower than the hopping electric fields in both ends of the toner carrier roller 41 in the axial direction. As a result, the toner carried in the central portion of the toner carrier roller 41 in the axial direction may not be activated to exhibit stable and effective hopping behavior.
Further, the electrode pitch of the second electrode 54 (i.e., intervals between narrow pointed teeth) is preferably the same width as the electrode width or wider than the electrode width. The electrode pitch of the second electrode 54 having the electrode pitch narrower than the electrode width may result in conversion of a large amount of lines of electric force on the second electrode 54 before allowing the lines of electric force to be outputted outside the surface layer 56. As a result, the hopping electric fields formed outside the surface layer 56 may be weakened. On the other hand, the second electrode 54 having the electrode pitch wider than the electrode width may result in forming weak hopping electric fields in the intervals between the electrodes. In the first embodiment, the preferable electrode pitch may be wider than the electrode width, and equal to or less than five times of the electrode width. In the first embodiment, the electrode width and the electrode pitch of the second electrode 54 are both set at 80 μm.
Further, in the first embodiment, the electrode pitch of the second electrode 54 is constant across the circumferential direction of the toner carrier roller 41. The constant electrode pitch arranged across the circumferential direction of the toner carrier roller 41 may result in generation of approximately constant hopping electric fields, which are generated between the first and the second electrodes, across the circumferential direction of the toner carrier roller 41. Thus, uniform toner hopping across the circumferential direction of the toner carrier roller 41 may be implemented in the developing region, resulting in uniform image development.
Next, descriptions are given of the voltages applied to the first electrode 53 and the second electrode 54. The first electrode 53 and the second electrode 54 formed on the toner carrier roller 41 are supplied with a first voltage and a second voltage by the first power supply 61 and the second power supply 62, respectively (see
In the first embodiment, the first and the second voltages include rectangular waves, and the first and the second voltages applied to the first and the second electrodes 53 and 54 have a phase difference n from each other (i.e., peak-to-peak voltage Vpp). Thus, there is a constant potential difference Vpp between the first electrode 53 and the second electrode 54. The potential difference Vpp generates electric fields between the first and the second electrodes 53 and 54, parts of which form the hopping electric fields outside the surface layer 56 to cause the toner to exhibit hopping behavior on the surface layer 56. In the first embodiment, the preferable potential difference Vpp may be in a range of 100 to 1000 V. The potential difference Vpp less than 100 V may result in failure in forming a satisfactory amount of hopping electric fields over the surface layer 56 and the toner may not stably exhibit hopping behavior over the surface layer 56. On the other hand, the potential difference Vpp greater than 100 V may result in too high potential difference between the first and the second electrodes 53 and 54, and the current leakage may occur due to aging of the electrodes. In the first embodiment, the potential difference Vpp is set at 500 V.
Further, in the first embodiment, the central value V0 of the first voltage and the second voltage may be set between a potential of an image-formed portion (potential of a latent image-formed portion) and a potential of a non-image formed portion (potential of a bare surface potion), and may be appropriately changed based on the developing condition.
In the first embodiment, a preferable frequency f of the first voltage and that of the second voltage may be in a range of 0.1 to 10 kHz. The first voltage or the second voltage having the frequency f lower than 0.1 kHz may prevent the toner hopping behavior from catching up with the developing speed. On the other hand, the first voltage or the second voltage having the frequency f higher than 10 kHz may cause the toner hopping to fail to follow the switchover of the electric fields and the toner may not stably exhibit hopping behavior over the surface layer 56. In the first embodiment, the frequency f is set at 500 Hz.
In this example, the first electrode 53 is supplied with the same voltage as illustrated in
Next, the features of the image forming apparatus according to the first embodiment are described.
In flaring type development conducted by the developing device 4 utilized in the image forming apparatus according to the first embodiment, if the potential difference between the first and the second electrodes 53 and 54 is significantly greater than the inter-electrode leak initiating voltage, the insulator layer 55 may be damaged due to the inter-electrode current leakage as illustrated
In the image forming apparatus according to the first embodiment, the voltage obtained by superimposing the alternating voltage on the direct voltage is applied to the first and the second electrodes 53 and 54 while conducting a cleaning and collecting process. When the voltage obtained by superimposing the alternating voltage on the direct voltage is applied to the first and the second electrodes 53 and 54, the first and the second electrodes 53 and 54 have the same phase and amplitude of the alternating voltage. Accordingly, the amplitude of the alternating voltage (Vpp) is greater than the development initiating voltage at the time of toner deterioration (i.e., the voltage applied for initiating the development of the image at a time where the toner is deteriorated).
Further, in the image forming apparatus according to the first embodiment, a toner flaring detector is provided to detect the toner flaring over the toner carrier roller 41 such that a deteriorated toner discharge mode to forcibly discharge the deteriorated toner may be set in the image forming apparatus. With this configuration, if the toner is not flaring, the voltage equal to or greater than the development initiating voltage at the time of toner deterioration may be applied between the photoreceptor 1 and the toner carrier roller 41 to forcibly discharge the deteriorated toner. Herein after such a deteriorated toner discharge mode is simply called a “toner discharge mode”.
In the toner discharge mode, the cleaning and collecting process is conducted. In the cleaning and collecting process, the deteriorated toner is discharged onto the photoreceptor 1, and the deteriorated toner on the photoreceptor 1 is removed by the cleaner device 74.
