JPS6260713B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic brush type dry developing device used in electronic copying machines and the like.

A magnetic brush type developing device, which is known as a type of dry developing device, includes a non-magnetic sleeve element and a magnet that is disposed within the sleeve element and applies a magnetic field of a predetermined magnetic pole to the outer peripheral surface of the sleeve element. In such a developing device, a developer containing magnetic powder is held in the form of brush-like ears on the outer peripheral surface of the sleeve element by the magnetic action of the magnet, and as the sleeve element rotates, the developer is applied to the photoreceptor. A developing action is carried out by being sequentially conveyed toward the surface of the electrostatic latent image carrier and directly contacting the photoconductive layer of the photoreceptor. The developing power in this type of developing process is expressed by the following equation.

F = F _C - F _M , where F is the developing force, F _C is the electric attraction force of the developer due to the electrostatic action of the photoreceptor, and F _M is the magnetic attraction of the developer due to the magnetic action of the magnetic brush developing device. It is power.

From the above equation, it will be understood that the magnetic attraction force F _M by the magnetic brush type developing device has a negative biasing role with respect to the developing force F. Therefore, when the development characteristics are expressed using the magnetic attraction force F _M as a parameter, it becomes as shown in FIG. In the graph of FIG. 1, the vertical axis shows the toner adhesion amount M, and the horizontal axis shows the surface charge Q on the photoreceptor. The solid line shows the development characteristics when the magnetic attraction force F _M is relatively small, and the broken line shows the development characteristics when the magnetic attraction force F _M is relatively large. Incidentally, the development time was set to be the same when the magnetic attraction force F _M was relatively large and small. As is clear from the graph shown in FIG. 1, when the magnetic attraction force F _M is reduced, the toner adhesion amount M becomes saturated from a point where the charge amount Q is relatively small, and uneven development becomes less likely to occur. Furthermore, if the magnetic attraction force F _M is small, the toner adhesion amount M at the same development time will be reduced by the magnetic attraction force F _M
Therefore, for the same toner adhesion amount M, the developing time can be shortened compared to when the magnetic attraction force F _M is large. However, when the magnetic attraction force F _M is reduced, background stains increase, the sharpness of the image is poor, and the image quality is not very good.

In contrast, conventionally, two magnetic brush type developing devices are provided spaced apart along the direction of movement of the photoreceptor, and the magnetic attraction force of the developing device located upstream in the direction of movement of the photoreceptor is The magnetic attraction force of the developing device located downstream in the direction of movement of the photoreceptor is set relatively small, and the magnetic attraction force of the developing device located upstream in the direction of movement of the photoreceptor is set to be relatively large. There is known a structure in which the toner is uniformly adhered to the photoreceptor and the image is adjusted to eliminate background smudges and the like by a developing device located downstream in the direction of movement of the photoreceptor. Although such a developing device achieves its intended purpose, it has a complicated structure, poses problems in terms of weight and space, and is also expensive.

The present invention aims to provide a new type of magnetic brush type developing device which has a simple structure and can obtain the same effects as the above-mentioned double sleeve type developing device.

By the way, the same applicant as the applicant of the present application is
In No. 54-95243, it was discovered that by devising the shape of the magnetic pole part of the magnet, one magnet could generate a magnetic attraction force distribution with multiple peaks on the sleeve surface at the development action position, A magnetic brush type developing device that effectively utilizes this fact has been proposed.

The present invention achieves the above-mentioned object by making more effective use of the fact that one magnet generates a magnetic attraction force distribution having multiple peaks at the development action position by devising the shape of the magnetic pole part of the magnet. This is what I am trying to do.

According to the invention, such an object is achieved by providing a magnetic brush having a rotating non-magnetic sleeve element and a magnet fixedly disposed within the sleeve element opposite to the developing position and generating a magnetic field on the outer circumferential surface of the sleeve element. In the developing device, the magnet has one magnetic pole portion having a magnetic pole surface shape capable of generating a magnetic attractive force distribution having a plurality of peaks at a developing action position on the outer circumferential surface of the sleeve; This is achieved by a magnetic brush developing device configured such that among the peaks of the magnetic attractive force distribution, those on the downstream side in the moving direction of the electrostatic latent image carrier are stronger than those on the upstream side.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the accompanying drawings.

