JP5453339B2 - Developing device and image forming apparatus - Google Patents

Description

  The present invention relates to an electrophotographic developing device and an image forming apparatus.

  An image forming apparatus such as a copier, a printer, or a facsimile using an electrophotographic method emits light based on an image carrier (for example, a photosensitive drum or a transfer belt) and image data and statically puts it on the image carrier. An exposure apparatus for forming an electrostatic latent image and a developing apparatus for developing the electrostatic latent image by supplying a developer (toner) to the electrostatic latent image formed on the image carrier are provided.

  In such a developing device, when the developing bias voltage applied to the developing roller is increased, it becomes easier to supply the toner necessary for forming the toner image to the image carrier, while the peak of the developing bias voltage is reached. The potential difference between the value and the surface potential of the image carrier increases, and leakage (air discharge) tends to occur between the image carrier and the developing roller. When the leak occurs, a so-called development leak occurs, in which random black spots (noise) are generated on the image carrier, and a toner image with good image quality is not formed. In addition, peripheral devices are likely to fail.

  Conversely, if the developing bias voltage is lowered to avoid leakage, it becomes difficult to supply the amount of toner necessary for forming the toner image to the image carrier, and density unevenness occurs in the toner image. As a result, a good quality toner image is not formed. Therefore, methods for suppressing the occurrence of leakage have been proposed (see Patent Documents 1 to 4).

JP 2007-171936 A JP 2005-258256 A JP-A-7-134480 JP 2007-279277 A

  In the methods proposed in Patent Documents 1 to 4, an AC amplifier circuit amplifies the waveform generated by the waveform generator to generate an AC voltage, and further generates a developing bias voltage by superimposing the DC voltage. Therefore, when the waveform generated by the waveform generator changes greatly, this change is amplified by the AC amplifier circuit and appears as a large peak value in the developing bias voltage. As the peak value increased, the potential difference between the image carrier and the developing roller became equal to or greater than the discharge start voltage, and leakage was likely to occur.

  Accordingly, the present invention has been made in view of such circumstances, and a developing device and an image forming apparatus that prevent leakage generated between the developing roller and the image carrier without using a special device. The purpose is to provide.

  The developing device according to claim 1 includes a waveform generating means capable of outputting control signals having different duty ratios, and an AC amplifying circuit for amplifying the control signals to generate an AC voltage, and the generated AC A high voltage generating means for generating a developing bias voltage by superimposing a DC voltage on the voltage, and a developing roller to which the developing bias voltage is applied and carrying a toner as a developer on a peripheral surface thereof, When the duty ratio of the control signal is changed from the first duty ratio to a second duty ratio different from the first duty ratio, the waveform generating means starts from the start point of outputting the control signal having the second duty ratio. Before, after changing the voltage level of the control signal linearly with a predetermined slope so that the amount of change in the waveform average value of the control signal is less than or equal to a predetermined value And it outputs a control signal of the second duty ratio at the starting point.

  Here, the waveform average value means a voltage average value during a period from a certain point in time of the control signal to a predetermined time. When the duty ratio of the control signal changes, the average value of the waveform of the control signal changes abruptly, and this change is amplified by the AC amplifier circuit and appears as a large peak value in the developing bias voltage. When such a peak value occurs, the potential difference between the developing roller and the image carrier becomes equal to or higher than the discharge start voltage, and leakage is likely to occur.

  Therefore, when changing the duty ratio of the control signal, the change amount of the waveform average value of the control signal is equal to or less than a predetermined value (the “predetermined value” means that the change amount of the waveform average value is the AC amplification circuit After the control signal is linearly changed with a predetermined slope so that the development bias voltage does not appear as a peak value due to amplification by (1), the target second duty ratio is set. To do. By doing so, there is no sudden change in the average value of the waveform of the control signal, and the change is not amplified by the AC amplifier circuit and does not appear as a peak value in the developing bias voltage. Therefore, the occurrence of leak can be prevented. Even in an environment where the atmospheric pressure is low and the discharge start voltage is low, the occurrence of leakage can be suppressed with a simple device.

  A second aspect of the present invention is the developing device according to the first aspect, wherein the waveform generating means has an analog terminal, and the control signal is output from the analog terminal. When changing the duty ratio from the first duty ratio to the second duty ratio, from the voltage level indicated by the first duty ratio to the voltage level indicated by the second duty ratio before the start point. After changing the voltage level of the control signal linearly with the predetermined slope, a control signal having a second duty ratio is output at the start point.

  According to this configuration, by using the analog output terminal of the waveform generating means, the voltage level of the control signal can be linearly changed without using a special device, and leakage can be prevented.

