US3550555A

US3550555A - Xerographic developer separation

Info

Publication number: US3550555A
Application number: US659520A
Authority: US
Inventors: Frederick W Hudson
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1967-08-09
Filing date: 1967-08-09
Publication date: 1970-12-29
Anticipated expiration: 1987-12-29
Also published as: GB1238032A

Description

United States Patent lnventor Frederick W. Hudson West Henrietta, N.Y.

Appl. No. 659,520

Filed Aug. 9, 1967 Patented Dec. 29, 1970 Assignee Xerox Corporation Rochester, N.Y. a corporation of New York XEROGRAPHIC DEVELOPER SEPARATION 3 Claims, 2 Drawing Figs.

US. Cl 118/637, 118/312, l18/603;117/17.5 Int. Cl. 1305c ll/IO, 603g 13/06 Field of Search 1 18/637,

[56] References Cited UNITED STATES PATENTS 1,049,217 12/1912 Fasting 209/481X 1,757,810 5/1930 Newman et al.. 209/481 3,357,399 12/1967 Fisher 118/637 3,379,169 4/1968 Lovercheck.. 1 18/258 3,393,663 7/1968 Donalies 118/637 Primary ExaminerPeter Feldman Attorneys-Stanley 2. Cole and Norman E. Schrader ABSTRACT: Apparatus for separating excess toner particles from over-toned two-component xerographic developer. A vibrating tray, offset from the horizontal, is positioned to receive over-toned two-component xerographic developer mix comprising carrier granules and excess toner particles. As the developer is deposited on the tray, optimumly toned carrier granules will move towards the lower end of the tray for use in the development of latent electrostatic images. Excess toner particles will move in the opposite direction for being removed from the mixture.

PATENTEBbEczQ mm INVENTOR. FREDERICK W. HUDSON ATTORNEYS XEROGRAPHIC DEVELOPER SEPARATION This invention relates in general to xerographic development, and in particular, relates to apparatus for ensuring that only optimumly toned two-component developer is supplied for use in developing latent electrostatic images.

In the practice of xerography, as described in US. Pat. No. 2,297,691, to Chester F. Carlson, a xerographic surface comprising a layer of photoconductive insulating material affixed to a conductive backing is used to support electrostatic images. ln the usual method of carrying out the process, the xerographic plate 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 resinous 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; and where the charge is least, little or no material is deposited. Thus, a powder image is produced in conformity with the light image of the copy being reproduced. The powder is subsequently transferred to a sheet of paper or other surface and suitably affixed to thereby form a permanent print.

The electrostatically attractable developing material com monly used in xerography consists of a pigmented resinous powder referred to here as toner and a carrier" of larger granular beads formed with glass, sand or steel cores coated with a material removed in the triboelectric series from the toner so that a triboelectric charge is generated between the toner powder and the granular carrier. Such charge causes the toner to adhere to the carrier. The carrier also provides mechanical control so that the toner can be readily handled and brought into contact with the exposed xerographic surface. The toner is then attracted to the electrostatic image to produce a visible powder image on the xerographic surface.

Toner particles which are mixed with carrier adhere to and coat the surface of the carrier due to the electrostatic attraction between them. This two-component mixture of carrier and toner constitutes the developer mixture. During development the toner-coated carrier moves across the xerographic surface at which time toner particles are electrostatically pulled away from the carrier by the charged areas of the surface and are selectively deposited thereon to form a visible powder image. The partially denuded carrier then moves beyond the xerographic surface. As toner images are formed, additional toner powder is generally supplied to the developer mixture in proportion to the amount of toner deposited on the xerographic surface.

The percentof toner particles to carrier granules within a developer mixture is generally referred to as the toner concentration. When there are insufiicient toner particles with a given quantity of carrier granules in the developer mixture, these toner particles will be tightly bonded to the carrier granules by the electrostatic forces therebetween. When such a low toner concentration developer is used to develop latent electrostatic images, the charges in the image areas are insufficiently strong to electrostatically attract sufficienttoner particles away from the carrier granules. Furthermore, insufficient toner particles will be available for the development of images. lmages developed with developer mixtures of a low toner concentration produce undesirably light copy.

On the other hand, when a high toner concentration developer is used to develop latent electrostatic images, the electrostatic bond between the toner particles and the carrier granules is very low. Because of this, the residual charges in nonimage areas of latent electrostatic images are often sufficient to attract away toner particles which are loosely held to carrier granules. Copy produced by developer of a higher toner concentration is characterized by overly dark image areas and undesirable toner deposition in background areas. In either event it is apparent that optimumly toned carrier granules or optimum toner concentration is essential for creating high quality xerographic reproductions.

The electrostatic force bonding toner particles to carrier granules is inversely proportional to the amount of toner particles on a carrier granule. The instant invention achieves the proper ratio of toner to carrier for any two-component developer mixture to ensure optimum development.

