Magnetic and electrostatic transfer of particulate developer

An apparatus for depositing electrostatically and magnetically responsive particulate matter on a conductive surface having an electrostatically charged latent image comprises an elongate permanent magnet that is disposed adjacent to the conductive surface and that is capable of producing a magnetic field having a region of concentrated magnetic flux that permeates the surface and also a region of dilute magnetic flux that is inclined and generally adjacent to the surface, a hopper for storing the particulate matter, and a channel connected to the hopper disposed in the region of dilute magnetic flux having two opposite converging walls that terminate adjacent to the conductive surface in the region of concentrated magnetic flux. The particulate matter when introduced to the region of dilute magnetic flux is caused to be moved by magnetic forces and gravitational forces from the region of dilute magnetic flux to the region of concentrated magnetic flux. The particulate matter is deposited on the surface by the electrostatic forces overcoming the magnetic forces in the region of concentrated magnetic flux. The application also discloses a process for depositing particulate matter on a moving conductive surface by producing a magnetic field having a region of concentrated magnetic flux that permeates the surface and a region of dilute magnetic flux that is inclined and generally adjacent to the surface, introducing a quantity of the particulate matter to the region of dilute magnetic flux, and then placing the conductive surface into the region of concentrated magnetic flux whereby the particulate matter is caused to move from the region of dilute magnetic flux to the region of concentrated magnetic flux by magnetic forces and gravitational forces and thence to the conductive surface by overwhelming electrostatic forces.

BACKGROUND OF THE INVENTION 
A. Field of the Invention 
This invention relates to a process for use in electrostatic copying 
machines, and more particularly, to a process for depositing 
electrostatically and magnetically responsive particulate matter on a 
moving photoconductive surface bearing a latent electrostatic image. 
B. Discription of the Prior Art 
In typical electrostatic photocopying processes a surface of a 
photoconductive insulating material is charged with a uniform 
electrostatic charge. The charged surface of the photoconductive material 
is then exposed to a light image through a photographic transparency or 
some other suitable means. The portions of the charged surface that are 
irradiated by light are discharged while the remaining portions of the 
charged surface maintain their charge to form a latent electrostatic image 
that corresponds to the light image. The latent electrostatic image on the 
surface is developed by applying electrostatically responsive powder to 
the surface. The powder image thus formed is fixed directly to the 
photoconductive surface by fusing or the like. 
More recently, magnetic forces and electrostatic forces have been used to 
develop latent electrostatic images in electrostatic photocopying 
machines. In some instances, the developer powder is applied to the 
conductive surface by using the well known "magnetic brush" technique. The 
developer powders that have been employed are well known in the art and 
generally comprise dyed or colored pigmented thermoplastic powders 
referred to as "toner" that are mixed with more course particles known as 
"carriers", such as, for example, iron filings. Developer powders can be 
formulated so that the "toner" carries a negative or positive charge. A 
typical positive developer powder is formulated from carbon black 
pigmented, polystyrene resin "toner" mixed with iron magnetites or 
ferrites. In any case, the "toner" and the "carrier" are selected so that 
the "toner" particle acquires the proper charge with respect to the latent 
electrostatic image. When the "developer brush" is brought into contact 
with the conductive surface greater attractive electrostatic forces of the 
charged image cause the "toner" particles to leave the "carrier" particles 
and adhere to the conductive surface. 
Apparatus for using the "magnetic brush" technique are well known in the 
art. Typically a magnetic brush consists of a non-magnetic rotatably 
mounted cylinder having magnets fixed inside the cylinder. The cylinder is 
adapted to rotate with a portion of its surface immersed in a hopper 
having a supply of developer powder. The developer powder, being a mixture 
of iron "carrier" particles and electrostatic "toner" particles, is 
magnetically attracted to the surface of the cylinder to form a brush-type 
arrangement thereon as a result of the magnetic flux developed by the 
magnets. The bristles of the brush conform to the lines of magnetic flux. 
The conductive surface such as, for example, a sheet of paper bearing a 
latent electrostatic image is brought into physical contact with the brush 
and "toner" is thereupon deposited on the sheet of paper. 
The rotating cylinder continues to attract developer powder and returns 
part or all of this material to the hopper within one revolution. 
Accordingly, a fresh mix is always available to the copy sheet surface at 
its point of contact with the brush. 
