U.S. patent number 3,915,121 [Application Number 05/416,898] was granted by the patent office on 1975-10-28 for development apparatus.
This patent grant is currently assigned to Xerox Corporation. Invention is credited to David G. Wilcox.
United States Patent |
3,915,121 |
Wilcox |
October 28, 1975 |
**Please see images for:
( Certificate of Correction ) ** |
Development apparatus
Abstract
A development apparatus for developing electrostatic images upon
a moving image-bearing surface including flow baffle means for
regulating the flow of developer to the development zone. The
baffle means is positioned between a supply means and the
development zone and extends inwardly of each of the ends of a
development means which preferably comprises a magnetic brush. The
baffle means comprises stationary magnetic brushes formed of
developer material. The stationary magnetic brushes are adapted to
limit the flow of developer at the end portions of the development
means.
Inventors: |
Wilcox; David G. (West Webster,
NY) |
Assignee: |
Xerox Corporation (Stamford,
CT)
|
Family
ID: |
23651764 |
Appl.
No.: |
05/416,898 |
Filed: |
November 19, 1973 |
Current U.S.
Class: |
399/275;
277/345 |
Current CPC
Class: |
G03G
15/09 (20130101) |
Current International
Class: |
G03G
15/09 (20060101); G03G 015/08 () |
Field of
Search: |
;118/623,637,636,DIG.24
;117/17.5 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Stein; Mervin
Assistant Examiner: Salser; Douglas
Attorney, Agent or Firm: Weinstein; Paul Green; Clarence A.
Ralabate; James J.
Claims
What is claimed is:
1. In a development apparatus for developing electrostatic images
upon an image bearing surface by the application of developer
thereto comprising: a moving member for supporting a first magnetic
brush of said developer; first magnetic field generating means for
forming said first magnetic brush so that it extends out from said
moving member with a first height; the improvement wherein, said
apparatus further includes:
means for reducing the height of said first magnetic brush, said
height reducing means comprising a stationary member for supporting
a second magnetic brush of said developer, said stationary member
being spaced from said moving member and second magnetic field
generating means for forming said second magnetic brush so that it
extends out from said stationary member toward said moving member
so as to engage said first magnetic brush to reduce said first
height.
2. An apparatus as in claim 1, further including a developer supply
means, and wherein said moving member comprises a development means
for applying developer to said imaging bearing surface, said
development means extending across said image bearing surface and
having first and second opposing ends and first and second end
portions extending inwardly from said ends, and further including
means for moving said moving member between said supply means and a
development zone.
3. An apparatus as in claim 2, wherein said first and said second
magnetic field generating means comprise permanent magnets.
4. An apparatus as in claim 3, further including a housing
substantially enclosing said development apparatus and having an
opening at said development zone to provide communication between
said development means and said moving image bearing surface and
wherein said second magnetic field generating means is positioned
externally of said housing.
5. An apparatus as in claim 4, wherein said stationary member
comprises a portion of said housing.
6. An apparatus as in claim 2, wherein said second magnetic field
generating means are positioned between said supply means and said
development zone and extend inwardly of each of the ends of said
development means a given amount and have a limited extension in
the direction of movement of said development means, whereby said
second magnetic brushes as formed tend to limit the flow of
developer at the end portions of said development means.
7. An apparatus as in claim 5, further including a housing
substantially enclosing said development apparatus and having an
opening at said development zone to provide communication between
said development means and said moving image bearing surface and
wherein said second magnetic field generating means are positioned
externally of said housing.
8. An apparatus as in claim 6 wherein said second magnetic field
generating means comprise permanent magnets positioned at the ends
of said housing.
9. An apparatus as in claim 7, wherein said permanent magnets have
a wedge shaped portion wherein the thickness of said magnets
decreases the further said magnets extend inwardly of said
development means.
10. An apparatus as in claim 8, further including flow blocking
members extending inwardly of each of the ends of said development
means said members being positioned between said supply means and
said second magnetic field generating means.
11. A development apparatus for developing electrostatic images
upon an image bearing surface by the application of developer
thereto comprising:
a moving member for supporting a first magnetic brush of said
developer, said member having first and second opposing ends and
first and second end portions extending inwardly from said
ends;
a stationary member for supporting a second magnetic brush of said
developer, said stationary member being spaced from said moving
member so as to define a gap extending from said moving member to
said stationary member;
first magnetic field generating means for forming said first
magnetic brush so that it extends out from said moving member
toward said stationary member in said gap;
second magnetic field generating means for forming said second
magnetic brush so that it extends out from said stationary member
toward said moving member over the entire of said gap,
said second magnetic field generating means extending inwardly of
the ends of said moving member a given amount and having a limited
extension in the direction of movement of said member;
whereby said second magnetic brushes as formed tend to limit the
flow of developer at the end portions of said member.
12. An apparatus as in claim 11, further including a developer
supply means, and wherein said moving member comprises a
development means for applying developer to said imaging bearing
surface, said development means extending across said image bearing
surface, and further including means for moving said moving member
between said supply means and a development zone.
13. An apparatus as in claim 12, further including a housing
substantially enclosing said development apparatus and having an
opening at said development zone to provide communication between
said development means and said moving image bearing surface and
wherein said second magnetic field generating means are positioned
externally of said housing.
14. An apparatus as in claim 13, wherein said second magnetic field
generating means comprise permanent magnets positioned at the ends
of said housing.
15. An apparatus as in claim 14, wherein said permanent magnets
have a wedge shaped portion wherein the thickness of said magnets
decreases the further said magnets extend inwardly of said
development means.
16. An apparatus as in claim 15, further including flow blocking
members extending inwardly of each of the ends of said development
means said members being positioned between said supply means and
said second magnetic field generating means.
Description
BACKGROUND OF THE INVENTION
This invention relates to a development apparatus for developing
electrostatic images upon a moving image-bearing surface. Flow
baffle means are included for regulating the flow of developer to
the development zone. The flow baffle means comprise stationary
magnetic brushes.
In prior art magnetic brush development apparatuses, a problem has
occurred with respect to the copy quality output of the
electrostatic reproducing machines in which they are employed. In
some machines a high background region is formed on each of the end
portions of the copy sheet due to higher flow rates of developer at
the end portions of a magnetic brush development means. The higher
flow rates at the ends of the magnetic brush development means are
due at least in part to the presence of fringe fields at the ends
of the brush forming magnets within the development means which
attract an increased amount of developer to the ends of the
magnetic roll. The increased flow of developer coupled with fringe
fields at the ends of the magnetic brush roll results in a higher
density of developer at the ends of the roll and, therefore, a
consequent increase in the background level on the end portions of
the copy sheet.
In U.S. Pat. Nos. 3,648,656, granted March, 1972, and 3,754,526,
granted August, 1973, there are disclosed magnetic brush
development apparatuses wherein magnetic field generating means are
employed to prevent the developer from being picked up by the end
portions of the magnetic brush rolls. These patents use magnetic
fields to control the flow of developer, but do not employ
stationary magnetic brushes in accordance with this invention to
mechanically control the flow of developer.
The use of a magnetic means interposed between a bearing and a flow
of magnetic particles is described in U.S. Pat. No. 2,996,162,
granted August, 1961, and in U.S. application Ser. No. 266,905,
filed June 28, 1972. In these devices a magnetic flux field
produced by the magnetic means entraps and aligns the magnetic
granules into a brush which acts to seal the bearings from the flow
of magnetic particles. The patent and application do not use the
magnetic seal brushes as flow baffles to regulate the flow of
developer to the development zone of a development apparatus.
SUMMARY OF THE INVENTION
In accordance with this invention, a development apparatus is
provided for developing electrostatic images upon a moving
image-bearing surface at a development zone by the application of
developer thereto. The development apparatus includes a developer
supply means and a development means for applying developer to the
image-bearing surface. The development means extends across the
image-bearing surface and has first and second opposing ends and
first and second end portions extending inwardly from the housing.
The development means is adapted to move between the supply means
and the development zone.
In accordance with this invention flow baffle means are provided
for regulating the flow of developer to the development zone. The
baffle means are positioned between the supply means and the
development zone and extend inwardly of each of the ends of the
development means and have a limited extension in the direction of
movement of the development means. The baffle means, in accordance
with this invention, comprise stationary magnetic brushes which are
effective to limit the flow of developer at the end portions of the
development means.
Preferably, in accordance with this invention, the development
apparatus comprises a magnetic brush development apparatus and the
development means includes a magnetic brush support means, means
for forming a magnetic brush of developer upon the support means,
and means for moving the support means between the supply means and
the development zone.
The stationary magnetic brush flow baffles of this invention are
preferably formed by means of a magnetic field generated externally
of the development means. The magnetic field generating means
preferably comprises a permanent magnet and most preferably a
magnet having a wedge shape to provide a less abrupt flow rate
disturbance. To provide a further improvement in developer flow
regulation at the ends of the development means, mechanical flow
blocks separate from the stationary brush flow baffles can be
employed which are positioned between the flow baffles and the
supply means.
Accordingly, it is an object of this invention to provide a
development apparatus including stationary magnetic brush flow
baffle means to regulate the flow of developer to the development
zone.
It is a further object of this invention to provide a development
apparatus as above which comprises a magnetic brush development
apparatus.
It is a still further object of this invention to provide a
reproducing apparatus employing the above-noted development
apparatus.
These and other objects of the invention will become more apparent
to those skilled in the art from the following description and
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a top view in partial cross-section of a prior art
magnetic brush development means.
FIG. 2 shows a schematic view in partial cross-section of an
electrostatographic reproducing machine in accordance with this
invention.
FIG. 3 is a partial front view in partial cross-section along the
line 3--3 in FIG. 2.
FIG. 4 is a top view in partial cross-section of a magnetic brush
development means in accordance with this invention.
FIG. 5 is a partial cross-section of a magnetic brush apparatus
having one embodiment of a flow baffle in accordance with this
invention.
FIG. 6 is a partial cross-section of a magnetic brush apparatus
having a flow baffle in accordance with a different embodiment of
the present invention.
FIG. 7a and 7b comprise a graph and partial cross-section
respectively illustrating the flow regulating effect of a
stationary brush forming magnet in accordance with one embodiment
of the invention.
FIGS. 8a and 8b comprise a graph and partial cross-section
respectively illustrating the flow regulating effect of a
stationary brush forming magnet in accordance with a preferred
embodiment of this invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 1, there is shown a magnetic brush 1 formed in
accordance with a prior art magnetic brush roll design 2. The
magnetic brush roll 2 comprises a cylindrical shell 3 which has a
stationary magnet 4 supported within it, which is adapted to orient
and form a developer mix into a magnetic brush 1 for application to
an electrostatic image on a moving image-bearing surface. A
generally normal field is provided along the length of the magnet 4
except at the ends 5 and 6 where fringe fields 7 and 8 are formed
which have an additive effect with the normal field to provide
stronger magnetic fields at the ends of the magnet. This results in
an increased amount of developer being picked up at the end
portions 9 and 10 of the mag brush roll 2 so that the resulting
magnetic brush 1 prior to contacting the image-bearing plate has a
cross-section substantially as shown. The increased amount of
developer material which goes into the portions 11 and 12 of the
brush 1 at the ends of the roll 2 results in a marked increase in
developer flow at these portions and a consequent reduction in
developer life. Besides reducing developer life the increased flow
rates at the end portions 9 and 10 of the roll 2 coupled with the
fringe fields 7 and 8, have a deleterious effect on copy quality.
When the brush 1 contacts the image-bearing surface, the bubous
portions 11 and 12 of the brush are compacted such that they have
an increased developer density. As a result, a greater portion of
background is developed by the end portions 11 and 12 of the
magnetic brush 2 which when transferred to the final support sheet
gives an undesirably high background appearance at each of the ends
of the sheet.
