JPH02219076A - dry developing device - Google Patents

Abstract

PURPOSE:To prevent toner from firmly sticking to a developing sleeve by providing a driving means so that a magnetic pole positioned roughly opposite to a latent image carrier can reciprocate either close to or apart from the latent image carrier, and fixing and arranging magnetic poles other than the magnetic pole. CONSTITUTION:The magnet P1 is provided in a position facing a photosensitive body 1, is independent of a magnet holder 3, and reciprocates in the normal direction of the peripheral surface of the developing sleeve 2. The other magnets P2 to P5 are fixed on the magnet holder 3. When the magnet P1 moves to position apart from the photosensitive body 1, a flux density on the surface of the developing sleeve 2 changes, whereby the napping height of a magnetic brush formed by the magnet P1 and the napping width in the circumferential direction of the developing sleeve 2 are minimized. Therefore, developer which shifts as if it follows an image trailing edge part L2 is separated from the surface of the photosensitive body 1 to reduce the influence of a reverse electrical field upon toner grains on carrier particles. Thereby, toner can be prevented from being fused on the developing sleeve and from firmly sticking thereto.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention provides a non-magnetic developing sleeve that is placed opposite to a latent image carrier and is rotationally driven, and a plurality of non-magnetic developing sleeves arranged in the circumferential direction inside the developing sleeve. A two-component developer is supported and conveyed by magnetic force on the circumferential surface of the developing sleeve, and the electrostatic latent image formed on the latent image carrier is visualized by the developer. In a dry developing device, in a developing area where a latent image carrier and a developing sleeve face each other, toner particles in the developer are placed between the electrostatic latent image of the latent image carrier and the developing sleeve on the side of the latent image carrier. An electric field is formed in a direction that pulls the L-ner particles in the developer toward the developing sleeve, and an electric field is formed between the background area other than the electrostatic latent image and the developing sleeve. The present invention relates to a dry developing device in which a bias voltage is applied to a developing sleeve and the developer moves relative to the surface of a latent image carrier in the developing region.

[Conventional technology]

2. Description of the Related Art Dry developing devices of the above type used in image forming apparatuses such as electronic copying machines, printers, and facsimile machines are well known.

In this type of developing device that uses a two-component developer consisting of a magnetic carrier and toner, a magnetic pole (main pole or A magnetic brush of developer is formed by the developing pole (also called a developing pole), thereby visualizing the electrostatic latent image formed on the latent image carrier. That is, development is performed by transferring the toner in the two-component developer to the latent image.

[Problems to be Solved by the Invention] However, according to this type of developing device, white color generally appears at the edge of a line image that is not parallel to the direction of developer movement on the development sleeve or a solid image in the direction of developer movement. There is a problem in that a missing part of the image, called a missing part, is created, and the image quality is degraded due to this.

In order to eliminate or suppress the above-mentioned problems, it is advantageous to rotate not only the developing sleeve but also the plurality of magnetic poles inside it in the circumferential direction of the sleeve. It is desirable to rotate at high speed.

However, when the magnetic pole within the developing sleeve is rotated, an eddy current is generated in the conductive developing sleeve, causing the sleeve to generate heat. Regarding this point, rJournal of the Japanese Society of Applied Magnetics J VO
L, 4 No. 4, 1981, page 140. When the developing sleeve heats up like this,
A problem arises in that the toner particles in the two-component developer supported by this melt and adhere to the surface of the developing sleeve over time.

An object of the present invention is to provide a developing device of the type described at the beginning, which can effectively suppress the phenomenon of white spots on images while preventing toner from sticking to the developing sleeve.

[Means to solve the problem]

In order to achieve the above object, the present invention provides that, among the magnetic poles located in the developing sleeve, the magnetic pole located at a position substantially facing the latent image carrier is reciprocated in a direction toward or away from the latent image carrier. A driving means is provided to drive this so that the
We propose a configuration in which magnetic poles other than this magnetic pole are fixedly arranged.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings, and the causes of the above-mentioned white spots will be explained in detail with reference to one drawing.