In every instance the systems and apparatuses of the prior art require a 
delicate balance between the ratio of iron "carrier" particles and the 
electrostatic "toner" particles as well as an intimate admixture of 
uniform quality. Quite often variations in the ratio of the inro "carrier" 
particles to the electrostatic "toner" particles in experienced resulting 
in poor coverage of the image to be developed. Furthermore, the iron 
"carrier" particles gradually deteriorate and frequently the entire system 
must be cleaned and replaced with a fresh admixture of "carrier" and 
"toner" 
It is well recognized that the step of developing the latent electrostatic 
image is perhaps the most critical step in all of the process steps of 
electrostatic copying. The final print quality can be no better than the 
quality of development step. Recently significant improvements have 
developed in the method of image developing, and particularly, a new 
developer powder has been developed as shown for example in U.S. Pat. No. 
3,639,245 involving a composite developer powder comprising magnetizable 
particles embedded in the "toner" particles. The composite developer 
powder of the above mentioned patent is used with the prior art 
apparatuses such as, for example, the brush-type applicators that use the 
rotating cylinder to carry the developer powder from its supply to the 
conductive surface. 
Despite this improvement in developer powders there is still a need for 
improvements in the devices employing such powders. For example, the 
cylinder being journalled to a shaft for rotation developes considerable 
misalignment between the cylinder and the conductive surface resulting in 
a poor nonuniform deposition of developer powders to the surface. Such 
failures result in customer complaints and considerable expense in 
replacing the cylinders and the like. Furthermore, the prior art devices 
are complex; a need for simplifying the structures utilizing the 
brush-type technique and to obtain savings in the cost of manufacture of 
such devices without sacrificing performance dependability are needed. 
Accordingly, I have developed a process that substantially eliminates the 
number of moving parts and particularly, the necessity for rotating 
cylinder of the prior art devices. My device and process being of a less 
complicated structure is considerably less expensive to manufacture than 
the prior art devices. My apparatus and process using the improved 
magnetically and electrostactically responsive developer powders is 
capable of developing latent electrostatic images of greater clarity and 
resolution than the prior art devices. 
SUMMARY OF THE INVENTION 
In accordance with my invention, my apparatus for depositing 
electrostatically and magnetically responsive particulate matter on a 
conductive surface bearing a latent image comprises a magnetic field 
producing means disposed adjacent to the conductive surface that is 
capable of producing a magnetic field having a region of concentrated 
magnetic flux and a region of dilute magnetic flux that is inclined and 
generally adjacent to the surface, storage means for storing the 
particulate matter and channel means adapted for use with the storage 
means and disposed adjacent to the surface in the region of dilute 
magnetic flux that is capable of channelling a quantity of the particulate 
matter from the storage means to the region of concentrated magnetic flux 
whereby the gravitational forces and magnetic forces in the region of 
dilute magnetic flux move the quantity of particulate matter from the 
storage means to the region of concentrated magnetic flux and the 
electrostatic forces cause the quantity of particulate matter to be 
deposited on the conductive surface. 
In a preferred embodiment of my invention my process includes an electric 
field producing means disposed adjacent to the magnetic field producing 
means and the conductive surface that is capable of producing an electric 
field at the region of concentrated magnetic flux and that is capable of 
imparting an electric charge to the particulate matter. 
In accordance with the process of my invention a magnetic field is produced 
having the region of concentrated magnetic flux and the region of dilute 
magnetic flux, a quantity of the particulate matter is introduced to the 
region of dilute magnetic flux, and the conductive surface is placed into 
the region of concentrated magnetic flux whereby the particulate matter is 
caused to move from the regions of dilute and concentrated magnetic flux 
by forces of magnetism to the conductive surface by electrostatic forces.

DETAILED DESCRIPTION 
In FIG. 1 there is illustrated an elongate permanent magnet 11 producing a 
region of concentrated magnetic flux generally indicated at 13 (although 
the lines of magnetic flux are not illustrated in FIG. 1) and a region of 
dilute magnetic flux generally indicated at 15 (although the lines of 
magnetic flux are not illustrated in FIG. 1), a storage hopper generally 
indicated at 17 that contains particulate matter 19, and a channel 21 that 
is capable of channelling the particulate matter 19 from the storage 
hopper 17 through the region of dilute magnetic flux 15 to the region of 
concentrated magnetic flux 13. Suspended beneath the hopper 17 is a 
conductive surface 23. 