  According to a third aspect of the present invention, there is provided an image forming apparatus comprising: a developing roller that carries a toner as a developer on a peripheral surface thereof and transports it; and a high voltage generating unit that applies a developing bias voltage to the developing roller. And an image carrier that carries a toner image in which an electrostatic latent image based on image data is formed and the electrostatic latent image is visualized by toner supplied from the developing roller, and the developing device The developing device according to claim 1 or 2 is used.

  According to this configuration, the same effect as in the first or second aspect can be obtained.

  According to the present invention, there is no sudden change in the waveform average value of the control signal, and the change in the waveform average value is amplified by the AC amplifier circuit and does not appear as a peak value in the developing bias voltage. Accordingly, it is possible to prevent a leak that occurs between the developing roller and the image carrier.

FIG. 3 is a cross-sectional view illustrating an example of a mechanical configuration of the image forming apparatus. FIG. 2 is a cross-sectional view illustrating a schematic configuration of a developing device. The figure which showed the electrical structure of the high voltage power supply circuit. The figure which showed the waveform of the control signal and development bias voltage which a waveform generator outputs. The figure which showed each waveform at the time of changing the duty ratio of a control signal from 100% to 10% in the conventional high voltage power supply circuit. The figure which showed each waveform at the time of changing the duty ratio of a control signal from 100% to 10% in the high voltage power supply circuit of this Embodiment. The figure which showed each waveform at the time of changing the duty ratio of a control signal from 50% to 10% in the high voltage power supply circuit of this Embodiment.

  Hereinafter, a developing device according to an embodiment of the present invention and an image forming apparatus including the developing device will be described with reference to the drawings. In this embodiment, a printer is described as an example of the image forming apparatus 1. However, an electrophotographic copying machine, a facsimile, or a multifunction machine having a plurality of these functions may be used.

  FIG. 1 is a cross-sectional view illustrating an example of a mechanical configuration of an image forming apparatus 1 according to the present embodiment. The image forming apparatus 1 includes an exposure device 11, a developing device 12, a charger 13, a photosensitive drum 14, a transfer roller 15, and a fixing device 16.

  The photosensitive drum 14 is a cylindrical member, and rotates in the clockwise direction in FIG. 1 in response to a driving force from a motor (not shown). The charger 13 charges the surface of the photosensitive drum 14 substantially uniformly. The exposure apparatus 11 includes a light source such as a laser diode, and irradiates light corresponding to image data onto the surface of the photosensitive drum 14 that is substantially uniformly charged by the charger 13 to form an electrostatic latent image. Form. The image data is data received by the image forming apparatus 1 that is transmitted by a personal computer or the like connected to the image forming apparatus 1.

  The developing device 12 includes a toner container that stores toner, and supplies toner to the surface of the photosensitive drum 14 on which the electrostatic latent image is formed to form a toner image. A toner image formed on the photosensitive drum 14 is transferred onto a sheet or a transfer belt (not shown) conveyed on the conveyance path P by a transfer roller 15 described later.

  A transfer roller 15 is disposed at a position facing the photosensitive drum 14. The transfer roller 15 is made of a conductive rubber material or the like, and transfers the toner image formed on the photosensitive drum 14 onto a sheet or transfer belt that is transported along the transport path P.

  The fixing device 16 includes a heating roller 160 including a heater and the like, and a pressure roller 161 provided at a position facing the heating roller 160. The fixing device 16 is transferred to the paper by heating and conveying the paper on which the toner image is formed. Fix the toner image.

  Next, an image forming operation of the image forming apparatus 1 will be briefly described. First, the surface of the photosensitive drum 14 is charged almost uniformly by the charger 13. Then, the charged surface of the photosensitive drum 14 is exposed by the exposure device 11, and an electrostatic latent image is formed on the surface of the photosensitive drum 14. Then, the toner is supplied to the surface of the photosensitive drum 14 by the developing device 12 to visualize the electrostatic latent image into a toner image, and the toner image on the surface of the photosensitive drum 14 is transferred to the paper by the transfer roller 15. Transcribed. The toner image transferred to the paper is fixed by the fixing device 16.

  FIG. 2 is a cross-sectional view showing an outline of the configuration of the developing device 12, and shows an enlarged peripheral portion of the developing device 12 shown in FIG. The developing device 12 includes a developing roller 72, a magnetic roller 73, a paddle mixer 74, a stirring mixer 75, a panning blade 76, a partition plate 77, and a voltage application unit 80.

  The developing roller 72 carries the toner on its surface and conveys it, thereby developing the electrostatic latent image formed on the surface of the photosensitive drum 14 as a toner image. The magnetic roller 73 attracts the two-component developer by a magnet disposed therein to generate a magnetic brush, and supplies toner to the developing roller 72.

