JPH11109750A - Developing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely prevent developer from rotating with a developing roller so as to prevent trouble such as stick and stain with developers, the lowering of image density, void or the drop of developer by making a scraper abut on the surface of a developing sleeve at the end of the developing roller, and to prevent trouble such as the breakage of the scraper and the rupture of the developing roller by the wear of the scraper and the developing sleeve caused by their abutting in a developing device using two-component developer. SOLUTION: This developing device is equipped with the developing roller 103 constituted of a magnet roller 103b having plural magnetic poles and the developing sleeve 103a including the magnet roller and constituted of a rotatable nonmagnetic cylinder, and the two-component developer consisting of carrier and toner for development is used in the device. The device is equipped with the scraper members 106 abutting on the surface of the developing sleeve at both ends of the developing roller, and the member 106 abuts on the surface of the developing sleeve at a part where magnetic force is the weakest out of plural magnetic poles of the magnet roller.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device in an image forming apparatus such as a copying machine, a facsimile, and a printer, and more particularly, to a magnetic brush developing system using a two-component developer.

[0002]

2. Description of the Related Art Conventionally, as a developing device used in an electrophotographic image forming apparatus such as a copying machine, a facsimile, a printer, etc., a magnet roller having a plurality of magnetic poles and a rotatable non-magnetic material including the magnet roller are included. 2. Description of the Related Art A developing device that performs magnetic brush development using a two-component developer with a developing roller configured by a developing sleeve formed of a cylindrical body is known. Since the above magnet roller usually has the property that the magnetic flux density at both ends is large,
In a general developing device of the type in which the developer is agitated and supplied substantially uniformly over the entire width of the developing roller from a direction orthogonal to the rotation axis direction of the developing roller, the amount of the developer attached to both ends of the developing roller (magnetic (The height of the brush ears) becomes larger than the other parts, and the developed image density becomes uneven at both ends and the center in the width direction, and the developer spills from both ends of the developing roller. There was a problem to do. In order to solve these problems, conventionally, a magnet provided with a soft magnetic material made of ferrite or the like at both ends of the magnet roller (JP-A-62-264078), or made of iron or magnetic stainless steel is used. A device provided with a magnetic metal plate (Japanese Utility Model Laid-Open No. 5-48303) has been proposed.

In recent years, with the miniaturization of the image forming apparatus, each unit has been required to be light and light and small. In a developing apparatus using a two-component developer, how the supplied toner is reduced in a small space. The problem is how to stir and charge sufficiently. For this reason, a developing device in a recent small machine usually has a method in which a plurality of developer conveying members for stirring and conveying the developer along a rotation axis direction are provided, and it takes a little more time to charge the toner. Is adopted. Further, in this type of developing device, the developing roller also has a small diameter, so that a new problem arises. That is, the developing roller using the two-component developer is supplied from the developer stirring member in order to develop the electrostatic latent image formed on the photoreceptor by the toner, which is a colored charged powder in the developer. In order to pump the developer to the developing sleeve and to replace the spent toner on the developing sleeve with new developer, the magnet roller has a low magnetic flux density (magnetic force) called the running-out pole. In addition, a function of releasing used developer from the developing roller is required.

[0004] Here, the electrode running out may be the same as or different from the preceding and following poles as long as the developing roller has a large diameter and the absolute value of the magnetic flux density is low. However, in the case of a small-diameter developing roller, the gap between the electrode running out and the preceding and succeeding poles becomes narrower. , And the same developer always rotates. For this reason, in such a small-diameter developing roller, the developer on the developing sleeve is not replaced forever, and the toner concentration of the developer on the developing roller is reduced, resulting in a problem such that an image becomes white.

Therefore, it is necessary to reduce the magnetic flux density of the developing roller having a small diameter in the developing roller, which has the same polarity as the preceding and following poles in accordance with the miniaturization of the developing device. However, if the small-diameter developing roller has the same run-out pole as the preceding and following poles, the magnetic flux density at both ends of the magnet roller becomes high, and the above-described developer rotation at both ends of the developing roller is caused. A phenomenon occurs, and the toner concentration of the developer at both ends of the developing roller is reduced, resulting in a problem such that an image at both ends becomes white.

