U.S. patent number 3,623,453 [Application Number 04/885,479] was granted by the patent office on 1971-11-30 for developing apparatus for electrophotography.
This patent grant is currently assigned to Konishiroku Photo Industry Co., Ltd.. Invention is credited to Ryubun Seimiya, Tohoru Uchida.
United States Patent |
3,623,453 |
Seimiya , et al. |
November 30, 1971 |
DEVELOPING APPARATUS FOR ELECTROPHOTOGRAPHY
Abstract
A powder cloud developing apparatus comprises a housing having a
top wall in which is formed an opening for receiving an image
member, and having an inclined sidewall which is contiguous with
the top wall. A flow control plate is arranged opposite the
sidewall and defines a flow channel therewith. The plate has a
width commensurate with the housing, and terminates adjacent the
top wall to define an exit from the channel. A rotor having a
length greater than its diameter is positioned horizontally below
the plate, but above the bottom of the housing, and is peripherally
provided with blades or projections which, upon rotation of the
rotor, scramble developer charged between the rotor and the bottom
and throw it against opposing surfaces of the flow control plate
and the inclined sidewall. An air stream, created either by the
bladed rotor or by separate fan means, conveys the developer
through the channel and the exit so as to travel across the
opening.
Inventors: |
Seimiya; Ryubun (Tokyo,
JA), Uchida; Tohoru (Tokyo, JA) |
Assignee: |
Konishiroku Photo Industry Co.,
Ltd. (Tokyo, JA)
|
Family
ID: |
14050922 |
Appl.
No.: |
04/885,479 |
Filed: |
December 16, 1969 |
Foreign Application Priority Data
|
|
|
|
|
Dec 18, 1968 [JA] |
|
|
43/92314 |
|
Current U.S.
Class: |
118/309; 118/634;
399/290 |
Current CPC
Class: |
G03G
15/0803 (20130101) |
Current International
Class: |
G03G
15/08 (20060101); B05b 005/04 () |
Field of
Search: |
;118/309,48,634,637 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Rimrodt; Louis K.
Claims
What is claimed is:
1. A developing apparatus for electrophotography comprising a
housing having an opening in the top wall and an inclined sidewall,
said opening being arranged to support an insulating member
carrying an electrostatic latent image, a flow control plate
positioned within said housing and being inclined in a manner
similar to the inclined said sidewall and being arranged in spaced
relationship to said sidewall, said flow control plate extending
within said housing from the lower end to the upper end thereof and
cooperating with said side plate to from an inclined flow
passageway, the upper end of said flow control plate terminating
adjacent to said top plate of said housing and defining an exit
from the passageway formed between said sidewall and said flow
control plate, the upper end of said flow control plate at the exit
being bent inwardly into said housing away from said sidewall and
extending therefrom in the direction of said top wall, a rotor
arranged below the lower end of said flow control plate and having
a plurality of projections spaced apart along the periphery
thereof, said rotor having a length substantially greater than the
diameter thereof, said rotor having a horizontal shaft arranged to
be driven for rotating said roter, a space within and at the bottom
of said housing for receiving a supply of developer, said rotor
being positioned and the supply being in such an amount that at
least part of said projections are immersed in said developer when
said rotor is at rest, said rotor acting upon rotation to agitate
the developer and throw it against the opposing surfaces of said
sidewall and said flow control plate for passage upwardly through
the passage formed therebetween to the exit adjacent the top wall
of said housing, and fan means operative to direct a flow of
developer through the passageway defined between the opposing
surfaces of said side plate and said flow control channel and to
flow across said opening in said top wall.
2. A developing apparatus according to claim 1, in which a choke
member is arranged in said exit adjacent one end of the
opening.
3. A developing apparatus according to claim 1, in which said
projections are formed by blades extending the length of the rotor,
whereby the rotor is operable as said fan means to produce an
airstream.
4. A developing apparatus according to claim 3, wherein the
developer comprises toner and carrier particles, and further
including a louver positioned in said flow channel adjacent said
rotor, whereby upon rotation of the rotor developer is flung
against the louver which separates toner from carrier particles,
the louver allowing toner particles to be carried therethrough as a
suspension in said airstream and further conveyed through the flow
channel and the exit to provide a powder cloud travelling across
the opening.
