Short paper path copy sheet transport system

In a copier wherein the fuser rolls are positioned closer than the dimensions of the copy sheet from the image transfer area, speed mismatch compensation between the fuser roll nip and the initial image support surface is provided by intentionally driving the fuser roll nip at a different pre-set velocity to form a buckle in the intermediate portion of the copy sheet. The buckle is controlled by a baffle arrangement which allows the buckle to develop in the copy sheet prior to entering the fuser. The buckle is used to absorb the speed mismatch between the initial image support surface and the fuser and thereby prevent smearing of the unfused image on the copy sheet.

BACKGROUND OF THE INVENTION 
This invention relates to a means for transporting a copy sheet from the 
transfer station to the fuser station of a copying machine. More 
particularly, it relates to a short paper path configuration within a 
copier in which copy paper is simultaneously subjected to both transfer 
and fusing of an image. 
In a transfer electrostatographic process such as conventional transfer 
xerography, in which an image pattern of dry particulate unfused toner 
material is transfered to a final image support surface, e.g., a copy 
sheet from an initial image bearing surface, e.g., a charged photoreceptor 
surface developed with toner, the transferred toner is typically only 
loosely adhered to the final support surface after transfer, and is easily 
disturbed by the process of stripping the final support surface away from 
the initial support surface and by the process of transporting the final 
support surface to the toner fusing station. The final support surface 
preferably passes through a fusing station as soon as possible after 
transfer so as to permanently fuse the toner image to the final support 
surface, thereby preventing smearing or disturbance of the toner image by 
mechanical agitation or electrical fields. For this reason, and also for 
reasons of simplifying and shortening the paper path of the copier and 
space savings, it is desirable to maintain the fusing station as close as 
possible to the transfer station. A particularly desirable fusing station 
is a roll type fuser, wherein the copy sheet is passed through a pressure 
nip between two rollers, preferably at least one of which is heated and at 
least one of which is resilient. 
However, when such a fuser roll nip for the final support surface is 
located close enough to the transfer station so that a lead portion of the 
final support surface can be in the fuser roll nip simultaneously with the 
rear or trailing portion of that same final support surface still being in 
contact with the photoreceptor, then a serious problem can arise, to which 
the present invention provides a solution. This problem is that of smears 
or skips in the unfused toner image which has been, or is being, 
transferred to the trailing portion of the final support surface. This 
condition is caused by relative movement or slippage between the initial 
support surface and the final support surface in those areas where they 
are still in contact, i.e., those areas of the final support surface which 
have not yet been stripped away from the initial support surface. A source 
of such slippage is a speed mismatch between the nip speed of the fuser 
rolls (the speed at which the fuser is pulling the lead edge of the paper 
through the fuser) relative to the surface speed of the initial support 
surface. If the fuser roll nip speed is slower, the final support can slip 
backwards relative to the initial image support surface. If the fuser roll 
is faster, the final support material can be pulled forward relative to 
the image on the initial support surface. In either case this can cause 
the aforementioned smears or skips in the toner image being transferred to 
the trailing edge of the final support, or image elongation. 
An exactly equal velocity drive connection between the initial support 
surface and the fuser rolls is difficult to maintain. Also, there is a 
further complication that the actual sheet driving velocity of the fuser 
roll nip can change with changes in the effective diameter of the driving 
roll in the nip. This can occur from replacement of the rollers, or 
changes in the resilient deformation of the rollers due to changes in the 
applied nip pressure, materials aging, temperature effects, etc. In 
addition, paper of different thicknesses travel through a fuser at 
different speeds. Thus, equal speed is difficult to maintain between the 
fuser roll nip and the photorecepter surface in a commercial apparatus and 
may require increased maintenance and speed adjustment mechanisms. 
Where the spacing between the fusing station and the transfer station is 
greater than the dimensions of the copy sheet, and a separate two-speed 
sheet transport is provided therebetween, then substantially different 
fuser roll nip speeds can be provided, as in U.S. Pat. No. 3,794,417, 
issued Feb. 26, 1974, to J. A. Machmer. However, this has the noted 
disadvantages of requiring additional space, increased unfused image sheet 
handling, and also the additional complexity and expense of the additional 
transport mechanism. 
It is known in the electrostatographic copying art to form a buckle in a 
copy sheet in its movement through the copier at other locations and for 
other functions. For example, it is known to interrupt the forward 
movement of a copy sheet with registration fingers and to form a buckle in 
the copy sheet by its continued feeding by upstream feed rollers to 
provide registration of the lead edge of the copy sheet before the copy 
sheet is fed into the image transfer station, e.g., U.S. Pat. No. 
