JP2012042667A - Development device, process cartridge, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a development device capable of suppressing fluctuation in density of an image formed on an image carrier body when changing a peak-to-peak voltage value of a pulse voltage; and to provide a process cartridge and an image forming apparatus having the development device.SOLUTION: A first power supply 31 is for crowd pulse output, and primary and secondary sides of a power supply circuit are separation types, namely, the secondary side being floating with respect to GND. A second power supply 32 is for a minus DC bias and the primary and secondary sides have a configuration to be connected to a common GND. Pulse voltage application means includes a pulse output generating circuit 37 as a pulse voltage generating circuit which comprises an A-phase pulse generating circuit 33 generating an A-phase pulse and a B-phase pulse generating circuit 34 generating a B-phase pulse. A crowd pulse control circuit 67, or control means, changes the output level of the first power supply 31 based on the detection result of a humidity sensor 40, or humidity detecting means, to adjust the peak-to-peak voltage value.

Description

  The present invention relates to a developing device used in an image forming apparatus such as a printer, a facsimile machine, and a copying machine, and a process cartridge and an image forming apparatus provided with the developing device.

  2. Description of the Related Art Conventionally, there has been known an image forming apparatus that employs a hopping development method in which toner hopped on the surface of a toner carrier is used for development. For example, the image forming apparatus described in Patent Document 1 includes a cylindrical toner carrier having a plurality of hopping electrodes arranged at a predetermined pitch in the circumferential direction. Among the plurality of hopping electrodes, the same A-phase repetitive pulse voltages are applied to those at even-numbered arrangement positions, while the same A is applied to those at odd-numbered arrangement positions. A repetitive pulse voltage of B phase different from the phase is applied. Thereby, an alternating electric field is formed between two hopping electrodes adjacent to each other, and the toner is hopped between the electrodes by an electrostatic force acting on the toner by the alternating electric field. Then, development is performed by attaching the hopped toner to the latent image on the image carrier.

In a high humidity environment, the liquid cross-linking force of the toner increases and the adhesion force acting between the toner and the surface of the toner carrier increases, or the charging efficiency of the toner decreases, so the toner charge amount decreases and the toner The electrostatic force due to the alternating electric field that acts on the electric field is reduced. Therefore, it becomes difficult for the toner to hop on the toner carrier, and the amount of toner adhering to the latent image portion on the image carrier is reduced, resulting in a lower image density.
On the other hand, in a low-humidity environment, the liquid crosslinking force of the toner is reduced, the adhesion force acting between the toner and the surface of the toner carrier is reduced, and the charge amount of the toner is increased because the toner charging efficiency is increased. The electrostatic force due to the alternating electric field acting on the toner may increase. For this reason, the toner violently and hops too much on the toner carrying member, and there is a possibility that the toner adheres to the non-image portion on which the electrostatic latent image is not formed on the image carrying member and the image is soiled.

  For this reason, in a high humidity environment, the peak-to-peak voltage value of the pulse voltage is increased, the electrostatic force acting on the toner on the toner carrier is increased, and good hopping of the toner is maintained. Suppresses the decrease in concentration. In a low-humidity environment, the peak-to-peak voltage value of the pulse voltage is reduced, the electrostatic force acting on the toner on the toner carrier is reduced, the toner is prevented from excessively hopping, and the background is prevented from being soiled. .

  However, the inventors of the present application change the peak-to-peak voltage value of the pulse voltage applied to the hopping electrode when performing various experiments using the image forming apparatus employing the hopping development method as described above. The density of the image formed on the image carrier varied. As a result, even if the peak-to-peak voltage value of the pulse voltage was changed according to the humidity, a good image could not be obtained.

  In addition, the toner reciprocating between the electrodes by hopping is not transported to the developing region by the surface movement of the toner carrier as in the developing device described in Patent Document 1, but the toner on the surface of the toner carrier is hopped. A developing device that moves in a certain direction and conveys it to a developing region is also known. For example, in a developing device using a toner carrier in which three electrodes of A phase, B phase, and C phase are repeatedly arranged in that order, toner is transferred from the A phase electrode to the B phase electrode on the surface of the toner carrier. Then, the toner is conveyed toward the developing region by sequentially hopping from the B-phase electrode to the C-phase electrode and from the C-phase electrode to the A-phase electrode. Even with such a developing device, the above-described problems occur.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a developing device capable of suppressing fluctuations in the density of an image formed on an image carrier when a peak-to-peak voltage value of a pulse voltage is changed. The present invention also provides a process cartridge and an image forming apparatus provided with the developing device.

In order to achieve the above object, a first aspect of the present invention is a toner carrier having a plurality of electrodes, a toner supply means for supplying toner to the surface of the toner carrier, and applying a pulse voltage to the plurality of electrodes. And a hopping electric field generating means for generating an electric field for hopping the toner carried on the surface of the toner carrying body on the surface of the toner carrying body, and is carried on the surface of the toner carrying body. In a developing device that develops the latent image by transporting the toner to the developing area facing the image carrier and attaching the toner to the latent image on the image carrier, the negatively charged toner is transferred to the latent image. The image is developed by being attached to the image, and only the maximum peak value of the pulse voltage is changed according to the detection result of the humidity detecting means, and the peak-to-peak voltage value of the pulse voltage is changed. Is characterized in that it comprises a control means for controlling so that the hopping electric field generating means.
According to a second aspect of the present invention, in the developing device according to the first aspect, the toner carrier includes an insulating base material, a first electrode member formed so as to cover the entire surface of the base material, And a second electrode member having a plurality of electrode portions arranged at equal intervals in the toner transport direction, the hopping electric field generating means comprising: a first electrode member; A pulse voltage is applied to each electrode member so that the potential difference with the second electrode member is temporally reversed.
According to a third aspect of the present invention, in the developing device according to the first or second aspect, the minimum peak value of the pulse voltage is set to be more positive than the non-image portion potential of the image carrier. Is.
According to a fourth aspect of the present invention, in the developing device of the second aspect, when the peak voltage value on the negative polarity side of the pulse voltage is set on the negative polarity side with respect to the non-image portion potential of the image carrier, The width of the electrode portion of the second electrode member so that electric lines of force are not formed between the electrode member to which the peak voltage value on the negative polarity side of the pulse voltage is applied and the non-image portion region of the image carrier. The gap between the electrode portions of the second electrode member and the gap between the image carrier and the toner image carrier are set.
According to a fifth aspect of the present invention, there is provided the developing device according to any one of the first to fourth aspects, wherein the control means is an image density relating to an image on the image carrier output from an image density detecting means provided in the image forming apparatus. The hopping electric field generating means is controlled so as to change the minimum peak value of the pulse voltage in accordance with a signal.
According to a sixth aspect of the present invention, in the developing device according to any one of the first to fifth aspects, the hopping electric field generating means includes a pulse voltage generating circuit for generating a pulse voltage, and the pulse voltage generating circuit includes the pulse voltage generating circuit. A first power supply that is a DC power supply that is floated from an electrical ground for supplying a bias that defines a peak-to-peak voltage value of the first power supply, and is provided between a low potential side of the first power supply and the ground. And a second power source that is a negative DC power source with a variable output level. When changing the peak-to-peak voltage value of the pulse voltage, the control means changes only the output level of the second power source. When changing the minimum peak value of the pulse voltage, the bias output level of the first power supply is changed.
According to a seventh aspect of the present invention, there is provided a toner carrier having a plurality of electrodes, a toner supply means for supplying toner to the surface of the toner carrier, and applying a pulse voltage to the plurality of electrodes, thereby providing the toner. Hopping electric field generating means for generating an electric field for hopping the toner carried on the surface of the carrier on the surface of the toner carrier, and carrying the image of the toner carried on the surface of the toner carrier In a developing device that develops the latent image by transporting it to a developing area facing the body and attaching the toner to the latent image on the image carrier, the toner is charged with positive polarity and developed. In accordance with the detection result of the humidity detection means, only the minimum peak value of the pulse voltage is changed, and the peak-to-peak voltage value of the pulse voltage is changed. It is characterized in further comprising control means for controlling the electric field generating means.
According to an eighth aspect of the present invention, in the developing device of the seventh aspect, the toner carrier includes an insulating base material, a first electrode member formed so as to cover the entire surface of the base material, And a second electrode member having a plurality of electrode portions arranged at equal intervals in the toner transport direction, the hopping electric field generating means comprising: a first electrode member; A pulse voltage is applied to each electrode member so that the potential difference with the second electrode member is temporally reversed.
According to a ninth aspect of the present invention, in the developing device of the seventh or eighth aspect, the maximum peak value of the pulse voltage is set on the negative polarity side with respect to the non-image portion potential of the image carrier. Is.
The invention of claim 10 is the developing device of claim 8, wherein the peak voltage value on the positive polarity side of the pulse voltage is set on the positive polarity side of the non-image portion potential of the image carrier. The width of the electrode portion of the second electrode member so that electric lines of force are not formed between the electrode member to which the peak voltage value on the positive polarity side of the pulse voltage is applied and the non-image portion region of the image carrier. The gap between the electrode portions of the second electrode member and the gap between the image carrier and the toner image carrier are set.
According to an eleventh aspect of the present invention, in the developing device according to any one of the seventh to tenth aspects, the control means controls the image density relating to the image on the image carrier output from the image density detecting means provided in the image forming apparatus. The hopping electric field generating means is controlled so as to change only the maximum peak value of the pulse voltage in accordance with a signal.
According to a twelfth aspect of the present invention, in the developing device according to any one of the seventh to eleventh aspects, the hopping electric field generating means includes a pulse voltage generating circuit for generating a pulse voltage, and the pulse voltage generating circuit includes the pulse voltage. A first power supply that is a DC power supply that is floated from an electrical ground for supplying a bias that defines a peak-to-peak voltage value of the first power supply, and is provided between a low potential side of the first power supply and the ground. The control means comprises a second power supply that is a positive DC power supply with variable output level, and the control means changes the output level of the second power supply when changing the peak-to-peak voltage value of the pulse voltage, When changing the maximum peak value of the pulse voltage, the output level of the bias of the first power supply is changed.
According to a thirteenth aspect of the present invention, an image obtained by developing a latent image formed on an image carrier by supplying a developer by developing means is finally applied to a recording material. In the image forming apparatus for forming an image on the recording material by using the developing device, the developing device according to any one of claims 1 to 12 is used as the developing means.
According to a fourteenth aspect of the present invention, in the process cartridge which is integrally provided with the developing means and at least one of the image carrier, the charging means, and the cleaning means, and is detachable from the main body of the image forming apparatus, the developing means The developing device according to any one of claims 1 to 14 is used.

