Cleaning method and apparatus for intermediate transfer member

In an electrostatographic machine such as a copier or printer, a cleaning apparatus for removing charged and uncharged particles from the surface of an image-transfer assist member such as an intermediate transfer member. The cleaning apparatus includes a plurality of potential sources for selectively biasing the intermediate transfer member and the image-bearing member of the machine, and a dc corona discharge device for actively charging such particles on the intermediate transfer member for transfer back to the image-bearing member.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to cleaning methods and apparatus for 
removing particles from surfaces in electrostatographic reproduction 
machines such as copiers and printers. More particularly, it relates to a 
method and apparatus for removing charged and uncharged particles from the 
image-bearing surface of an intermediate transfer member in such a 
machine. 
2. Description Relative to the Prior Art 
Electrostatographic process apparatus or machines, such as copiers and 
printers, which produce or reproduce toned images on receiver sheets are 
well known. In such machines, a toner particle image is formed on a moving 
image-bearing member, and is subsequently transferred onto a suitable 
receiver sheet, such as a sheet of paper. The transferred toner image is 
then fused onto the sheet to form a hard copy. Such hard copy production 
can be repeated over and over when a plurality of copies is desired. In 
order to ensure the quality of each subsequently produced image, each such 
apparatus or machine usually includes a cleaning device for removing 
residual particles, for example, from the surface of the image-bearing 
member. 
As disclosed, for example, in U.S. Pat. No. 4,081,212, issued Mar. 28, 1978 
to Wetzer, and in U.S. Pat. No. 4,183,655, issued Jan. 15, 1980 to 
Umahashi et al., in one group of such apparatus, the toner particle image 
formed on the image-bearing member is ordinarily transferred directly from 
such surface to a receiver sheet which is fed through an image transfer 
nip that is formed by the image-bearing member and a back up transfer-nip 
roller. During such transfer, the transfer-nip back up roller directly 
contacts the back of the receiver sheet in areas where such sheet is 
present, but undesirably also contacts the image transfer member in areas 
where there is no sheet. As such, the transfer-nip back up roller can 
become contaminated with toner and other particles which transfer from the 
image-bearing member onto the roller in such no-sheet areas. Accordingly, 
means are usually provided for cleaning such back up rollers as disclosed, 
for example, in the above-cited patents. 
Another group of such electrostatographic machines or apparatus are 
disclosed for example in (a) U.S Pat. No. 4,712,906, issued Dec. 15, 1987 
to Bothner et al., (b) U.S. Pat. No. 4,588,279, issued May 13, 1986 to 
Fukuchi et al., and (c) U.S. Pat. No. 4,899,198, issued Feb. 6, 1990 to 
Mahoney. This group includes those machines or apparatus capable of 
producing color images. As disclosed, each of them includes either a 
transfer member (TM) or an intermediate transfer member (ITM). In those 
machines that include a transfer member (TM), the toner particle images 
are formed on the image-bearing member, a receiver sheet is attached to 
the transfer member (TM,) and then moved repeatedly, for example, through 
an image-transfer nip formed by the TM and the image-bearing member for 
receiving the toner images thereonto. In those machines that include an 
intermediate transfer member (ITM), the toner particle images formed on 
the image-bearing member are first transferred to the ITM before they are 
then transferred from such ITM to a receiver sheet. The ITM therefore 
forms a pair of toner image transfer-nips, one with the image-bearing 
member and the other with a back up transfer-nip roller. The transfer-nip 
roller forms a transfer nip with the ITM through which the sheet is fed 
for receiving the toner images from the ITM. As discussed above, the back 
up transfer-nip roller in this case can similarly become contaminated with 
toner particles and must therefore be cleaned. 
Additionally, however, the TM and the ITM can and do also become 
contaminated with residual toner particles as well as with other 
particles, for example, paper dust particles from sheets such as sheets of 
paper carried by the TM or fed into contact with the ITM. Such 
contamination of the TM or ITM is particularly a problem when different 
color toner particles are used to form a multiple color toner images in 
such machines. 
Because the residual particles which contaminate transfer assist members 
(TAM) such as the transfer nip back up roller, the transfer member TM or 
the ITM include toner as well as other particles such as dust particles, 
some of such particles, as can be expected, will be charged and others 
will be uncharged. Furthermore, in the case of charged particles, the 
exact polarity of each particle is ordinarily not known precisely. 
