US 3626898 A
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Description (OCR text may contain errors)
United States Patent Primary ExaminerHenry S. Jaudon Attorney-Sol L. Goldstein ABSTRACT: A high-speed magnetic brush assembly is provided in which an array of magnets are arranged inside a nonmagnetic cylinder to control the movement of the developer mixture of iron powder and toner. The cylinder rotates about the fixed magnets. One set of magnets attracts a quantity of mix to the cylinder and subsequent magnets transport the mix to the next station where a single or multiple magnets brush develops the paper. At another station, the magnet discharges the mix from the cylinder. The assembly is enclosed to contain the mix and includes a spillway for the mix leading to mixing chambers where the mix is reconditioned for reuse.
Patented Dec. 14, 1971 2 Sheets-Shoot 2 u/ez Jaw M m4; JZ. awmn I yaz qfiaw HIGH-SPEED MAGNETIC BRUSH DEVELOPER APPARATUS This invention relates generally to magnetic brush developer arrangements and in particular to a magnetic brush construction equipped with means for controlling the developer mix in the vicinity of the rotating brush cylinder so that it meets the environmental requirements of a high-speed photocopy machine.
The construction of developer brushes useful in photoelectrostatic copying is well known and is a well-developed art. In general the principles of operation are well defined calling for magnetic means mounted inside a rotating cylinder which is partially immersed in a supply of magnetically attractable developer mix. As the cylinder rotates, a quantity of the developer mix is accumulated on its surface in a brushlike formation which is then caused to sweep across a photoconductive member carrying a latent electrostatic image thereon thereby developing the image.
One important problem which has confronted developer brush systems is the compaction of the toner particles in the various types of feed systems which attempt to feed and distribute the developer mix to the surface of the rotating cylinder. Since the toner materials are made of thermoplastic materials caking is a common problem when the developer mix is exposed to a high-compressive force in feeding and distributing systems. Another problem is the cornminution of both the carrier particles and the toner particles which are continually recycled in a magnetic brush system consisting of a rotating drum and various types of feeding and delivery systems. A significant requirement of the successful operation of such a system is to maintain the proper concentration of toner in the developer so that the development of successive sheets is of uniform quality. Finally, there is the problem of the escape of fine particles of the toner into the general atmosphere of the working area.
Most of the magnetic brush systems used heretofore had an output of -20 copies a minute. High-speed dry electrostatic copiers, which are required to produce anywhere from 50-80 copies a minute, greatly magnify the forces described above and consequently the deficiency of prior art systems now render them inoperable in the environment of such a highspeed system.
The magnetic brush assembly of the instant invention achieved a high-degree of success in such high-speed systems by utilizing the magnetic fields of force to create specific zones within the magnetic flux field generated by the magnetic means through which the surface of the cylinder rotates.
The device of the present invention provides an applicator drum having zones with varying magnetic field strengths which selectively pick up, convey, form a developer brush and then discharge the mass from the surface of the applicator to a collector. The system provides for recycling the mix after each application so the mix is given an opportunity to be replenished with fresh toner. The present invention provides a magnetic brush developer unit for a photoelectrostatic copying machine that is particularly suited to a high-rate of copy output while protecting the granular developer mix from undue cornminution and throwout of fine particles into the atmosphere.
A particular feature of the developer unit of the instant invention is its ability to create a magnetic brush that is effective to completely develop a latent image bearing member moving FIG. 3 is a vertical cross section of another form of a developer showing the magnetic field generating means and the resulting magnetic flux distribution at the various zonal areas.
Referring now to the drawing, there is shown in FIG. 1 the magnetic brush developer assembly identified generally with the reference character 10 equipped with a pair of infeed rollers l2 and 14 which direct the paper into the developing station identified generally as 16. Leading from the infeed rollers 12 and 14 a pair of spaced apart guide elements 18 and 20 forming a throat 22 through which the sheet is guided into the developing station 16. A rod 21 which is part of the paper guide 20, controls the height of the developer mix on the cylinder that can enter the developing station.
At the other end of the developing station is a set of feedout rollers 24 and 26 which provide an exitway for the paper from the developing station. Included in the exitway construction is a guide element 28 that receives the lead edge of the sheet guiding it into the nip of the feed-out rollers 24 and 26.