  The maximum peak value of the pulse voltage is as follows. That is, if both of the two peak values are negative, it means a peak value with a small absolute value, and if both of the two peak values are positive, it means a peak value with a large absolute value. is there. Moreover, when one peak value is negative polarity and the other peak value is positive polarity, it is a positive polarity peak value. The minimum peak value of the pulse voltage is as follows. That is, if both of the two peak values are negative, it means a peak value with a large absolute value, and if both of the two peak values are positive, it means a peak value with a small absolute value. is there. Moreover, when one peak value is negative polarity and the other peak value is positive polarity, it is a negative peak value.

  According to the present invention, the peak-to-peak voltage value of the pulse voltage is changed in accordance with the detection result of the humidity detecting means provided in the image forming apparatus. As a result, in a high humidity environment, even if the peak-to-peak voltage value of the pulse voltage is increased and the liquid crosslinking power of the toner is increased, good hopping can be maintained and the image density is lowered. Can be suppressed. In a low-humidity environment, the peak-to-peak voltage value of the pulse voltage is reduced to suppress the toner from hopping on the toner carrying member even if the liquid crosslinking power of the toner is reduced. And soiling can be suppressed.

According to the first aspect of the present invention, in the case where negatively charged toner is used for development, only the maximum peak value of the pulse voltage is changed, and the peak-to-peak voltage value of the pulse voltage is changed. Control the electric field generating means. As will be described later, the applicant changes only the maximum peak value of the pulse voltage, changes the image density fluctuation when the peak-to-peak voltage is changed, and changes the maximum peak value and the minimum peak value of the pulse voltage. Then, the image density fluctuation when the peak-to-peak value was changed and only the minimum peak value of the pulse voltage were changed, and the image density fluctuation when the peak-to-peak value was changed were examined. As a result of investigation, when only the maximum peak of the pulse voltage is changed and the peak-to-peak voltage value of the pulse voltage is changed, the image density fluctuation when the peak-to-peak voltage value of the pulse voltage is changed can be minimized. I found out that I can do it.
It is considered that the change in image density was most suppressed by changing only the maximum peak value of the pulse voltage and changing the peak-to-peak voltage value of the pulse voltage for the following reason. That is, when changing only the maximum peak value of the pulse voltage and changing the peak-to-peak voltage value of the pulse voltage, the minimum peak value of the pulse voltage is maintained constant and the peak-to-peak voltage value of the pulse voltage is changed. Is done. When the pulse voltage has the minimum peak value, the toner on the toner carrier flies to the latent image. For this reason, fluctuations in the minimum peak value most affect the image density. Therefore, it is considered that when only the maximum peak value of the pulse voltage is changed and the peak-to-peak voltage value of the pulse voltage is changed, the image density fluctuation is suppressed.

  Further, when using positive toner, the positive toner on the toner carrier flies to the latent image portion when the pulse voltage has the maximum peak value. Therefore, according to the seventh aspect of the present invention, when positive polarity toner is used, only the minimum peak value of the pulse voltage is changed, and the maximum peak value of the pulse voltage is maintained at a constant value. Thus, even after the peak-to-peak voltage value of the pulse voltage is changed, fluctuations in the image density due to the change of the peak-to-peak voltage value of the pulse voltage can be suppressed.

  According to the present invention, it is possible to suppress fluctuations in the density of an image formed on an image carrier.

The schematic block diagram of the cloud pulse generation circuit at the time of negatively charged toner use. 1 is a schematic configuration diagram showing a copier according to an embodiment. FIG. 2 is a schematic configuration diagram showing a photoconductor and a developing device in the copying machine according to the embodiment. (A) The typical top view shown in the state which developed the toner carrying roller. (B) A schematic cross-sectional view of a toner carrying roller. The graph which shows an example of the voltage for A phases applied to the electrode for A phases, and the electrode for B phases, respectively, and the voltage for B phases. (A) The typical top view shown in the state which developed the toner carrying roller. (B) A schematic cross-sectional view of a toner carrying roller. The graph which shows an example of the inner side voltage and outer side voltage which are applied to an inner side electrode and an outer side electrode, respectively. The schematic block diagram of the cloud pulse generation circuit at the time of negatively charged toner use. The wave form diagram at the time of using the cloud pulse generation circuit shown in FIG. The schematic block diagram of the cloud pulse generation circuit at the time of positively charged toner use. FIG. 3 is a circuit diagram of a cloud pulse generation circuit in which a cloud pulse and a bias voltage are supplied from each power source. 6 is a flowchart illustrating an example of control performed by the copier according to the embodiment. The graph which shows the result of having investigated the relationship between the electric potential difference of the average electric potential of a cloud pulse with respect to a latent image electric potential, and developing toner amount. 6 is a graph showing a result of examining a relationship between a potential difference of a high peak value of a cloud pulse with respect to a latent image potential and a developing toner amount. The graph which shows the result of having investigated the relationship between the electric potential difference of the low side peak value of the cloud pulse with respect to a latent image electric potential, and developing toner amount. FIG. 6 is a diagram illustrating a simulation evaluation result of electric lines of force formed by an electric field between a peak value potential of a pulse voltage applied to each electrode of a toner carrying roller and a photoreceptor potential. The figure which shows the result of having carried out the simulation evaluation of the electric line of force when making the phase of the pulse voltage to each electrode into a phase opposite to the example shown in FIG. The strength of the developing electric field between the outer electrode and the latent image portion when the outer electrode has the low peak value, and the strength of the developing electric field between the inner electrode and the latent image portion when the inner electrode has the low peak value. The figure which shows the result of having compared.

Hereinafter, an embodiment in which the present invention is applied to a copying machine which is an electrophotographic image forming apparatus will be described.
FIG. 2 is a schematic configuration diagram illustrating the copying machine according to the embodiment. In the figure, a drum-shaped photosensitive member 49 as an image carrier is driven to rotate clockwise in the drawing. When an operator places a document (not shown) on the contact glass 90 and presses a print start switch (not shown), a first scanning optical system 93 including a document illumination light source 91 and a mirror 92 and a second including mirrors 94 and 95 are provided. The scanning optical system 96 moves to read the original image. The scanned original image is read as an image signal by an image reading element 98 disposed behind the lens 97, and the read image signal is digitized and image-processed. Then, a laser diode (LD) is driven by the signal after image processing, and after the laser light from the laser diode is reflected by the polygon mirror 99, the photoconductor 49 is scanned via the mirror 80. Prior to this scanning, the photosensitive member 49 is uniformly charged by the charging device 50, and an electrostatic latent image is formed on the surface of the photosensitive member 49 by scanning with a laser beam.

  Toner adheres to the electrostatic latent image formed on the surface of the photosensitive member 49 by the developing process of the developing device 1, thereby forming a toner image. The toner image is conveyed to a transfer position that is opposite to the transfer charger 60 as the photoconductor 49 rotates. With respect to this transfer position, the first paper supply unit 70 having the first paper supply roller 70a or the second paper supply having the second paper supply roller 71a is synchronized with the toner image on the photoconductor 49. The recording paper P is fed from the paper section 71. The toner image on the photoreceptor 49 is transferred onto the recording paper P by corona discharge of the transfer charger 60.