In order to reduce the developer flow rates at the end portions 9
and 10 of the magnetic brush roll 2 in accordance with this
invention as shown in FIG. 2, baffle flow means 20 are provided
which comprise stationary magnetic brushes 21 which are effective
to regulate the flow of developer at the end portions 9 and 10 of
the roll 2.
Referring now to FIG. 2 there is shown by way of example an
automatic xerographic reproducing machine 30 which incorporates the
magnetic brush flow baffles 20 and magnetic brush apparatus 31 of
the present invention. The reproducing machine 30 depicted in FIG.
1 illustrates the various components utilized therein for producing
copies from an original. Although the magnetic brush flow baffles
20 and magnetic brush apparatus 31 of the present invention are
particularly well adapted for use in an automatic xerographic
reproducing machine 30, it should become evident from the following
description that they are equally well suited for use in a wide
variety of processing systems including other electrostatographic
systems and they are not necessarily limited in their application
to the particular embodiment or embodiments shown herein.
The reproducing machine 30 illustrated in FIG. 2 employs an image
recording drum-like member 32, the outer periphery of which is
coated with a suitable photoconductive material 33. One type of
suitable photoconductive material is disclosed in U.S. Pat. No.
2,970,906, issued to Bixby in 1961. The drum 32 is suitably
journaled for rotation within a machine frame (not shown) by means
of shaft 34 and rotates in the direction indicated by arrow 35 to
bring the image-bearing surface 33 thereon past a plurality of
xerographic processing stations. Suitable drive means M are
provided to power and coordinate the motion of the various
cooperating machine components whereby a faithful reproduction of
the original input scene information is recorded upon a sheet of
final support material 36 such as paper or the like.
The practice of xerography is well known in the art and is the
subject of numerous patents and texts including Electrophotography
by Schaffert, published in 1965, and Xerography and Related
Processes by Dessauer and Clark, published in 1965.
The various processing stations for producing a copy of an original
are herein represented in FIG. 2 as blocks A to E. Initially, the
drum 32 moves the photoconductive surface 33 through a charging
station A. In the charging station A, an electrostatic charge is
placed uniformly over the photoconductive surface 33 preparatory to
imaging. The charging may be provided by a corona generating device
of the type described in U.S. Pat. No. 2,836,725, issued to
Vyverberg in 1958.
Thereafter, the drum 32 is rotated to exposure station B wherein
the charged photoconductive surface 33 is exposed to a light image
of the original input scene information whereby the charge is
selectively dissipated in the light exposed regions to record the
original input scene in the form of a latent electrostatic image. A
suitable exposure system may be of a type described in U.S. Pat.
No. 3,062,110, issued to Shepardson et al. in 1962. After exposure
drum 32 rotates the electrostatic latent image recorded on the
photoconductive surface 33 to development station C in accordance
with the invention wherein a conventional developer mix is applied
to the photoconductive surface 33 of the drum 32 rendering the
latent image visible. A suitable development station is disclosed
in U.S. Pat. No. 3,707,947, issued to Reichart in 1973. That patent
describes a magnetic brush development system utilizing a
magnetizable developer mix having ferromagnetic carrier granules
and a toner colorant. The developer mix is brought through a
directional flux field to form a brush thereof, the electrostatic
latent image recorded on the photoconductive surface 33 is
developed by bringing the brush of developer mix into contact
therewith.
Further details of the development apparatus which comprises
development station C will be described later by specific reference
to the present invention.
The developed image on the photoconductive surface 33 is then
brought into contact with the sheet 36 of final support material
within a transfer station D and the toner image is transferred from
the photoconductive surface 33 to the contacting side of the final
support sheet 36. The final support material may be paper, plastic,
etc., as desired.
After the toner image has been transferred to the sheet of final
support material 36 the sheet with the image thereon is advanced to
a suitable fuser 37 which coalesces the transferred powder image
thereto. One type of suitable fuser is described in U.S. Pat. No.
2,701,765, issued to Codichini et al. in 1955. After the fusing
process the sheet 36 is advanced to a suitable output device.
