US3390664A - Xerographic toner dispensing apparatus - Google Patents

Description

July 2, 1968 D. J. DONALIES 3,390,664

XEROGRAPHIC TONER DISPENSING APPARATUS Filed Jan. 5, 1967 I? f I 15/8 20 42 4a 42 4a INVENTOR a 3 I DANIEL J. DONALIES A TTOR/VE Y United States Patent ice 3,390,664 XEROGRAPHIC TONER DISPENSING APPARATUS Daniel J. Donalies, Rochester, N.Y., assignor to Xerox gorporation, Rochester, N.Y., a corporation of New ork Filed Jan. 3, 1967, Ser. No. 606,987 7 Claims. (Cl. 118637) ABSTRACT OF THE DISCLOSURE A self-regulating toner dispenser in a two-component development system of the fluidized bed type. The toner dispenser includes a briquette of compacted toner particles and means to position it within the mass of fluidized developer. Undertoned carrier granules of the developer abrade and triboelectrically attract toner from the briquette while fully toned carrier granules do not abrade the briquette. A second embodiment of the dispenser includes apparatus for spring feeding extended briquettes with cone-shaped portions into the fluidized developer, the feeding being proportionate to the toner lost from the system through the development of images.

This invention relates in general to controlling the amount of toner particles on carrier beads in two component xerographic development systems and in particular relates to apparatus for maintaining optimum toner concentration of developer during the development of latent electrostatic images.

In the practice of Xerography, as described in US. Patent No. 2,297,691 to Chester F. Carlson, a Xerographic surface comprising a layer of photoconductive insulating material afiixed to a conductive backing is used to support electrostatic images. In the usual method of carrying out the process, the xerographic surface is electrostatically charged uniformly over its surface and then exposed to a light pattern of the image being reproduced to thereby discharge the charge in the areas where light strikes the layer. The undischarged areas of the layer thus form an electrostatic charge pattern in conformity with the configuration of the original light pattern.

The latent electrostatic image can then be developed by contacting it with a finely divided electrostatically attractable material such as a powder. The powder is held in image areas by the electrostatic charges on the layer. Where the charge is greatest, the greatest amount of material is deposited; where the charge is least, little or no material is deposited. Thus a powder image is produced in conformity with the light image of copy being reproduced. The powder is subsequently transferred to a sheet of paper or other surface and suitably affixed thereto to form a permanent print.

The electrostatically attractable developing material commonly used in Xerography consists of a pigmented resinous powder referred to herein as toner and a coarse granular material called carrier. The carrier is coated with a material removed in the triboelectric series from the toner so that charge is generated between the powder and the granular carrier upon mutual interaction. Such charge causes the powder to adhere to the carrier. The carrier, besides providing a charge to the toner, permits mechanical control so that the toner can readily be brought into contact with the exposed xerographic surface. The powder particles are attracted to the electrostatic image from the granular material to produce a visible powder image on the xerographic surface.

The quality of the developed image may be affected by the ratio of toner particles to carrier beads used for development, or, as this ratio is commonly called, the toner 3,390,664 Patented July 2, 1968 concentration. For example, if there is a deficiency of toner, the image areas will be unable to attract sufiicient toner to fully develop the image, hence, undesirably light images result. On the other hand, if there is an excess amount of toner in a development system, the image areas become overly dark with quantities of toner becoming attached to non-image areas. This is because the attractive force holding toner particles on a carrier head is inversely proportional to the number of particles on such bead. Consequently, if there are few toner particles on a carrier bead, such particles will be strongly attracted thereto and will not be readily given up to the charge of the image area. If excess toner particles are on a carrier bead, the mutual attraction is decreased often to the point where the residual charge on non-image areas is sufficient to attract the toner particles from their associated carrier beads.

In the past, various attempts have been made to control the ratio of toner to carrier in the developer. These attempts have generally been directed to the periodic addition of raw toner into the developer mix to supplant the toner lost from the system by its deposition on the image. Various systems have accomplished this by adding toner periodically to the developer mixture on the basis of a time cycle or some suitable apparatus which automatically measures the developer characteristics directly or the density of the developed image. Then in response to the information measured, a suitable amount of toner may be added to the system.