As more clearly illustrated in FIG. 4 the permanent magnet 11 is elongate 
and extends entirely across the hopper 17 and transversely across and 
beyond the conductive surface 23. In the embodiment of FIG. 1, the 
permanent magnet 11 has a generally quarter-spherical cross-sectional 
configuration and comprises an arcuate face 25 facing towards the 
particulate matter 19 and storage hopper 17, a first planer face 27 
extending from one end of the arcuate face 25 from a point 29 and a second 
planar face 31 extending from the other end of the arcuate face to the 
first planar face 27. The permanent magnet 11 is oriented with respect to 
the hopper 17 the particulate matter 19 contained therein and surface 23 
so that the point 29 from which the region of concentrated magnetic flux 
emanates is facing the conductive surface 23 and the region of dilute 
magnetic flux extends towards the hopper 17. 
The elongate magnet is carried by the structure of the hopper 17 and is 
integral therewith as will be more fully explained. If desired, the 
permanent magnet need not be integral with the hopper but may comprise a 
separate component and either be appropriately suspended above the surface 
or fixed to a side wall of the hopper (not illustrated). 
The elongate magnet is carried to the right of the slit 51 in the drawings 
but it could also be carried to the left of the slit 51 with appropriate 
design changes in the hopper 17 and trough 45 in accordance with my 
invention. 
The permanent magnet 11 is composed of a non-magnetic matrix which may be a 
resinous or plastic composition, an elastomeric semi-solid or a viscous 
liquid that is capable of hardening, setting or being cured to a solid 
state in which there is evenly dispersed anisotropic ferrite domain-sized 
particles that are capable of achieving a physical orientation when acted 
upon by internal sheer stresses. The example of such particles are certain 
fine-grain permanent magnet materials, particularly the ferrites of 
barium, lead and strontium that are easily magnetized to saturation. The 
non-magnetic matrix may also be composed of natural rubber with compound 
agents, plasticizers, vulcanizing agents and the like to provide the 
hardness of the matrix desired, or may be thermoplastic or thermosetting 
materials, such as for example, polyvinyl chloride. Such magnets may be 
formed by extrusion and manners well known in the art. 
Alternatively, rather than using permanent magnets, electromagnetic devices 
may be used in accordance with the invention. 
The elongate magnet 11 as illustrated in the drawings comprises a single 
member, however, the permanent magnet may comprise a plurality of members, 
all of which must possess the same orientation of polarity across its 
entire length so that uniform fields of magnetic flux extend across the 
length of the elongate magnet and permeate the surface 23. 
FIG. 5 illustrates the lines of magnetic flux emanating from the pole 
surfaces of the magnet. As illustrated, the north pole of the magnet 
exists at point 29 and the south pole exists at the second planar face 31, 
although the polarity of the magnet could be reversed. Lines of magnetic 
flux emanate from the point 29 and pass through the air, through a portion 
of the hopper 17 to return to the second planar surface 31 at the south 
pole. The lines of magnetic flux are distorted and asymmetrical. There is 
a greater concentration of magnetic flux on the west side of the 
north-south magnetic line 33 away from the hopper 17, than on the east 
side of the north-south magnetic line 33 towards the hopper FIG. 5. The 
distorted and asymmetrical nature of the magnetic flux of the magnet in 
FIG. 5 is a desirable feature of my invention in that a longer magnetic 
distance is provided between the poles on the east side of the north-south 
magnetic line and a shorter magnetic distance is provided on the other 
opposite west side of the north-south magnetic line. This distortion 
results in a magnet having a lower gauss level and a wider array of flux 
travel around the east side of the magnet than the west side of the 
magnet. The magnet being oriented with respect to the hopper 17 and the 
conductive surface 23 presents magnetic flux of the lower gauss level 
facing the hopper 17 as illustrated in FIGS. 1 and 5. Consequently, there 
will not be any magnetic attraction of particulate matter 19 on the side 
walls of the hopper 17, and there will not be any magnetic attraction 
until the particulate matter is in close proximity to the region of dilute 
magnetic flux. 
The cross-sectional configuration of the magnet illustrated in the drawings 
is not particularly critical, although as previously explained, the 
orientation of the magnetic flux with respect to the hopper and conductive 
surfaces is critical. Any cross-sectional configuration that develops a 
distorted and asymmetrical magnetic flux with the magnetic flux having the 
lower gauss level being oriented towards the hopper 17 will be 
satisfactory. Alternatively, a magnet providing a uniform magnetic flux 
such as for example, a magnet having a square or circular cross-sectional 
configuration may be employed, however, such magnets will require 
appropriate magnetic shielding to reduce the magnetic flux emanating from 
the magnet in the area facing the hopper 17. The disadvantage of employing 
magnetic shielding is that such designs are complicated, expensive and may 
well tend to restrict the design of the interior walls of the hopper as 
magnetic shielding does not actually block magnetic flux but simply 
attenuates the flux to a point where it will not cause an attraction of 
the particulate matter to the side walls of the hopper 17. 
