Apparatus for feeding both cut sheet and fan fold paper in a printer

An apparatus for feeding paper in a printer adapted to utilize both fan fold paper and cut sheet paper includes a push tractor for feeding fan fold paper. A print head is positioned downstream of the push tractor along the paper path. A paper feed roller is positioned intermediate the push tractor and the print head. The feed roller selectively feeds paper towards the print head. A discharge roller is positioned downstream of the print head for feeding paper. The apparatus detecting the type of paper being fed and varying the pressure utilized by the feed roller to feed the paper in response thereto.

BACKGROUND OF THE INVENTION 
The present invention relates to an apparatus for feeding both cut-sheet 
and fan fold sheet paper within a printer, and in particular to preventing 
the slack formed in paper fed in a printer. 
A conventional paper feeding apparatus as shown in FIG. 1 includes a print 
head 106. A push tractor 101 feeds fan fold paper 102 downstream in the 
direction of arrow G to print head 106. A pair of feed rollers 103 are 
positioned on the downstream side of print head 106. Cut sheet paper is 
fed by feed rollers positioned upstream of print head 106 in conjunction 
with feed rollers 103. 
The conventional paper feeding apparatus has been satisfactory. However, 
there is a large space between push tractor 101 and feed rollers 103 to 
allow for feeding a cut sheet to print head 106. Therefor, when fan fold 
sheet 102 is fed by push tractor 101, as fan fold paper 102 travels in the 
direction of arrow G toward feed rollers 103 slack is likely to occur in 
the paper. This results from the fact that the paper travels such a large 
distance unsupported. This slack does not become removed until fan fold 
paper 102 has been fed for several lines to as many as ten lines after the 
leading edge of fan fold paper 102 has reached feed rollers 103. Because 
the paper feed rate fluctuates due to the slack, the printing dot produced 
on the paper by print head 106 cannot be located accurately on fan fold 
paper 102 during this slack and slack recovery period. As a result, high 
precision printing cannot be guaranteed. 
Accordingly, it is desired to provide a paper feeding apparatus which 
overcomes the disadvantages of the prior art device described above by 
providing an intermediate paper feeding structure to eliminate slack 
during the feeding of fan fold paper. 
SUMMARY OF THE INVENTION 
Generally speaking, in accordance with the present invention, an apparatus 
for feeding paper within a printer adapted to utilize both fan fold and 
cut sheet paper is provided. The apparatus for feeding paper includes a 
push tractor for feeding fan fold paper. A print head is positioned 
downstream in the paper feeding direction from the push tractor. A first 
feed roller is disposed intermediate the push tractor and the print head 
for feeding both cut sheet paper and fan fold paper towards the print 
head. The first feed roller applies a variable pressure to the paper to be 
fed. A second feed roller is located downstream in the paper feeding 
direction from the print head for feeding the paper. The first feed roller 
feeds the paper until the paper has reached the second feed roller. The 
first feed roller then disengages from the paper to allow feeding by the 
second feed roller when fan fold paper is being used. 
When a cut sheet is being fed through the apparatus, the first feed roller 
does not disengage when the second feed roller engages the paper. 
Additionally, a greater pressure is applied by the first feed roller when 
cut sheet paper is being fed. 
Accordingly, it is an object of this invention to provide an improved 
apparatus for feeding both fan fold and cut sheet paper within a printer. 
Another object of this invention is to provide an apparatus for feeding fan 
fold paper within a printer in which print dots may be placed on the paper 
with high precision by enhancing the sheet feed precision. 
Yet another object of the invention is to provide an apparatus for feeding 
fan sheet paper in a printer adapted to use both fan fold and cut sheet 
paper which eliminates slack when feeding fan fold paper. 
Still other objects and advantages of the invention will in part be obvious 
and will in part be apparent from the specification and drawings. 