In this case, even when the phenomenon of rotation of the developer occurs, it does not mean that 100% of the developer on the developing roller is not replaced. Therefore, the rotating shaft of the developing roller is used as in a general developing device. If the developer having a sufficient toner concentration can be stirred and supplied substantially simultaneously with respect to the entire width of the developing roller from a direction perpendicular to the direction, there is no problem. However, in a small-sized developing device of a type in which the developer is agitated and transported along the rotation axis direction of the developing roller, the exchange rate of the developer on the upstream side of the developer transport path is relatively high,
Since the developer exchange rate on the downstream side of the developer transport path is significantly reduced, as described above, when the phenomenon of the developer rotating at both ends of the developing roller occurs, the developing roller moves along the developer transport path. There has been a problem that the toner concentration of the developer at the downstream end becomes extremely low, and the corresponding image at the end becomes white.

Accordingly, the present inventors have previously found that the toner concentration of the developer at both ends of the developing roller is reduced due to the entrainment phenomenon of the developer generated at both ends of the developing roller, and that the images at both ends are blank. For the purpose of eliminating the disadvantages such as becoming, a magnet roller having a plurality of magnetic poles and a developing sleeve including the magnet roller constitute a developing roller, and are arranged along the rotation axis direction of the developing roller. Proposed that a developer is circulated and conveyed by a plurality of developer agitating members, and a means for promoting replacement of the developer is provided at an appropriate position of the developing roller (Japanese Patent Application No. 8-68231).
issue). As means for promoting the replacement of the developer,
It is only necessary that the used developer on the developing roller can be released at the developer exhausting pole of the developing roller. For example, (1) a magnetic material that reduces the magnetic flux density of the developing roller is appropriate, and A magnetic body is provided at a downstream end of a developer transport path circulated and transported by a stirring member close to the developing roller. Also,
(2) Means for facilitating replacement of the developer by mechanically scraping off the developer on the developing roller is also effective, and the end of the developing roller is brought into contact with or near the peripheral surface of the end. Then, a scraper for scraping off the developer on the peripheral surface of the end portion is provided.

[0008]

In a developing device for performing magnetic brush development using a two-component developer, as described above, if the developing roller has a small diameter, the magnetic force at the end of the developing roller increases, and the developer is attracted. Rotation occurs, causing problems such as a decrease in image density and white spots. Further, since the end portion of the developing roller has a high magnetic force, the amount of the developer conveyed to the surface of the developing roller (the surface of the developing sleeve) also increases. The adhering developer goes further to the end of the developing roller in search of an escape place. That is, the developer tends to spread out of the magnetized region in the longitudinal direction of the developing roller. It is good that the developer is retained under the influence of the magnetic force from the developer in the magnetized area, but it gradually separates with time and is pushed to the end of the developing roller, and this is in a range where the magnetic force does not reach If it spreads, it will lead to the developer dropping at the end. Therefore, it is better to scrape off excess developer conveyed at the end of the developing roller. For this purpose, it is more effective to scrape off the developer on the sleeve surface with a scraper as in the means (2) than in the above-mentioned prior application (1). It is.

However, when the scraper is brought into contact with the developing roller, the scraper gradually wears and breaks, causing the scraper to lose its function. On the other hand, the developing sleeve surface is worn to break the developing roller. Happens. The developing sleeve is usually made of a metal such as aluminum, and the scraper may be any flexible member. However, if the scraper is made of the same metal, the sleeve surface is easily shaved. When the developing sleeve is scraped, the gap between the developing roller and the photoreceptor (developing gap: Gp) and the gap between the developing roller and the doctor blade (doctor gap: Gd), as well as the breaking of the developing roller.
This must be avoided because it spreads and causes various problems. Therefore, a resin (for example, PET or the like) is suitable for the scraper. Then, since the scraper is more vulnerable to wear, the scraper will be worn first. To prevent the scraper from being damaged, it is possible to control the material and thickness, the pressing force against the surface of the developing sleeve, and the like.

