Title: Classifier, developer, and image forming apparatus
Abstract: A classifier having a simple constitution for classifying powder with a high accuracy is provided. The classifier is provided with a transfer board having a plurality of electrodes for generating electric fields for transferring and hopping the powder by an electrostatic force. The classifier is further provided with an opposite roller generating an electric field for transporting and attaching the powder (toner) transferred and hopped on the transfer board to the opposite roller, which is opposite to the transfer board.
Patent Number: 6,941,098 Issued on 09/06/2005 to Miyaguchi, et al.
| Inventors:
|
Miyaguchi; Yohichiro (Kanagawa-ken, JP);
Horike; Masanori (Kanagawa-ken, JP);
Takemoto; Takeshi (Kanagawa-ken, JP);
Ebi; Yutaka (Kanagawa-ken, JP);
Higuchi; Toshiroh (Kanagawa-ken, JP)
|
| Assignee:
|
Ricoh Company, LTD (Tokyo, JP)
|
| Appl. No.:
|
385535 |
| Filed:
|
March 12, 2003 |
Foreign Application Priority Data
| Mar 13, 2002[JP] | 2002-069106 |
| Current U.S. Class: |
399/252; 399/266; 399/291 |
| Intern'l Class: |
G03G 015/08 |
| Field of Search: |
399/251,265,266,289,290,291,252,294,295
347/55,140
|
References Cited [Referenced By]
U.S. Patent Documents
| 3113042 | Dec., 1963 | Hall.
| |
| 4558941 | Dec., 1985 | Nosaki et al.
| |
| 4598991 | Jul., 1986 | Hosoya et al.
| |
| 5027157 | Jun., 1991 | Hotomi et al.
| |
| 5142336 | Aug., 1992 | Hotomi et al.
| |
| 5200762 | Apr., 1993 | Katano et al.
| |
| 5281982 | Jan., 1994 | Mosehauer et al.
| |
| 5317438 | May., 1994 | Suzuki et al.
| |
| 5327522 | Jul., 1994 | Furuta et al.
| |
| 5333241 | Jul., 1994 | Furuta et al.
| |
| 5402220 | Mar., 1995 | Tanaka et al.
| |
| 5412413 | May., 1995 | Sekiya et al.
| |
| 5504838 | Apr., 1996 | Furuta et al.
| |
| 5508520 | Apr., 1996 | Shoji et al.
| |
| 5532807 | Jul., 1996 | Takemoto.
| |
| 5581662 | Dec., 1996 | Furuta et al.
| |
| 5619617 | Apr., 1997 | Furuta et al.
| |
| 5761591 | Jun., 1998 | Yamaguchi.
| |
| 5854465 | Dec., 1998 | Kishi et al.
| |
| 6134412 | Oct., 2000 | Thompson.
| |
| 6137979 | Oct., 2000 | Gartstein et al.
| |
| 6175707 | Jan., 2001 | Eklund et al.
| |
| 6367914 | Apr., 2002 | Ohtaka et al.
| |
| 6597884 | Jul., 2003 | Miyaguchi et al.
| |
| 6708014 | Mar., 2004 | Miyaguchi et al.
| |
| Foreign Patent Documents |
| 63-013068 | Jan., 1988 | JP.
| |
| 07-267363 | Oct., 1995 | JP.
| |
| 08-149859 | Jun., 1996 | JP.
| |
| 2000/-143026 | May., 2000 | JP.
| |
| 2002/-287495 | Oct., 2002 | JP.
| |
Other References
U.S. Appl. No. 10/385,535, filed Mar. 12, 2003, Miyaguchi et al.
U.S. Appl. No. 10/863,294, filed Jun. 9, 2004, Horike et al.
U.S. Appl. No. 10/385,535, filed Mar. 12, 2003, Miyaguchi et al.
U.S. Appl. No. 10/805,362, filed Mar. 22, 2004, Miyaguchi et al.
U.S. Appl. No. 10/385,535, filed Mar. 12, 2003, Miyaguchi et al.
U.S. Appl. No. 10/817,249, filed Apr. 5, 2004, Nakano et al.
U.S. Appl. No. 10/385,535, filed Mar. 12, 2003, Miyaguchi et al.
U.S. Appl. No. 10/659,468, filed Sep. 11, 2003, Shakuto et al.
U.S. Appl. No. 10/385,535, filed Mar. 12, 2003, Miyaguchi et al.
U.S. Appl. No. 10/825,318, Apr. 16, 2004, Naruse et al.
U.S. Appl. No. 09/330,669, filed Jun. 11, 1999, Yasui.
U.S. Appl. No. 09/765,608, filed Jan. 22, 2001, Hayashi et al.
U.S. Appl. No. 09/948,576, filed Sep. 10, 2001, Miyaguchi et al.
U.S. Appl. No. 10/050,865, filed Jan. 18, 2002, Ohtaka et al.
U.S. Appl. No. 10/098,125, filed Mar. 15, 2002, Miyaguchi et al.
U.S. Appl. No. 10/385,535, filed Mar. 12, 2003, Miyaguchi et al.
|
Primary Examiner: Tran; Hoan
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier & Neustadt, P.C.
Claims
1. A classifier for classifying a powder comprising:
a transfer member which has a plurality of electrodes for generating electric
fields and which is configured to transport said powder while transferring and
hopping said powder by an electrostatic force; and
an opposite member configured to selectively catch particles of said powder transferred
and hopped by the transfer member, the opposite member being arranged in a position
substantially opposite to the transfer member,
wherein said opposite member is an opposite transfer member which has a plurality
of electrodes for generating electric fields and which is configured to for transfer
said powder by an electrostatic force.
