Magnetic brush developing apparatus

Abstract

An efficient magnetic brush developing apparatus for the development of an electrostatic latent image which generally comprises a housing with an opening adjacent to a photoreceptor surface, a magnetic brush developing roller, a toner powder dispenser, and a rotatable vaned cylinder with a plurality of outwardly extending vanes forming buckets for transporting developer material, the mixing and diffusion for the developer material being carried out during the rotation of the vaned cylinder without causing the fatigue of developer material, and thus uneven density of the developed image being eliminated.

Description

The present invention relates to a developing apparatus and, more particularly, to improvements in a magnetic brush developing apparatus wherein a developer material comprising a magnetizable carrier and toner is adhered magnetically to the surface of a developing roller, the tips of magnetic brush bristles being rubbed, at a developing position, against an electrostatic latent image bearing surface of a photoreceptor to be developed thereby effecting the development thereof.

According to a conventional developing apparatus of a similar character, developer material is stored in the bottom of the apparatus, while an adjusting plate for adjusting the tips of magnetic brush bristles, a cleaning plate for cleaning the used developer material, a toner supplying means, a developer material stirrer, etc. are arranged near a developer material storing portion.

Accordingly, heat has been produced particularly in the portions such as the bristle tip adjusting plate, the cleaning plate, the developer material stirrer, etc. through the rotation of the developing roller and the developer material stirrer, resulting in the fatigue of the developer material. Especially, the fatigue of the developer material tends to increase with an increase of the number of revolutions of the developing roller. The fatigue of the developer material results in insufficient image density of the copies obtained even when the frequency of toner replenishment is increased also bringing about deterioration of the latent image-bearing photosensitive surface of the photoreceptor.

On the other hand, a drastic decrease of the number of rotations of the developing roller to relieve the fatigue of the developer material will give rise to the deterioration of image density of the copies to be obtained resulting in frequent uneven developments.

In the conventional developing apparatus of the above construction, it is sometimes difficult to carry out efficient mixing of the developer material only by the developer material stirrer provided in the storing portion for the developer material, the toner supplied to the magnetic brush bristles not being uniform in some cases with resultant uneven density of the image in development.

Therefore, in order to overcome the disadvantages inherent in the above-mentioned apparatus, a magnetic brush developing apparatus has been proposed wherein the developer material stored in the bottom is transported upwards by means of a developer conveyor comprising a belt and a plurality of buckets, with a toner supplying means positioned in the transporting path thereof, the developer material to be supplied being adapted to fall on the developing roller to effect the mixing and diffusing operation of the toner and the carrier material.

However, the above apparatus also has such disadvantages that although the fatigue of the developer material arising from the rotation of the developing roller is reduced by the considerable distance between the developing roller and the developer material storing portion the intermittent supply of the developer material to the developing roller effected by the falling of the developer material from each of the conveyer buckets tends to cause uneven supply of developer material and consequent unevenness in the developing density unless the developer conveyer is driven at high speeds.

Accordingly, an essential object of the present invention is to provide a magnetic brush developing apparatus which provides copies without uneven density of the developed image even at high speed development with substantial elimination of the disadvantages inherent in the conventional developing apparatus.

Another important object of the present invention is to provide a magnetic brush developing apparatus which provides stable density of developer material through sufficient mixing and diffusion of the developer material during transit in the apparatus with minimum fatigue of the developer material.

According to a preferred embodiment of the present invention, the magnetic brush developing apparatus comprises a housing with an opening adjacent to a conventional photoreceptor surface, a magnetic brush developing roller provided at the lower part of the housing close to the opening of the housing and adjacent to the photoreceptor surface bearing an electrostatic latent image to be developed, a magnetic brush bristle tip adjusting plate provided under and close to the developing roller between the developing roller and the photoreceptor surface, a developer material sump provided under the developing roller, a toner powder dispenser provided above the developing roller to supply the toner, a vaned cylinder having a plurality of vanes forming buckets for conveying developer material rotatably provided above and close to the surface of the developing roller, a used developer material sump provided under the vaned cylinder and a slit adjusting plate movably attached to the underside of the used developer material sump close to the surface of the developing roller so as to adjust the width of a slit between the developing roller and the used developer material sump, the magnetic brush developing roller further comprising an outer cylinder of non-magnetic material within which elongated bar magnets for the formation of magnetic brush bristles are rigidly fixed on a fixed metallic fixture with the outer cylinder adapted to rotate counter-clockwise in relation to the fixed metallic fixture.

