JP2006227525A - Developing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device capable of adequately developing both of a sold image part and a dot image part without frequency-modulating an AC component, and an image forming apparatus. <P>SOLUTION: The developing device 10 is a contactless type developing device 10 which develops a latent image on a photoreceptor 11 with a toner by a developing roller 12, and has a power source 16 which applies a vibrating voltage between the developing roller 12 and photoreceptor 11 and selectively uses a 1st reference voltage having a small difference from a collection-side peak voltage or a 2nd reference voltage having a large difference from the collection-side peak voltage as a development-side peak voltage while keeping the collection-side peak voltage constant. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a printer and a copying machine, and a developing device thereof. More specifically, the present invention relates to a non-contact type developing device and an image forming apparatus for developing an electrostatic latent image formed on a photoreceptor.

  Conventionally, in an electrophotographic image forming apparatus such as a copying machine or a printer, a toner image is formed by developing an electrostatic latent image formed on an image carrier, and the toner image is transferred to a recording material. An image is formed by fixing. As a non-contact type developing device using a one-component toner, there is one in which a superimposed voltage of direct current and alternating current is applied between the developing device and a photosensitive member. As a result, an oscillating electric field is applied to the toner particles to fly between the developing device and the photosensitive member. That is, the toner is attracted from the developing device to the photosensitive member at the timing when the voltage in the direction in which the toner is attracted from the developing device to the photosensitive member is applied. At the reverse voltage, excess toner is collected into the developing device.

Here, there are cases where an image to be formed includes both a solid image portion such as a photograph and graphics and a dot image portion such as a character and a line drawing. In general, the edge portion of an image requires a large voltage for development, and has a property that it is difficult to collect once developed. Therefore, an AC voltage having a large peak-to-peak voltage value is suitable for developing the edge portion of a solid image or a dot image. On the other hand, in the central portion of the solid portion, development and recovery are possible with a small voltage, and an AC voltage with a small peak-to-peak voltage value is suitable. If the voltage value between peaks is too large, the voltage may be recovered and white spots may occur. For this reason, for example, Patent Document 1 proposes an image forming apparatus in which an alternating voltage to be superimposed is periodically changed in order to appropriately develop an image in which these are mixed.
JP 11-44985 A

  In the conventional image forming apparatus described above, two types of operation periods are provided, and the frequency of the AC voltage and the peak-to-peak voltage value are changed in each of them. However, in order to change the frequency in the AC power supply, a special circuit configuration for that purpose is required. Therefore, there is a problem that the control of the apparatus becomes complicated and the cost becomes high.

  The present invention has been made to solve the problems of the conventional image forming apparatus described above. That is, an object of the present invention is to provide a developing device and an image forming apparatus that can appropriately develop both a solid image portion and a dot image portion without frequency modulation of an AC component.

  The developing device and the image forming apparatus of the present invention, which have been made for the purpose of solving this problem, are non-contact type developing devices that develop a latent image on a photosensitive member with toner by a developing member, and include a developing member and a photosensitive member. An oscillating voltage is applied between them, the recovery side peak voltage is constant, and the development side peak voltage is a second level where the difference between the recovery side peak voltage and the recovery side peak voltage is large. And a developing power source that selectively uses the voltage.

  According to the developing device of the present invention, since an oscillating voltage is applied between the developing member and the photosensitive member, an oscillating electric field is applied to the toner particles to develop the electrostatic latent image on the photosensitive member and to remove excess toner. Recovery is performed alternately. At this time, since the first level voltage and the second level voltage are selectively used as the development-side peak voltage, different peak voltages suitable for the development of the solid image portion and the dot image portion should be used. it can. The change of only the peak voltage does not require a special circuit configuration as compared with the frequency modulation of the AC component, and can be implemented with easy control. Accordingly, the developing device can appropriately develop both the solid image portion and the dot image portion without frequency modulation of the AC component.

Furthermore, in the present invention, it is desirable that the development power supply periodically use the first level voltage and the second level voltage as the development side peak voltage.
If it is such, control is easy and no special circuit configuration or the like is required.