3,601,392, issued Aug. 24, 1971, to Merton R. Spear, Jr., et al. It is 
also known to provide for pre-form a buckle in a web of copy material to 
compensate for the braking of the web during a cutting operation in which 
the web is cut into individual sheets, e.g., U.S. Pat. No. 3,882,744, 
issued May 13, 1975, to Alan F. McCarroll. The later patent also 
illustrates that the copy web may be pre-formed into an initial convex 
buckle over an apertured surface and that air pressure may be utilized to 
expand the buckle when the web is stopped downstream thereof. 
U.S. Pat. No. 3,774,907, issued Nov. 27, 1973, to Stephen Borostyan 
illustrates a vacuum sheet stripping device for removing copy sheets from 
the initial image support member and advancing them to a roll fuser, 
wherein the copy sheets assume a convex shape. A rotating cylindrical 
apertured vacuum member is utilized, to which the copy sheet is attracted. 
During a portion of its rotation, the vacuum is automatically cutoff to 
the vacuum stripping member to release the copy sheet. 
U.S. Pat. No. 3,508,824, issued Apr. 18, 1970, to R. K. Leinback et al. 
describes a conductive curved guide plate for attracting a copy sheet at 
the stripping area and guiding it towards a fusing station. 
The present invention provides a speed mismatch compensation system which 
allows the fusing roll nip to be closely spaced from the transfer station 
of a printer or copier, by a distance less than the movement dimension of 
an individual copy sheet, to provide the above-stated advantages of such a 
system, yet overcome or substantially reduce the above-stated 
disadvantages thereof. The intermediate portion of the copy sheet is 
selectively supported and guided in a series of critically positioned 
baffles and guides which accommodate a speed differential between the 
fuser roll nip velocity and the velocity of the initial image support 
surface. A speed variation and differential is accommodated between the 
leading edge and trailing edge areas of the same final image support 
surface, in a manner which avoids disturbance of the unfused toner image 
in any area thereon.

Referring now to the drawings, and specifically to the embodiment 10 of 
FIGS. 1-4, it may be seen that the xerographic transfer, stripping and 
roll fusing system illustrated therein is generally similar in many 
respects to commercially available xerographic copiers. Accordingly, the 
following description will be directed to the novel aspects of the 
embodiment providing the above-discussed speed mismatch compensation. 
However, briefly describing the conventional aspects of the disclosed 
system 10, it may be seen that a copy sheet 12 as shown in FIG. 2 is 
sequentially brought into contact with, and transported at the same speed 
as, the image bearing surface 14 of a moving photoreceptor belt 16. The 
copy sheet 12 passes under a transfer corona generator 18, preferably a 
pin corotron, which applies electrostatic transfer charges to the back of 
a the sheet and electrostatically tacks the copy sheet against the surface 
of photoreceptor belt 16. The copy sheet is then transported on the 
photoreceptor 16 under a detacking corona geneator 20 which substantially 
reduces the charge thereon, preferably with a pin corotron. It should be 
understood that the detacking corona generator is optional. The lead edge 
of the copy sheet is then self stripped from photoreceptor belt 16 due to 
the sharp curvature given the belt by stripper roller 31, which preferably 
has a 0.75" diameter. 
Turning now to the major areas of differences between the system 10 and 
prior systems of this type, an optimized multiple baffle arrangement and 
configuration is disclosed in FIGS. 1-4 and adapted such that an incoming 
sheet stripped from belt 16 by roll 31 always hits passive acquisition 
baffle first, then hits the bottom baffle 41, slides up the bottom baffle 
to fuser 50 and into the fuser nip formed between fuser roll 51 and backup 
roll 52 and matches the fuser nip speed by buckling into the passive 
baffle 41 and prefuser baffle 42. The baffle arrangement could be made of 
one piece if desired. 
A conventional direct mechanical drive interconnection (not shown) is used 
to connect the axis of one of the fuser rolls and the axis of the drive 
roll 30 for photoreceptor belt 16. This drive interconnection is provided 
with a suitable difference pulley or gear diameters to provide a slightly 
slower speed for the fuser roll nip 53 than for the photoreceptor belt 16 
in the transfer station. Thus, as the copy sheet 12 is advanced thrugh the 
fuser nip 53, the lead edge of the sheet is moving downstream at a 
slightly slower velocity than the intermediate and trailing areas of the 
same copy sheet are being advanced downstream by the photoreceptor belt 
16. This would cause a potential force for slippage beteen the copy sheet 
12 and belt 16, which would cause toner image smears or skips or 
elongation of the image except that the system 10 provides means to allow 
the intermediate portion of the copy sheet 12, between the fuser roll nip 
and the stripping roll, to form a buckle away from its imaged side and 
away from paper guide 42. The baffle arrangement is designed to allow the 
buckle of the sheet 12 to expand freely out to a maximum position to take 
up or absorb the full accumulated speed mismatch or differential of the 
entire copy sheet 12 until the trail edge of the copy sheet is removed 
from the photoreceptor. The buckle is always concave and expands further 
concavely as the copy sheet advances after having reached the fuser roll 
nip. 
