JP2006301420A - Developing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device capable of charging developer in a suitable quantity, hindering fog, and assuring satisfactory development, and to provide an image forming apparatus incorporating the developing device and capable of forming an image of high image quality. <P>SOLUTION: The developing device 300 develops an electrostatic latent image on a photoreceptor 100 by the use of toner t, and the image forming apparatus P1 incorporates the developing device. The developing device 300 includes: a developing roller 301; a charging member 306 for charging the toner t on the circumferential face of the developing roller in contact with the toner t; a developing bias application device B1 for applying an AC development bias voltage V1 to the developing roller 301; a charging bias application device B2 for applying an AC charging bias voltage V2(V2') to the charging member 306, the AC charging bias voltage V2 (V'2) being synchronous with the AC developing bias voltage V1 in phase and having an off-set potential difference Vd in phase on the positive or negative side; and a control section CT for the device B2. The control section CT controls the device B2 according to one of factors affecting toner chargeability, thereby controlling the offset potential difference Vd so that toner may be charged in normal quantity. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine or a printer that develops an electrostatic latent image formed on an image carrier using a developer to form an image, and a developing device mounted on the image forming apparatus.

  Nowadays, image forming apparatuses such as copiers and printers that develop an electrostatic latent image formed on an image carrier using a developer to form an image are widely used, and color image forming apparatuses are also rapidly developing. It has become widespread. Under such circumstances, the user's awareness regarding image quality and image formation cost is increasing.

  In terms of image quality, there is no or no image noise, and as few images as possible are desired. One of the image noises is so-called “fogging”. The “fogging” phenomenon occurs mainly due to a decrease in developer charge amount due to deterioration of the developer used for image formation.

  Such a decrease in the developer charge amount due to the deterioration of the developer increases not only the image quality deterioration due to the fog but also the amount of the developer consumed by the occurrence of the fog, thereby increasing the cost burden on the user.

  The developing device that develops the electrostatic latent image on the image bearing member employs a so-called two-component developer (two-component developing device) mainly composed of toner and carrier depending on the type of developer used, and a carrier. It is broadly classified into one that employs a so-called one-component developer (one-component developing device) that does not include toner and that mainly includes toner.

  In any type of developing device, generally, a developing roller that carries the developer on the peripheral surface and conveys it to the developing region is employed. In developing the electrostatic latent image, a developing bias voltage is generally applied to the developing roller in order to smoothly transfer the developer on the developing roller to the electrostatic latent image. As such a development bias voltage, an AC development bias voltage (for example, a DC voltage and an AC voltage are used together (typically, in order to obtain a high-quality image by suppressing the detachment of the developer to the developing roller). In many cases, an AC developing bias voltage (in which an AC voltage is superimposed on a DC voltage) is employed.

  In a developing device (one-component developing device) using a developer mainly composed of toner, generally, a developer charged amount required for developing an electrostatic latent image is carried on a developing roller. A charging member is brought into contact with the developer conveyed to the developing region, and friction charging is performed by the charging member. The charging member usually also serves as a developer regulating member that regulates the amount of the developer conveyed to the developing area to make it a thin layer.

  However, if developer deterioration occurs while image formation is repeated, developer charging failure occurs only by frictional charging. Therefore, a potential difference is set between the developer charging member that also serves as the regulating member and the developing roller, or between the developer charging member and the developing roller that are provided separately from the developer charging member that also serves as the regulating member. Thus, the developer is electrically charged.

Such a potential difference between the developer charging member and the developing roller is preferably generated by applying an AC charging bias voltage in order to prevent the developer from sticking to the developing roller or the developer charging member.
In this regard, JP 2001-109243 A
(1) In a developing device that employs an AC developing bias voltage in which an AC voltage is superimposed on a DC voltage as a developing bias voltage applied to the developing roller, a potential difference is generated between the developer charging member that also serves as a regulating member and the developing roller. Therefore, a developing device that applies an AC charging bias voltage in which an AC voltage is superimposed on a DC voltage to the developer charging member,
(2) To obtain an AC charging bias voltage to be applied to the developer charging member at a low cost, a zener diode is used to offset only one phase of the AC developing bias voltage (the phase on the positive side or the negative side). A developing device is disclosed that generates the applied AC charging bias voltage and applies it to the developer charging member.

FIG. 23A shows an example of a voltage application circuit in the latter developing device.
According to the circuit shown in FIG. 23A, a power source in which a DC power source Vdc and a rectangular wave AC power source Vac are connected in series is adopted as the AC developing bias power source pw, and a Zener diode is connected to the output terminal a ″ of the power source pw. The td ″ and the resistance element r ″ are connected in series, the developing roller is connected to the output terminal a ″, and the charging member is connected to the contact b ″ between the Zener diode td ″ and the resistance element r ″.

  This circuit employs a negatively chargeable photoreceptor as an image carrier for forming an electrostatic latent image, and reversely develops the electrostatic latent image formed on the photoreceptor using a negatively charged toner. This is an example of the circuit. According to this circuit, for example, when the output voltage of the DC power source Vdc in the developing bias power source pw is −400V, the peak-to-peak voltage Vpp of the AC power source Vac is 1800V, and the voltage drop due to the Zener diode td ″ is 200V, An AC developing bias voltage having a waveform shown by a solid line in Fig. 23B is applied, and the charging member has an AC developing bias voltage and a phase applied to the developing roller as shown by a broken line in Fig. 23B. Synchronously, an AC charging bias voltage indicating an offset potential difference of 200 V is applied in the plus phase, and in the minus phase, the voltages applied to the developing roller and the charging member are substantially the same potential.

  According to this circuit configuration, the AC charging bias voltage is obtained at a lower cost by using the AC power source Vac in the AC developing bias power source pw. Further, an attempt has been made to optimize the toner charge amount by offsetting the AC charging bias with respect to the developing bias (setting an offset potential difference) in the plus phase.

  In any case, according to such a conventional developing device, the charge level of the deteriorated developer can be increased, and the developer charged to the opposite polarity to the developer charged to the normal charge polarity, which is the main cause of the fog phenomenon. (Reverse polarity charged developer) can be reduced, and as a result, a higher quality image can be obtained.