5. A developing apparatus according to claim 1, in which another
fan means is located adjacent the top wall of the housing near the
end of the opening remote from said exit, said another fan means
acting to draw the powder cloud moving across the opening, whereby
a substantially uniform travelling velocity of the powder cloud is
maintained over the length of the opening.
6. A developing apparatus according to claim 1, in which another
fan means is located in said channel intermediate between said exit
and said rotor.
7. A developing apparatus according to claim 1, in which said space
is broad enough to receive an initial supply of developer in an
amount sufficient to develop a number of latent image members
without additional supply.
8. A developing apparatus according to claim 1, in which the
housing is V-shaped in cross section with rounded corners, the top
bar of the V-shape constituting the top wall of the housing and the
bottom corner of the V-shape defining the space for receiving a
supply of developer, said flow control plate being arranged
opposite one sidewall of the V-shaped housing and having a
contiguous portion extending opposite the other sidewall of the
housing, thereby defining a second space below said opening whereby
to receive developer that falls down intermediate the travelling
path across said opening.
9. A developing apparatus according to claim 8, in which said
portion of the flow control plate defines together with said other
sidewall of the housing a return path for said flow, and further
including another fan means located in said return path for drawing
said flow horizontally across said opening.
10. A developing apparatus according to claim 1, in which a louver
is positioned in said flow channel adjacent said rotor, whereby
upon rotation of the rotor developer is flung against the louver.
Description
The invention relates to an apparatus for developing an
electrostatic latent image formed on the surface of an insulating
member, and more particularly to such apparatus incorporating the
known powder cloud developing technique.
It is known that the development of an electrostatic latent image
in the cascade process involves the difficulty to avoid the effect
of fringing fields, that is, the toner particle being attracted
strongly by the fringing fields around the periphery of charged
areas of the latent image carrying member and leaving the middle of
these areas undeveloped or underdeveloped. The toner cloud
technique avoids the difficulty by providing a good, faithful
development with varying potentials in various image areas, with
good resolution and without appreciable nonuniformity in
development.
Various proposals have been made to produce a powder cloud of toner
charged oppositely to the polarity of the latent image. For
example, U.S. Pat. No. 3,060,131 issued to H. E. Crumrine et al.
Oct. 23, 1962 describes a powder cloud generating apparatus which
is adapted for use in aircraft for a rapid development to permit
repetitive processing of successive xerographic plates used in
taking aerial photographs, but which is too large scale and complex
in construction to permit its use in commercial copying machines.
More practical method for developing electrostatic images is
disclosed in U.S. Pat. No. 2,759,450 issued to R. G. Vyverberg,
Aug. 21, 1956, in which a xerographic plate is supported in an
opening in the top plate of a closed box with the electrostatic
latent image facing down, and a cloud of charged carrier is sprayed
upwardly against the plate by the action of a motor driven
impeller. Further improvement of the continuous tone reproduction
can be provided by locating an array of conductors or grid closely
spaced from the xerographic plate and oppositely charged to the
latter so as to cause a realignment of the electrostatic field
surrounding the image, as described in U.S. Pat. No. 2,784,109
issued to L. E. Walkup, Mar. 5, 1957.
However, the prior art devices for developing electrostatic images
by powder cloud technique have a number of drawbacks, i.e.
expensive to manufacture, wasteful of developing material, the
necessity of frequent replenishment or replacement of developer,
for example, after only a few times of development, to warrant
uniform image quality, possible degradation of image quality by
blocky toner or fragments accumulated on the inner wall of the
casing and subsequently blown off or sputtered to adhere the image
carrying member, disturbances in the cloud caused by a fan
resulting in differential toner density in the cloud, a long time
period to develop, and poor maneuverability
Therefore, it is an object of the invention to provide an improved
developing apparatus which overcomes all of above mentioned
disadvantages.