In reference to the novel baffle arrangement in FIG. 1, a sheet is stripped 
from photoreceptor 16 due to a detacking current from corotorn 20 and the 
sharp curve that the photoreceptor follows around stripping roll 31. In 
addition, the photoreceptor is mounted on drive roll 30 and stripper roll 
31 at an angle of 15.degree. with a line drawn horizontally and tangent to 
stripper roll 31. This positioning of the photoreceptor in addition to 
enhancing stripping, works in conjunction with the baffle arrangement 40 
to provide a smooth nonsmear transition for a copy sheet from the transfer 
point on the photoreceptor through the fuser. More particularly, and in 
accordance with the present invention, after a sheet is stripped from the 
photoreceptor as shown in FIG. 2, it is attracted by passive acquisition 
baffle 41 from the position shown in dotted lines in FIG. 3 to provide 
paper and strip point control after stripping due to the attraction. The 
passive acquisition baffle is grounded and aids in stripping the sheet 
from the photoreceptor because it acts as a ground plane resulting in 
electrostatic attraction between paper with a charge density and the 
baffle. Also, a conductive metal or a dielectric baffle will work equally 
well in the present invention. The passive acquistion baffle is most 
effective when the paper charge is high (no detack) and dimensions A and B 
(shown in FIG. 1) are small. For example, most machine space constraints 
would limit dimension A to 7 mm and B to 2 mm. Dimension C is preferably 
1.5 mm. Isolating the passive acquistion baffle from ground allows it to 
charge to the same polarity as the sheet passing thereover due to contact 
resulting in electrostatic repulsive forces between the paper and the 
baffle. The passive acquisition baffle is made from a polished austenitic 
stainless steel annealed sheet of 1 mm thickness. A high impedance member 
56 is positioned between the passive acquisition baffle and ground in 
order to stop current leakage from the transfer corotron in high humidity 
environments. The high impedance member could be a zener diode, R.C. 
circuit, voltage source, resistor or any other suitable impedance means. 
After leaving the passive acquisition baffle, the copy sheet strikes 
upwardly inclined pre-fuser baffle 42 at an angle of approximately 
30.degree. as shown in dotted lines in FIG. 1 and by copy sheet 12 in FIG. 
4. Pre-fuser baffle 42 is made from a carbon steel sheet with a polished 
electroless nickel plate and has a thickness of about 1.5 mm. Continued 
driving of the copy sheet by the photoreceptor belt causes it to buckle in 
the chamber formed by passive baffle 41, pre-fuser baffle 42 and paper 
guide 43 as more clearly shown in FIG. 5. Paper guide 43 is preferably in 
wire form with very little solid area so that it does not attract the 
paper. It also serves as a redundant stripper to prevent paper jams. The 
15.degree. tilt away from the horizontal of the photoreceptor belt, the 
configuration of the top surface of passive baffle 41 that is slanted 
toward pre-fuser baffle 42, the angling of the pre-fuser baffle upward 
toward fuser nip 53 and canting the fuser nip by 6.degree. 
counterclockwise all serve to insure that the copy sheet is buckled toward 
and along the surface of the pre-fuser baffle thereby insuring that the 
imaged side of the copy sheet will not be disturbed by paper guide 42 nor 
will that portion of the image still being fed by the photoreceptor be 
smudged since the sheet has plenty of room to buckle before resistance is 
encountered. Fuser rolls 51 and 52 will take control of the copy sheet and 
transport it toward an output area thereby controlling buckle resistance 
of the copy sheet and smearing or smudging of the imaged surface of the 
copy sheet against the photoreceptor. A pre-clean corona generator 22 is 
shown for preparing residual toner left on the photoreceptor after image 
transfer for cleaning by a cleaning brush or other conventional cleaning 
means. 
A low cost, highly efficient means for transporting copy sheets from a 
transfer station to a fuser station in a copier or printer is disclosed 
that makes far more compact machine architectures and faster first copy 
out times because the distance from the photoreceptor strip point to the 
fuser is much less than the length of a copy sheet. This short paper path 
is enabled by a flexible photoreceptor belt and incorporates high 
electrostatic tacking forces between the copy sheet and the photoreceptor 
in the transfer zone due to the transfer field acting over a large area. 
This drives the copy sheet to the fuser. The highly efficient transport 
means of the instant invention comprises a baffle configuration that 
allows a concaved buckle to develop in the copy sheet prior to the copy 
sheet entering the fuser. The buckle is used to absorb the speed mismatch 
between the photoreceptor and the fuser. While the apparatus and steps 
disclosed herein are preferred, it will be appreciated that numerous 
variations and improvements may be made without significantly departing 
from the scope of the invention by those skilled in the art. The following 
claims are intended to cover all such variations and improvements as fall 
within the spirit and scope of the invention.