More specifically, in the cleaning and collecting process, initially, the photoreceptor 1 is rotationally driven. When the charger 2 uniformly charges the surface of the photoreceptor 1 to −500 V, the optical writer 3 carried out optical scanning over the entire region of the uniformly charged photoreceptor 1 surface to attenuate the charged voltage of the photoreceptor 1 to approximately −50 V. The rotation of the toner carrier roller 41 is stopped until the attenuated part of the photoreceptor 1 surface enters into the developing region along with the rotational movement of the photoreceptor 1. When the attenuated part of the photoreceptor 1 surface enters into the developing region, the rotational driving of the toner carrier roller 41 is initiated. At this moment, the first electrode 53 and the second electrode 54 on the toner carrier roller 41 are supplied with the voltage obtained by superimposing the alternating voltage on the direct voltage via the first power supply 61 and the second power supply 62 as illustrated in
Note that the phase of the alternating voltage applied to the first electrode 53 and the second electrode 54 is adjusted by a phase adjuster 60, which is connected to the first power supply 61 and the second power supply 62, and is controlled by a phase adjuster controller 24 of the main body controller 100 illustrated in
When the above-described voltage is applied to the first electrode 53 and the second electrode 54 on the toner carrier roller 41, electric fields that cause the toner charged with a minus polarity to be electrostatically moved from the toner carrier roller 41 to the photoreceptor 1 may be formed.
Note that when the toner is flaring on the toner carrier roller 41, the respective phases of the alternating voltages applied to the first the first electrode 1 and the second electrode 53 are shifted by 180 degrees as illustrated by a wave A and a wave B in
Meanwhile, when the developing device 4 in the image forming apparatus according to the first embodiment is in the toner discharge mode, the first electrode 53 and the second electrode 54 are supplied with the voltage obtained by superimposing the alternating voltage having the same amplitude and phase indicated by a wave D in
Thus, when the toner is discharged by causing the toner to hop from the toner carrier roller 41 and become attached to the photoreceptor 1, the transfer roller 73 (see
The toner on the photoreceptor 1 surface that has passed through the transfer nip along with the rotational driving of the photoreceptor 1 is removed (rubbed off) from the photoreceptor 1 surface and collected by the cleaner device 74.
As described above, the developing device 4 in the image forming apparatus according to the first embodiment is capable of detecting the toner flaring and appropriately discharging the deteriorated toner. Thus, the life-span of the developing device 4 may be increased. Further, the developing device 4 is capable of increasing the potential difference between the toner carrier roller 41 and the photoreceptor 1 without breaking the insulator layer 55. Thus, the toner with a low flaring level may be attached to the latent image on the photoreceptor 1 to carry out the development and the deteriorated toner may be discharged from the developing device 4. In addition, the toner flaring may be stabilized to provide a stable image quality.
The toner flaring on the toner carrier roller 41 may be detected by a photosensor.
As illustrated in
The sensor unit 86 includes a laser sensor emitter 86a utilized as an emitter formed of a light source configured to emit a laser beam and a laser sensor receiver 86b utilized as a receiver configured to receive reflection of the laser beam emitted from the laser sensor emitter 86a.
The laser sensor emitter 86a emits a laser beam to a position on the surface of the toner carrier roller 41 to which the nozzle unit 87 blows air.
The laser sensor receiver 86b outputs a signal based on the intensity of the laser beam reflected off the toner and the surface of the toner carrier roller 41 to a not-illustrated flaring level controller.
Note that the sensor unit 86 utilizes the laser with high sensitivity; however, the light source for the laser may be a light emitting diode (LED).
The nozzle unit 87 includes a nozzle 87a having an air blower nozzle port with an internal diameter of 1 mm, and a not-illustrated air compressor utilized as a fluid supplier connected to the nozzle 87a and configured to blow air from the nozzle port with a predetermined pressure of 200 Pa (in the first embodiment). The nozzle 87a is arranged such that the nozzle port is located at a height h of 2 mm from the surface of the toner carrier roller 41 and is directed toward a part of the surface of the toner carrier roller 41 off which part the laser beam reflects.
As illustrated in
When the toner has a high flaring activity ratio and a high flaring level, the toner has low adhesion to the toner carrier roller 41, so that the toner is easily blown off. Thus, the diameter φ of the spot 41a is increased as illustrated in
Note that the “flaring activity ratio” indicates the proportion of the toner that exhibits hopping behavior between the first electrode 53 and the second electrode 54 when the hopping electric fields having predetermined intensity are formed between the first electrode 53 and the second electrode 54. Note also that the “flaring level” indicates the amount of toner flaring in proportion to the total amount of toner. The flaring activity ratio indicates a condition of the toner whereas the toner flaring level indicates a condition of flaring of the toner. Thus, even if the flaring activity ratio is low, the flaring level may be increased by increasing the intensity of the hopping electric field.
In the laser application region 41b, since the reflectance of the laser beam may be lowered by the toner flaring in a region outside the spot 41a, the reflectance of the laser beam emitted from the laser beam sensor emitter 86a is high and the intensity of the laser beam entering into the laser beam sensor receiver 86b is high with the spot 41a having a large diameter. Note that since an orifice diameter of the nozzle 87a is 1 mm, the maximum diameter of the spot 41a may be approximately 1 mm. The closer to 100% the flaring activity ratio approaches, the closer to the maximum diameter the diameter of the spot 41a approaches.
In measuring the flaring level, it is sufficient that the air blowing be performed to form the spot 41a for a time as short as 5 seconds or less. There is no adverse effect of formation of the spot 41a on the development. This is because the toner may soon hop and flaring again in a region where the spot 41a is formed when the air blowing is stopped.
The nozzle unit 87 may not necessarily be required for measuring the flaring level; however, the accuracy in detecting the flaring level may be increased when the nozzle unit 87 is provided.
Further, an image sensor 75 is provided as an image detector such that the image sensor 75 faces the photoreceptor 1 or a not-illustrated intermediate transfer belt. The image sensor 75 is configured to detect partial intensity or defects of the image forming on the surface of the photoreceptor 1 or the intermediate transfer belt.