In accordance with the invention, there is provided a developing
apparatus for electrophotography which comprises a housing having
an opening in the top wall thereof and an inclined sidewall, said
opening being adapted to support an insulating member carrying an
electrostatic latent image, a flow control plate arranged opposite
said sidewall in spaced relationship therewith, said plate having
an upper end terminating adjacent said top wall of the housing to
define an exit, a rotor arranged below the flow control plate and
having a plurality of projections spaced apart along the periphery
thereof, said rotor having a length substantially greater than the
diameter thereof, said rotor having a horizontal shaft which is
adapted to be driven for rotation, a space within and at the bottom
of said housing for receiving a supply of developer, said rotor
being positioned and the supply being in amount such that at least
part of the projections are immersed in said developer when the
rotor stands still, said rotor acting upon rotation to agitate the
developer and throw it against opposing surfaces of said sidewall
and said flow control plate, and fan means operative to direct a
flow of the developer through a flow channel defined between said
opposing surfaces and then through said exit so as to travel across
said opening.
For better understanding of the invention, several embodiments
thereof will be described with reference to the drawings,
wherein:
FIG. 1 shows a schematic vertical section of one embodiment of the
developing apparatus according to the invention,
FIG. 2 is a similar view to FIG. 1 of a modification of the
apparatus shown therein,
FIG. 3 is a schematic section of another apparatus of the
invention, illustrating an alternate arrangement of the louver used
in the apparatus of FIG. 2,
FIG. 4 is a similar view to FIG. 3, but illustrating another
embodiment of the invention,
FIG. 4a is a section along the line A--A shown in FIG. 4, and
FIG. 5 is a schematic section of a preferred embodiment of the
invention.
Referring to the drawings, and particularly to FIG. 1, the
developing apparatus show comprises a housing 1 generally in the
form of an inverted pyramid frustum. The housing 1 may be made from
any suitable material, and has a top wall 2 in which is formed an
opening 3 for receiving an insulating member, shown as a plate 4,
carrying an electrostatic latent image. The member 4 is placed in
the opening 3 with its image side facing down. The housing 1 has a
pair of inclined sidewalls 5, which terminate in a curved bottom 6
which defines together with the lowest part of the sidewalls 5 a
space or tub 7 for developer 8. The sidewalls 5 may have a suitable
angle of inclination with respect to the vertical and the sidewall.
It will be appreciated that the housing 1 is closed by a pair of
end plates (not shown). Closely spaced from the bottom 6 of the
housing 1 is located therein a rotor 10 having a rotary shaft 11
which extends horizontally and is supported by bearings (not shown)
secured in the end plates. The shaft 11 extends externally of the
housing 1 for coupling with suitable motor means (not shown). The
rotor 10 carries a plurality of radially extending blades 12 which
are equiangularly spaced apart along the periphery of the rotor 10.
The rotor has a length substantially greater than the diameter
thereof, and is positioned in the space 7 so that at least part of
the blades 12 is immersed in a supply of developer charged into the
space 7 through a suitable inlet or conduit (not shown) provided in
the lower part of the sidewall 5. As is well known, the developer
used in powder cloud technique comprises a mixture of toner and
particulate carrier having a particle size from about 20 to 300
meshes, the particle size of the toner being substantially less
than that of the carrier. As a result, when a predetermined amount
of developer is charged into the developer space 7, the volume
occupied by the developer mixture does not vary greatly as the
toner component is consumed by application to electrostatic images
to be developed. The carrier may comprise any conventional carrier
used in the prior art electrophotography, such as glass beads and
iron powders, metal powder being preferred for reason of
durability.
Above the rotor 10 is arranged a flow control plate 15 which is
inclined to the vertical and which is fixed to the end plates of
the housing by conventional fittings. The flow control plate 15 is
located opposite one of the inclined sidewalls 5 of the housing,
which is the left-hand sidewall in the example shown, over
substantially the whole extent thereof. Thus the flow control plate
15 has a width equal to the spacing between the end plates of the
housing, and has an upper end 16 adjacent one end of the opening 3
in the top wall 2, the end 16 being turned back round to define an
exit 17 together with the latter for a flow of developer, as will
be described later. The lower end 18 of the flow control plate
terminates short of the other of the sidewalls 5 to define a return
passage 19 of developer to the space 7. In this manner, the flow
control plate 15 divides the interior of the housing into a cloud
generating chamber 20 and a developer chamber 22. Preferably, the
opening 3 extends across the pair of end plates of the housing in
order to facilitate to keep the lower surface of the image member 4
flush or level with the inner surface of the top wall 2 of the
housing.