In the above construction of the magnetic brush developing apparatus according to the present invention, one of the most essential features resides in that the mixing and diffusion of the developer material is carried out while the vaned cylinder having a plurality of buckets formed by vanes rotates as a developer conveyer, requiring no separate stirrer for the developing material which will generate heat by consuming electric power, with consequent reduction of the fatigue of the developer material, and also in that, since the tips of the vanes of the vaned cylinder serve as cleaning plates for scraping the used developer material off the surface of the developing roller, it is not necessary to provide separate cleaning plates as in a conventional apparatus, thus eliminating the possibility of the developer material accumulating on the cleaning plates generating heat which results in the fatigue of the developer material.

Furthermore, the provision of the slit adjusting plate to adjust the width of the slit between the developing roller and the edge of the used developer material sump is effective because the amount of the developer material to be supplied to the developing roller is adjusted by the slit adjusting plate, and at the brush bristle tip adjusting plate, only slight stroking of the tips of the magnetic brush bristles by the adjusting plate is sufficient for the tip adjusting purpose with minimum heat being generated thereby.

These and other objects and features of the present invention will become apparent from the following description taken in conjunction with the preferred embodiment thereof with reference to the accompanying drawings, in which;

FIG. 1 is a schematic diagram showing a sectional side view of a magnetic brush developing apparatus according to an embodiment of the present invention,

FIG. 2 is a schematic diagram showing a sectional side view of a magnetic brush developing apparatus according to a second embodiment of the present invention, and

FIG. 3 is a schematic diagram showing a sectional side view of a magnetic brush developing apparatus according to a third embodiment of the present invention.

Before the description of the present invention proceeds, it is to be noted that like parts are designated by like reference numbers throughout the several views of the accompanying drawings.

Referring now to FIG. 1, the magnetic brush developing apparatus which extends the width of a known photosensitive photoreceptor 10 of an electrostatic copying machine generally comprises a housing H having an opening Ha adjacent to the photoreceptor 10, a magnetic brush developing roller 1 located at the lower part of the housing H close to the opening Ha, a toner powder dispenser 11 provided above the developing roller 1 and a vaned cylinder 14 also provided above the developing roller 1. The photosensitive photoreceptor 10 is a known device driven by conventional means.

The magnetic brush developing roller 1 further comprises an outer cylinder 8 of non-magnetic material which extends the width of the housing H and within which elongated bar magnets 3, 4, 5, 6 and 7 extending nearly the entire length of the outer cylinder 8 are rigidly secured on a fixed metallic fixture 2, the outer cylinder 8 being adapted to rotate counter-clockwise in relation to the fixed metallic fixture 2.

A brush 12 made of resilient fibers connected to a conventional driving means such as a motor (not shown) is rotatably provided at the lower part of a toner powder box 11a of the toner powder dispenser 11 immediately above a hole 13 formed at the bottom of the toner box 11a so as to apply a fixed amount of toner power continuously over the developing roller 1. The vaned cylinder 14 also connected to a suitable driving means (not shown) has a plurality of vanes 15 outwardly, almost tangentially extending from the surface of the cylinder 14 with the tips of the vanes 15 located close to the surface of the developing roller 1, each space between the vanes 15 forming a bucket 16 for cleaning and carrying used developer material form the developing roller 1.

A sump portion 17 for the used developer material is provided in the housing H immediately below and close to the vaned cylinder 14, and a slit adjusting plate 18 is movably attached to the underside of the sump portion 17 close to the developing roller 1 so as to adjust the width of a slit A between the developing roller 1 and the edge of the sump portion 17, thus making the amount of developer material to be fed to a developing position B by the developing roller 1 equal to that to be applied to the developing roller 1 through the slit A by the rotation of the vaned cylinder 14.

A developer material sump 19 for supplying developer material to the developing roller 1 is provided at the bottom of the housing H immediately below and close to the developing roller 1, and an adjusting plate 9 for adjusting the tips of magnetic brush bristles formed on the developing roller 1 by the magnetic force from the magnets 3 and 4 is also provided under and close to the right of the developing roller 1 between the developing roller 1 and the photoreceptor 10.

By this arrangement, the developer material composed of a magnetizable carrier material and an electroscopic toner power supplied to the developer material sump 19 is attracted to the surface of the outer cylinder 8 of the developing roller 1 by the attraction of the magnet 3, forming magentic brush bristles radially outwardly extending from the surface of the outer cylinder 8, the brush bristles of developer material subsequently attracted by the magnets 4 and 5 being transferred to the developing position B as the developing roller 1 rotates and thus development of the latent image on the photoreceptor 10 being effected in a known manner.

It should be noted here that the bristle tip adjusting plate 9 is adapted to adjust the tips of the magnetic brush bristles formed by the magnets 3 and 4 to such an extent that the tips are slightly longer than the distance between the developing roller 1 and the latent image-bearing surface of the photoreceptor 10.

