JP3231627B2 - Developing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device for visualizing an electrostatic latent image formed on a photoreceptor with a developer in an electrophotographic process in, for example, a copying machine or a laser printer.

[0002]

2. Description of the Related Art In a conventional electrophotographic process, an electrostatic latent image formed on the surface of a photoconductor as an electrostatic latent image carrier is developed and visualized to obtain an image. The developing device used in this process uses a rotatable non-magnetic sleeve and a magnet body having a plurality of magnetic poles disposed in the sleeve to transfer a two-component developer, which is a mixture of a magnetic carrier and a toner, to the sleeve. Adsorb and hold on the surface,
A magnetic brush developing method using sleeve rotation is often used, in which the sleeve is rotated to move the developer to the photoconductor, and the developer is raised to form a magnetic brush for development.

[0003]

In the above-described developing device, the developer is conveyed into the developing tank of the developing device in a process of collecting the developer after the completion of the development. At this time, the developer falls and scatters around the developing device. As a result, there is a problem that not only the inside of the copier or the like is stained, but also the image adheres to the photoreceptor to deteriorate the image.

To solve these problems, the developer is sucked by air flow, the shape of the developing tank under the sleeve is changed, and the magnet body in the sleeve is arranged as close as possible to the developing tank. An attempt was made to balance the curtain with the brush and the transportability to prevent the developer from falling and scattering. However, an increase in the pressure in the developer tank due to the movement of the developer causes a backflow of the air mixed with the developer from the downstream side of the opening of the developer tank, and the developer drops and scatters.

That is, regarding the recovery of the developer, the above problem occurs because sufficient consideration is not given to the strength of the magnetic field on the downstream side of the opening and its action. For example, Japanese Utility Model Publication No. 3-50536 discloses a developing device in which the relationship between the position of the magnetic pole of the magnet body and each function on the sleeve is examined, but the function of collecting the developer after the development is completed. It cannot be said that the relationship between and the distribution of the magnetic field has been sufficiently studied.

[0006] In view of the above, the present invention provides a developing apparatus which can completely recover the developer in the developing tank without scattering the developer by optimizing the strength of the magnetic field on the downstream side of the opening. For the purpose of providing.

[0007]

The object of the present invention is to provide a developing tank containing a magnetic developer, a rotatable non-magnetic sleeve, and a magnet body fixed in the sleeve and having a plurality of magnetic poles. An opening is formed on the photoreceptor side of the developing tank, a sleeve is disposed facing the photoreceptor from the opening, and the developing device conveys the developer with the rotation of the sleeve. The magnetic field strength in the tangential direction on the sleeve surface is smaller than the magnetic field strength on the upstream and downstream sides of the sleeve surface.

The magnet body has a developing magnetic pole facing the photoreceptor and a transport magnetic pole located downstream of the developing magnetic pole, and the magnetic field in the tangential direction on the surface of the sleeve has a maximum value on the developing magnetic pole side and a maximum on the transport magnetic pole side. The minimum value is obtained at a position on the sleeve surface where the distance between the downstream end of the opening and the sleeve facing the downstream end is minimum.

That is, the intensity of the magnetic field becomes small in the region between the position of the sleeve surface where the developing magnetic pole side has the maximum value and the position of the sleeve surface where the carrying magnetic pole side has the maximum value.

Here, assuming that the maximum value on the developing magnetic pole side is a, the maximum value on the conveying magnetic pole side is b, and the minimum value is c, a> c or b
> C, and the relationship of 0.6a ≦ c ≦ 0.9a may be satisfied.

The position of the sleeve surface at which the magnetic field intensity in the tangential direction has a minimum value is a fixed value centered on the closest position where the distance between the downstream end of the opening and the sleeve facing the opening is minimum. It is within the range.

The strength of the magnetic field in the tangential direction on the sleeve surface has a minimum value between the position corresponding to the developing magnetic pole and the position corresponding to the transport magnetic pole on the sleeve surface. Distance d between the position of the surface and the downstream end of the opening
(Mm) is 180 <, where the minimum value is c (Gauss).
c / d <270.