In operation, the shaft 11 is driven by an external motor to rotate
the rotor 10 in the direction indicated by an arrow at a high speed
such as 1,000 to 3,000 r.p.m., whereby the blades 12 take up
developer 8 and throws it against the opposing surfaces of the flow
control plate 15 and the left-hand sidewall 5. Because a continued
rotation of the rotor 10 with the blades 12 scrambles the mixture
of toner and carrier powders within the space 7, sufficient
agitation is provided to charge the toner particles by
triboelectrification. The polarity of charge on the toner powder is
made opposite to the polarity of the charge on the image member 4.
The mixed particles of toner and carrier form agglomerates by
electrostatic attraction, but when they strike the flow control
plate 15 and the left-hand sidewall 5, the agglomerates are broken
into pieces and the toner particles are separated from the larger
and heavier carrier particles, which then fall back to the bottom
or space 7 to be subjected to further agitation with the remainder
of the toner. The blades 12 on the rotor 10 extend substantially
the length thereof and creates, by rotation, an airstream indicated
by an arrow which serves to carry the mixture particles towards the
opposite walls 5 and 15 and also to carry the charged toner
particles freed from the carrier as a suspension along a channel 24
defined by the opposing surfaces of the left-hand sidewall 5 and
the flow control plate 15. As shown, the channel 24 has a
relatively broad inlet aperture adjacent the rotor 10 for the ease
of generating the airstream, and is narrowed gradually upwardly to
the minimum width at the exit 17, from where the powder cloud, i.e.
the airstream carrying the charged toner in suspension, flows out
into the developing chamber 22. The expansion and concomittant
diffusion of the powder cloud in the chamber 22 produces a uniform
density or concentration of toner in the cloud as the latter moves
past the surface of the image member 4 horizontally. While it is
not intended that operation of the invention be limited to any
theory, it is believed that the airstream or flow of powder cloud
produced according to the invention has more of the nature of a
laminar flow than a turbulent flow that would be produced when a
powder cloud is created by a toner-carrying airflow wreathed or
curled up directly from a bottom situated fan. It is considered
that the choice of a length of the rotor 10 substantially greater
than the diameter thereof assists in the formation of an airstream
having a weblike cross section. It is believed also that such an
airstream is best guided by an inclined surface to provide a top
horizontal flow where the space requirements are imperative. The
flow in the developing chamber 22 is substantially horizontal for
the most part of the powder cloud, thereby forming a virtual
electrode in front of the lower surface of the image member 4. Thus
charged toner is attracted imagewise onto the latent image areas on
the member 4, thereby developing the latent image. It will be
appreciated that because the flow is across the surface of the
member 4 and there is no substantial vertical component of motion
towards this surface except for the electrostatic interaction, the
developed toner image will be a faithful reproduction of the
original. After travelling across the developing chamber 22, the
airstream proceeds along the opposite or right-hand sidewall 5 to
pass through the passage 19 to return into the space 7, under the
influence of suction produced by the rotation of the bladed rotor
10.
Thus, according to the invention, a powder cloud is generated in
the chamber 20 and circulated through the developing chamber 22 to
the developer space 7. It is found that the quality of development
achieved according to the invention is excellent in that the
development reproduces varying potentials on the latent image. In
addition, the developed image had a good stability.
The flow control plate 15 may have any suitable inclination, but an
angle of inclination in the range from about 30.degree. to
60.degree. with respect to the vertical proved satisfactory in that
the flow achieved maintained the nature of a laminar flow, even
though this does not mean of course that the flow is completely
laminar. The flow control plate 15 may be made from any suitable
material having a smooth surface, and in one example brass was used
satisfactorily. Furthermore, the plate 15 may be adjustably
attached to the end plates of the housing as by pivotal
mounting.