  The recording paper P onto which the toner image has been transferred in this manner is separated from the surface of the photoreceptor 49 by corona discharge of the separation charger 61, and then conveyed toward the fixing device 76 by the conveyance belt 75. In the fixing device 76, the fixing roller 76a is sandwiched between fixing rollers 76a including a heat source such as a halogen lamp (not shown) and a pressure roller 76b pressed against the fixing roller 76a. Thereafter, the toner image is fixed on the surface by pressurization or heating in the fixing nip, and then discharged toward a discharge tray 77 outside the apparatus.

  The transfer residual toner adhering to the surface of the photoconductor 49 that has passed the transfer position is removed from the surface of the photoconductor 49 by the cleaning device 45. The surface of the photoreceptor 49 that has been subjected to the cleaning process in this way is discharged by the charge removing lamp 44 and is prepared for the next latent image formation.

  Further, the developing device 1 and at least the photosensitive member 49, the charging device 50, and the cleaning device 45 are integrally unitized as a process cartridge that can be attached to and detached from the image forming apparatus main body. As a result, it is possible to improve the maintainability of the developing device 1 and the like.

  FIG. 3 is a schematic configuration diagram showing the photoreceptor 49 and the developing device 1 in the copying machine according to the embodiment. In the figure, a drum-shaped photoconductor 49 is rotationally driven in a clockwise direction in the drawing by a driving means (not shown). A developing device 1 having a toner carrying roller 101 as a developer carrying member is disposed on the right side of the photoconductor 49 in the drawing.

  The developing device 1 includes a toner supply roller 18 and a toner friction blade 22 in addition to the toner carrying roller 101. The toner supply roller 18 having a sponge surface carries the toner contained in the developing device 1 on the roller surface while being driven to rotate counterclockwise in the figure by a driving means (not shown). In the drawing, an example in which the rotation direction of the toner supply roller 18 is set to a direction in which the surface is moved in a direction opposite to the toner carrying roller 101 at a portion facing the toner carrying roller 101 is shown. On the contrary, the surface may be set to move in the same direction as the toner carrying roller 101 at the facing portion.

  A supply bias is applied to the rotating shaft member made of metal of the toner supply roller 18 by a supply bias power source 24. On the other hand, a plurality of A-phase electrodes and B-phase electrodes, which will be described later, are formed on the toner carrying roller 101, and a repetitive pulse voltage is applied to these electrodes by a pulse voltage applying means 30. The average value of these pulse voltages is larger than the supply bias described above on the side opposite to the toner charging polarity. As a result, an electric field for electrostatically moving the toner from the former to the latter is formed between the toner supply roller 18 and the toner carrying roller 101.

  The toner carried on the surface of the toner supply roller 18 is supplied from the toner supply roller 18 to the toner carrying roller 101 at a contact portion between the toner supply roller 18 and the toner carrying roller 101. The supply amount at this time can be adjusted according to the magnitude of the supply bias. The supply bias may be a DC voltage, an AC voltage, or a bias in which the AC voltage is superimposed on the DC voltage.

  The toner supplied on the surface of the toner carrying roller 101 circulates as the toner carrying roller 101 rotates counterclockwise in the figure while hopping on the surface of the toner carrying roller 101 for the reason described later. . On the surface of the toner carrying roller 101, there is a cantilever-supported toner friction blade 22 in a position before passing the contact portion with the toner supply roller 18 and before entering the developing region facing the photoreceptor 49. The free end is in contact. While hopping on the surface of the toner carrying roller 101, the toner that moves in the whole counterclockwise direction in the drawing as the toner carrying roller 101 rotates enters between the toner carrying roller 101 and the toner friction blade 22. Then, it is rubbed against the surface of the toner carrying roller 101 and the surface of the toner friction blade 22. Thereby, frictional charging is promoted. Thereafter, when the toner carrying roller 101 rotates, the toner carrying roller 101 and the toner friction blade 22 pass through the contact portion, and then the toner is hopped again on the surface of the toner carrying roller 101 and conveyed to the developing region. The

  The toner carrying roller 101 exposes a part of the outer peripheral surface from an opening provided in the casing 11 of the developing device 1. This exposed portion is opposed to the photoreceptor 49 with a gap of several tens to several hundreds [μm]. The position where the toner carrying roller 101 and the photoconductor 49 are opposed to each other in this manner is a development area in the copying machine. The toner transported to the developing area while hopping on the surface of the toner carrying roller 101 is electrostatic latent on the surface of the photoreceptor due to the developing electric field between the toner carrying roller 101 and the electrostatic latent image on the photoreceptor 49. It adheres to the image area and is developed. The toner that has not contributed to development is further conveyed by the rotation of the toner carrying roller 101 while hopping, and is repeatedly used.

  The toner friction blade 22 may be brought into contact with the toner supply roller 18 instead of the toner carrying roller 101 so as to promote toner friction charging by the toner friction blade 22 on the surface of the toner supply roller 18.

  Next, an example of the toner carrying roller 101 will be described with reference to FIG. 4A is a schematic plan view showing the toner carrying roller 101 in a developed state, and FIG. 4B is a schematic cross-sectional view of the toner carrying roller 101.

  In this example, a plurality of electrodes are provided on the surface of the toner carrier, two pairs of electrodes are provided in common, and two-phase pulses having different phases of 180 [°] (see FIG. 5) are applied. This is an example of a toner carrier that forms a two-phase electric field that repeats suction and repulsion between adjacent electrodes.

  In the toner carrying roller 101, an insulating layer 101B is formed on the surface of a conductive base material 101A which is a base material of the roller. On this insulating layer 101B, an A-phase electrode 111A and a B-phase electrode 111B are provided as a plurality of electrodes 111, and a surface protective layer 101C as a surface layer is provided thereon. Comb-shaped A-phase electrode 111A and B-phase electrode 111B are provided in parallel at a fine pitch in a direction orthogonal to the toner transport direction, and external buses 111Aa and 111Ba are provided on both sides through external buses 111Aa and 111Ba. Each is connected to a two-phase pulse output circuit.

  The pulse voltage applied to the A-phase electrode 111A and the B-phase electrode 111B is a pulse voltage having a frequency of 0.3 [kHz] to 2 [kHz] and including a DC voltage as a bias. A pulse voltage corresponding to the electrode width and electrode interval, such as V] to 600 [V], is applied. In the case of this two-phase electric field, toner repulsion flight and suction flight are repeated in accordance with the switching of the electric field direction of the electric field generated between the adjacent A-phase electrode 111A and B-phase electrode 111B. Reciprocate between the electrodes.

Next, voltages applied to the A-phase electrode 111A and the B-phase electrode 111B will be described.
The A-phase voltage and the B-phase voltage are applied from the pulse voltage applying means 30 to the A-phase electrode 111A and the B-phase electrode 111B on the toner carrying roller 101. A rectangular wave is most suitable for the A-phase voltage and the B-phase voltage applied by the pulse voltage applying means 30. Further, in this copying machine, the electrodes for forming the cloud electrodes have a two-phase configuration of an A-phase electrode 111A and a B-phase electrode 111B, and each of the electrodes 111A and 111B has a voltage having a phase difference π. Are applied respectively.

  FIG. 5 is a diagram illustrating an example of the A-phase voltage and the B-phase voltage applied to the A-phase electrode 111A and the B-phase electrode 111B, respectively. In this copying machine, each voltage is a rectangular wave, and the A-phase voltage and the B-phase voltage applied to the A-phase electrode 111A and the B-phase electrode 111B, respectively, have the same magnitude with the phase shifted by π. (Peak-to-peak voltage Vpp). Therefore, a potential difference of only Vpp always occurs between the A-phase electrode 111A and the B-phase electrode 111B. Due to this potential difference, an electric field is generated between the electrodes, and the toner hops on the surface layer 101C by a cloud electric field formed outside the surface layer 101C.

  As described above, the means for flying the toner on the surface of the toner carrying roller to form a cloud has a plurality of electrodes arranged on the surface of the toner carrying roller extending in a direction perpendicular to the toner transport direction and arranged at predetermined intervals. The voltage applied to each electrode applies a voltage that alternately repeats the direction of attracting toner and the direction of repulsion between adjacent electrodes, and the toner carrying roller 101 rotates to move the toner. By adopting a cloud configuration, it is possible to transport toner stably on the surface of the toner carrying roller regardless of the charge quality of the toner, and a highly reliable copier can be realized as the entire apparatus.

  Next, another example of the toner carrying roller 101 used in the developing device according to the present embodiment will be described with reference to FIG. 6A is a schematic plan view showing the toner carrying roller 101 in a developed state, and FIG. 6B is a schematic cross-sectional view of the toner carrying roller 101.

  In this example, a plurality of electrodes are provided on the surface of the toner carrying roller, each electrode on the surface layer side is common, and two phases having a phase difference of 180 [°] between the conductor base electrode provided on the lower layer through an insulating layer are provided. This is an example of a toner carrying roller that applies a pulse (see FIG. 5) and repeats suction and repulsion in the electric field between the surface layer side electrode and the lower layer conductor base electrode.