As described above, when the intensity of the tangential magnetic field on the sleeve surface is optimized at the downstream end of the opening in order to improve the performance of transporting the developer, the developer is collected into the developing tank. At this time, the developer forms ears according to the strength of the magnetic field between the downstream end of the opening and the sleeve, and the magnetic field acts on the developer on the sleeve surface in the sleeve rotation direction. As a result, the developer moves smoothly and is drawn into the developing tank, so that the developer does not collide with the downstream end of the opening and the impact force of the developer is reduced.
In addition, even in the vicinity of the opening in the developing tank, the developer is conveyed without stagnation, and the backflow of air from the opening as in the related art is eliminated. Therefore, the developer is completely collected in the developing tank without being scattered.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 2 is a schematic configuration diagram of a copying machine provided with the photoreceptor 1. The photoreceptor 1 has a surface uniformly charged by a main charger 2 and is then exposed to light irradiated by an optical system 3. As a result, an electrostatic latent image is formed on the surface of the photoconductor 1, and this electrostatic latent image is developed by the developing device 4 to become a visible image. The visible image formed on the photoconductor 1 is transferred by a transfer charger 8 onto transfer paper fed from a transfer paper cassette 5 by a feed roller 6 and a registration roller 7. The transfer paper is peeled off from the surface of the photoconductor 1 by a peeling charger 9, and the fixing device 1 is transported by a transport unit 10.
It is transported to 1. The toner image transferred to the transfer paper is fixed by the fixing device 11, and thereafter, the transfer paper is transferred to the discharge tray 1.
2 is discharged. On the other hand, residual toner on the surface of the photoconductor 1 is collected from the surface of the photoconductor 1 by the cleaner 13.

As shown in FIG. 3, the developing device 4 includes a non-magnetic sleeve 14 that rotates in the arrow direction Y and is disposed opposite the photosensitive member 1 that rotates in the arrow direction X as shown in FIG. It has a fixed magnet body 15 and these are housed in a developing tank 16 containing a two-component developer. 17 and 18 are stirring rollers, 19 is a doctor,
Reference numeral 20 denotes a toner density sensor, 21 denotes a flow plate, and 22 denotes a toner supply port.

The sleeve 14 is made of cylindrical aluminum or stainless steel, and the developing tank 1 faces the photoconductor 1 from an opening 23 formed on the photoconductor side of the developing tank 16.
6 and is rotatably supported by a motor.

The magnet body 15 is a roller in which a plurality of magnets 25 are joined and arranged on a central shaft 24 supported by the developing tank 16 coaxially with the sleeve 14.
It is fixed so that it does not rotate with respect to. The magnet body 15 may be a multi-pole magnetized integral-molded type magnet roller.

The magnet body 15 has magnetic poles formed by seven magnets 25. Of these magnetic poles, one magnetic pole at a position facing the photoreceptor 1 develops an electrostatic latent image on the photoreceptor 1. Therefore, the N pole is used as a developing magnetic pole A for raising the developer, and the other magnetic poles are used as magnetic poles for transporting the developer, and the S magnetic pole and the N pole are alternately arranged in order from the developing magnetic pole A along the sleeve rotating direction. Are arranged. In particular, the first magnetic pole located downstream of the developing magnetic pole A in the sleeve rotation direction is a transport magnetic pole B for drawing the developer remaining on the surface of the sleeve 14 without transferring to the photoconductor 1 into the developing tank 16. Is done.

The area of the surface of the sleeve 14 located between the developing magnetic pole A and the transport magnetic pole B is opposed to the downstream end 16 a downstream of the opening 23. The downstream end 16a is inserted between the photosensitive member 1 and the sleeve 14, so that the developer does not spill. At the downstream end 16a, a projection 26 is formed toward the sleeve 14. The distance between the projection 26 and the sleeve 14 becomes smaller toward the downstream side, and becomes minimum at the tip of the projection 26.
Then it is getting bigger.

The area of the surface of the sleeve 14 facing the projection 26 is closer to the downstream end 16a than the other areas, and the sleeve 14 faces the tip of the projection 26.
Is a closest position, and a straight line L connecting the closest position to the center of the sleeve 14 passes through substantially the middle between the developing magnetic pole A and the transport magnetic pole B, and reaches the tip of the projection 26.

FIG. 4 shows the sleeve 14 on the surface of the sleeve 14.
This shows the distribution of the magnetic field by the magnet body 15 as viewed from the cross section. In the figure, a solid line R indicates a magnetic field component in the radial direction on the surface of the sleeve 14, and a dotted line θ indicates a magnetic field component in a tangential direction perpendicular to the radial direction. According to this, in the radial direction, each magnetic pole has a peak on the radial extension, the developing magnetic pole A has a magnetic field strength of about 1100 gauss of the N pole, and the transport magnetic pole B has a magnetic field strength of the S pole. Although the magnetic field strength is about 1100 gauss, it is slightly lower than the developing magnetic pole A. In the tangential direction, each magnetic pole is close to 0 Gauss in the radial extension.