After the developing operation has been completed, the used developing material is gradually delivered upwardly with the rotation of the developing roller 1 by the action of the magnets 5, 6 and 7, while the toner is supplied from the toner powder dispenser 11, at the position of the magnet 7. Thereafter, the majority of the supplied toner scraped off by the vanes 15 with the rotation of the developing roller 1 and the vaned cylinder 14 enters the buckets 16 formed by the vanes 15, and is carried upwards. At about every half turn of the vaned cylinder 14, the mouths of approximately half of the buckets face downward, emptying the content onto the sump 17. At this time, an effective mixing and diffusion operation between the toner and the carrier is performed. Thereafter, the developer material in the sump portion 17 falls onto the developer material sump 19 successively through the slit A, which is adjusted by means of the slit adjusting plate 18, with the counter-clockwise rotation of the vaned cylinder 14, thus the mixing and diffusion operation between the toner and the carrier being conducted again, with the developer material kept in the sump 19 in a sufficiently stirred condition. A similar action is subsequently repeated.

The slit A does not have to be necessarily located between the developing roller 1 and the vaned cylinder 14, but it may be located, for example, at any place along the bottom of the sump 17.

As described in detail hereinbefore, according to the first embodiment of the present invention, no separate stirrer is required for stirring the developer material, since the stirring thereof is effected by the rotation of the vaned cylinder 14. Consequently, since the consumption of electric power, or the heat produced resulting from the stirring action is almost negligible, the fatigue of the developer material is greatly reduced. As the rotating buckets formed by the vanes 15 carry out not only the cleaning and conveying, but also the storing of the developer material the replenishment of the developer material to the developing roller 1 is effected properly. Furthermore, since all the developer material is mixed and diffused, while falling down, the stirring efficiency thereof is highly satisfactory, whereby, a stabilized density of developer material can be obtained. In the second embodiment of the present invention described later, the same advantage as described above can also be obtained.

In the developing apparatus according to the present invention as the used developer material is scraped off the surface of the developing roller 1 as the vanes 15 of the vaned cylinder 14 rotate, without requiring any other cleaning plates, efficient operation of the developing apparatus can be expected with minimum fatigue of the developer material as compared with the conventional developing apparatus in which a fixed cleaning plate is adopted with the possibility of the developer material which has accumulated on the cleaning plate generating heat.

Furthermore, in the developing apparatus according to the present invention, since the width of the slit A between the developing roller 1 and the edge of the sump 17 can be varied by moving the slit adjusting plate 18 to adjust the amount of the developer material to be supplied to the developing roller 1, slight stroking of the tips of the magnetic brush bristles by the adjusting-plate 9 is sufficient for the purpose with minimum heat being generated thereby.

Referring now to FIG. 2 showing the second embodiment of the present invention, two developing rollers 1' and 1 closely located in parallel to each other close to the surface of the photoreceptor 10 at the developing position B are employed, each of which is adapted to rotate in the same direction. In this case, the vaned cylinder 14 is on the left close to and slightly above the upper developing roller 1' in the same manner as in FIG. 1, while the lower developing roller 1 is provided below the vaned cylinder 14. The developing rollers 1' and 1 comprise outer cylinders 8' and 8 respectively within which three elongated bar magnets 3', 5' and 7' for the roller 1' and two elongated bar magnets 3 and 5 for the roller 1 are secured on the fixed metallic fixtures 2' and 2, each of the outer cylinders 8' and 8 being adapted to rotate counter-clockwise in relation to the fixed metallic fixtures 2' and 2 respectively. As the function of the developing apparatus is similar to that in the first embodiment, the description thereof is abbreviated for brevity.

Referring now to FIG. 3 showing the third embodiment of the present invention, two developing rollers 1' and 1 closely located in parallel to each other close to the surface of the photoreceptor 10 at the developing position B are employed, but the rollers 1' and 1 are adapted to rotate in opposite directions. The vaned cylinder 14 is on the left close to and between the lower roller 1 and the upper roller 1' and the toner powder dispenser 11 is located above the vaned cylinder 14. The developing rollers 1 and 1' comprise outer cylinders 8 and 8' respectively within which three elongated bar magnets 3, 5 and 7 for the roller 1 and two elongated bar magnets 20 and 21 for the roller 1' are secured on the fixed metallic fixtures 2 and 2', the outer cylinder 8 being adapted to rotate counter-clockwise and the outer cylinder 8' clockwise in relation to the fixtures 2 and 2' respectively.

It should be noted here that the direction of rotation for the vaned cylinder 14 is opposite to that for the developing roller 1.