The invention accordingly comprises the features of construction, 
combination of elements, and arrangement of parts which will be 
exemplified in the construction hereinafter set forth and the scope of the 
invention will be indicated in the claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Reference is first made to FIG. 2, wherein an apparatus for feeding paper 
in a printer adapted to utilize both cut sheet and feed paper, generally 
indicated at 200, and constructed in accordance with the present 
invention, is depicted. Apparatus 200 includes a frame 50. A guide shaft 3 
is mounted on frame 50. A carriage 2 is slideably mounted on guide shaft 3 
and a print head 1 is mounted on carriage 2. A motor 4 mechanically 
coupled to carriage 2 moves carriage 2 along guide shaft 3 in a printing 
direction. A platen 8 is supported on frame 50 within the paper path. 
A pair of push tractors 18 include pins which engage perforations provided 
on opposite edges of fan fold paper 7. Push tractors 18 are positioned 
upstream of printing head 1 in the paper path. A motor 9 is mounted on 
frame 50 by supports 55. A first gear 10 is rotated by motor 9. A second 
gear 11 engages gear 10 and a gear 12 so that motor 9 causes gear 12 to 
rotate. Gear 12 is coupled to the lower (FIG. 2) or downstream of tractor 
shafts 19 for driving push tractors 18. Tractor shafts 19 are rotatably 
supported on frame 50. Tractors 18 are mounted on tractor shafts 19, are 
axially shiftable relative to tractor shafts 19 and the sprocket belts 
(not shown) thereof rotate with tractor shafts 19. 
A feed roller shaft 21 is mounted on frame 50 substantially parallel to 
guide shaft 3. First feed rollers 20 are mounted on feed shaft 21 and are 
disposed within the paper feed path intermediate print head 1 and tractors 
18. A gear 13 is coupled to gear 10 and a gear 14. Gear 14 is coupled to 
feed shaft 21 so that feed shaft 21 is also rotated by motor 9. 
A discharge roller shaft 23 is mounted on frame 50 within the paper feed 
path downstream of print head 1. Discharge rollers 22 are mounted on 
discharge roller shaft 23. A belt pulley 16 is affixed to discharge roller 
shaft 23. A belt pulley 15 is integrally formed with gear 14 affixed to 
feed shaft 21. Belt pulley 15 is coupled to belt pulley 16 by a timing 
belt 17 so that discharge roller 23 is simultaneously rotated with gear 
14. 
Reference is now made to FIG. 3a in which a side elevational view of 
apparatus 200 is provided. A shaft 26 is mounted below the paper path 
parallel to feed roller 20. A pressure roller 24 for acting in cooperation 
with feed roller 20 is mounted on shaft 26. Pressure roller 24 selectively 
comes in pressure contact with feed roller 20. Similarly, a shaft 27 is 
supported on frame 50 below the paper feed path parallel to discharge 
rollers 22. A pressure roller 25 for coming in contact with discharge 
rollers 22 is provided. Pressure rollers 24, 25 are rotatably journaled on 
shafts 26, 27 respectively and therefor rotate when fan fold paper 7 is 
forwarded past pressure rollers 24, 25. 
Pressure roller 24 may be moved in three stages towards feed roller 20 and 
is thus positionable in accordance with the desired pressure corresponding 
to the type of paper being fed. A detector 6 is provided downstream of 
pressure roller 24 and upstream of print head 1. Detector 6 recognizes the 
leading edge of fan fold paper 7 as well as the position of the leading 
edge and detects the trailing edge of the paper being fed. 