2. The classifier of claim 1, wherein part or the whole of said opposite transfer
member is inclined position against said transfer member.
3. A classifier for classifying a powder comprising:
a transfer member which has a plurality of electrodes for generating electric
fields and which is configured to transport said powder while transferring and
hopping said powder by an electrostatic force; and
an opposite member configured to selectively catch particles of said powder transferred
and hopped by the transfer member, the opposite member being arranged in a position
substantially opposite to the transfer member,
wherein said opposite member is a rotary roller member.
4. A classifier for classifying a powder comprising:
a transfer member which has a plurality of electrodes for generating electric
fields and which is configured to transport said powder while transferring and
hopping said powder by an electrostatic force; and
an opposite member configured to selectively catch particles of said powder transferred
and hopped by the transfer member, the opposite member being arranged in a position
substantially opposite to the transfer member,
wherein said opposite member is a rotary pelt member.
5. The classifier of claim 4, wherein said belt member is inclined against said
transfer member.
6. A classifier for classifying a powder comprising:
a transfer member which has a plurality of electrodes for generating electric
fields and which is configured to transport said powder while transferring and
hopping said powder by an electrostatic force; and
an opposite member configured to selectively catch particles of said powder transferred
and hopped by the transfer member, the opposite member being arranged in a position
substantially opposite to the transfer member,
wherein said opposite member comprises electrode wires.
7. The classifier of claim 6, wherein said each of the electrode wires is covered
with a protective layer.
8. The classifier of claim 6, further comprising a slit member having slit holes
arranged between the electrode wires, which are arranged at a position substantially
opposite to said transfer member, and the transfer member.
9. A classifier for classifying a powder comprising:
a transfer member which has a plurality of electrodes for generating electric
fields and which is configured to transport said powder while transferring and
hopping said powder by an electrostatic force; and
an opposite member configured to selectively catch particles of said powder transferred
and hopped by the transfer member, the opposite member being arranged in a position
substantially opposite to the transfer member,
wherein said opposite member comprises an array of electrode wires.
10. The classifier of claim 9, wherein a voltage for generating electric fields
is applied to each of the electrode wires.
11. A classifier for classifying a powder comprising:
a transfer member which has a plurality of electrodes for generating electric
fields and which is configured to transport said powder while transferring and
hopping said powder by an electrostatic force; and
an opposite member configured to selectively catch particles of said powder transferred
and hopped by the transfer member, the opposite member being arranged in a position
substantially opposite to the transfer member,
wherein said opposite member comprises a slit member having slit holes; and
electrodes formed on wall surfaces of the slit holes.
12. A classifier for classifying a powder comprising:
a transfer member which has a plurality of electrodes for generating electric
fields and which is configured to transport said powder while transferring and
hopping said powder by an electrostatic force; and
an opposite member configured to selectively catch particles of said powder transferred
and hopped by the transfer member, the opposite member being arranged in a position
substantially opposite to the transfer member,
wherein a width of each of said electrodes of said transfer member in a transporting
direction of said powder is 1 to 20 times an average grain diameter of said powder,
and each space between said electrodes in the transporting direction of said powder
is 1 to 20 times the average grain diameter of said powder, wherein drive waveforms
of n phases are applied to each of the plurality of electrodes, wherein a represents
an integer not less than 3.
13. A classifier for classifying a powder comprising:
a transfer member which has a plurality of electrodes for generating electric
fields and which is configured to transport said powder while transferring and
hopping said powder by an electrostatic force; and
an opposite member configured to selectively catch particles of said powder transferred
and hopped by the transfer member, the opposite member being arranged in a position
substantially opposite to the transfer member,
wherein said transfer member has an inorganic or organic surface protective layer
covering said plurality of electrodes, and wherein a thickness of the surface protective
layer is not more than 10 μm.
14. A classifier for classifying a powder comprising:
a transfer member which has a plurality of electrodes for generating electric
fields and which is configured to transport said powder while transferring and
hopping said powder by an electrostatic force; and
an opposite member configured to selectively catch particles of said powder transferred
and hopped by the transfer member, the opposite member being arranged in a position
substantially opposite to the transfer member,
wherein the classifier bas a plurality of said opposite members, and the plurality
of said opposite members selectively catch the particles of said powder depending
on a quantity of charge or a mass of the particles of said powder.
15. A developer, comprising:
a classifier configured to classify a powder; and
a developing means for developing a latent image on a latent image carrier the
classified powder to form a visual image on the latent image carrier, and
wherein said classifier comprises:
a transfer member which has a plurality of electrodes for generating electric
fields and which is configured to transport said powder while transferring and
hopping said powder by an electrostatic force; and
an opposite member configured to selectively catch particles of said powder transferred
and hopped by the transfer member, the opposite member being arranged in a position
substantially opposite to the transfer member.
16. The developer of claim 15, wherein said developing means comprises a developing
roller facing to said latent image carrier.
17. The developer of claim 16, wherein said developing roller also functions
as said opposite member.
18. The developer of claim 15, wherein said developing means is a member having
a plurality of electrodes for generating electric fields for transferring and hopping
the powder by an electrostatic force at a position near said latent image carrier.
19. The developer of claim 18, wherein said member having a plurality of electrodes
also functions as said opposite member.
20. The developer of claim 15, wherein said developer means comprises a rotary
belt facing to said latent image carrier.