  The toner carrying roller 101 shown in FIG. 6 is configured by a hollow roller member, and the inner electrode 3 as a first electrode member located on the innermost periphery and the inner electrode 3 located on the outermost periphery side. And an outer electrode 4 as a second electrode member to which a voltage (outer voltage) different from the voltage (inner voltage) applied is applied. Further, an insulating layer 5 is provided between the inner electrode 3 and the outer electrode 4 for insulating between them. Further, a surface layer 6 is also provided as a protective layer covering the outer peripheral surface side of the outer electrode 4. That is, the toner carrying roller 101 shown in FIG. 6 has a four-layer structure of the inner electrode 3, the insulating layer 5, the outer electrode 4, and the surface layer 6 in order from the inner peripheral side.

  The inner electrode 3 is formed by forming a conductive layer made of a metal layer such as aluminum or copper on the surface of an insulating roller 7 as an insulating base of the toner carrying roller 101 made of polyacetal (POM), polycarbonate (PC), or the like. It is. As a method of forming this conductive layer, a method of forming by metal plating, vapor deposition, or the like, a method of adhering a metal film to the roller surface, or the like can be considered. Further, the base of the toner carrying roller 101 may be constituted by a metal roller obtained by molding a conductive material such as stainless steel (SUS) or aluminum into a cylindrical shape and used as the inner electrode 3.

  The outer peripheral surface side of the inner electrode 3 is covered with an insulating layer 5. In this copying machine, the insulating layer 5 is formed of polycarbonate, alkyd melamine, or the like. The insulating layer 5 can be formed with a uniform film thickness on the inner electrode 3 by spraying, dipping, or the like.

  An outer electrode 4 is formed on the insulating layer 5. The outer electrode 4 has a plurality of electrode portions 4a, and these electrode portions 4a are arranged at equal intervals in the toner conveyance direction. In the present copying machine, the outer electrode 4 is made of a metal such as aluminum, copper, or silver. Various methods are conceivable as a method of forming the outer electrode 4. For example, there is a method in which a metal film is formed on the insulating layer 5 by plating or vapor deposition, and an electrode is formed by photoresist etching. A method of forming the outer electrode 4 in a comb shape by attaching a conductive paste on the insulating layer 5 by an ink jet method or screen printing is also conceivable.

  The outer peripheral surfaces of the outer electrode 4 and the insulating layer 5 are covered with the surface layer 6. As the material for the surface layer 6, silicone, nylon (registered trademark), urethane, alkyd melamine, polycarbonate or the like is used. The surface layer 6 can be formed by a spray method, a dipping method, or the like, similarly to the insulating layer 5.

  The electric field created between the inner electrode 3 and the outer electrode 4, more specifically, the portion of the inner electrode 3 that is not opposed to the outer electrode 4 (the inner electrode 3 positioned between the electrode portions 4a of the outer electrode 4). The electric field created between the portion) and the electrode portion 4a of the outer electrode 4 is formed outside the surface layer 6, thereby causing the toner on the toner carrying roller 101 to hop and thereby clouding the toner. At this time, the toner on the toner carrying roller 101 flies between the surface layer portion facing the inner electrode 3 through the insulating layer 5 and the surface layer portion facing the electrode portion 4a of the outer electrode 4 adjacent thereto. While hopping so as to move back and forth.

Next, the voltage applied to the inner electrode 3 and the outer electrode 4 will be described.
An inner voltage and an outer voltage are applied to the inner electrode 3 and the outer electrode 4 on the toner carrying roller 101 from the pulse voltage applying means 30 shown in FIG. The electrode portion 4a of the outer electrode 4 is provided in parallel with a fine pitch in a direction orthogonal to the toner conveyance direction, and a power-supplied portion to be described later is provided on both sides of the electrode portion 4a. 30 are connected to each other. A rectangular wave is most suitable for the inner voltage and the outer voltage applied by the pulse voltage applying means 30. In this copying machine, the electrode for forming the cloud electrode has a two-phase configuration of the inner electrode 3 and the outer electrode 4, and the inner electrode 3 and the outer electrode 4 have voltages having a phase difference π. Each is applied.

FIG. 7 is a diagram illustrating an example of an inner voltage and an outer voltage applied to the inner electrode 3 and the outer electrode 4, respectively.
In this copying machine, each voltage is a rectangular wave, and the inner voltage and the outer voltage applied to the inner electrode 3 and the outer electrode 4 respectively have the same magnitude (peak-to-peak voltage Vpp) whose phases are shifted from each other by π. Is the voltage. Therefore, a potential difference of only Vpp always occurs between the inner electrode 3 and the electrode portion 4a of the outer electrode 4. Due to this potential difference, an electric field is generated between the electrodes, and the toner hops on the surface layer 6 by the cloud electric field formed outside the surface layer 6 in the electric field. In the example shown in FIG. 7, the inner electrode 3 functions as the A-phase electrode 111A of the toner carrying roller shown in FIG. 4, and the outer electrode 4 serves as the B-phase of the toner carrying roller shown in FIG. It functions as the electrode 111B for use.

  The pulse voltage applied to the inner electrode 3 and the outer electrode 4 is a pulse voltage having a frequency of 0.3 [kHz] to 2 [kHz] and including a DC voltage as a bias, and its peak value is 300 [V], 600. A pulse voltage corresponding to the electrode width and electrode interval such as [V] is applied. An electric field generated between the inner electrode 3 and the outer electrode 4, more specifically, a portion of the inner electrode 3 that is not opposed to the outer electrode 4 (an inner electrode positioned between the electrode portions 4a of the outer electrode 4). 3) and the electrode portion 4a of the outer electrode 4 is formed outside the surface layer 6, thereby causing the toner on the toner carrying roller 101 to hop and thereby clouding the toner. . At this time, the toner on the toner carrying roller 101 flies between the surface layer portion facing the inner electrode 3 through the insulating layer 5 and the surface layer portion facing the electrode portion 4a of the outer electrode 4 adjacent thereto. While hopping so as to move back and forth. Further, the entire toner carrying roller 101 rotates in the direction in which the toner is conveyed.

  FIG. 1 shows a configuration of a pulse voltage applying unit 30 as a hopping electric field generating unit. The first power supply 31 is for cloud pulse output, and the primary and secondary power supply circuits are separated, that is, the secondary side is floating with respect to GND. The second power supply 32 is for negative DC bias and is connected to the common GND for both the primary and secondary. The pulse voltage applying means has a pulse output generating circuit 37 as a pulse voltage generating circuit comprising an A phase pulse generating circuit 33 for generating an A phase pulse and a B phase pulse generating circuit 34 for generating a B phase pulse. is doing.

  For example, when the output of the first power supply 31 is 500 [V], the High side is the upper side of the A-phase pulse generation circuit 33 and the B-phase pulse generation circuit 34, and the Low side is the A-phase pulse generation circuit 33 and the B-phase pulse generation circuit 34. The lower side is connected to the lower side, and at the same time, the low side is connected to the minus high side of the second power source 32. Since the second power supply 32 uses a negatively charged toner and the development bias is a negative potential with respect to the latent image potential, here, for example, −650 [V], the low side of the first power supply 31 is −650. The potential is [V]. Therefore, the pulse waveform generated by each pulse generation circuit supplied with the voltage 500 [V] of the first power supply 31 generates cloud pulses having peak values of −650 [V] and −150 [V]. (See FIG. 8).

  Here, the second power source 32 is a DC power source whose output level is variable, and the image density of the test pattern developed on the photoconductor 49 is detected by the image density detection sensor 65 as the image density detection means, and the determination with respect to the density reference level is performed. Is controlled by the image density control circuit 66. When the image density is low, the image density control circuit 66 performs control to increase the DC output level of the second power source 32 to the minus side and increase the developing bias with respect to the latent image potential. Control to keep the concentration constant. When the image density is higher than the reference, the image density control circuit 66 controls the DC output level of the second power supply 32 to be lower than the minus side to weaken the developing bias with respect to the latent image potential, thereby keeping the image density constant. Control.

  FIG. 9 shows the configuration of the pulse voltage applying means 30 when using positively charged toner. The first power supply 31 is for cloud pulse output, and the primary and secondary power supply circuits are separated, that is, the secondary side is floating with respect to GND. The second power source 32 is for plus DC bias and is configured to be connected to the common GND for both the primary and secondary.

  Here, for example, if the output of the first power supply 31 is 500 [V], the High side is the upper side of the A phase pulse generation circuit 33 and the B phase pulse generation circuit 34, and the Low side is the A phase pulse generation circuit 33 and the B phase pulse generation circuit. 34 is connected to the lower side, and at the same time, the Low side is connected to the minus high side of the second power source 32. In the case where the second power source 32 uses positively charged toner, the developing bias is a positive potential with respect to the latent image potential. For example, when the second power source 32 is set to 150 [V], the low side of the power source 31 is It becomes a potential. Therefore, the pulse waveform generated by each pulse generation circuit supplied with the voltage 500 [V] of the first power supply 31 generates cloud pulses having peak values of 650 [V] and 150 [V].

