JP2009115862A - Developing device and electrophotographic image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact developing device with a low cost in which ripple of output fluctuation of toner density detection voltage (Vt) detecting toner density in a developing container is reduced, a difference with true toner density is small, the toner density in the developing container is held at a constant value, and toner images of high quality are formed, and also to provide an image forming apparatus provided with the developing device. <P>SOLUTION: The developing device includes: the developing container 1 for storing a developer consisting of a magnetic carrier and a toner; a conveying screw 3 for conveying the developer supplied to a developing roller by being rotatably held in the developing container; a toner density detecting means 4 for outputting as the toner density detection voltage (Vt) by detecting a mixed ratio of a carrier and toner in the developer conveyed by rotation of the conveying screw; and a scraping means 10 installed between outer peripheral parts of a screw blade 3b composing the conveying screw in order to scrape the developer in the vicinity of the toner density detecting means. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a developing device and an image forming apparatus used in an electrophotographic image forming apparatus such as a copying machine, a printer, and a facsimile machine.

In a developing device installed in an electrophotographic image forming apparatus such as a copying machine, a printer, or a facsimile machine, a developing roller, a developing sleeve, a doctor blade, and a conveying screw are installed in order to maintain the image quality output from the image forming apparatus. Control is performed to keep the toner concentration in the two-component developer in the developer container to be held at a constant value.
In Patent Documents 1 to 7, the toner concentration in the developer is detected using toner concentration detecting means that detects a change in magnetic permeability of the two-component developer composed of toner and carrier as a change in toner concentration and outputs this as a voltage value. Is disclosed, and the toner concentration of the developer in the developing container is maintained at a constant value.
Furthermore, in recent years, as image forming apparatuses such as electrophotographic copying machines have become widespread, their applications have been expanded to various types, and demands for high definition and high image quality are increasing. Therefore, since the toner can be synthesized by dispersion polymerization or the like, it is easy to manufacture, and since it is spherical, the fluidity is excellent, the variation in individual characteristics of the toner is small, and the so-called polymerization method toner in which the particle size of the toner is fine. Is used to achieve high image quality (Patent Document 8, Patent Document 9, Patent Document 10, and Patent Document 11).

By the way, generally, the toner concentration detecting means is attached to an optimum location in the developing container so that the toner concentration in the developer in the developing container can be detected accurately and stably.
When the developer that has not been sufficiently stirred is detected by this toner concentration detection means, the sensitivity of the toner concentration detection voltage (Vt) is reduced with respect to the actual toner concentration change, so that the toner concentration can be accurately controlled. Disappear.
Also, if the developer container is composed of a hard member, the predetermined mechanical accuracy is maintained, so that the screw blades of the conveying screw reach the vicinity where it does not contact the inner wall of the developer container, and the developer in the developer container is removed. It can be transported smoothly.
However, since a cheap and relatively soft material is actually used as the developing container constituent material, it tends to bend and warp, and the toner screw sticks due to contact between the conveying screw and the inner wall of the developing container. May occur.

Therefore, in order to provide a margin between the inner wall of the developing container and the screw blades of the conveying screw, a distance for avoiding contact is provided. However, when the screw blade and the container inner wall are separated from each other in this way, the conveying screw reaches only a position away from the container inner wall, and the developer near the container inner wall is stagnated.
Therefore, when the toner density is controlled by attaching the toner density detecting means to the developing container and detecting the toner density, if the mechanical accuracy such as bending of the developing container made of a soft material cannot be maintained, the detection surface A system is used in which a stirring member for sufficiently stirring the developer in the vicinity is attached to the local portion of the conveying screw so that the developer with sufficient stirring can be detected. Since the stirring member is locally fixed in a state where the range from the screw shaft of the conveying screw to the outer peripheral edge of the screw blade is filled, the amount of developer to be scraped increases.
As the stirring member for stirring the developer on the toner concentration detection surface of the toner concentration detection means, a stirring member made of a resin such as urethane and having durability and capable of stirring sufficiently without causing toner fixation was determined. Attach to the screw blades of the conveying screw under conditions.

By the way, since a new developer is conveyed by the conveying screw in the gap generated after the developer is agitated by the agitating member having a radial width extending from the screw shaft to the outer peripheral edge of the screw blade, the agitating member As a result, the developer flows not only in the part scraped by the toner but also in the developer before and after that (in the vicinity of the inner wall of the container). When the toner density around the part stirred by the stirring member is detected, an output fluctuation ripple is likely to occur in the toner density detection voltage (Vt) of the toner density detection means.
When using a toner concentration detector that outputs a low detection voltage (Vt) when the toner concentration is high and outputs a high detection voltage (Vt) when the toner concentration is low, the developer is scraped out by the stirring member. The detection voltage (Vt) is lowered immediately before the detection is performed, and the developer is not present on the detection surface immediately after being scraped, so that the detection voltage (Vt) is output high. Therefore, a large output fluctuation ripple has occurred in the toner concentration detection voltage (Vt) of the conventional developing device (see FIG. 7).