21. The developer of claim 20, wherein said rotary belt member also functions
as said opposite member.
22. An image forming apparatus, comprising:
a latent image carrier; and
a developer configured to develop a latent image with a powder,
wherein the developer is the developer of claim 15.
Description
CROSS-REFERENCE TO RELATED APPLICATION
This application claims the priority benefit of Japanese application serial
no.2002-069106, filed on Mar. 13, 2002.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates in general to a classifier, a developer, and an image
forming apparatus.
2. Description of Related Art
Copiers, printers, facsimiles and the like, have been known as image forming
apparatuses. Some of them employs such an image forming process that a latent image
is formed on a latent image carrier using an electrophotographic process, and a
powder developing agent (hereinafter, also called toner) is attached to the latent
image to develop it as a visible toner image, then the toner image is transferred
to a recording medium, including an intermediate transferring member, so that an
image is formed.
As a developer developing latent images, which is employed for such image forming
apparatuses, such a developer has been known that toner agitated in a developer
is carried on the surface of a developing roller, which is a developing agent carrier,
and the developing roller is rotated to transfer the toner to the position where
the toner is opposite to the surface of a latent image carrier, then the latent
image of latent image carrier is developed. After the development, the part of
the toner that has not been transferred to the latent image carrier is collected
into the developer as the developing roller is rotated, then new toner is agitated,
charged and carried on the developing roller to be transferred again.
Another application of an image forming apparatus is also disclosed in the
Japanese Laid Open Publication No. 9-197781 and 9-329947. In the disclosed apparatus,
a jumping developing method is employed, in which toner is transferred from a developing
roller to a latent image carrier without any contact in-between.
Another application of an image forming apparatus is further disclosed in
the Japanese Laid Open Publication No. 5-19615. In this apparatus, toner is transferred
on the surface of a developing roller by an electrostatic force, and an attractive
force generated between the toner and a latent image carrier separates the toner
from the surface of the developing roller, thus attaching the toner to the surface
of the latent image carrier. Still, another application of an image forming apparatus
is disclosed in the Japanese Laid Open Publication No. 59-181375. In this application,
toner is transferred to a position where the toner is opposite to a latent image
carrier, using a transfer board for transferring the toner by an electrostatic
force, then the toner is separated by an attractive force generated between the
toner and the latent image carrier and is attached on the surface of latent image carrier.
The Japanese Laid Open Publication No. 7-267363 discloses a powder transfer apparatus
for transferring powder, such as toner, using space-traveling-waves fields. This
apparatus is provided with electrodes, to which a drive voltage is applied to form
space traveling wave fields around the electrodes. The traveling wave fields repel
and drive the charged powder, transferring it in the transporting direction of
electric fields.
As for a classifier for classifying powder, such as toner, a classifier using
a screening or wind force classifying method is known. Other application is disclosed
in the Japanese Laid Open Publication No. 8-149859, in which such a classifier
is described that classification (separation) is carried out by using the space-traveling-wave
fields described above, which make electrostatic force, gravity, and centrifugal
force act all together on toner. Besides, the Japanese Laid Open Publication No.
2000-140683 and the Japanese Laid Open Publication No. 2000-140700 disclosed another
method such that a voltage is applied to generate a potential vertical to the transfer
direction of charged powder so that the powder is separated from the transfer surface
according to its specific charge.
To form high quality images using such image forming apparatuses, it is important
to keep uniform the quantity of charge and mass of the grains of toner for development.
However, it has been found difficult for conventional image forming apparatuses
to achieve a uniform attachment of toner. Therefore, in conventional methods, toner
is pre-classified in the manufacturing process by screening or applying wind force
to uniform the toner to a certain extent, and is supplied to an image forming apparatus.
However, even if the substantially uniformed toner is supplied to the image
forming apparatus, the toner is not always uniformly charged because the toner
is charged in the image forming apparatus in the first place. Charging the toner
in the apparatus inevitably cause the unevenness of q/m (quantity of charge per
mass) and of the diameters of the grains of toner, thus posing a problem that there
is a limit for forming a high quality image.
Besides, a conventional classifier tends to become a large-sized one. A
classifier using a method of electrostatic transfer and gravity to classify toner
also has a problem that an exact classification is difficult.
SUMMARY OF THE INVENTION
According to the foregoing description, it is an object of this invention
to provide a classifier having a simple constitution, which achieves a high classification
accuracy utilizing a ETH (Electrostatic Transport & Hopping) phenomenon, a developer
provided with the classifier, which enables high quality development, and an image
forming apparatus provided with the above classifier and developer enabling the
forming of high quality images.
The ETH represents a phenomenon that powder receives the energy of phase-shifting
fields and the energy is transformed into a mechanical energy, which moves the
powder itself dynamically. The phenomenon includes the horizontal moves (transfer)
and vertical moves (hopping) of the powder by an electrostatic force. It is the
phenomenon that the powder comes to have a component in the transporting direction
and hops on the surface of an electrostatic transfer member, due to the phase-shifting
fields. Hereinafter, a development utilizing the ETH phenomenon is called ETH development.
In separately describing the behavior of powder on a transfer member, hereinafter,
the terms of "transfer", "transfer velocity", "transfer direction" and "transfer
distance" are used for the powder moving in the horizontal direction to a board,
the terms of "hopping", "hopping velocity", "hopping direction" and "hopping height
(distance)" are used for the powder jumping up (moving) in the vertical direction
on the board, and "transfer and hopping" on the transfer member is generally called
"transport." The term "transfer" included in the terms "transfer apparatus" and
"transfer board" is synonymous with "transport."
