JPH0277771A - Developing device - Google Patents

Abstract

PURPOSE:To prevent image trouble such as tailing and scattering and to obtain an image of invariably high quality by magnetizing and setting an area where development is possible so that the absolute value of the density variation rate of a vertical magnetic field component is maximum. CONSTITUTION:A magnet 3 for development 3 is fixed as a magnetic field producing means in a developing sleeve 2 at a specific position. A developing pole (a) in the magnet 3 is so set that the absolute value of the density variation rate of the vertical magnetic field component is maximum at a specific distance from the center position of the development area. In this case, if the maximum magnetic flux density is obtained on a straight line L passing the center 1a of a photosensitive drum and the center 2a of sleeve rotation, a groove 13a is formed almost at an angle theta of 80 deg. and a groove 13b is formed at an angle thetaof 20 deg. to cause an abrupt variation in magnetic force distribution, thereby obtaining a desired magnetic flux distribution.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is utilized in the field of technology for developing electrostatic latent images with a developer, and in particular, a developing device that performs development by restraining the developer with magnetic force. Regarding.

[Prior Art] Conventionally, this type of developing device has an electrostatic latent image carrier and an electrostatic latent image carrier, which is disposed with its outer circumferential surface facing each other so as to form a close area with the electrostatic latent image carrier. It is configured as a non-magnetic developer carrier that supports a magnetic developer. A predetermined area within the above-mentioned proximity area where the distance between the two outer peripheral surfaces facing each other is equal to or less than a certain value, that is, an area where the magnetic field strength is constant is defined as a development area.

In this case, as a means for supporting the developer on the surface of the developer carrier, a magnetic field generating means or fixedly installed magnetic field generating means in which a plurality of magnets are disposed inside the developer carrier with one magnetic pole facing toward the outer peripheral surface of the developer carrier. has been done. One magnet among the plurality of magnets constituting the magnetic field generating means is disposed in the vicinity of a position corresponding to the closest portion within the vicinity of the electrostatic latent image body and the developer carrier. The magnetization is set so that one magnetic pole on the outer circumferential surface of the rotating body has the maximum density point of the perpendicular magnetic field component (the magnetic field component perpendicular to the surface of the developer carrier) approximately at the center of the development area. . This perpendicular magnetic field component magnetically restrains the developer on the outer circumferential surface of the developer carrier within the range of the development area to form a so-called "spike" and transfer the developer to the electrostatic latent image carrier. ing.

[Problem to be solved by the invention] However, in the conventional developing device, the density of the vertical magnetic field component of the magnet gradually decreases toward both ends of the developing area, and conversely, the density of the horizontal magnetic field component ( The density of the magnetic field component in the circumferential direction of the developer carrier gradually increases. The developer spikes become more inclined towards both ends of the formed image area, and various problems occur in the image developed in those areas. For example, this is called "tailing", and as the developer carrier rotates, the developer may extend linearly in a direction opposite to the direction of image formation (the conveyance direction of the recording material on which the image is formed). This adversely affects image formation, such as a state in which developer particles appear to be trailing, or a state in which the above-mentioned "tailing" (referred to as "splatter") worsens and developer particles scatter near the periphery of the copied image. This is remarkable when an integrally molded member made of resin or polymeric material mixed with a magnetic material is used as the magnetic field generating means.

FIG. 7 shows an enlarged view of the developing area at this time, showing the appearance of spikes of developer. In the figure, a developer 10 is supported on a developing sleeve 2 serving as a developer carrier. Further, an electrostatic latent image (represented by reference numeral 11 of negative polarity in FIG. 7) is carried on the photosensitive tram l as an electrostatic latent image carrier. Then, at the closest part between the photosensitive drum 1 and the developing sleeve 2 (in the case shown, the central part of the developing area), the developer 10 that has stood up on the developing sleeve 2 moves toward the photosensitive drum 1 due to the electric attraction force. do. However, as one moves from the center of the developing area to the non-developing areas at both ends, the spikes gradually become slanted due to the influence of the horizontal magnetic field component. This tendency is quite noticeable at both ends of the developing area, as indicated by reference numeral 12. For example, in the left side portion of the developing area shown in FIG. 7, part of the spikes of the developer IO tilted on the developing sleeve 2 causes the distance between the photosensitive drum l and the developing sleeve 2 to become large. Despite this trend, since the developer is electrically attracted to the photosensitive drum l in the direction of the arrow W, only a deviation of the developer IO occurs in the image forming direction A on the rotating photosensitive drum l. . This developer 1
A deviation of 0 is the above-mentioned "tailing" that extends linearly backward on the copied image.