When partial defects or inconsistent density of the image are detected by the image sensor 75, an image sensor controller 31 determines that the toner flaring level on the toner carrier roller 41 is low and performs the cleaning and collecting process in the toner discharge mode to discharge the toner on the toner carrier roller 41 onto the photoreceptor 1, which is detected as a suspected cause of the partial defects or inconsistent density of the image. By detecting the defects or inconsistent density of the image and appropriately discharging the toner that is slightly flaring, the image quality may be stabilized and the life-span of the developing device 4 may be increased.
One example of a time at which the image sensor 75 detects the defects and inconsistent density of the image may be as follows. The image sensor 75 may be configured to detect the defects and inconsistent density of the image at a time where a first image operation of the image forming apparatus for forming a first image after a predetermined time has elapsed since a last image forming operation of the image forming apparatus for forming a last image has been conducted. The predetermined time may be measured by a timer 2 of the main body controller 100.
In general, the charge or adhesion of the toner after the predetermined time has passed differ from those of the toner in the normal condition, which may degrade the image quality. Specifically, since the adhesion of the toner to the toner carrier roller 41 is frequently increased in a contact region of the toner supply roller 42 with which the regulator blade 43 is brought into contact, the defects or inconsistent density of the image may be easily induced. Accordingly, if the image sensor 75 is configured to detect the defects and inconsistent density of the image at the time where a first image operation for forming a first image after a predetermined time has elapsed since a last image forming operation for forming a last image has been conducted and the toner that is slightly flaring is appropriately discharged from the toner carrier roller 41 to the photoreceptor 1, the stable image quality may be obtained.
Another example of a time at which the image sensor 75 detects the defects and inconsistent density of the image may be at a time at which the developing operations of images are successively conducted on a predetermined number of sheets. In this example, whether the developing operations are successively conducted on the predetermined number of sheets is determined based on the number of recording sheets fed by a paper feeder.
When the developing operations are successively conducted on the predetermined number of recording sheets, the electrostatic charge of the toner may be increased due to reset failure. As a result, the adhesion of the toner to the toner carrier roller 41 may be increased. Accordingly, the inconsistent toner attachment to the toner supply roller 42 or the regulator blade 43 may induce the inconsistent flaring level of the toner; that is, the toner on some part of the toner carrier roller 41 may exhibit a feasible flaring level whereas the toner on other part of the toner carrier roller 41 may exhibit an inferior flaring level. Accordingly, if the image sensor 75 is configured to detect the defects and inconsistent density of the image at the time at which the developing operations of images have been conducted on the predetermined number of recording sheets and the toner that is slightly flaring is appropriately discharged from the toner carrier roller 41 to the photoreceptor 1, the stable image quality may be obtained.
Further, still another example of a time at which the image sensor 75 detects the defects and inconsistent density of the image may be at a time at which a temperature-humidity environment of the developing device 4 has been changed.
If the temperature-humidity environment of the developing device 4 is drastically changed by the changes of the temperature and humidity of the environment where the developing device 4 resides and condensation is formed on the developing device 4 as a result, the adhesion of the toner to the toner carrier roller 41 may be increased, resulting in no flaring of the toner on the toner carrier roller 41. In this case, much condensation is formed on part of the toner carrier roller 41 near the opening of the developing device 4 and less condensation is formed on part of the toner carrier roller 41 inside of the developing device 4. As a result, significantly inconsistent image intensity may be formed in a roller circumferential direction of the toner carrier roller 41.
Accordingly, a temperature sensor 76 and a humidity sensor 77 are provided near the developing device 4 in the image forming apparatus as illustrated in
In addition, a development toner amount detector may be provided in the image forming apparatus to detect the amount of toner utilized for the development of the image (i.e., the amount of toner attached to the developed image on the photoreceptor 1), such that a predetermined amount of toner is utilized for the development of the image by controlling the voltage applied to the first electrode 53 or the second electrode 54 of the toner carrier roller 41 based on the detected amount of the toner utilized for the development of the image. If the developing device 4 is capable of controlling the voltage to be applied to the first electrode 53 or the second electrode 54 of the toner carrier roller 41 based on the amount of the toner utilized for the development of the image detected by the development toner amount detector, the appropriate voltage to be applied to the first electrode 53 or the second electrode 54 may be constantly maintained such that the predetermined amount of the toner is utilized for the development of the image, regardless of the environment where the developing device 4 resides.
The development toner detector may be implemented by computing a relationship between predetermined image intensity obtained based on the image intensity detected by the image sensor 75 and the amount of the toner utilized for the development of the image.
In this embodiment, the voltage obtained by superimposing the alternating voltage on the direct voltage may be applied to the first electrode 53 or the second electrode 54 of the toner carrier roller 41 so as to form the alternating electric fields causing the toner to hop from the toner carrier roller 41 toward the photoreceptor 1 and the electric fields causing the toner to hop from the photoreceptor 1 toward the toner carrier roller 41 between the toner carrier roller 41 and the photoreceptor 1. In this case, since the toner carrier roller 41 is attacked by the toner that is reciprocally hopping between the toner carrier roller 41 and the photoreceptor 1, the toner having extremely strong adhesion to the toner carrier roller 41 may be detached from the toner carrier roller 41.
There are three examples of the power supply configuration to apply the voltage to the first electrode 53 or the second electrode 54 of the toner carrier roller 41 in the toner flaring mode or in the toner discharge mode.