The present invention provides a classifier for classifying a powder. The classifier
comprises a transfer member which has a plurality of electrodes for generating
electric fields and which is configured to transport said powder while transferring
and hopping said powder by an electrostatic force; and an opposite member configured
to selectively catch particles of said powder transferred and hopped by the transfer
member, the opposite member being arranged in a position substantially opposite
to the transfer member. It will be appreciated that, in this specification, the
term "powder" is used to also represent "fine powder", "grains of powder", "fine
grains of powder", "particles", "fine particles", etc, so such terms are not excluded
as the terminology not standing for the definition of "powder."
The opposite member may be an opposite transfer member which has a plurality
of electrodes for generating electric fields and which is configured to for transfer
said powder by an electrostatic force. In this case, the opposite transfer member
may be arranged in such a way that part or the whole of the opposite transfer member
is inclined against the transfer member.
The opposite member may be provided as a rotary roller member, or a rotary belt
member which may be inclined against the transfer member.
Further, the opposite member may comprise an array of electrode wires, where
a voltage for generating electric fields is applied to each of the electrode wires.
It is desirable to form a protective film on the electrode wires. It is also desirable
to further comprise a slit member having slit holes arranged between the electrode
wires, which are arranged at a position substantially opposite to said transfer
member, and the transfer member.
Further, the opposite member may comprise a slit member having slit holes;
and electrodes formed on wall surfaces of the slit holes.
It is desirable for the transfer member of the classifiers described above that
the width of respective electrodes of the transfer member in the transporting direction
of the powder be more than 1 to 20 times the average grain diameter of the powder,
as well as the space between respective electrodes in the same direction be also
more than 1 to 20 times the average grain diameter of the powder, and that drive
waveforms of more than n (a natural number of 3 or more) phases be applied to each electrode.
It is also desirable that the transfer member has an organic or inorganic surface
protective layer whose thickness is not more than 10 μm.
It may be also arranged in such a way that the classifier has a plurality of
said
opposite members, and the plurality of said opposite members selectively catch
the particles of said powder depending on a quantity of charge or a mass of the
particles of said powder.
The present invention further provides a classifier for classifying powder, in
which the classifier transports said powder while transferring and hopping the
powder by an electrostatic force, comprising a member configured to selectively
catch particles of said powder transferred and hopped by forming an electric field.
The invention also provides a developer, comprising: a classifier configured
to classify a powder; and a developing means for developing a latent image on a
latent image carrier the classified powder to form a visual image on the latent
image carrier. The classifier is any classifier described above.
The developing means may comprise a developing roller facing to the latent image
carrier, which can also be used as the opposite member. The developing means may
also be a member having a plurality of electrodes for generating electric fields
for transferring and hopping the powder by an electrostatic force at a position
near the latent image carrier, and the member can also be used as the opposite
member. Further, the developing means may comprises a rotary belt member, at least
part of which is opposite to the latent image carrier, and the belt member can
also be used as the opposite member.
The present invention further provides an image forming apparatus, comprising:
a latent image carrier; and a developer configured to develop a latent image with
a powder. The developer can be the developer mentioned above.
BRIEF DESCRIPTION OF THE DRAWINGS
While the specification concludes with claims particularly pointing out and
distinctly claiming the subject matter which is regarded as the invention, the
objects and features of the invention and further objects, features and advantages
thereof will be better understood from the flowing description taken in connection
with the accompanying drawings in which:
FIG. 1 is a schematic block diagram for explaining the first embodiment of the
classifier of this invention;
FIG. 2 is a front view of the transfer board of the classifier of this invention;
FIG. 3 is a flat view of the above transfer board;
FIG. 4 is an explanatory drawing showing one example of drive waveforms which
are given to the transfer board;
FIG. 5 is an explanatory drawing for describing the transfer and hopping of powder;
FIG. 6 is an explanatory drawing showing a specific example of the transfer
and hopping of the powder;
FIG. 7 is an explanatory drawing for describing the time and duty of applied
voltage generating drive waveforms;
FIG. 8 is an explanatory drawing showing one example of the drive waveforms,
which is generated by an applied voltage with a duty of 67%;
FIG. 9 is an explanatory drawing showing one example of the drive waveforms,
which is generated by an applied voltage with a duty of 33%;
FIG. 10 is an explanatory drawing for describing the width of and the spaces
between electrodes;
FIG. 11 is an explanatory drawing for describing the relation between the width
of electrodes and the electric field (X direction) at the end of an electrode with
zero voltage;
FIG. 12 is an explanatory drawing for describing the relation between the width
of electrodes and the electric field (Y direction) at the end of an electrode with
zero voltage;
FIG. 13 is an explanatory drawing for describing the shape of drive waveform;
FIG. 14 is an explanatory drawing for describing the relation between the shape
of drive waveform and the distance of horizontal travel of the powder;
FIG. 15 is an explanatory drawing for describing the relation between the voltage
value of drive waveform and the Y directional velocity and hopping height of the powder;
FIG. 16 is an explanatory drawing for describing one example of the relation
between a thick film of surface protective layer and the strength of fields;
FIG. 17 is an explanatory drawing for describing the relation between the thick
film of surface protective layer and the strength of fields;
FIG. 18 is another explanatory drawing for describing the relation between the
thick film of surface protective layer and the strength of fields;
FIG. 19 is an explanatory drawing for describing the operation of the classifier
of the first embodiment;
FIG. 20 is an explanatory drawing for describing the classifying operation of
the above classifier;
FIG. 21 is an explanatory drawing for describing one example showing that the
grains of toner is classified according to the quantity of charge by a roller applied voltage.
