JP2005316083A - Development apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To surely prevent developer leakage from a gap between a developing roller and a magnetic roller of a development apparatus using two component developers. <P>SOLUTION: A magnetic brush is formed on the magnetic roller 25a by a DC bias Vdc 2 (first development bias) applied thereto and a second development bias superposed with an AC bias Vac on the DC bias Vdc 1 is applied to a developing roller 26a. While the developing roller is slidingly rubbed by the magnetic brush, a toner is transferred from the magnetic roller and a thin toner layer is formed thereon. A voltage Vs meeting an electrolytic current Iac (inflow current between the magnetic roller and the developing roller) flowing between the magnetic roller and the developing roller appears in a resistor 47 and the voltage Vs is sent as a detection voltage through a filter/amplifier section 51 to a controller unit 52. When the detection voltage exceeds a preset threshold voltage level in the controller unit, the controller unit stops the application of the second development bias by controlling an AC generation circuit 53 and stops the application of the first development bias. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a developing device used in an image forming apparatus such as a copying machine, a printer, a facsimile, or a composite machine using an electrophotographic method, and more particularly, a two-component developer including a magnetic carrier and a non-magnetic toner (hereinafter referred to as a “component developer”) The present invention relates to a developing device that performs development using a simple developer.

  In general, in an image forming apparatus, an electrostatic latent image is formed on a photosensitive drum, which is an image carrier, and the electrostatic latent image is developed by a developing device to become a toner image. The toner image on the photosensitive drum is transferred to a recording sheet, and the toner image on the recording sheet is fixed by a fixing device. As a developing method in such a developing apparatus, there are a two-component developing method using a carrier and a toner, and a one-component developing method using no carrier. The two-component development method is excellent in the charging property of the toner by the carrier and can extend the life, but has disadvantages such as a large and complicated developing device and unevenness of the image by the magnetic brush. In addition, the one-component development method has a compact development device and is excellent in dot reproducibility and image uniformity. However, in the non-magnetic one-component development method that does not use magnetic powder used in color machines, it is suitable for the developing roller. The life is shortened because the blade is brought into contact. Taking advantage of the characteristics of both development methods, a toner layer is formed on the development roller with a magnetic brush formed by a magnetic roller using a two-component developer composed of a magnetic carrier and toner, and photosensitive as in the one-component development method. A developing system that develops an electrostatic latent image formed on a body is drawing attention.

  In such a developing device, when continuous printing is performed, toner having a high charge amount accumulates on the developing roller, so-called selective development occurs, and the image density tends to decrease. Further, when a toner consumption area and a non-consumption area are generated on the developing roller, the toner adhesion state and the toner charge amount vary on the developing roller, so that a part of the previous developed image is displayed during the next development. A phenomenon history that appears as an afterimage (ghost) may occur.

  In order to prevent the development history, it is necessary to stabilize the toner charge amount in the toner thin layer on the developing roller. For this purpose, the toner remaining on the developing roller after development is efficiently collected on the magnetic roller side. There is a need to. For example, the magnetic pole member provided in the magnetic roller is provided with a magnetic pole for supplying toner that faces the developing roller, and the gap between the magnetic roller and the developing roller is a gap that is at least five times the shortest gap. In addition, there is a configuration in which a half-value width region in which at least both sides of the magnetic pole for toner supply are half the peak value of the magnetic flux density is set to supply toner to the developing roller and collect toner from the developing roller (Patent Document 1). reference).

Japanese Patent Laid-Open No. 7-128983 (pages 4 to 7, FIGS. 1 to 9)

  By the way, in the developing device of the above type using the two-component developer, the magnetic carrier is inevitably deteriorated by long-term use, and as a result, the toner charge amount changes with time (that is, the toner charging ability is reduced). descend). In addition, the toner charging ability is reduced when the power is turned on after being left for a long time. When the toner charging capability is lowered, the developer leaks from between the magnetic roller and the developing roller (gap), and the inside of the image forming apparatus is contaminated.

  In the conventional developing device, the toner is efficiently collected from the developing roller to the magnetic roller side. However, when the toner charging ability is reduced as described above, the gap between the magnetic roller and the developing roller (gap). The developer leaks and the inside of the image forming apparatus is contaminated by the developer leak (particularly, in a high-temperature and high-humidity environment, the toner charging ability is significantly reduced, so that the developer leak is likely to occur. ). That is, the conventional developing device has a problem that it is not possible to prevent developer leakage due to a decrease in toner charging ability.

  In view of the above circumstances, an object of the present invention is to provide a developing device that can reliably prevent developer leakage from between a gap between a developing roller and a magnetic roller.

  In order to solve the above-mentioned problems, the present invention uses a two-component developer having at least a magnetic carrier and a toner, and a magnetic roller that forms a magnetic brush made of the two-component developer by applying a first developing bias. A developing device in which the magnetic brush is rubbed, a second developing bias is applied, and toner is transferred from the magnetic roller in accordance with the second developing bias to form a thin toner layer. And detecting means for detecting a current flowing between the magnetic roller and the developing roller and outputting a detection signal; and when the detection level indicated by the detection signal exceeds a preset threshold level, And stop control means for stopping application of the second developing bias.

  The detection means outputs, for example, a detection voltage corresponding to a current flowing between the magnetic roller and the developing roller as the detection level, and the threshold level is between the magnetic roller and the developing roller. It is set based on the relationship between the developer leakage generated in the gap and the current flowing between the magnetic roller and the developing roller.

  Furthermore, in the present invention, the stop control means stops the application of the first and second development biases, and after the aging period during which the development roller is aged by the magnetic brush, A developing bias is applied to the developing roller and the first developing bias is applied to the magnetic roller. The aging period is a time for at least the developing roller to make a round.

  As described above, the developing device of the present invention detects the current flowing between the magnetic roller and the developing roller, and when the detected level exceeds a preset threshold level, the first and second developing biases. The threshold level is specified according to the relationship between the developer leakage that occurs in the gap between the developing roller and the magnetic roller and the current that flows between the magnetic roller and the developing roller (flowing current). If this is done, there is an effect that the developer leakage caused by the gap between the developing roller and the magnetic roller can be surely prevented.

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention unless otherwise specified, but are merely illustrative examples. Not too much.

  Referring to FIG. 1, FIG. 1 is a diagram showing an example of a color image forming apparatus in which a developing device according to Embodiment 1 of the present invention is used. This image forming apparatus 20 includes an endless belt (conveying belt) 21. The endless belt 21 conveys the recording paper fed from the paper feed cassette 22 toward the fixing device 23. Above the endless belt 21, a black developing device 24a, a yellow developing device 24b, a cyan developing device 24c, and a magenta developing device 24d are arranged along the conveyance direction of the recording paper. The developing devices 24a to 24d are respectively provided with supply rollers (magnetic rollers) 25a to 25d and developing rollers 26a to 26d, and a toner thin layer is formed on the developing rollers 26a to 26d as described later. .

  Photosensitive drums 27a to 27d, which are image carriers, are arranged facing the developing rollers 26a to 26d, and chargers 28a to 28d and exposure devices 29a to 29d are arranged around the photosensitive drums 27a to 27d, respectively. Has been placed. Then, after the photosensitive drums 27a to 28d are charged by the chargers 28a to 28d, the photosensitive drums 27a to 27d are exposed by the exposure devices 29a to 29d according to the image data, and the photosensitive drums 27a to 27d are exposed on the photosensitive drums 27a to 27d. An electrostatic latent image is formed. Then, as will be described later, the electrostatic latent images on the photosensitive drums 27a to 27d are developed by the developing rollers 26a to 26d to form toner images of respective colors.

  Then, the color toner images are sequentially transferred onto the recording paper conveyed by the endless belt 21 by the transfer devices 30a to 30d, and a color toner image is formed on the recording paper. Thereafter, the recording paper is sent to the fixing device 23, where it is fixed and discharged. The toner remaining on the photosensitive drums 27a to 27d is cleaned by the cleaning units 20a to 20d.

  Referring to FIG. 2, when attention is paid to the developing device 24a (the developing devices 24b to 24d have the same configuration as the developing device 24a, description thereof is omitted here), the developing device 24a is as described above. A magnetic roller 25a and a developing roller 26a. The magnetic roller 25a has a cylindrical rotating sleeve 31a made of a nonmagnetic metal material and a fixed magnet body 31b disposed therein. Has a plurality of magnetic poles.

