JP2007148250A - Developing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent an image forming apparatus from malfunctioning owing to a leak between a magnetic roll and a developing roll of a hybrid type developing device. <P>SOLUTION: The developing device is equipped with a developing bias application unit 402 which applies a first DC bias and a first AC bias to the developing roll, a supply bias application unit 403 which applies a second DC bias and a second AC bias opposite in phase to the first AC bias to the magnetic roll, and a capacitor 408 provided between a bias output of the supply bias application unit 403 and the ground. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a developing device and an image forming apparatus, and more particularly to a hybrid type developing device having a magnetic roll and a developing roll, and an image forming apparatus such as a copying machine, a printer, a facsimile machine, and a multi-function machine having the same.

In an electrophotographic image forming apparatus, a developer is attached to an electrostatic latent image formed on a photoconductor to develop the electrostatic latent image. In the hybrid developing device, development is performed using a magnetic roll and a developing roll. The magnetic roll captures the two-component developer charged by stirring and supplies the toner to the developing roll with a magnetic brush. The developing roll is disposed in the vicinity of the photoreceptor, and attaches toner from the magnetic roll to the electrostatic latent image on the photoreceptor. A bias is applied to the magnetic roll and the developing roll in order to move the toner. For example, in Patent Document 1, a DC bias and an AC bias are applied to the developing roll, and a DC bias is applied to the magnetic roll. This facilitates toner replacement between the magnetic roll and the developing roll.
JP 2003-21966 A

  Increasing the potential difference between the magnetic roll and the developing roll facilitates toner movement between the magnetic roll and the developing roll. However, when the potential difference is increased, leakage is likely to occur. When the leak occurs, noise is generated in various signal lines through the substrate generating the bias, causing malfunction of the apparatus.

  In order to prevent the occurrence of leakage, means for detecting leakage and stopping or changing the output are known. However, noise has already occurred at the time of detection, and its effect is limited. In addition, measures are taken in advance to measure leak points at the time of assembly and prevent the occurrence of leaks. However, if the output load changes due to changes over time, leaks will occur.

  The present invention has been made in view of the above-described problems in the conventional technology, and includes a developing device capable of preventing malfunction of the image forming apparatus due to leakage between the magnetic roll and the developing roll, and the same. An object of the present invention is to provide an image forming apparatus.

  In order to achieve the above object, a developing device provided by the present invention includes a developing roll for developing an electrostatic latent image on a photoreceptor with toner, a magnetic roll for supplying toner to the developing roll, and a first roll. A developing bias applying unit for applying a first DC bias and a first AC bias to the developing roll, and a supply bias for applying a second AC bias having a phase opposite to the second DC bias and the first AC bias to the magnetic roll An application unit, and a capacitor provided between the bias output of the supply bias application unit and the ground.

  In this developing device, a capacitor is provided between a bias output of a supply bias applying unit that applies a bias to the magnetic roll and the ground. Thereby, even if a leak occurs between the magnetic roll and the developing roll, it is difficult for noise to be generated in the signal line, and malfunction of the image forming apparatus due to the influence of noise can be prevented. Further, by providing a capacitor on the magnetic roll side having a smaller bias than that on the developing roll side, an alternating current flowing through the capacitor can be suppressed, and an increase in cost for measures against heat caused by the alternating current can be avoided. Since a leakage current flows to the ground through the terminal of the magnetic roll, malfunction of the apparatus can be sufficiently prevented even if a capacitor is provided on the magnetic roll side.

  By adopting the configuration as described above, in the present invention, malfunction of the image forming apparatus due to occurrence of a leak between the magnetic roll and the developing roll can be prevented at a low cost and sufficiently.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In this embodiment, the present invention is embodied as a digital copying machine.

  FIG. 1 is a diagram for explaining the overall configuration of the copying machine according to the present embodiment. The copying machine 101 includes an image reading unit 102 and an image forming unit 103. The image reading unit 102 reads an image of a document and generates digital data of the image. The image reading unit 102 has a document table 104 such as contact glass on the top surface of the housing. The document can be placed on the document table 104. A scanning optical system 105 is disposed below the document table 104. The scanning optical system 105 includes a first carriage 106, a second carriage 107, and a condenser lens 108. The first carriage 106 is provided with a linear light source 109 and a mirror 110, and the second carriage 107 is provided with mirrors 111 and 112. A light source 109 illuminates the document. The mirrors 110 to 112 guide the reflected light from the document to the lens 108, and the lens 108 forms an image of the light on the light receiving surface of the line image sensor 113. In the scanning optical system 105, the first carriage 106 and the second carriage 107 are provided so as to be able to reciprocate in the sub-scanning direction 114. By moving the first carriage 106 and the second carriage 107 in the sub-scanning direction 114, the image of the document placed on the document table 104 can be read by the image sensor 113. The image sensor 113 generates document image data from the light image incident on the light receiving surface.