FIG. 22 is an explanatory drawing for further describing the example shown in
FIG. 21;
FIG. 23 is a schematic block diagram for explaining the second embodiment of
the classifier of this invention;
FIG. 24 is a schematic block diagram for explaining the third embodiment of
the classifier of this invention;
FIG. 25 is a schematic block diagram for explaining the fourth embodiment of
the classifier of this invention;
FIG. 26 is a schematic block diagram for explaining the fifth embodiment of
the classifier of this invention;
FIG. 27 is a schematic block diagram for explaining the sixth embodiment of
the classifier of this invention;
FIG. 28 is a schematic block diagram for explaining the seventh embodiment of
the classifier of this invention;
FIG. 29 is a schematic block diagram for explaining the eighth embodiment of
the classifier of this invention;
FIG. 30 is a schematic block diagram for explaining the ninth embodiment of
the classifier of this invention;
FIG. 31 is an explanatory drawing for describing the different shapes of the
slit holes and electrodes employed in the ninth embodiment of the classifier;
FIG. 32 is a schematic block diagram for explaining the tenth embodiment of
the classifier of this invention;
FIG. 33 is an explanatory drawing for describing the constitution of the electrode
wires in the tenth embodiment and another example of the same;
FIG. 34 is a schematic block diagram for explaining the eleventh embodiment
of the classifier of this invention;
FIG. 35 is an explanatory drawing showing different examples of the drive waveforms
generated through the bias drive circuits in the eleventh embodiment;
FIG. 36 is an important element on large scale for explaining the twelfth embodiment
of the classifier of this invention;
FIG. 37 is a schematic block diagram for explaining the thirteenth embodiment
of the classifier of this invention;
FIG. 38 is an enlarged detail of FIG. 37;
FIG. 39 is a schematic block diagram for explaining the fourteenth embodiment
of the classifier of this invention;
FIG. 40 is a plain view showing the electrode wire line member in the fourteenth embodiment;
FIG. 41 is a schematic block diagram for explaining the fifteenth embodiment
of the classifier of this invention;
FIG. 42 is a schematic block diagram for explaining the first embodiment of
the developer of this invention;
FIG. 43 is a schematic block diagram for explaining the second embodiment of
the developer of this invention;
FIG. 44 is a schematic block diagram for explaining the third embodiment of
the developer of this invention;
FIG. 45 is a schematic block diagram for explaining the fourth embodiment of
the developer of this invention;
FIG. 46 is a schematic block diagram for explaining the fifth embodiment of
the developer of this invention;
FIG. 47 is a schematic block diagram for explaining the first embodiment of
the image forming apparatus of this invention;
FIG. 48 is a schematic block diagram for explaining the second embodiment of
the image forming apparatus of this invention;
FIG. 49 is a magnified view showing the developer of the above image forming apparatus;
FIG. 50 is an explanatory drawing for describing the developing operation of
the above developer;
FIG. 51 is an explanatory drawing for describing one example of the relation
between the drive frequency of drive waveform and a toner transfer velocity;
FIG. 52 is an explanatory drawing for describing other examples of the drive waveforms;
FIG. 53 is a flat view showing a powder charging and selecting apparatus constituted
according to the classifier of this invention; and
FIG. 54 is another flat view showing the powder charging and selecting apparatus
constituted according to the classifier of this invention;
DESCRIPTION OF THE PREFERRED EMBODIMENT
Hereinafter, the preferred embodiments of the present invention are
to be described referring to the drawings. First, the first embodiment of the classifier
of this invention is described referring to FIG. 1, which is a schematic block
diagram of the classifier.
The classifier comprises a transfer board
1, which is a transfer member
having a plurality of electrodes for generating electric fields for transferring
and hopping toner, i.e., powder, and an opposite roller
2, which is an opposite
member (also functions as other member) to which the toner transferred on the transfer
board
1 is transported and attached.
The classifier also comprises a drive circuit
3 applying drive waveforms
Pv
1 having n phases (n stands for a natural number of 3 or more) to each
electrode of the transfer board
1 so as to generate traveling waveform fields
for transferring and hopping the toner. The opposite roller
2 is provided
with a bias power source
4 for applying a bias voltage having a polarity
opposite to the charge of the toner. The bias voltage is positive when the toner
is negatively charged, and the bias voltage is negative when the toner is positively
charged. It will be appreciated that the description is made on the assumption
that the toner is negatively charged.
A charging means
5 is arranged on the toner supply side of the transfer
board
1. The charging means
5 comprises a charging brush (or maybe
a unit other than the charging brush) and a magnet roller for charging the toner,
which is supplied from a toner supply (not shown in the drawings) or recovered,
and sending the toner to the transfer board
1. A collecting electrode
6
is arranged on the residual toner discharging side of the transfer board
1,
where the electrode
6 collects the part of toner that is not transported
and attached to the opposite roller
2. A recovery/transport member
7
is also provided for transporting the toner collected by the collecting electrode
6 to the charging means
5 by an electrostatic force, where the recovery/transport
member is provided with a drive circuit
8 for applying a drive voltage Pv
2
to the electrodes provided on the recovery/transport member
7, the drive
voltage generating electric fields for transporting the toner.