Further, in the present invention, it is desirable that the development power supply uses the second level voltage once in each cycle and uses the first level voltage for the remaining development-side peak voltages.
In such a case, the first level voltage is set as a reference development voltage for obtaining a predetermined solid image density, and the second level voltage is configured to compensate only for an insufficient dot image density due to the first level voltage. Can do.

Furthermore, in the present invention, it is desirable that the difference between the recovery side peak voltage and the second level voltage is 1.2 times or more the difference between the recovery side peak voltage and the first level voltage.
If this is the case, both an appropriate solid image density and dot image density can be obtained. More preferably, the difference between the recovery-side peak voltage and the second level voltage is 1.5 times or less than the difference between the recovery-side peak voltage and the first level voltage.

  The present invention also provides an image forming apparatus having a photosensitive member and a non-contact type developing device that develops a latent image on the photosensitive member with toner by a developing member, and an oscillation voltage between the developing member and the photosensitive member. , The recovery-side peak voltage is constant, and the development-side peak voltage is selected as the first level voltage with a small difference from the recovery-side peak voltage and the second level voltage with a large difference between the recovery-side peak voltages The present invention also extends to an image forming apparatus having a developing power supply for use.

  According to the developing device and the image forming apparatus of the present invention, both the solid image portion and the dot image portion can be appropriately developed without frequency modulation of the AC component.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the best mode for embodying the present invention will be described in detail with reference to the accompanying drawings. In this embodiment, the present invention is applied to a non-contact type developing device.

  The developing device 10 of the present embodiment is for developing an electrostatic latent image formed on a photosensitive drum 11 as schematically shown in FIG. The developing device 10 includes a developing roller 12 and a developing device 13, and the developing roller 12 is disposed such that a part thereof is exposed from the developing device 13. Further, toner 14 is accommodated in the developing device 13 and a supply roller 15 is disposed so that the toner 14 is supplied to the surface of the developing roller 12 by the supply roller 15. Further, a power source 16 for applying a developing voltage between the photosensitive drum 11 and the developing roller 12 is provided.

  Here, the developing device 10 is a non-contact type developing device 10 using a negatively charged one-component toner 14. That is, the developing roller 12 is not in contact with the photosensitive drum 11. When a voltage is applied between the developing roller 12 and the photosensitive drum 11 by the power supply 16, an electric field is formed in a gap portion between the photosensitive drum 11 and the developing roller 12. The charged particles of the toner 14 are moved beyond the gap between the photosensitive drum 11 and the developing roller 12 by the electric force. In general, a voltage in which a direct current component and an alternating current component are superimposed is applied between the photosensitive drum 11 and the developing roller 12, so that the toner 14 is moved in any direction depending on the timing.

  For example, the negatively charged toner 14 is blown from the developing roller 12 toward the photosensitive drum 11 at a timing when a negative voltage is applied to the developing roller 12. Then, the electrostatic latent image is developed by being attracted to and attached to the electrostatic latent image on the photosensitive drum 11. Hereinafter, a voltage applied in a direction in which the toner 14 is blown from the developing roller 12 toward the photosensitive drum 11 is referred to as a developing side voltage. Further, at the timing when a positive voltage is applied to the developing roller 12, the toner 14 is attracted to the developing roller 12, and excess toner 14 is collected. Hereinafter, the voltage applied in this direction is referred to as a recovery side voltage. Since the DC component is on the development side, the development side is dominant over the collection side as a whole.

  In the developing device 10 according to the present embodiment, a developing voltage V applied to the developing roller 12 by the power source 16 has a waveform as shown in FIG. This is obtained by partially changing the peak voltage value of the basic voltage V0 shown in FIG. The basic voltage V0 is a superimposed voltage of the DC component of the voltage Vdc and the AC component of the peak-to-peak voltage Vpp. On the other hand, the development voltage V in FIG. 2 has the same frequency, duty, and recovery-side peak voltage as that of the basic voltage V0, and the absolute value of the development-side peak voltage is increased once every several cycles.

  For example, as the basic voltage V0 shown in FIG. 3, a rectangular wave having an AC component of Vpp = 1000 V, a frequency of 2000 Hz, and a duty of 30% and a DC component of Vdc = −320 V is used. The developing voltage V shown in FIG. 2 is obtained by increasing the absolute value of the developing-side (lower side in the figure) peak voltage value of the AC component of the basic voltage V0 once every three cycles. The peak-to-peak voltage value VppB when it is changed is preferably Vpp × 1.2 or more. In these figures, the upper side corresponds to the recovery side voltage, and the lower side corresponds to the development side voltage.