  The document feeder 115 can be attached to the upper side of the image reading unit 102 so as to be opened and closed. The document feeder 115 includes a document tray 116, a conveyance path 117, and a paper discharge tray 118. The user places a document on the document table 104 or sets the document on the document feeder 115. The document feeder 115 feeds the documents set on the document tray 116 one by one to the conveyance path 117. There is an image reading position 119 on the conveyance path 117. When reading an image of a document set on the document feeder 115, the image reading unit 102 temporarily fixes the first carriage 106 and the second carriage 107 to the image reading position 119. When the document passes through the image reading position 119, the document is illuminated by the light source 109 to read the image of the document. The document that has passed the image reading position 119 is discharged to the paper discharge tray 118.

  The image forming unit 103 prints image data obtained by the image reading unit 102 or image data received from another device via a network on a sheet. The image forming unit 103 is provided with a photosensitive drum 120. The photosensitive drum 120 rotates in the direction of the arrow 121 at a constant speed. Around the photosensitive drum 121, a charger 122, an exposure unit 123, a developing unit 124, a transfer unit 125, a cleaning unit 126, and the like are arranged in this order from the upstream side in the rotation direction. The charger 122 uniformly charges the surface of the photosensitive drum 120. The exposure device 123 irradiates the uniformly charged surface of the photosensitive drum 120 with light according to image data, and forms an electrostatic latent image on the photosensitive drum 120. The developing device 124 attaches toner to the electrostatic latent image and forms a toner image on the photosensitive drum 120. The transfer unit 125 transfers the toner image on the photosensitive drum 120 to a sheet. The cleaning unit 126 cleans the surface of the photosensitive drum 120. These processes are performed in a series as the photosensitive drum 120 rotates.

  The image forming unit 103 feeds paper from a paper feed cassette 127 or the like to a transfer unit between the photosensitive drum 120 and the transfer unit 125. The paper placed on the bottom plate 128 is pulled out from the paper feed cassette 127, transported through the transport path 130 by the transport roller 129, and then sent to the transfer unit in synchronization with the reading of the original by the registration roller 131. The sheet on which the toner image is transferred is conveyed to the fixing device 132. The fixing device 132 includes a fixing roller 133 and a pressure roller 134, and fixes the toner image on the sheet by heat and pressing force. The image forming unit 103 discharges the paper that has passed through the fixing device 132 to the paper discharge tray 135.

  FIG. 2 is a diagram for explaining a schematic configuration of the developing device. In the copying machine in this embodiment, a so-called hybrid developing device is employed as the developing device 124 of the image forming unit. The developing device 124 includes a stirrer 201, a magnetic roll 202, and a developing roll 203 in a housing 204. The stirrer 201 frictionally charges the carrier and the toner by stirring the two-component developer composed of the toner and the carrier. The magnetic roll 202 has a multipolar magnet in a rotating sleeve that can rotate in the direction of an arrow 205. The magnetic roll 205 captures the carrier on which the toner is electrostatically attracted by the magnetic force, and forms a magnetic brush on the surface of the rotating sleeve. The regulating blade 206 regulates the height of the magnetic brush. The toner is supplied to the developing roll 203 by the magnetic brush that has passed through the regulating blade 206 by the rotation of the rotating sleeve. The developing roll 203 comes close to the photosensitive drum 120 that can rotate in the direction of the arrow 121 through the opening of the housing 204. The toner from the magnetic roll 205 forms a thin layer on the surface of the developing roll 203, and is conveyed to the photosensitive drum 120 when the developing roll 203 rotates in the direction of arrow 207. The electrostatic latent image on the photoconductive drum 120 is developed when the toner flying from the developing roll 203 adheres.

  FIG. 3 is a diagram for explaining the relationship between the bias to the developing roll and the bias to the magnetic roll. Bias 301 and 302 are applied to the developing roll and the magnetic roll, respectively, in order to move the toner between the magnetic roll and the developing roll and to attach the toner on the developing roll to the photosensitive drum. In the developing device in this embodiment, the AC bias is superimposed on the DC bias in both the bias 301 to the developing roll and the bias 302 to the magnetic roll. The AC bias applied to the developing roll is larger than the AC bias applied to the magnetic roll. For example, an AC bias of about 1.5 kV is applied to the developing roll, and an AC bias of about 460 V is applied to the magnetic roll. The AC bias applied to the magnetic roll is in the opposite phase of the AC bias applied to the developing roll. For this reason, the potential difference 303 between the developing roll and the magnetic roll is larger than the potential difference 304 when only a DC bias is applied to the magnetic roll. By applying the bias in this way in the image forming section, toner can be easily supplied from the magnetic roll to the developing roll.