JP 2001-109243 A

However, according to the research of the present inventor, in a developing device that sets a potential difference between the developer charging member and the developing roller, for example, the initial developer whose charging ability is at an appropriate level is overcharged.
The overcharged developer is strongly restrained by the developing roller due to the Coulomb force, and does not smoothly move toward the electrostatic latent image on the image carrier, so that desired development cannot be performed. Furthermore, fogging occurs due to excessively charged components.

  Therefore, if the potential difference between the charging member and the developing roller is set to be small in order to solve such a problem, the problem relating to the initial developer can be solved, but it becomes difficult to eliminate the occurrence of fogging due to the deteriorated developer. .

  In addition, in a developing device configured to replenish the developer according to the consumption of the developer, immediately after the new developer (initial developer) is replenished, the deteriorated developer and the initial developer are mixed in the developing device. Thus, a large amount of reverse-polarity charged developer is temporarily generated, and the fogging phenomenon becomes remarkable.

  Accordingly, the present invention provides a developing device that develops an electrostatic latent image formed on an image carrier using a developer, and charges the developer to an appropriate charge amount for developing the electrostatic latent image. Accordingly, a first object is to provide a developing device that can satisfactorily develop an electrostatic latent image while suppressing the occurrence of fogging.

  The present invention also relates to an image forming apparatus for developing an electrostatic latent image formed on an image carrier using a developer to form an image, the developer being charged appropriately for developing the electrostatic latent image. It is a second object to provide an image forming apparatus that can be charged in a large amount and that can develop a latent image and form a high-quality image while suppressing the occurrence of fogging. .

The present inventor has conducted research to solve the above-mentioned problems, and has come to know the following.
That is, by adopting the circuit configuration shown in FIG. 23A and applying an AC charging bias voltage to the charging member, various Zener diodes having different breakdown voltages are employed as the Zener diode td ″. As shown in FIG. 22, even when the initial toner under low humidity environment (toner to be used) is used, the toner under high humidity environment (used toner) is used to some extent. Even in such cases, (1) the toner charge amount is governed by the offset potential difference, and (2) the initial toner tends to have a charge amount larger than that of the used toner. For example, an appropriate charge amount of the toner is −20 μC / g In the case of −40 μC / g, with the toner used, even if the offset potential difference that can keep the toner charge amount in the range of −20 μC / g to −40 μC / g, With regard to toner, it has been found that the toner charge amount increases from −40 μC / g, and more specifically, if the offset potential difference is controlled according to the factors that influence the chargeability of the developer, proper development can be achieved. It was found that the charge amount of the agent can be obtained.

Based on such knowledge, the present invention solves the first problem,
A developing device for developing an electrostatic latent image formed on an image carrier using a developer,
A developing roller that carries a developer on the peripheral surface and conveys the electrostatic latent image on the image carrier to a developing region for developing;
A charging member that is carried on the peripheral surface of the developing roller and that contacts the developer conveyed to the developing area to charge the developer;
A developing bias applying device for applying an AC developing bias voltage to the developing roller;
An AC charging bias voltage that is in phase with the AC developing bias voltage and has an offset potential difference with respect to the AC developing bias voltage at least on one of the positive side and the negative side. A charge bias applying device for applying a voltage;
A control unit for controlling the charging bias application device,
The control unit controls the charging bias application device according to at least one of the factors that influence the chargeability of the developer conveyed to the development area, thereby reducing the offset potential difference. Provided is a developing device that controls to be charged to a regular charge amount for developing an electrostatic latent image.

Here, the “AC developing bias voltage” is an AC voltage, a bias voltage using a DC voltage and an AC voltage in combination (for example, a bias voltage obtained by superimposing an AC voltage on a DC voltage), or the like.
Further, the “regular charge amount” of the developer can be said to be an appropriate charge amount, but it need not be a fixed amount value, for example, −20 μC / g to −40 μC. The case where the regular charge amount is within the range of / g is also included.

  The developing device according to the present invention may include a regulating member that regulates a thin layer while frictionally charging the developer carried on the circumferential surface of the developing roller and conveyed to the developing area. Alternatively, the charging member may also serve as a regulating member.

  As the voltage waveforms of the AC developing bias voltage and the AC charging bias voltage, various waveforms that can solve the problem of the present invention can be adopted, and for example, a rectangular wave can be cited. That is, an example in which each of the AC developing bias voltage and the AC charging bias voltage is a rectangular wave voltage can be given.

Examples of the “factor that affects the charging property of the developer conveyed to the development area” include environmental conditions, development device drive integration time, number of developments, and average print area ratio.
Here, as the “environmental condition”, a temperature and / or humidity around the developing device, particularly humidity can be given as a representative example.

The “developing device driving integrated time” is an integrated value of the time during which the developing device is driven.
This drive integration time is longer when image formation is often performed intermittently for each sheet than when image formation is performed continuously for a plurality of sheets. That is, the drive integration time depends on the frequency of continuous image formation and the frequency of intermittent image formation.

  The “number of times of development” is the number of times that the development operation has been performed, in other words, the number of images formed.

The “average print area ratio” is obtained by dividing the total number of image forming dots by the number of image forming sheets up to the number of dots.
Among these factors, the integrated driving time of the developing device, the number of times of development, and the average print area ratio tend to affect the deterioration of the developer, and hence the chargeability of the developer.

  When the ambient environment of the developing device is a low humidity environment, the developer is easily charged, and in a high humidity environment, the developer is difficult to be charged. When the drive integration time of the developing device and the number of times of development increase, a deteriorated developer is likely to be generated, and if left as it is, the developer charge amount decreases. The average print area ratio is a factor related to the developer consumption. When the average print area ratio is high, the developer consumption is large and the deteriorated developer is difficult to increase. However, when the average print area ratio is low, the developer consumption is low. The amount is small and the deteriorated developer increases.

  Therefore, as an example of the control unit, the offset potential difference is controlled by controlling the charging bias application device according to at least one of environmental conditions, developing device drive integration time, number of development times, and average printing area ratio. Things can be mentioned.