An object of the present invention is to solve the adverse effects on image formation such as "tailing" and "splatter" that conventional developing devices have.

[Means for Solving the Problems] In order to achieve the above-mentioned object, the developing device of the present invention includes an electrostatic latent image carrier and a developer carrier which is provided with a magnetic field generating means therein and rotates in a predetermined direction. The electrostatic latent image carrier and the developer carrier are disposed so as to form a proximal region having the closest portion between the outer peripheral surfaces of the electrostatic latent image carrier and the developer carrier, and the magnetic field is generated. In a developing device having a magnetic field generating section in the vicinity of the nearest portion of the means, the magnetic field generating means described in 2.2 above is a magnetic field generating section that generates magnetic force of a component perpendicular to the surface of the magnetic field generating means of the magnetic field generated by the magnetic field generating section. The magnetic field changing means is provided to change the intensity distribution at a predetermined position near the magnetic field generating section.

[Operation] When the developing device configured as described in L is started, the developer formed in a thin layer on the surface of the developer carrier is transported to the area adjacent to the electrostatic latent image carrier and the developer carrier. Ru. The developer is
In the developing circuit region of the above-mentioned adjacent region, the magnetic field generated by the magnetic field generating section of the magnetic field generating means and the magnetic field changing means causes the magnetic field to stand up, and responds to the charge of the electrostatic latent image carried on the electrostatic carrier. form a visible image.

[Example] Hereinafter, an example device of the present invention will be described based on the accompanying drawings.

FIG. 1(A) is a sectional view showing the periphery of a developing sleeve as a developer carrier in a developing device as the first embodiment, and FIG. FIG. 2 is an enlarged view of a close area formed by a sleeve and a photosensitive drum serving as an electrostatic latent image carrier, and schematically shows the distribution of perpendicular magnetic field components in the close area.

In FIG. 1(A), the developing sleeve 2 is rotatably disposed in the direction A at a position facing the photosensitive tram 1 with a predetermined gap therebetween. Inside the developing sleeve 2, a developing magnet 3 made of a material such as resin and serving as a magnetic field generating means is fixedly arranged at a predetermined position. When the developing magnet 3 is manufactured, for example, as shown in FIG. 1(A), four magnetic field generating parts a are formed at predetermined positions on the circumference.

b, c, and d are formed, the magnetic field generating part a is the developing pole, the magnetic field generating part is the developer carrier (cut pole), and the magnetic field generating part C is the developer carrier (cut pole).
and d form developer transport poles, respectively. Second
The figure shows an enlarged sectional view of the developing Macnet 3. In the figure, 1a is the center of the photosensitive drum, 2a is the center of rotation of the developing sleeve, and L is the center of the photosensitive tram 1a.
This is a straight line passing through the developing sleeve rotation center 2a. The developing magnet 3 is formed at a predetermined angle θ1.about.the developing sleeve rotation center 2a with respect to the straight line. Straight line Ml having θ2,
A semicircular groove 13a and a groove 13b are formed around the intersection of M2 and the outer circumferential line of the developing magnet 3.

The grooves 13a and +3b are formed in parallel with the axis of the developing magnet 3.

