Device For Dry Development In Electrophotography

Abstract

An electrophotographic developing device using developing powder containing a tuner and a carrier, which developing powder is applied to each photosensitive paper being developed by a magnetic developing roller. The magnetic developing roller consists of a plurality of sliced permanent magnets with spacers inserted between adjacent magnets. The sliced permanent magnets facilitate formation of magnetic brush ears of the developing powder on the peripheral surface of the magnetic developing roller, so as to insure even distribution of said developing powder over the entire span of the photosensitive paper.

Parent Case Text

This application is a division of the application Ser. No. 729,681 of Teizo Kushima and Masaya Ogawa, filed May 16, 1968, for DEVICE FOR DRY DEVELOPMENT IN ELECTROPHOTOGRAPHY, now U.S. Pat. No. 3,557,751.

Description

This invention relates to a device for dry development in electrophotography, and more particularly to an electrophotographic dry developing device for developing each exposed photosensitive paper by keeping the photosensitive paper in contact with the rotary magnetic brush ears, so as to develop static latent images on the exposed photosensitive paper, which magnetic brush ears are hairlike. These ears are formed with binary system dry developing powder comprising a carrier and a toner, and are deposited onto the peripheral surface of a revolving permanent magnet roller with the aid of a means for forming such ear, for instance, another magnet roller.

A known electrophotographic developing device using magnetic brush ears has a shortcoming in that developed images have a certain degree of unevenness due to the particular disposition of the magnetic brush "ears" formed with the developing powder on a revolving permanent magnet roller with the aid of any means. The word magnetic brush "ears" refers to developing powder particles attracted onto the peripheral surface of the magnetic roller by concentrated magnetic lines of force in the proximity of each magnetic pole on the magnetic roller, and such magnetic lines of force act to pick up developing powder in a form similar to ears of cereal grains, such as wheat ears. With such unevenness in the developed images, it has been difficult to carry out the high-speed development in electrophotography.

Therefore, an object of the present invention is to obviate the aforesaid difficulties of known electrophotographic developing devices, i.e. the unevenness and the incapability of high-speed development, by providing a novel developing device. According to the present invention, a developing roller is used, which comprises a plurality of sliced cylindrical pieces of permanent magnet, e.g. obliquely sliced permanent magnets, so that rows of magnetic brush ears are generated on the peripheral surface of the roller in a continuous fashion. Thereby, as the roller rotates, the magnetic brush ears reciprocate in the axial direction of the roller, so as to sweep the entire surface of each photosensitive paper to carry out the even development thereof. In addition, a separate magnetic roller of similar construction can be used in cooperation with the aforesaid magnetic roller having the magnetic brush ears, so that the two magnetic rollers are rotated in the opposite direction but at the same peripheral speed while keeping magnetic poles of opposite polarities adjacent with each other. As a result, the magnetic brush ears on one of the magnetic roller are kept erect on the surface thereof, to evenly cover the entire surface of the photosensitive paper so as to facilitate high-speed development.

Another object of the present invention is to provide an electrophotographic developing device comprising a developing roller having magnetic poles secured on the peripheral surface thereof and a cooperating magnet adapted to reciprocate in parallel with the axis of said developing roller in synchronism with the rotation of said developing roller, said cooperating magnet having other magnetic poles secured thereto in such fashion that said other magnetic poles always have opposite polarities to the corresponding magnetic poles secured on said developing roller over the entire peripheral surface thereof.

Other objects and a fuller understanding of the present invention may be had by referring to the following description, taken in conjunction with the accompanying drawings, in which:

FIGS. 1 and 2 are, respectively, a sectional view and an elevational view, showing a different known dry developing device usable in electrophotography;

FIGS. 3A and 3B are schematic views illustrating the manner in which uneven stripes are formed on known developing rollers and images developed thereby, respectively;

FIGS. 4A, 4B and 4C are, respectively, a sectional view, a front view, and a plan view of a permanent magnet piece to be used in the device of the present invention;

FIG. 5 is a perspective view of a magnetic roller usable in the device according to the present invention, shown with a part thereof cut away;

FIG. 6 is a perspective view, illustrating the configuration of magnetic brush ears formed on the peripheral surface of the magnetic roller;

FIG. 7 is an elevational view of a pair of the aforesaid magnetic roller, working in cooperation with each other;

FIG. 8 is a transverse sectional view of an embodiment of the device according to the present invention;

FIG. 9 is a schematic front view of another embodiment of the device of the present invention; and

FIGS. 10A and 10B are, respectively, a perspective view and a longitudinal sectional view of a cooperating magnet used in the embodiment of FIG. 9.

Like parts are designated by like numerals and symbols throughout the drawings.