Therefore, attempting to remove all such particles from a TAM (transfer 
assist member) merely by reversing the relative polarity of such a member 
can often be significantly ineffective. The alternative, of course, is to 
use a separate and dedicated cleaning device. 
Such cleaning devices for removing contaminating particles from an ITM are 
disclosed, for example, in the above cited patents U.S. Pat. No. 4,588,279 
and U.S. Pat. No. 4,899,198. Such cleaning devices, however, are usually 
separate or bulky and expensive. In addition, the effectiveness of each 
may still be detrimentally affected by the presence of charged and 
uncharged particles among such particles on the ITM. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a simple, and 
relatively less bulky cleaning method and apparatus for removing residual 
particles from a transfer assist member (TAM) such as an intermediate 
transfer member (ITM) of an electrostatographic machine, such as a copier 
or printer. 
It is another object of the present invention to provide such a cleaning 
method and apparatus for effectively removing charged and uncharged 
particles from such a transfer assist member (TAM). 
In accordance with the present invention, a cleaning apparatus is provided 
for removing charged and uncharged particles from movable intermediate 
transfer member (ITM) of an electrostatographic machine. The cleaning 
apparatus of the present invention includes a first biasing means for 
selectively biasing the movable image-bearing member of the 
electrostatographic machine to a first potential V.sub.1 which has a first 
polarity P.sub.1, or to a second potential V.sub.2 which has a second 
polarity P.sub.2. The cleaning apparatus further includes a second biasing 
means for selectively biasing the intermediate transfer member (ITM) of 
the machine to a fourth or a fifth potential V.sub.4, V.sub.5, 
respectively, which have fourth and fifth polarities P.sub.4, P.sub.5, 
respectively, such that P.sub.4 and P.sub.5 are each relatively opposite 
to P.sub.2. The cleaning apparatus of the present invention also includes 
a corona discharge device for actively charging all charged and uncharged 
particles on the ITM to a sixth potential V.sub.6 that has a sixth 
polarity P.sub.6. The polarity P.sub.6 should be relatively the same as 
the fourth polarity P.sub.4 of the fourth potential of the ITM, and hence 
should be relatively opposite to P.sub.2 so as to cause the actively 
charged particles to transfer from the ITM back to the image-bearing 
member. 
According to another aspect of the present invention, a cleaning method for 
removing charged and uncharged particles from a moving intermediate 
transfer member (ITM) forming an image transfer nip with the moving 
image-bearing member of an electrostatographic machine includes the steps 
of (a) selectively biasing the image-bearing member to a potential V.sub.2 
having a polarity P.sub.2, (b) selectively biasing the ITM to a potential 
V.sub.5 having a polarity P.sub.5 such that P.sub.5 is relatively opposite 
to P.sub.2 ; and(c) activating a corona discharge device for actively 
charging all particles on the ITM to a potential V.sub.6 having a polarity 
P.sub.6 which is relatively the same as P.sub.5, and hence relatively 
opposite to P.sub.2, thereby causing all such actively charged particles 
to transfer from the ITM back to the image-bearing member.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Because electrostatographic process apparatus or machines are well known, 
the present description will be directed in particular to elements forming 
part of or cooperating more directly with the present invention. Elements 
not specifically shown or described herein are selectable from those known 
in the prior art. 
Referring now to FIG. 1, an electrostatographic process apparatus or 
machine such as a copier or printer is generally illustrated as 10. As is 
well known, such a machine 10 can produce or reproduce hard copy toned 
images on suitable receiver sheets. As shown, the copier or printer 10 
includes a housing 12, a platen 14, and an image-bearing member 16 which 
is shown as an endless flexible belt trained about a plurality of rollers 
18, 20. One of the rollers 18, 20, for example the roller 20, can be a 
drive roller for moving the member 16, for example, in the direction of 
the arrow 22. As is well known, the image-bearing member 16 can also be a 
rotatable rigid drum. In any case, the member 16 has an image-bearing 
surface 24, which for imaging purposes has an uncharged potential, for 
example V.sub.1 having a polarity P.sub.1. Charges at a desired potential 
having a desired polarity can then be uniformly sprayed on the surface 24. 
The values for V.sub.1 P.sub.1, for example ground, should be selected 
such that in pos/pos development type machines, in which the image pattern 
to be developed consists, for example, of fully undischarged areas of the 
surface 24, toner particles are prevented from being attracted to the 
fully discharged areas of the surface 24 at V.sub.1 P.sub.1. In neg/pos or 
reverse development type machines the opposite is, of course, the case. 