  The magnetic roller 25a and the developing roller 26a are disposed in the developing container 32, and a partition plate 37 is disposed between the magnetic roller 25a and the developing roller 26a. A paddle mixer 35 and a stirring mixer 36 are disposed in the developing container 32. The paddle mixer 35 and the two-component developer (hereinafter simply referred to as a developer) are charged while being stirred and conveyed by the stirring mixer 36. The developer is supplied to the magnetic roller 25 a while being stirred and charged by the paddle mixer 35. A spike cutting blade (layer thickness regulating blade) 38 is provided facing the magnetic roller 25a, and the height of the magnetic brush formed on the magnetic roller 25a is regulated by the layer thickness regulating blade 38.

  Here, referring also to FIG. 3, a DC bias Vdc1 (second DC bias) is applied to the developing roller 26a from a direct current (DC) bias power source 33a, and an AC bias Vac is applied from an alternating current (AC) bias power source 33b. Applied (the second DC bias and the AC bias Vac are the second developing bias). A DC bias Vdc2 (first DC bias: first developing bias) is applied to the magnetic roller 25a from a direct current (DC) bias power source 34. The bias power sources 33a and 33b and the DC bias power source 34 are controlled by a control device (not shown in FIGS. 2 and 3) as described later.

  A magnetic brush 39c made of a two-component developer including a magnetic carrier 39a and a non-magnetic toner 39b is formed on the magnetic roller 25a, and only the toner 39b is supplied from the magnetic roller 25a to the developing roller 26a. Layer 39d is formed. The layer thickness of the toner thin layer 39d formed on the developing roller 26a is regulated according to the potential difference | (Vdc2) − (Vdc1) | (hereinafter referred to as Δ) between the DC bias Vdc2 and the DC bias Vdc1. When Δ is increased, the toner thin layer 39d on the developing roller 26a is thickened, and when Δ is decreased, the toner thin layer 39d is thinned. Then, according to the potential difference between the photosensitive drum 27a and the developing roller 26a, the toner jumps from the toner thin layer 39d on the developing roller 26a to the electrostatic latent image formed on the photosensitive drum 27a, and development is performed. .

As the magnetic carrier, a carrier having a resistance value of 10 ⁶ Ωcm ³ to 10 ⁹ Ωcm ³ is used. In order to increase the contact point with the toner, it is necessary to increase the surface area of the carrier by using a carrier having a small diameter of 40 μm or less. preferable. As the magnetic carrier, magnetite carrier, Mn ferrite, Mn-Mg ferrite or the like is used. In the illustrated example, a ferrite carrier having a volume resistivity of 10 ⁷ Ωcm and a silicone resin coating, a saturation magnetization of 40 emu / g and a weight average particle size of 35 μm was used.

  The mixing ratio of the toner and the carrier is 5 to 20% by weight, preferably 5 to 15% by weight, based on the total amount of the carrier and the toner. When the mixing ratio of the toner is less than 5% by weight, the charge amount of the toner becomes high and a sufficient image density cannot be obtained, and when it exceeds 20% by weight, a sufficient charge amount cannot be obtained.

  Here, referring to FIG. 4, FIG. 4 is a diagram showing the relationship between the developer leakage in the gap between the developing roller 26a and the magnetic roller 25a and the inflow current value between the magnetic roller and the developing roller when development is performed. In the normal state (state where developer leakage does not occur: indicated by a straight line L1), the flowing-in current is substantially constant. However, as indicated by symbol P in FIG. 2, the gap between the developing roller 26a and the magnetic roller 25a (gap) ), The developer leakage increases, and the flowing-in current increases with the passage of time (indicated by a curve L2).

  Therefore, here, the developer leakage was suppressed as follows. Referring to FIG. 5, in FIG. 5, the same components as those in FIG. 3 are denoted by the same reference numerals. The AC bias power supply 33b shown in FIG. 3 is defined as the secondary side of the transformer (transformer) 41, and the DC bias power supply 33a shown in FIG. In the example shown in FIG. 5, the photosensitive drum 27 a is grounded, the developing roller 26 a is connected to the secondary winding of the transformer 41, and the secondary winding is grounded via the resistor 42. . Note that a series unit 45 including a diode 43 and a resistor 44 is inserted in parallel with the secondary winding of the transformer 41.

  Further, the secondary winding of the transformer 41 is connected to a resistor 47 through a capacitor 46, and the resistor 47 is grounded. A capacitor 49 and a resistor 50 are connected in parallel to the resistor 47 via the diode 48, and the resistor 50 is connected to the input port (A / D port) 51 a of the control device 52 via the filter / DC amplifier 51. It is connected to the.

  An AC amplification circuit 54 is connected to the output port 52 b of the control device 52 via an AC generation circuit 53, and the AC amplification circuit 54 is connected to the primary winding of the transformer 41 via a capacitor 55. The magnetic roller 25 a is grounded via a capacitor 56 and connected to a DC bias power source 34 via a diode 57.

  Now, when developing, an on-remote signal is sent from the control device 52, whereby the AC generation circuit 53 generates an AC signal such as a rectangular wave or a sine wave. This AC signal is amplified by the AC amplifier circuit 54, and then the DC component is cut by the capacitor 55 and is given to the primary winding of the transformer 41. As a result, a voltage (AC voltage) corresponding to the winding ratio is generated in the secondary winding of the transformer 41 (here, this AC voltage is used as the AC bias Vac).

  A current Idc flows in the forward direction of the diode 43 due to the AC bias Vac, and Vdc1 = Idc × R1 (R1 is the resistance value of the resistor 42) is generated at both ends of the resistor 42. That is, the developing bias (second developing bias) in which the DC bias Vdc1 is superimposed on the AC bias Vac is applied to the developing roller 26a.

  On the other hand, the alternating current Iac flows through a path indicated by a broken line in FIG. 5, that is, a path returning to the transformer 41 through the transformer 41, the developing roller 26a, the magnetic roller 25a, the capacitor 55, the resistor 47, and the capacitor 46. In other words, the impedance of the resistor 47 and the capacitor 46 is set to about 1/100 of the resistance value R1 of the resistor 41, and the alternating current Iac is passed through the resistor 47 and the capacitor 46. As a result, a voltage Vs proportional to the alternating current Iac is generated at both ends of the resistor 47 (that is, Vs = Iac × R3 (R3 is the resistance value of the resistor 47)). Functions as part of the detection means).

  Since the above-described AC current Iac flows between the developing roller 26a and the magnetic roller 25a, detecting the voltage Vs corresponds to detecting an inflow current between the developing roller 26a and the magnetic roller 25a, as described with reference to FIG. When the developer leakage occurs in the gap between the developing roller 26a and the magnetic roller 25a, the flowing-in current value (AC current Iac), that is, the voltage Vs increases.

  The voltage Vs (hereinafter referred to as the detection voltage Vs) is rectified by the diode 48 and applied to the filter / DC amplification unit 51 as a DC detection voltage, where it is amplified after the noise component is removed, and the developer leakage detection voltage. It is given to the control device 52 as (detection level). A threshold voltage level (threshold level) is set in advance in the control device 52, and the threshold voltage level is determined in advance by developer leakage and AC current Iac (that is, the output of the filter / DC amplification unit 51 corresponding to the detection voltage Vs). And is set based on the relationship.

  For example, in the example shown in FIG. 5, the threshold voltage level is set according to the straight line L1 shown in FIG. As an example, when the DC bias Vdc1 = 100V, the AC bias Vac is Vpp = 1.6 kV, the frequency = 2.7 kHz, and the duty ratio = 27%, the current flowing into the level indicated by the straight line L1 shown in FIG. The output of the filter / DC amplification unit 51 when the value increases by 0.2 mA is set to the threshold voltage level.

  When the developer leakage detection voltage exceeds the threshold voltage level, the control device 52 determines that developer leakage has occurred and sends an off-remote signal. As a result, the AC generation circuit 53 stops generating the AC signal. As a result, the application of the AC bias Vac and the DC bias Vdc1 (that is, the second developing bias) is stopped (the control device 52 functions as a detection unit and a stop control unit). Further, although not shown in FIG. 5, the control device 52 turns off the connection between the magnetic roller 25a and the DC bias power source 34 by a switch element or the like, and stops the application of the first developing bias. That is, when the developer leakage detection voltage exceeds the threshold voltage level, the control device 52 stops applying the first and second developing biases.