Further, when the duty ratio of the AC developing bias voltage (in other words, the ratio of the time during which the voltage is on the same polarity side as the normal charging polarity of the developer during one AC cycle) is high, the developer charge amount increases accordingly. If it is low, the charge amount of the developer is reduced accordingly.
Therefore, the control unit may control the offset potential difference based on the duty ratio of the AC developing bias.

As described above, when the developer is replenished according to the consumption of the developer, immediately after the new developer (initial developer) is replenished, the deteriorated developer and the initial developer are mixed in the developing device. In this case, a large amount of reverse polarity charged developer is temporarily generated, and the fogging phenomenon becomes remarkable.
Therefore, in the case of a developing device provided with a developer replenishing device that replenishes the developer according to the amount of developer consumed, the control unit serves as a predetermined time from developer replenishment by the developer replenishing device. You may employ | adopt the control part which sets the said offset potential difference large compared with out of this time until it passes.
Here, “from developer replenishment” is any of “from developer replenishment start”, “after developer replenishment end”, and “from a predetermined time between developer replenishment start to end” Good.

  As the “predetermined time” that should be adopted by the control unit, the environmental conditions when the developer is replenished, the developing device drive accumulated time when the developer is replenished, the developing device drive accumulated time after completion of the developer replenishment, It is determined based on at least one of the number of times of development at the time of developer replenishment, the number of times of development after the end of developer replenishment, the average print area ratio at the time of developer replenishment, and the average print area ratio after the end of developer replenishment. Time can be illustrated.

  In addition, when the developer is replenished according to the consumption of the developer, the control unit controls the offset potential difference according to the AC development bias voltage (typically the amplitude) at the time of the developer replenishment. It may be a thing. When the charging bias value is the same, the larger the amplitude, the larger the charge amount of the developer by the charging member. The smaller the amplitude, the smaller the charge amount of the developer by the charging member.

Note that “at the time of developer replenishment” may be any of “at the start of developer replenishment”, “after developer replenishment end”, or “when predetermined from start to end of developer replenishment”. .
The control unit may perform control by combining two or more of the various controls described above as appropriate.

Examples of the developing bias applying device include a developing bias power source that applies the AC developing bias voltage to the developing roller.
The charging bias application device includes a resistance element, a diode, and a DC power source for variable output voltage, and the anti-element, diode, and DC power source for variable output voltage are output in this order in the output of the developing bias power source. The thing connected in series with the edge can be illustrated.
This charging bias applying device uses a developing bias power source and can be provided at a lower cost.

  In the case of employing such a developing bias applying device and a charging bias applying device, an example in which the developing roller is connected to the output end of the developing bias power source and the charging member is connected between the resistance element and the diode is given. be able to. Furthermore, the control unit can be exemplified by controlling the offset potential difference by controlling the output voltage of the charging DC power supply.

  When such a developing bias applying device and a charging bias applying device are employed, a zener diode may be inserted and connected between the output terminal of the developing bias power source and the resistance element. Thereby, an offset potential difference can be set on both the positive side and the negative side of the AC charging bias voltage.

  Alternatively, for example, a Zener diode and a second resistor element may be connected in series in this order to the output terminal of the developing bias power source, and the developing roller may be connected between the Zener diode and the second resistor element. .

As a result, the AC developing bias voltage applied to the developing roller can be offset on the plus side or the minus side depending on the circuit configuration, so that, on the same side, the AC charging bias voltage is changed to the AC developing bias voltage. The offset potential difference can be set relatively.
Further, in this case, an example can be given in which the charging member is connected between the resistance element and the diode connected in series to the output terminal of the developing bias power supply together with the DC power supply for charging.

  The present invention also provides an image forming apparatus equipped with the developing device according to the present invention described above. Since this image forming apparatus is equipped with the developing device according to the present invention, the developer can be charged to an appropriate charge amount for developing the electrostatic latent image, and the occurrence of fog is suppressed accordingly. However, it is possible to form a high-quality image by developing the electrostatic latent image satisfactorily.

  As described above, according to the present invention, there is provided a developing device for developing an electrostatic latent image formed on an image carrier using a developer, and the developer is appropriately charged for developing the electrostatic latent image. Thus, it is possible to provide a developing device that can be charged in a large amount and that can satisfactorily develop an electrostatic latent image while suppressing the occurrence of fogging.

  According to the present invention, there is also provided an image forming apparatus for developing an electrostatic latent image formed on an image carrier using a developer to form an image, wherein the developer is suitable for developing an electrostatic latent image. Accordingly, it is possible to provide an image forming apparatus that can be charged to an amount of charge, and that can satisfactorily develop an electrostatic latent image and form a high-quality image while suppressing the occurrence of fogging.

FIG. 1 shows an example of an image forming apparatus provided with an example of a developing device according to the present invention.
The image forming apparatus P1 in FIG. 1 is a printer that forms a monochrome image by reversal development using a one-component developer (here, negatively chargeable toner t), and includes a drum-type photoreceptor 100. The photoconductor 100 is a negatively chargeable photoconductor. Around the photoreceptor 100, a charging device 200, a developing device 300, a transfer roller 400, a cleaner 500, and an eraser 600 are arranged in this order. An image exposure device 700 is provided below the photoconductor 100, and a fixing device 800 is provided on the right side of the transfer roller 400 in the drawing.

  According to this printer, an image is formed as follows. That is, the photosensitive member 100 is rotated in the clockwise direction in the figure, and the surface of the photosensitive member is uniformly charged by the charging device 200 to a predetermined negative potential (here, for example, −500 V. The image exposure device 700 in the charged region. Is exposed to the original image, thereby forming an electrostatic latent image on the photoreceptor 100. The electrostatic latent image is transferred to a developing area facing the developing device 300 by the rotation of the photoreceptor. In the developing area, the toner is reversely developed by the developing device 300 to become a visible toner image, and the visible toner image is sent to the transfer area facing the transfer roller 400 by the rotation of the photosensitive member.