The output value from the toner density detection means is processed on the software of the image forming apparatus, and is used as a predetermined toner density detection voltage (Vt) for controlling the toner density. However, a ripple of large output fluctuation as described above occurs. Therefore, an error from the true toner density becomes large. If density control is performed based on this output value, the toner density in the developing container cannot be maintained at a constant value, which causes the quality of the formed toner image to deteriorate.
JP 2000-112221 A Japanese Patent Laid-Open No. 5-289499 JP-A-8-248774 JP 2002-296236 A JP 2002-296240 A JP 2002-296890 A JP 2002-296893 A JP 2002-244355 A Japanese Patent Laid-Open No. 5-188443 Japanese Patent Laid-Open No. 6-180512 JP 2002-328551 A

In the developing device in which the agitating member is attached to the conveying screw, since the radial width of the agitating member is large, the amount of developer scraped by the agitating member is increased, and the toner concentration at the scraped portion is detected by the toner density detecting means. When detected, a large output fluctuation ripple occurs in the toner density detection voltage (Vt), and an error from the true toner density increases, so that the toner density in the developing container cannot be maintained at a constant value, and is formed. There has been a problem that the quality of the toner image is lowered.
Therefore, an object of the present invention is to solve such problems. That is, the ripple of the output fluctuation of the toner density detection voltage (Vt) for detecting the toner density in the developing container is small and the error from the true toner density is small, and the toner density in the developing container is kept at a constant value. Another object of the present invention is to provide a compact and low-cost developing device capable of forming a high-quality toner image, and an image forming apparatus including the developing device.

In order to achieve the above object, a developing device according to a first aspect of the present invention provides a magnetic carrier in a developing device that visualizes the electrostatic latent image by supplying toner to the electrostatic latent image on the image carrier. A developing container that contains a developer composed of toner and a toner, a developing roller that is disposed in the developing container and rotates while facing the image carrier through an opening of the developing container, and supplies the toner; Toner density by detecting the mixing ratio of carrier and toner in a developer screw that is rotatably held in a developer container and conveys the developer supplied to the developing roller, and the developer conveyed by the rotation of the carrier screw A toner density detector that outputs a detection voltage (Vt), and a scraper installed between the outer peripheral portions of screw blades that constitute the conveying screw to scrape off the developer in the vicinity of the toner density detector. Ri and member, characterized by comprising a.
According to a second aspect of the present invention, in the first aspect, the magnitude of the output fluctuation of the toner density detection voltage (Vt) detected by the toner density detection means is 10% or less of the maximum value of the toner density detection voltage (Vt). As described above, the radial width of the scraping member is set.
A third aspect of the present invention is characterized in that, in the first or second aspect, the scraping member is positioned in an angle range from 0 degrees to 45 degrees with respect to the screw shaft of the conveying screw.

According to a fourth aspect of the present invention, in the first, second, or third aspect, a part of the scraping member is protruded in the outer diameter direction from the screw blade.
According to a fifth aspect of the present invention, in any one of the first to fourth aspects, an elastic body is installed on the scraping member.
A sixth aspect of the invention is characterized in that, in the fifth aspect, an elastic body provided on the scraping member is brought into contact with the developing container.
An electrophotographic image forming apparatus according to a seventh aspect of the invention includes the developing device according to any one of the first to sixth aspects.

In the first aspect of the present invention, the scraping member is disposed between the adjacent outer peripheral tips of the screw blades constituting the conveying screw, and a space is formed between the conveying screw shaft. The variation in the developer amount at the position facing the density detection means can be reduced. Therefore, the ripple of the output fluctuation of the toner density detection voltage (Vt) can be reduced, the toner density detection error in the developing container can be reduced, and the toner density can be kept constant.
According to the second aspect of the present invention, the radial width of the scraping member provided at a position facing the toner concentration detecting means in the developing container is set so that the ripple of the output fluctuation of the toner concentration detection voltage (Vt) is 10% or less. Thus, the toner concentration in the developing container can be kept constant, and a high-quality toner image can be obtained.
In the invention of claim 3, the scraping member provided between the outer peripheral tips of the screw blades is installed at an angle of 0 ° to 45 ° with respect to the screw shaft. The developer amount fluctuation at the opposite position can be reduced, and the ripple of the output fluctuation of the toner density detection voltage (Vt) can be reduced without affecting the developer transportability, and the toner density detection error in the developing container can be reduced. The toner density can be kept constant.