FIG. 2 is a schematic diagram showing one embodiment of the dry developing device according to the present invention. The dry developing device shown in FIG. 2 includes a non-magnetic sleeve element 1 which is rotationally driven in a counterclockwise direction as viewed in FIG. 2 about its own central axis. It has a magnet 2 inside. A portion of the sleeve element 1 faces the peripheral surface of a drum-shaped electrostatic latent image carrier, so-called photosensitive drum 3, with a predetermined distance therebetween, and the magnet 2
has one magnetic pole portion, for example, an N magnetic pole, which faces the circumferential surface of the photoreceptor drum 3 across the sleeve element 1 at its opposing region, that is, at the development action position, and at the development action position. A magnetic field is generated on the outer peripheral surface of the sleeve element 1. This magnet is fixedly arranged at the above position. In addition,
Although not shown, a magnet for transporting the developer is built into the sleeve element 1. The magnetic pole part is a third
As shown in the enlarged view, the magnetic pole part has a concave groove 4 at a position offset to the downstream side in the photoconductor drum movement direction on the magnetic pole surface, and the concave groove 4 is on the upstream side in the photoconductor drum movement direction. A wide first magnetic pole portion 5 is formed on the downstream side in the direction of movement of the photoreceptor drum, and a narrow second magnetic pole portion 6 is formed on the downstream side in the direction of movement of the photosensitive drum.

Each magnetic pole part 5, 6 may be formed by cutting a groove 4 into the magnetic pole face of one of the magnetic pole parts of a single magnet, or by cutting individual magnetized magnet pieces at intervals on the magnetic pole face. It may also be formed by placing two parts and integrating them by adhesion or the like. As shown in FIGS. 5 and 7, the magnetic pole surface of the magnetic pole part at one end of the magnet facing the sleeve element 1 is formed in an uneven manner, so at first glance it appears that there are multiple magnetic poles. , each magnetic pole part has the same polarity (N in the case shown)
Since it is a magnetic pole (pole), it essentially consists of one magnetic pole part. It can be said that.

Now, in this way, in a magnet that has an uneven part on the magnetic pole surface of one magnetic pole part, the distance between the magnetic poles at both ends (between N and S poles) is different between the concave part and the convex part, and therefore,
The demagnetizing field generated inside the magnet
field) is different between concave portions and convex portions.

To explain in more detail, the demagnetizing field generated inside a magnet changes depending on the size and shape of the magnet, and generally speaking, the demagnetizing field generated inside a magnet changes depending on the size and shape of the magnet. The longer the distance, the smaller it becomes. Therefore, even if the magnet is uniformly magnetized, by forming uneven parts on the magnetic pole face of the magnetic pole part and partially changing the distance between the magnetic poles, the demagnetizing field acting on the concave and convex parts can be reduced. You can change the strength.

In other words, when a recess is formed on the magnetic pole face of the magnet,
A strong demagnetizing field acts on the recessed portion, so that the strength of the magnetic field generated outside the magnet by the recessed portion is weaker than that generated by other portions of the magnetic pole. vice versa,
When a convex portion is formed on the magnetic pole surface, the strength of the magnetic field at the convex portion is stronger than at other portions.

Therefore, as shown in FIG. 3, when one concave groove 4 is provided on the magnetic pole face of the magnet 2 (the N pole in the figure), two grooves are formed in the magnetic pole part having the concave groove 4. A magnetic field with a magnetic attraction force distribution having a peak is obtained, and a magnetic field with a magnetic attraction force distribution as shown in FIG. 4 is generated on the outer peripheral surface of the sleeve element 1.

Next, details of generating a magnetic attraction force distribution having a plurality of peaks will be explained based on FIG. 9. At the position closest to the magnet, four acute-angled hip peaks are formed, as shown in Figure a, but as you move away from the magnet, the peaks become blunter and their number decreases, as shown in Figure b. There will also be three. Then, at a position further away from the magnet (the position of the outer circumferential surface of the sleeve), the peak becomes even more blunt, and the number of peaks decreases to 2, as shown in Figure c. The number and shape of the peaks shown in FIG. 9c are those shown in FIG. That is, when comparing the first magnetic pole part 5 and the second magnetic pole part 6, since the groove 4 is formed to be biased toward the downstream side in the moving direction of the sleeve 1, the demagnetizing field acting on both magnetic pole parts is The strength of the magnetic field is different, and the magnetic field of the second magnetic pole part 6 is stronger. Therefore, the magnetic flux density generated from the second magnetic pole part 6 is higher than that of the first magnetic pole part 5, so the magnetic attraction force of the second magnetic pole part 6 is higher than that of the first magnetic pole part 5. The magnetic attraction of is becoming stronger.

Therefore, during development, the electrostatic latent image on the photoreceptor drum 3 is effectively attracted by the relatively weak magnetic attraction force of the first magnetic pole portion 5 located on the upstream side in the moving direction of the photoreceptor drum 3. The developer is uniformly attached, and then the image on the photoreceptor drum 3 is aligned by a relatively strong magnetic attraction force by the second magnetic pole part 6 located downstream in the direction of movement of the photoreceptor drum. The statue is performed. This makes it possible to obtain high-quality images without uneven density and background smudges.

