Note: Descriptions are shown in the official language in which they were submitted.
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~047757
1 This lnvention relates to the field of xerogra-
phic development stations.
In spite of the fact that a tremendous amount
of research has been performed in the field of the
5 development of electrostatic lmages by the application
of developer thereto, it is desirable to still further
increase development efficiency. In ordinary commercial
cascade development stations, the development mixture
first contacts an upper drum portion and is thereafter
10 accelerated by gravity so that often a large portion of
the development powder does not contact lower portions
of the drum due to high centrlfugal forces acting on the
developer. Furthermore, background toner on the drum still
exists which often produces unattractive copies, and
15 additionally, excessive buildup of toner is often produced
on the development electrode. Thus, it is highly desirable
` to substantially reduce these undesirable effects to allow
for a more ef~icient use of available developer mixture
and to produce cleaner copy. The attainment of increased
20 development efficiency results in the production of a
greater number of copies per minute for any given drum
size, or conversely results in the employment of a smaller
drum for a fixed rate of copy output. Additionally,
because of the increased developer efficiency, the carrier
25 will tend to become more depleted of toner. This condition
causes a greater charge imbalance to exist on the carrier
which in turn can enhance developer scavenging of the
background areas to produce copy free from background toner.
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lV47757
A straightforward inexpensive means for accomp-
lishing these results is greatly desired.
Thus the present invention provides a xerographic
development station including an imaging member having a
surface for bearing an electrostatic image to be developed,
a development plate having a surface spaced from said imag-
ing member surface for defining a development zone there-
between and means for introducing developer into said
development zone to be cascaded therethrough along paths
of travel adjacent said imaging member surface for develop-
ing said electrostatic image, the improvement comprising
said development plate surface comprising a roughened surface
for defining a large plurality of angled deflection elements
thereon, said deflection elements covering at least a
substantial portion of said development plate surface and
being shaped to introduce a substantial component of motion :
to said developer in a direction transverse to said paths
of travel thereof through said development zone for direct-
ing said cascading developer toward said imaging member
surface for increasing development efficiency.
More particularly, the invention provides a
xerographic development station including a cylindrical
` imaging member having a surface for bearing an electrostatic
image to be developed; a development plate spaced from
said imaging member for defining a development zone there-
between, said development zone having an input end and an
output end; means for rotating said imaging member for
moving said electrostatic image bearing surface through
said development zone from said input end to said output
3~ end; and means for introducing developer into said develop-
ment zone to be cascaded therethrough from said input end
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1047~57
to said output end along paths of travel generally in a
tangential direction with respect to said imaging member
surface for developing said electrostatic image, the improve-
ment comprising: wherein said development plate is spaced
from said imaging member by a distance which generally
decreases from said input end of said development zone
toward said output end of said development zone, and wherein
said development plate includes a development plate surface,
said development plate surface being roughened over at least
a substantial portion thereof for defining a large plurality
of angled deflection elements thereon, the decreasing spac-
ing of said development zone providing a reduction in the
- tangential velocity of said developer for increasing the
density of the developer within said development zone, and
said deflection elements providing an increase in the radial
velocity of said developer with respect to said imaging
member surface for directing said developer toward said
imaging member surface.
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The foregoing goals have been accomplished by
2~ virtue of the employment, in the preferred embodiment,
of a development electrode which has a surface which is
. roughened to a sufficient extent to modify the paths of
travel of developer between the electrostatic drum
surface and the development electrode surface. By doing
so, it has been found that a great many of the above-men-
tioned goals are attained. Preferably, the surface is
roughened by producing protuberances thereon which are
diamond or waffle-shaped to increase radial developer
veloclty and decrease tangential developer velocity to
thereby increase development efficiency. Also, the
: electrode is designed to provicle a variable spacing
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104'77Si'
between the electrode and the drum -- generally wider at
the beginning and narrower at the end. This permits a
reduction in the tangential velocity of the falling
developer and hence, a greater developer density.
Other ob~ects, features and advantages of the
present invention will become apparent upon perusal of
the following detailed description taken in con~unction
with the drawings in which:
FIGURE 1 schematically illustrates the positioning
of the development electrode with respect to the drum;
FIGURE 2 discloses a planar view of the roughened
; surface of the development electrode facing the drum; and
FIGURE 3 illustrates a cross section of a portion
of the electrode of FIGURE 2.
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1 In FIGURE l, a conventional xerographic drum l
is illustrated together with toner applicator 2 and
development plate 3. Other conventional portions of a
xerographic machine such as the corona charging station,
5 the exposure station and the drum cleaning station have
not been shown in the interests of clarlty. The developer
is emitted from developer applicator 2 and cascades
downwardly through the development gap formed between the
surface of development plate 3 and the drum surface.
10 The developer thereafter falls to the bottom of the machine
as illustrated, and is thereafter transported by conveyor
6 to the top of the machine to be recirculated therethrough.
