Sheet stripping apparatus

An apparatus in which a sheet is separated from a moving member. The apparatus includes a pair of elastomeric diaphragms coupled to a stripping member. A detector senses the spacing between the moving member and the stripping element of the stripping member. The diaphragms, in response to the sensed spacing, pivot the stripping member so as to maintain the space between the moving member and stripping element substantially constant.

The foregoing abstract is neither intended to define the invention 
disclosed in the specification nor is it intended to be limiting as to the 
scope of the invention in any way. 
BACKGROUND OF THE INVENTION 
This invention relates generally to an electrophotographic printing 
machine, and more particularly concerns an apparatus for separating copy 
sheets having a toner powder image transferred thereto from a moving 
photoconductive surface. 
In the process of electrophotographic printing, a charged photoconductive 
member is exposed to a light image of an original document being 
reproduced. The irradiated areas of the photoconductive surface are 
discharged to record thereon an electrostatic latent image corresponding 
to the informational areas contained within the original document. A 
development system moves a developer mix of carrier granules and toner 
particles into contact with the photoconductive surface. The toner 
particles are attracted electrostatically from the carrier granules to the 
latent image forming a toner powder image thereon. Thereafter, the toner 
powder image is transferred to a sheet of support material. After 
transferring the toner powder image to the sheet of support material, a 
fusing device permanently affixes the toner powder image thereto. 
During the transfer process, the sheet of support material is generally 
placed in contact with the toner powder image on the photoconductive 
surface and the backside of the sheet subjected to a spray of ionized air. 
This results in a charge being formed on the sheet having a magnitude and 
polarity sufficient to electrostatically attract the toner particles 
thereto. However, during transfer, a charge opposite to the charge found 
in the non-image areas of the photoconductive surface is induced on the 
sheet of support material. This causes the sheet to become 
electrostatically tacked to the photoconductive surface. The removal of 
the sheet of support material from the photoconductive surface has long 
been a problem in electrophotographic printing. Mechanical and pneumatic 
stripping devices have been used for quite some time in the printing art 
with varying degrees of success. However, devices of this type frequently 
suffer from misalignment problems. When the stripping mechanism is 
misaligned, it fails to act upon the sheet of support material either at 
the proper time or at the proper place. The sheet of support material may 
then remain on the photoconductive surface, i.e. it is not stripped, or 
the toner powder image is marred. In the case of a mechanical stripper 
wherein the pick off fingers are interposed between the photoconductive 
surface and the sheet of support material, misalignment of the fingers may 
produce abrasion or scratches on the photoconductive surface necessitating 
replacement thereof. Any of these malfunctions can seriously impair the 
reliability of the printing machine involving a great deal of lost machine 
time and, in the extreme case, result in permanent damage to the machine 
components. To this end, devices have been developed for floating the 
stripper finger on a cushion of air. This requires that the stripping 
fingers be spaced at a substantially constant distance from the 
photoconductive surface. However, a rotating photoconductive drum 
frequently has run-out which causes variations in the spacing between the 
stripping fingers and the photoconductive surface. To overcome this 
problem, the stripping finger has to be mounted movably. Hereinbefore, 
pneumatic devices, such as bellows, controlled the movement of the 
stripping fingers. Systems of this type generally have high spring 
constants requiring a large volume control chamber. This may result in a 
slow system response time causing errors which may result in 
mis-stripping. 
Accordingly, it is a primary object of the present invention to improve the 
sheet stripping apparatus employed in an electrophotographic printing 
machine. 
PRIOR ART STATEMENT 
Various types of devices have hereinbefore been developed to improve the 
sheet stripping system. The following prior art appears to be relevant: 
Stange, U.S. Pat. No. 3,804,401, 4/16/74 
Norton et al., U.S. Pat. No. 3,837,640, 9/24/74 
Bar-on, U.S. Pat. No. 3,891,206, 6/24/75 
Martin, U.S. Pat. No. 3,992,000 11/16/76 
The pertinent portions of the foregoing prior art may be briefly summarized 
as follows: 
Stange discloses a stripping member having a wedge shaped stripping element 
positioned adjacent to the drum surface to affect separation of the paper 
from the drum surface. The stripping member is supported by a gimballed 
spring which holds the wedge shaped stripping element against the 
photoconductive surface. A manifold is connected to an air supply which 
furnishes low pressure air to the stripping element. This produces an air 
cushion on the bottom of the stripping element to float it. The action of 
the spring is opposed to the action of the air pressure. In this manner, 
the striping element pivots conforming to the irregularities in the drum 
surface. 