  Even when the first and second developing biases are stopped, the magnetic roller 25a and the developing roller 26a are rotationally driven, and the developing roller 26a is aged by the magnetic brush formed on the magnetic roller 25a, and the developing roller 26a. The upper toner is collected on the magnetic roller 25a side. Then, the control device 52 sends the on-remote signal again after the preset time has elapsed after sending the off-remote signal (this preset time is at least the time for the developing roller 26a to make a round: an aging period). Then, the second developing bias is applied as described above. At this time, the control device 52 turns on the switch element and applies the first developing bias from the DC bias power source 34 to the magnetic roller 25a.

  In this manner, when the developer leakage detection voltage (that is, the alternating current Iac) exceeds the threshold voltage level, the application of the first and second developing biases is stopped, so that the developing roller 26a-magnetic roller 25a. It is possible to easily prevent the developer leakage due to the gap therebetween. In the above-described example, a so-called tandem type image forming apparatus has been described as an example of the image forming apparatus. However, this type of developing apparatus has a degree of freedom in the arrangement of the developing roller and the magnetic roller, and between the image carriers. The distance can be shortened, that is, the apparatus width can be made compact, and it is particularly effective when used in a tandem type image forming apparatus. However, other types of color image forming apparatuses and monochrome image forming apparatuses can be used. The same applies to the above.

  Since the current flowing between the magnetic roller and the developing roller is detected and the detection level exceeds a preset threshold level, the application of the first and second developing biases is stopped. If the threshold level is defined in accordance with the relationship between the developer leakage that occurs in the gap between the roller and the magnetic roller and the current that flows between the magnetic roller and the developing roller, the development that occurs in the gap between the developing roller and the magnetic roller As a result of reliably preventing the leakage of the agent, it can be applied to a developing device of various image forming apparatuses such as a copying machine using a two-component developer.

1 is a diagram schematically showing an example of an image forming apparatus in which a first embodiment of a developing device according to the present invention is used. FIG. 2 is a cross-sectional view illustrating an example of a developing device used in the image forming apparatus illustrated in FIG. 1. It is a figure for demonstrating operation | movement of Example 1 of the developing device by this invention. It is a figure for demonstrating the relationship between the developer leakage produced in the gap of a developing roller and a magnetic roller, and the inflow electric current value between a magnetic roller and a developing roller. It is a figure for demonstrating the control system which performs the development bias application and stop which are used with the image development apparatus shown in FIG.

Explanation of symbols

20 Image forming apparatus 21 Endless belt (conveyance belt)
22 Paper feeding cassette 23 Fixing devices 24a to 24d Developing devices 25a to 25d Supply roller (magnetic roller)
26a to 26d Developing rollers 27a to 27d Photosensitive drums 28a to 28d Chargers 29a to 29d Exposure devices 30a to 30d Transfer devices 33a and 34 Direct current (DC) bias power source 33b Alternating current (AC) bias power source 35 Paddle mixer 36 Stirring mixer 37 Partition Plate 38 ear cutting blade (layer thickness regulating blade)
41 Transformer
51 Filter / DC Amplifier 52 Controller 53 AC Generator 54 AC Amplifier

Claims (5)

A two-component developer having at least a magnetic carrier and a toner is used, and a first developing bias is applied to form a magnetic brush made of the two-component developer, and the magnetic brush is rubbed to form a second And a developing roller in which a toner thin film is formed by transferring toner from the magnetic roller in response to the second developing bias.
Detecting means for detecting a current flowing between the magnetic roller and the developing roller and outputting a detection signal;
A developing apparatus comprising: stop control means for stopping application of the first and second developing biases when a detection level indicated by the detection signal exceeds a preset threshold level.   The developing device according to claim 1, wherein the detection unit outputs a detection voltage corresponding to a current flowing between the magnetic roller and the development roller as the detection level.   The threshold level is set based on a relationship between a developer leakage generated in a gap between the magnetic roller and the developing roller and a current flowing between the magnetic roller and the developing roller. The developing device according to claim 1 or 2.   When the aging period during which the developing roller is aged by the magnetic brush has elapsed after the application of the first and second developing biases is stopped, the stop control unit sets the second developing bias to the developing roller. The developing device according to claim 1, wherein the first developing bias is applied to the magnetic roller.   The developing device according to claim 4, wherein the aging period is at least a time required for the developing roller to make a round.

Images