However, this alone does not solve the problem of wear. Since the scraper is designed to forcibly scrape off the developer adhering to the developing roller by magnetic attraction, a small amount of small developer (wedge) is formed at the contact portion between the developing sleeve surface and the scraper. Gap)
Get into it. The developer only needs to pass through the scraper abutment as it is, but a small amount of the developer is held in place by the pressing force of the scraper, and this becomes a polishing agent and a new type of abrasive is used to scrape the surface of the developing sleeve. Problems arise. For this reason, even if the scraper is not damaged, and even if the surface of the developing sleeve is not scraped by the scraper itself, this another polishing operation gradually proceeds, and eventually the developing roller is broken.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and in a developing apparatus using a two-component developer, a scraper is brought into contact with the surface of a developing sleeve to surely eliminate the accompanying rotation of the developer so that the image density is reduced. While preventing the occurrence of problems such as dropping, white spots, and developer drop, its function is to prevent the scraper and the developing sleeve from being worn due to contact, thereby causing the scraper to break and the developing roller to break. The purpose is to maintain.

[0012]

In order to achieve the above object, the invention according to claim 1 is directed to a developing device comprising a magnet roller having a plurality of magnetic poles and a rotatable non-magnetic cylindrical body including the magnet roller. A developing device using a two-component developer comprising a carrier and a toner for development, comprising a scraper member in contact with the surface of the developing sleeve at both ends of the developing roller; The member is brought into contact with a portion having the lowest magnetic force among the plurality of magnetic poles of the magnet roller. As described above, in the developing device according to the first aspect, the developer at the end of the developing roller is scraped off by using the scraper member, so that the entrainment of the developer can be reliably eliminated, and the image density is reduced due to the entrainment and white spots are generated. Since the scraper member is brought into contact with a relatively low magnetic force portion where the developer is not easily held, it is possible to reduce the embrace of the developer due to the pressing force of the scraper member as much as possible. it can.

According to a second aspect of the present invention, there is provided a developing roller including a magnet roller having a plurality of magnetic poles, and a developing sleeve formed of a rotatable non-magnetic cylindrical body including the magnet roller. In a developing device using a two-component developer composed of a carrier and a toner, a scraper member is provided at both ends of the developing roller, which is in contact with the surface of the developing sleeve, and a contact portion of the scraper member with the developing sleeve is a part of the developing roller. It is characterized by being arranged obliquely with respect to the rotation axis. As described above, in the developing device according to the second aspect, the developer at the end of the developing roller is scraped off by using the scraper member, so that the entrainment of the developer can be reliably eliminated, and the image density is reduced due to the entrainment and white spots are generated. And the like, and the contact of the scraper member is inclined with respect to the rotation axis of the developing roller, so that the developer can flow along the contact portion, and the developer at the contact portion can flow. Since the stagnation can be reduced, it is possible to reduce the possibility that the developer enters the gap formed between the scraper member and the surface of the developing sleeve and is held.

According to a third aspect of the present invention, there is provided a developing roller comprising a magnet roller having a plurality of magnetic poles, and a developing sleeve made of a rotatable non-magnetic cylindrical body including the magnet roller. In a developing device using a two-component developer composed of a carrier and a toner, a scraper member is provided at both ends of the developing roller, which comes into contact with the surface of a developing sleeve, and the scraper member vibrates minutely to periodically apply a contact pressure. It is characterized by having changed to. As described above, in the developing device according to the third aspect, the developer at the end of the developing roller is scraped off by using the scraper member, so that the rotation of the developer can be reliably eliminated.
Problems such as reduced image density and white spots caused by entrainment can be eliminated, and a small vibration is applied to the scraper member to change the pressing force on the developing sleeve. The developer can be passed when the pressing force is weak, and the trapping of the developer by the scraper member can be eliminated.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail based on illustrated embodiments.