The remaining portions of the developer transport system
form no part of the present invention and thus will not be
- 15 described.
It is greatly preferred, although not required,
-- that development plate 3 function as a metallic electrode
which is electrically connected to a conventional bias
source 7 as is well understood by those skilled in the art.
In order to obtain the above-described ob~ects
and goals with regard to increased development efficiency,
the inside surface of the metallic electrode 3 is treated
during,the manufacturing process to produce a large
plurality of tiny protuberances which function as deflec-
25 tion elements to enhance turbulence in the development
zone in the desired fashion. The stationary electrode has
a surface morphology which functions to partially convert
the tangential momentum of the carriers to radial
momentum.
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1047757
1 In the machine constructed by the inventor and
his colleagues, a surface morphology corresponding to a
knurled surface was produced on a metallic plate which
was formed as illustrated in FIGURE 1. The resulting
5 surface has a large plurality of diamond-shaped protuber-
ances 8, 8' and 8" illustrated in FIGURE 2. These protu-
berances are formed by producing cuts such as 9, 9' and
9" as illustrated in the FIGURE. A cross section indicated
by cross sectional line 11 is illustrated in FIGURE 3
10 which shows one shape of the diamond protuberances. Arrow
12 illustrates the direction of toner fall.
In the constructed machine the "roughness" or
~ average height of the protuberances, namely the peak to
- valley distance between the arrows 13 and 13' in FIGURE 3
15 was 9 mils. The spatial frequency of the diamond pattern
in the direction of developer fall was 21.7 cycles per
inch or, putting it another way, the spatial separation
between corresponding portions in the pattern was about
7.5 to 200 mils for a carrier diameter of 15-20 mils.
20 The developer flow rate was approximately 41 grams per
second for each inch of width of the development zone. A
conventional developer having carrier and toner was
employed, having a carrier diameter of about 15 mils.
It is believed that the most economical method of manufac-
25 turing the development electrode is to employ a knurlingroller for alterlng the surface morphology as described
above. The scale of the surface roughness is carrier
size dependent. It is preferred that the above-mentioned
spatial separation in the direction of developer flow be
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1~47757
1 within the range of 0.5 to lO times, preferably about 7-8
times, the mean carrier diameter, and it is also preferred
that the above-mentioned height of the protuberances be
within the range of .3 to l.5 times the mean carrier
5 diameter. Numerous variations in the shape of the protu-
berances are believed to fall within the scope of the
present invention although the diamond pattern is preferred.
For example, a rounded diamond pattern resembling longitudi-
nal rows of diamonds with ad~acent rows being arranged in
; 10 a staggered relationship also works very well. In addition,
the surface may resemble the pattern of a waffle plate
greatly reduced in scale or may take numerous other forms.
For example, elongated triangular ridges aligned in a
direction transverse to the direction of toner fall could
15 be employed. However, the diamond knurl pattern whether
rounded or as described above is preferred because the
~~~~ ~ ~ sides of the diamond-shaped elements produce carrier
deflections in directions transverse to toner fall to
produce further mixing of carriers in directions across
20 the width of the development zone. Other contemplated
shapes are cones, pyramids, mushrooms, hemispheres, etc.
Randomly distributed patterns of the foregoing shapes may
be employed. Shot blasted or similarly produced surfaces
may be useful.
The term "plate" as used herein could comprise
a non-metallic plate which does not function as a develop-
ment electrode although it is greatly preferred that a
metallic plate, functioning as a developing electrode, be
employed. The average tangential velocity of the ~alling
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1047 7~7
1 toner should be about equal to or greater than the tangen-
tial velocity of the photoconductor in order to obtain
hlgh density copies. In the constructed machine, the
spacing between the surface of the development electrode
5 and the surface of the drum was varied somewhat as
schematically illustrated in FIGURE 1. This spacing at
portion 16 was about 175 mils, at portion 17 was about
- 100 mils, at portion 18 was about 85 mils and at portion
19 was about 105 mils. While other spacing configurations
10 are possible, in general, the spacing should smoothly Yary
from a relatively wide spacing in area 16 to a relatively
narrow spacing in area 18. Area 19 is somewhat wider
to prevent clogging. It is believed important that the
separation not be restricted unduly at lower drum portions,
15 which restriction could create excessive pile up of
developer whose tangential velocity is much lower than
~~- ~ that of the photoconductor. A plate having indentations
therein of sufficient size to produce the above-mentioned
effects may be employed and in such a case the term -
20 protuberances is intended to cover plate areas separating
such indentations.
In summary, a development plate is employed
having a surface morphology which partially converts the
tangential momentum of the carriers into radial momentum
25 in a highly controlled manner to produce enhanced develop-
ment efficiency as discussed hereinabove.
While preferred embodiments of the invention -
have been described, the teachings of this in~ention will
readily suggest many other embodiments to those skilled
30 in the art.
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