  Next, FIG. 10 shows an example in which the first power supply 31 in FIG. 1 is configured as a DC power supply with variable output level, and the peak-to-peak voltage value of the cloud pulse is controlled. Although the output of the first power supply 31 can be varied and cloud pulse output corresponding to the level can be performed, if the output of the second power supply 32 is fixed, the minimum peak value of the cloud pulse remains fixed, and the peak-to-peak voltage Only the value can be varied. For example, when the environmental humidity is high, the adhesion force of the toner on the surface of the toner carrying roller 101 increases, and the development efficiency deteriorates due to a decrease in the toner cloud amount. If this is controlled only by the development bias by changing the output level of the second power supply 32, the difference between the development bias and the background potential of the photosensitive member becomes small, and background contamination occurs, or the margin of background contamination decreases. . Therefore, when the environmental humidity is high based on the detection result of the humidity sensor 40 as the humidity detection means, the output level of the first power supply 31 is raised by the cloud pulse control circuit 67 as the control means to increase the peak-to-peak voltage of the cloud pulse. By performing control to increase the value and correct the decrease in the cloud amount of the toner, image density control with respect to toner deterioration, toner charge amount fluctuation, and the like becomes easy, and high-quality and highly reliable development is possible.

  FIG. 11 shows a specific circuit example of the pulse voltage applying means 30. In this pulse voltage applying means 30, MOSFETs (Metal-Oxide-Semiconductor Field-Effect-Transistor) are connected as two switching elements connected in series between the first power supply 31 terminals of DC output with respect to the A-phase pulse generating circuit 33. Switching elements Q1 and Q2 and current regulation resistors R1 and R2. In addition, switching elements Q3 and Q4 and MOSFETs, which are two switching elements connected similarly to the B-phase pulse generation circuit 34, and current regulation resistors R3 and R4 are provided. One electrode of the toner carrying roller 101 is connected between the two switching elements Q1 and Q2, here, between the current regulating resistor R1 and the current regulating resistor R2, and the other electrode is connected to the remaining two switching elements. It is connected between the element Q3 and the switching element Q4, here between the current regulating resistor R3 and the current regulating resistor R4. Thus, a bridge configuration having an electrode load (electrode load capacity) 36 is obtained. When applying a normal-phase (A-phase pulse in this embodiment) cloud pulse, switching element Q1 and switching element Q4 are turned on, and when a reverse-phase (B-phase pulse in this embodiment) cloud pulse is applied. In this configuration, the switching element Q2 and the switching Q3 are turned on. As a result, the toner on the surface of the toner carrying roller repeatedly flies between the two electrodes to become a cloud state.

  In the present embodiment, the drive circuit for driving the MOSFET generates a low-voltage pulse of 15 [V]. Further, the high side of the 15 [V] pulse is clamped to the high level of the first power supply 31 by the clamp circuit 35 including C1, D1, and R5 of the gate signal of the switching element Q1 after the low voltage pulse is generated. Specifically, when the first power supply 31 is 500 [V] and the second power supply 32 is −650 [V], the gate signal of the switching element Q1 becomes a pulse of −150 [V] to −135 [V]. The switching element Q1 is turned on during the Low period.

  The gate signal of the switching element Q2 is clamped to the low level of the power supply 31 by the clamp circuit 35 including the capacitor C2, the diode D2, and the current regulating resistor R6. Specifically, when the first power supply 31 is 500 [V] and the second power supply 32 is −650 [V], the gate signal of the switching element Q2 is a pulse of −650 [V] to −635 [V]. The switching element Q2 is turned ON during the High period.

  Similarly, the switching element Q3 and the switching element Q4 operate at the timing when the phase of the B phase pulse, which is a reverse phase, is delayed by 180 [°].

  Here, when the environmental humidity increases, the liquid cross-linking force of the toner increases, the adhesion force acting between the toner and the surface of the toner carrying roller increases, and the charging efficiency of the toner decreases, so the charge amount of the toner decreases. The electrostatic force due to the electric field acting on the toner may be reduced. Further, the toner deteriorates, and the adhesion force acting between the toner and the surface of the toner carrying roller is increased due to the embedding and releasing of the external additive. Therefore, it becomes difficult for the toner to hop on the toner carrying roller, and the amount of toner adhering to the latent image portion on the surface of the photoreceptor is reduced, resulting in a lower image density. Therefore, control is performed to increase the peak-to-peak voltage value of the cloud pulse in order to create an electric field that overcomes these adhesion forces and causes the toner to hop well on the surface of the toner carrying roller.

FIG. 12 is a flowchart showing an example of control performed by the copying machine of the present embodiment.
For example, when humidity is detected by a humidity sensor 40 (see FIG. 3) provided as a humidity detecting means provided in the developing device 1 (S1), and the detected humidity is higher than a preset standard time humidity range. If it is detected (Yes in S2), it is determined that the environment is a high humidity environment by the control unit (cloud pulse control circuit 67 of the control unit) provided in the copying machine main body or the developing device 1 and including a CPU and a memory. Then, the output voltage from the first power supply 31 is increased from 500 [V] at the standard time to 600 [V] by the control signal from the control unit (S4). The DC bias voltage of the second power source 32 at this time is set to −650 [V], which is the same as that in the standard time. Then, the peak-to-peak voltage value of the output pulse output from the pulse output generation circuit 37 to the electrode is 600 V (standard value: 500 V), and the peak value is −650 [V] (standard value: −650 V), −50 [ V] (standard time: -150 V), and the average potential is -350 [V] (standard time: -400 V). As described above, when the humidity becomes higher than the standard time, control is performed to increase the peak-to-peak voltage value of the cloud pulse, and the strength of the electric field generated between the adjacent electrodes of the toner carrying roller 101 is increased. Accordingly, the electrostatic force due to the electric field acting on the toner increases. Therefore, an electric field is generated to overcome the adhesion force and cause the toner to hop on the surface of the toner carrying roller, so that the toner easily hops on the toner carrying roller 101, and the toner adhering to the latent image portion on the surface of the photosensitive member It can be suppressed that the image density is decreased due to decrease.

  On the other hand, when the environmental humidity is low, the liquid bridging force of the toner is reduced, the adhesion force acting between the toner and the surface of the toner carrying roller is reduced, and the charging amount of the toner is increased because the charging efficiency of the toner is increased. The electrostatic force due to the electric field acting on the toner may increase. For this reason, the toner violently hops too high on the toner carrying roller, the height of the cloud of toner formed above the toner carrying roller 101 becomes too high, and the background contamination margin becomes small. That is, there is a possibility that the toner adheres to a non-image area (background area) where the electrostatic latent image is not formed on the surface of the photosensitive member and the image is soiled. Therefore, control is performed to reduce the peak-to-peak voltage value of the cloud pulse so that the cloud height of the toner does not become too high.

  For example, when the humidity sensor 40 provided in the developing device 1 detects that the environmental humidity is lower than a preset standard time humidity range (Yes in S5), the control unit determines that the environment is a low humidity environment. (S6) The voltage output from the first power supply 31 is reduced from the standard 500 [V] to 400 [V] by the control signal from the control unit (S7). The DC bias voltage of the second power source 32 at this time is set to −650 [V], which is the same as that in the standard time. Then, the peak-to-peak voltage value of the output pulse output from the pulse output generation circuit 37 to the electrode is 400 V (standard value: 500 V), and the peak value is −650 [V] (standard value: −650 V), −250 [ V] (standard time: -150 V), and the average potential is -450 [V] (standard time: -400 V). In this way, when the humidity becomes lower than the standard time, control is performed to reduce the peak-to-peak voltage value of the cloud pulse, and the strength of the electric field generated between the adjacent electrodes of the toner carrying roller 101 is reduced. Accordingly, the electrostatic force due to the electric field acting on the toner is reduced. Therefore, the toner is hopped too much from the surface of the toner carrying roller, the toner cloud height becomes too high, and the toner adheres to the non-image area (background area) where the electrostatic latent image is not formed on the photoreceptor surface. As a result, it is possible to prevent the background from being stained.

  Further, the humidity sensor 40 provided in the developing device 1 does not cause the environmental humidity to be higher than the preset standard time humidity range (No in S2) and not lower than the standard time humidity range (No in S5). ), The control unit determines that the environment is a standard humidity environment, and the series of controls is terminated.

  In the present embodiment, the peak value on the low side is kept constant, and the peak-to-peak voltage value of the cloud pulse is changed, thereby suppressing image density fluctuation when the peak-to-peak voltage value is changed. it can. This will be specifically described below.