As the vaned cylinder 14 rotates, the used developer material on the surface of the lower developing roller 1 is scraped off by the tips of the vanes 15, accumulated on the sump 17 and subsequently carried by the buckets 16 formed by the vanes 15, during which time part of the developer material falls into the sump 19, thoroughly mixed and diffused during falling, through the slit A adjustable by means of the slit adjusting plate 18, while the developer material remaining in the buckets 16 is supplied to the upper developing roller 1'.

The toner powder is supplied to the buckets 16 formed by the vanes 15 on the vaned cylinder 14 by means of the toner powder dispenser 11, the amount of toner being adjusted by the slit adjusting plate 18 movably attached to the underside of the sump 17 at the edge thereof opposite to the lower developing roller 1. On the other hand, the amount of toner to be supplied to the upper developing roller 1' is adjusted by the distance between the vaned cylinder 14 and the developing roller 1' and also by the location and magnetic field strength of the magnet 20 for developer material attraction.

It should be noted here that in the upper developing roller 1', the developer material carried by the buckets 16 formed by the vanes 15 of the vaned cylinder 14 is attracted by the magnet 20 and then forwarded to the main magnet 21 where magnetic brush bristles are formed for the first development of the latent image on the photoreceptor 10, while the lower developing roller 1 carries out the development in the same manner as in FIG. 1.

As described hereinabove, according to the third embodiment of the present invention the rotating buckets formed by the vanes on the vane cylinder carry out not only the cleaning and transporting operation of the used developer material, but also the storing operation of the developer material, so that the developer material is supplied smoothly to the developing rollers with all the supplied developer material sufficiently mixed and diffused during falling, through the slit A, thus resulting in a stabilized density of the developer material. Carrying out the developing operation at two places by means of two developing rollers allows extremely clear and vivid picture images to be obtained even in a high speed developing operation.

Although the present invention has been fully described by way of example with reference to the attached drawings, it is to be noted that various changes and modifications will be apparent to those skilled in the art. For example, the slit A in FIG. 3 which is described as provided at the edge of the used developer material sump opposite to the lower developing roller may be provided at the bottom portion of the sump. Therefore, unless otherwise such charges and modifications depart from the scope of the present invention, they should be construed as included therein.

Claims

What is claimed is:

1. A magnetic brush developing apparatus for developing an electrostatic latent image which comprises a housing structure with an opening adjacent to a photoreceptor surface, a magnetic brush developing roller provided at the lower part of said housing and adjacent to said photoreceptor surface, a toner powder supplying means provided above said developing roller, a vaned cylinder having a plurality of outwardly extending vanes which form buckets for transporting developer material rotatably provided close to the surface of said developing roller and a used developer material sump provided under said vaned cylinder, the majority of developer material on said developer roller being scraped off by vane tips of said vaned cylinder, carried upward in said buckets, and subsequently emptied into said used developer sump for mixing and diffusing of said developer material as said vaned cylinder rotates.

2. A magnetic brush developing apparatus as claimed in claim 1, which further comprises a developer material sump provided under said used developer material sump and said developing roller, and also a slit adjusting plate movably attached to the underside of said used developer material sump for adjusting the width of a slit between said used developer material sump and said developer material sump.

3. A magnetic brush developing apparatus as claimed in claim 1, further comprising a second developing roller below said firstmentioned developing roller, said developing rollers rotating in the same direction.

4. A magnetic brush developing apparatus as claimed in claim 1, further comprising a magnetic brush bristle tip adjusting plate provided under and close to said developing roller.

5. A magnetic brush developing apparatus for developing an electrostatic latent image which comprises a housing structure with an opening adjacent to a photoreceptor surface, an upper developing roller and a lower developing roller in said housing structure in parallel to each other and close to said photoreceptor surface, a vaned cylinder having a plurality of outwardly extending vanes which form buckets for transporting developer material rotatably provided above said lower developing roller and also close to said upper developing roller, a toner supplying means provided over said vaned cylinder, and a used developer material sump provided under said vaned cylinder, the majority of developer material on said lower developing roller being scraped off by vane tips of said vaned cylinder and carried upward in said buckets being subsequently emptied into said used developer sump for mixing and diffusion with the remaining part of said developer material in said buckets being supplied onto said upper developing roller as said vaned cylinder rotates.

6. A magnetic brush developing apparatus as claimed in claim 5, which further comprises a developer material sump provided under said lower developing roller and a slit adjusting plate movably attached to the underside of said used developer material sump for adjusting the width of a slit between said used developer material sump and said developer material sump.

7. A magnetic brush developing apparatus as claimed in claim 5, wherein a magnetic brush bristle tip adjusting plate is provided under and close to said lower developing roller.