The magnets employed in accordance with the preferred embodiment of the 
invention contemplate a gauss level of about 120 measured directly at the 
pole surface. A magnetic strength of 120 gauss is adequate for my 
invention, however, it will be recognized that the actual gauss level 
required in any embodiment of my invention will be dictated in great 
measure by the configuration and dimensions of the hopper and location of 
the magnet so as to provide a sufficient quantity of particulate matter 
for development in accordane with the invention. 
In the drawings hopper 17 comprises two oppositely facing in end walls 35 
and 37 that are generally vertically disposed in the drawings, oppositely 
facing side walls 39 and 41 to provide a generally rectangular 
configuration as viewed from the plan view of the device at FIG. 4. The 
side walls 39 and 41 of the hopper 17 converge towards each other as 
illustrated in FIGS. 1 and 2 to provide an elongate opening or slit 43. 
The opening 43 enters into a channel or trough 45. Trough 45 comprises two 
converging faces, a leading face 49 and a trailing face 47 that converge 
to form a trough opening or slit 51 that is disposed adjacent to surface 
23 in the region of concentrated magnetic flux 13 as illustrated in FIG. 
1. 
The trough opening 51 extends across the entire length of the hopper 17 as 
well as across the width of the conductive surface 23 so that a uniform 
deposition of particulate matter 19 may be provided on the conductive 
surface 23. 
The trough 45 illustrated in the drawings is generally inclined to and must 
have its leading face or wall 49 inclined to the conductive surface 23 at 
an angle. The trough itself is positioned so as to lie within the region 
of dilute magnetic flux. I have found that the leading wall 49 must be 
inclined to the conductive surface 23 at an angle not less than 
26.degree., especially in the region of dilute magnetic flux. If the angle 
is less than 26.degree. the particulate matter will tend to clog and poor 
deposition of particulate matter will occur. The angle of inclination is 
designed in accordance with the flow properties of the particulate matter 
used. It should be recognized that the trough is inclined to the left in 
FIG. 1 but it could be reversed and inclined to the right if desired. In 
such case the trailing wall would have to be inclined at an angle not less 
than 26.degree.. 
The particulate matter will move from the hopper 17 through the trough 45 
by the forces of gravity and the magnetic forces generated by the region 
of dilute magnetic flux. The trough opening 51 will have a width that will 
be determined by the flux density of the magnetic field employed and the 
magnetic permeability of the particulate matter employed. I have found 
that the region of the dilute magnetic flux should range from 90 to 95 
gauss and in such instances, I have discovered that the trough opening 
should be within at least one quarter of an inch in distance from the 
magnetic pole of the magnet on the point 29 where the region of maximum 
flux density occurs and that the trough opening must have a width not in 
excess of three eights of an inch. A wider trough opening would cause a 
portion of the particulate matter to fall from the hopper to the trough 
solely by the forces of gravity thereby forming lumps of particulate 
matter on the conductive surface as well as depositing particulate matter 
on the unexposed regions of the conductive surface. 
The hopper 17 further comprises exterior side walls 53 and 55 that are 
generally parallel to each other and are essential perpendicular to the 
conductive surface 23, although their particular orientation is not 
critical. Further, there is provided exterior bottom walls 57 and 59 
meeting the respective exterior side walls 53 and 55 and terminating at 
the trough opening 51 or slit, as illustrated in FIG. 1. Bottom wall 59 is 
inclined away from the conductive surface 23 to provide ample clearance 
for the deposition of particulate matter 19 onto the conductive surface 
23. Bottom wall 57 at the region nearest the trough opening 51 is 
essentially parallel to the conductive surface 23 and in rubbing contact 
therewith to stabilize and guide the movement of the conductive surface 23 
with respect to the trough opening 51. 
The hopper may be extruded from such materials as rigid nylon, polyvinyl 
chloride, polystyrene, acrylonitrile butadiene styrene resins, aluminum 
and the like. Such materials have electrical conductivity properties that 
are compatible with the triboelectric properties of the particulate matter 
so that the particulate matter does not adhere to the walls of the hopper. 