(Embodiment 1) FIG. 1 is an explanatory view of the structure of a developing device according to an embodiment of the present invention, wherein (a) is a sectional view of the developing device, and (b) is a developing roller from the stirring roller side. FIG. 3C is a front view of the unit when the unit is viewed, and FIG. In FIG. 1, reference numeral 101 denotes a photosensitive drum;
Is a developing roller unit, 103 is a developing roller composed of a magnet roller 103b having a plurality of magnetic poles fixed to a shaft 103c, and a developing sleeve 103a made of a rotatable non-magnetic cylinder enclosing the magnet roller 103b. Reference numeral 104 denotes a doctor blade that regulates the amount of developer (height of the magnetic brush) carried and conveyed on the developing sleeve 103a, 105 denotes a development entrance seal for preventing toner from scattering, and 106 denotes both ends of the developing roller 103. A scraper member (hereinafter, referred to as a scraper) provided in the section and abutting against the surface of the developing sleeve, 107 is a holding member for the developing entrance seal 105 and the scraper 106, 110 is a developing hopper storing developer, and 108a and 108b are developing A stirring roller for mixing the toner and the carrier in the hopper 110; A partition plate for partitioning the image hopper 110, 1
Reference numeral 11 denotes a case which also serves as a housing for the developing hopper 110 and the developing device. A portion 112 is a developing gap G which is a gap between the photosensitive drum 101 and the developing roller 103.
A portion p and 113 is a doctor gap Gd which is a gap between the developing roller 103 and the doctor blade 104.

FIG. 2 is an explanatory view of the structure and magnetic force distribution of the magnet roller inside the developing roller. As shown in FIG. 2A, the magnet roller 103b inside the developing roller has a magnet (permanent) having a plurality of magnetic poles. ), And each magnet piece has a role at each position, so that the magnitude of the magnetic force differs. That is, FIG.
The magnet roller 103 inside the developing roller 103 shown in FIG.
2B, each of the magnet pieces is referred to as P1 to P6 as shown in FIG. 2A. For example, P5 pumps up the developer and holds it on the developing sleeve 103a. 500-6 to do
A magnetic force of 00 [gauss] is given, and P1 is even stronger 80 so that the ears of the magnetic brush stand sufficiently in the developing gap Gp.
The magnetic force P4 of 0 to 900 [gauss] is set to 0 to 5 so that the developer used for the development is returned to the inside of the developing hopper 110 and easily separated from the developing roller in order to be mixed with the toner again.
For example, a magnetic force of 0 [gauss]. FIG. 2B illustrates the magnitude (magnetic force distribution) of the magnetic force generated by each of the magnet pieces.

In the case of a small-diameter developing roller, FIG.
As shown in (d) (magnetic force distribution in the roller axis direction by each magnet piece), the magnetic force at the roller end tends to increase, and the magnetic force (magnetic force distribution at the roller end) as viewed in cross section at that portion is shown in FIG. 2 (c). As can be seen by comparing FIGS. 2B and 2C, the magnetic force is generally increased and the magnetic force of the P4 pole is also high, so that the developer is separated from the developing roller 103 at the end of the developing roller 103. I will be taken around without it. Since this causes some problems as described in the above-mentioned problem, it is effective to provide the scrapers 106 at both ends of the developing roller 103.

In the case of the layout as in the embodiment shown in FIG. 1, the contact position of the scraper 106 is designated by the reference numeral 30 shown in FIG.
1 can be placed anywhere, but if it is placed in contact with a place where the magnetic force is relatively high, it is difficult to scrape off the developing roller 103 because the developing roller 103 has a strong force to hold the developer. Here, FIG. 4 is an enlarged drawing of the contact portion of the scraper. However, since the developer is very small, the portion that cannot be scraped enters the wedge portion 401 in the drawing. Then, it is sufficient that the entered developer passes through the abutting portion 402 as it is, but some of the developer is held by the abutting portion 402 by the pressing force of the scraper 106, and this becomes an abrasive and the developing agent becomes This will cut the sleeve surface.

Therefore, in the invention of claim 1, the scraper 1
The contact portion 06 is placed in a portion where the magnetic force of the developing roller 103 is relatively low, that is, in the range of reference numeral 302 shown in FIG. The range of reference numeral 302 shown in FIG.
This is the range 201 of (c), which is the P4 pole portion where the magnetic force is weak. The magnetic force at the end of the developing roller is increased as a whole. Among them, P4 pole originally has a low magnetic force.
The end portion of the developing roller also has the lowest magnetic force. Therefore, if the scraper 106 is brought into contact with this portion, the scraping of the developer from the developing roller (the surface of the developing sleeve) is facilitated as compared with the case where the scraper 106 is brought into contact with another portion, and the scraper 106 is held at the contact portion. Developer can be reduced as much as possible, which in turn reduces wear on the developing sleeve,
The worst case of breakage of the developing roller 103 can be prevented and the function can be maintained.