FIG. 1 shows an example of known electrophotographic dry developing devices, in which an exposed photosensitive paper 1 travels horizontally with the photosensitive layer thereof facing downwards. The photosensitive layer has an electrostatic latent image formed thereon by the preceding exposure, and the opposite side surface of the photosensitive paper is guided by a guide plate 2, which is directly grounded or biased by a suitable voltage. A developing powder tank 3 contains developing powder 4 therein, and a magnetic roller 6 secured to a shaft 5 rotates about the axis of the shaft 5. As the magnetic roller 6 revolves, the developing powder 4 is adhered to the peripheral surface of the roller along the magnetic field pattern thereon, so that magnetic brush ears are formed on the roller 6. The developing powder contains toner particles and carrier particles electrostatically holding said toner particles. Such developing powder 4 is successively poured on the exposed photosensitive layer of the photosensitive paper 1, responsive to the revolution of the magnetic roller 6. With such setup of the developing device, the developed image tends to have unevenness due to the particular pattern of the magnetic brush ears on the surface of the magnetic roller 6.

Referring to FIG. 3A, a known magnetic roller is magnetically divided along radial directions, so that each magnetic pole is shown as a straight line on the peripheral surface of the roller, and opposite polarities N and S are disposed alternately along the peripheral direction thereof. With the magnetic roller of such construction, the image on the developed photosensitive paper tends to be uneven, in the form of stripes disposed perpendicular to the traveling direction of the photosensitive paper at certain intervals corresponding to the spacings of the magnetic poles on the magnetic roller. On the other hand, if the magnetic roller 6 comprises a plurality of disklike magnets having magnetic poles formed on the opposite circular and surfaces thereof, as shown in FIG. 3B, the magnetic brush ears are formed continuously in the peripheral direction of the roller but discontinuously in the longitudinal direction thereof. Accordingly, photosensitive paper developed by using a magnetic roller as shown in FIG. 3B tends to have stripes formed along the travelling direction of the photosensitive paper in the developing device.

In other words, the magnetic brush ears have heretofore been disposed on the magnetic roller so as to be continuous only in the longitudinal direction of the roller with intervals in the lateral direction thereof, or to be continuous only in the peripheral direction at right angles to the axis of the roller with intervals in the longitudinal direction thereof. Such disposition of the magnetic brush ears causes unevenness in the developed image on the photosensitive paper.

In order to obviate such difficulty, it has been proposed and practiced to place a separate auxiliary permanent magnet 7 at the back of the guide plate 2, as shown by dotted lines in FIG. 1. The magnetic lines of force issuing from the permanent magnets constituting the magnetic roller 6 are directed toward the auxiliary magnet 7, so that each magnetic brush ear can be kept erect and extended as far as possible to evenly distribute the magnetic lines of force on the photosensitive paper to mitigate the aforesaid unevenness in the developed image. However, the effects of such auxiliary magnet are also limited, because when the polarities of the auxiliary magnet 7 and the constituent magnet of the magnetic rollers 6 are the same the magnetic lines of force repel each other to prevent erection of the magnetic brush ears. Accordingly, the unevenness of the developed image cannot be eliminated completely by such auxiliary magnet. With such unevenness of the developed image, it has been very difficult to speed up the developing process, as pointed out hereinbefore.

In another known construction of the developing device, a bar magnet 8 is placed at the back of the guide plate 2, which bar magnet is so magnetized as to have one magnetic pole, e.g. N pole, is formed on the side closer to the photosensitive paper 1, while forming the other magnetic pole on the opposite side of the bar magnet, as shown in FIG. 2. In this case, for instance, magnetic lines of force 9 issuing from S poles on the magnetic roller 6 are erected by being attracted by the opposite magnetic pole of the auxiliary magnet 8, while those issuing from N poles of the magnetic roller 6 are suppressed by the aforesaid magnetic poles of the auxiliary magnet 8 having the same polarity. Accordingly, when an exposed photosensitive paper 1 travels between the magnetic roller 6 and the bar magnet 8 with the photosensitive layer 10 facing downward or toward the magnetic roller 6, as shown in FIG. 2, those portions of the photosensitive layer 10, where the erected magnetic brush ears intersect therewith, are well developed, while the remaining portions of the photosensitive layer are developed insufficiently. Thus, unevenness of the development occurs.

The inventors have succeeded in completely eliminating such unevenness of the development by providing a magnetic roller consisting of a plurality of sliced permanent magnet pieces.