In the invention of claim 4, since the scraping member protrudes from the outer periphery of the screw blade between the outer peripheral tips, the toner concentration detection error due to the stay of the developer can be reduced, and the toner concentration can be kept constant. .
In the invention of claim 5, by attaching an elastic body to the scraping member, it is possible to reduce the toner density detection error due to the stay of the developer and to keep the toner density constant.
In the invention of claim 6, since the elastic body is in contact with the inner wall of the developing container, the toner concentration detection error due to the stay of the developer can be reduced, and the toner concentration can be kept constant.
According to the seventh aspect of the present invention, it is possible to obtain an excellent image quality by incorporating a developing device having the effects described in the respective claims into the image forming apparatus.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a cross-sectional view showing an internal configuration of a developing device according to an embodiment of the present invention, and FIG. 2 is an enlarged view of a main part thereof.
In an electrophotographic image forming apparatus, toner is applied from a developing device to an electrostatic latent image formed by irradiating optical image data onto an image carrier uniformly charged by a charging device. Develop by feeding. The developed image on the image carrier is transferred onto a transfer sheet by a transfer device, then fixed by a fixing device, and discharged outside the apparatus.

  The developing device 0 contains a developer including a carrier including a magnetic material and toner, and has a developing container 1 having an opening 1 a at a portion facing the image carrier 5, and is rotatably held in the developing container 1. At the same time, it contacts the surface 5a of the image carrier 5 (photoreceptor drum) facing each other through the opening 1a or rotates at the time of image formation while maintaining a minute interval to supply toner to the surface of the image carrier. A developing roller 2 for rotating, a conveying screw 3 that is rotatably held in the developing container 1 and conveys the developer supplied to the developing roller 2, a carrier and toner in the developer conveyed by the rotation of the conveying screw 3, And a toner density detecting means 4 for detecting the mixing ratio and outputting it as a toner density detecting voltage (Vt).

  The conveying screw 3 includes a screw shaft 3a and a screw blade 3b made of a thin plate that spirally protrudes around the screw shaft 3a. The screw blade 3b includes a detection surface 4a of a toner concentration detection unit. A scraping member (stirring member) 10 is fixedly arranged so that the developer located near the position can be stirred and scraped. The scraping member 10 is disposed between the outer peripheral portions of adjacent blades. As a result, the scraping member 10 is disposed only on the outer periphery of the screw blade, and a space (developer flow space) is formed between the scraping member 10 and the screw shaft 3a. The developer passes through the void, and the amount of developer scraped off by the scraping member is reduced. On the other hand, only the developer in the vicinity of the detection surface can be sufficiently stirred, and the concentration of the developer that has been sufficiently stirred can be detected.

In the present invention, the ripple magnitude (Vtr) of the output fluctuation of the toner density detection voltage (Vt) detected and output by the detection surface 4a of the toner density detection means 4 further corresponds to the toner density detection voltage (Vt). By setting the radial dimension (width) of the scraping member 10 to the optimum value H so as to be 10% or less of the maximum value (Vt0), the toner concentration detection voltage (Vt of the detection surface 4a of the toner concentration detection means 4 is set. ) Output fluctuation ripple is small and the error with the true (real) toner density at the time of detection is reduced, and the toner density in the developing container 1 is kept at a constant value, so that a high-quality toner image is formed. Is done. That is, since the density value corresponding to the actual toner density can always be detected, toner density control (adjustment of toner supply amount) performed based on this density value can be accurately performed.
Further, the toner contained in the developer accommodated in the developing container 1 is synthesized by dispersion polymerization or the like and is spherical, so that it has excellent fluidity, little variation in individual characteristics of the toner, and an average particle diameter of 4 μm to 8 μm. By using a small particle size toner, it is possible to obtain a high quality toner image.

  In the toner concentration detection means 4 using the magnetic permeability detection method, there is a theory that the ease of movement of the developer, that is, the fluidity of the developer contributes to the maintenance of detection accuracy. Instead, the substance is actually detecting the distribution of the magnetic material, such as a large or small number of carriers. The toner concentration detection means 4 detects the location in the developing container 1 where the developer is agitated and the distribution changes significantly, but the scraping member 10 installed on the conveying screw 3 is displaced to the outer periphery of the screw blade 3b. Since it is arranged locally and the radial width H is made as narrow as possible, the space generated on the opposite side in the rotational direction (the space formed after stirring the developer by the scraping member) can be reduced, and the toner concentration The ripple of the output fluctuation of the detection voltage (Vt) does not increase. Further, since a space through which the developer passes is formed between the scraping member 10 and the screw shaft 3a, the amount of developer scraped by the scraping member is reduced, and an error associated with toner density detection is eliminated. be able to.