  The paddle mixer 74 and the agitation mixer 75 have spiral blades, and agitate the toner while conveying the two-component developer in opposite directions to charge the toner. Further, the paddle mixer 74 supplies a two-component developer containing charged toner and a carrier to the magnetic roller 73. The ear cutting blade 76 regulates the thickness of the magnetic brush formed on the magnetic roller 73. The partition plate 77 is provided between the paddle mixer 74 and the stirring mixer 75 so that the two-component developer can freely pass outside the both end sides of the partition plate 77.

  The high-voltage power circuit 80 is a power source that applies a developing bias voltage to the developing roller 72 and the magnetic roller 73. FIG. 3 is a diagram showing an electrical configuration of the high-voltage power supply circuit 80. The high voltage power supply circuit 80 includes a waveform generator 801, an AC amplification circuit 802, a transformer 803, and a DC power supply 804. The waveform generator 801 is a circuit that can output control signals having different duty ratios from analog terminals.

  The AC amplifier circuit 802 is configured by an operational amplifier or the like, and is a circuit for amplifying the control signal (voltage) output from the waveform generator 801 and bringing it close to a voltage level required as a developing bias voltage of the developing device 12. The voltage amplified by the AC amplifier circuit 802 is boosted by the transformer 803 and superimposed on the DC voltage generated by the DC power source 804 on the secondary side of the transformer 803 and applied to the developing device 12 as a developing bias voltage.

  FIG. 4 is a diagram showing a control signal (left side) output from the waveform generator 801 and a waveform (right side) of the development bias voltage. The duty ratio of the control signal is 0%, 10%, 50%, 90%, and An example at 100% is shown. When the duty ratio of the control signal is 0% and 100%, there is no voltage change in the control signal, so the AC amplifier circuit 802 does not function and the development bias voltage becomes zero. In the following description, it is assumed that the surface potential of the photosensitive drum 14 and the DC voltage component of the DC power source 804 are zero.

  When the duty ratio of the control signal is 10%, the time ratio between the high level and the low level of the control signal is 1: 9, and the waveform average value of the control signal is 10% of the high level value as indicated by the dotted line. The development bias voltage has a waveform with a large change on the plus side where the level of the waveform average value is 0 [V]. Here, the waveform average value means a voltage average value during a period from a certain point in time of the control signal to a predetermined time before.

  When the duty ratio of the control signal is 50%, the time ratio between the high level and the low level of the control signal is 5: 5, and the average value of the waveform of the control signal is a voltage level of 50% of the high level value as indicated by the dotted line. become. The development bias voltage is a rectangular wave that changes around 0 [V].

  When the duty ratio of the control signal is 90%, the time ratio between the high level and the low level of the control signal is 9: 1, and the waveform average value of the control signal is a voltage level of 90% of the high level value as indicated by the dotted line. become. The development bias voltage has a waveform with a large change on the negative side, where the level of the waveform average value is 0 [V].

  FIG. 5 is a diagram showing each waveform when the duty ratio of the control signal is changed from 100% to 10% in the conventional high-voltage power supply circuit. The control signal changes its duty ratio at the change point t1, that is, changes from a high level to a low level. Therefore, as shown by the dotted line, the waveform average value changes rapidly immediately after the change point t1. The voltage change of the waveform average value is amplified by a coupling capacitor or a transformer included in the AC amplifier circuit 802 and appears as a large peak value on the minus side of the developing bias voltage. When such a peak value occurs, the potential difference between the photosensitive roller 14 and the developing roller 72 becomes equal to or higher than the discharge start voltage, and leakage is likely to occur.

  Therefore, in the high-voltage power supply circuit 80 in the image forming apparatus according to the present embodiment, when the waveform generator 801 changes the duty ratio, the voltage value of the control signal is linearly changed and output, thereby outputting the waveform of the control signal. Improvements were made to prevent the change in average value from appearing as a peak value when amplified. This will be described in detail below.

  FIG. 6 is a diagram illustrating each waveform when the duty ratio of the control signal is changed from 100% to 10% in the high-voltage power supply circuit 80 of the present embodiment. When the duty ratio of the control signal is changed from 100% to 10%, the waveform generator 801 has a voltage level (that is, a high level value) indicated by the duty ratio before the change of the voltage level of the control signal before the change point t2. ) To the voltage level of the ratio indicated by the target duty ratio (that is, the voltage value of 10% of the high level value) is linearly changed with a predetermined slope and output. Since the control signal is output from the analog terminal of the waveform generator 801, a continuously changing waveform as shown in FIG. 6 can be output in addition to the rectangular wave.