As is known in the art, the copier or printer 10 includes a logic and 
control unit (LCU) 62 for variously controlling the electrostatographic 
process of the copier or printer 10 based, for example, on the sensed 
instantaneous location of the moving image-bearing member 16. The LCU 62, 
for example, has a digital computer, preferably a microprocessor which 
includes stored programs that are responsive to sensed input signals for 
sequentially actuating and deactuating the various process stations and 
components of the copier or printer 10, as well as for controlling the 
various functions of each station and component. Additional encoding means 
may be provided as known in the art for providing desired precise timing 
signals for the control of the various functions and components. 
Programming of a number of commercially available microprocessors such as 
an INTEL Model 8086 Microprocessor (which along with others can be used in 
the LCU 62 according to the present invention) is a conventional skill in 
the art. 
Under the control of the LCU 62, the copier or printer 10 can selectively 
be set to an imaging mode in which the various stations and components of 
the copier cycle so as to form, transfer and fuse toned images. Under such 
control, the copier or printer 10 can be similarly set to a non-imaging 
mode in which the various stations and components of the copier or printer 
10 cycle such that no images are formed, transferred or fused. In other 
words, in the non-imaging mode, the copier or printer 10 and the various 
stations and components perform what can be described as a dry-run. 
For forming toned images on the surface 24, the copier or printer 10 
includes a first corona discharge device 26, for example an ac corona 
device with a suitable biased control grid electrode, for uniformly and 
electrostatically charging the surface 24. A latent image-forming device 
28, such as an LED printhead, for example, is used for image-wise exposing 
the uniformly charged surface 24 thereby forming an electrostatic latent 
image pattern on the surface 24. A plurality of development stations 30A, 
30B, 30C and 30D, for example, each contains developer material which may 
include carrier particles and toner particles of different colors, such as 
cyan, magenta, yellow and black. The toner particles in the developer 
material are charged to a desired potential, for example, V.sub.3 having a 
polarity P.sub.3 that, for example, is relatively the same as that P.sub.1 
of the background areas of the surface 24. As is well known, P.sub.3 is 
also relatively opposite to the polarity of the image pattern areas on the 
surface 24 that are to be developed with such charged toner particles. As 
such, latent images formed electrostatically on the surface 24 can be 
developed or made visible by such charged toner particles being attracted 
onto such latent images. 
As is well known, the polarity of a charged body is ordinarily positive or 
negative when the body is charged to, respectively, a positive or negative 
potential. The polarity of a first positively charged body, however, may 
be relatively negative to that of a second positively charged body if the 
second body is charged to a higher positive potential than the first. The 
electrostatic transfer of charged particles as discussed here relies on 
the attraction and repulsion characteristics of opposite and relatively 
opposite polarity bodies, and same and relatively same polarity bodies, 
respectively. Because the selection of same, opposite, relatively same and 
relatively opposite polarities may be varied, as desired, for various 
purposes throughout the electrostatographic process of the machine or 
apparatus 10 of the present invention, the relevant polarities of the 
various bodies or members described will be labeled P.sub.1, P.sub.2, 
P.sub.3, etc., for ease of identification. Each such polarity, however, is 
simply positive or negative relative to another. 
As further shown, the copier or printer 10 includes an image transfer 
assist member (TAM) such as an intermediate transfer member (ITM) 40. The 
member 40 is shown as a drum but can also be a flexible web. In either 
case, the member 40 forms a first toner image transfer nip 42 with the 
surface 24 of the image-bearing member 16. The transfer nip 42 is formed, 
as such, at a point that is downstream of the development stations 
30A-30D, relative to the movement of the image-bearing member 16. The 
principles of the present invention will be described with specific 
reference to the cleaning of an image transfer assist member (TAM) that is 
an intermediate transfer member (ITM). It is understood, however, that the 
invention is equally applicable to the cleaning of other types of transfer 
assist members such as a transfer-nip back up roller or a transfer member 
to which the receiver sheet is attached for repeated movement, if 
necessary, through a toner image transfer nip such as 42. 