Reference is now made to FIGS. 4a-4c wherein the movement of pressure 
roller 24 is depicted. A step motor 30 supported on frame 50 is coupled to 
a gear 31. A gear 32 meshes with a gear 31 and gear 33. A square shaft 34 
is disposed eccentrically on gear 33. A leaf spring 36 extends across 
square shaft 34 and beneath rotatable shaft 26. As seen in FIG. 4a, square 
shaft 34 is supported at one end on frame 50, the other end being free. At 
the position depicted in FIG. 4a of square shaft 34 does not come in 
contact with leaf spring 36. Accordingly, leaf spring 36 acts only to bear 
the weight of pressure roller 24 at a distance from feed roller 20. In 
this position, feed roller 20 and pressure roller 24 do not exert an 
influence on paper passing therebetween. When motor 30 rotates in the 
direction indicated by arrow A as seen in FIG. 3b, gear 31 rotates in the 
direction indicated by arrow C, gear 32 rotates in the direction indicated 
by arrow D causing gear 33 and square shaft 34 to rotate in the direction 
indicated by arrow B. Because square shaft 34 is disposed eccentrically on 
gear 33, leaf spring 36 is forced upward by square shaft 34 and is rotated 
about its free end shifting pressure roller 24 in the direction indicated 
by arrow F.sub.1. In this position, pressure roller 24 exerts a moderate 
pressure against feed roller 20, preventing the pressure between the 
rollers from leaving an impression on sensitive paper. The eccentricity of 
square shaft 34 relative to gear 33 is set so that leaf spring 36 is 
deflected moderately causing a feeding force from feed roller 20 on the 
paper being fed. 
As shown in FIG. 4c when motor 30 is further rotated in the direction of 
arrow A, square shaft 34 is rotated in the direction indicated by arrow D. 
The eccentricity of square shaft 34 is determined to allow a greater 
deflection of leaf spring 36 by this further rotation. Accordingly, the 
force applied on rotatable shaft 26 by leaf spring 36 becomes greater and 
the force applied by pressure roller 24 in the direction of arrow F.sub.2 
is greater than the force applied in the direction of arrow F.sub.1, 
providing a satisfactory force for feeding paper between feed roller 20 
and pressure roller 24. 
Reference is now made to FIGS. 3a-3d wherein operation of the invention is 
illustrated. The pins of tractor 18 engage fan fold paper 7 to feed fan 
fold paper 7 in the direction of arrow K so that the leading edge of fan 
fold paper 7 is adjacent feed roller 20 as shown in FIG. 3a. At this 
stage, pressure roller 24 is separated from feed roller 20 and thus exerts 
no influence on fan fold paper 7. 
Fan fold -paper 7 continues to travel along the paper feed path in the 
direction of arrow K until the leading edge of fan fold paper 7 is 
detected by detector 6 positioned between feed rollers 20 and print head 
1. Fan fold paper 7 has now traveled a distance V.sub.1 between tractor 18 
and a position at which detector 6 detects the leading edge of fan fold 
paper 7 as seen in FIG. 3d. This distance is substantially one half the 
distance V.sub.2 corresponding to the distance between discharge roller 22 
and push tractor 18. The distance V.sub.1 is short enough so that all of 
the feeding force required to reach feed roller 20 may be supplied by 
tractor 18 and the stiffness of fan fold paper 7 will prevent the paper 
from becoming slack as it travels. 
When the leading edge of fan fold paper 7 is detected by detector 6 motor 
30 rotates to shift pressure roller 24 to apply a force F.sub.1 as seen in 
FIG. 3b. Feed roller 20 provides a driving force to feed fan fold paper 7 
by the pressure exerted on fan fold paper 7 by roller 20 and pressure 
roller 24. Fan fold paper 7 is now driven at two points along the paper 
path by feed roller 20 and push tractor 18. The stiffness of fan fold 
paper may now be used to prevent slack within fan fold paper 7 between the 
intermediate drive point represented by drive roller 20 and the end drive 
point at discharge roller 22. Accordingly, no slack occurs in fan fold 
paper 7 as it travels the distance V.sub.3. 
When paper is driven by drive roller 20, discharge roller 22 and push 
tractor 18, the driving force obtained by push tractor 18 is an additional 
driving force which is not required when driving cut sheet paper. 