Norton et al. describes a stripping finger supported on an air cushion. The 
air cushion supports the stripping finger at a uniform distance from the 
drum surface due to the action of springs. The springs urge the stripper 
finger upwardly into contact with the drum surface. Movement of the finger 
normal to the drum is effected by pivoting. The tip portion of the 
stripping finger member extends slightly beyond the point of tangency of 
the drum surface. In this manner, the tip strips the leading edge of the 
sheet from the drum surface. 
Bar-on describes an automatically positionable sheet stripping finger which 
removes individual sheets from a moving photosensitive plate. The 
stripping finger is supported upon a pivotable arm provided with a 
pneumatic sensing nozzle. The nozzle senses variations in the pressure 
between the stripping finger and photosensitive surface. The nozzle, in 
turn, is connected to an amplifier which is arranged to control the 
positioning of the arm in response to the back pressure developed at the 
nozzle. As the stripper finger moves toward or away from the 
photoconductive surface, the back pressure changes causing the amplifier 
to move the arm in a direction so as to restore the stripping finger to 
the desired sheet stripping position. 
Martin discloses a stripping element having bearing surfaces at the leading 
and trailing ends thereof. The stripping element is mounted pivotably 
being resiliently urged toward the surface of the photoreceptor. 
It is believed that the scope of the present application, as defined by the 
appended claims, is patentably distinguishable over the foregoing prior 
art taken either singly or in combination with one another. 
SUMMARY OF THE INVENTION 
Briefly stated and in accordance with the present invention, there is 
provided an apparatus for separating a sheet from a moving member. 
Pursuant to the features of the invention, the apparatus includes a 
stripping member mounted pivotably on a support member. The stripping 
member has a stripping element spaced closely adjacent to the moving 
member and arranged to be interposed between the moving member and sheet. 
Means are provided for detecting the spacing between the stripping element 
of the stripping member and the moving member. A pair of elastomeric 
diaphragms, coupled to the stripping member, are in communication with the 
detecting means. The diaphragms pivot the stripping member in response to 
the detected spacing between the stripping element and the moving member. 
In this manner, the spacing between the moving member and the stripping 
element is maintained substantially constant.

While the present invention will hereinafter be described in connection 
with a preferred embodiment thereof, it will be understood that it is not 
intended to limit the invention to that embodiment. On the contrary, it is 
intended to cover all alternatives, modifications and equivalents as may 
be included within the spirit and scope of the invention as defined by the 
appended claims. 
DETAILED DESCRIPTION OF THE INVENTION 
For a general understanding of an electrophotographic printing machine in 
which the features of the present invention may be incorporated, reference 
is had to FIG. 1 which depicts schematically the various components 
thereof. Hereinafter, like reference numerals will be employed throughout 
to designate identical elements. Although the apparatus for separating the 
sheet of support material from the photoconductive surface after 
transferring the toner powder image thereto is particularly well adapted 
for use in electrophotographic printing, it should become evident from the 
following discussion that it is equally well suited for use in a wide 
variety of devices and is not necessarily limited in its application to 
the particular embodiment shown herein. 
Inasmuch as the practice of electrophotographic printing is well known in 
the art, the various processing stations for producing a copy of an 
original document are represented in FIG. 1 schematically. Each processing 
station will be discussed briefly hereinafter. 
As in all electrophotographic systems of the type illustrated, a drum 10 
having a photoconductive surface 12 entrained about and secured to the 
exterior circumferential surface of a conductive substrate is rotated, in 
the direction of arrow 14, through the various processing stations. One 
type of suitable photoconductive material is described in U.S. Pat. No. 
2,970,906 issued to Bixby in 1961. Preferably, the conductive substrate is 
made from aluminum. 
Initially, drum 10 rotates a portion of photoconductive surface 12 through 
charging station A. Preferably, charging station A utilizes a corona 
generating device, indicated generally by the reference numeral 16, to 
sensitize photoconductive surface 12. Corona generating device 16 is 
positioned closely adjacent to photoconductive surface 12. When energized, 
corona generating device 16 charges at least a portion of photoconductive 
surface 12 to a relatively high substantially uniform potential. For 
example, corona generating device 16 may be of the type described in U.S. 