The first example of the power supply configuration indicates a configuration where the respective power supplies (first and second power supplies 61 and 62 in this example) are utilized for applying the same voltage to the first electrode 53 and the second electrode 54 in the toner discharge mode, and also for applying different voltages having a potential difference between the first electrode 53 and the second electrode 54 temporarily inverting from each other to the first electrode 53 and the second electrode 54 in the toner flaring mode. That is, the first power supply 61 is utilized for applying the voltage to the first electrode 53 in the toner discharge mode and in the toner flaring mode, and the second power supply 62 is utilized for applying the voltage to the second electrode 54 in the toner discharge mode and in the toner flaring mode as illustrated in
Thus, since the same power supply is utilized in the toner discharge mode and in the toner flaring mode, the number of power supplies may be reduced to lower production cost compared to a case where an additional power supply to be used in the toner discharge mode is separately provided from the first power supply 61 or the second power supply 62 that are utilized in the toner flaring mode. Further, it may be not necessary to provide a switching member or a switching device for switching the first and second power supplies 61 and 62 utilized in the flaring mode to the additional one utilized in the toner discharge mode that is separately provided from the first and second power supplies 61 and 62, and hence the ordinary toner flaring mode and the toner discharge mode may be switched in a short time.
The second example of the power supply configuration indicates a configuration where the different power supplies (first and second power supplies 61 and 62 in this example) are utilized for applying different voltages having a potential difference between the first electrode 53 and the second electrode 54 temporarily inverting from each other to the first electrode 53 and the second electrode 54 in the toner flaring mode. Meanwhile, the same power supply is utilized for applying the same voltage to the first electrode 53 and the second electrode 54 in the toner discharge mode. That is, the first power supply 61 is utilized for applying the voltage to the first electrode 53 and the second power supply 62 is utilized for applying the voltage to the second electrode 54 in the toner flaring mode as illustrated in
Since the common power supply (i.e., power supply 61 in this example) is utilized for applying the voltage to the first electrode 53 and to the second electrode 54 in the toner discharge mode, consumed power may be lowered to conserve energy compared to a case where the different power supplies are utilized for applying the voltages to the first electrode 53 and the second electrode 54 in the toner discharge mode. Note that in this example, the switching device 66 is also configured to cancel the electrical coupling of the first electrode 53 and the second electrode 54 in the toner flaring mode.
The third example of the power supply configuration indicates a configuration where the respective power supplies (first and second power supplies 61 and 62 in this example) are utilized for applying different voltages having a potential difference between the first electrode 53 and the second electrode 54 temporarily inverting from each other to the first electrode 53 and the second electrode 54 in the toner flaring mode, and the same power supply (a third power supply 63 in this example) is utilized for applying the same voltage to the first electrode 53 and the second electrode 54 in the toner discharge mode. That is, the first power supply 61 is utilized for applying the voltage to the first electrode 53 in the toner flaring mode, and the switching device 66 switches the first power supply 61 to the third power supply 63 in the toner discharge mode such that the third power supply 63 is utilized for applying the voltage to the first electrode 53 in the toner discharge mode as illustrated in
Since the different power supplies for applying the voltage to the first electrode 53 or the second electrode 54 of the toner carrier roller 41 are utilized between the ordinary toner flaring mode and the toner discharge mode, the optimal power supply may be selected for the toner flaring mode and the toner discharge mode. As a result, if the necessary performance greatly differs between the toner flaring mode and the toner discharge mode, the respective power supplies may be effectively designed without waste.
Further, when a high voltage is applied to the first electrode 53 or the second electrode 54 of the toner carrier roller 41 in the toner discharge mode, the current leakage may occur between the toner carrier roller 41 and the toner supply roller 42 due to the potential difference between the toner carrier roller 41 and the toner supply roller 42. Accordingly, a fourth power supply 64 is further provided to apply a voltage to the toner supply roller 42 as illustrated in
Likewise, when a high voltage is applied to the first electrode 53 or the second electrode 54 of the toner carrier roller 41 in the toner discharge mode, the current leakage may occur between the toner carrier roller 41 and the regulator blade 43 due to the potential difference between the toner carrier roller 41 and the regulator blade 43. Accordingly, a fifth power supply 65 is further provided to apply a voltage to the regulator blade 43 as illustrated in
Further, the first and the second electrodes 53 and 54 are not only supplied with the above-described alternating voltage but also supplied with the direct voltage that is equal to or greater than the development initiating voltage at the time of toner deterioration in the toner discharge mode. Accordingly, the electric fields formed between the photoreceptor 1 and the toner carrier roller 41 may be enhanced such that the toner may hop from the toner carrier roller 41 to the photoreceptor 1 due to enhanced electric fields. As a result, the toner may effectively hop from the toner carrier roller 41 to the photoreceptor 1. Further, the first electrode 53 and the second electrode 54 may be supplied with the same direct voltage, which may almost eliminate the potential difference between the first electrode 53 and the second electrode 54. Accordingly, the breakage of the insulator layer 55 caused by too large potential difference between the first electrode 53 and the second electrode 54 may be prevented while applying the high direct voltage to the first electrode 53 and the second electrode 54.
In the flaring developing system, the capacitance of the toner carrier roller 41 may greatly vary with the electrode width of the electrodes formed on the toner carrier roller 41. If the electrode is wide, the capacitance may be reduced, whereas if the electrode is narrow, the capacitance may be increased. Further, if the electrode is too wide, inconsistent density of the electrode pitch may be formed, and the electrode width may need to be sufficiently reduced in such a case. Thus, the capacitance of the toner carrier roller 41 may be large. In this case, since a large amount of current may be required for forming the temporarily varying electric fields capable of effectively allowing the toner to hop on the toner carrier roller 41 having large capacitance, power consumption may be significantly increased.
Thus, the image forming apparatus according to the second embodiment includes a high quality image output mode in which a large amount of current is consumed for outputting high quality images and a low quality image output mode in which a small amount of current is consumed for outputting low quality images, such that the high quality image output mode and the low quality image output mode may be appropriately switched by a user's selecting one of such modes. Accordingly, the power consumption may be reduced compared to a case where the high quality images are constantly produced.
The following examples may be given of the power supply configuration to apply the voltage to the first electrode 53 or the second electrode 54 of the toner carrier roller 41 in the high quality image output mode or in the low quality image output mode.