Further, on the upper part of the developing sleeve 2, a plate 4 is disposed at a position opposite to the above-mentioned magnetic field generating section for regulating the height of the spikes of the developer IO and thinning the developer on the developing sleeve. It is set up. The right side of the developing sleeve 2 has an opening in which the left portion of the upper developing sleeve 2 is placed in a protruding state, and serves as a container 8 for accommodating the developer 10 to be supplied to the developing sleeve 2. Note that 2a is the rotation center of the developing sleeve 2 and also the fixing center of the developing magnet 3.

FIG. 1(B) shows an enlarged view of the adjacent region in FIG. 1(A) indicated by -, and in the same figure, the developing pole (this example The distribution of the perpendicular magnetic field components of the N and N poles is shown by the length of the arrow indicating the magnetic flux density at the circumferential surface position of the developing sleeve 2.

As is well known, the magnetic field of the magnetic field generating part a is formed in all directions with the magnetic field generating part a as the center. Therefore, a vertical magnetic field component and a horizontal magnetic field component are formed on the surface of the developing sleeve 2. It's decided. Here, the horizontal magnetic field component is a magnetic field component in the direction of a tangent to the circumference of the sleeve.

By modifying the density distribution state of the horizontal magnetic field component or the vertical magnetic field component of this development pole, development due to slanted spikes of developer occurring at both ends of the development area, which was pointed out as a problem with the conventional device mentioned above, can be solved. It can be prevented.

That is, the above-mentioned problem is solved by correcting and setting the rate of change of the magnetic flux density of the horizontal magnetic field component or the vertical magnetic field component of the developing pole at both ends of the developing area to be large.

In the following, the density distribution state of the perpendicular magnetic field component formed by the developing pole of the present embodiment apparatus in which the grooves 13a and 13b are formed on the surface of the developing magnet '3 as described above will be explained in detail with reference to the drawings. FIG. 4 shows the density distribution of the perpendicular magnetic field component.

The solid line in the figure shows the density distribution of the vertical magnetic field component of the developing pole of the apparatus according to this embodiment, and the two-dot chain line shows the vertical magnetic field component of the developing pole of the conventional apparatus.

The horizontal axis is located at an intermediate position between the magnetic field generating part a shown in FIG. The reference position θ is the position where the density of the vertical magnetic field component of the pole is θ Gauss. The binding is shown at an angle θ toward the downstream side (towards the developing pole) with respect to the rotation center 2a of the developing sleeve 2. The vertical axis represents the vertical magnetic field component density G (Gauss) on the surface of the developing sleeve 2. In the figure, when comparing the perpendicular magnetic field component density of this example and the conventional device, in the case of this example (
The rate of change in density is relatively stable in the vicinity of the maximum density point S at the center position (near the angle θ - 50 degrees) with the maximum density point S at the center position (near the angle θ - 50 degrees) as the apex, compared to the conventional system M (two-dot chain line). The rate of change becomes large at positions that are a predetermined distance from the position on both sides. In order to clarify the above relationship, the density (G (Gaussian)) of the vertical magnetic field component on the vertical axis in Figure 4 is differentiated by the angle θ, and the rate of change with respect to the angle 0 is plotted on the vertical axis. When comparing the two, the rate of change is large at positions a certain distance from the center position to both sides, and it is clear whether it is a local maximum value (maximum value) or a local minimum value (minimum value). As mentioned above, the development pole of the apparatus of this embodiment is set in steps such that the absolute value of the density change rate of the vertical magnetic field component is maximum at a position a predetermined distance from the center of the development area. As shown in No. 31, "tailing" often occurs when the density change of the horizontal magnetic field component per unit center angle with respect to the center of the developer carrier is 30 Gauss or less.
It has been confirmed that image disturbances such as "splatters" have occurred.
Generally, it is preferable to set the magnetization so that the maximum absolute value of the density change rate is 30 Gauss/degree or more.