(Embodiment 2) FIG. 5 is an explanatory view of the structure of a developing device according to a second embodiment of the present invention, and is a front view when the developing roller unit is viewed from the stirring roller side. The basic configuration of the developing device is the same as that shown in FIG. 1. In FIG. 5, reference numeral 503 denotes a developing roller, and 506 denotes a scraper. While obliquely with respect to the rotation axis of the developing roller 503.

FIG. 6 is a view showing the shape of the contact portion of the scraper with the developing roller and the flow of the developer by changing the shape of the contact portion of the scraper. The part corresponding to the left end is depicted), FIG.
In FIG. 6A, the contact portion of the scraper 506 'is parallel to the rotation axis of the developing roller 503. In such a case, as shown by an arrow in FIG. The developer that stays at the abutting portion and does not run on the scraper 506 ′ seeks an escape area and the scraper 506 ′
In the wedge-shaped gap (see FIG. 4).
Therefore, if the contact portion of the scraper 506 is inclined as in the present embodiment, the developer that is scraped off can flow as shown in FIG. 6B, so that the stagnation is reduced, and the developer entering the wedge is reduced as much as possible. be able to. Therefore, the amount of the developer caught in the scraper 506 is reduced, and the wear of the developing sleeve can be suppressed. Therefore, the worst case of the breakage of the developing roller 503 can be prevented and the function can be maintained.

Although the contact portion of the scraper is inclined, if the contact portion of the scraper is inclined toward the end of the developing roller like the contact portion of the scraper 506 "shown in FIG. The developer flows toward the end of the developing roller 503, and the amount of the developer toward the end is increased, thereby causing “end developer drop” or the like. Obviously, it is better to be inclined toward the center of the developing roller as in b).

(Embodiment 3) FIG. 7 is an explanatory view of the structure of a developing device according to a third embodiment of the present invention, in which (a) is a sectional view of a main part showing a developing roller unit of the developing device. b)
FIG. 4 is a front view when the developing roller unit is viewed from the stirring roller side. The basic configuration of the developing device is the same as that of FIG. 1. In FIG. 7, reference numeral 702 denotes a developing roller unit, 703 denotes a developing roller, and 706 denotes a scraper. Further, members 7 provided at both ends of the developing roller 703 are provided.
Reference numeral 12 denotes a cam, which rotates together with the developing roller 703.
When the developing roller 703 rotates, a protrusion 713 of the cam 712 is formed.
Pushes up the scraper 706 and gives the scraper 706 a minute vibration. The height of the projection is set such that the contact portion of the scraper 706 does not completely separate from the surface of the developing sleeve when the projection pushes up the scraper 706. By doing so, the scraper 706
Even when the contact portion is parallel to the rotation axis of the developing roller 703, when the scraper 706 vibrates minutely, the pressing force of the scraper 706 against the developing sleeve 703a changes periodically. The developer held in the contact portion can be passed when the pressing force is weak. Therefore, in this embodiment, the scraper 70
6 can be eliminated and the surface of the developing sleeve 703a can be prevented from being scraped, so that the worst case of breakage of the developing roller 703 can be prevented and the function can be maintained.

[0025]

As described above, in the developing device of the first aspect, the developer at the end of the developing roller is scraped off by using the scraper member, so that the entrainment of the developer can be eliminated without fail. In addition to eliminating the disadvantages such as image density reduction and white spots caused by the above, the scraper member is brought into contact with a relatively low magnetic force portion where the developer is not easily held, so that the developer is pressed by the scraper member. Hugging can be reduced as much as possible. Therefore, the wear of the developing sleeve surface due to the holding of the developer can be minimized, and the functions of the scraper member and the developing roller can be maintained.