In the high quality image output mode, the respective voltages having a potential difference between the first electrode 53 and the second electrode 54 temporarily inverting from each other are applied from the respectively different power supplies to the first electrode 53 and the second electrode 54. In the low quality image output mode, the same voltages are applied from the same power supplies to the first electrode 53 and the second electrode 54. That is, the first power supply 61 is utilized for applying the voltage to the first electrode 53 and the second power supply 62 is utilized for applying the voltage to the second electrode 54 in the high quality image output mode as illustrated in
In the low quality image output mode, the alternating voltage Vpp applied to the first electrode 53 or the second electrode 54 may be in a range of 500 to 3000 V. In the second embodiment, the alternating voltage Vpp is set at 1800 V.
When the user selects the low quality image output mode, the voltage that has the same phase and the same amplitude and is greater than the development initiating voltage at the time of toner deterioration is applied to the first electrode 53 and the second electrode 54 of the toner carrier roller 41. This causes the toner to hop from the toner carrier roller 41 to the photoreceptor 1 such that the hopping toner is attached to the latent image formed on the surface of the photoreceptor 1. The development of the image is thus carried out. In this manner, the deteriorated not-flaring toner that is wasted while carrying out the cleaning and collecting process in the toner discharge mode in the first embodiment may be effectively utilized for forming images. Further, since the deteriorated not-flaring toner is discharged from the toner carrier roller 41 in the low quality image output mode, the toner flaring is stabilized and hence the stable image may be produced in the high quality image output mode.
Note that the developing characteristics in developing images may differ between the flaring developing system utilized in the high quality image output mode and the one-component jumping developing system utilized in the low quality image output mode as illustrated in
Accordingly, a patch composed of a high-density filled-in pattern illustrated in
Alternatively, a patch composed of a low-density pattern illustrated in
Further, the patch composed of a high-density filled-in pattern illustrated in
Reference Configuration Example
In the reference configuration example, the voltage obtained by superimposing the alternating voltage on the direct voltage is applied to the first and the second electrodes 53 and 54 of the toner carrier roller 41. In the reference configuration example, the alternating voltage is not changed between the toner flaring forming process and the toner collecting process. That is, the voltages are applied to the respective first electrode 53 and second electrode 54 as illustrated below.
On the other hand, the direct voltage applied to the first electrode 53 and the second electrode 54 is greatly changed between the toner flaring forming process and the toner collecting process.
In flaring development conducted by the developing device 4 utilized in the reference configuration example, if the potential difference between the first and the second electrodes 53 and 54 is increased too much, the insulator layer 55 may be broken or damaged. If, on the other hand, the direct voltage applied to the first and the second electrodes 53 and 54 is increased without changing the alternating voltage applied to the first and the second electrodes 53 and 54, the potential difference between the photoreceptor 1 and the toner carrier roller 41 is increased such that the electric fields are formed between the photoreceptor 1 and the toner carrier roller 41 to cause the toner to hop from the toner carrier roller 41 to the photoreceptor 1 while allowing the potential difference between the first and the second electrodes 53 and 54 to be unchanged.
Further, in the reference configuration example, the toner flaring detector is provided to detect the toner flaring over the toner carrier roller 41, and the direct voltage applied to the first and the second electrodes 53 and 54 is increased such that the direct voltage is greater than the development initiating voltage at the time of toner deterioration if the toner is not flaring or the toner flaring level is low. Thus, the voltage equal to or greater than the development initiating voltage at the time of toner deterioration may be applied between the photoreceptor 1 and the toner carrier roller 41 to forcibly cause the toner to hop from the toner carrier roller 41 to the photoreceptor 1, thereby forcibly discharging the deteriorated toner.
In the toner discharge mode, the cleaning and collecting processing is conducted. In the cleaning and collecting processing, the deteriorated toner is discharged from the toner carrier roller 41 to the photoreceptor 1, the deteriorated toner is attached onto the photoreceptor 1, and the deteriorated toner attached to the photoreceptor 1 is then removed by the cleaner device 74.
More specifically, in the cleaning and collecting process, initially, the photoreceptor 1 is rotatably driven. Subsequently, when the charger 2 uniformly charges the surface of the photoreceptor 1 to −500 V, the optical writer 3 carried out optical scanning over the entire region of the uniformly charged photoreceptor 1 surface to attenuate the charged voltage of the photoreceptor 1 approximately to −70 V. The rotation of the toner carrier roller 41 is stopped until the attenuated part of the photoreceptor 1 surface enters into the developing region along with the rotational movement of the photoreceptor 1. When the attenuated part of the photoreceptor 1 surface enters into the developing region, the rotationally driving of the toner carrier roller 41 is initiated. At this moment, the first electrode 53 and the second electrode 54 on the toner carrier roller 41 are supplied with the voltage obtained by superimposing the alternating voltage on direct voltage via the first power supply 61 and the second power supply 62 as illustrated in
When the above-described voltage is applied to the first electrode 53 and the second electrode 54 on the toner carrier roller 41, the electric fields that cause the toner charged with a minus polarity to electrostatically move from the toner carrier roller 41 to the photoreceptor 1 may be formed. Accordingly, the electric fields formed in this manner may cause the toner to hop from the toner carrier roller 41 toward the photoreceptor 1. Thus, the toner may be discharged from the toner carrier roller 41 onto the surface of the photoreceptor 1, thereby allowing the discharged toner to be attached to the surface of the photoreceptor 1. When the toner is discharged by causing the toner to hop from the toner carrier roller 41 and become attached to the photoreceptor 1, the transfer roller 73 is supplied with the bias voltage greater than −70 V in a minus side that is the electric potential of the photoreceptor 1. Accordingly, the toner attached to the photoreceptor 1 surface may remain attached on the surface of the photoreceptor 1 without being transferred from the photoreceptor 1 surface to the surface of the transfer roller 73 even when the toner is carried into the transfer nip.