I have found that the performance of my device may be significantly 
improved by the use of an electric field at the region of concentrated 
magnetic flux 13. In the drawings there is illustrated a conductive strip 
61 that extends along the length of the hopper and transversely to the 
conductive surface 23 and that is adjacent thereto. In the drawings the 
conductive strip 61 is fixed to bottom wall 59 of hopper 17. On the other 
side of the conductive surface 23, there is another conductive strip 63, 
substantially underneath conductive strip 61. Conductive strip 63 is in 
essentially rubbing contact with the conductive surface 23 and serves as a 
guide for the conductive surface 23 as it moves with respect to the trough 
opening 45. Conductive strip 61 is connected to a source of potential and 
conductive strip 63 is connected to a ground although the respective 
conductive strips could be connected in reverse order. The conductive 
strips when energized provide an electric field between them and serve a 
dual purpose in accordance with the invention. First, the electric field 
is capable of imparting an electric charge to the particulate material of 
an opposite polarity to the charge of the latent electrostatic image on 
the conductive strip 23. Secondly, the electric field is capable of 
neutralizing any residual electrostatic charges on the conductive strip 23 
that are undesirably left on the non-image portions of the surface. Thus 
the field is capable of "washing" undesirable images from the conductive 
surface 23 to provide a final copy product of improved resolution and 
clarity. 
The amount of biasing voltage applied to the conductive strip may vary in 
accordance with my invention. The biasing voltage is determined by several 
factors including the amount of charge contained on the conductive surface 
23, the affinity of the particulate matter to such charge, the distance 
from the conductive surface 23 to the outer-most surface of the 
particulate matter being deposited on the conductive surface 23. I have 
found that a voltage varying from a fraction of a volt for some materials 
to between 200 and 600 volts for other types of materials such as for 
example, zinc oxide and resin binder systems, may be used in accordance 
with the invention. 
It is preferred that a smooth direct current (D.C.) be employed by a 
transformer and appropriate rectifying and filtering equipment that 
normally operates from a common 115 volt 60 cycle power source. It is to 
be understood however, that for some applications an alternating current 
(A.C.) may be preferred over a D.C. field to achieve special results. It 
is also to be recognized that in some applications a non-filtered D.C. 
voltage source may be employed in accordance with the invention. 
As illustrated in the drawings the electric field produced by the 
conductive strips 61 and 63 is positioned coincidentally with the region 
at which the particulate matter is being deposited upon the conductive 
surface 23. The position of the electric field must exist at this point so 
that the field may neutralize the undesired residual charges existing on 
the conductive surface 23. 
As previously explained, the particulate matter must possess an electric 
charge that is opposite in polarity to the charge of the latent 
electrostatic image on the conductive surface 23. In the devices of the 
prior art, the particulate matter is charged triboelectrically, or an 
electric charge must be induced on the particulate matter being contained 
in the hopper. 
In my invention, the particulate matter does not have the opportunity to be 
charged triboelectrically as compared to the devices of the prior art 
because of the reduced amount of agitation in my invention. Accordingly, 
the electric field previously described may be necessary to impose such a 
charge on the particulate matter. Alternatively, suitable probes and the 
like mounted within the hopper (not illustrated) may be employed to induce 
a static charge on the particulate matter. 
In FIG. 1 the conductive surface 23 comprises a sheet of paper that is 
esentially a photoconductive surface having thereon a coating of zinc 
oxide with a resin binder. In operation a latent image is formed on the 
photoconductive surface by first imposing a uniform electrostatic charge 
onto the surface by any conventional means (not illustrated) and then 
subjecting the surface to a pattern of light by conventional means (not 
illustrated) whereby the regions on the photoconductive surface that have 
been impinged with light will have their electrostatic charge dissipated 
by the proton energy of the light beam. Areas on the surface not receiving 
light energy will retain their charge to be later developed with the 
electrostatically and magnetically responsive particulate matter as 
previously described. 
The paper or photoconductive surface is then drawn through contact rollers 
65 and 67 both of which are aligned with respect to each other as 
illustrated in FIG. 1. In FIG. 1 there is illustrated a guide plate 69 
that is used to guide the paper between the guide plate 69 and bottom wall 
57 of the hopper. Alternatively, two guide plates one above and one below 
the paper could be employed instead of using the bottom wall 57 of the 
hopper, however, in such an instance the configuration of the hopper would 
have to be modified. 