While such systems are somewhat satisfactory, they have certain obvious shortcomings. For example, when toner is added to the developer it is generally added equally across the length of the development zone. If, however, the image being reproduced has large dark sections in one area, as the middle, then the central portions of the developer mix would be reduced to a lesser toner concentration than the side portion. The addition of toner to the developer evenly across the length of the development zone would not rectify this inbalance. Furthermore, systems of the known type which are somewhat self-regulating generally need time to react to a sudden depletion of toner caused by the development of large dense image areas. Hence, this time delay might cause sporadic density of development. This problem can be aggravated in some types of the time regulated toner dispensers. While these problems are not overly critical today it appears that they will become magnified in the future due to increasing speeds and the advent of improved solid area capabilities.

The present invention overcomes the shortcomings of the prior art through a self-regulating toner dispenser primarily adapted for use in a fluidized bed development system. Such a fluidized bed development system is described in my copending U. S. Patent application Ser. No. 566,944, filed July 21, 1966. The instant invention is based upon certain inherent characteristics that carrier particles exhibit with respect to toner.

When a carrier bead strikes a surface of a briquette formed of compacted toner particles, one of two things can happen. If the carrier bead surface contacting the briquette already has toner particles attracted thereto at the interface of the contact, that toner particle will exhibit a lubricous effect on the briquette and slide away therefrom causing minimal abrasive change to the briquette. Furthermore, the developer to briquette impact is somewhat cushioned by the toner layer on a toned carrier granule. This also helps to minimize briquette abrasion. If, however, that portion of the carrier bead contacting the briquette is barren of toner, then that portion of the carrier bead will abrade the briquette, scraping substantial toner from the briquette and attracting the freed toner particles to the previously bare surface of the ahrading carrier granule as well as to other adjacent undertoned carrier granules. This ability of a compacted toner briquette to dispense toner to carrier in accordance with the amount of toner already on the carrier may be utilized for dispensing toner to a developer mixture in a self-regulating manner.

In fluidized bed development systems, as described for example in the above referred to application, the particles which make up the developer are in constant motion in the development zone. By inserting a compacted toner briquette into the midst of the moving developer, the individual carrier beads may thus contact it and remove toner particles therefrom to replenish the carrier granules in proportion to that which was given up by the system through the development of images.

By the self-regulation toner dispenser of the instant invention, it is now possible to keep the two component developer mix toned to an optimum degree. Undcrtoning is prevented by virtue of the carriers ability to remove toner from the briquette when untoned. Conversely, the overtoning of developer is prevented by the negligible abrading characteristic that toned carrier will exhibit on the same briquette. Selective toner dispensing is also achieved across the development zone since each individual carrier head acts, in effect, as its own individual toner dispenser. Toner dispensing of this nature also has the ability to respond virtually instantaneously to changes in toner concentration caused by varying degrees of development. From an operational standpoint, notwith standing improved and more consistent copy quality, the handling of raw toner particles in powder form is eliminated. The handling of toner in its powdered form has in the past shown to be inconvenient and in general undesirable. Briquettes, on the other hand, are more easily stored and handled. The shortcomings of prior art toner dispensers are thus overcome with the system of the present invention which combines simplicity of machine structure in the absence of moving machine elements.

It is, therefore, an object of the instant invention to dispense toner into a two component xerographic development system.

It is also an object of the instant invention to dispense toner particles into a xerographic development zone equal to the amount of toner depleted from the system through the development images.

A further object of the invention is to control the toner concentration of developer by self-regulating means.

A further object of the invention is to maintain optimum toner concentration in fluidized bed development zones.

A further object of the instant invention is to maintain equal toner concentration across xerographic development zones.

A further object of the invention is to add toner to xerographic development systems in virtually immediate response to toner depletion.

Still a further object of the instant invention is to eliminate the need for handling raw toner powder.

These and other objects of the instant invention are obtained by positioning a compacted toner briquette in a fluidized bed development zone whereby carrier beads, depleted of toner, may abrade toner particles from the briquette and attract them thereto for the maintaining of optimum toner concentration within the development zone.