On the other hand, the recording medium S is conveyed from the recording medium (recording paper or the like) supply unit (not shown) to the timing roller pair TR. The timing roller pair TR conveys the recording medium S between the photoconductor 100 and the transfer roller 400 (transfer region) in accordance with the movement of the toner image on the photoconductor.
Thus, the toner image on the photoreceptor 100 is transferred to the recording medium S by the transfer roller 400. The recording medium S is subsequently conveyed to the fixing device 800 where the transferred toner image is heated and fixed on the recording medium S.

Each movable part of the image forming apparatus P1 is rotationally driven at a predetermined timing by a driving device (not shown). A charging voltage is applied to the charging device 200 from a power supply (not shown) when charging the surface of the photoreceptor. When the toner image is transferred to the transfer roller 400, a transfer voltage is applied from a power supply (not shown).
The developing device 300 will be described in further detail below.

  As shown in FIG. 2, the developing device 300 includes a developing roller 301. The developing roller 301 is rotatably supported by the developing device case 302, and a part of the developing roller 301 is exposed to the outside from the case 302 and faces the photoconductor 100 with a slight gap. In the case 301, a developer supply roller 303 is provided adjacent to the developing roller 301, and a developer stirring member 304 is disposed behind the developer supply roller 303. Both the developer supply roller 303 and the developer agitating member 304 are rotatably supported by the case 302.

  In the case 302, a blade-like developer regulating member 305 that is cantilevered and supported by the case 302 and pressed against the developing roller 301, and a developing roller 301 that is cantilevered and supported by the case 302 from the regulating member 305. Is provided with a blade-like charging member 306 which is weakly pressed.

A seal member 307 is disposed between the upper portion of the developing roller 301 and the case 302 to prevent developer leakage. The developer leakage from between the lower portion of the developing roller 301 and the case 302 This is prevented by the developer regulating member 305.
In addition, a toner replenishing device 900 is connected to the case 302, and new toner can be replenished into the developing device case according to the amount of toner consumption.

A developing bias applying device B1 is connected to the developing roller 301, and a charging bias applying device B2 is connected to the charging member 306.
In this example, the developing bias applying device B1 is a DC power source DC1 having an output voltage of −400V, and an AC power source AC1 that outputs a rectangular wave voltage having a peak-to-peak voltage Vpp of 1800V and a duty of 40% (duty ratio 2/3). And a developing bias power source PW1 connected in series. In developing the electrostatic latent image on the photosensitive member, the power source PW1 applies an AC developing bias voltage V1 having a rectangular waveform shown by a solid line in FIG. To the electrostatic latent image. The developing roller 301 may be disposed in contact with the photoconductor 100 depending on the developing bias or the like.

The charging bias applying device B2 uses a developing bias power source PW1 in order to simplify the circuit configuration and reduce the price, and is sequentially connected in series to the output end (developing roller contact) a of the power source PW1 to the developing roller 301. A resistive element r, a diode d, and a variable output DC power source DC2. An output terminal (charging member contact) b to the charging member 306 is set between the resistance element r and the diode d.
The output voltage of the power supply DC2 is controlled by the control unit CT as will be described later.

When developing the electrostatic latent image on the photoconductor, the charging bias applying device B2 outputs a rectangular wave AC charging bias voltage V2 or V2 ′ indicated by a broken line in FIG. 3 and applies it to the charging member 306.
In FIG. 3, the waveform of the developing bias voltage V1 and the waveform of the charging bias voltage V2 (V2 ′) are shown shifted from each other. In practice, the phase of the voltage V2 (V2 ′) is synchronized with the voltage V1. is doing. However, the charging bias voltage V2 (V2 ′) shows an offset potential difference Vd with respect to the developing bias voltage V1 in the positive phase (in the positive waveform).

  In the example shown in FIG. 3, when the output voltage of the charging DC power supply DC2 is controlled to + 400V by the control unit CT, the AC charging bias voltage becomes V2 and the offset potential difference Vd becomes 100V. When controlled to + 200V, the AC charging bias voltage is V2 ', and the offset voltage difference Vd is 300V.

More specifically, when the output of the charging DC power supply DC2 is controlled to + 400V, in the positive phase of the developing bias voltage V1, a current flows through the diode d, and the voltage is offset by the resistor r (in this example, 100V offset). The Thus, the positive side of the AC charging bias voltage is + 400V, and the offset potential difference Vd is 100V.
On the other hand, in the negative phase of the developing bias voltage V1, no current flows through the diode d, the current flowing through the resistor r is only a very weak process current, and the developing bias voltage V1 and the charging bias voltage V2 are substantially the same. It becomes a potential.

  Similarly, when the output of the charging DC power supply DC2 is controlled to + 200V, in the plus phase, the plus voltage of the AC charging bias voltage is 200V with respect to the developing bias voltage V1 (+ 500V), and is offset by 300V to the minus side. (Offset potential difference 300V).

In this way, the offset potential difference Vd can be controlled by controlling the output of the charging DC power supply DC2 by the control unit CT.
Further, as the charging bias is increased on the plus side and the offset potential difference Vd is decreased as in the AC charging bias voltage V2, the charge amount of the toner on the developing roller 301 by the charging member 306 is correspondingly decreased. When the charge bias is reduced on the plus side and the offset potential difference Vd is increased as in the case of the AC charge bias voltage V2 ′, the charge amount of the toner on the developing roller 301 by the charging member 306 increases accordingly.

  The control of the offset potential difference (control of the toner charge amount) by the control unit CT, which will be described later, is performed in these two stages. However, you may carry out in three steps or more as needed.

  In the developing device 300 described above, the developing bias applying device B1 and the charging bias applying device B2 shown in FIG. 2 are adopted. However, as shown in FIG. 4, the output of the developing bias power supply PW1 is used in the circuit of FIG. A Zener diode td may be inserted and connected between the end a and the resistance element r. Thereby, as shown in FIG. 5, the offset potential difference can be set on both the positive side and the negative side of the AC charging bias voltage V2 (V2 ').

  Alternatively, as shown in FIG. 6, a Zener diode td ′ and a second resistance element r ′ are connected in series in this order to the output terminal a of the developing bias power source PW1, and the developing roller 301 is connected to the Zener diode td ′ and the second Zener diode td ′. You may connect between two resistance elements r '.