FIG. 5 is a longitudinal sectional view showing an enlarged main part of another embodiment of the dry developing device according to the present invention.
In the case of such an embodiment, the magnetic pole portions of the magnet 2 include a first magnetic pole portion 7 having a predetermined first spacing with respect to the outer circumferential surface of the sleeve element 1 and a first magnetic pole portion 7 having a predetermined first spacing with respect to the outer circumferential surface of the sleeve element 1. and a second magnetic pole portion 8 having a second spacing smaller than the first spacing, resulting in a stepped end. In this case, the first magnetic pole part 7 is provided on the lag side of the second magnetic pole part 8 in the moving direction of the photosensitive drum 3.

In such an embodiment, the sleeve element 1
A magnetic field having a magnetic attractive force distribution as shown in FIG. 6 is generated on the outer circumferential surface of the magnet, and the same effect as in the embodiment described above is obtained. The distribution of the magnetic attraction force shown in FIG. 6 is that of the outer circumferential surface of the sleeve 1, and the distribution in the portion near the magnet will be easily understood from what was explained in FIG. 9.

FIG. 7 is a longitudinal cross-sectional view of the essential parts of yet another embodiment of the developing device according to the present invention. In the case of such an embodiment, the magnetic pole part of the magnet 2 has two grooves 9,
10 spaced apart from each other, first, second, and third magnetic pole parts 1 separated by respective grooves.
1, 12, and 13. Of the three magnetic pole parts, the two on the upstream side in the direction of movement of the photoreceptor drum have equal spacing from each other with respect to the outer circumferential surface of the sleeve element 1, but the two on the upstream side in the direction of movement of the photoreceptor drum are the most downstream in the direction of movement of the photoreceptor drum. Some third pole sections 13 are closer to the outer circumferential surface of said sleeve element 1 than others. In the case of such an embodiment, as shown in FIG. 8, a magnetic field with a magnetic attractive force distribution having three peaks is obtained, and among the peaks, the one located on the downstream side in the direction of movement of the photoreceptor drum 3 is the strongest. It has magnetic attraction. The distribution of the magnetic attraction force shown in FIG. 8 is that of the outer circumferential surface of the sleeve 1, and the distribution in the portion near the magnet will be easily understood from what was explained in FIG. 9. In the case of this embodiment, a good and uniform developer is applied to the electrostatic latent image on the photoreceptor drum 3 under the condition of relatively weak magnetic attraction force by the first and second magnetic pole parts 11 and 12. The adhesion is performed, and the image on the photoreceptor drum 3 is imaged under the condition of a relatively strong magnetic attraction force by the third magnetic pole portion 13. The magnetic developer used in the present invention may be a two-component developer consisting of a non-magnetic toner and a magnetic carrier, or a one-component developer consisting only of magnetic toner.

As described above, according to the present invention, a relatively weak magnetic attraction condition and a relatively strong magnetic attraction condition are provided to the developing position by substantially one magnet, so that the structure is not complicated. A high-quality copy image with no density unevenness and background smudge can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a graph showing the development characteristics using the magnetic attraction force of the developing device as a parameter, Fig. 2 is a schematic vertical sectional view showing an embodiment of the magnetic brush developing device according to the present invention, and Fig. 3 is the main part thereof. FIG. 4 is a graph showing the magnetic attraction force distribution on the outer peripheral surface of the sleeve element when the magnet shown in FIG. 2 is used. FIG. A vertical cross-sectional view showing the main parts of another embodiment of the device,
FIG. 6 is a graph showing the magnetic attraction force distribution on the outer peripheral surface of the sleeve element when the magnet shown in FIG. 5 is used, and FIG. 7 is a graph showing still another embodiment of the developing device according to the present invention. FIG. 8 is a graph showing the magnetic attraction force distribution on the outer peripheral surface of the sleeve element when the magnet shown in FIG. 7 is used, and FIG. FIG. 3 is an explanatory diagram for explaining a change in magnetic attraction force that changes with the change in magnetic attraction force. DESCRIPTION OF SYMBOLS 1... Sleeve element, 2... Magnet, 3... Photosensitive drum, 4... Concave groove, 5... First magnetic pole part, 6
...Second magnetic pole part, 7...First magnetic pole part, 8...
Second magnetic pole part, 9, 10... Concave groove, 11... First magnetic pole part, 12... Second magnetic pole part, 13... Third magnetic pole part.

Claims (1)

[Scope of Claims] 1. A rotating non-magnetic sleeve element that is disposed close to a developing position of the electrostatic latent image carrier, and a rotating non-magnetic sleeve element that is fixedly disposed within the sleeve element opposite to the developing position. and a magnet that generates a magnetic field on the outer circumferential surface of the sleeve element, wherein the magnet generates a magnetic attraction force distribution having a plurality of peaks at a developing action position on the outer circumferential surface of the sleeve. It has a magnetic pole part having a magnetic pole surface shape, and is configured such that among the peaks of the magnetic attractive force distribution, the peaks on the downstream side in the moving direction of the electrostatic latent image carrier are stronger than the peaks on the upstream side. A magnetic brush developing device characterized by: