US3058405A - Device for preparing a copy by means of latent electrostatic images - Google Patents

Description

Oct. 16, 1962 W. LIMBERGER DEVICE FOR PREPARING A COPY BY MEANS OF LATENT ELECTROSTATIC IMAGES Filed OOb. 22, 1957 5 //V VENTOR.

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United States Patent @hice 3,058,485 Patented Oct.- 16, 1962 3,858,405 DEVICE FOR PREPARING A CGPY BY MEANS F LATENT ELECTRSTATIC IMAGES Walter Limberger, Hamburg, Germany, assigner to Lumoprint Zindler KG., Hamburg, Germany, a company of Germany Filed Oct. 22, 1957, Ser. No. 691,691 Claims priority, application Germany Oct. 22, 1956 12 Claims. (Cl. 95-1.7)

The invention relates to a device for preparing a copy by means of latent electrostatic images, in which are provided a device for forming the xerographic layer of the copy sheet, an illuminating device for transferring an image from a master sheet to the Xerographic layer, a distributing device for the developer, which consists of carrier particles of magnetisable material and toner, as well as a fusing device.

The invention is directed to the problem of improving Vknown apparatus as regards the supply of the toner to the xerographic layer and the construction of the apparatus,

particularly the heating device.

This problem is solved according to the invention in that, between the xerographic layer, which carries the electrostatic image, and a distributing device one or more magnets are arranged which are moved relatively to the Xerographic layer and pick up the developer for the purpose of transferring the toner to the xerographic layer.

In a preferred embodiment, several magnets are cornbined into a magnet roller from which the lines of force pass radially outwards substantially perpendicular to the axis of the roller. This roller is formed, advantageously, by several, erg. bar-shaped, magnets secured approximate- 1y at their neutral zones to a shaft in planes running perpendicular to the shaft axis. It will often suiiice to provide a simple bar-shaped magnet in each of these planes, all the magnets secured to the shaft being arranged parallel to one another. The roller-shaped device is completed by a'cylinder of non-magnetizable material mounted concentrically on the shaft, the front faces of the pole pieces of the magnets lying in the outer covering surface thereof.

The magnet arrangement can consist of permanent magnets or of electro-magnets. Furthermore, in a particularly advantageous embodiment, the invention provides for the similarly polarized magnets to be arranged side-byside. There is also the possibility of oppositely polarizing the magnets which are arranged side-by-Side. The similar polarization has the advantage that a uniform, substantially radial field is produced at the outer circumference of the magnet arrangement at least in the axially extending sections.

The copy sheet is guided in the region of the magnetic array in a surface which runs parallel to at least one section of the surface envelope of the solid of rotation defined by the movement of the magnetic array. 'Ihe invention provides, in an advantageous embodiment, an arrangement of the parts aifecting the magnetic flux so that the lines of force, in the section in which the sheet runs parallel to the moving magnetic array, pass perpendicularly through the sheet. The parts directing the ilux are so spaced that no developer particles are released by the magnetic array and developer particles falling to the guide path can drop into the collecting container.

`In accordance with a further feature of the invention, one or more additional magnets are further provided which increase the magnetic iield of the magnetic array, for the purpose of directing the threads formed from the developer behind the section in which the toner is supplied to the xerographic layer. 'Ihese additional magnets may be constructed as electro-magnets whose exciter windings are polarized in dependence upon the rotation of the magnet roller if north and south poles alternate along the circumference of the magnet roller. The polarization of the additional magnets is lthen effected through a commutator, for example, so that a field increasing the magnetic eld of the magnet roller is produced by the additional magnets. Preferably, the additional magnets are arranged at a partition which subdivides the housing of the apparatus into a iirst chamber, in -which the development of the latent electrostatic image occurs, and a second chamber, containing the heating device.

The guide path for the copy sheet through the heating device consists of a preferably heatable perforated plate, in accordance with still another feature of the invention; further heating elements may be disposed above this path. The suction side of a blower communicate with the space beneath the perforated plate which ensures a satisfactory guiding of the copy sheet on the perforated plate, the sheet being held flat on the plate through the openings in the plate, and also an extraction of the fumes arising in the fusing of the pigment particles. This therefore safely prevents the fumes from reaching other devices, particularly the forming device, in which the fumes would be detrimental. In the present case, the chamber containing the heating device is separated from the other parts of the apparatus, while at the same time a partial vacuum is produced lthrough the connection of this chamber to the suction side of a blower which prevents the escape of air from the chamber containing the heating device into the other parts of the apparatus.

By arranging the forming device, which includes an illuminating device, as Well as the powder-distributing device, the magnetic array and the heating device behind one another, it is possible to construct the device as a desk-shaped table apparatus which, because of a substantially V-shaped guide path for the copy sheet between the illuminating device and the exit slot, is of decreased height. This arrangement permits the construction of a readily operable apparatus, in which the master sheet and the copy sheet are guided parallel to one another through two directly adjacent slots in the apparatus and the master sheet can be removed after illumination at the readily accessible upper side of the apparatus.

Further advantages and features of the invention will appear from the following description of an embodiment which is illustrated in the accompanying drawing.

In the drawing:

FIG. l shows a side view lof the apparatus in section; and

FIG. 2 shows a plan view of the apparatus -according to FIG. 1, partly in section on the line II-II of FIG. l.

The device according to the invention is provided in a desk-shaped housing 1, at the front side of which two superposed slots Z, v3 are arranged for inserting the master sheet and the copy sheet. In the front part of the housing 1 a further `slot 4- is located at the upper side, through which the master sheet can be removed after illumination. A slot 5 for removing the developed copy is located at the upper rear edge of the housing 1. At the upper side of the desk-shaped housing 1, behind the removal slot 4 for the master, a cover `6 for the supply container 18 for the developer is provided. This supply container is thus readily accessible so that its contents can be conveniently replenished.

A forming device 7, is located behind the slot 3, preferably comprises several wires, to which the forming potential is applied, stretched transversely to the direction of advance of the layer support. An associated counterelectrode is indicated at 8 and is grounded. A cabinet containing a source of electrical potential for the electrodes 7, 8 is indicated at 9. At the upper wall of this cabinet there are located a pair of insulators 10 from which electrical connections lead to the forming electrodes 7 and the counter-electrode 8.

A conventional illuminating device is arranged behind the forming device and consists, for example, of two illuminating tubes 11, reflectors 12 and a glass plate 13 to which the master and a copy are guided rby the roller 14. The roller 14 preferably consists of rubber and has a covering of cotton fabric on its surface.

Behind the illuminating device the master is separated from the copy, so that the master is guided along the arrows 15 to the outlet slot 4, whereas the copy sheet is further conveyed on the guide path 16. The separation of the master from the copy can be effected by hand, which is quite easy in the arrangement illustrated because of the readily accessible arrangement of the slot 4, or by some known mechanical separating device, not shown. The guide surface 17 for the master also serves as a wall lfor separating the section of the apparatus with the forming device and the heating device from the section of the apparatus in which are located the means for developing the electrostatic image. This part of the apparatus receives the supply container 18 'for the developer and this supply container includes in its lower part a known device, for example in the form of a roller 19, for dispensing a measured supply of developer. This roller 19 is driven in dependence upon the movement of other parts of the apparatus.

The developer consists of magnetizable carrier particles, for example, iron filings, and a toner formed by pigment particles. The composition is preferably such that the developer is considerably enriched with toner, since in the preferred construction the toner is transmitted to the xerographic layer, whereas the carrier particles operate in functional co-operation with a magnetic arrangement as conveying devices which during the drive must be guided into the remaining toner. The supply container 18 may therefore be divided into two chambers, in one of which contains only toner, so that a supply of toner alone or of toner and carrier particles can be given as desired.

Under the distributing device there is disposed a magnetic array which, in the embodiment illustrated, is rollershaped. Bar magnets 21 are so arranged parallel and side-by-side on a shaft 20, mounted in the housing, that the poles (provided, if desired, with supplemental pole pieces not shown), project diametrically from the shaft 20. In the embodiment illustrated, all of the bar magnets 21 lying side-by-side are `magnetised in the same way, so that the north poles N are located at one side of the shaft and the south poles S at the opposite side. Furthermore, the shaft 20 is surrounded by a concentrically arranged cylinder 33 of non-magnetiz-able material. This cylinder 33 rotates with the shaft 20. The overall diameter of the cylinder 30 is so selected that the end faces of the poles or pole-pieces of the magnets 21 lie on the outer periphery of the -cylinder 33.

By means of this arrangement, a strong magnetic eld is produced, in the sections extending axially of the cylinder 33 in which the pole pieces of the magnets 21 are located, which is directed substantially radially of the cylinder. The developer falls from the distributing device 19 into this magnetic field and, as a result of the magnetizable constitution of the carrier particles, forms threads or needle-shaped accumulations projecting radially from the roller-shaped magnetic array corresponding to the lines of force of the magnetic field.

The magnetic array 20, 21, 33 rotates with such a velocity that its peripheral speed is greater than the speed of advance of the copy. The developer accumulations on the circumference of the magnet roller are made brush-shaped and guided over the xerographic layer of the copy sheet which is advanced over the path 16. In the region of the cylinder 33, the path 16 is centered on the roller axis over an arc of 90 and runs parallel to the surface envelope of the roller-shaped magnetic array whereby the time of contact between toner and Xero graphic layer is extended.

By virtue of the abovedescribed mechanism for supplying toner to the xerographic layer, a strong and intensive treatment of the latent electrostatic image with the toner is ensured on the one hand and, on the other hand, the Xerographic layer is in no way adversely affected by its contact with the yieldingly cohering carrier particles; since these carrier particles are lost in but slight amounts from the magnet roller, substantially all of the toner is transferred to the xerographic layer.

A container 22 for released carrier particles is located under the guide path 16, the carrier particles falling into it through openings in the guide path 16. A handle 34 of the container projects laterally from the housing 1, so that the container 22 can be removed and the collected toner particles can be returned to the supply container 18.

A set of magnets 23 are mounted on a partition 24 to strengthen the radially directed magnetic field of the array 20, 21 behind the section in which this array transmits toner to the xerographic layer. These additional magnets are so oriented as to help erect the developer accumulations on the circumference of the magnet roller 20, 21, thereby counteracting the deformation or flattening these accumulations which occur to a greater or less extent on contact with the xerographic layer. In the.

presence of a magnet roller which has :a unipolar field over its Whole circumference, these additional magnets could be constructed as permanent magnets; the magnets 23 of the present embodiment, however, are each constructed as electro-magnets with a reversible exciter winding 123 so that their polarity can be adjusted according to the position of the magnets 21 in the magnet drum. To this end, as shown in FIG. 2, the windings 123 are energizable over two commutator segments 121', 121" on the shaft 120 of roller 33, a brush 122 contacting these segments while being connected to one lead of the energizing windings 123 whose other lead is grounded. In FIG. l a position of the magnets 21 is shown in which their north poles are facing the additional magnets 23. To increase the field produced by these poles, the additional magnet 23 must be so excited that the pole facing the magnets 2t), 33 is a south pole. 'If the magnet roller is now rotated through about the polarity of the additional magnets 23 is reversed. The brush-like character of the developer accumulations on the circumference of the magnet roller is thus renewed by the additional magnets 23 on each revolution of the roller.

In order to obtain srnall apparatus dimensions, the invention provides a generally V-shaped construction of the guide path 16, with the magnet roller 20, 21, 33 disposed in the lower part of the apparatus between the remaining devices of the apparatus. The partition 24 carrying the magnets 23 separates the fusing device from the other parts of the apparatus.

The copy sheet is guided through the fusing device over a plate 25, which is perforated by being provided with openings 26. A partial vacuum is produced at these openings by a connection of the space 27 beneath the guide plate 25 to the suction side 28 of a blower 29. This ensures that the layer support is guided on the guide plate 25 in a at condition without the use of other guide means. This partial vacuum also has the purpose of extracting the fumes given off in the fusing of the pigment particles, so that they cannot reach to the other parts of the apparatus.

For fusing in the pigment particles the guide plate 25 can be heated, as by being equipped with electric heating coils 25. Radiators 30 are provided above the guide plate 25, either instead o-f or in addition to the heating elements in the guide plate 25, whose heat is directed by reflectors 31 towards the copy sheet guided on the guide plate 25. Further guide elements 32 are provided at the ends of the guide plate 25 in front of the exit slot 5, in the form of one or preferably more driven rollers or Wheels operating only on the edges of the sheet. The plate 25 is so arranged as to form a virtual extension of the rising leg of the V-shaped guide path 16, so that the copy is guided slopingly upwardly toward the exit slot 4.

What I claim is:

1. An apparatus for ydeveloping latent electrostatic images present on a photoconductive layer, comprising supporting means for guiding a sheet carrying said layer along a predetermined path, feed means for advancing said sheet along said path, a rotatable horizontal shaft extending transversely above said path, an array of permanent bar magnets -on said shaft having their extremities located on a cylinder surface centered on said shaft, said supporting means including an arcuate element substantially concentric with and spaced `from said cylinder surface, a source of magnetic developing particles disposed above said path, distributor means directly above Said array adapted to direct particles om said source in a steady stream toward said shaft whereby brush-shaped accumulations of particles are formed at the poles of said magnets as the latter pass underneath said distributor means, said distributor means extending over substantially the entire length of said array, and drive means for rotating said shaft with said magnets, thereby displacing said accumulations in a wiping motion across the photoconductive-layer surface of the advancing sheet.

.2. An apparatus according to claim l wherein all of said bar magnets extend radially and parallel to one another in a common axial plane of said shaft.

3. An apparatus according to claim 2 wherein a plurality of adjacent ones of said magnets are polarized in the same sense.

4. An apparatus according to claim 1 wherein said array further comprises a cylindrical non-magnet sleeve concentrically surrounding said shaft, said bar magnets penetrating said sleeve and terminating ush with the outer surface thereof.

5. An apparatus according to claim 1, `further comprising a container underneath said arcuate element, said element being apertured at its lowest point for admitting spent particles into said container.

6. An apparatus according to claim l, further comprising stationary magnet means positioned adjacent a surface portion of said array remote from said path for establishing an accumulation-erecting magnetic field at said surface portion.