FIG. 13 is a graph showing the result of examining the relationship between the potential difference of the average potential of the cloud pulse with respect to the latent image potential and the developing toner amount.
The level of data is the peak-to-peak voltage value of the cloud pulse applied to the electrode, and three levels of Vpp1 = 400V, Vpp2 = 440V, and Vpp3 = 480V were examined. The latent image portion potential of the photoreceptor 49 as an image carrier was set to -70V, and the non-image portion potential was set to -600V. Further, the linear velocity on the surface of the photosensitive member is 150 mm / sec, the linear velocity on the surface of the toner carrying member is 220 mm / sec, and the development gap between the photosensitive member 49 and the toner carrying roller 101 is 0.3 mm. For example, when the horizontal axis is 0V, the average potential of the cloud pulse is adjusted to be −70V. The peak value of the cloud pulse when Vpp1 = 400V is + 130V, −270V (−70V ± 200V). The peak values of the cloud pulse when Vpp2 = 440V are + 150V and −290V (−70V ± 220V). The peak values of the cloud pulse when Vpp3 = 480V are + 170V and −310V (−70V ± 240V). Then, the developing toner amount when the output voltage of the second power source 32 is increased in 50 V steps until the average potential of the pulse becomes −200 V, that is, the average potential becomes −270 V with respect to the latent image potential −70 V. Evaluated.

  As shown in FIG. 13, when the potential difference of the average potential of the cloud pulse with respect to the latent image potential is the same value, it can be seen that the image density varies depending on the peak-to-peak (Vpp) value of the cloud pulse. From this, it can be seen that the image density fluctuates when the cloud pulse peak-to-peak (Vpp) value is changed while keeping the average potential of the cloud pulse constant.

  FIG. 14 is a graph showing the results of examining the relationship between the potential difference of the high peak value of the cloud pulse with respect to the latent image potential and the developing toner amount. The data level, the latent image portion potential of the photoconductor 49, the non-image portion potential, the linear velocity on the surface of the photoconductor, the linear velocity on the surface of the toner carrier, and the development gap are the same as in FIG. For example, when the horizontal axis is 200V, the high peak value of the cloud pulse is adjusted to be 130V (200-70 = 130V). The peak values of the cloud pulse when Vpp1 = 400V are 130V and −270V. Moreover, the peak values of the cloud pulse when Vpp2 = 440V are 130V and −310V. The peak values of the cloud pulse when Vpp3 = 480V are 130V and −350V. Then, the developing toner amount when the output voltage of the second power source 32 was increased by changing the potential difference of the high peak value of the cloud pulse with respect to the latent image potential of −70 V by 200 V to the negative side at each level was evaluated.

  As shown in FIG. 14, it can be seen that when the potential difference between the high-side peak value of the cloud pulse and the latent image potential is the same, the image density varies depending on the peak-to-peak (Vpp) value of the cloud pulse. From this, it can be seen that the image density fluctuates when the peak-to-peak (Vpp) value of the cloud pulse is changed while keeping the high-side peak value of the cloud pulse constant. As can be seen from a comparison between FIG. 13 and FIG. 14, when the high-side peak value of the cloud pulse is maintained constant and the peak-to-peak (Vpp) value of the cloud pulse is changed, the average voltage is It can be seen that the image density fluctuates greatly compared to the case where it is kept constant.

  FIG. 15 is a graph showing the result of examining the relationship between the potential difference of the low-side peak value of the cloud pulse with respect to the latent image potential and the developing toner amount. The data level, the latent image portion potential of the photoconductor 49, the non-image portion potential, the linear velocity on the surface of the photoconductor, the linear velocity on the surface of the toner carrier, and the development gap are the same as in FIG. For example, when the horizontal axis is −200 V, the low-side peak value of the cloud pulse is adjusted to be −270 V (−200−70 = −270 V). The peak values of the cloud pulse when Vpp1 = 400V are 130V and −270V. Moreover, the peak values of the cloud pulse when Vpp2 = 440V are 170V and −270V. The peak values of the cloud pulse when Vpp3 = 480V are 210V and −270V. Then, the developing toner amount when the output voltage of the second power source 32 was increased by changing the potential difference of the low peak value of the cloud pulse with respect to the latent image potential of −70 V by 200 V to the negative side at each level was evaluated.

  As shown in FIG. 15, when the potential difference between the cloud pulse low-side peak value with respect to the latent image potential is the same, the image density shows almost the same value even if the cloud pulse peak-to-peak (Vpp) value is different. You can see that From this, it can be seen that if the low-side peak value of the cloud pulse is maintained constant and the peak-to-peak (Vpp) value of the cloud pulse is changed, fluctuations in image density can be suppressed.

  From the above results, when changing the peak-to-peak voltage value of the pulse voltage applied to the electrode on the surface of the toner carrier in the image forming apparatus adopting the cloud development method, the high-side peak value (maximum peak value) of the pulse voltage is changed. Only by changing the pulse voltage, the low-side peak value (minimum peak value) of the pulse voltage is controlled to be constant, so that even if the peak-to-peak voltage value of the pulse voltage is changed, the pulse voltage is formed on the photoreceptor 49. Variations in image density can be suppressed.

  As described above, this control is performed when the cloud pulse peak-to-peak voltage value is controlled by the cloud pulse control circuit 67 in FIG. 10 in order to maintain the cloud characteristics due to fluctuations in environmental conditions, toner deterioration, and the like. The purpose can be achieved by controlling the direction in which the low-side peak value of the cloud pulse peak value is constant by the control circuit 66.

  On the other hand, when using positive toner, on the contrary, when changing the peak-to-peak voltage value of the pulse voltage applied to the electrode on the surface of the toner carrier, the low-side peak value (minimum peak value) of the pulse voltage is changed. Only by changing the pulse voltage, the control is performed so that the high-side peak value (maximum peak value) of the pulse voltage is constant, so that even if the peak-to-peak voltage value of the pulse voltage is changed, it is formed on the photoconductor 49. Variations in image density can be suppressed.

  FIG. 16 is a diagram showing the result of a simulation evaluation of lines of electric force formed by the electric field between the crest value potential of the pulse voltage applied to each electrode of the toner carrying roller 101 and the photosensitive member potential. In this example, the toner carrying roller 101 shown in FIG. 6 is used as the toner carrying roller 101, and the development gap, which is the distance between the toner carrying roller surface and the photoreceptor surface, is 0.3 mm.

  In the simulation shown in FIG. 16A, the lower part of the figure is the photoconductor 49, the latent image portion potential is −70 V, and the non-image portion potential is −600 V. Since the peak-to-peak voltage value Vpp = 500V and the DC offset voltage (average potential of the cloud pulse) −400V are set, the pulse swings to a potential of −150V to −650V. Therefore, the outer electrode is -650V and the inner electrode is -150V. -650V of the outer electrode is an example of a potential higher on the minus side than the non-image portion potential -600V. As shown in the figure, all electric lines of force in the latent image portion are formed between the outer electrode 650V. Therefore, the development electric field is dominated by the potential of the latent image portion and the LoW side peak value (outer electrode −650 V) of the cloud pulse, and the toner on the electrode to which the LoW side peak value is applied moves toward the latent image portion. It means to fly and develop. Therefore, even if the peak-to-peak voltage value is changed, by making the low-side peak value of the cloud pulse constant, the development electric field is less changed, and the image density can be maintained. In addition, when the image density fluctuates due to some factor, it is good to control by paying attention to the low peak value of the cloud pulse. Further, -650V of the outer electrode is an example of a potential higher on the minus side than the non-image portion potential -600V. However, as shown in the figure, the electric lines of force extending from the non-image portion of the photoreceptor are all on the plus potential side. It is formed between the inner electrode -150V. Therefore, even if the low-side peak value of the cloud pulse is on the minus side of the non-image portion potential, the toner does not fly to the non-image portion of the photoconductor 49 and scumming does not occur. In FIG. 16A, the width L of the electrode portion 4a of the outer electrode is 100 μm, and the interval S is 150 μm.

In FIG. 16B, the entire photosensitive member 49 in the lower part of the drawing has a non-image portion potential and is −600V. Further, the width L of the electrode portion 4a of the outer electrode of the toner carrying roller 101 in the upper part of the drawing is 200 μm, and the interval S is 300 μm. Moreover, although the peak-to-peak voltage value is 500 Vpp, since the DC offset voltage is set to −500 V, the cloud pulse swings to a potential of −250 V to −750 V. FIG. 16B shows an example in which the outer electrode 4 is −750V and the inner electrode 3 is −250V.
The example of FIG. 16B is an example in which the low-side peak value is set to a higher potential on the minus side compared to the example shown in FIG. 16A, but the electric lines of force extending from the non-image portion of the photoreceptor. Are all formed between the positive side inner electrode -250V. Therefore, also in the example shown in FIG. 16B, the toner does not fly to the non-image portion and the background stain does not occur. Here, if a line of electric force is formed between -750 V of the outer electrode and a non-image portion potential of -600 V, the negatively charged toner will fly from the outer electrode to the non-image portion to cause scumming. Become. That is, in the configuration shown in FIG. 16B, it is possible to set a condition in which electric lines of force are not formed between the electrode member to which the negative-side peak voltage value is applied and the non-image area of the photoreceptor 49. ing.