Here, the grooves 13a and 1 formed in the developing magnet 3 are
The position of 3b will be explained. - When the maximum magnetic flux density point S in Fig. 4 mentioned above is on the straight line Lf, the maximum point to be set is It is necessary to make a sudden change in the magnetic flux density at a point. Therefore, by forming the groove 13a in the vicinity of θ of about 80° in FIG. 4 and the groove 13b in the vicinity of θ of about 20°, a sudden change is caused in the magnetic force distribution. It is possible to obtain a magnetic flux distribution as shown in Fig. 5. Note that the width and depth of the grooves 13a and 13b are arbitrary, and may be adjusted depending on the desired magnetic force distribution.

Further, in this embodiment, the grooves 13a and 13b are formed at angles θ and θ2 with respect to the straight line, and the shape is semicircular, or the grooves are formed, for example, as shown in No. It may be formed at a position at an angle θ1 with respect to the straight line, and its shape is not limited to a semicircular shape.

FIG. 6 is an enlarged view of the developing area of the apparatus of this embodiment having developing poles magnetized as described above, showing the state of developer spikes. Both ends Nl of the development area,
Since the rate of change in the density of the perpendicular magnetic field component in N2 is large, it is clear whether or not there is a spike at the end of the development area. As a result, the vertical spikes of developer in the sleeve 2 are arranged in an orderly manner within the developing area. As a result, developer 1
o is suctioned and transferred to the photosensitive drum 1 without disturbance, and does not cause image disturbances such as "tailing" and "scattering".

Next, as another embodiment of the present invention, a magnetic flux density distribution adjustment mechanism using a Df dynamic magnetic member provided inside the developing magnet 3 according to the present invention will be described. FIG. 9 shows an example in which the movable magnetic member 14a is disposed inside the groove 13 formed in the developing magnet 3. FIG. This movable magnetic member 14a is movable to a position 14b indicated by a broken line, and moves along a guide rail (not shown) on the inner wall of the groove 13. Further, a magnetic member driving device 15 is connected to the movable magnetic member 14a, and the movable magnetic member 14a can be freely moved in the direction of the arrow Y in the figure. Therefore, it becomes possible to finely adjust the magnetic flux density, and it becomes easy to optimize the shape of the magnetic flux density distribution. In FIG. 10, the movable magnetic member 14a is movable in the circumferential direction of the developing magnet 3 and the developing sleeve 2. It is configured to be driven in a pendulum interlocking direction by a magnetic member driving device 15.

Further, a magnetic flux density detector 16 as a detection means is provided around the magnetic force generating member 3, and the developing mcnet 3 is rotated in the X direction about 2a by a magnetic force generating member rotation drive device (not shown), so that the magnetic flux on the surface of the developing mcnet 3 is The density is detected, the magnetic flux distribution is detected by a magnetic flux distribution detector (not shown), and the amount of change in magnetic flux density with respect to the rotation angle of the magnetic flux distribution is calculated. Next, an adjustment means (not shown) compares the calculated pattern of magnetic flux density variation with a desired preset pattern of magnetic flux density variation, and moves the movable magnetic member 14a to obtain the desired pattern. The mechanism is such that a signal is sent to the magnetic member drive power source 18 to move the magnetic member drive device 15.

Further, this magnetic member driving f-film device 15 can also combine the pendulum movement shown in FIG. 10 and the telescopic movement shown in FIG. 9, and can automatically adjust to the optimum magnetic flux density distribution.

Incidentally, the automatic adjustment mechanism as described below can also be applied to the apparatus of the embodiment shown in FIG.

The developing magnet 3 of the apparatus of the present invention described above can be widely applied to Ferra, sintered type, resin integrally molded type, etc. Also, the development pole magnetization can be set with the maximum density point of the vertical component at the center. It does not have to be bilaterally symmetrical, and may be asymmetrical.

[Effects of the Invention] As described above, the developing device according to the present invention changes a part of the magnetic field generated by the magnetic field generating section of the magnetic field generating means by the magnetic field changing means formed in the generated magnetic field generating means, and After magnetization is set to the absolute value or maximum value of the density change rate of the horizontal magnetic field component in the possible region, the density of the vertical magnetic field component changes rapidly at both ends of the development region, causing spikes of developer to rise. It is possible to clarify the presence or absence of Therefore, there is no longer a situation where the development is done by tilted developer, and the "tailing" that conventional devices had,
This has the effect of preventing image disturbances such as "splatters" and constantly providing high-quality images. The magnetic field generator is
It can be manufactured by integrally molding a fixed magnet and resin.
It is also possible to significantly reduce the price and weight compared to sintered ferrite type magnets, bonded type magnets, and embedded type magnets.