In FIG. 1, the reference numeral 1 indicates a drum-shaped photoreceptor, which is an example of the configuration of a latent image carrier, and a dry developing bag @100 is disposed opposite to the photoreceptor 1. As shown in FIG.

The developing device 100 has a developing sleeve 2 that is rotated and opened in one counterclockwise direction, and the sleeve 2 is disposed facing the photoreceptor 1 with a predetermined gap therebetween. The developing sleeve 2 is made of non-magnetic and conductive material such as aluminum or stainless steel.

The developing sleeve 2 of the developing device 100 contains a two-component developer consisting of a magnetic carrier and a toner, as indicated by diagonal lines, and the toner and carrier are mixed in a predetermined ratio. The developer is stirred by a paddle wheel (not shown) and supplied to the circumferential surface of the developing sleeve 2 . It is well known that toners include toners consisting only of toner particles and toners to which additives are added.

Inside the developing sleeve 2, a plurality of magnets P to Ps, in the example shown in FIG. 1, are arranged in the circumferential direction of the developing sleeve 2 so as to face the inner circumferential surface thereof. The magnetic poles S and N of each magnet facing the developing sleeve 2 are set as illustrated in the figure, and among these, the magnet P1 facing the photoreceptor 1
The magnetic pole is called the developing pole or main pole.

Note that this magnetic pole may be completely opposed to the photoreceptor 1, or may be arranged with a slightly shifted position in the circumferential direction of the developing sleeve 2. In any case, the magnetic pole of the magnet P1 facing the photoreceptor 1, that is, the main pole, is located substantially opposite the photoreceptor 1.

With respect to the magnet P, other magnets P2 to P5 are fixed to the magnet holder 3 at intervals as shown in the figure. The developing sleeve 2 is rotatably driven in the direction of the arrow as described above.
Ps is held in a non-rotating state.

As the developing sleeve 2 rotates in the direction of the arrow, the two-component developer (hereinafter simply referred to as developer) D supplied to the developing sleeve 2 is magnetically attracted by the magnetic field of each magnet and developed. It is carried in the direction of rotation while being carried on the circumferential surface of the sleeve.

A doctor blade 5 is disposed on the sleeve surface between the magnets P4 and P so as to closely face each other, thereby scraping off excess of the carried developer and adjusting the conveyance amount to be suitable for development. Regulated.

When the developer regulated in this manner is conveyed close to the magnet P1, the developer becomes brush-shaped by the magnetic force of the magnet P2, forming a magnetic brush of the developer.

On the other hand, the photoreceptor 1 is rotatably driven in the direction of the arrow, and an electrostatic latent image is formed on the surface of the photoreceptor 1 by a latent image forming means (not shown).

The photoreceptor 1 passes through the magnetic brush formed by the magnet P1 as described above, that is, the development area A, and at this time, the magnetic brush is rubbed against the electrostatic latent image on the photoreceptor 1, and the developing image forming the brush is The toner in the agent electrostatically transfers to a latent image, making this electrostatic latent image visible.

A bias voltage having an absolute value higher than the surface potential of the background portion other than the electrostatic latent image on the photoreceptor 1 is applied to the developing sleeve 2 by the power supply 101. -For example,
The average surface potential of the electrostatic latent image formed on the photoreceptor 1 is −
When the average surface potential of the background portion is -100V, a bias voltage of -300V is applied to the developing sleeve 2. In this example, the toner particles and carrier particles in the developer are charged by friction, so that the toner particles are charged with positive polarity and the carrier particles are charged with negative polarity, and the toner particles with positive polarity form an electrostatic latent image with negative polarity. At the same time, toner particles in the developer facing the background area are electrostatically attracted to the developing sleeve 2 side, preventing toner from adhering to the background area. Ru. Namely.