  As a result, as shown in FIG. 7, the AC developing bias voltage V1 applied to the developing roller 301 can be offset on the minus side, so that even on the minus side, the AC charging bias voltage is changed to the AC developing bias voltage. On the other hand, an offset potential difference can be set relatively.

In the developing device 300 described above, the toner regulating member 305 and the charging member 306 are separately provided. However, as shown in FIG. 8, a toner regulating member 305 ′ also serving as a charging member is provided, and an AC charging bias voltage is applied thereto. You may make it apply.
The developing device 300 ′ shown in FIG. 8 has substantially the same structure as the developing device 300 shown in FIG. 2 except that a toner regulating member 305 ′ that also serves as a charging member is provided. The same reference numerals as those in FIG. 2 are assigned to the same parts and components in the apparatus of FIG. In the developing device 300 ′ of FIG. 8, the lower portion of the developing roller 301 and the case 302 are closed by a regulating member 305 ′.

  The image forming apparatus P1 described above is an apparatus that forms a monochrome image, but the developing device according to the present invention can also be applied to a developing device of a color image forming apparatus. For example, the present invention can be applied to the developing device 14 of each image forming unit of the tandem type full-color image forming apparatus P2 shown in FIG. 9, the developing device 14Y of the four-cycle type full-color image forming apparatus P3 shown in FIG.

Here, the image forming apparatuses P2 and P3 in FIGS. 9 and 10 will be described.
The image forming apparatus P2 in FIG. 9 includes an endless transfer belt 4 wound around a driving roller 31 and a roller 32 facing the driving roller 31. The transfer belt 4 is rotationally driven in a counterclockwise direction (arrow direction in the figure) by a driving roller 31 that is rotationally driven by a driving means (not shown). The counter roller 32 faces a cleaner CL for cleaning secondary transfer residual toner and the like on the transfer belt 4, and the drive roller 31 faces the secondary transfer roller 5. A fixing device 6 is installed above the secondary transfer roller 5.

Between the rollers 31 and 32, the yellow image forming unit Y, the magenta image forming unit M, the cyan image forming unit C, and the black image forming unit K are arranged in this order along the transfer belt 4 from the rollers 32 to 31. Has been placed.
Each image forming unit includes a drum-type photoconductor 11 as an electrostatic latent image carrier, and a charging device 12, an image exposure device 13, a developing device 14, a primary transfer roller 2, and a photoconductor are disposed around the photoconductor. Cleaners 15 for removing primary transfer residual toner and the like on the body are arranged in this order. The primary transfer roller 2 faces the photoconductor 11 with the transfer belt 4 in between.

  The developing device 14 in each image forming unit employs, for example, negatively chargeable toner, and reversely develops the electrostatic latent image formed on the photoreceptor 11.

According to this image forming apparatus, an image is formed as follows.
First, an image is formed in at least one of the image forming portions Y, M, C, and K according to an image to be finally formed.
Taking a case where a full color image is formed using all of the image forming portions Y, M, C, and K as an example, first, a yellow toner image is formed in the yellow image forming portion Y, and this is primarily transferred onto the transfer belt 4. Is done.

  That is, in the yellow image forming portion Y, the photoconductor 11 is rotated in the clockwise direction in the drawing, and the surface of the photoconductor 11 is uniformly charged to a predetermined potential by the charging device 12, and the image exposure device 13 is placed in the charged area. Then, image exposure for yellow image is performed, and an electrostatic latent image for yellow is formed on the photoreceptor 11. This electrostatic latent image is developed by a developing roller 141 to which a developing bias of a developing device 14 having yellow toner is applied to become a visible yellow toner image, and the toner image is transferred onto the transfer belt 4 by the primary transfer roller 2. Transcribed.

  Similarly, a magenta toner image is formed in the magenta image forming unit M and transferred to the transfer belt 4, a cyan toner image is formed in the cyan image forming unit C and transferred to the transfer belt 4, and in the black image forming unit K. A black toner image is formed and transferred to the transfer belt 4.

The yellow, magenta, cyan, and black toner images are formed at the timing when they are transferred onto the intermediate transfer belt 4 in an overlapping manner.
Thus, the multiple toner image formed on the transfer belt 4 moves toward the secondary transfer roller 5 by the rotation of the transfer belt 4.

  On the other hand, the recording medium S is pulled out from a recording medium supply unit (not shown), and is continuously synchronized with the multiple toner images on the belt 4 by the pair of timing rollers 71 and 72 between the transfer belt 4 and the secondary transfer roller 5. The secondary toner is secondarily transferred onto the recording medium S by the secondary transfer roller 5. Thereafter, the recording medium S is passed through the fixing device 6 where the multiple toner images are fixed on the recording medium S under heat and pressure, and a predetermined color image is formed on the recording medium S. Thereafter, the recording medium S is discharged out of the apparatus.

  In each image forming unit, the primary transfer residual toner and the like remaining on the photoconductor 11 after the primary transfer is cleaned and removed by the cleaner 15. Further, after the secondary transfer, secondary transfer residual toner and the like remaining on the transfer belt 4 are cleaned and collected by the cleaner CL.

  As the developing device 14 of each image forming unit, the developing device according to the present invention can be employed. An AC developing bias voltage, an AC charging bias voltage, an offset potential difference, and the like may be determined for each image forming unit as necessary.

  An image forming apparatus P3 shown in FIG. 10 has a drum-type photoconductor 110 around which a charging device 120, a yellow developing device 14Y, a magenta developing device 14M, a cyan developing device 14C, and a black developing device 14K. The transfer roller 20 and the cleaner 150 are arranged in this order.

An image exposure device 130 is disposed above the photoconductor 110, and an endless transfer belt 40 is disposed below. The endless transfer belt 40 is wound around a driving roller 310 and driven rollers 320 and 330. The transfer roller 20 is disposed to face the photoconductor 110 with the transfer belt 40 therebetween.
A secondary transfer roller 50 is provided on the transfer belt 40 at a portion of the driving roller 310, and a fixing device 60 is disposed above the secondary transfer roller 50.