The opposite member
2 has a blade
9 for removing the toner sticking
on the opposite roller
2, and a gutter
10 for storing the toner removed
by the blade
9. (The removed toner can be supplied to the developing means
of the developer).
Now, the transfer board
1 is described in detail referring to FIG.
2
and FIG.
3. FIG. 2 is the schematic sectional view of the transfer board
1 and FIG. 3 is the flat view of the same. The transfer board
1 has
a support board
11 on which a plurality of electrodes
12 are arranged
at every a prescribed distance in the transport direction of powder, (i.e., transporting
direction of powder or moving direction of powder shown by an arrow in FIG.
2),
where three units of the electrode
12 are made one set for generating drive
waveforms. The support board
11 is laminated with a surface protective film
13 made of an inorganic or organic insulating material, which functions
as an insulating transfer surface forming member, i.e., a protective film covering
the surface of the electrodes
12, on which a transfer surface is formed.
The support board
11 may be a board consisting of such an insulating material
as glass, resin, or ceramic, or a board consisting of a conductive material, such
as SUS, with an insulating film, such as SiO
2, formed thereon, or a
board consisting of a deformable material, such as polyimide.
In forming the electrodes
12, a film of conductive material, such as Al,
Ni—CR and the like, is formed on the support board
11 at a thickness
of 0.1 to 1.0 μm, or desirably a thickness of 0.5 to 2.0 μm. Then a
required electrode patterns is formed on the film, using a photolithography technique,
to form the electrodes
12. The width L of the respective electrodes
12
in the transporting direction of powder is made 1 to 20 times the average diameter
of the grains of traveling powder. The space R between each electrode
12
in the transporting direction of powder is also made 1 to 20 times the average
diameter of the grains of traveling powder.
The surface protective layer
13 is formed as a film consisting of such
a substance as SiO
2, TiO
2, TiO
4, SiON, BN, TiN,
or Ta
2O
5, where the thickness of the film is 0.5 to 10 μm,
or desirably 0.5 to 3 μm.
The recovery/transport member
7 has the same constitution as that of the
transfer board
1. The base board of the recovery/transport member
7
is a flexible board consisting of a polyimide film or the like on which a plurality
of electrodes are provided, and the base board is covered with a surface protective
film. Using the flexible board in such a manner makes possible to set the course
of recovering and transferring the toner freely. The drive circuit
8 for
applying drive waveforms to the electrodes of the recovery/transport member
7
applies multiple phase drive waveforms having the phase patterns reverse to that
of the waveforms from the drive circuit
3 so as to transport the charged
toner in the direction reverse to the transport direction on the transfer board
1.
Next, the operation and function of transfer board
1 are described.
The recovery/transport member
7 also operates in similar to the transfer
board
1, but the recovery/transport member
7 functions mainly as
a transfer member.
When the drive circuit
3 applies drive waveforms of n phases to a plurality
of the electrodes
12 of the transfer board
1, the electrodes
12
generate phase-shifting fields (traveling wave fields), which either repel or attract
respective grains of charged powder on the transfer board
1. As a result,
the powder is transferred as it hops in the transporting direction of the electric fields.
For example, as shown in FIG. 4, respective pulse drive waveforms Va, Vb, and
Vc, each of which shifts between the ground potential of G (0 V) and a positive
voltage, are applied by the drive circuit to the electrodes
12 of the transfer
board
1 in such a way that the applying timing of each waveform is shifted
to each other.
At a given moment, as shown in FIG. 5, when a negatively charged grain of the
toner T is on the transfer board
1 as the pulse drive waveform is applied
to a series of the electrodes
12 of the transfer board
1 to give
them the potential status of shown in FIG. 5, the negatively charged grain of toner
T is attracted to the electrode
12 with a positive potential.
When another waveform is applied according to a prescribed timing, the potential
status of the electrodes becomes {circle around (2)} as shown in FIG. 5, where
a repulsive force from the electrode
2 of "G" on the left and an attractive
force from the electrode
12 with a positive potential on the right act together
on the negatively charged grain of toner T. As a result, the grain of toner T moves
to the positive electrode
12. Then, another waveform is applied according
to a prescribed timing, the potential status of the electrodes becomes {circle
around (3)} as shown in FIG. 5, where a repulsive force and an attractive force
act together on the negatively charged grain of toner T as in the case of {circle
around (2)}, moving the grain of toner T further to another positive electrode
12.
As described above, when the multiphase drive waveforms with shifting voltage
are applied to a plurality of the electrodes
12, the traveling waveform
fields are generated on the transfer board
1, and the negatively charged
toner T is transferred as it hops in the transporting direction of the traveling
waveform fields. It will be appreciated that when the toner is positively charged,
reversing the shifting pattern of the drive waveforms brings the same result as
described above.
FIG.
6(
a) shows a state that the negatively charged grains of
toner T are on the transfer board
1 when the electrodes A to F have no potential
(G). When the electrodes A and D become positive, as shown in FIG.
6(
b),
the negatively charged grains of toner T are attracted to the electrodes A, D and
move onto them. Then, according to the prescribed timing, the voltage of both electrodes
A, D become zero, as shown in FIG.
6(
c), while the electrodes B,
E become positive. At this moment, the grains of toner T on the electrodes A, D
are repelled by the electrodes A, D and attracted to the electrodes B, E, simultaneously,
thus transferred to the electrodes B, E. Then, at another shift of waveforms, the
voltage of both electrodes B, E become zero, as shown in FIG.