Here, paying attention to the tangential magnetic field in the area downstream of the opening 23 which affects the developer transport performance in collecting the developer into the developing tank 16, the sleeve 1
4 has a maximum between the position corresponding to the developing magnetic pole A and the closest position, and has a maximum between the closest position and the position corresponding to the conveying magnetic pole B, and is located at an intermediate position between the positions. It has been reduced from a decrease to an increase. This minimum position is almost the closest position. In this case, if the maximum value on the developing magnetic pole side is a, the maximum value on the transport magnetic pole side is b, and the minimum value is c, a> c, b>
c, a>b> c. Note that a = b may be satisfied.

That is, the developing magnetic pole A and the transport magnetic pole B
Are arranged at a position equidistant from the position corresponding to the closest position on the surface of the sleeve 14 in the magnet body 15. And the strength of each magnetic field is also a,
The values are set so as to satisfy the respective relationships of b and c.

As shown in FIG. 1, by making the magnetic field strength in the tangential direction smaller at the nearest position on the surface of the sleeve 14 than the magnetic field strength on the upstream side, a magnetic field is applied to the developer in the arrow direction. In the vicinity of the closest position of the sleeve 14 downstream of the opening 23, the radial thickness of the developer ears on the surface of the sleeve 14 becomes smaller than before and after. Therefore, when the developer is drawn into the developing tank 16, the developer flows smoothly and the downstream end 16
a is eliminated, and the impact force of the developer is reduced.

Further, by making the strength of the magnetic field in the tangential direction smaller at the closest position on the surface of the sleeve 14 than the strength of the magnetic field on the downstream side thereof, the magnetic pole B can be conveyed even after being conveyed into the developing tank 16. As a result, the developer conveying force increases. Therefore, the developer does not stay in the developing tank 16 near the closest position and the pressure of the developer does not increase, so that the backflow of the air from the opening 23 can be prevented.

Therefore, the positions of the magnetic poles and the magnetic field are set so that the magnetic field strength in the tangential direction at the closest position on the surface of the sleeve 14 is smaller than the magnetic field strength at positions upstream and downstream of the closest position. By optimizing the strength, the developer can be completely recovered into the developing tank 16 and the scattering and falling of the developer can be prevented.

Here, the relationship between the maximum value a on the developing magnetic pole side and the minimum value c will be examined. Table 1 shows the results of experiments on contamination by the developer in the copying machine when the maximum value a = 600 gauss. According to Table 1, when 0.60a ≦ c ≦ 0.90a, the impact force of the developer on the downstream end 16a is reduced, and the contamination in the copying machine is within an allowable range, so that the scattering of the developer can be improved. I understand. That is, if the minimum value c is too small with respect to the maximum value a, the developer conveyance force decreases at the closest position on the surface of the sleeve 14, and the developer cannot be drawn into the developing tank 16. On the other hand, if the minimum value c is too large with respect to the maximum value a, the thickness of the developer ears in the radial direction on the surface of the sleeve 14 becomes too large, the impact force of the developer becomes large, and the developer scatters. Would.

[0028]

[Table 1]

Next, the relationship between the position at which the minimum value c is reached and the closest position will be examined. Table 2 shows the sleeve 1 on both sides of the straight line L connecting the tip of the projection 26 and the center of the sleeve 14.
4 shows the results of experiments on toner falling into the copying machine when the position where the minimum value c is taken on the four surfaces is changed. From Table 2,
If the position where the minimum value c is located is within a range of 5 ° with respect to the upstream side and the downstream side, respectively, the impact force of the developer on the downstream end portion 16a is reduced, and the toner drop into the copying machine is reduced. It can be seen that the scattering of the developer can be prevented. That is, at positions outside the range of ± 5 ° with respect to the closest position, the strength of the magnetic field in the tangential direction becomes large, and the thickness of the radial developer ears on the sleeve surface 14 becomes too large. As a result, the impact force of the developer increases, and the developer scatters.

[0030]

[Table 2]

Further, the relationship between the minimum value c and the distance between the surface of the sleeve 14 and the projection 26 will be described. Table 3 shows the results of experiments on toner falling into the copying machine when this distance is d = 2 mm. From Table 3, it can be seen that when 180 <c / d <270, the impact force of the developer on the downstream end 16a is reduced, and the amount of toner falling into the copying machine is reduced, so that the scattering of the developer can be improved. That is, the distance d and the minimum value c
When the balance with the developer 14 is lost, the developer conveyance force decreases near the closest position on the surface of the sleeve 14, and the developer cannot be drawn into the developing tank 16. The thickness of the ears of the developer becomes too large, the impact force of the developer increases, and the developer is scattered.

[0032]

[Table 3]

It should be noted that the present invention is not limited to the above-described embodiment, and it goes without saying that many modifications and changes can be made to the above-described embodiment within the scope of the present invention. For example, as long as the magnet body has the developing magnetic pole A and the transport magnetic pole B, the magnet body may have not only seven magnetic poles but also three or five magnetic poles. Further, the sleeve is not limited to a cylindrical shape, and may be an endless belt. Further, the shape of the downstream end may be set so that the sleeve approaches the downstream end at a certain interval in the vicinity of the opening.