For a better understanding of the nature of the invention as well as other objects and further features thereof, reference is had to the following detailed description of the invention to be read in conjunction with the accompanying claims wherein:

FIG. 1 is a schematic sectional view of a xerographic reproducing machine embodying the principles of the instant invention with parts of the developing and toner dispensing instrumentalities broken away for clarity;

FIG. 2 is a sectional view taken along the line 22 of FIG. 1; and,

FIG. 3 is a sectional view similar to that shown in FIG. 2 but with modified toner dispensing elements.

The first illustrated embodiment is represented by FIG- URES 1 and 2 and shows a xerographic surface 10 formed in the shape of a drum and mounted for movement upon a main drum drive shaft 12 for rotation in the direction of the arrow. The drum and main drum drive shaft may be moved by any conventional power source, not shown. The motion of the surface of the drum is such as to sequentially and continuously move the surface past the several xerographic processing stations as illustrated in FIGURE 1. The elements of this machine are all conventional in the xerographic art with the exception of. those at the developing station which form the basis of the present invention. For the purpose of the present disclosure, the several xerographic processing stations in the path of movement of the xerographic surface may be briefly described as follows:

A charging station A at which a uniform electrostatic charge is deposited on the photoconductive layer of the Xerographic drum;

An exposure station B at which a light or radiation pattern of copy to be reproduced is projected onto the drum surface to dissipate the drum charge in the exposed areas thereof to thereby form a latent electrostatic image of the copy to be reproduced;

A developing station C at which a xerographic developing material including toner particles having an elec trostatic charge opposite to that of the electrostatic image, are moved into contact with the drum surface, whereby the toner particles adhere to the electrostatic image to form the xerographic powdered image in the configuration of the copy to be reproduced and whereat toner is dispensed into the developer material to replace that depleted from the developer mixture through the development of images;

A transfer station D at which the xerographic powdered image is electrostatically transferred from the drum surface to a transfer material or a support surface; and

A drum cleaning and discharge station E, at which the drum surface is brushed to remove residual toner particles remaining thereon after image transfer, and at which the drum surface is exposed to a relatively bright light source to effect substantially complete discharge of any residual electrostatic charge remaining thereon.

Development takes place within a main developer rocker assembly 14 supported by opposed end faces 16. The end faces are each provided with apertures 18 for mounting the rocker assembly on the main drum drive shaft 12 adjacent the ends of the xerographic drum. A lower support plate 20 interconnects the end faces adjacent the xerographic development zone 22. A reciprocatory motion is imparted to the rocker assembly by a motor 24 and pivoted linkage means 26 which interconnect One of the end faces with the motor for imparting a rapid oscillation to the rocker assembly. It has been found that the end of the linkage assembly connected to the end face should be secured thereto at the center of percussion of the rocker assembly for minimizing extraneous vibration thereof.

Insofar as has been described, the development instrumentalities are substantially as described in my aforementioned copending application Ser. No. 566,944.

When a quantity of two component developer is located upon the support plate 20 and a rapid reciprocation is imparted thereto by motor 24 through linkage assembly 26, the vibrated developer will suspend itself in a fluidized state throughout the entire development zone for contacting the surface and developing latent electrostatic images which have been formed thereon. Furthermore, a developing electrode 28 may be provided with the development zone. The development electrode as shown here takes the form of a screen of such mesh as to permit the developer to freely flow from the lower to the upper region of the development zone. The development electrode may either be biased or grounded as will be understood by anyone skilled in the art for the minimization of background or the improvement of solid area capabilities.

In the above referred to former application, developer was gravity fed through the development zone for maintaining adequate toner concentration within the develop ment zone. According to the instant invention, however, this problem is overcome by virtue of the novel toner dispenser.

According to the instant invention, the support plate 20 is formed in one portion with a toner dispensing cavity 30 extending the length of the support plate 20. Apertures 32 are formed within each of the end faces 16 for the reception and holding of a toner briquette 34 within the toner dispensing cavity for a purpose to be later described. Since there is no continuing flow of developer through the development zone of the instant invention, retaining lips 36 are provided on the supporting plate 20 between the end faces 16 for restricting the movement of the fluidized developer from beyond the development zone.

As mentioned above, a toner briquette 34 formed of compacted toner particles is adapted to be positioned within the development zone during development while the developer mixture is in its fluidized state. The briquette is preferably formed in the shape of an elongated cylinder extending through the development zone for a length equal to that of the drum. It may be formed of materials and in the manner as described, for example, in US. Patent No. 2,974,632 to Westervelt et al. or compacted from any of the well-known xerographic toners. It may be of any cross-sectional configuration and of substantially larger volumes than shown for the purpose of extending its life.