  According to the image forming apparatus P3, an image can be formed using at least one of the four developing devices. In the case of forming a full-color image using all four developing devices, for example, the photoconductor 110 is driven to rotate clockwise in the figure, and the surface of the photoconductor 110 is uniformly charged to a predetermined potential by the charging device 120. Then, the image exposure device 130 performs image exposure for the yellow image on the charged area, and an electrostatic latent image for yellow is formed on the photoreceptor 110. This electrostatic latent image is developed by a developing roller to which a developing bias of a developing device 14Y having yellow toner is applied to become a visible yellow toner image, and the toner image is transferred onto the transfer belt 40 by the primary transfer roller 20. Is done.

  Similarly, a magenta toner image is formed using the magenta developing device 14M and transferred to the transfer belt 40. A cyan toner image is formed using the cyan developing device 14C and transferred to the transfer belt 40, and the black developing device 14K. A black toner image is formed using the toner and transferred to the transfer belt 40.

The yellow, magenta, cyan, and black toner images are formed at the timing when they are transferred onto the intermediate transfer belt 40 in an overlapping manner.
Thus, the multiple toner images formed on the transfer belt 40 are moved toward the secondary transfer roller 50 by the rotation of the transfer belt 40.

  On the other hand, the recording medium S is pulled out from a recording medium supply unit (not shown), and is continuously synchronized with the multiple toner images on the belt 40 by the timing roller pair 710 and 720 between the transfer belt 40 and the secondary transfer roller 50. The secondary toner is secondarily transferred onto the recording medium S by the secondary transfer roller 50. Thereafter, the recording medium S is passed through the fixing device 60 where the multiple toner images are fixed on the recording medium S under heat and pressure, and a predetermined color image is formed on the recording medium S. Thereafter, the recording medium S is discharged out of the apparatus.

  In the formation of each color toner image, the primary transfer residual toner remaining on the photoreceptor 110 after the primary transfer is cleaned and removed by the cleaner 150. Further, after the secondary transfer, secondary transfer residual toner or the like remaining on the transfer belt 40 is cleaned by a cleaner CL ′ that is in contact with the belt 40 after the secondary transfer is completed.

  As the developing device for each color, the developing device according to the present invention can be employed. An AC developing bias voltage, an AC charging bias voltage, an offset potential difference, and the like may be determined for each image forming unit as necessary.

Next, an example of controlling the offset potential difference (toner charge amount) by the control unit CT shown in FIGS. 2, 4, 6 and 8 will be described. In addition, the control demonstrated below can also combine 2 or more as needed.
(1) Control based on the environment around the developing device, particularly relative humidity (see FIG. 11)
When the relative humidity is read from a temperature / humidity detection unit (not shown) provided in the image forming apparatus, and the relative humidity is equal to or lower than a predetermined value determined in advance through experiments or the like, a charge bias value (a positive side of the AC charge bias voltage) (Bias value in phase) is set to “large”, and the offset potential difference Vd is set to “small”. When the relative humidity is larger than the predetermined value, the charge bias value is set to “small”, and the offset potential difference Vd is set to “large”. Thus, the charge amount of the toner by the charging member 306 used for development is set to a regular charge amount.
The charge bias value “large” is 400 V in this example, the offset potential difference Vd at that time is 100 V, and the charge bias value “small” is 200 V in this example, and the offset potential difference at that time Vd is 300V. This also applies to the control described later.

(2) Control based on the accumulated driving time of the developing device (see FIG. 12)
The drive accumulated time is read from a developing device drive accumulated time detection unit (not shown) provided in the image forming apparatus, and the charge bias value is set to “large” when the accumulated time is equal to or less than a predetermined value determined in advance through experiments or the like. And the offset potential difference Vd is set to “small”. When the integrated time is larger than a predetermined value, the charge bias value is set to “small”, and the offset potential difference Vd is set to “large”. Thus, the charge amount of the toner by the charging member 306 used for development is set to a regular charge amount.

(3) Control based on the number of times of development by the developing device (see FIG. 13)
The number of developments is read from a development number detection unit (not shown) provided in the image forming apparatus, and when the number of developments is equal to or less than a predetermined value determined in advance through experiments or the like, the charge bias value is set to “large”, The offset potential difference Vd is set to “small”. When the number of developments is greater than a predetermined value, the charge bias value is set to “small”, and the offset potential difference Vd is set to “large”. Thus, the charge amount of the toner by the charging member 306 used for development is set to a regular charge amount.

(4) Control based on average print area ratio (see FIG. 14)
The area ratio is read from an average printing area ratio detection unit (not shown) provided in the image forming apparatus, and the charge bias value is set to “large” when the area ratio number is equal to or larger than a predetermined value determined in advance through experiments or the like. And the offset potential difference Vd is set to “small”. When the area ratio is smaller than the predetermined value, the charge bias value is set to “small”, and the offset potential difference Vd is set to “large”. Thus, the charge amount of the toner by the charging member 306 used for development is set to a regular charge amount.

(5) Control based on duty ratio of AC developing bias (see FIG. 15)
The duty ratio is read from a duty ratio detection unit (not shown) provided in the image forming apparatus, and the charge bias value is set to “large” if the duty ratio is equal to or larger than a predetermined value determined in advance through experiments or the like. The offset potential difference Vd is set to “small”. When the duty ratio is smaller than the predetermined value, the charge bias value is set to “small”, and the offset potential difference Vd is set to “large”. Thus, the charge amount of the toner by the charging member 306 used for development is set to a regular charge amount.

(6) Control based on toner supply (see FIG. 16)
A toner remaining amount detecting unit (not shown) provided in the developing device detects the remaining amount of toner, and if the detected remaining toner amount is equal to or less than a predetermined value determined in advance through experiments or the like, the toner replenishing device 900 is replenished with toner. When the toner supply device 900 notifies the end of toner supply, the charge bias value is set to “small”, and the offset potential difference Vd is set to “large”. Further, after the toner replenishment, when a predetermined time determined in advance by an experiment or the like has elapsed, the charge bias value is restored (in this example, the charge bias value is set to “large” and the offset potential difference Vd is set to “small”. Set to). Thus, the charge amount of the toner by the charging member 306 used for development is set to a regular charge amount.