The toner on the photoreceptor 1 surface that has passed through the transfer nip along with the rotational driving of the photoreceptor 1 is removed (rubbed off) from the photoreceptor 1 surface and collected by the cleaner device 74.
As described above, the developing device 4 in the image forming apparatus according to the second embodiment is capable of detecting the toner flaring and appropriately discharging the deteriorated toner. Thus, the life-span of the developing device 4 may be increased. Further, the developing device 4 is capable of increasing the potential difference between the toner carrier roller 41 and the photoreceptor 1. Thus, the toner with the low flaring level may be attached to the latent image on the photoreceptor 1 to carry out the development and the deteriorated toner may be discharged from the developing device 4. In addition, the toner flaring may be stabilized to provide a stable image quality.
Examples of the method for detecting the toner flaring on the toner carrier roller 41 may include the method for detecting the toner flaring on the toner carrier roller 41 by utilizing the photosensor 86 as illustrated in the first embodiment, and a method for detecting the toner flaring on the toner carrier roller 41 based on the result detected by the image sensor 75.
Further, a development toner amount detector may be provided in the image forming apparatus to detect the amount of toner utilized for the development of the image, such that a predetermined amount of toner is utilized for the development of the image by controlling the voltage applied to the first electrode 53 or the second electrode 54 of the toner carrier roller 41. If the developing device 4 is capable of controlling the voltage to be applied to the first electrode 53 or the second electrode 54 of the toner carrier roller 41 based on the amount of the toner utilized for the development of the image detected by the development toner amount detector, the appropriate voltage to be applied to the first electrode 53 or the second electrode 54 may be constantly maintained such that the predetermined amount of the toner is utilized for the development of the image, regardless of the environment where the developing device 4 resides.
The development toner detector may be implemented by computing a relationship between predetermined image intensity obtained based on the image intensity detected by the image sensor 75 and the amount of the toner utilized for the development of the image.
Next, a method for applying the voltage to the first electrode 53 or the second electrode 54 on the toner carrier roller 41 in the toner discharge mode is described with reference to
Since the electric fields are formed between the first electrode 53 and the second electrode 54 such that the toner is reciprocally hopping between the first electrode 53 and the second electrode 54 at time t2, the toner with less deteriorated flaring level may be reciprocally hopping between the first electrode 53 and the second electrode 54. As a result, when the toner hopping from one of the electrodes is attached to the other electrode, the toner hopping from one of the electrodes collides with the deteriorated toner adhered to the surface of the toner carrier roller 41 to rub off the deteriorated toner from the surface of the toner carrier roller 41. Accordingly, the deteriorated toner may be more effectively discharged from the toner carrier roller 41 to the photoreceptor 1.
Further, an alternative method for applying the voltage to the first electrode 53 or the second electrode 54 on the toner carrier roller 41 in the toner discharge mode is described with reference to
Accordingly, since the intensity of the electric fields that may cause the toner to hop from the toner carrier roller 41 to the photoreceptor 1 may be increased, the image may be developed with the toner including the completely not-flaring toner and the deteriorated toner (not-flaring toner) may be discharged from the toner carrier roller 41 to the photoreceptor 1.
Further, when a high voltage is applied to the first electrode 53 or the second electrode 54 of the toner carrier roller 41 in the toner discharge mode, the current leakage may occur between the toner carrier roller 41 and the toner supply roller 42 due to the potential difference between the toner carrier roller 41 and the toner supply roller 42. Accordingly, an additional power supply may be provided for applying a voltage to the toner supply roller 42, such that the toner supply roller 42 may be supplied with the same voltage as that supplied to the first electrode 53 or the second electrode 54. Accordingly, the potential difference between the toner carrier roller 41 and the toner supply roller 42 may be almost eliminated and hence the current leakage between the toner carrier roller 41 and the toner supply roller 42 may be prevented.
Likewise, when a high voltage is applied to the first electrode 53 or the second electrode 54 of the toner carrier roller 41 in the toner discharge mode, the current leakage may occur between the toner carrier roller 41 and the regulator blade 43 due to the potential difference between the toner carrier roller 41 and the regulator blade 43. Accordingly, an additional power supply may be provided for applying a voltage to the regulator blade 43, such that the regulator blade 43 may be supplied with the same voltage as that supplied to the first electrode 53 or the second electrode 54. Thus, the potential difference between the toner carrier roller 41 and the regulator blade 43 may be almost eliminated and hence the current leakage between the toner carrier roller 41 and the regulator blade 43 may be prevented.