Pat. No. 2,836,725 issued to Vyverberg in 1958. 
Thereafter, drum 10 rotates the charged portion of photoconductive surface 
12 to exposure station B. Exposure station B includes an exposure 
mechanism, indicated generally by the reference numeral 18, having a 
stationary, transparent platen, such as a glass plate or the like, for 
supporting an original document thereon. Scan lamps illuminate the 
original document. Scanning of the original document may be achieved by 
oscillating a mirror in a timed relationship with the movement of drum 10. 
This mirror is positioned beneath the platen to reflect the light image of 
the original document through a lens onto a mirror, which, in turn, 
transmits the light image through an apertured slit onto the charged 
portion of photoconductive surface 12. Irradiating the charged portion of 
photoconductive surface 12 selectively discharges the charge thereon to 
record an electrostatic latent image corresponding to the informational 
areas contained within the original document. 
Drum 10 next rotates the electrostatic latent image recorded on 
photoconductive surface 12 to development station C. Development station C 
includes a developer unit, indicated generally by the reference numeral 
20, having a housing with a supply of developer mix contained therein. The 
developer mix comprises carrier granules having toner particles adhering 
triboelectrically thereto. The carrier granules are preferably formed from 
a magnetic material with the toner particles being formed from a 
heat-settable plastic. Preferably, developer unit 20 is a magnetic brush 
development system. In a system of this type, the developer mix is brought 
through a directional flux field to form a brush thereof. The 
electrostatic latent image recorded on photoconductive surface 12 is 
developed by bringing the brush of developer mix into contact therewith. 
In this manner, the toner particles are attracted electrostatically to the 
latent image forming a toner powder image on photoconductive surface 12. 
With continued reference to FIG. 1, a sheet of support material is advanced 
by sheet feeding apparatus 22 to transfer station D. Sheet feeding 
apparatus 22 includes a feed roll 24 contacting the uppermost sheet of the 
stack of sheets of support material 26. Feed roll 24 rotates in the 
direction of arrow 28 so as to advance the uppermost sheet from stack 26. 
Registration rollers 30, rotating in the direction of arrow 32, align and 
forward the advancing sheet of support material into chute 34. Chute 34 
directs the advancing sheet of support material into contact with drum 10 
in a timed sequence so that the toner powder image developed thereon 
contacts the advancing sheet of support material at transfer station D. 
At transfer station D, corona generating device 36 applies a spray of ions 
to the backside of the sheet of support material. This attracts the toner 
powder image from photoconductive surface 12 to the sheet of support 
material. However, in addition, it frequently tacks the sheet of support 
material to drum 10. Thus, during the step of transfer, the sheet of 
support material becomes electrostatically tacked to drum 10. In order to 
advance the sheet with the toner powder image thereon to the fusing 
station, it must be separated from drum 10. This is achieved by sheet 
stripping apparatus 38. Sheet stripping apparatus 38 will be described 
hereinafter more fully with reference to FIGS. 2 and 3. 
After transferring the toner powder image to the sheet of support material 
and separating the sheet of support material from drum 10, the sheet of 
support material is advanced to a fusing station E. Fusing station E 
includes a fuser assembly, indicated generally by the reference numeral 
40. Fuser assembly 40 permanently affixes the transferred toner powder 
image to the sheet of support material. After the toner powder image is 
permanently affixed to the sheet of support material, the sheet of support 
material is advanced by a series of rollers 42 to catch tray 44 for 
subsequent removal therefrom by the machine operator. 
Invariably, after the sheet of support material is stripped from 
photoconductive surface 12 of drum 10, some residual toner particles 
remain adhering to photoconductive surface 12. These residual toner 
particles are removed from photoconductive surface 12 at cleaning station 
F. Cleaning station F includes a cleaning system, indicated generally by 
the reference numeral 45. Initially, toner particles are brought under the 
influence of the cleaning system's corona generating device (not shown). 