Referring to FIGS. 4A, 4B, and 4C, a cylinder made of ferromagnetic substance and having a through hole along the longitudinal axis thereof is obliquely sliced with respect to the longitudinal axis thereof, by a known slicing process. A plurality of obliquely sliced permanent magnet pieces 11 are formed by magnetizing each of the thus sliced pieces in such direction as to produce magnetic poles N and S on opposite elliptic surfaces thereof, respectively. In order to facilitate radial erection of the magnetic lines of force, a spacer ring 12 is inserted between adjacent magnet pieces 11 during the assembly thereof. The magnet pieces 11 are, of course, so disposed as to have the same polarity poles located adjacent to each other, as illustrated in FIG. 5. A magnetic roller 13 is formed by inserting a shaft 16 through the thus assembled magnet pieces 11 and the spacers 12, and fastening them together by inserting metallic end holding fittings 14 at both ends of the assembly. In the particular embodiment, as shown in FIG. 5, the magnetic roller 13 is covered by a nonmagnetic cylinder 15.

If developing powder 4 usable for electrophotographic development is applied on the surface of the magnetic roller 13 of the last mentioned construction, a series of magnetic brush ears 17 are formed obliqueness on the peripheral surface of the nonmagnetic cylinder 15, due to the obliquity of the constituent permanent magnet pieces 11, as depicted in FIG. 6. When such magnetic roller 13 is rotated on a photosensitive paper, the magnetic brush ears 17 reciprocate as a whole in the axial direction of the roller 13, so as to cover evenly the entire surface of the photosensitive paper 1 to develop evenly the latent image thereon.

In a preferred embodiment of the present invention, a pair of such magnetic rollers 13 are disposed in parallel with each other in such manner that each magnetic pole on the one roller 13 is so positioned as to face the corresponding magnetic poles of opposite polarity on the other magnetic roller 13, as shown in FIG. 7. More particularly, each N pole on the lower roller 13 is located directly below the corresponding S pole on the upper roller 13, while each S pole of the lower roller 13 is located directly below the corresponding N pole on the upper roller 13. The two magnetic rollers 13 are rotated at the same peripheral speed around the shaft thereof, respectively, in opposite directions. Then, the aforesaid relation between the corresponding magnetic poles of the two magnetic rollers is always maintained, so that almost uniform and parallel magnetic lines of force intersect with the photosensitive paper throughout the entire span thereof, while reciprocating in the axial direction of the rollers. Thus, a continuous line of developing powder 4 is applied to the photosensitive paper 1 by the magnetic brush ears 17 formed by such evenly distributed magnetic lines of force. Accordingly, as the roller 13 rotates, the linearly disposed developing powder 4 reciprocates in the axial direction of the rollers, to cover the entire photosensitive layer 10 of the photosensitive paper 1, without any gap. Thereby, the danger of unevenness in the development, or formation of stripes in the developed image, is totally eliminated.

The magnetic roller 13, usable in the device according to the present invention can be used in combination with a bar magnet 7, as shown in FIG. 1, and in this case, the alternate magnetic poles of the roller 13 face an elongated magnetic pole of particular polarity N or S of the bar magnet 7. With such arrangement, the unevenness of the developed image can be improved. However, magnetic brush ears of one magnetic polarity are erected, while those of the opposite polarity are suppressed, as in the case of the construction of FIG. 2. The development produced by such combination of the bar magnet 7 and the magnetic roller 13 is not as even as the development produced by using two magnetic rollers 13 in the manner as illustrated in FIG. 7.

FIG. 8 illustrates the use of a pair of magnetic rollers 13. A photosensitive paper 1 is fed at a constant speed by pairs of roller 19, and at least one pair of them is driven by a separate driving means (not shown). A scraper 18 is provided to collect such developing powder 4 which is picked up by the magnetic brush ears 17 but not used for developing the photosensitive paper 1. The developing powder 4 thus collected falls into the tank 3 by gravity. The scraper 18 per se is known to those skilled in the art.

As described in the foregoing, according to the present invention, a magnetic developing roller is formed by using a plurality of obliquely sliced cylindrical permanent magnet pieces, each being so magnetized as to have magnetic poles on the opposite elliptic end surfaces thereof, so that magnetic brush ears are produced uniformly over the entire span of the thus formed roller. Besides, the magnetic developing roller revolves around its own axis while reciprocating the magnetic brush ears in the axial direction of the roller, so as to develop each photosensitive paper in two-dimensional fashion. Thereby, unevenness in the developed image is completely eliminated. In a preferred embodiment of the present invention, a pair of such magnetic developing rollers are disposed in parallel with each other with the magnetic poles of opposite polarities positioned side by side, and the two rollers are rotated around the axes thereof respectively at the same peripheral speed in opposite directions while maintaining the magnetic poles of the opposite polarities side by side. Thus, the magnetic brush ears are well erected, to apply the developing powder uniformly on the photosensitive paper to be developed. As a result, uniform developing is insured not only for normal speed development but also for high-speed development.