Superimposed over the developer station 16 is an enclosure 34 which includes a developing electrode 36 whose function and operation is fully described in U.S. Pat. No. 3,369,917, issued to Daniel Granzow, et al., issued Feb. 20, 1968.
In the general center of the apparatus is a hollow cylinder 40 which is rotatably mounted on a fixed shaft 42, the hollow cylinder being suitably supported on the shaft by bearing members 43. The shaft 42 is appropriately secured at its one end to the side frame of the apparatus. The other end of the shaft 42 terminates inside the cylinder 40 being received in one of the bearing members 43.
Affixed to the shaft 42 is a magnetic flux generating assembly 44 which includes an array of several magnets disposed within the cylinder adjacent the inside surface 46 thereof. The magnets 50, 52 54, 56, and 58 are secured to conductive support plates 60, 62, and 64 which act as pole pieces and are in turn secured to a series of plates 66 (one shown) mounted on the shaft 42. One of the bearing members 43 extends through the end face of the cylinder exposing a shaft portion through which the drive mechanism (not shown) is connected for driving the cylinder 40. As the cylinder rotates on the bearing members 43 and the shaft 42 and the assembly 44 remain stationary.
Forming a part of the enclosure that surrounds the cylinder 40 is a dispenser unit identified generally as 70 which contains the material for replacing the powder that is removed during the course of development. The dispenser unit 70 is spaced apart from the rotating cylinder providing a spillway 72 through which the developer mix falls as it departs from the surface of the cylinder 40 when the cylinder surface moves out of the magnetic flux field. At the bottom of the spillway is a collection hopper 74 made up of two chambers 76 and 77, each equipped with rotating augers and 82. The material falling off the surface of the cylinder 40 is deposited in the chamber 76 and is carried in a direction transverse the movement of the cylinder into the chamber 77. The chambers 76 and 77 are separated by a wall 78 that extends longitudinally between the augers 80 and 82.
The floor 86 of the container 71 is sloped so that it converges at the dispensing auger 88 which dispenses the granular mass from one end of the container into the chamber 77 onto the auger 82. The new powder that is added is blended with the used mass as it is conveyed by the auger 82. Centrally located in the container 71 is a mixing blade 90 which gently stirs the granular mass to prevent any caking or agglomeration. The container 71 is closed off with a hinged cover 92 which together with a cover plate 98 serves to enclose a substantial portion of the circumference of the cylinder 40.
The auger 82 gently feeds the replenished mass into the V-shaped supply chamber 84 so that the mass accumulates at the bottom of the chamber near the pickup station of the assembly 44.
The particles as they leave the magnetic flux pattern generated by the magnetic means 58 leaves the surface of the amass drum 40 and are received on the auger 80. As much as 75 percent of the mass leaving the surface of the drum is returned directly to the supply chamber 84 after receiving some agitation from the auger 80 through ports (not shown) in the wall 78. The remainder of the granular mass is carried into the chamber 77 for replenishment with fresh powder from the container 71, which is dispensed by the auger $8 through openings 99 at the bottom of the container.
The operation of the auger may be achieved by a manual control at the option of the operator or it may be associated with an automatic control such as described in US. Pat. No. 3,399,652, issued to Stanley A. Gawron on Sept. 3, 1968.
Referring now to FIG. 2 of the drawings there is shown a magnetic flux generating assembly dd and the resulting mag netic flux pattern generated by the array of magne s disposed within the cylinder 40. The magnets 50 and 52?; mounted on the pole piece 60 comprise the pickup zone T which attracts a quantity of the granular mix from the supply The external magnetic strength rating of each of these magnets is in the range of 600-800 gauss units, preferably about 700 gauss units. It will be understood that in addition to the gaussian values it is necessary that the magnets be of sufficient size in order to produce the necessary attractive force. The magnets 50 and 52 are mounted with their south and north poles respectively, affixed to the pole piece providing a flux pattern that extends and bridges the distance between the north pole of magnet 50 and the south pole of magnet 52.