The corona generating device neutralizes the remaining electrostatic 
charge on photoconductive surface 12 and that of the residual toner 
particles. The neutralized toner particles are cleaned from 
photoconductive surface 12 by a rotatably mounted fibrous brush in contact 
therewith. Subsequent to cleaning, a discharge lamp (not shown) floods 
photoconductive surface 12 with light to dissipate any residual 
electrostatic charge remaining thereon prior to the charging thereof for 
the next successive imaging cycle. 
It is believed that the foregoing description is sufficient for purposes of 
the present application to illustrate the general operation of an 
electrophotographic printing machine. Referring now to the specific 
subject matter of the present invention, FIG. 2 depicts sheet stripping 
apparatus 38 in greater detail. 
As shown in FIG. 2, stripping assembly 38 includes a housing 46 mounted on 
the machine frame. Housing 46 is U-shaped and has a pair of diaphragms 48 
and 50 interposed between opposed legs thereof. Stripping member 52 is 
supported pivotably by pin 54 attached fixedly to housing 46. The tail 
portion 56 of stripping member 52 is interposed between and secured to 
diaphragms 48 and 50. A helical coil spring 58 has one end portion thereof 
connected to tail portion 56 and the other end portion thereof connected 
to housing 46. Stripping element 60 of stripping member 52 is disposed 
closely adjacent to photoconductive surface 12 of drum 10. The surface of 
stripping element 60 opposed to photoconductive surface 12 is spaced a 
substantially constant distance therefrom. Inasmuch as drum 10 has 
run-out, stripping element 60 must move to maintain the spacing between 
the surface thereof opposed to photoconductive surface 12 and 
photoconductive surface 12 substantially constant. Spring 50 resiliently 
urges stripping member 52 to pivot about pin 54 spacing the surface of 
stripping element 60 opposed to photoconductive surface 12 at a nominal 
distance therefrom. Variations in this nominal spacing are detected and 
diaphragms 48 and 50 pivot stripping member 52 so as to compensate for any 
spacing changes. 
A sensing nozzle 62 is provided within the relatively wider main body of 
stripping element 60 with the nozzle orifice facing photoconductive 
surface 12 just above the sheet pick-off region. The nozzle is connected 
to compressor 64 via line 66. Line 66 is also connected to diaphragms 48 
and 50. The mass flow rate of air or gas is controlled by nozzle 62 and 
the spacing of the lowermost portion of surface of stripping element 62 
from photoconductive surface 12. As drum 10 rotates, the run-out thereof 
causes the spacing between photoconductive surface 12 and the surface of 
stripping element 60 opposed therefrom to vary. As this space increases, 
the air flow causes a pressure drop across restrictor 68 and in nozzle 62. 
This decrease in pressure reduces the air pressure in chamber 51 causing 
diaphragms 50 to contract. This pivots stripping member 52 toward 
photoconductive surface 12 so as to maintain the spacing between 
photoconductive surface 12 and the stripping element 60 substantially 
constant. Contrawise, if the distance between stripping element 60 and 
photoconductive surface 12 decreases, the pressure in chamber 51 increases 
causing diaphragm 50 to expand. This results in stripping member 52 
pivoting away from photoconductive surface 12. Stripping member 52 pivots 
sufficiently to return the surface of stripping element 60 opposed from 
photoconductive surface 12 to substantially the original spacing, i.e. a 
pre-determined distance or spacing from photoconductive surface 12 within 
an allowable error band. In this manner, the spacing between the stripping 
element 60 and photoconductive surface 12 is maintained substantially 
constant. It should be noted that the pressure in chamber 49 remains 
substantially constant while the pressure in chamber 51 is variable 
depending upon the spacing between the stripping element 50 and 
photoconductive surface 12. Restrictor 68 acts as a resistance to air flow 
and causes the varying pressures in chamber 51 as affected by the change 
in spacing between photoconductive surface 12 and stripping element 60. 
Compressor 64 furnishes air at a pressure preferably of about 15 psi and 
at a flow rate preferably of about 0.03 cubic feet per minute. Thus, 
movement of stripping member 52 from the nominal position toward or away 
from photoconductive surface 12 causes the pressure in nozzle 62 to vary. 
This, in turn, increases or decreases the pressure within chamber 51. 