(7) Control based on toner replenishment and relative humidity (see FIG. 17)
When the remaining toner amount is detected by the toner remaining amount detecting unit and the detected remaining toner amount is equal to or less than a predetermined value determined in advance through experiments or the like, the toner replenishing device 900 starts toner replenishment. When the end of toner supply is notified, the charge bias value is set to “small”, and the offset potential difference Vd is set to “large”.
Next, the relative humidity is read, and when the relative humidity is equal to or less than a predetermined value determined in advance by experiment or the like, the charge bias value is restored after a predetermined time T1 determined in advance by experiment or the like after the toner replenishment. (In this example, the charge bias value is set to “large” and the offset potential difference Vd is set to “small”).
When the relative humidity is higher than the predetermined value, the charge bias value is returned to the original value after a predetermined time T2 (> T1) determined in advance by an experiment or the like after completion of toner replenishment.
Thus, the charge amount of the toner by the charging member 306 used for development is set to a regular charge amount.

(8) Control based on toner replenishment and developing device drive accumulated time (or developing device drive accumulated time after completion of toner replenishment) (see FIG. 18)
When the remaining toner amount is detected by the toner remaining amount detection unit and the detected remaining toner amount is equal to or less than a predetermined value determined in advance through experiments or the like, the toner replenishing device 900 starts toner replenishment. When the end of toner supply is notified, the charge bias value is set to “small”, and the offset potential difference Vd is set to “large”.
Next, a driving integrated time (or developing device driving integrated time after completion of toner replenishment) is read from a developing device driving integrated time detection unit (not shown), and the integrated time is equal to or less than a predetermined value determined in advance through experiments or the like. After the toner replenishment, the charge bias value is returned to the original value after the elapse of a predetermined time T1 determined in advance by experiments or the like (in this example, the charge bias value is set to “large” and the offset potential difference Vd is set to “small”. Set).
When the integrated time is larger than the predetermined value, the charge bias value is returned to the original value after the elapse of a predetermined time T2 (> T1) determined in advance by an experiment or the like after the toner replenishment.
Thus, the charge amount of the toner by the charging member 306 used for development is set to a regular charge amount.

(9) Control based on the number of toner replenishment and development (or the number of development after toner replenishment) (see FIG. 19)
When the remaining toner amount is detected by the toner remaining amount detection unit and the detected remaining toner amount is equal to or less than a predetermined value determined in advance through experiments or the like, the toner replenishing device 900 starts toner replenishment. When the end of toner supply is notified, the charge bias value is set to “small”, and the offset potential difference Vd is set to “large”.
Next, the number of developments (or the number of developments after completion of toner replenishment) is read from a development number detection unit (not shown), and if the number of developments is equal to or less than a predetermined value determined in advance through experiments, etc. The charge bias value is returned to the original value after the elapse of a predetermined time T1 determined by the above (in this example, the charge bias value is set to “large” and the offset potential difference Vd is set to “small”).
When the number of times of development is greater than a predetermined value, the charge bias value is returned to the original value after a predetermined time T2 (> T1) determined in advance by an experiment or the like after completion of toner replenishment.
Thus, the charge amount of the toner by the charging member 306 used for development is set to a regular charge amount.

(10) Control based on toner supply and average print area ratio (or average print area ratio after completion of toner supply) (see FIG. 20)
When the remaining toner amount is detected by the toner remaining amount detection unit and the detected remaining toner amount is equal to or less than a predetermined value determined in advance through experiments or the like, the toner replenishing device 900 starts toner replenishment. When the end of toner supply is notified, the charge bias value is set to “small”, and the offset potential difference Vd is set to “large”.
Next, an average print area ratio (or an average print area ratio after completion of toner replenishment) is read from an average print area ratio detection unit (not shown), and if the area ratio is equal to or greater than a predetermined value determined in advance through experiments or the like, After the replenishment, the charge bias value is restored after the elapse of a predetermined time T1 determined in advance by experiments or the like (in this example, the charge bias value is set to “large” and the offset potential difference Vd is set to “small”. To do).
When the area ratio number is smaller than the predetermined value, the charge bias value is returned to the original value after a predetermined time T2 (> T1) determined in advance by an experiment or the like after the toner replenishment.
Thus, the charge amount of the toner by the charging member 306 used for development is set to a regular charge amount.

(11) Toner replenishment and control based on the amplitude of the AC developing bias (see FIG. 21)
When the remaining toner amount is detected by the toner remaining amount detection unit and the detected remaining toner amount is equal to or less than a predetermined value determined in advance through experiments or the like, the toner replenishing device 900 starts toner replenishment. When the end of toner supply is notified, the amplitude of the AC developing bias is read from an AC developing bias detecting unit (not shown), and if the amplitude is equal to or greater than a predetermined value determined in advance by experiments or the like, the charging bias value is set to “large”. And the offset potential difference Vd is set to “small”. When the amplitude is smaller than the predetermined value, the charge bias value is set to “small”, and the offset potential difference Vd is set to “large”.
Thus, the charge amount of the toner by the charging member 306 used for development is set to a regular charge amount.

  INDUSTRIAL APPLICABILITY The present invention can be used for optimizing the charge amount of a developer used for developing an electrostatic latent image formed on an image carrier, and thus for forming a high-quality image.