In the developing area A where the photoreceptor #-1 and the developing sleeve 2 face each other, between the electrostatic latent image on the photoreceptor 1 and the developing sleeve 2,
An electric field is formed in the direction in which the toner particles in the developer are drawn toward the photoreceptor 1, and between the background area other than the electrostatic latent image and the developing sleeve 2, the toner particles in the developer are developed. A bias voltage is applied to the developing sleeve 2 so that an electric field that is pulled toward the sleeve 2 is formed.

Furthermore, in order to increase the development efficiency, in the illustrated example, the linear velocity of the developing sleeve 2 is higher than the linear velocity of the photoreceptor 1.
The developer is configured so that the developer carried by the developing sleeve 2 and passing through the developing area moves faster than the moving speed of the surface of the photoreceptor. That is, in the development area A, the developer is in contact with the surface of the photoreceptor and moves relative to the surface.

Here, as will be explained in detail later, the magnet P, which is provided at a position facing the photoreceptor 1, is not provided in the magnet holder 3, unlike other magnets, and is independent from it. In addition, in this example, the developing sleeve 2 is configured to reciprocate in the normal direction of the circumferential surface of the developing sleeve 2 .

On the other hand, in a conventional dry developing device in which the developing sleeve is rotationally driven and the magnet is supported in a non-rotating state,
All the magnets, including the magnet facing the photoreceptor, and therefore their respective magnetic poles, were fixed immovably. For this reason, as explained above, white spots occur at the edges of the developed image.

This will be explained in a little more detail with reference to FIGS. 5(a) and 5(b).

FIGS. 5(a) and 5(b) show the magnet P1 facing the photoreceptor 1.
FIG. 2 is an explanatory diagram showing a developing area A where a magnetic brush of developer formed by magnetic force comes into contact with the photoreceptor 1. FIG. C is a schematic diagram showing a part of the chain-shaped carrier particles of the developer magnetically supported on the developing sleeve 2. In this example, these carrier C are combined with the toner particles T. The toner particles T attached to the toner particles are positively charged.

On the other hand, as explained earlier, an electrostatic latent image with a surface potential of, for example, -800V is formed on the surface of the photoreceptor 1, and the average surface potential of the background area (non-image area) L1 is, for example, - 1
It is 00V. Against this.

For example, a bias voltage of -300V is applied to the developing sleeve 2.

When the electrostatic latent image passes through the development area A, it is visualized by the toner in the developer, as shown in FIG. 5(a). The 1-toner particles attached to the photoreceptor 1 are labeled with T1 to distinguish them from the toner particles T attached to the carrier particles C.

Here, the trailing edge L2 of the image visualized by the toner particles T1 is in the development area A as shown in FIG. 5(a), for example.
Considering the case where the developer reaches the middle part of the developing sleeve 2, the developer on the developing sleeve 2 is transported at a faster speed than the photoreceptor 1, so at the time of FIG. 5(a), the trailing edge of the image L
Carrier particles C located behind 2 move so as to follow the image. At this time, the carrier particles close to the photoconductor 1 come into sliding contact with the background area L1 on the photoconductor 1, but the surface potential at the background area L2 is low (-100V), whereas the developing sleeve 2 is biased at -300V. Since the voltage is applied, as explained earlier, the background part L1
The toner particles T on the carrier particles C that are in sliding contact with the developing sleeve 2 are electrostatically attracted to the developing sleeve 2 side. That is, photoreceptor 1
A reverse electric field is applied between the developing sleeve 2 and the developing sleeve 2 in the opposite direction to that when normal development is performed. This prevents toner from adhering to the background portion L1. When the toner particles on the carrier particles C are drawn toward the developing sleeve 2 side in this way, there are no toner particles T on the surface of the carrier particles C facing the background portion L1, as shown in FIG. 5(a). Alternatively, almost no particles exist, and the surface of the negatively charged carrier particles C is exposed to the photoreceptor 1.

When these carrier particles C catch up with the trailing edge L2 of the image on the photoreceptor 1 as shown in FIG. 5(b), the positive polarity toner adhering to the electrostatic latent image on the photoreceptor 1 particle,
That is, the toner particles T1 constituting the trailing edge of the image are attracted by the negative charge of the exposed carrier particles C and adhere to the carrier particles C as shown by the arrow. As a result, the toner at the trailing edge of the image is missing, resulting in a blank image.