Optimum toner concentration, however, is dependent on the atmospheric conditions in which the xerographic development is carried out. This is because the electrostatic bond between toner and carrier is inversely proportional to humidity. For example, if a xerographic machine were operated with a two-component developer mixture having a toner concentration optimum for an average humidity, it will develop optimumly at an average humidity. lf however, the same machine with the same developer were operated at a high humidity, the copy produced would be overly dark since toner would be given up to the image area charges too easily due to the decreased toner-to-carrier bond caused by the high humidity. This humidity problem also exists for low humidity.

When, however, developer is separated in accordance with the instant invention, the same humidity factors affecting development are also present at the developer separating station. Consequently, developer may be supplied from the separator at a toner concentration optimum for the atmospheric conditions at which the xerographic development takes place.

In the past, efforts have been made to control toner concentrations by various methods and means. An initial attempt to control the toner concentration involved the visual observation of copies produced by a xerographic system. When the copies became too light in image areas, thus indicating a low toner concentration, additional toner would be added by manually energizing a gravity feed of toner to the system from a toner dispenser. More sophisticated approaches to the problem involved the adding of additional toner automatically in response to the density of the developer mixture before being moved into contact with the image to be developed or automatic toner dispensing in response to copy density. Note US. Pat. No. 3,094,049.

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 mixture would be reduced to a lesser toner concentration than the side portions. The addition of toner to the developer evenly across the length of the development zone would not rectify this inbalance.

The present invention contemplates overcoming the problems of maintaining optimum toner concentration of twodeveloper by sorting out the excess toner particles from the developer mixture prior to xerographic development. In one mode of operation, this can be carried out immediately before the xerographic development step within a xerographic reproducing machine.

it is, therefore, an object of the present invention to maintain optimum toner concentration in two-component xerographic development systems.

lt is another object of the present invention to remove excess toner particles from two-component xerographic developer.

Another object of the present invention is to prepare quantities of two-component developer having toner concentrations which are optimum for the atmospheric conditions at which it is prepared.

Another object of the invention is to control toner concentration across the length of xerographic development zones.

Another object of the invention is to mechanically separate two-component xerographic developer into optimumly toned carrier granules and excess toner particles.

These and other objects of the invention are obtained by depositing over-toned two-component developer on a vibrating tray. When the vibrating tray is positioned offset with respect to the horizontal, optimumly toned carrier granules will move toward and beyond the lower end of the tray. Excess toner particles not electrostatically bound to carrier granules will move against the flow of the optimumly toned carrier towards the raised end of the vibrating tray and therebeyond. The optimumly toned xerographic developer may be immediately used for the development of latent electrostatic images.

For a better understanding 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 drawings wherein:

FIG. 1 is a diagrammatic sectional view illustrating developer separating apparatus operable in accordance with the principles of the instant invention as incorporated in a xerographic machine adapted for continuous and automatic use.

FIG. 2 is a perspective view showing the developer separating unit removed from the xerographic machine.

Shown in the FIG. 1 is a xerographic machine employing a developer separator constructed in accordance with the instant invention. The elements of this machine, which is constructed for continuous and automatic operation, are all conventional in the xerographic arts except for the novel developer separator. For the purpose of the present disclosure, the several xerographic processing stations in the path of movement of the xerographic surface for each machine 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 the 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 leave 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 electrostatic charge opposite to that of the electrostatic latent image, are cascaded across the drum surface, whereby the toner particles adhere to the electrostatic latent image to form a xerographic powdered image in the configuration of the copy being reproduced;

A transfer station D, at which the xerographic powder 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.

The latent electrostatic images to be developed are formed on a xerographic surface formed in the shape of a drum or other cylinder. The drum is adapted to be rotated about its axis by a main drum drive shaft 12 by any conventional power source. not shown. The movement of the drum permits its surface to be moved past the various processing stations including the development zone.

The developing instrumentalities are preferably confined within a housing 14 having a lower sump portion 16 adapted to contain a supply of over-toned two-component developer material.

A conveyor assembly 18 is provided within the housing 14 to raise developer from within the sump to a raised location for cascading across the xerographic surface in the development zone 20. The conveyor assembly comprises a belt 22 formed with elongated buckets 24 thereon. The belt is trained for movement by rollers 26, at least one of which is power driven to move the belt 22 and buckets 24 in the direction of the arrow as shown.

As the buckets conveying the developer to a raised location move around the upper rollers 26, the developer falls through a developer sorting apparatus and into guide plates 28 for directing the flow of developer across the xerographic surface 10 in the development zone 20. A pickoff baffle 30 guides the developer as it falls away from the xerographic surface and directs the developer back into the sump 16.

The developer sorting instrumentalities, which can be seen more clearly in FIG. 2, are positioned within the development housing 14 to intercept the developer as it moves from the buckets 24 to the guide plate 28 adjacent the xerographic development zone 20. The developer sorting instrumentalities are generally designated by numeral 32 and are positioned within the housing on a support member 34 secured at its ends to the end faces of the developer housing.

As developer falls from the buckets 24 under the influence of gravity, it is guided by an elongated funnel 36 onto a chute 38. The chute 38 is inclined with respect to the horizontal at an angle of about 15. Angles from about 10 to 20 may be also employed. It has a lower end 42 positionable over the guide plates 28 to direct the flow of developer into the development zone 20. The chute 38 also has an upper end 40 of sufficient length as to permit excess toner particles moved thereacross to fall back into the sump 16. The chute also has sidewalls 44 to prohibit the movement of developer toner from moving beyond the sides of the chute.