Inasmuch as the pressure within chamber 49 remains substantially constant, 
the change in pressure in chamber 51 pivots stripping member 52 about pin 
54 so as to balance the forces exerted by diaphragms 48 and 50. In this 
way, the spacing between photoconductive surface 12 and stripping element 
60 is substantially constant when the forces of diaphragms 48 and 50 are 
in balance with one another. Preferably, diaphragms 48 and 50 are made 
from an elastomeric material having a low spring constant. This insures a 
narrow steady state error band within which stripping member 52 must 
operate in detecting spacing changes. Moreover, this enables the system to 
employ low volume chambers within each of the diaphragms. By way of 
example, diaphragms 48 and 50 are preferably made from rubber, such as are 
manufactured by the Bellofram Corporation of Burlington, Mass. 
In operation, stripping element 60 is supported at a pre-selected distance 
from photoconductive surface 12 within a range of about one-half the 
thickness of the sheet of support material. Stripping element 60 is 
maintained at a substantial uniform distance from photoconductive surface 
12, i.e. within an allowable error band, due to the actions of diaphragms 
48 and 50 in pivoting stripping member 52 about pin 54 so that their 
forces always tend to be in equalibrium with one another. The desire for 
the diaphragms to always return to an equalibrium situation maintains the 
spacing between stripping element 60 and photoconductive surface 12 
substantially constant. The tip portion of stripping element 60 is 
substantially located at the point of tangency of photoconductive surface 
12. In this manner, the tip strips the leading edge of the sheet of 
support material from photoconductive surface 12. 
It will be appreciated that stripping element 60 does not contact 
photoconductive surface 12 during the stripping operation, but is held 
therefrom at a pre-selected distance, within an allowable error band. In 
this manner, stripping element 60 will not damage or otherwise abrade 
photoconductive surface 12. 
Turning now to FIG. 3, there is shown the detailed structure of nozzle 62. 
As depicted therein, the spacing between stripping element 60 and 
photoconductive surface 12 is designated by X. As X increases, the air 
flow causes a pressure drop across d.sub.0 and reduces the pressure 
P.sub.2 in the control chamber of nozzle 62. The pressure P.sub.2 in 
nozzle 62 corresponds to the pressure in chamber 51. Contrawise, the 
pressure P.sub.1 in nozzle 62 corresponds to the pressure in chamber 49 50 
and remains substantially constant. The decrease in pressure P.sub.2 
reduces the upward force exerted by diaphragm 50. Inasmuch as the force 
exerted by diaphragm 48 is now greater than the force exerted by diaphragm 
50, stripping member 52 pivots about pin 54 moving stripping element 60 
toward photoconductive surface 12. This reduces the air flow and increases 
the pressure P.sub.2 to restore diaphragm 50 and 48 to an equalibrium 
condition. This back and forth motion of photoconductive surface 12 due to 
the run-out of drum 10 varies the pressure P.sub.2 pivoting stripping 
member 52 so as to maintain the spacing between stripping element 60 and 
photoconductive surface 12 substantially constant. 
As has hereinbefore been shown, this stripping system provides a 
self-regulating arrangement which will continually position stripping 
element 60 at a substantially constant distance relative to 
photoconductive surface 12 regardless of drum run-out or other 
eccentricities that may be established between the two coacting surfaces. 
The required change in distance is sensed by nozzle 62. In response 
thereto, diaphragms 48 and 50 pivot stripping member 52 to maintain the 
spacing between stripping element 60 and photoconductive surface 12 
substantially constant. 
In recapitulation, it is apparent that pursuant to the features of the 
present invention, as heretofore described, the stripping apparatus pivots 
so as to maintain the stripping element thereof at a pre-selected 
substantially constant distance from photoconductive surface 12. The 
system response time is rapid so as to correct for any drum run-out 
conditions. The foregoing is achieved by a pair of elastomeric diaphragms 
coacting with one another to pivot the stripping member relative to the 
photoconductive surface. 
It is, therefore, evident that there has been provided, in accordance with 
the present invention, an apparatus for separating sheets of support 
material electrostatically tacked to a photoconductive surface. The 
apparatus of the present invention fully satisfies the objects, aims and 
advantages hereinbefore set forth. While this invention has been described 
in conjunction with a specific embodiment thereof, it is evident that many 
alternatives, modifications and variations will be apparent to those 
skilled in the art. Accordingly, it is intended to embrace all such 
alternatives, modifications and variations as fall within the spirit and 
broad scope of the appended claims.