6(
d),
while the electrodes C, F become positive. At this moment, the grains of toner
T on the electrodes B, E are repelled by the electrodes B, E and attracted to the
electrodes C, F, simultaneously, thus transferred to the electrodes C, F. In this
manner, the negatively charged grains of toner are sequentially transferred to
the right, as shown in FIG. 6, by the traveling waveform fields.
The multiphase (3 phase) drive waveforms applied to the electrodes of the transfer
board
1 is described in detail. First, the relation between the polarity
of voltage applied to the electrodes and the moving direction of the charged toner
(powder) is described. When the toner is negatively charged and the applied voltage
is zero or positive, the grains of toner jump in the reverse direction to that
of an electric line of force heading from a positive electrode to an electrode
of zero voltage. When the toner is positively charged, the grains of toner jump
in the same direction of the electric line of force.
In FIG. 7 shows grains of toner on the electrode (B phase electrode) to which
B phase pulse (drive waveform Vb) is applied. The behavior of the toner to an applying
voltage pulse duty is described using FIG.
7. When the negatively charged
grains of toner T are attracted to the B phase electrode while it is positive,
the grains of toner T start jumping in the reverse direction to that of an electric
line of force heading from a positive electrode to the B phase electrode at the
point that the voltage of the B phase electrode is shifted to zero.
When the traveling waveform fields are generated by applying pulse voltage (drive
waveforms) of n phase (n stands for a natural number of 3 or more) to each electrode,
the positive voltage applying duty of applied voltage pulse is set in such a way
that a voltage applying time per one phase is less than {repetition frequency time×(n-1)/n}.
In this manner, transfer and hopping of the toner can be made more effectively.
For example, when three phases of drive waveforms A, B, C are applied and the
voltage applying time t a of each phase is set to about 67% of the repetition frequency
time t f, as shown in FIG. 8, both A phase and C phase come to positive when B
phase come to zero voltage. Therefore, an electric field distribution given by
a series of electrode of A phase, of B phase, and of C phase is symmetrical with
respect to the electrode of B phase, as shown in FIG.
14.
As a result, grains of toner on the half side in the transfer direction of the
electrode of B phase are moved in the direction of transfer and hopping, but grains
of toner on the opposite half side is moved in the reverse direction, which reduces
the efficiency of the transfer. Therefore, setting the voltage applying time t
a for each phase to less than about 67% of the repetition frequency time t f prevents
the decline of transfer efficiency when three-phase drive waveforms are used. When
four-phase drive waveforms are used, setting the voltage applying time for each
phase to less than about 75% of the repetition frequency time prevents the decline
of transfer efficiency. For a purpose of making grains of toner jump straight up
from the electrode (less priority to the transfer), setting the voltage applying
time for each phase t a to less than about 67% of the repetition frequency time
t f will make the grains of toner hop in the most effective manner.
FIG. 9 shows a case where the drive waveforms of three phases of A, B, C are
applied and the voltage applying time t a for each phase is set to about 33% of
the repetition frequency time t f, that is, set to {repetition frequency time/n}.
In this setting, at the moment when the applied voltage of the electrode of B phase
comes to zero, the electrode of A phase comes to zero voltage and the electrode
of C phase comes to positive, thus the transporting direction of powder becomes
A to C. Therefore, the grains of toner on the electrode of B phase become under
influence of an electric field making the grains of toner repelled by the electrode
of A phase and attracted to the electrode of C phase. Thus, the efficiency of transfer
and hopping is improved.
Therefore, in adjusting an applied voltage for each electrode, the transfer
efficiency can be improved when the voltage applying time is set so as to make
the electrode on the upstream side of transporting direction repulsive and one
on the downstream side attractive when a given electrode is adjacent to the electrodes
on both sides of transfer direction. When a drive frequency is high, setting the
voltage applying time to more than {repetition frequency time/n} to less than {repetition
frequency time×(n-1)/n} allows grains of toner on the given electrode to easily
gain an initial velocity, so that the repetition frequency of transfer can be increased
without reducing the transfer efficiency, which is particularly advantageous for
a high speed transfer.
To achieve effective transfer and hopping, it is important to give an initial
velocity higher than a prescribed value to the powder (toner) on the transfer board.
For that purpose, an electric field having a necessary strength is made to act
on the toner on the transfer board. The necessary strength is a strength needed
to allow each grain of toner break away from an absorption force, such as a mirror
image force, a van der Waals force and the like capturing the grain according to
its charge, and jump up.
The strength of a desirable electric field capable of giving a force effective
for transfer and hopping of the toner is more than (5E+5) V/m. As a strength for
eliminating a problem of absorption, more than (1 E+6) V/m is desirable. Further,
as a more desirable strength to give an enough force, more than (2E+6) V/m is desirable.
When the grains of toner gaining an enough velocity from an electric field having
this strength move to a distance where the influence of the field does not reach,
the efficiency of transfer and hopping is hardly affected even when the voltage
relation, as described for A, B, and C phases above, between a given electrode
and the adjacent positive electrodes on the downstream and the adjacent electrode
of zero voltage on the upstream comes to collapse.
For example, when a voltage of 100 V is applied to the electrode, the effect
of field from the electrode becomes almost none at the point 50 μm above
the electrode. Besides, the strength of field is reduced to ⅕ at the point
30 μm above the surface of the electrode. Therefore, when a grain of toner
accelerated to jump upward has an average velocity of 0.3 to 1 m/sec, it takes
30 to 100 μsec for the grain to travel through the distance of 30 μm
to reach the point where the strength of field declines to ⅕.