At the exitway 1102 (FIG. ll) there is a bladelike member 103 which controls and meters the thickness of the granular mass that adheres to the surface of the cylinder 40 as it pmses through the exitway 102 from said supply chamber, and is conveyed on the surface of the cylinder All) to the developing station. As part of the pickup zone 1100, the second magnet 52. generates a flux pattern so as to retain the metered amount of developer mix on the surface of the cylinder. The granular mass that adheres to the surface of the drum at the pickup zone is flattened against the surface due to the flux pattern passing through the magnetically conductive iron particles as the major constituent of the developer mix.
As the cylinder continues its rotation in a clockwise direction it is brought under the influence of the magnets in the transporting zone 104! formed by the magnetic flux generated from the magnet 54. It will be observed that the south pole of the magnet M is mounted against the pole piece 62 which produces the pattern shown in FIG. 2, which holds the granular mass flattened against the surface The magnetic flux field generated in the zone 110d securely holds the material against the surface delivering the'material to the developing zone 106 opposite the magnet 56.
The magnet 56 is mounted with its poles arranged opposite to the magnet 54 so that the north pole is in contact with the pole piece 664.
The gaussian rating of the magnet ss at the developing station is in the range of 400-600 units. This produces a weaker magnetic field than the magnets in the zones lltlll and 1104 since it is desirable to produce a brush formation that is erect, closely formed and yet sufficiently soft so that it does not abrade the surface of the photoelectrostatic member. As the surface of the cylinder, with it granular mass enters the field in zone 106 the brush becomes upstanding following the converging lines of magnetic flux into the magnet 56 so that as it passes through the developing station 116 it sweeps across the surface of the sheet.
From the developing station 16 (FIG. 11) and beyond zone 106 the cylinder carrying the granular mass moves to zone H08 where it is continued to be held by a more strong magnet, having in the range of 500-700 gauss units, and thereby assuring a strong retention of the granular mass against the surface of the cylinder, but not in a manner which is related to a brush formation. The pole piece 641 terminates at the magnet having a leg portion 107 extending upward shielding the free end of magnet 58 so that the flux field generated in zone b terminates in an abrupt pattern. The granular mass beyond the station 1108 will fall away from the surface of the cylinder d0 since it is no longer under the influence of a magnetic flux field and falls through the spillway '72 by force of gravity. The zone 1-113 serves a discharging function moving the granular mass in the direction of the spillwuy 72.
it is characteristic of the granular mass to follow the lines of force causing the granular mass to move through as it passes through converging lines of force such as when leaving station Mill moving through stations NM and Mill and when it leaves E08. The movement is from a flat position, to an upstanding position and then to a flattened position moving in the direction of rotation of the cylinder 30.
iteierring to FlG. 3 the magnetic flux generating assembly is identified generally as ll Ml. The magnetic assembly is disposed inside the cylinder Ill ti the latter being rotatably mounted on a fixed shaft .lllt'l. Aft'ixed to the shaft is the flux generating assembly i1 1, which includes an array of individual magnets T20, T22, T24, 3126, T28, 130, and M12. The magnets are mounted on pole pieces Ti t M0, and lt-Il. which in turn are secured to a series of plates ll l l (one shown) axially mounted on the shaft 1 18 to that the magnetic flux generating assembly remains stationary with respect to the rotating cylinder 31b. The cylinder is driven through the shaft extension of the bearing member Mo which engages the shaft M8.
The array of magnets juxtaposed the inside surface ll? of the cylinder results in the creation of a series of zones through which the surface of the cylinder passes as it rotates. Magnets T20 and T22 mounted on pole piece T30 form a first zone l4?) at which the mass of developer mix is picked up or attracted to the surface of the cylinder. The granular mass attracted to the cylinder, passes through the exitway E02 in lFlG. ll. The mass is held by virtue of the lines of magnetic flux emanating from the magnets 1 .20, 122 and which are overlapped by the magnetic flux generated from the magnet i2 3 attached to the pole piece M0 which is the transport zone M9.