In the developing device according to the second aspect, the developer at the end of the developing roller is scraped off by using a scraper member, so that the entrainment of the developer can be reliably eliminated, and the image density is reduced due to the entrainment, white spots, etc. In addition, since the contact of the scraper member is inclined with respect to the rotation axis of the developing roller, the developer can flow along the contact portion, and the stagnation of the developer at the contact portion can be prevented. Therefore, it is possible to reduce the possibility that the developer enters and is held in the gap formed between the scraper member and the surface of the developing sleeve. Therefore, the wear of the developing sleeve surface can be suppressed, so that the functions of the scraper member and the developing roller can be maintained.

In the developing device according to the third aspect, the developer at the end of the developing roller is scraped off by using the scraper member, so that the entrainment of the developer can be eliminated without fail, and the image density is reduced due to the entrainment, white spots, etc. In addition to the fact that the pressing force applied to the developing sleeve is changed by applying a slight vibration to the scraper member, the developer held by the scraper member at the time of strong pressing force is passed when the pressing force is weak. And the developer can be prevented from being caught by the scraper member. Therefore, since the surface of the developing sleeve can be prevented from being polished, the functions of the scraper member and the developing roller can be maintained.

[Brief description of the drawings]

FIGS. 1A and 1B are explanatory diagrams of a configuration of a developing device according to an embodiment of the present invention, wherein FIG. 1A is a cross-sectional view of the developing device, and FIG. Figure,
(C) is a sectional view of the developing roller.

FIG. 2 is an explanatory diagram of a configuration and a magnetic force distribution of a magnet roller inside a developing roller shown in FIG.

FIG. 3 is a diagram for explaining a contact position of a scraper with respect to a developing roller, and is a cross-sectional view of a developing roller unit of the developing device.

FIG. 4 is an enlarged cross-sectional view of a main part showing a contact portion of a scraper with a developing roller.

FIG. 5 is an explanatory diagram of a configuration of a developing device according to an embodiment of the present invention, and is a front view when the developing roller unit is viewed from a stirring roller side.

FIG. 6 is a diagram showing the shape of the contact portion of the scraper with the developing roller and the flow of the developer by changing the shape of the contact portion of the scraper.

FIGS. 7A and 7B are explanatory views of a configuration of a developing device according to an embodiment of the present invention, wherein FIG. 7A is a cross-sectional view of a main part showing a developing roller unit of the developing device, and FIG. FIG. 5 is a front view when the developing roller unit is viewed.

[Explanation of symbols]

 101: photosensitive drums 102, 702: developing roller units 103, 503, 703: developing rollers 103a, 503a, 703a: developing sleeve 103b: magnet roller 103c: shaft 104: doctor blade 105: developing entrance seals 106, 506, 706: Scraper member 107: holding members 108a, 108b: stirring roller 109: partition plate 110: developing hopper 111: case 712: cam 713: cam projection

Claims (3)

[Claims] A magnet roller having a plurality of magnetic poles;
A developing device comprising: a developing sleeve formed of a rotatable non-magnetic cylindrical body enclosing the magnet roller; and a developing device using a two-component developer including a carrier and a toner for development. The developing device further comprises a scraper member abutting on a surface of the developing sleeve, and the scraper member is abutted on a portion having the lowest magnetic force among a plurality of magnetic poles of the magnet roller. 2. A magnet roller having a plurality of magnetic poles,
A developing device comprising: a developing sleeve formed of a rotatable non-magnetic cylindrical body enclosing the magnet roller; and a developing device using a two-component developer including a carrier and a toner for development. The developing device further comprises a scraper member that contacts the surface of the developing sleeve, and a portion of the scraper member that contacts the developing sleeve is disposed obliquely with respect to the rotation axis of the developing roller. 3. A magnet roller having a plurality of magnetic poles,
A developing device comprising: a developing sleeve formed of a rotatable non-magnetic cylindrical body enclosing the magnet roller; and a developing device using a two-component developer including a carrier and a toner for development. A developing device provided with a scraper member in contact with a surface of the developing sleeve, the contact pressure being periodically changed by minute vibration of the scraper member.