In the part of the background L1 adjacent to the trailing edge L2 of the image, the above-mentioned reverse electric field is particularly noticeable due to the so-called edge effect, so that particles on the carrier particles passing through this part are strongly attracted to the developing sleeve 2. , and tends to move far away from the photoreceptor surface. For this reason, as shown in FIG. 6, white spots occur particularly in the part indicated by X of the cross-shaped image, that is, at the rear edge of the horizontal image G1 and in the vicinity of the vertical image G2. Such white spots are also called solid cross white spots.

Above, we have explained the case where the photoconductor 1 and the developing sleeve 2 move in the same direction in the development area A, that is, in the forward direction, and the developer moves faster than the surface of the photoconductor 1. For the same reason, the edge of the image (front edge In some cases, white spots may occur in the area (in some cases). In short, unless the photoreceptor and the developing sleeve move at a constant speed in the forward direction, there is a risk that white spots may occur.

In order to suppress the above-mentioned white spot phenomenon, the width W in the circumferential direction of the developing sleeve (the width of the developing area A) where the developer on the developing sleeve 2 contacts the surface of the photoreceptor 1 should be shortened. (See Figure 2). In this way, the influence of the above-mentioned reverse electric field acting on the developer is reduced, and the occurrence of white spots can be suppressed. However, like this, @ of development area A
If W is narrowed, the developing ability itself will be reduced, the toner density of the entire visible image will be reduced, and the quality of one image will be degraded.

Therefore, by rotating not only the developing sleeve, but also the magnets inside it, and therefore its magnetic poles, in the circumferential direction of the developing sleeve, the developer can be brought into contact with the electrostatic latent image more efficiently, increasing the developing ability, and increasing the width of the developing area. One possible method is to narrow W to prevent white spots. However, with this configuration, as described above, the rotation of the magnetic poles generates eddy currents in the developing sleeve, and the resulting heat melts the toner, which may stick to the developing sleeve.

Therefore, the present invention proposes a configuration in which the magnetic pole of the magnet P, which substantially faces the photoreceptor, is reciprocated in a direction toward or away from the photoreceptor. In this embodiment, as shown in FIGS. 1 and 2, the magnet P1 is reciprocated in the normal direction of the circumferential surface of the developing sleeve 2, and the magnet P□ is attached to the photoreceptor 1 shown in FIG. It is configured to reciprocate during a developing operation between a close position and a position away from the photoreceptor 1 shown in FIG.

When the magnet P4 occupies a position away from the photoreceptor 1 as shown in FIG. 2, the magnetic flux density on the surface of the developing sleeve 2 is
This is different from the case shown in FIG. 1, and the height of the spikes of the magnetic brush formed by the magnet P1 and the width of the spikes in the circumferential direction of the sleeve 2 are smaller than in the case of FIG. That is, the width of the magnetic brush in contact with the photoreceptor 1, in other words, the width W of the developing area A becomes smaller. As a result, as shown in FIG. 5(a), the developer (carrier particles C) moving to follow the trailing edge L2 of the image is pulled from the surface of the photoreceptor 1, and an air layer is formed there. . Therefore, the influence of the above-mentioned reverse electric field on the toner particles on the carrier particles is weakened, and the probability of existence of carrier particles with exposed surfaces without toner particles T attached thereto is reduced. Moreover, by changing the standing state of the magnetic brush from the state shown in FIG. 1 to the state shown in FIG.
The carrier particles to which the toner particles T have not adhered are mixed into other developer parts, and the carrier particles to which the toner particles T have sufficiently adhered can be brought into contact with the trailing edge L2 of one image.

In this way, it is possible to reliably suppress the phenomenon in which the carrier particles from which the toner particles T are removed remove the toner particles T1 from the trailing edge L2 of the image. Moreover, the magnetic brush immediately returns to the state shown in FIG. 1 from the state shown in FIG.
Since the width W, that is, the width of the magnetic brush in contact with the photoreceptor 1 is increased, it is possible to prevent a decrease in the developing ability and to prevent a decrease in the toner concentration of a visible image.