The ITM 40, as shown, has an image-bearing surface 44, and for image 
transfer purposes is biasable, for example, to a potential V.sub.4 having 
a polarity P.sub.4 that is relatively opposite to the polarity P.sub.3 of 
the toner particles of the toned images on the surface 24. The ITM 40 is 
rotatable, for example, in the direction of the arrow 43 for receiving, in 
registration, toned images from the surface 24. As such, the copier or 
printer 10 can produce a multiple color toner image by forming successive, 
different color toned color-separation components of such a multiple color 
image, and then transferring such components, in registration, onto the 
surface 44. By so doing, a toned composite of the multiple color image can 
be created on such surface 44. 
The composite multiple color toned image (on the surface 44) can thereafter 
be transferred from the surface 44 to a suitable receiver such as a sheet 
of paper 46. As shown, the sheet 46 can be fed, for example, by a roller 
47, from a supply 48 thereof, through a second toner image transfer nip 
50. The nip 50 is formed by the ITM 40 with an articulatable back up 
roller 52 which during image transfer thereat directly contacts the back 
of the receiver sheet 46 The roller 52, however, is articulated away from 
the ITM 40 during image composition on the surface 44. As further shown, 
the copier or printer 10 includes sheet transport means 54 for moving the 
image-carrying sheet 46, from the nip 50 to a fusing station 56 where the 
toned image is fused onto such sheet. As such, the copier or printer 10 
can repeatedly form, transfer and fuse such toned images as desired. 
However, in order to form high quality images on the image-bearing surface 
24 repeatedly, each portion of such surface 24, from which a toned image 
has been formed and transferred to the ITM 40, must be thoroughly cleaned, 
for example, by a cleaning device 60, before such portion is again used 
for forming another image. 
The quality of subsequently produced images is also affected by the 
cleanliness condition of the surface 44 of the ITM 40. It should be noted 
that the composition of toned images on the surface 44, and the subsequent 
transfer of such images to the sheet 46, result in contamination of the 
surface 44 with toner and, for example, dust particles, some of which are 
charged and others of which are uncharged. Accordingly, the surface 44 
must therefore be cleaned periodically in order to ensure continued 
composition thereon and transfer therefrom of high quality images. 
Therefore, in accordance with the present invention, a cleaning apparatus 
designated generally 70 is provided for effectively removing such charged 
and uncharged particles from the surface 44. The apparatus 70, and the 
method thereof, are simple and relatively less bulky and less expensive 
than conventional dedicated cleaning apparatus for such purpose. The 
method and apparatus 70 are operable when the copier or printer 10 is 
selectively set to the non-imaging mode. As shown, the apparatus 70 
includes first and second biasing means 72, 74, and a second corona 
discharge device 76. 
The first biasing means 72, which is under the control of the LCU 62, 
includes a potential source for the first potential V.sub.1 of the 
image-bearing member which may be ground, and which has a polarity 
P.sub.1, a second potential source V.sub.2 which has a polarity P.sub.2, 
and means such as a switch S.sub.1 under the control of the LCU 62 for 
selectively biasing the image-bearing member 16 to either V.sub.1 P.sub.1 
or V.sub.2 P.sub.2. The potential V.sub.2 polarity V.sub.2 here is that of 
the surface or member that will receive the contaminating particles from 
the transfer assist member (TAM) being cleaned. In o the case of the ITM 
40, the values for V.sub.2 P.sub.2 should be selected so as to facilitate 
the transfer from the surface 44 of the ITM 40, of relatively oppositely 
charged toner and other particles, directly onto the surface 24 of the 
member 16 when such surface 24 is not charged by the corona device 26 and 
hence not developed by developer from any of the stations 30A-30D. 
The second biasing means 74, which also is under the control of the LCU 62, 
includes a potential source for the fourth potential V.sub.4 of the ITM 40 
which has a polarity P.sub.4, a fifth potential source V.sub.5 which has a 
polarity P.sub.5, and means such as a switch S.sub.2 for selectively 
biasing the ITM 40 to either V.sub.4 P.sub.4 or V.sub.5 P.sub.5. The 
polarities P.sub.4 and P.sub.5 should each be relatively opposite to the 
second polarity P.sub.2 of the image-bearing member 16 in order to 
facilitate the transfer of charged particles from the ITM 40 to the member 
16. The difference between V.sub.4 P.sub.4 and V.sub.2 P.sub.2, however, 
should be greater than that between V.sub.5 P.sub.5 and V.sub.2 P.sub.2. 