According to the first and second embodiments, there is provided an image forming apparatus that includes: a photoreceptor 1 utilized as a latent image carrier; an optical writer 3 utilized as a latent image writing unit configured to write a latent image on the photoreceptor 1; a developing device 4 utilized as a developing unit having a toner carrier roller 41 having a first electrode 53 and a second electrode 54 that are insulated from each other via an insulator layer 55 utilized as an insulator member; a first power supply 61 and a second power supply 62 utilized as voltage applying units configured to apply respective voltages to the first electrode 53 and the second electrode 54 to form first electric fields due to a potential difference between the first electrode 53 and the second electrode 54 such that the first electric fields cause toner to hop from the toner carrier roller 41 to the photoreceptor 1 to develop a toner image by attaching the hopping toner to a latent image formed on the photoreceptor 1; and a transfer roller 73 utilized as a transfer unit configured to transfer the toner image developed on the photoreceptor 1. In such an image forming apparatus, alternating voltages having a same phase and a same amplitude are applied to the first electrode 53 and the second electrode 54 to form second electric fields between the photoreceptor 1 and the toner carrier roller 41 such that the second electric fields between the photoreceptor 1 and the toner carrier roller 41 cause the toner to hop from the toner carrier roller 41 to the photoreceptor 1 to discharge the toner from the toner carrier roller 41 to the photoreceptor 1. With this configuration, since the respective alternating voltages applied to the first and the second electrodes 53 and 54 on the toner carrier roller 41 have the same phase and the same amplitude, the potential difference may not occur between the first and the second electrodes 53 and 54. Accordingly, the insulator layer 55 may not be broken due to a current leakage between the first and the second electrodes 53 and 54. Thus, the alternating voltages relatively greater than those applied to the electrodes having a high potential difference between the electrodes may be applied to the respective first and second electrodes 53 and 54. Accordingly, the electric fields may be formed between the toner carrier roller 41 and the photoreceptor 1 by setting the potential difference between the toner carrier roller 41 and the photoreceptor 1 greater than the potential difference between the two electrodes such that the electric fields formed between the toner carrier roller 41 and the photoreceptor 1 may cause the toner having lowered electrostatic charge to hop from the toner carrier roller 41 to the photoreceptor 1. The toner having the lowered electrostatic charge may be discharged from the toner carrier roller 41 to the photoreceptor 1. Thus, the toner having the drastically lowered electrostatic charge may be discharged from the toner carrier roller 41 to the photoreceptor 1 while suppressing breakage of the insulator 55.
According to the first embodiment, the image forming apparatus further includes a cleaner device 74 configured to clean the surface of the photoreceptor 1; and a toner flaring detector 57 utilized as a toner flaring detector configured to detect flaring of the toner on the surface of the toner carrier roller 41. In the image forming apparatus having such a configuration, when a result detected by the toner flaring detector 57 indicates that the toner on the surface of the toner carrier roller 41 does not satisfy a predetermined flaring condition, alternating voltages having the same phase and the same amplitude, the amplitude being greater than the development initiating voltage at the time of toner deterioration, are applied to the first electrode 53 and the second electrode 54 such that while the toner on the surface of the toner carrier roller 41 is transferred from the surface of the toner carrier roller 41 to the surface of the photoreceptor 1, the toner transferred on the surface of the photoreceptor 1 is collected by the cleaner device 74 to carry out a cleaning and collecting process. Accordingly, the developing device 4 in the image forming apparatus may appropriately discharge the deteriorated toner, and the life-span of the developing device 4 may be increased. Further, the developing device 4 may increase the potential difference between the toner carrier roller 41 and the photoreceptor 1 without breaking the insulator layer 55. Thus, the toner with a low flaring level may still be attached to the latent image formed on the photoreceptor 1 to carry out the development of the image, and the deteriorated toner may be discharged from the developing device 4. In addition, the toner flaring may be stabilized to provide a stable image quality.
Further, according to the second embodiment, the user may be able to select one of a high quality image output mode and a low quality image output mode in the image forming apparatus. If the user selects the low quality image output mode, the alternating voltages having the same phase and the same amplitude that are greater than the development initiating voltage at the time of toner deterioration are applied to the first electrode 53 and the second electrode 54 of the toner carrier roller 41. Accordingly, the toner is caused to hop from the toner carrier roller 2 to the photoreceptor 1 such that the hopping toner is transferred to the latent image formed on the surface of the photoreceptor 1 to carry out the development of the image. Thus, the deteriorated not-flaring toner that is wasted while carrying out the cleaning and collecting process in the toner discharge mode in the first embodiment may be effectively utilized for forming images. Further, since the deteriorated not-flaring toner is discharged from the toner carrier roller 41 in the low quality image output mode, the toner flaring is stabilized and hence the stable image may be produced in the high quality image output mode.
Further, according to the second embodiment, the image forming apparatus further includes a main body controller 100 utilized as an image density adjuster configured to adjust density of the toner image by altering laser power of the optical writer 3 or by altering the developing bias such that the developed toner image includes appropriate density. Note that duty of the alternating voltages may also be changed when changing the developing bias.
According to the first embodiment, the image forming apparatus includes the cleaner device 74 configured to clean the surface of the photoreceptor 1; and an image sensor 75 utilized as an image detector configured to detect defects of the toner image or inconsistent density of the toner image. In the image forming apparatus having such a configuration, when a result detected by the toner flaring detector 75 indicates that there is a defect of the toner image or inconsistent density of the toner image, alternating voltages having the same phase and the same amplitude, the amplitude being greater than the development initiating voltage at the time of toner deterioration, are applied to the first electrode 53 and the second electrode 54 such that while the toner on the surface of the toner carrier roller 41 is transferred from the surface of the toner carrier roller 41 to the surface of the photoreceptor 1, the toner transferred on the surface of the photoreceptor 1 is collected by the cleaner device 74 to carry out a cleaning and collecting process. Accordingly, the developing device 4 in the image forming apparatus may appropriately discharge the not-flaring deteriorated toner, and the image quality may be stabilized and the life-span of the developing device 4 may be increased.
Further, according to the first embodiment, the defect or inconsistent density of the image may be detected by the image sensor 75 at a time where a first image operation for forming a first image after a predetermined time has elapsed since a last image forming operation for forming a last image has been conducted. Accordingly, the charged amount or the attached amount of the toner after the predetermined time has elapsed since the last image forming operation has been conducted may differ from those of the toner in an ordinary time to produce an image with degraded image quality. However, in such a case, the deteriorated toner that is slightly flaring may be appropriately discharged from the toner carrier roller 41 to the photoreceptor 1, and hence the stable image quality may be obtained.