The third zone 152 is the developing zone formed by the magnets 11%, llifit] and secured at the north poles of each magnet to the pole piece 1140. The south pole of the magnet faces in the direction of the inside surface ill? of the cylinder lid. The developer mix accumulated and held on the surface of the cylinder moves into the developing zone i532. it follows the converging lines of force entering magnet i215 becoming upstanding in a bristlelike formation 152A. As the cylinder lib rotates clockwise the bristlelilie formation becomes flattened moving in a direction of rotation. The latent image bearing sheet of electrostatic paper receives its first sweep by the brush formation llfiZA formed opposite the magnet P126.
As the cylinder successively moves past station 1552B, 1152C, and T52D, the process is repeated with the granular mass mov ing in an end-over-end type pattern as it enters and leaves each station. Such movement forms up renewed bristlelilte structures and tends to present toner enriched iron-carrier particles by virtue of the gentle mixing action. Further rotation of the cylinder 1116 brings the granular mass between magnets 3126 and 1128 where a second brush 1152b develops under the influence of the flux field continuing the development of the latent image and hence passing through the flux field and subsequent brush formation i520 and also T524 which are created in the vicinity of magnets Md and 1130. it will be appreciated that the multiple magnet location in the developing zone as contrasted to the magnet array in zone T06 of H6. 2 greatly increases the area of available brush formation for developing and contacting a corresponding area on the photoconductive layer as it passes through the developing zone. This has the net affect of providing multiple development of the sheet in contrast to the development achieved in FIG. Ii. Such multiple brush formation is of particular importance in a high-speed developing machine where it is critical that the fast moving photoconductive member with its charged image on the surface is brushed with as great a volume of electroscopic powder as possible in order to greatly increase the probability of attraction of the material to the image resulting in increased image density. The flux pattern generated by magnet 132 forms the discharge station 154 which returns the developer mix to the dispenser unit.
It will be appreciated that the magnetic flux generating assembly shownin FIG. 3 may be readily substituted for the array in FIG. 1.
In operation a quantity of granular mass is deposited in the supply chamber 84 which in the usual mixture contains a ratio of a magnetically attractable carrier particles to thermoplastic toner particles in the range of -40 carrier particles to one particle of toner. Inside the container 71 is a charge of thermoplastic powder which is gently agitated by the blade 90.
As a copy demand is placed on the photoelectrostatic copier the granular mass in the supply chamber 84 opposite the magnet 50 which is zone 100 a large quantity of the granular mass is attracted to the surface of the drum. As the drum rotates the mass is carried through the exitway 102 of the supply station where. a quantity of the mass'is doctored off by the wiper or blade 103 to a unifonn thickness. The material continues to adhere in the pickup zone 100 as it comes under the influence of the flux field generated by the magnet 52.
At zone 104 the high-strength magnet 54 retains the material on the surface of the drum. It will be appreciated that the magnets 50 52 and 54 are high-strength magnets being in the range of 600-800 gauss units so that the granular mass is retained in a flattened condition against the surface.
As the cylinder enters zone 106 it is again doctored by the rod 21. The granular mass that passes opposite the magnet 56 becomes upstanding in a brushlike formation.
Responsive to the copy demand a photoelectrostatic member begins its movement through the copying apparatus to be charged and exposed producing a latent image on the surface. The photoelectrostatic member enters the rollers 12 and 14 with the surface bearing the latent electrostatic image facing roller 14, that is face down, and is advanced into the guideway 22 between the guide elements 18 and 20, so that the surface of the sheet is urged against the brush formation in zone 106 where the developer mix is swept across the surface depositing electroscopic powder in the charged areas. The sheet continues to advance through the developing zone 16 and is directed to the exitway at which rollers 24 and 26 are located for driving the sheet out from the developer unit into the next station of the machine for further processing. The brush formation that is formed at zone 106 is brought into the next zone 108 where it is again firmly held in a somewhat flat tened condition by the high-intensity magnet 58 so that the mass is then discharged into the spillway 72 where the magnetic flux pattern terminates at magnet 58. By gravity the granular mass falls into the chamber 76 where it is picked up by the auger 80 and moved longitudinally along the length of the cylinder where it is picked up by the auger 82 and moved through the chamber 77.