In a preferred embodiment, for example, V.sub.5 P.sub.5 is ground and 
V.sub.2 P.sub.2 is positive (that is higher than ground), and V.sub.4 
P.sub.4 is about -2000V dc. 
As further shown, the corona discharge device 76 of the cleaning apparatus 
70, can be an open cell, single wire dc corona. Under the control of the 
LCU 62, the device 76 can be selectively activated to actively charge all 
particles (previously charged as well as uncharged), that desirably should 
be removed from the surface 44 of the ITM 40. The device 76, as such, can 
actively charge such particles to a potential and polarity shown, for 
example, as V.sub.6 P.sub.6. The source V.sub.6 P.sub.6 is such that the 
polarity P.sub.6 is relatively the same as that of P.sub.4 of the ITM 40 
so as to cause the ITM 40 to repel such actively charged particles. 
Referring now to FIG. 2, there is shown a flow chart including a series of 
steps used in the method of the present invention. As shown, when the 
copier or printer 10 is first turned on, or when the number of images K 
formed and transferred thereby has reached a predetermined value, for 
example, K.sub.c, as counted by the LCU 62 the copier or printer 10 under 
the control of the LCU 62 can be set to the non-imaging mode in which the 
ITM 40 can then be cleaned according to the present invention. The series 
of steps for such cleaning include: (a) selectively biasing the moving 
image-bearing member 16 to V.sub.2 P.sub.2, for example, a positive 
potential having a positive polarity; (b) selectively biasing the moving 
ITM 40 at V.sub.5 P.sub.5, where V.sub.5 P.sub.5, for example, is ground, 
such that P.sub.5 is relatively opposite to P.sub.2 ; and (c) activating 
the corona discharge device 76 to actively charge all particles on the 
surface 44 of the ITM 40 to V.sub.6 P.sub.6, such that P.sub.6 is 
relatively opposite to P.sub. 2, for example, negative. As such, in a 
first phase of the present invention, when the surfaces 44 of the ITM 40 
and that 24 of the image-bearing member 16 make contact within the 
image-transfer nip 42, the actively charged particles on the surface 44 
with a polarity P.sub.6, will tend to transfer to the surface 24 which has 
the polarity P.sub.2 relatively opposite to P.sub.6. Such particles can 
thereafter be removed conventionally from the surface 24 by means, for 
example, of the image-bearing-member cleaning device 60 which can be a 
blade or a fiber brush. 
To ensure effective removal of such actively charged particles from the 
surface 44 of the ITM 40, the cleaning method of the present invention 
includes a second cleaning phase. In the first phase, when the ITM 40 was 
at V.sub.5 P.sub.5, and the corona device 76 was kept activated, the ITM 
40 should be moved through the nip 42 for a number of complete revolutions 
N.sub.1, where N.sub.1 is at least greater than 1. A predetermined number, 
for example, NC1 of such revolutions N.sub.1 can be used during the first 
cleaning phase in order to ensure substantial cleaning of the ITM 40. In 
the second phase, the method of the present invention additionally 
includes the steps of (a) selectively rebiasing the ITM 40 from V.sub.5 
P.sub.5, such as ground, to V.sub.4 P.sub.4, for example, -2000V dc, such 
that P.sub.4 is relatively the same as P.sub.6, and such that the 
difference between V.sub.4 and V.sub.2 is substantially greater than that 
between V.sub.5 and V.sub.2 ; (b) deactivating the corona device 76; and 
(c) moving the ITM 40 for a predetermined number of revolutions N.sub.2, 
for example, NC2 (where NC2 is at least greater than 1) through the nip 
42. By so doing, even more of the actively charged particles with polarity 
P.sub.6 on the ITM 40 will be repelled by the surface 44 at V.sub.4 
P.sub.4 (while also being attracted by the surface 24 at V.sub.2 P.sub.2) 
onto the surface 24. Such first and second phase cleaning or removal of 
the actively charged particles from the surface 44 ensures that 
substantially all such particles are removed from such surface 44. 
As can be seen, the method and apparatus of the present invention is 
simple, not bulky, and is therefore relatively less expensive. The active 
charging of particles on the ITM 40 as well as the first and second phase 
cleaning method advantageously ensure the removal of substantially all as 
well as both charged and uncharged particles therefrom. 
The invention has been described in detail with particular reference to a 
presently preferred embodiment, but it will be understood that variations 
and modifications can be effected within the spirit and scope of the 
invention.