7. An apparatus according to claimI l6 wherein said stationary magnet means comprises a series of electromagnets and commutator means yfor periodically reversing the polarity of said electromagnets in synchronism with the rotation of said shaft.

8. An apparatus according to claim l, further comprising a housing, a partition dividing said housing into two chambers, said array being located in one of said chambers, fusion means in the other of said chambers above the level of said array for xing the developed iniage by thermally bonding the adhering particles onto the photoconductive layer, said path sloping upwardly through said partition from said array to said Ifusion means, and stationary magnet means carried on said partition above said path in an axial plane of said cylinder surface for establishing an accumulation-erecting magnetic field at a location remote Ifrom said path.

9. An apparatus -for developing latent electrostatic images present on a photoconductive layer, comprising supporting means for guiding a sheet carrying said layer along a predetermined path, feed means for advancing said sheet along said path, a rotatable array of permanent bar magnets positioned `for rotation about an axis above Said path with suicient clearance to leave an air space between it and said layer, said supporting means comprising an arcuate element positioned below said array and concentric with said axis, a source of magnetic developing particles disposed above said path, distributor means adjacent said array adapted to direct particles from Said source in a steady stream toward said array at a lo- 6 cation remote from said path whereby brush-shaped accumulations of particles are formed at the poles of said magnets as the latter sweep past said distributor means, and drive means for rotating said array in a manner displacing said accumulations in a wiping motion across the photoconductive-layer surface of the advancing sheet.

10. An apparatus for developing latent electrostatic images present on a photoconductive layer, comprising supporting means for guiding a sheet carrying said layer along a predetermined path, feed means -for advancing said sheet along said path, a rotatable non-magnetic cylindrical body positioned above said path for rotation about an axis, permanent-magnet means in said body having a plurality of spa-ced-apart poles terminating ush with the surface of said cylindrical body, said supporting means comprising an arcuate element concentric with said axis and spaced from said surface While extending over an arc of substantial-ly 90 therearound, a source of magnetic developing particles disposed above said path, distributor means at said source `for cascading a stream of particles from said source onto said surface at a location thereon forwardly along said path of an axial plane of said body substantially bisecting said arcuate element whereby brush-shaped accumulations of particles are formed at said poles and sweep said sheet at said arcuate element and particles falling onto non-magnetic portions of said surface are cast onto said sheet, and drive means for rotating said body.

ll. An apparatus for reproducing a master copy carried by a master sheet on a copy sheet carrying a photoconductive layer, comprising a housing having a bottom Wall, a top wall and side Walls bridging said bottom and top walls, at least one of said side walls being provided with an inlet for said sheets; supporting means for guiding said sheets along respective predetermined paths within said housing, said paths including a common rst portion adjacent said inlet, a second portion beyond said first portion for said master sheet, and a third portion beyond said first portion for said copy sheet, said top wall being provided with an outlet for said master sheet in line with said second path portion; charging means at said inlet `for electrostatically sensitizing said layer; illuminating means in said housing along said 'first path portion for exposing said photoconductive layer; feeding means for advancing said sheets along said paths whereby a latent electrostatic image of said master copy is formed in said layer; separating means at the junction of said second and third path portions `for directing said master sheet along said second path portion and said copy sheet along said third path portion; a rotatable array of permanent bar magnets in said housing positioned for rotation about an axis above said third path portion with suicient clearance to leave an air space between it and said layer, said third path portion comprising an arcuate element below said array and concentric with said axis; a source of magnetic developing particles disposed above said third path portion; distributor means at said source adapted to direct particles from said source toward said array whereby brush-shaped accumulations of particles are formed at the poles of said magnets and sweep across the photoconductive layer surface of the advancing copy sheet; fixing means in said housing including a plurality of heating elements disposed above said third path portion beyond said array for fusing adhering particles to said copy sheet, said housing being provided with an opening adapted to pass said copy sheet, said third path portion terminating at said opening; and sheet-transport means in said housing at said opening for discharging said copy sheet.

l2. An apparatus according to claim ll wherein said third path portion comprises a rigid :guide plate in the vicinity of said heating elements, said guide plate being provided with a plurality of bores terminating at a surface thereof in contact with said copy sheet, further com- UNITED STATES PATENTS Re. 20,6610 Schacht Feb. 22, 1938 2,703,280 Butterfield et a1 Mar. 1, 1955 2,763,204 Sims Sept. 18, 1956 8 Young Mar. 216, 1957 Giaimo Mar. 26, 1957 Young Mar. 26, 1957 Lowrie Aug. 20, 1957 Grant Mar. 11, 19518 Byrne Apr. 29, 1958 Reuter Sept. 16, 1958 Giaimo Oct. 7, 19518 Kulesza Apr. 278, 1959

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