Although a preponderance of the toner powder is transferred to the
final support material 36, invariably some residual toner remains
on the photoconductive surface 33 after the transfer of the toner
powder image to the final support material. The residual toner
particles remaining on the photoconductive surface 33 after the
transfer operation are removed from the drum 32 as it moves through
a cleaning station E. The toner particles may be mechanically
cleaned from the photoconductive surface 33 by any conventional
means as, for example, the use of a blade as set forth in U.S. Pat.
No. 3,740,789, issued to Ticknor in 1973.
It is believed that the foregoing description is sufficient for
purposes of the present application to illustrate the general
operation of an automatic xerographic copier 30 which can embody
the magnetic brush flow baffles 20 and magnetic brush apparatus 31
in accordance with the present invention.
Referring again to the development apparatus 31 it includes a
storage portion or sump 40 in a housing 41 for storing the
developer material. The top of the housing may include an opening 0
that could have a removable cover or cap (not shown). The system
could include a toner dispenser (not shown) disposed over the
opening which periodically dispenses toner into the housing in a
manner similar to that taught in U.S. Pat. No. 3,608,792.
Alternatively, the circulating system could be of the type where
toner and/or toner plus carrier is added periodically by an
operator or an attendant to the machine.
The development apparatus 31 includes magnetic brush rolls 42 and
43. The magnetic brush applicator roll 42 includes a rotatably
mounted support member in the form of a cylindrical shell or sleeve
44 and a stationary permanent magnet 45 suspended within the
sleeve. The magnetic field of the magnet is oriented to form a
brush-like structure of the developer mix. The applicator roll 42
is immersed in the sump 40 of developer material which comprises
ferromagnetic carrier particles and a toner colorant. The developer
mix is picked up by the outer support surface of the roll 42 by
means of a pick-up magnetic field generated by stationary magnet 46
suspended within the sleeve 44, and is formed into a brush-like
structure for application to the photoconductive surface 33 for
development of the latent electrostatic image presented thereon.
While only one applicator roll 42 is shown, any number of
applicator rolls could be employed as desired.
Continued rotation of the roll past the development zone brings the
magnetic brush 47 into the field of a lifting magnetic brush roll
43. The lifting roll 43 attracts the developer mix from the
magnetic brush applicator roll 42 and carries it upward to be
deposited on a slide 48 from which it flows into a cross-mixer 49
for return to the sump 40. The lifting roll 43 is also a magnetic
brush roll and comprises a cylindrical sleeve 50 rotatably
supported in the housing 41 and a fixed permanent magnet 51
supported in a stationary position within the sleeve. It is also
possible in accordance with this invention to employ any desired
number of lifting rolls 43. Further details of the apparatus 31 of
FIG. 1 can be gained from a consideration of the aforenoted U.S.
Pat. No. 3,707,947. In accordance with this invention magnetic
brush flow baffles 20 are provided to regulate the flow of
developer at the end portions of the magnetic brush applicator roll
42.
Referring to FIGS. 2 and 3, the relative positions and structure of
the magnetic brush flow baffles 20 in accordance with this
invention are illustrated. As shown therein, the flow baffles 20
comprise stationary magnetic brushes 21 formed by means of the
magnetic field generated by permanent magnets 22 and 23. The
stationary magnetic brushes 21 extend inwardly from the housing 41
and inwardly of the development means which in the embodiment shown
comprises the axial direction of the magnetic brush roll 42. The
stationary magnetic brush baffles 20 are positioned between the
supply means 52 and the development zone 53. They have a limited
extension or width in the direction of movement of the mag brush
roll 42. This is significant since it is apparent from the drawings
that the baffles 20 do not act to seal the end portions 54 and 55
of the mag brush roll 42 from the developer mix. While they can
reduce or eliminate the flow of developer mix on the end portions
54 and 55 of the roll 42 between the baffles 20 and the development
zone 53, they are not so operative between the baffles 20 and the
supply means 52.
In order to form the stationary magnetic brushes 21 in accordance
with this invention, it is preferred to employ permanent magnets 22
and 23 extending out from the sides of the housing 41 and
positioned externally of the housing. The magnets may be held in
place by any desired means such as, for example, the use of spring
clips 56 as shown. The field of each magnet 22 and 23 is oriented
as shown to form stationary magnetic brushes 21 extending outwardly
from the bottom of the housing 41 toward the applicator roll
surface.