[Brief explanation of the drawing]

FIG. 1(A) is a cross-sectional view of a schematic configuration of an embodiment of the present invention, and FIG. 1(B) is an enlarged view of the adjacent region of FIG. 1(A) to show the perpendicular magnetic field component density distribution in the region. 2 is an enlarged sectional view of the magnetic field generating means, FIG. 3 is a diagram showing the relationship between the rate of change of the vertical magnetic field component density and the state of occurrence of image disturbance, and FIG. 4 is an apparatus according to an embodiment of the present invention. Figure 5 is a diagram showing the density distribution of the vertical magnetic field component of the developing pole of the conventional device and the developing pole of the conventional device. 7 is an enlarged view of the development area of the device of the present invention showing the state of developer spikes; FIG. 8 to 1O are enlarged sectional views showing other examples of magnetic field generating means. 1... Electrostatic latent image carrier (photosensitive drum) 2
......-Developer carrier (developing sleeve) 3.
......Magnetic field generating means (developing tube net) 1
0...Developer a--Magnetic field generating part forming the development magnetic pole Patent applicant Canon Co., Ltd. Agent Patent attorney Toru Fujioka Fig. 1 (A) Fig. 1 Figure (B) Re\-1/

Claims (1)

[Scope of Claims] (1) comprising an electrostatic latent image carrier and a developer carrier having a magnetic field generating means disposed therein and rotating in a predetermined direction; The body and the developer carrier are arranged so as to form a proximate region having a proximate portion between their outer peripheral surfaces, and the magnetic field generating means has a magnetic field generating portion near the proximate portion. In the developing device, the magnetic field generating means changes the magnetic force intensity distribution of the component of the magnetic field generated by the magnetic field generating section perpendicular to the surface of the magnetic field generating means at a predetermined position near the magnetic field generating section. A developing device characterized in that it is equipped with a magnetic field changing means that enables. (2) A developable region is formed in a region close to the electrostatic latent image carrier and the developer carrier, and the magnetic field changing means controls the density of the perpendicular magnetic field component in the circumferential direction of the developer carrier in the developable region. The developing device according to claim 1, wherein the developing device is formed at a position where the rate of change takes a maximum value. (3) The magnetic field changing means is a groove formed with a predetermined depth toward the center at a predetermined position on the surface of the magnetic field generating means, and the groove is formed to extend in the axial direction of the magnetic field generating means. The developing device according to claim (1) or (2). (4) The developing device according to claim 3, wherein the magnetic field changing means includes a movable magnetic member disposed inside the groove that is movable in the depth direction of the groove. (5) The magnetic field changing means has a predetermined space formed inside the magnetic field generating means, and a movable magnetic member that can perform a predetermined operation is disposed within the space.
2) The developing device according to item 2). (6) A detection means for detecting the magnetic flux density on the surface of the magnetic field generation means is disposed near the magnetic field generation means, and the amount of change in magnetic flux density is calculated from the detected magnetic flux density and the rotational speed of the magnetic field generation means at the time of detection. Then, the position of the movable magnetic member is adjusted so that the actual pattern of change in magnetic flux density matches the set pattern of magnetic flux density by comparing it with a preset pattern of change in magnetic flux density on the surface of the magnetic field generating means. The developing device according to claim 4 or 5, further comprising an adjusting means for applying a drive signal to a magnetic member driving means connected to the movable magnetic member. (7) A developing device in which the magnetic field generating means is formed at a position in the developing region where the density change rate of the perpendicular magnetic field component in the circumferential direction of the developer carrier is 30 Gauss per degree or more.