FIG. 2 shows a modification of the apparatus shown in FIG. 1, by
additional provision of a louver 26 and a choke member 28. The
louver 26 consists of a plurality of strips 27 arranged between the
lower end portion of the flow control plate 15 and the rotor 10 and
extending horizontally to be secured at opposite ends to the end
plates of the housing 1. Their purpose is to provide surfaces
against which combined toner-and-carrier particles can be flung in
order to improve the separation between the toner and carrier and
to minimize the carrier residue in the powder cloud. The
arrangement and size of these strips can be varied extensively, as
illustrated by one alternate arrangement shown at 29 in FIG. 3. In
addition, the louver 26 may comprise rods, wires or screen as
desired. The configuration, size, spacing and inclination of the
members constituting the louver depend upon the construction of the
blades 12, the number of revolutions of the rotor 10, the amount of
developer supplied and other factors, but the choice should be made
such that carrier particles cannot pass through the louver in the
direction of airstream through the channel 24 and that toner does
not accumulate on the louver members. The louver members can also
be adjustably located. Preferably the louver 26 is located close to
the rotor 10 to allow the developer to strike it with an increased
impact, thereby facilitating the separation between the toner and
carrier. This increases the amount of powder cloud formed. The
choke member 28 is an elongate rib extending across the width of
the housing 1 or perpendicularly to the sheet of the drawing
adjacent the end of the opening 3 nearer the exit 17. The member 28
functions to slow down and deflect slightly the generally
horizontal flow from the exit 17 in order to remove the
differential concentrations of developed image across the opening 3
that may be produced as a result of vertical component of motion
imparted to the charged toner.
It should be also noted that "fogging" may also occur as a result
of mirror effect in the uncharged or nonimage areas on the member 4
because the charged toner induces mirror images of opposite
polarity behind these areas, which induce an attraction on the
charged toner. According to this invention, such a mirror effect is
avoided conveniently by the horizontal speed of the toner.
In FIG. 3 which shows an alternative form of louver, the channel 24
defined by the flow control plate 15 and an inclined sidewall 5' of
the housing has a constant height throughout its length, which can
be satisfactorily employed when the airstream produced has a
sufficient speed for the intended purpose. In this instance, the
flow control plate 15 has a horizontally extending lower end
portion 15a, the length of which can be adjusted t0 vary the amount
of flow produced.
FIG. 4 shows another embodiment of the invention which incorporates
a crossflow fan 30 to draw the airstream through the channel 24 and
across the developing chamber 22 for circulation around a flow
control plate 32. In this embodiment, the housing 34 is in the form
of a box having an inclined sidewall portion 35, a vertical
sidewall portion 36, a top wall 37 having an opening 3 formed
therein, a vertical sidewall 38, and a bottom wall 39. As before,
the bottom wall 39 defines with the lowest parts of the walls 35
and 38 a space 7 for developer. The flow control plate 32 has a
portion 40 opposite the sidewall portion 35 of the housing 34, a
generally vertically extending portion 41 including a semicircular
recess 42 near the top thereof, and a horizontal portion 43
interconnecting the portions 40 and 41. The free end of the portion
40 is turned back to provide a guide 44 for the airstream. A
similar guide 45 is formed at the top end of the vertically
extending portion 41. Between the horizontal portion 43 of the flow
control plate 32 and the bottom of the housing 34 is located the
rotor 10 which may be similarly constructed as before. The louver
29 shown in FIG. 3 is located near the rotor 10 between the
portions 40 and 35. The fan 30 is positioned adjacent the recess
42.
The operation of the apparatus shown in FIG. 4 is generally similar
to the previous description given in connection with the apparatus
of FIG. 1. Thus where the rotor 10 is provided with axially
extending blades 12 as in FIG. 1, the rotation of the rotor 10 is
effective to create an airstream through the channel 24 to carry
toner in suspension, which is charged and freed from carrier by the
process mentioned previously. The outlet flow from the exit 17 is
directed horizontally to travel across the surface of the image
member 4, and such horizontal flow is aided by the suction created
by the crossflow fan 30. In addition, the fan 30 helps eliminate or
reduce a speed differential across the length of the image member
4, which would give rise to a variation in the cloud density. A
part of the toner may fall down from the main body of the powder
cloud moving along the image body 4, onto the back of the flow
control plate 32, which therefore can be used as a reservoir for
toner, and an opening (not shown) may be provided in the portion 43
for toner supply to the space 7.