When the developer mixture is vibrated into a fluidized state during the development of images, toner is continuously being lost from the fluidized developer material by the development of xerographic image. The toner briquette, however, by being inserted within the fluidized developer acts to maintain an optimum toner concentration in spite of varying losses of toner removed from the developer mixture through image development.

As toner is given up to the images through development, the tonerle-ss carrier particles, or those even partially stripped of toner, are in constant motion throughout the development zone. The constant motion brings these particles into contact with the briquette at which time they abrade toner from the briquette. The abraded toner is immediately t-riboelectrically attracted to the unt-oned portion or portions of the carrier granules in the vicinity. On the other hand, if the carrier is toned, the toned surface of the carrier particles will slide over the briquette in a lubricous fashion and will abrade virtually no toner therefrom. As such, the briquette is abraded and toner dispensed only when carrier granules are incompletely toned and toner concentration is reduced.

While various manners and modes may be used to retain the toner briquette in position within the development zone during development, it may be sufficient to support the ends of the briquette by apertures 32 within the end faces 16. In order to permit the removal and replacement of a new toner briquette, the side of each end plate remote from the development zone is formed with circular threaded flanges 38 concentric with apertures 32. Each of these flanges has with it an associated threaded cap 40. Thus when it is desired to insert or remove a toner briquette from the development zone, all that is required is the unscrewing of either cap 40 and the physical withdrawal or insertion of a briquette. This may be required after extensive use of the briquette during development since the volume thereof will be continuously reduced through the dispensing of toner in accordance with the need of developer.

According to the second embodiment of the invention,

as illustrated in FIGURE 3, provision is made for the feeding of the toner briquette into the development zone during development so that new briquettes need be inserted less frequently. As can be seen in FIGURE 3, two similarly shaped briquettes 42 are adapted to be inserted into the development zone instead of the unitary briquette 34 of the first embodiment. Each of the briquettes is formed in a cone-like configuration with the points thereof located adjacent the center of the development zone. The diameters of each then increase to a maximum diameter at a point adjacent the apertures 32 in the end faces 16.

A portion of each toner briquette 42 is then formed with a cylindrical extension. This cylindrical portion of each briquette is received within the apertures 32 of the end faces 1-6. The threaded cap 44 of this second embodiment is enlarged and is provided with a cylindrical briquette guiding aperture. Within each cap 44 there is provided a suitable coil spring 46 for urging the briquette toward the center of the development zone. Also positioned within the development zone are secondary briquette supporting means in the form of rigid restraining screens 48 which act in resistance to the force of the spring to keep the briquettes in position. Each screen is held with in the cavity portion 30 of the supporting plate 20 as by embedding, cementing or other suitable securement techniques.

The mesh of screen 48 should be such that the width of any aperture is equal to the cross-sectional diameter of an intermediate portion of the cone-shaped briquette 42. By suitably selecting the screen mesh, the screen will support the briquette as well as restrain it from moving into the development zone beyond the point where the tip of the cone would cross the midpoint of the development zone.

In both embodiments of the device, the briquette will be worn away substantially evenly across the entire development zone assuming the natural development of images across the entire length of the drum. In the second em bodiment, however the substantially even wearing away of the briquette will constantaly reduce the size of the conical section of the briquette within the development zone. As the briquette is continually reduced in size, that portion of the briquette contacted by the screen 48 will be reduced so that the springs 46 may feed a new section of the briquette into the development zone. In this manner, the toner briquette has a much extended life over that of the first embodiment. As will be understood, the length of the modified cap 44 may be of a greatly extended length so that changing of the briquettes 42 need only be done over extended intervals of time.