Beneath the paper and between contact rollers 65 and 67 and the guide plate 
69 there is an aligning roller 71 used for the purpose of urging the paper 
against the bottom wall 57 of the hopper to assure a perfectly flat 
transverse contact of the paper's surface with the region in which the 
particulate matter is being deposited onto the paper. 
Down stream of the region in which particulate matter is being deposited 
there exists a conveyor means 73 comprising a continuous conveyor belt 75 
that is mounted on conveyor rollers 77 and 79 and that is used to pull the 
sheet of paper through the system. Preferably the conveyor belt 75 extends 
transversely across the entire width of the sheet of paper to provide a 
uniform base upon which the paper may be drawn through the system and the 
conveyor means 73 are coordinated and synchronized in their movement to 
provide a uniform movement of the sheet of paper through the system. The 
synchronized movement is accomplished as illustrated in FIG. 5 (but not 
illustrated in FIG. 1) by the contact roller 67 (the bottom roller in FIG. 
1) and the conveyor rollers 77 and 79 being linked together with an 
appropriately designed cog and chain arrangement 81 connecting all rollers 
together as shown in FIG. 4. A suitable drive system such as for example, 
an electric motor, is connected with the cog and chain arrangement of FIG. 
4 (not illustrated) to drive the moving parts in synchronization. 
Contact rollers 65 and 67 are appropriately linked together by a spring 83 
mounted in bushings 85 on both ends as shown in FIG. 4 (but not shown in 
FIG. 1). This connection provides synchronized movement of both contact 
rollers 65 and 67 for the uniform movement of the sheet of paper 23 
through the system. 
In use the elongate magnet 11 produces a magnetic field that has a region 
of concentrated magnetic flux 13 that permeates the conductive surface 23 
and a region of dilute magnetic flux 15 that is inclined and generally 
adjacent to the surface 23. The region of concentrated magnetic flux 
emanates from the north pole of the magnet at point 29 that is adjacent to 
the surface 23. The lines of magnetic flux emanating from the point 29 are 
substantially perpendicular to the conductive surface 23. Subsequently a 
quantity of particulate matter 19 is introduced into the regions of 
magnetic flux by the trough 45 that lies within the region of dilute 
magnetic flux. A conductive surface is placed into the region of 
concentrated magnetic flux having thereon a latent electrostatic image 
developed in a manner well known to the art. Consequently the particulate 
matter is caused to move from the region of dilute magnetic flux to the 
region of concentrated magnetic flux by magnetic forces and gravity and 
thence to the surface by electrostatic forces overcoming the magnetic 
forces there. 
Preferably the conductive strips are biased with a voltage to produce an 
electric field at the region of concentrated magnetic flux for the purpose 
of inducing a charge to the particulate matter and for the purpose of 
neutralizing diffuse unwanted electrostatic charges on the surface to 
improve the quality and clarity of the deposition of particulate matter 
onto the surface. 
As illustrated in FIG. 4, the conductive surface 23 has a latent 
electrostatic image in the form of an arrow illustrated in phantom lines 
on the left of the hopper. As the paper is advanced through the contact 
rollers underneath the hopper and through the region of concentrated 
magnetic flux, the particulate matter is deposited onto the conductive 
surface to develop an image as illustrated by the darkened arrow on the 
surface 23 as shown in FIG. 4 to the right of the hopper. Subsequently, 
the image is fixed to the surface in manners well known to those skilled 
in the art. 
While my invention has been described with the hopper being positioned 
above the conductive surface to develop images on the upper portion of the 
surface, it will be understood that the hopper could be used to develop 
images on the underneath portions of the surface by disposing the hopper 
under the conductive surface 23 and employing various mechanical means to 
convey the particulate matter to the region of dilute magnetic flux and 
thence to the surface as above described. Such devices, however, would 
requre additional equipment and more moving parts. 
The advantages of my invention are readily recognizable. My invention 
minimizes and eliminates the need to rely on multiple mechanical devices 
to convey and transfer particulate matter from the storage hopper to the 
region of deposition on the image surface. Several beneficial results are 
obtained by my invention such as reducing the cost of the apparatus and 
eliminating the possibilities of various parts failing under use. Further, 
my system and apparatus has a performance dependability that is extremely 
reliable in contrast to the devices and processes of the prior art. By the 
use of the electric field as described I am able to develop latent images 
with greater clarity and precision than heretofore known in the art.