  FIG. 4 is a diagram for explaining the electrical configuration of the developing device according to this embodiment. In the developing device 124, the magnetic roll 202 and the developing roll 203 are connected to the bias substrate 401. The bias substrate 401 includes development bias application units 402 and 403. The developing bias applying unit 402 is connected to the developing roll 203 and the ground. The developing bias application unit 402 includes a DC bias power supply 404 and an AC bias power supply 405, and applies the AC bias to the developing roll 203 by superimposing the AC bias on the DC bias. The supply bias application unit 403 is connected to the magnetic roll 202 and the ground. The supply bias application unit 403 also includes a DC bias power source 406 and an AC bias power source 407, and applies the AC bias to the magnetic roll 202 by superimposing the AC bias on the DC bias. Here, the peak-to-peak voltage of the AC bias power supply 407 is smaller than the peak-to-peak voltage of the AC bias power supply 405. The AC bias power supply 407 outputs an AC bias having a phase opposite to that of the AC bias power supply 405. As a result, the potential difference between the developing roll and the magnetic roll can be increased as described above, and the toner can be easily moved between the magnetic roll and the developing roll.

  However, when the potential difference between the developing roll 203 and the magnetic roll 202 becomes large, leakage is likely to occur between the developing roll 203 and the magnetic roll 202, and noise is generated in various signal lines from the bias substrate 401 through the main substrate. As a result, the copier malfunctions. If it is attempted to prevent such leakage, it becomes difficult to design the developing device, toner and carrier.

  For this reason, in the developing device 124 in this embodiment, the bias substrate 401 includes the capacitor 408. The capacitor 408 is connected in parallel to the supply bias applying unit 403. According to experiments, the leakage current flows to the ground through the terminal of the magnetic roll 202. The amplitude of the AC bias output from the AC bias power source 405 is larger than the amplitude of the AC bias output from the AC bias power source 407. For this reason, if a capacitor is connected in parallel to the developing bias applying unit 402, a large amount of alternating current flows, leading to heat generation of the bias substrate 401. Therefore, when a capacitor is connected in parallel to the developing bias applying unit 402, measures against the heat generation are required, and the cost increases. Conversely, if a capacitor 408 is connected in parallel to the supply bias application unit 403, such an increase in cost can be avoided.

  By connecting the capacitor 408 in parallel to the supply bias applying unit 403, even if a leak occurs between the developing roll 203 and the magnetic roll 202, it is difficult for noise to be generated in the signal line, thereby suppressing malfunction of the apparatus. It becomes possible. Further, since the capacitor 408 is provided on the bias substrate 401, the design of the developing device, toner, and carrier becomes easy.

  As described above, in the developing device and the copying machine according to the present embodiment, malfunction of the copying machine due to the occurrence of a leak between the magnetic roll and the developing roll can be sufficiently prevented at a low cost. Further, providing the capacitor on the bias substrate facilitates the design of the developing device, toner, and carrier.

  The embodiment described above does not limit the technical scope of the present invention, and various modifications and applications can be made within the scope of the present invention other than those already described. For example, a Zener diode may be connected in parallel with the capacitor.

  In the above-described embodiment, the present invention is embodied as a digital copying machine including a document conveying device, but the present invention is not limited to this. The present invention can also be applied to other image forming apparatuses such as a printer, a facsimile machine, and a multifunction machine.

  According to the developing device and the image forming apparatus according to the present invention, it is possible to prevent the malfunction of the image forming apparatus due to the occurrence of a leak between the magnetic roll and the developing roll at a low cost and sufficiently for copying machines, printers, facsimiles, and composites. It is useful for various devices such as a machine.

1 is a diagram for explaining an overall configuration of a copying machine according to an embodiment. It is a figure for demonstrating schematic structure of a developing device. It is a figure for demonstrating the relationship between the bias to a developing roll, and the bias to a magnetic roll. It is a figure for demonstrating simply the electrical structure of a developing device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Copier 102 Image reading part 103 Image forming part 120 Photoconductor 124 Developing device 202 Magnetic roll 203 Developing roll 401 Bias substrate 402 Developing bias applying part 403 Supply bias applying part 404, 406 DC bias power supply 405, 407 AC bias power supply 408 Capacitor

Claims (2)

A developing roll for developing the electrostatic latent image on the photoreceptor with toner;
A magnetic roll for supplying toner to the developing roll;
First bias applying means for applying a first DC bias and a first AC bias to the developing roll;
A second bias applying means for applying a second AC bias opposite in phase to the second DC bias and the first AC bias to the magnetic roll;
A developing device comprising: a capacitor provided between a bias output of the second bias applying means and a ground. An image forming apparatus comprising the developing device according to claim 1.

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