In order to reproduce copy with the machines of the instant invention, it is first necessary to initiate a general cycle initiating means, not shown. This will act to rotate the drum to move the xerographic surface through the various processing stations as discussed above in the description of the station. The general cycle initiating means will also initiate the reciprocation of the developer rocker assembly 14 by virtue of the motion of motor 24. A quantity of two component developer material within the development zone will thus be vibrated into a fluidized state in contact with the xerographic surface for the development of images thereon. Positioned within the development zone between the aperture 32 of end faces 16 may either be cylindrical briquette 34 of the first embodiment or the conical briquettes 42 of the second embodiment. As toner is given up to the latent electrostatic image through the normal development processes, those carrier granules which have lost their toner will abrade and attract additional toner from the briquette in accordance with their needs. If minimum areas are developed, a lesser quantity of toner is deplete-d from the developer mixture and thus a lesser quantity of toner is removed from the briquette. If, on the other hand, large solid areas are developed, a greater quantity of toner will be removed from the briquette for maintaining a high toner concentration of the developer mixture. As the cylindrical briquettes of the second embodiment are abraded and reduced in size, additional lengths of briquettes will be fed into the development zone under the pressure of springs 46 against the screens 48.

It should be noted that each of the cylindrical briquettes 42 of the second embodiment operates independent of each other. Thus, if large solid areas are being developed on one side of the xerographic drum and relatively none on the other side, one briquette may be worn away faster than the other. Replacement of one briquette is thus possible without the replacement of the other. It should be also noted in this respect that toner concentration is regulated across the development zone independently of the other areas of the zone since only carrier granules which have given up their toner through development will abrade and wear away noticeable portions of the briquette.

While it has been disclosed that this device is advantageously used on a xerographie machine employing a xerographic surface in the shape of a drum, it should be understood that this invention could be readily practiced on a flexible xerographic belt or the like. It is also unnecessary that the fluidized bed development mechanisms be of the type which oscillates about the main drum drive shaft. As can be understood by one versed in the arts, the toner disepnsing abilities are equally applicable to systems wherein developer is vibrated into a fluidized state by arcuate or longitudinal reciprocations, with the reciprocations being vertical or horizontal, towards and away from the drum, or even transverse with respect to the motion of the drum. Other apparatus may likewise be employed for holding the briquette within the development zone. For example, the toner briquette may be held stationary while the developer fluidizing instru' mentalities are reciproeated with respect thereto.

While the present invention, as to its objects and advantages, has been described as carried out in specific embodiments thereof, it is not desired to be limited thereby; but it is intended to cover the invention broadly within the scope of the appended claims.

What is claimed is:

1. In a xerographic development system of the type having means to retain a quantity of developer material in a development zone beneath a surface bearing a latent electrostatic image to be developed, the developer material including carrier granules and toner particles, the system also having means to vibrate the developer material into a fluidized state in contact with the surface bearing the latent electrostatic image for the development thereof, the improvement comprising t5 toner dispensing means adapted to support a briquette of compacted toner particles within the development zone for dispensing toner to the developer material upon abrasion by untoned carrier granules in amounts equal to that depleted from the developer material through the development of images.

2. The apparatus as set forth in claim 1 and further including means to feed a toner briquette into the development zone.

3. The apparatus as set forth in claim 1 wherein the toner dispensing means includes an apertured plate on each side of the development zone, the apertures being of sufficient size to retain the opposite ends of a cylindrical toner briquette positioned across the development zone.

4. The apparatus of claim 3 wherein the apertured plates are secured to the means to retain the developer in the development zones.

5. The apparatus as set forth in claim 1 wherein the toner dispensing means includes an apertured plate on each side of the development zone and a pair of secondary apertured members positioned therebetween, the apertured plates being adapted to support the larger ends of conically shaped toner briquettes and the secondary apertured members being adapted to support the smaller ends of the conically shaped toner briquettes.

6. The apparatus as set forth in claim 5 and further including reception means located on the sides of the apertured plates remote from the secondary apertured members to receive cylindrical extensions of the conically shaped briquettes.

7. The apparatus as set forth in claim 6 and further including spring means within the reception means to mechanically urge the toner briquettes toward the secondary apertured members whereupon reduction of the size of the briquettes as caused through abrasive toner dispensing will permit the spring means to move additional portions of the briquettes into the development zone.

References Cited UNITED STATES PATENTS 3,008,826 11/1961 Mott et al. 118-637 XR 3,233,586 2/1966 Cranskens et a1 118-637 3,263,234 7/1966 Epstein et al. 118-637 XR CHARLES A. WILLMUTH, Primary Examiner. P. FELDMAN, Assistant Examiner.

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