It is preferred in accordance with this invention that the
stationary magnetic brushes 21 extend out from the housing 41
toward the roll 42 over less than the entire gap 57 between the
housing and the roll. This type of a structure permits some
developer flow at the end portions 54 and 55 of the roll 42. The
amount of developer flow which is permitted should preferably be
less than, or equal to, the rate of developer flow at the middle
portion, in an axial sense, of the roll. This can result as shown
in FIG. 4, in a substantially uniform magnetic brush 47 being
formed over the entire operative length of the roll 42 or in one
(not shown) with end portions of the brush having a reduced height
as compared to the axial middle portion of the brush. Comparing
FIG. 4 to FIG. 1, the effect of the magnetic brush flow baffles 20
of this invention is clearly illustrated, namely, the bulbous
portions 11 and 12 of the brush 1 have been reduced to a height
equal to or less than that of the brush at the axial middle of the
roll 42.
Referring again to FIG. 3, it is apparent that the magnetic brush
47 on the surface of the roll is not formed over the entire axial
length of the roll 42, but rather the length of the brush is
dictated by the length of the magnets 45 and 46 within the roll.
Since the magnetic brush flow baffles 20 of this invention are
directed at eliminating the effect of the fringe fields at the ends
of the magnet 45, it is preferred that they extend inwardly past
the ends 58 and 59 of the magnet 45 a desired amount to offset the
effect of the fringe fields.
In an exemplary embodiment a magnetic brush roll 42 approximately
15 inches long was employed having magnets 45 and 46 suspended
therein of approximately 141/2 inches long. The magnets 22 and 23,
in accordance with this invention to provide the stationary
magnetic brush baffles 20, were selected to be approximately 11/4
inches long. This specific example, however, is not meant to be
limitative of the invention.
Referring to FIG. 5, a magnetic field arrangement in accordance
with the preferred embodiment of this invention is shown. As shown
in FIG. 5, the baffle forming magnet 22 has a magnetic field 61
associated therewith which is capable of forming a stationary
magnetic brush 21. The stationary magnetic brush 21 does not
extend, however, over the entire gap 57 between the roll surface 44
and the bottom of the housing 41 in order to allow developer
material flow in the gap 60 between the brush 21 and the roll
surface 44. In operation, the field 61 cooperates with the field 62
of the magnet 46 so that a magnetic brush will be formed over the
entire gap 57 between the housing 41 and the roll surface 44 which
is made up of two components. The first component will comprise the
stationary brush 21 of this invention. The second component lies
between the end of the stationary brush 21 and the roll surface 44
and comprises the moving magnetic brush 47 formed by the field
associated with the pick-up magnet 46.
In accordance with an exemplary embodiment the field intensity of
the stationary brush forming magnet 22 0.1 inches above the magnet
was selected to be from about 260 to about 300 gauss. This should
approximate the field intensity at the interior surface of the
housing 41 adjacent the magnet 22. The field intensity of the
pick-up magnet 46 measured about 0.060 inches below the applicator
roll surface was approximately 150 gauss. The gap 57 was about 0.1
inches. In an apparatus employing these magnets a stationary
magnetic brush was formed which did not extend over the entire gap
57 between the roll 42 and the interior of the housing 41.
Referring now to FIG. 6, an alternative embodiment in accordance
with the present invention is shown. In this embodiment the field
strength of the stationary brush forming magnet 22' has been
substantially increased to overcome the field of the pick-up magnet
46 so as to form a stationary brush over the entire gap 57 between
the interior of the housing 41 and the roll surface 44. This type
of baffle is not preferred in accordance with this invention, but
is included in the broad scope of the invention. Referring again to
FIG. 3, it is apparent that if a stationary baffle brush 21' is
formed over the entire gap 57 between the interior of the housing
41 and the roll surface 44, the degree to which the stationary
brushes project axially inwardly of the roll surface would have to
be reduced. To provide axially shorter brushes 21' the magnets 22
and 23 would have to be reduced in length as shown in phantom by
lines 25 and 26. In accordance with this embodiment the distance
between the stationary brushes 21' in the axial direction of the
roll would have to be sufficiently large to permit a development
brush 47 to be formed having an operative length sufficient to
cover the entire copy sheet 36.