In addition, by alternating the magnetic brush between the state shown in Figure 1 and the state shown in Figure 2, the effect of randomly stirring the toner and carrier in the developer is enhanced, which results in the formation of toner particles on the surface. It can also be considered that the number of removed carrier particles is reduced to suppress the phenomenon in which the toner T1 is removed from the trailing edge of the T1 image.

As mentioned above, there are various reasons why the phenomenon of white spots can be prevented, but whatever the reason, the developing ability can be improved by repeating the operation of moving the magnet P closer to or away from the photoreceptor. It has been confirmed through many experiments that white areas can suppress the occurrence of the phenomenon while preventing a decrease in the temperature, and that the same effect as rotating a magnet can be obtained.

Moreover, since the magnets P2 to P5 outside the magnet P tool remain immovably fixed, eddy currents are not formed in the developing sleeve portion facing each magnet, unlike when all the magnets are driven to rotate. Instead, eddy currents are generated only in the portion of the developing sleeve 2 facing the reciprocating magnet P1, that is, in the developing area A. Moreover, since the developing sleeve 2 is rotating, there is no possibility that only a part of the sleeve generates heat, and the amount of heat generated by the entire developing sleeve remains small, eliminating the problem of toner melting and sticking to the surface of the developing sleeve. Does not occur.

As a countermeasure against heat generation in the developing sleeve 2, it is known that the sleeve 2 is made of stainless steel with relatively high resistance.However, if the structure according to the present invention is adopted, the developing sleeve 2 can be made of aluminum. There is no problem. Aluminum is easier to process and cheaper than stainless steel, so using an aluminum developing sleeve can reduce the cost of the developing device.

Next, a configuration example of a driving means for repeatedly reciprocating the magnet Pi as described above will be described.

In FIG. 3, the developing sleeve 2 has flange plates 22, 22a fixed to each end thereof! ! It is rotatably supported by each side plate 21, 21a of the imaging device via a bearing. The developing sleeve 2 has a gear 30a fixed to its flange plate 22a.

It is rotationally driven in the counterclockwise direction in FIG. 1 by a drive device (not shown) through a gear (not shown) that meshes with this and the like.

Magnet holder 3 provided inside the developing sleeve 2
Although not shown, the shaft 11 is immovably fixed to each side plate 21, 21a, and the magnet P fixed to the boulder 3
2 to Ps (not shown in FIG. 3) are immovably supported as described above.

A cylindrical boss portion 32 of a cam member 23 is rotatably inserted into the hollow portion of one flange plate 22 via a bearing 15, and this cam member 23 and the other flange plate 2
Each end of the magnet holder shaft 11 is inserted into the hollow part 2a. For each end of the shaft 11, a cam member 23 and a flange plate 22a are rotatable by bearings 14.14a.

A gear 17 is fixed to the cylindrical boss portion 32 of the cam member 23, and an input key 716 meshes with this gear 17. The cam portion 34 of the cam member 23 located inside the developing sleeve 2 is
As shown in FIG. 4, it is in contact with the shaft 24 of the above-mentioned magnet P4 constituting the main pole. At that time, magnet holder 3
The shaft 24 is pressed against the cam surface of the cam part 34 by the holding members 12, 12a fixed to each end of the shaft 11 and the elastic members 13.13a engaged with each end of the shaft 24. There is. The elastic members 13, 13a are, for example, the holding members 12.12a.
It is made of ring-shaped rubber such as a rubber band wrapped around the shaft 24, or a ring-shaped coil spring, and draws the shaft 24 toward the center of the holding member 12.12a.

Elongated holes 35, 35a extending in the normal direction of the curved surface of the developing sleeve 2 are formed in the holding members 12, 12a, and each end of the shaft 24 is slidably fitted into these holes.