The thermoplastic powder that has been removed in the developing station 16 is replenished from the dispenser unit 70 by the action of the auger 88 which dispenses incremental quantities of the toner into the chamber 77 where it is intermixed by the auger 82 with the retum developer mix. From chamber 77, where the replenished toner is thoroughly intermixed with the existing developer mix it is returned to the chamber 84 and the cycle is repeated.
lt should be pointed out that the chamber 84 is sloped in the direction of the exitway 102 so that the developer mix accumulates in the area immediately opposite the zone 100. This obviates the need for any physical movement or compression of the developer mix in the direction of the cylinder avoiding any compaction or agglomeration of the thermoplastic materials. Further, the magnets at the zone 100 attracts substantial quantities of the developer mix from the supply station so that through the use of the magnets the quantity of material is picked up and held on the drum and transported to the developing station.
The entire cylinder is enclosed by the elements 34 and 94, dispenser unit 70, supply unit 74, and the cover plate 110, so
as to completely surround the cylinder restricting any airborne thermoplastic powder from coming into contact with the general atmosphere.
The aforedescribed arrangement substantially reduces the opportunities wherein the developer mix is exposed to comminution forces. As the granular mass falls down the spillway it is received into the chamber 76 and is generally moved away from the working area by the auger 80. As greater quantities of material fall into the spillway there is an overflow port 160 through which the material may freely fall into the supply chamber 84. The chambers 76 and 77 are separated by the wall 78 so that the redistribution of replenished material into the developer mix proceeds independently of the materials falling through the spillway 72. The accumulation of any developer mix in the space between the cylinder 40 and the guide plate is minimized by doctoring the surface of granular mass as it leaves the supply station 84. One of the important advantages of terminating the magnetic flux pattern at station 108 is that it provides a large segment of the perimeter of the cylinder free of flux so that the granular material no longer adheres. This is particularly effective when using a cylinder made of a nonconductive material such as a plastic, obviating the need for any scraping means which would tend to remove any adhering developer mix from the surface and thus eliminates the need for an instrument which tends to grind the particles.
The invention has been described in some detail with reference to two embodiments, but it will be understood the changes in modification by one having skill in the art can be affected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.
What I claim is:
1. A magnetic brush assembly for a brush developer adapted to develop electrostatic images carried on a sheet material at high-speed comprising:
an applicator drum comprising a rotatable hollow cylinder having a fixed magnetic flux generating assembly disposed adjacent the inside surface of the cylinder for attracting and releasably retaining a mass of developer mix on the surface thereof,
a supply station for supplying developer mix juxtaposed a portion of the outer surface of the cylinder,
a developing station having ingress and egress means for said sheet material and feeding said sheet material immediately adjacent the cylinder,
a developer mix collecting statlon,
mixing means disposed between said supply and collecting stations for mixing the developer mix and feeding it from the collecting station to the supply station,
said magnetic flux generating assembly including a series of radially spaced magnet means with said cylinder creating at least four distinct developer mix handling zones extending along the path of rotation of the cylinder from a point adjacent the supply station to a point beyond the developing station, a first zone being located adjacent the supply stationfor picking up a mass of developer mix, a second zone being located adjacent the developer station for causing the developer mass to become upstanding on the cylinder surface, a third zone for conveying the mass between said first and second zones, and a fourth zone for conveying the developer mass away from the developing station toward the collecting station, the strength of the magnetic field in the second zone where the developer mass becomes upstanding on the cylinder surface being low compared to other of the zones so as to reduce abrasion of the sheet material during developing.
2. The magnetic brush assembly as claimed in claim 1, wherein said zones have gaussian values in the range of 5008-7008 with the exception of the second zone which is in the range of 2008 to 6008.
, 3. The magnetic brush assembly as claimed in claim 1 wherein said magnetic means at each zone is affixed on a side opposite the cylinder to a magnetically permeable support acting as a pole piece.
4. The magnetic brush assembly set forth in claim 3 in which the support for the magnetic means in the fourth zone extends toward the cylinder adjacent the end of the zone to provide a magnetic shunt abruptly terminating the fourth zone to free 5. The magnetic brush assembly as claimed in claim 1 wherein a plurality of magnetic means are located in the second zone for creating a plurality of brush formations the developer mix for gravity discharge from the cylinder to thereby producmg the effect ofmumple development the developer mix collecting station.
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