While this embodiment would be operative to reduce developer flow
at the ends 54 and 55 of the roll 42, it would not do so to the
same degree as the embodiment of FIG. 5. This is because the fringe
fields 7 and 8 extend into the operative length of the development
brush 47. Therefore, by blocking off only that portion of the brush
47 which is not operative to develop the image, the ends of the
brush will still include an increased developer flow due to the
effect of the fringe fields, and, therefore, a somewhat increased
background development as compared to the development by the axial
center of the brush.
Referring now to FIGS. 7a and 7b, there is shown the effect of a
stationary brush forming magnet 22 having a substantially uniform
cross-section over its entire length. The stationary brush 21
formed by this magnet has a substantially uniform height over
substantially the entire length of the magnet and the height then
falls off very rapidly at the end of the magnet. This should result
approximately, as shown in FIG. 7a, in a fairly abrupt change in
developer flow rate along the length of the roll 42 and, therefore,
in a corresponding abrupt change in the density of the developer in
the brush 47 during development of the image and a noticeable
corresponding abrupt change in the density of the image transferred
to the copy sheet 36.
Referring to FIGS. 8a and 8b, there is shown a stationary brush
forming magnet 22 which has a wedge shaped form wherein the
thickness of the magnet decreases as the magnet projects inwardly
of the applicator roll 42. The stationary brush 21 formed by this
type of magnet 22 is illustrated in FIG. 8b. As shown therein,
there is a gradual reduction in the height of the stationary brush
21 the further it extends inwardly of the development roll 42.
Referring to FIG. 8a, the flow rate of the developer is shown
extending in from the housing 41. The flow rate shown changes
gradually in substantial correspondence to the height of the
stationary brush. This gradual change in flow rate allows the
density of the developer in the development brush 47 to also change
gradually so that the density change in the image on the copy sheet
also changes more gradually, therefore, creating an acceptable
appearance. Therefore, it is quite apparent from a consideration of
FIGS. 7 and 8 that the use of a wedge shaped stationary brush
forming magnet 22 and 23 is highly desirable and preferred in
accordance with this invention.
It is also apparent that it is preferred in accordance with this
invention to position the stationary brush forming magnets 22 and
23 externally of the housing 41. Positioning the magnets externally
of the housing allows greater flexibility since one or both magnets
could be changed in the event that developer flow at the ends of
the roll 42 is not acceptable. If desired, however, the magnets can
be positioned internally of the housing 41 or the magnetic brush
rolls 42 and 43. This approach could well be used, for example,
with stationary brushes 21' which extend over the entire gap 57
between the roll surface 44 and the housing 41.
While the stationary brushes flow baffles 21 have been described
with reference to their use in conjunction with the applicator roll
42, they could be employed with other magnetic brush rolls, if
desired.
It has been found desirable to provide impervious flow blocking
members 70 as shown in FIG. 2. The members have a cross-section as
shown and extend inwardly of the roll 42 an amount similar to the
brushes 21' of the embodiment of FIG. 6. They are located between
the supply means 52 and the baffles 20. The members 70 further
improve the regulation of developer flow rate at the ends of the
roll 42.
The patents and texts referred to specifically in this application
are intended to be incorporated by reference into the
application.
It is apparent that there has been provided in accordance with this
invention, a support member, process and apparatus which fully
satisfies the objects, means and advantages set forth hereinbefore.
While the invention has been described in conjunction with specific
embodiments thereof, it is evident that many alternatives,
modifications and variations will be apparent to those skilled in
the art in light of the foregoing description. Accordingly, it is
intended to embrace all such alternatives, modifications and
variations as fall within the spirit and broad scope of the
appended claims.
* * * * *