The width of sump 46, buckets 24, funnel-shaped member 36 and chute 38 should be equal to the length of the xerographic surface 10. In this manner, developer will be cascaded across the length of image bearing surface for developing the entire image.

The funnel-shaped member 36 is rigidly held in position with respect to base 34 by a pair of end plates 36. The chute member 38 is held in position between the funnel-shaped member 36 and base 34 by a pair of leaf spring elements 48 which permit the reciprocation of the chute with respect to the base plate 34 and the funnel-shaped member 36. The lower ends of these springs are rigidly secured to the base plate 34 and chute 38.

Motion is imparted to the chute by an electromagnetic motor. The motor includes a first terminal 50 rigidly secured with respect to the upper end of the leaf springs 48 and chute 38. A coacting second terminal 52 is rigidly secured to an alternating source of potential 54. When the alternating source of potential is activated, it will intermittently cause terminal 50 to be drawn towards terminal 52 to move terminal 52 and chute 38 towards the source of power. When the source of alternating power is reversed, the attraction between the terminals is terminated and the leaf spring causes the chute to return to a normal position with the terminals 50 and 52 separated. When the source of alternating potential is operating in a normal fashion, the action between the two terminals causes an extremely rapid pulsation between the terminals and vibrates the chute at a very high rate.

A source of alternating potential of the type described can vibrate the chute 38 at a frequency of about 60 cycles a second and at an amplitude from between one thirty-second of an inch to one sixty-fourth of an inch. Such frequency and amplitude has been found sufficient to cause the separation of developer at a rate adequate for incorporation in a xerographic machine.

When the xerographic machine of the instant invention is operated at functioning speeds and developer is continually being deposited onto the vibrating chute, optimumly toned two-component is continuously being fed to the development zone through chutes 28. The excess toner from within the developer is moved up the incline of the chute toward the back end of the chute and falls under the influence of gravity back into the developer sump for remixing with the developer and movement again by the bucket onto the chute. Any of the conventional-type toner dispensers may be employed to add toner to the system to replace that lost through the development of images.

As has been explained, the atmospheric conditions at which two-component xerographic development takes place affects the quality of development. The same toner concentration can thus produce overly light, overly dark or optimum copy depending on the humidity at which the development occurs. When, however, developer is prepared in accordance with the instant invention for use in a machine at the same atmospheric conditions, optimum toner concentration and optimum development are ensured. This is because the carrier granules in the development zone 20 have the same electrostatic attractive force for toner as they-do on the developer separating chute 28. Consequently, optimumly toned carrier will be prepared and delivered tothe development zone regardless of the humidity at which the apparatus is operated.

It has been shown that the toner separator unit of the instant invention is readily incorporated into a xerographic machine employing cascade development. The developer mixture of an optimum toner concentration need not necessarily be used, however, for cascade development. It could readily be introduced into a xerographic reproducing machine employing development instrumentalities of the magnetic brush, fluidized bed or any of the known two-component development systems. It should likewise be understood that the toner separator unit could be employed to provide optimumly toned developer for storage and subsequent sue in xerographic development. As such, its" utility is not necessarily linked to its use in combination with a xerographic reproducing machine.

Furthermore, the vibrating action of the chute upon the,

developer moved thereacross has an ability to cause complete interaction between the toner and carrier to effect a complete rubbing between the two components. This permits the complete triboelectric charging of all toner particles moved into the development zone. Consequently, by employing the toner separator of the instant invention all the developer supplied to the development zone includes fully charged toner particles, fully toned carrier granules and no uncharged or unassociated toner particles to be intermixed therewith. This type of developer mix is generally considered fully blended.

While a specific amplitude, frequency and angle of repose have been assigned to the toner separator of the instant invention, it should be understood that the device is operable through a wide range of parameters.

While the instant invention as to its objects andadvantages has been described herein as carried out in a specific embodiment 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.

I claim: I

1. In a xerographic reproducing machine of the type having a sump for containing a quantity of two-component developer comprising carrier granules and charged toner particles, elevating means to raise the developer to an elevated location for cascading the developer across the latent electrostatic image bearing surface for the development thereof and means to direct the cascaded developer back to the sump, the improvement comprising:

a developer guiding chute positioned in the path of flow of the developer to direct the developer from the elevating means towards a surface to be developed;

positioning means to retain the chute offset with respect to the horizontal with its lower end positioned to direct the developer into cascading contact with the surface to be developed and with itshigher end above said sump; and

motor means to vibrate the chute so that two-component developer flowing thereover will pass optimumly toned developer past the lower end of the chute and across the photoconductive surface for its development and the excess toner particles, not electrostatically attached to carrier granules, past the upper end of the chute and back into said sump.

2. The apparatus as set forth in claim 1 wherein the motor means includes a chute pulsing motor capable of reciprocating the chute within its plane of orientation.

3. The apparatus as set forth in claim 2 and further including spring means interconnecting the motor and the chute tending to return the chute to a rest position between activating pulses of said motor.