Therefore, it is desirable to set a voltage applying time of more than
30 μsec to apply a voltage to a given electrode of a specific phase for repelling
the powder, to the adjacent electrode on the upstream for repelling, and to the
adjacent electrode on the downstream for attracting, simultaneously. In the above
example shown in FIG. 7, more than 30 μsec of the voltage applying time makes
the upstream side adjacent electrode (electrode of A phase) zero voltage and the
downstream side adjacent electrode (electrode of C phase) positive against the
electrode of B phase. The voltage applying time described above is a narrower condition
for a positive voltage applying pulse duty.
Next, a description is to be made for the width L of a plurality of the electrodes
12 of the transfer board
1, on which the toner (powder) is transferred
as it hop, the space R between the electrodes, the shape of drive waveforms, and
the surface protective layer
13. The width L of electrodes and the space
R between the electrodes substantially affects the transfer efficiency and hopping
efficiency of the powder (toner).
The grains of toner between electrodes are moved along the surface of the board
to the adjacent electrode due to electric fields formed horizontally. Meanwhile,
most of the grains of toner on the electrode jump upward from the board surface
with a given initial velocity at least having a vertical component.
The grains of toner near the end of electrode jump across the adjacent electrode
as they move. Therefore, when the width L of electrodes is wide, the number of
the grains of toner on the electrodes increase, so the grains of toner to make
a long leap increase since they jump across a wide electrode, thus improving the
transfer efficiency. However, a too large width of electrodes leads to a decrease
of the strength of an electric field near the centers of electrodes, allowing the
grains of toner to stick to the electrodes, thus reducing the transfer efficiency.
The inventor found an appropriate width of the electrode for enabling an effective
transfer and hopping of powder at a low voltage.
The space R between electrodes determines the strength of electric field between
the electrodes because the strength of electric field changes according to the
relation between a distance and an applied voltage. The narrower the space R is,
the stronger the electric field is, so it becomes easy for grains of toner to acquire
an initial velocity for the transfer and hopping when the space R is narrow. However,
the moving distance of grains of toner traveling from electrode to electrode at
one leap get shorter if the space R is narrower. In such a case, the transfer efficiency
cannot be improved unless the drive frequency is increased. In solving this problem,
the inventor also found an appropriate space between the electrodes for enabling
an effective transfer and hopping of powder at a low voltage.
The thickness of a protective layer covering the surface of electrode affects
the strength of electric fields on the surface of electrode. Particularly, the
electric line of force of vertical component is strongly affected in determining
the efficiency of hopping.
Therefore, it is necessary to set an appropriate relation among the width
of electrodes, the space between electrodes, and the thickness of the surface protective
layer in order to solve the problem of toner absorption on the electrode surface
and enable the effective transfer at a low voltage.
When the width L of electrodes is set to the same size as that of the diameter
of grains of toner (diameter of grains of powder), the width L is the minimum size
for transferring or hopping at least one grain of toner. If the width L is narrower
than the above size, the electric field acting on the grain of toner becomes weaker,
which leads to less force of transfer and jumping, thus it becomes difficult to
put the electrodes in practical use.
As the width L go wider, the electric line of force come to incline in the transfer
direction (horizontal direction), especially near the center of the space above
the electrode, generating an area where a vertical electric field is weak, thus
reducing the force for hopping the grains of toner. Too large width L may cause
the grains of toner to deposit on the electrode as an absorption force capturing
the grains according to their charge, such as a mirror image force, a van der Waals
force, and an absorption force caused by water content, surpasses the vertical
component of the grains of toner.
In consideration for transfer and hopping, it is concluded that the width L for
allowing 20 grains of toner to be positioned on the electrode will suppress the
absorption, making possible to carry out an effective transfer and hopping with
given drive waveforms having a low voltage of about 100 V. The width L wider than
the above size will form an area where the absorption occurs over the electrode.
In this case, for example, when the average grain diameter of toner is 5 μm,
the width L is set to 5 μm to 100 μm.
A more desirable range of the width L for effective transfer by drive waveforms
having an applied voltage of lower than 100 V is the range 2 to 10 times the average
grain diameter of powder. By setting the width L within this range, the decrease
of the strength of electric field near the center of the electrode surface can
be suppressed to the ratio of ⅓ or less, and the decrease of the hopping
efficiency becomes the ratio of 10% or less, thus a sharp decline of the transfer
efficiency can be avoided. In this case, for example, when the average grain diameter
of toner is 5 μm, the width L is set to 10 μm to 50 μm.
Further desirable width L of electrodes is the range 2 times to 6 times the
average grain diameter of powder. In this case, for example, when the average grain
diameter of toner is 5 μm, the width L is set to 10 μm to 30 μm.
It has proved that setting the width L within this range substantially improves
the transfer efficiency.
A test has been conducted in the condition as shown in FIG. 10, where the width
L of the electrode
12 on the transfer board
1 is 30 μm, the
space R between electrodes is 30 μm, the thickness of the electrode
12
is 5 μm, the thickness of the protective layer
13 is 0.1 μm,
and each voltage applied to adjacent two electrodes
12,
12 is +100
V and zero. In this condition, the strength of a transfer field TE and a hopping
field HE for the width L and the space R are measured, respectively. The result
of the measurement is shown in FIGS. 11 and 12.
Each appraisal data is a combined result from simulations, measurements, and
observations of the behavior of the grains of toner using a high speed video. Though
only two electrodes
12 are shown