Alternatively, the rotor 10 in this embodiment may have projections
such as rods or narrow strips in place of the blades 12, the
function of these projections being to scramble the developer
mixture and to throw it against the portions 35 and 40 and the
louver 29. The airstream which carries the toner freed from the
carrier is produced in this instance by the fan 30.
As shown in FIGS. 4 and 4a, a pair of curved guide plates 46 may be
provided centrally in the channel 24 in transversely spaced
relationship with each other and with the end plates 39 of the
housing 34. The guide plates 46 are more closely spaced from each
other at their end nearer the louver 29 than at the opposite end,
thereby resulting in a flaring cross section, even though the both
end portions are substantially parallel to the longitudinal axis of
the channel 24. The purpose of the guide plates 46 is to provide a
speed reducing effect, by diffusion, upon the central part of the
flow, indicated by an arrow, in order to achieve a more uniform
speed profile in the transverse direction across the channel 24. As
indicated by pivots 47 in FIG. 4a, the guide plates 46 may be
pivotally mounted to allow for proper adjustment of the flow
through the channel.
FIG. 5 shows a preferred embodiment of the invention. The apparatus
comprises a housing 50 of generally V-shaped cross section with
rounded corners. Such housing can be supported in a box-shaped
enclosure or on a horizontal base by suitable means such as struts
so as to assume the position shown. The housing 50 includes a top
wall 51 in which a rectangular opening 52 is formed so as to
receive an electrostatic latent image carrying member 53. To place
the member 53 flush with the inner surface of the top wall 51, it
is preferred that the opening 52 extends the full width of the top
wall 51 so that the member 53 placed therein may rest on top of the
end plates (not shown) of the housing 50. Suitable tension can be
maintained in the member 53 by using a rigid support against which
it is held firmly. The housing further includes a pair of inclined
sidewalls, left-hand side at 55 and right-hand side at 56, which
are joined together by a rounded bottom wall 57 and which are also
joined with opposite ends of the top wall 51 by rounded corners 58
and 59, respectively. Within the housing 50 is placed a flow
control plate 60, which may be secured at its lateral ends to the
end plates (not shown) of the housing 50. The flow control plate 60
includes a portion 61 opposite to and spaced from the inclined
sidewall 55 of the housing 50 to define a flow channel 62
therebetween. The upper end 63 of the portion 61 is curved in a
similar configuration to the curved corner 58 and is turned back to
run parallel to the top wall 51, thereby defining an exit 54. The
lower end of the portion 61 is curved upwardly, at a position over
the bottom 57 of the housing 50, to form a return flow control
portion 64 having a turned-back top end 65. Between the bottom wall
57 and the flow control plate 60 is located a rotor 66 mounted on a
rotary shaft 67 and having a plurality of projections in the form
of blades 68 attached around the periphery thereof. A louver 69 of
the form shown in FIG. 3 is arranged adjacent the rotor 66 in the
flow channel 62. A pair of guide plates 70 of the form shown in
FIG. 4a are disposed in the channel 62 beyond the louver 69 as
viewed in the direction of airstream passing therethrough. In the
particular example shown, such airstream is produced by the blades
68 upon rotation of the rotor 66. A crossflow fan 71 is positioned
in the return path 72 defined between the portion 64 of the flow
control plate 60 and the sidewall 56 of the housing 50.
