Exit tray corrugation slip rolls with a variable force idler

An apparatus and method that describes utilizing a corrugation slip nip system, including a variable force idler that encompasses three stages, to prevent buckling of copy sheets traveling at a high rate of speed upon exiting from a high speed printing machine to the exit tray for stacking. Buckling concerns are eliminated by allowing the sheet, driven by a high speed positive drive nip, to slip through the slower speed corrugation nip, yet still having enough drive force in the slip nip to drive the sheet into the exit tray. In order to vary the normal force on the sheet, a three stage variable force idler is used. The first stage oversizes the inner diameter of the idler rollers on the idler shaft. The second stage uses a slot in the spring which allows the idler shaft to move upward without deflecting the spring. These first two stages are particularly adapted for light weight paper. The third stage occurs when the idler shaft is topped out in the shaft slot such that the paper deflects the spring causing additional force to be applied to the paper to drive the paper out of the system and into the exit tray. The third stage is reached only where heavy weight paper is used because heavy weight paper has sufficient beam strength to deflect the spring.

BACKGROUND OF THE INVENTION 
This invention relates generally to exit tray corrugation in printers or 
copiers, and more particularly concerns a three stage variable force idler 
for exit tray corrugation. 
As xerographic copiers and printers of all kinds increase in speed, it is 
increasingly important to provide copy sheet output devices that can 
reliably stack copy sheet output devices that can reliably stack copy 
sheet output from such machines. At present, some machines feed copy 
sheets to stacking trays at such high rates that jams are caused in the 
trays because preceding sheets do not have time to settle to the bottom of 
the stacking tray before succeeding sheets are forced into the trays by 
the transport systems of the machines. Stacking problems occur when the 
exit rolls send the copy sheet so far up the stacking ramp that the 
following copy sheet runs into the trail edge of the previous copy sheet 
before the previous copy sheet has an opportunity to settle down the 
stacking ramp. Also, the trail edge of preceding copy sheets are sometimes 
lifted up and out of the stacking tray by the lead edges of incoming 
sheets because of a small interdocument sheet gap. 
The following disclosures may be relevant to various aspects of the present 
invention and may be briefly summarized as follows: 
U.S. Pat. No. 5,280,901 to Smith et al. discloses a sheet feeding and 
corrugating system, especially for output of image substrate sheets of a 
reproduction apparatus, wherein the sheets are fed in a normal path 
through a sheet feeding nip comprising plural spaced sheet feeding 
rollers. Both feeding and variable corrugation of flimsy or stiff sheets 
is provided by spherical balls freely mounted in generally vertical ball 
retainers providing for vertical movement and dual axis rotation against 
the sheet feeding rollers to define the sheet feeding nip and by 
additional similar balls (in additional similar ball retainers) 
intermediately of the feed rollers, which additional balls are unsupported 
vertically except by bottom-of-travel retainers so that these additional 
intermediate balls roll gravity-loaded against a sheet being fed through 
the nip to provide sheet corrugation varying automatically with the 
stiffness of the sheet, and are freely liftable up to the level of the nip 
by stiff sheets resisting corrugation. These balls may be readily added to 
or removed to independently increase or decrease the sheet nip and/or 
corrugation forces at their respective locations transverse the nip. A 
sheet side shifting mechanism can laterally offset the sheets in the same 
nip to eject offset, by moving only the sheet feeding rollers, without 
resistance from the stationarily mounted balls, all of which roll freely 
laterally as well in the normal feeding direction. 
U.S. Pat. No. 4,789,150 to Plain discloses a sheet stacking apparatus for 
use with throughput from high speed copiers or printers includes dual 
independently acting control flaps that provide positive control of sheets 
being stacked in the apparatus by controlling the trail edges as well as 
the entire sheets as they are fed into a catch tray. 
Xerox Disclosure Journal entitled "Sheet Skewing Systems for Passive 
Decelerating Eject Rolls" by B. Mandel et al, Vol. 17, No. 3, May/June, 
1992, pp. 135-137, discloses non-nip corrugation systems with common size 
passive decelerating eject rolls that insure proper registration in an 
up-hill compiling tray by skewing sheets. 
SUMMARY OF INVENTION 
Briefly stated, and in accordance with one aspect of the present invention, 
there is provided an apparatus for corrugating copy sheets travelling at 
high rates of the speed toward an exit tray, comprising: an idler shaft; 
idler rollers defining an aperture centrally located in the idler rollers 
for the idler shaft to be placed therethrough; a drive shaft containing 
drive rollers thereon with the drive shaft being adjacently positioned 
relative to the idler shaft such that one of the drive rollers is 
positioned between two of the idler rollers; and means for applying 
different forces on the copy sheets passing between the idler rollers and 
the drive rollers. 
Pursuant to another aspect of the present invention, there is provided a 
method for corrugating copy sheets traveling at high rates of speed, in a 
printing machine, by sending the copy sheets, having a weight thereto, 
between idler rollers, located on an idler shaft, and drive rollers, 
located on a drive shaft, the idler shaft and the drive shaft are 
positioned adjacent to one another, comprising: moving each of the copy 
sheets between the idler rollers and the drive rollers for slowing down 
the speed of the copy sheets upon; varying force applied to the copy 
sheets according to the weight of the copy sheets; and stacking the copy 
sheets in an exit tray.

DETAILED DESCRIPTION OF THE INVENTION 
Reference is now made to the drawings where the showings are for the 
purpose of illustrating a preferred embodiment of the invention and not 
for limiting same, the various processing stations employed in the 
printing machine illustrated in FIG. 5 will be briefly described. 
Referring now to FIG. 5, printer section 8 comprises a laser type printer 
and for purposes of explanation is separated into a Raster Output Scanner 
(ROS) section 87, Print Module Section 95, Paper Supply section 107, and 
Finisher 120. ROS 87 has a laser, the beam of which is split into two 
imaging beams 94. Each beam 94 is modulated in accordance with the content 
of an image signal input by acousto-optic modulator 92 to provide dual 
imaging beams 94. Beams 94 are scanned across a moving photoreceptor 98 of 
Print Module 95 by the mirrored facets of a rotating polygon 100 to expose 
two image lines on photoreceptor 98 with each scan and create the latent 
electrostatic images represented by the image signal input to modulator 
92. Photoreceptor 98 is uniformly charged by corotrons 102 at a charging 
station preparatory to exposure by imaging beams 94. The latent 
electrostatic images are developed by developer 104 and transferred at 
transfer station 106 to a print media 108 delivered by Paper Supply 
section 107. Media 108, as will appear, may comprise any of a variety of 
sheet sizes, types, and colors. For transfer, the print media is brought 
forward in timed registration with the developed image on photoreceptor 98 
from either a main paper tray 110 or from auxiliary paper trays 112, or 
114. The developed image transferred to the print media 108 is permanently 
fixed or fused by fuser 116 and the resulting prints discharged to either 
output tray 118, or to output collating trays in finisher 120. Finisher 
120 includes a stitcher 122 for stitching (stapling) the prints together 
to form books, a thermal binder 124 for adhesively binding the prints into 
books and a stacker 125. A finisher of this type is disclosed in U.S. Pat. 
No. 4,828,645 and 4,782,363 whose contents are hereby incorporated by 
reference. 
Reference is now made to FIG. 1, which shows an elevational schematic view 
of an exit tray system incorporating the present invention. A drive shaft 
40 and idler shaft 12, 30 are positioned in adjacent proximity to one 
another so that a copy sheet can be corrugated between them. The drive 
shaft 40 contains a drive roller 20 between two corrugation rolls 22 (e.g. 
polyurethane material). An end plate 46 and a pulley 45 are present on 
either end of the drive shaft 40. 
With continued reference to FIG. 1, the drive roller 20 is positioned 
adjacent the inner idler shaft 30 between a pair of idler rollers 10. The 
copy sheet passes between the idler rollers 10 and the drive rollers 20 as 
the copy sheet heads toward the exit tray 118. The inner idler shaft 30 
between the two idler rollers 10 has an outer diameter at least 2 mm 
greater then the outer diameter of the end idler shaft 12. A step is 
formed in the idler shaft where the inner idler shaft 30 and the end idler 
shaft 12 meet. 
Reference is now made to FIG. 2, which shows a front elevational view of 
the idler rollers relative to drive roller. A drive roller 20, located on 
a drive shaft 40, is positioned between a pair of idler rollers 10, 
located on an idler shaft, for corrugation of a copy sheet passing 
therethrough. The outer diameter, OD, of the inner idler shaft 30 is 
greater than the outer diameter of the end idler shaft 12 (see FIG. 1) 
that passes through the bored out idler roller 10. Slots 55 are present in 
the spring 50 for corrugation adjustments for the copy sheet passing 
through. 
As the speeds of printing and copying machines continue to increase, the 
exit speeds (e.g. 1300 mm/s) of the copy sheet increase. This increase in 
exit speed creates stacking problems due to the sheets exiting at such a 
high rate of speed that the sheets cannot be contained in the output tray. 
Further complications arise from sheet buckling. In the present invention, 
the exit speed of the sheets is reduced by slowing down the last nip 
before exit into the tray. A corrugation drive system is used, which 
contains a three stage variable force idler of the present invention, to 
slow down (i.e. to less than 950 mm/s) the exit speed of the sheets. 
However, while the present invention reduces the exit speed of the copy 
sheet, the reduction in speed is not sufficient to use all of the 
Interdocument gap that would cause the copy sheets to collide with one 
another. Buckling of the copy sheet concerns arise when a copy sheet is 
driven from the faster positive nip into a reduced speed nip of the exit 
tray. This problem is eliminated using the present invention. In the 
present invention, the corrugation system enables the positive drive nips 
to drive the sheet through the corrugation nips, while still allowing the 
nips enough drive at the lower speed to move the sheet into the exit tray. 