Next, FIG. 3 is a diagram showing a specific configuration example of the scraping member 10 in the developing device of the present invention, and the outer peripheral edge of the blade 3b of the conveying screw corresponding (facing) to the detection surface 4a of the toner concentration detection means 4 By disposing the scraping member 10 installed along the screw shaft 3a in parallel (at 0 degree) with the screw shaft 3a of the conveying screw 3, it is possible to detect without reducing the developer conveying speed.
Next, FIG. 4 is a diagram showing another specific configuration example of the scraping member 10 in the developing device of the present invention, and the outside of the conveying screw blade 3b corresponding to (facing to) the detection surface 4a of the toner concentration detection means 4. By disposing the scraping member 10 installed along the periphery within the range of 0 ° to 45 ° with respect to the screw shaft 3a, it is possible to detect without reducing the developer conveyance speed.
As described above, in the present invention, the scraping member 10 is interposed between the outer peripheral tips of the two screw blades adjacent to each other among the screw blades 3b constituting the conveying screw 3 (the space between the screw shafts). Therefore, the developer amount fluctuation at the position facing the detection surface 4a of the toner density detection means can be reduced. For this reason, the ripple of the output fluctuation of the toner density detection voltage (Vt) accompanying the rotation of the conveying screw can be reduced, the toner density detection error in the developing container can be reduced, and the toner density can be kept constant.

Next, FIG. 5 is a diagram showing another configuration example of the scraping member. In this example, the outer diameter side end portion of the scraping member 10 is only a width H1 than the outer peripheral edge of the screw blade 3b of the conveying screw. By projecting toward the outer diameter side, the clearance between the conveying screw 3 and the inner wall 1b of the developing container 1 is reduced, and the stay of the developer at this portion is prevented. For this reason, detection accuracy can be further improved.
Next, FIG. 6 is a figure which shows the other structural example of a scraping member, and in this example, the mylar etc. which consist of the elastic body 15 is installed in the scraping member 10, and a part of elastic body 15 is outside diameter. By projecting to the side, the clearance between the conveying screw 3 and the inner wall 1b of the developing container 1 can be reduced, and the retention of the developer at this portion can be further prevented to improve the detection accuracy. As shown in the figure, the tip of the elastic body 15 may be brought into sliding contact with the inner wall of the developing container to eliminate the clearance.

FIG. 2 is a cross-sectional view illustrating an internal configuration of a developing device according to an embodiment of the present invention. It is a principal part enlarged view of FIG. It is a figure which shows the specific structural example of the scraping member in the image development apparatus of this invention. It is a figure which shows the other specific structural example of the scraping member in the image development apparatus of this invention. It is a figure which shows the other structural example of a scraping member. It is a figure which shows the other structural example of a scraping member. It is a figure which shows the state in which the ripple of an output fluctuation has generate | occur | produced in the toner density detection using the conventional toner density | concentration detection means.

Explanation of symbols

DESCRIPTION OF SYMBOLS 0 ... Developing apparatus, 1 ... Developing container, 1a ... Opening part, 2 ... Developing roller, 3 ... Conveying screw,
3a ... screw shaft, 3b ... screw blade, 4 ... toner density detecting means, 4a ... detection surface, 5 ... image carrier, 5a ... surface, 10 ... scraping member, 15 ... elastic body.

Claims (7)

  In a developing device that supplies toner to an electrostatic latent image on an image carrier to visualize the electrostatic latent image, a developing container that contains a developer made of a magnetic carrier and toner, and the developer container A developing roller that is disposed and rotates while facing the image carrier through the opening of the developing container to supply toner, and a developer that is rotatably held in the developing container and supplied to the developing roller A toner screw for detecting the toner density detection voltage (Vt) by detecting the mixing ratio of the carrier and the toner in the developer conveyed by the rotation of the screw, and the toner density detection A developing device comprising: a scraping member installed between the outer peripheral portions of the screw blades constituting the conveying screw in order to scrape off the developer in the vicinity of the means.   The radial width of the scraping member so that the output fluctuation of the toner density detection voltage (Vt) detected by the toner density detection means is 10% or less of the maximum value of the toner density detection voltage (Vt). The developing device according to claim 1, wherein   The developing device according to claim 1, wherein the scraping member is positioned in an angle range of 0 to 45 degrees with respect to the screw shaft of the conveying screw.   4. The developing device according to claim 1, wherein a part of the scraping member is protruded in an outer diameter direction from the screw blade.   The developing device according to claim 1, wherein an elastic body is installed on the scraping member.   The developing device according to claim 5, wherein an elastic body installed on the scraping member is brought into contact with the developing container.   An electrophotographic image forming apparatus comprising the developing device according to claim 1.

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