The apparatus shown in FIG. 5 operates in the similar manner as
mentioned before. Developer comprising toner and carrier particles
is charged (not shown) in the space defined by the bottom wall 57
and the lowest parts of the sidewalls 55, 56 in an amount in
relation to the position of the rotor 66 such that part of certain
lower blades or projections 68 on the rotor 66 is immersed into the
bulk of developer when the rotor 66 stays at rest. Upon rotation of
the rotor 66 in the direction indicated by an arrow, the blades 68
take up and throw the developer particles against the louver 69 as
well as the opposing surfaces of the flow control plate 60 and the
sidewall 55, as mentioned previously, thereby agitating the mixture
particles to charge the toner to the desired polarity and
separating the latter from the carrier. Charged toner particles are
carried by the airstream produced by the rotating blades 68 to pass
through the louver 69 and then through the guide plates 70 to flow
out of the exit 54. Thereafter the airstream carrying the charged
toner in suspension travels across the lower surface of the image
member 53 horizontally, thereby developing the electrostatic latent
image thereon, and is guided by the end 65 of the flow control
plate 60 into the return path 72. This portion of the flow is aided
by the suction created by the crossflow fan 71. The airstream
completes its circulation by passing through the path 72 and being
drawn by the rotating blades 68.
Alternatively, the rotor 66 may be provided with rodlike
projections instead of blades 68, as mentioned above in connection
with FIG. 4. In this instance, the airstream for conveying the
toner cloud will be produced by the fan 71 or any other suitable
fan located in the path of such stream. Conveniently, the fan 71
can be used in association with another crossflow fan (not shown)
which is partly or half exposed in the flow channel 62 at a
position short of the exit 54, as viewed in the direction of
circulation of the airstream.
The upwardly open space partially enclosed by the flow control
plate 60 may be used as a reservoir for supply of toner, and
carrier if necessary, and an opening (not shown) may be formed in
the flow control plate 60 which can be opened and closed by manual
operation. This is advantageous in saving the space within the
apparatus and recovering toner that falls down intermediate the
flow path along the member 53. However, it should be noted that
such reservoir is not primarily for use as a source of toner (and
carrier as required) that supplies toner to the developer space
above the bottom wall 57 every time a single member or a few
members 53 have been developed. Instead, the invention contemplates
that a supply of toner and carrier once charged in the developer
space below the rotor be such as would be sufficient in amount to
develop a number of image members 53. The reservoir mentioned above
is intended therefore to store a large quantity of toner (and a
given amount of carrier as required) which can be subdivided into
given amounts of supply to the developer space.
In one example, the housing 50 measured 400 mm. in axial length or
across rounded corners 58 and 59, and 500 mm. in height taken
between top wall 51 and bottom 57. The length of the opening 52 was
200 mm., and the lateral width or the distance between the end
plates was 260 mm. In the developer space above the bottom wall 57
was charged 4.5 kg. of developer, of which 10 percent by weight was
toner. The rotor 66 was formed by an aluminum cylinder having axial
length corresponding to the lateral width of the housing and a
diameter of 60 mm. Eight blades 68 having a width of 15 mm. were
mounted spaced around the periphery of the rotor at an angle of
inclination of 55 degrees with respect to the radius of the rotor.
The rotor 66 was positioned so that upon rotation at 3,000 r.p.m.,
it experienced a countertorque by developer between 1.8 and 3.8
kg./cm. of axial length. The velocity of the air stream produced
was measured as 60 cm./sec. at the exit, and the speed differential
across the length of the opening 52 was nearly 10 cm./sec. The
speed differential was removed by the crossflow fan 71 which was
operated at a relatively low speed. The apparatus was operated
until the supply of toner in the developer space exhausted after
150 image members had been developed. The developing time required
for individual image members varied with decreasing amount of toner
present in the developer, but remained between 5 and 10 seconds.
However, it was noted unexpectedly that the quality of developed
images remained uniform throughout the entire run. The developed
images had a resolution in excess of 20 lines per millimeter on the
average.
While the rotational speed of the rotor was as high as 3,000 r.p.m.
in the above example, it can be reduced down to 1,000 r.p.m. or
less with a corresponding increase in the developing time. A lower
rotational speed of the rotor may be desirable in certain
applications, since this reduces the amount of heat that is
produced by friction of blades or projections on the rotor with the
developer, thereby minimizing the risk that the toner may be fused
with the carrier to lower the toner efficiency.
While the invention has been described with reference to particular
embodiments, it should be obvious that various changes and
modifications are possible to those skilled in the art, so that it
is intended that the invention be solely limited by the appended
claims.
* * * * *