Experimentation has also shown that the present invention improves 
stacking at existing exit speeds (e.g. about 750 mm/s). 
Reference is now made to FIGS. 3A, 3B, and 4 which show the three stages of 
the variable force idler of the present invention. Present corrugation 
systems provide excessive force on light weight paper (e.g. about 16 
lbs.), causing sheet damage, in order to provide the required force for 
driving heavyweight paper (e.g. about 110 lbs.). Thus, the present 
invention provides a variable force loading system to vary the drive force 
needed depending upon the paper weight being used. Also, due to problems 
involving stubbing of the lead edge of the copy sheet into the corrugation 
nips, the present invention has a minimal initial normal force on the copy 
sheet, so that the copy sheet (e.g. paper) enters the nip without having 
to deflect the entire weight of the idler shaft and the spring 50. The 
first two stages of the present invention, shown in FIGS. 3A and 3B, occur 
for light weight paper. The third stage, shown in FIG. 4, of the variable 
idler force is only required for heavy weight paper. The beam strength of 
the paper through the corrugation nip determines how many of the three 
stages are used in the present invention. Each copy sheet goes through the 
variable force idler which enables copy sheets of various paper weights to 
be used during a print run without requiring separation according to paper 
weight. 
Referring now to FIG. 3A, stage one of the variable force idler involves an 
oversizing of the inner diameter hole 11, 1D, of the plastic idler rollers 
10 on the end idler shaft 12 by approximately 1 mm .+-.0.05 mm. For 
example, if the ID of the idler roller is about 5 mm, then the outer 
diameter of the end idler shaft must be about 4 mm to provide the 1 mm of 
play therebetween. This 1 mm of play between the end idler shaft 12 and 
the inner diameter 11 of the idler roller 10 allows light weight paper 
(e.g. about 16 lbs.), in particular, to enter the corrugation nip without 
having to deflect a significant force. The only force acting upon the 
light weight paper at this point is the weight of the plastic (e.g. 
polycarbonate) idlers. 
Referring now to FIG. 3B, stage two of the variable force idler involves a 
slot 51 in the spring 50 which allows the idler shaft which contains the 
idlers to be raised upward without deflecting the spring 50 (shown in 
phantom). This allows light weight paper, in particular, to pass through 
the corrugating nip system without experiencing excess force from the 
spring 50. In this stage, the light weight paper receives the necessary 
normal force required to make the corrugation system effective without 
causing copy sheet damage. 
Reference is now made to FIG. 4, the third and final stage of the variable 
force idler is when the idler shaft 12, 30 has been raised to the highest 
point (i.e. topped out) in the slot 55 (see FIG. 2). (This normally occurs 
when a heavy paper weight is used.) Then, the paper, having sufficient 
beam strength, begins to deflect the leaf spring 50, which provides 
additional force to the paper or copy sheet. (The deflection of the spring 
50 is shown in phantom lines and arrow 60 shows the deflection movement.) 
This added force is necessary to drive heavy weight paper out of the 
corrugating system and into the tray 118 (see FIG. 1). 
With continued reference to FIG. 4, the spring 50 is mounted on a bracket 
61 by a mounting screw 62 which allows for spring adjustment in the 
directions shown by the arrow 63 directions. The slot 51 has about a 1 mm 
slot tolerance about the end idler shaft 12 to allow movement of the idler 
shaft 30, 12 to provide the ideal force for light weight paper without 
experiencing the additional force of the spring used for paper of heavier 
weight. 
The present invention, upon initiation, provides an ideal corrugation for 
light weight paper in stages one and two and the heavy weight paper is 
compensated for by the springs in the third stage. Each of the two drive 
rolls have one of the spring idler systems shown in FIG. 4, which can be 
adjusted or set-up using spring mounting features. 
In recapitulation, the present invention utilizes a reduced speed 
corrugation drive roll system, in combination with a variable force idler 
that encompasses three stages, to prevent buckling of copy sheets 
traveling at a high rate of speed on exit from the printing machine to the 
exit tray for stacking. Buckling concerns are eliminated by allowing the 
sheet, driven by a high speed positive drive nip, to slip through the 
slower speed corrugation nip, yet still having enough drive force in the 
slip nip to drive the sheet into the exit tray. In order to vary the 
normal force on the sheet, a three stage variable force idler is used. The 
first stage oversizes the inner diameter of the idler rollers on the idler 
shaft. The second stage uses a slot in the spring which allows the idler 
shaft to move upward without deflecting the spring. The third stage occurs 
when the idler shaft is topped out in the shaft slot such that the paper 
deflects the spring causing additional force to be applied to the paper to 
drive the paper out of the system and into the exit tray. These first two 
stages are for light weight paper. The third stage is reached only where 
heavy weight paper is used because heavy weight paper has sufficient beam 
strength to deflect the spring. 
It is, therefore, apparent that there has been provided in accordance with 
the present invention, a variable force idler for corrugating that fully 
satisfies the 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 
that fall within the spirit and broad scope of the appended claims.