  Here, whether or not a peak value that causes a leak appears in the development bias voltage depends on the amount of change in the average value of the waveform of the control signal. Therefore, when changing the duty ratio, the amount of change in the average value of the waveform of the control signal needs to be equal to or less than the amount of change that does not appear as a peak value in the developing bias voltage due to amplification by the AC amplifier circuit 802. Therefore, the amount of change in the waveform average value that appears as a peak value in the development bias voltage during circuit design is calculated, and the slope when changing the control signal so that the waveform average value is less than or equal to this calculated value. Is determined in advance. The waveform generator 801 changes and outputs the control signal using this predetermined slope. Then, after the change point t2 when the voltage level of the control signal reaches the voltage level of the ratio indicated by the target duty ratio (that is, the voltage value of 10% of the high level value), the waveform generator 801 sets the target duty. A control signal with a ratio (that is, a duty ratio of 10%) is output.

  Here, the average value of the waveform of the control signal corresponds to the voltage level indicated by the duty ratio of the control signal, as shown in FIG. Therefore, in order to eliminate an unnecessary change in the waveform average value, the change start point of the control signal is assumed to be when the control signal is at the voltage level (that is, the high level value) of the ratio indicated by the duty ratio before the change, and the change point t2 Is a point at which the voltage level of the control signal reaches the voltage level of the ratio indicated by the target duty ratio (that is, the voltage value of 10% of the high level value). In order to make this point easy to understand, another example will be described with reference to FIG.

  FIG. 7 is a diagram illustrating each waveform when the duty ratio of the control signal is changed from 50% to 10% in the high-voltage power supply circuit 80 of the present embodiment. When the duty ratio of the control signal is changed from 50% to 10%, the waveform generator 801 changes the voltage level of the ratio indicated by the duty ratio before the change of the voltage level of the control signal before the change point t3 (high level value). 50%) to a voltage value at a ratio indicated by the target duty ratio (10% of the high level value) is linearly changed with a predetermined slope and output. Similarly to the above, since the waveform average value of the control signal does not change abruptly during this time, the peak value does not appear in the developing bias voltage, and leakage can be prevented. The waveform generator 801 outputs the control signal as a rectangular wave having a duty ratio of 10% after the change point t3.

  As described above, when changing the duty ratio of the control signal for determining the duty ratio of the developing bias voltage, after the waveform generator 801 linearly changes the voltage level of the control signal before the change point. By outputting the target duty ratio, there is no sudden change in the waveform average value of the control signal, and the voltage change is not amplified by the AC amplifier circuit 802 and appears as a peak value. Therefore, the occurrence of leak can be prevented. Further, even in an environment where the atmospheric pressure is low and the discharge start voltage is low, the occurrence of leakage can be suppressed with a simple device.

  In the present embodiment, only changes in the duty ratio of the control signal from 100% to 10% and from 50% to 10% are illustrated. However, the duty ratio of the control signal is determined by the above method regardless of the numerical value of the duty ratio. The occurrence of leakage can be prevented by changing.

  Further, although the control signal has been described as a signal output from the analog terminal of the waveform generator 801, it may be output from a digital terminal. However, when the control signal is output from the digital terminal, an abrupt change in the voltage level of the waveform average value of the control signal can be suppressed by providing an analog adder circuit at the subsequent stage of the waveform generator 801. Thereby, the effect similar to the above is acquired.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 12 Developing apparatus 14 Photosensitive drum (image carrier)
72 Development Roller 80 High Voltage Power Supply Circuit 801 Waveform Generator (Waveform Generator)
802 AC amplifier circuit (high voltage generator)
803 Transformer (High voltage generator)
804 DC power supply (high voltage generator)

Claims (3)

Waveform generating means capable of outputting control signals having different duty ratios;
A high voltage generating means for generating an AC voltage by amplifying the control signal and generating a developing bias voltage by superimposing the DC voltage on the generated AC voltage;
A developing roller to which the developing bias voltage is applied and carrying a toner as a developer on a peripheral surface;
And the waveform generating means starts outputting the control signal having the second duty ratio when the duty ratio of the control signal is changed from the first duty ratio to a second duty ratio different from the first duty ratio. Before the starting point, the voltage level of the control signal is linearly changed with a predetermined slope so that the amount of change in the waveform average value of the control signal is not more than a predetermined value, and then the start A developing device which outputs the control signal of the second duty ratio at a point.   The waveform generating means has an analog output terminal and outputs the control signal from the analog output terminal, and when changing the duty ratio of the control signal from the first duty ratio to the second duty ratio, Before the start point, the voltage level of the control signal is linearly changed with the predetermined slope from the voltage level indicated by the first duty ratio to the voltage level indicated by the second duty ratio. The developing device according to claim 1, wherein a control signal having a second duty ratio is output at the start point. A developing device having a developing roller for carrying and transporting toner, which is a developer, on its peripheral surface, and a high voltage generating means for applying a developing bias voltage to the developing roller;
An image carrier that carries a toner image in which an electrostatic latent image based on image data is formed and the electrostatic latent image is visualized by toner supplied from the developing roller;
An image forming apparatus in which the developing device according to claim 1 is used as the developing device.

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