[0034]

As is apparent from the above description, according to the present invention, the strength of the magnetic field in the tangential direction of the sleeve surface facing the downstream end of the opening of the developing tank is increased on the upstream and downstream sides of the sleeve surface. Is smaller than the strength of the magnetic field. In other words, the developer has a minimum value between the maximum value on the developing magnetic pole side facing the photoconductor and the maximum value on the transport magnetic pole side located downstream of the developing magnetic pole. The tangential magnetic field strength at the sleeve surface at the downstream side of the opening is optimized so as to enhance the transfer performance of the sleeve.

Therefore, when the developer is collected into the developing tank, the intensity of the magnetic field in the tangential direction is minimized at the downstream end of the opening. The developer does not collide with the downstream end of the developer, thereby preventing the developer from scattering.

Further, even after the developer has moved into the developing tank, the developer is smoothly transported by the magnetic field of the transport magnetic pole.
The pressure due to the rotation of the developer in the developing tank does not increase on the downstream side of the opening, so that it is possible to prevent the air from flowing backward from the opening and to prevent the developer from scattering. From the above, the developer can be completely collected in the developing tank without being scattered.

[Brief description of the drawings]

FIG. 1 is a diagram showing a state of a sleeve surface of a developing device according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of a copying machine.

FIG. 3 is a sectional view of a developing device.

FIG. 4 is a diagram showing distribution of a magnetic field on a sleeve surface.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor 14 Sleeve 15 Magnet 16 Developing tank 16a Downstream end 23 Opening 26 Projection A Development magnetic pole B Transport magnetic pole

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-209489 (JP, A) JP-A-5-204248 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 15/09 G03G 15/08 G03G 15/095

Claims (5)

(57) [Claims] A developing tank containing a developer is provided with a rotatable non-magnetic sleeve and a magnet body fixed in the sleeve and having a plurality of magnetic poles, and an opening is formed on the photoconductor side of the developing tank. is, the sleeve is arranged so as to face to the photosensitive member from the opening, the developing device for conveying the developer with the rotation of the sleeve, said magnet body
Is the developing magnetic pole facing the photoconductor and below the developing magnetic pole.
With a carrier pole located on the flow side, tangent to the sleeve surface
The magnetic field in the direction is the maximum value of the developing magnetic pole side and the maximum value of the transport magnetic pole side.
Between the downstream end of the opening and the opposite
The surface of the sleeve where the distance to the sleeve is minimized
A developing device , wherein the minimum value is obtained at a position . 2. The developing device according to claim 1, wherein 0.6a ≦ c ≦ 0.9a, where a is the maximum value on the developing magnetic pole side and c is the minimum value. 3. A developing tank containing a developer, a rotatable non-magnetic sleeve, and a magnet body fixed in the sleeve and having a plurality of magnetic poles are provided, and an opening is formed on the photosensitive tank side of the developing tank. In the developing device, wherein the sleeve is arranged to face the photoconductor from the opening, and the developer is conveyed with the rotation of the sleeve, the magnet body is located downstream of the developing magnetic pole facing the photoconductor and the developing magnetic pole. Side, and the strength of the tangential magnetic field on the sleeve surface has a minimum value between a position corresponding to the developing magnetic pole and a position corresponding to the transport magnetic pole. The developing device is characterized in that the position of the sleeve surface which becomes a value is within a certain range centered on the closest position where the distance between the downstream end of the opening and the sleeve facing the opening is minimum. 4. A developing tank containing a developer, a rotatable non-magnetic sleeve and a magnet body fixed in the sleeve and having a plurality of magnetic poles are provided, and an opening is formed on the photoconductor side of the developing tank. In the developing device, wherein the sleeve is arranged to face the photoconductor from the opening, and the developer is conveyed with the rotation of the sleeve, the magnet body is located downstream of the developing magnetic pole facing the photoconductor and the developing magnetic pole. Side, and the strength of the tangential magnetic field on the sleeve surface has a minimum value between a position corresponding to the developing magnetic pole and a position corresponding to the transport magnetic pole. The developing device is characterized in that the distance d (mm) between the position of the surface of the sleeve and the downstream end of the opening is 180 <c / d <270, where c (Gauss) is the minimum value. 5. At the downstream end of the opening towards the sleeve
A protrusion is formed, and the distance between the protrusion and the sleeve is lower.
It becomes smaller toward the flow side, and at the tip of the protrusion
It is characterized by the minimum and gradually increasing from here
The developing device according to claim 1.