1 is a diagram schematically illustrating a configuration of an example of an image forming apparatus according to the present invention. FIG. 2 is a diagram illustrating a configuration of a developing device in the image forming apparatus illustrated in FIG. 1 including a circuit configuration. It is a figure which shows the waveform of the alternating current development bias by the developing device circuit of FIG. 2, and alternating current charge bias. It is a figure which shows the other example of a developing device circuit. It is a figure which shows the waveform of the alternating current development bias by the developing device circuit of FIG. 4, and alternating current charge bias. It is a figure which shows the further another example of a developing device circuit. It is a figure which shows the waveform of the alternating current development bias by the developing device circuit of FIG. 6, and alternating current charge bias. It is a figure which shows the other example of a developing device structure. It is a figure which shows the outline of a structure of the other example of the image forming apparatus which concerns on this invention. It is a figure which shows the outline of a structure of the further another example of the image forming apparatus which concerns on this invention. 5 is a flowchart illustrating an example of offset potential difference control (toner charge amount control). 10 is a flowchart illustrating another example of offset potential difference control (toner charge amount control). 10 is a flowchart showing still another example of offset potential difference control (toner charge amount control). 10 is a flowchart showing still another example of offset potential difference control (toner charge amount control). 10 is a flowchart showing still another example of offset potential difference control (toner charge amount control). 10 is a flowchart showing still another example of offset potential difference control (toner charge amount control). 10 is a flowchart showing still another example of offset potential difference control (toner charge amount control). 10 is a flowchart showing still another example of offset potential difference control (toner charge amount control). 10 is a flowchart showing still another example of offset potential difference control (toner charge amount control). 10 is a flowchart showing still another example of offset potential difference control (toner charge amount control). 10 is a flowchart showing still another example of offset potential difference control (toner charge amount control). FIG. 6 is a diagram illustrating a relationship between an offset potential difference and a toner charge amount. FIG. 1A is a diagram showing an example of a conventional developing device circuit, and FIG. 2B is a diagram showing a bias waveform by the circuit.

Explanation of symbols

P1 Image forming apparatus t Toner 100 Photoconductor 200 Charging device

300 developing device 301 developing roller 302 developing device case 303 developer supplying roller 304 developer stirring member 305 developer regulating member 306 charging member 307 sealing member B1 developing bias applying device B2 charging bias applying device DC1 DC power supply AC1 AC power supply PW1 developing bias Power supply V1 AC developing bias voltage V2, V2 'AC charging bias voltage Vd Offset potential difference a Output terminal r of power supply PW1 Resistance element d Diode DC2 Charging DC power supply b Output terminal to charging member (charging member contact)
CT controller t toner

400 Transfer roller 500 Cleaner 600 Eraser 700 Image exposure device 800 Fixing device 900 Toner replenishing device TR Timing roller pair S Recording medium

td, td ′ Zener diode r ′ resistance element 305 ′ charging member 307 ′ sealing member also serving as a regulating member

P2 Image forming apparatus Y Yellow image forming section M Magenta image forming section C Cyan image forming section K Black image forming section 11 Photoconductor 12 Charging device 13 Image exposing device 14 Developing device 141 Developing roller 15 Cleaner 2 Primary transfer roller 31 Driving roller 32 Counter roller 4 Endless transfer belt CL Cleaner 5 Secondary transfer roller 6 Fixing device

P3 Image forming device 110 Photoconductor 120 Charging device 14Y Yellow developing device 14M Magenta developing device 14C Cyan developing device 14K Black developing device 20 Transfer roller 150 Cleaner 130 Image exposure device 40 Endless transfer belt 310 Drive roller 320, 330 Driven roller 50 Secondary Transfer roller 60 fixing device

Claims (12)

A developing device for developing an electrostatic latent image formed on an image carrier using a developer;
A developing roller that carries a developer on the peripheral surface and conveys the electrostatic latent image on the image carrier to a developing region for developing;
A charging member that is carried on the peripheral surface of the developing roller and that contacts the developer conveyed to the developing area to charge the developer;
A developing bias applying device for applying an AC developing bias voltage to the developing roller;
An AC charging bias voltage that is in phase with the AC developing bias voltage and has an offset potential difference with respect to the AC developing bias voltage at least on one of the positive side and the negative side. A charge bias applying device for applying a voltage;
A control unit for controlling the charging bias application device,
The control unit controls the charging bias application device according to at least one of the factors that influence the chargeability of the developer conveyed to the development area, thereby reducing the offset potential difference. A developing device that controls to be charged to a regular charge amount for developing an electrostatic latent image.   The developing device according to claim 1, wherein each of the AC developing bias voltage and the AC charging bias voltage is a rectangular wave voltage.   The control unit controls the offset potential difference by controlling the charging bias application device according to at least one of an environmental condition, a developing device drive integration time, the number of times of development, and an average print area ratio. 2. The developing device according to 2.   The developing device according to claim 1, wherein the control unit controls the offset potential difference by controlling the charging bias applying device based on a duty ratio of the AC developing bias voltage.   A developer replenishing device that replenishes the developer according to the amount of developer consumed, and wherein the control unit is configured to wait until a predetermined time elapses after the developer replenishment by the developer replenishing device. The developing device according to claim 1, wherein the offset potential difference is set to be larger than that outside time.   The control unit includes, as the predetermined time, the environmental conditions when the developer is replenished, the developing device drive accumulated time when the developer is replenished, the developing device drive accumulated time after completion of the developer replenishment, and the developer replenishment time. Time determined based on at least one of the number of developments at the time, the number of developments after completion of the developer replenishment, the average print area rate at the time of developer replenishment, and the average print area rate after the completion of developer replenishment The developing device according to claim 5.   The developing device according to claim 5, wherein the control unit controls the offset potential difference according to the AC developing bias voltage when the developer is replenished. The developing bias applying device includes a developing bias power source for applying the AC developing bias voltage to the developing roller,
The charging bias applying device includes a resistance element, a diode, and a DC power source for variable output voltage. The anti-element, diode, and DC power source for variable output voltage are arranged in this order in the development bias power source. It is connected in series to the output end,
The developing device according to claim 1, wherein the control unit controls the offset potential difference by controlling an output voltage of the charging DC power supply.   The developing device according to claim 8, wherein the developing roller is connected to an output terminal of the developing bias power source, and the charging member is connected between the resistance element and the diode.   The developing device according to claim 9, wherein a zener diode is inserted and connected between the output terminal of the developing bias power source and the resistance element.   A zener diode and a second resistor element are connected in series in this order to the output terminal of the developing bias power source, and the developing roller is connected between the zener diode and the second resistor element, and The developing device according to claim 8, wherein the member is connected between the resistor element and the diode connected in series to the output terminal of the developing bias power source together with the charging DC power source.   An image forming apparatus comprising the developing device according to claim 1.