  That is, the development voltage V of the present embodiment is obtained by changing only the AC component Vpp of the basic voltage V0 once every predetermined period. In this way, if only Vpp is changed, no new device or additional parts are required, and it can be handled in a programmatic manner. Therefore, this correspondence is easy and an increase in cost can be suppressed.

  Next, a procedure for setting an appropriate development voltage V will be described. First, the direct current component Vdc of the basic voltage V0 and the alternating current components Vpp and duty are selected and set so as to obtain a predetermined solid density. These may be used as a development voltage having a constant waveform in a conventional equivalent type of developing device. Next, the recovery-side peak voltage of the basic voltage V0 was fixed, and the development-side peak voltage was changed once every three cycles. Here, as the image forming apparatus of the test machine, a magiccolor-2300DL manufactured by Konica Minolta Printing Solutions was used, and the distance between the photosensitive drum 11 and the developing roller 12 was fixed to 135 μm. The toner 14 used for magiccolor-2300DL was used.

  FIG. 4 shows the result of examining the quality of the dot image by changing the peak-to-peak voltage value VppB when the change is made. As shown in this figure, when VppB is set so that VppB / Vpp is 1.2 to 1.5, both solid images and dot images have good image quality. On the other hand, when VppB is not so different from Vpp (VppB / Vpp <1.2), a good dot image could not be obtained. Therefore, it has been found that if the development side voltage is set to VppB = Vpp × 1.2 once every three periods, a good image quality can be obtained even for a general image in which a solid image and a dot image are mixed.

  As described above in detail, according to the developing device 10 of this embodiment, the developing voltage of the basic voltage V0 is changed about once every three periods as the developing voltage V. The amount of change is 1.2 to 1.5 times the absolute value of the peak-to-peak voltage value. Since only the peak-to-peak voltage value is changed, no additional parts are required for the conventional device, and this can be easily implemented. As a result, both the solid image portion and the dot image portion can be appropriately developed.

In addition, this form is only a mere illustration and does not limit this invention at all. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof.
For example, in the above embodiment, the negatively charged toner 14 has been described, but a positively charged toner may be used. In this case, the development side voltage is a positive voltage, and the peak voltage of a part of the development side voltage may be increased in the positive direction.
Further, for example, the present invention can be applied to various image forming apparatuses equipped with the developing device.

It is a schematic block diagram around a developing device. It is explanatory drawing which shows the waveform of a developing voltage. It is explanatory drawing which shows the waveform of a basic voltage. It is explanatory drawing which shows the result of having investigated the image quality by changing the voltage value between peaks.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Developing device 11 Photoconductor 12 Developing roller (Developing member)
16 Power supply (Development power supply)

Claims (5)

In a non-contact type developing device that develops a latent image on a photoreceptor with toner by a developing member,
Applying an oscillating voltage between the developing member and the photoconductor;
The recovery-side peak voltage is constant,
A development power supply that selectively uses, as the development side peak voltage, a first level voltage having a small difference from the collection side peak voltage and a second level voltage having a large difference from the collection side peak voltage. apparatus. 2. The developing device according to claim 1, wherein the developing power source is:
A developing device characterized by periodically using a first level voltage and a second level voltage as a development-side peak voltage. 3. The developing device according to claim 2, wherein the developing power source is
2. A developing device, wherein the second level voltage is used once in each period, and the first level voltage is used for the remaining development-side peak voltage. The developing device according to claim 1,
A developing device characterized in that the difference between the recovery-side peak voltage and the second level voltage is 1.2 times or more of the difference between the recovery-side peak voltage and the first level voltage. In an image forming apparatus having a photoconductor and a non-contact type developing device for developing the latent image of the photoconductor with toner by a developing member,
While applying an oscillating voltage between the developing member and the photoreceptor,
The recovery-side peak voltage is constant,
An image having a developing power source that selectively uses a first level voltage having a small difference from the collection side peak voltage and a second level voltage having a large difference from the collection side peak voltage as the development side peak voltage. Forming equipment.

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