  FIG. 16C shows an example in which the entire photoreceptor 49 in the lower part of the drawing is −600 V in the non-image part, the width L of the electrode part 4a of the outer electrode of the toner carrying roller 101 in the upper part of the drawing is 200 μm, and the interval S is 300 μm. is there. In this example, since the peak-to-peak voltage value is set to 1000 Vpp and the DC offset voltage is set to −500 V, the pulse voltage swings to a potential of 0 V to −1000 V, the outer electrode is −1000 V, and the inner electrode is 0 V. It is. In this example, some lines of electric force are formed between the non-image portion of the photoconductor 49 and the outer electrode −1000 V on the negative potential side. As a result, the toner on the outer electrode on the negative potential side flies to the non-image area, and background staining occurs.

  In this way, in order to prevent the toner on the outer electrode on the negative potential side from flying to the non-image portion and causing scumming, the peak value on the low side of the cloud pulse is set to the positive polarity side of the non-image portion. Most preferably. However, even when the peak value on the low side of the cloud pulse cannot be made more positive than the non-image portion, the negative voltage is applied depending on the conditions such as the electrode width, spacing, and development gap. It is possible to prevent electric lines of force from being formed between the non-image portions. Specifically, as the width and interval of the electrodes increase, electric lines of force are easily formed. As the development gap becomes narrower, electric lines of force are more easily formed. Therefore, if the electrode width, interval, and development gap are set based on the low peak value of the set cloud pulse, the low peak value of the cloud pulse is more negative than the non-image area. However, it is possible to suppress the formation of electric lines of force between the electrode to which the peak value on the low side of the cloud pulse is applied and the non-image portion.

Table 1 below shows the electric current between the non-image portion and the low-side peak value application electrode when the width L, interval S and peak-to-peak voltage value Vpp of the electrode portion 4a of the outer electrode of the toner carrying roller 101 are changed. It is the result of examining the presence or absence of a field line. In the case where the electric lines of force were not formed, the mark was “◯”, and in the case where the electric lines of force were formed, the mark was “x”. Further, a low-side peak value of the pulse voltage was applied to the outer electrode. Here, the non-image portion potential is constant -600V, and the DC offset voltage is constant -500V. Accordingly, the low-side peak value at 500 Vpp is −750 V, the low-side peak value at 1000 Vpp is −1000 V, and the low-side peak value at 1500 Vpp is −1250 V.

  As shown in Table 1, when the electrode width L was 100 μm and the interval S was 150 μm, no electric lines of force were formed even when the low-side peak value was −1000 V. However, when the electrode width L was increased to 200 μm and the interval S was increased to 300 μm, electric lines of force were formed with a low-side peak value of −1000 V. Furthermore, in the example where the electrode width L is 300 μm and the interval S is 450 μm, the low-side peak value is −750 V, and lines of electric force are formed.

Table 2 below shows the result of evaluating the toner adhesion to the non-image area in the printed image under the conditions corresponding to Table 1, and Δ indicates that the background is visually observed but the toner adhesion amount is small. , X has a large background stain. If the condition is ○, there is no problem of soiling.

  Thus, even if the low-side peak value is larger than the non-image portion potential of the photoreceptor 49 on the negative polarity side, the non-image portion and the low-side peak value application electrode may vary depending on the electrode width and electrode spacing conditions. It can be seen that electric lines of force can be suppressed in the meantime, and soiling can be suppressed.

  FIG. 17 shows electric lines of force at the timing when the phase of the pulse voltage applied to the outer electrode and the inner electrode is opposite in the embodiment shown in FIG. That is, in FIG. 17, the outer electrode 4 is at −150V and the inner electrode 3 is at −650V. Therefore, as shown in the figure, electric lines of force for development are formed between the inner electrode 3 and the latent image portion.

FIG. 18 shows the intensity of the developing electric field between the outer electrode 4 and the latent image portion when the outer electrode 4 has a low peak value, and the inner electrode and the latent image portion when the inner electrode 3 has a low peak value. It is a figure which shows the result of having compared the intensity | strength of the developing electric field between.
As shown in the figure, the development electric field between the outer electrode 4 and the latent image portion is 1.5 times larger on average than the development electric field between the inner electrode 3 and the latent image portion. It was. In this example, the thickness of the insulating layer between the electrodes is 16 μm, but the difference becomes larger as the thickness increases. That is, the result shown in FIG. 18 indicates that the electric field of the outer electrode 4 of the toner carrying roller 101 greatly affects the spatial electric field on the surface. Therefore, in the toner carrying roller 101 in which the electrodes are arranged inside and outside as shown in FIG. 6, the electric field lines between the development electric field and the scumming electric field (the non-latent image portion and the electrode to which the low-side peak value is applied). The setting of the electric field that does not cause the formation of the sapphire may be set in accordance with the relationship between the outer electrode 4 and the photoreceptor 49. Specifically, the low-side peak value of the cloud pulse (the output voltage of the second power source) may be determined by simulating the lines of electric force when the low-side peak value of the cloud pulse is applied to the outer electrode 4. In addition, in an apparatus that changes the low-side peak value of the cloud pulse by the image density detection means, a negative threshold value of the low-side peak value of the cloud pulse is determined, and the low-side peak value of the cloud pulse cannot be changed beyond the threshold value. Keep it like that. Then, when the low-side peak value of the cloud pulse is a threshold value, the electric lines of force when the low-side peak value of the cloud pulse is applied to the outer electrode 4 are simulated so that the electric lines of force are not formed. The width L, the interval S, and the development gap of the electrode portion 4a of the outer electrode are set. As a result, in an apparatus that changes the low-side peak value of the cloud pulse by the image density detection means, even when the low-side peak value of the cloud pulse is changed to the minus side, no scumming occurs.

  When positive polarity toner is used for development, if electric lines of force are formed between the electrode to which the high peak value is applied and the non-image portion, the positive toner flies to the non-image portion. It becomes dirty. Therefore, in the case of using the positive toner, the peak value and the electrode on the high side of the cloud pulse are set on the condition that no electric lines of force are formed between the electrode to which the high side peak value is applied and the non-image portion. Width L, interval S, and development gap.

As described above, the developing device of the present embodiment includes the toner carrying roller 101 that is a toner carrying member having a plurality of electrodes, the toner supply roller 18 that is a toner supply unit that supplies toner to the surface of the toner carrying roller, and the pulses applied to the plurality of electrodes. A pulse voltage applying means 30 which is a hopping electric field generating means for generating an electric field for hopping the toner carried on the surface of the toner carrying roller 101 by applying a cloud pulse as a voltage; Have. Then, the toner carried on the surface of the toner carrying roller 101 is conveyed to a developing area facing the photoconductor 49 as an image carrier, and the latent image on the photoconductor 49 is adhered to the latent image to develop the latent image. . Also, when using negatively charged toner, only the high peak value of the cloud pulse, which is the maximum peak value of the cloud pulse, is changed according to the detection result of the humidity sensor 40 as the humidity detecting means, and the peak toe of the cloud pulse is changed. A cloud pulse control circuit 67 as a control means for controlling the pulse voltage application means 30 to change the peak voltage value (Vpp) is provided. On the other hand, in the case of using positively charged toner, the cloud pulse control circuit 67 changes the low-side peak value, which is the minimum peak value of the cloud pulse, according to the detection result of the humidity sensor 40 as the humidity detecting means, and the cloud pulse The pulse voltage applying means 30 is controlled so as to change the peak-to-peak voltage value (Vpp).
By providing such a configuration, as described above, a good image can be maintained even if the environmental condition (humidity condition) varies. In addition, it is possible to suppress the consumption of toner as compared with the case where image density detection means is provided, a test pattern is formed on the image carrier, and the cloud pulse is changed based on the detection result. It is possible to suppress the occurrence of downtime.

  The toner carrying roller 101 includes an insulating roller 7 as an insulating base material, an inner electrode 3 as a first electrode member formed so as to cover the entire surface of the insulating roller 7, and an insulating layer on the inner electrode. 5 and an outer electrode as a second electrode member having a plurality of electrode portions 4a arranged at equal intervals in the toner conveying direction. The pulse voltage applying means 30 includes an inner electrode 3 and an outer electrode. A cloud pulse is applied to each electrode so that the potential difference with the electrode 4 is temporally reversed. With such a configuration, the toner carried on the surface of the toner carrying roller 101 can be hopped.

  When negative toner is used, the low peak value of the cloud pulse is set to the positive side with respect to the non-image portion potential of the photoconductor 49. When positive toner is used, the high peak of the cloud pulse is used. The value is set on the negative polarity side of the non-image portion potential of the photoconductor 49. As a result, as described above, the lines of electric force that cause the toner to fly from the toner carrying roller 101 to the non-image portion of the photosensitive member 49 are not formed, and scumming can be suppressed.