During the developing operation, the input gear 16 is directly connected to the immediate action device.
Alternatively, it rotates by receiving rotation from another rotating member of the developing device (for example, the aforementioned paddle wheel). This rotation is transmitted to the cam member 23 via the gear 17. As a result, the cam portion 34 rotates while being pressed against the shaft 24, and the shaft 24,
Therefore, the magnet P1 is guided by the long holes 35 and 35a.

The cam portion 34 is reciprocated between the positions shown in FIG. 1 and FIG. 2 by the height difference (H-h) (FIG. 4).

In addition, as shown in FIG. 7, it was provided inside the developing sleeve 2. The magnet P facing the photoreceptor 1 is S.

There are rotating magnets whose north poles are alternately magnetized and which are rotated at high speed (for example, the
Publication No. 36). This configuration also makes it possible to prevent the above-mentioned white spot phenomenon from occurring.

However, in this example, when magnet P rotates, relative to an adjacent magnet, for example magnet P'.

When the repelling magnetic poles of the rotating magnet face each other, the rotational torque of the magnet P decreases; on the other hand, when the attracting magnetic poles face each other, the torque increases.

In other words, torque fluctuation becomes large. In order to deal with this problem, it is necessary to increase the capacity of the shaking motor, but in the configuration shown in Figures 1 to 4, the magnet serving as the developing pole is not rotary. There is no need to take such measures.

In addition, in the example shown in FIG. 7, when the repelling magnetic pole of the rotating magnet P faces the adjacent magnet P'', the developer tends to separate from the sleeve 2 due to the repulsive magnetic field, and the developer casing 4' and the photosensitive Therefore, in this type of developing device, there was a layout constraint that required the developing device to be placed below the photoreceptor 1. In the configurations shown in FIGS. 1 to 4, there are no constraints in this sense.

It goes without saying that the present invention can be widely applied to image forming apparatuses that use a belt-like photoreceptor as a latent image carrier, and to developing devices in image forming apparatuses that use a latent image carrier other than such a photoreceptor. It is.

[Effects of the Invention] According to the present invention, it is possible to prevent the occurrence of white spots in a developed image while preventing a decrease in developing ability.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an example of a dry developing device according to the present invention, FIG. 2 is a sectional view showing a state where the magnet facing the photoreceptor is further away than in FIG. 1, and FIG. 3 is a sectional view showing the photoreceptor. A cross-sectional view showing an example of a driving means for reciprocating the magnet facing the developing sleeve in the normal direction of the developing sleeve, FIG. 4' is a front view of the cam member, and FIGS. 5(a) and (b) are white. Figure 6 is a schematic explanatory diagram illustrating the mechanism of occurrence of the phenomenon, and Figure 6 is a perspective view showing an example of an image with white spots. 2...Developing sleeve D...Two-component developer Ll...Background part

Claims (1)

[Scope of Claims] A non-magnetic developing sleeve that is opposed to a latent image carrier and rotationally driven, and a plurality of magnetic poles arranged in the circumferential direction inside the developing sleeve, the peripheral surface of the developing sleeve A two-component developer is supported and conveyed by magnetic force, and the developer
A dry developing device that visualizes an electrostatic latent image formed on a latent image carrier, in which the electrostatic latent image on the latent image carrier and a developing area where the latent image carrier and a developing sleeve face each other are An electric field is formed between the developing sleeve and the toner particles in the developer in a direction that draws them toward the latent image carrier, and between the developing sleeve and the background area other than the electrostatic latent image, the toner particles in the developer are drawn toward the latent image carrier. Applying a bias voltage to the developing sleeve so as to form an electric field in a direction that draws the toner particles toward the developing sleeve,
In a dry-type developing device in which the developer moves relative to the surface of the latent image carrier in the development area, a magnetic pole located at a position substantially facing the latent image carrier among the magnetic poles is arranged to move toward the surface of the latent image carrier. 1. A dry-type developing device, comprising: a driving means for driving the dry developing device so as to reciprocate in a direction toward or away from the developing device; and magnetic poles other than the magnetic poles are fixedly arranged.