Further, according to the first embodiment, the defect or inconsistent density of the image may be detected by the image sensor 75 when the developing device 4 sequentially conducts development operations of images on a predetermined number of recording sheets. Accordingly, the charge amounts that may be increased due to reset failure differ, which may increase the adhesion of the toner to the toner carrier roller 41. However, in such a case, the adhering toner that is slightly flaring may be appropriately discharged from the toner carrier roller 41 to the photoreceptor 1, and hence the stable image quality may be obtained.
Further, according to the first embodiment, the defect or inconsistent density of the image may be detected by the image sensor 75 when the temperature and humidity environment where the developing device 4 resides is changed. Accordingly, when the condemnation is obtained on the toner carrier roller 41 due to the drastic change in the temperature and humidity environment of the developing device 4, the adhesion of the toner to the toner carrier roller 41 may be increased, which may inhibit flaring of the toner on the toner carrier roller 41. However, in such a case, the adhering toner that is slightly flaring may be appropriately discharged from the toner carrier roller 41 to the photoreceptor 1, and hence the stable image quality may be obtained.
According to the first and the second embodiments, the image forming apparatus further includes the toner supply roller 42 utilized as a toner supply member configured to supply the toner to the toner carrier roller 41 provided in the developing device 4; and a fourth supply power 64 utilized as a toner supply member voltage applying unit configured to apply a voltage the same as those applied to the first and the second electrodes 53 and 54 to the toner supply roller 42. Accordingly, the potential difference between the toner carrier roller 41 and the toner supply roller 42 may be almost eliminated and hence the current leakage between the toner carrier roller 41 and the toner supply roller 42 may be prevented.
According to the first and the second embodiments, the image forming apparatus further includes the regulator blade 43 utilized as a toner regulator member configured to regulate an amount of the toner on the toner carrier roller 41 provided in the developing device 4; and a fifth supply power 65 utilized as a voltage applying unit configured to apply a voltage the same as those applied to the first and the second electrodes 53 and 54 to the regulator blade 43. Accordingly, the potential difference between the toner carrier roller 41 and the regulator blade 43 may be almost eliminated and hence the current leakage between the toner carrier roller 41 and the regulator blade 43 may be prevented. Further, according to the first and the second embodiments, in the image forming apparatus, the toner carrier roller 41 includes the internally integrated first electrode 53, the insulator layer 55 covering the first electrode 53, the second electrode 54 formed on the insulator layer 55, and the surface layer 56 covering the insulator layer 55 and the second electrode 54 formed on the outer circumferential surface of the toner carrier roller 41. In order to cause the toner to be flared, substantially strong hopping electric fields may need to be formed. Thus, it may be necessary to generate a significantly large potential difference between the first electrode 53 and the second electrode 54 for forming such strong hopping electric fields. However, in order to generate such a significantly large potential difference between the first electrode 53 and the second electrode 54, the first electrode 53 may need to be efficiently insulated from the second electrode 54 with stability to prevent the current from leaking via intervals between the first electrode 53 and the second electrode 54. Note that if two different types of electrodes are concentrically formed in a comb-like (ladder-like) shape on the cylindrical insulator substrate as the first electrode and the second electrode and narrow pointed teeth along one side of the first electrode are alternately arranged between narrow pointed teeth along the other side of the second electrode, the insulating property between the two electrodes may be drastically reduced due to the structural defects in forming the electrodes, which may induce the current leakage from the intervals between the two electrodes. Accordingly, hopping electric fields may not appropriately be formed. However, if the insulator layer 55 is formed on the first electrode 53 and the comb-like (ladder-like) second electrode 54 is formed on the insulator layer 55, there are no interfaces that may cause the current leakage from the intervals between the two electrodes 53 and 54. Further, the conductive material that is a possible factor of the current leakage may hardly intrude in the intervals between the two electrodes in forming the toner carrier roller 41. Accordingly, the first electrode 53 may be effectively insulated from the second electrode 54 with stability, and even if a relatively high voltage is applied to the electrodes, the current leakage may be effectively prevented.
Further, in the first and the second embodiments, the image formed by superimposing plural toner images on the photoreceptor 1 is transferred by the transfer roller 73 onto the recording material utilized as a transferring member. In the image forming apparatus having this configuration, since the four color images are recorded on the surface of the same photoreceptor 1, positional deviations in superimposing the four color images scarcely occur, compared to a generally used tandem type image forming apparatus including four photoreceptors from which different color images are superimposed to form a full-color image.
Note that in the first and second embodiments, a belt-type photoreceptor is utilized as the photoreceptor 1. However, the photoreceptor 1 may be a drum-type photoreceptor as illustrated in
Further, since the respective alternating voltages applied to the two electrodes on the toner carrier roller have the same phase and amplitude, the current leakage may not occur between the two electrodes and hence the insulator layer may not be broken due to the current leakage. Thus, the alternating voltages relatively greater than those applied to the electrodes having a large potential difference may be applied to the respective two electrodes. Accordingly, the electric fields may be formed by setting the potential difference between the toner carrier and the latent image carrier to be greater than the potential difference between the two electrodes such that the electric fields may cause the toner having degraded electrostatic charge to hop from the toner carrier to the latent image carrier. The toner having the degraded electrostatic charge is discharged from the toner carrier in this manner.
According to the first and second embodiments, there is provided the image forming apparatus that exhibits excellent advantages and is capable of discharging the toner having the drastically lowered electrostatic charge from the toner carrier roller onto the latent image carrier while suppressing inducement of insulator breakage.
Further, the present invention is not limited to these embodiments, but various variations and modifications may be made without departing from the scope of the present invention.
The present application is based on Japanese Priority Application No. 2010-200030 filed on Sep. 7, 2010, and Japanese Priority Application No. 2011-125383 filed on Jun. 3, 2011, with the Japanese Patent Office, the entire contents of which are hereby incorporated by reference.
Number | Date | Country | Kind |
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2010-200030 | Sep 2010 | JP | national |
2011-125383 | Jun 2011 | JP | national |
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