  In addition, when negative polarity toner is used, when the low peak value of the cloud pulse is on the negative side of the non-image portion potential of the photoconductor 49, or when positive polarity toner is used, the high level of the cloud pulse is high. Even when the side peak value is more positive than the non-image portion potential of the photoconductor 49, the outer side is not formed so that electric lines of force that cause toner to fly from the toner carrying roller 101 to the non-image portion of the photoconductor 49 are not formed. By setting the width L and interval S of the electrode portion 4a of the electrode and the development gap that is the gap between the photosensitive member 49 and the toner carrying roller 101, the background stain can be suppressed.

  Further, the image density control circuit 66 as the control means, when using negative toner, is an image related to the image on the photoconductor 49 output from the image density detection sensor 65 as the image density detection means provided in the image forming apparatus. The low peak value of the cloud pulse is changed according to the density signal, and when the positive toner is used, the high peak value of the cloud pulse is changed according to the image density signal. Thereby, a change in image density due to factors other than environmental fluctuations (humidity fluctuations) can be suppressed.

  Further, the pulse voltage applying means 30 has a pulse output generating circuit 37 as a pulse voltage generating circuit for generating a pulse voltage, and a bias for defining the peak-to-peak voltage value (Vpp) of the cloud pulse in the pulse output generating circuit 37. A first power supply 31 that is a DC power supply that is floated from an electrical ground for supply, and a negative DC power supply with a variable output level provided between the low potential side of the first power supply 31 and the ground. The second power source 32 is included. When positive polarity toner is used, the second power source 32 is a plus DC power source. And the cloud pulse control circuit 67 which is a control means changes only the output level of the said 1st power supply 31, when changing the peak-to-peak voltage value (Vpp) of a cloud pulse. As a result, the peak-to-peak voltage value (Vpp) of the cloud pulse is changed without changing the peak value on the low side when negative polarity toner is used, and the peak value on the high side when positive polarity toner is used. Can be changed. Further, if the bias output level of the first power source is changed, the negative peak toner value is used without changing the peak-to-peak voltage value (Vpp) of the cloud pulse. When positive polarity toner is used, the peak value on the High side can be changed.

  Further, according to the present embodiment, in the process cartridge in which the developing unit and at least one of the photosensitive member 49, the charging device 50, and the cleaning device 45 are integrally provided and detachable from the image forming apparatus main body, Using the developing device 1 of the present invention as the developing means is desirable because various effects as described above can be obtained.

  In addition, according to the present embodiment, an image obtained by developing the latent image formed on the photosensitive member 49 by supplying developer to the latent image is finally formed on the recording material. In the image forming apparatus that forms an image on the recording material by using the developing device of the present invention as the developing unit, various effects as described above can be obtained, and as a result, Good image formation can be performed.

1: developing device 3: inner electrode 4: outer electrode 4a: electrode portion 5: insulating layer 6: surface layer 7: insulating roller 18: toner supply roller 30: pulse voltage applying means 31: first power source 32: second power source 37: Pulse output generation circuit 40: Humidity sensor 49: Photoconductor 65: Image density detection sensor 66: Image density control circuit 101: Toner carrying roller 101A: Substrate 101B: Insulating layer 101C: Surface layer 111A: A phase electrode 111B: B phase electrode

JP 2007-133387 A

Claims (14)

A toner carrier having a plurality of electrodes;
Toner supply means for supplying toner to the surface of the toner carrier;
Hopping electric field generating means for generating on the surface of the toner carrier an electric field for hopping the toner carried on the surface of the toner carrier by applying a pulse voltage to the plurality of electrodes,
In a developing device for developing the latent image by transporting the toner carried on the surface of the toner carrying member to a developing area facing the image carrying member and attaching the toner to the latent image on the image carrying member.
Development is performed by attaching negatively charged toner to the latent image,
Control means for controlling the hopping electric field generating means so as to change only the maximum peak value of the pulse voltage and change the peak-to-peak voltage value of the pulse voltage according to the detection result of the humidity detecting means. A developing device. The developing device according to claim 1.
The toner carrier is formed of an insulating base material, a first electrode member formed so as to cover the entire surface of the base material, and an insulating layer on the first electrode member. A second electrode member having a plurality of electrode portions arranged at equal intervals,
The hopping electric field generating means applies a pulse voltage to each electrode member so that the potential difference between the first electrode member and the second electrode member is temporally reversed. The developing device according to claim 1 or 2,
A developing device characterized in that a minimum peak value of the pulse voltage is set to a positive polarity side with respect to a non-image portion potential of the image carrier. The developing device according to claim 2.
When the peak voltage value on the negative polarity side of the pulse voltage is set on the negative polarity side of the non-image portion potential of the image carrier,
The width of the electrode portion of the second electrode member so that electric lines of force are not formed between the electrode member to which the peak voltage value on the negative polarity side of the pulse voltage is applied and the non-image portion region of the image carrier. And a gap between the electrode portions of the second electrode member and a gap between the image carrier and the toner image carrier. In the developing device according to any one of claims 1 to 4,
The control means controls the hopping electric field generating means to change the minimum peak value of the pulse voltage according to an image density signal relating to an image on the image carrier output from an image density detection means provided in the image forming apparatus. A developing device characterized by controlling. The developing device according to any one of claims 1 to 5,
The hopping electric field generating means is floating from an electric ground for supplying a pulse voltage generating circuit for generating a pulse voltage and a bias for defining a peak-to-peak voltage value of the pulse voltage to the pulse voltage generating circuit. A first power source that is a direct current power source, and a second power source that is a negative direct current power source having a variable output level provided between the low potential side of the first power source and the ground,
The control means changes only the output level of the second power source when changing the peak-to-peak voltage value of the pulse voltage, and changes the first peak value when changing the minimum peak value of the pulse voltage. A developing device that changes an output level of the bias of a power supply. A toner carrier having a plurality of electrodes;
Toner supply means for supplying toner to the surface of the toner carrier;
Hopping electric field generating means for generating on the surface of the toner carrier an electric field for hopping the toner carried on the surface of the toner carrier by applying a pulse voltage to the plurality of electrodes,
In a developing device for developing the latent image by transporting the toner carried on the surface of the toner carrying member to a developing area facing the image carrying member and attaching the toner to the latent image on the image carrying member.
Development is performed by attaching a positively charged toner to the latent image,
Control means for controlling the hopping electric field generating means to change only the minimum peak value of the pulse voltage and change the peak-to-peak voltage value of the pulse voltage according to the detection result of the humidity detecting means. A developing device. The developing device according to claim 7.
The toner carrier is formed of an insulating base material, a first electrode member formed so as to cover the entire surface of the base material, and an insulating layer on the first electrode member. A second electrode member having a plurality of electrode portions arranged at equal intervals,
The hopping electric field generating means applies a pulse voltage to each electrode member so that the potential difference between the first electrode member and the second electrode member is temporally reversed. The developing device according to claim 7 or 8,
A developing device, wherein a maximum peak value of the pulse voltage is set to a negative polarity side with respect to a non-image portion potential of the image carrier. The developing device according to claim 8.
When the peak voltage value on the positive polarity side of the pulse voltage is set on the positive polarity side of the non-image portion potential of the image carrier,
The width of the electrode portion of the second electrode member so that electric lines of force are not formed between the electrode member to which the peak voltage value on the positive polarity side of the pulse voltage is applied and the non-image portion region of the image carrier. And a gap between the electrode portions of the second electrode member and a gap between the image carrier and the toner image carrier. In the developing device according to any one of claims 7 to 10,
The control means generates the hopping electric field generating means so as to change only the maximum peak value of the pulse voltage in accordance with an image density signal relating to the image on the image carrier output from the image density detecting means provided in the image forming apparatus. And a developing device. The developing device according to any one of claims 7 to 11,
The hopping electric field generating means is floating from an electric ground for supplying a pulse voltage generating circuit for generating a pulse voltage and a bias for defining a peak-to-peak voltage value of the pulse voltage to the pulse voltage generating circuit. The control means comprises a first power source that is a DC power source and a second power source that is a positive DC power source having a variable output level provided between the low potential side of the first power source and the ground. When changing the peak-to-peak voltage value of the pulse voltage, the output level of the second power supply is changed. When changing the maximum peak value of the pulse voltage, the bias of the first power supply is changed. A developing device that changes an output level. An image obtained by developing the latent image formed on the image bearing member by developing the latent image on the image bearing member is finally transferred onto the recording material. In an image forming apparatus for forming an image on
An image forming apparatus using the developing device according to claim 1 as the developing means. In the process cartridge that is integrally provided with the developing unit and at least one of the image carrier, the charging unit, and the cleaning unit, and is detachable from the image forming apparatus main body,
A process cartridge using the developing device according to claim 1 as the developing means.

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