In the preceding description, the permanent magnet pieces are illustrated as obliquely sliced. However, it should be noted that the permanent magnet pieces usable for the developing device according to the present invention are not limited to those obliquely sliced, but any configuration of the permanent magnet piece which allows the uniform distribution of the magnetic brush ears can be used in the device of the present invention, as would be apparent to those skilled in the art.

FIG. 9 shows a different embodiment of the present invention, in which a reciprocating auxiliary permanent magnet means including a plurality of permanent magnet elements is used. A magnetic developing roller 13 of the same construction as that shown in FIG. 8 is so disposed as to face the photosensitive layer 10 of photosensitive paper 1 to be developed. As shown in FIGS. 10A and 10B, a reciprocating auxiliary permanent magnet means 7 includes a plurality of permanent magnet elements 20, each having a width substantially the same as the width of each constituent permanent magnet piece 11 of the magnetic developing roller 13. The permanent magnet elements 20 are disposed in a row on a plane so as to place the magnetic poles of the same polarity side by side with a spacer 21 inserted therebetween. The magnet elements 20 thus assembled are tightened together by using a tightening framework 22. The reciprocating auxiliary magnet means 7 of such structure is held in parallel with the magnetic developing roller 13, by a suitable means (not shown), so that one magnetic pole of the roller 13 faces the magnetic poles of the opposite polarity of the auxiliary magnet means 7. In other words, the N and S magnetic poles of the roller 13 face the S and N poles of the magnet means 7, respectively. A bevel gear 23 is secured to a shaft 16 of the roller 13, which bevel gear in turn engages with another bevel gear 24 secured to the one end of a crankshaft 25. The opposite end of the crankshaft 25 is connected with the permanent magnet means 7 through a crank 26 and a link lever 27.

The gear ratio between the bevel gears 23 and 24, and the dimension of the crank 26 and the link lever 27 are such that, the magnet means 7 completes one linear reciprocation for each full rotation of the developing roller 13. The linear reciprocation of the magnet means 7 is made in the axial direction of the roller 13 in parallel therewith, and the stroke of the reciprocation corresponds to the width of the permanent magnet piece 11 of the roller 13, which is substantially the same as the width of the permanent magnet element 20 of the magnet means 7.

Accordingly, when the magnetic developing roller 13 rotates around its own shaft 16, both the permanent magnet pieces 11 constituting the roller 13 and the permanent magnet elements 20 of the magnet means 7 are reciprocated as a whole, while keeping the magnetic poles of the opposite polarities side by side. Thereby, uniformly distributed magnetic lines of force 9 are generated substantially in parallel with each other over the entire width of the photosensitive paper 1 to be developed. The magnetic brush ears 17 formed by such magnetic lines of force 9 are uniformly erected, and reciprocated at right angles with the travelling direction of the photosensitive paper 1 being developed in the axial direction of the roller 13.

As described in the foregoing, according to the present invention, the photosensitive layer of each photosensitive paper can be swept over the entire width thereof by evenly distributed magnetic brush ears, so that the possibility of unevenness in the developed image is completely eliminated. Accordingly, the developing powder is applied uniformly to the photosensitive layer of the photosensitive paper, by means of the reciprocation of the magnetic brush ears in the axial direction of the roller, so that excellent uniform developing effect is insured not only for normal speed developing but also for high-speed developing.

Claims

Although the present invention has been described with a certain degree of particularity, it is understood that the present disclosure has been made only by way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and the scope of the invention as hereinafter claimed.

1. An electrophotographic developing device using developing powder of two-component system containing a carrier and a toner, comprising a magnetic developing roller, a developing powder tank located on one side of said developing roller, a feeder to feed a photographic paper to be developed on the opposite side of said developing roller, said developing powder being magnetically attracted to the peripheral surface of said magnetic developing roller and formed into magnetic brush ears which pick up said developing powder from said tank to distribute said powder on said photosensitive paper, said magnetic developing roller having a plurality of sliced cylindrical permanent magnets jointed together by a common shaft with spacers inserted between adjacent sliced cylindrical permanent magnets, said common shaft penetrating through the center of each of said sliced permanent magnets at an acute angle, and an auxiliary magnet roller identical with said magnetic developing roller, said auxiliary magnet roller being arranged in parallel with said magnetic developing roller and adapted to rotate inversely and synchronously with the rotation of said magnetic developing roller in one to one relationship, the magnetic poles of each of sliced cylindrical permanent magnets of said auxiliary magnet are so disposed as to be located side by side with magnetic poles of the opposite polarity on said magnetic developing roller over the entire span of the auxiliary magnet and through the synchronized rotation therebetween.