Accordingly, due to this additional driving force applied by tractor 18, 
drive roller 20 need not exert such a great influence on fan fold paper 
being fed. Therefor, pressure roller 4 need push against feed roller 20 
with only a moderate amount of pressure. This also allows for feeding of 
pressure sensitive fan fold paper 7. 
The feed velocity of feed roller 20, V.sub.2 and the feed velocity of push 
tractor 18, V.sub.1, are set equal so that: 
EQU V.sub.1 =V.sub.2 
Because feed roller 20 feeds fan fold paper at the same speed as push 
tractor 18, no deflections occur along the distance V.sub.2 and 
deflections which occur while fan fold paper travels across the short 
distance V.sub.3 may be neglected even where deflections are caused by 
differences in roller outer diameters, imperfections in part precision or 
the like. 
When detector 6 detects the leading edge of fan fold paper 7 a CPU 40 on a 
control board (not shown) begins counting the feed rate of motor 9, which 
controls feeding of push tractor 18, to determine the position of the 
leading edge of fan fold paper 7 as it travels along the paper path. Once 
the CPU has calculated that the fan fold sheet 7 has passed between 
discharge roller 22 and pressure roller 25, motor 30 rotates to detach 
pressure roller 24 from feed roller 20 as shown in FIG. 3d. 
Fan fold paper 7 is now fed by discharge roller 22, pressure roller 25 and 
push tractor 18. The velocity of discharge roller 22, V.sub.3, is greater 
than push tractor velocity, V.sub.1, and the relationship may be 
represented as: 
EQU V.sub.3 &gt;V.sub.1 
Therefor, fan fold sheet 7 is tensioned across distance V.sub.2. However, 
the driving force of discharge roller 22 is proportionally small relative 
to the driving force of push tractor 18 so that fan fold paper 7 is 
primarily fed by the pins of tractor 18 when fan fold paper 7 is fed as 
shown in FIG. 3d. This insures high precision paper feeding. 
As discussed above, the feed force provided by push tractor 18 is 
additional to that of the feed force provided by feed roller 20. 
Accordingly, cut sheet 41 may be fed in the direction of arrow H without 
the use of push tractor 18 as shown in FIG. 3e. When feeding cut sheet 41, 
pressure roller 24 is maintained in contact with drive roller 20 by motor 
30 with a force F.sub.2 greater than force F.sub.1, so that drive roller 
20 may provide a large driving fore to cut sheet 41. This result is 
achieved by the CPU 40 positioning motor 30 in response to a paper type 
indication input. 
The feed roller velocity, V.sub.2 is still equal to push tractor velocity, 
V.sub.1, and may be expressed as: 
EQU V.sub.2 &lt;V.sub.1 
Therefor, there is no difference in the feed rate between cut sheet and fan 
fold paper 7. Additionally, feed roller velocity, V.sub.2, of feed roller 
20 is less than discharge roller velocity, V.sub.3, of discharge roller 22 
so that: 
EQU V.sub.2 &lt;V.sub.3 
Again, a tension is provided so that cut sheet 41 is continuously tensioned 
across a distance V.sub.4 between feed roller 20 and discharge roller 22. 
Due to the tensioning, no slack occurs in cut sheet 41 and the sheet may 
be fed with high precision. 
In the above embodiment in which the pressure applied by drive roller 20 is 
controlled, a step motor has been used by way of example. However, a 
solenoid, magnetic clutch or the like may be used in place of the step 
motor. 
By providing a paper feeding apparatus which includes a push tractor for 
feeding fan fold paper towards a print head and a first paper feeding 
roller intermediate the print head which may variably apply pressure to 
the fan fold paper and a second feeding roller downstream of the print 
head the slack which occurs in feeding fan fold paper may be eliminated 
providing a high precision paper feeding apparatus. 
It will thus be seen that the objects set forth above, among those made 
apparent by the preceding description, are efficiently attained and since 
certain changes may be made in the above construction without departing 
from the spirit and scope of the invention, it is intended that all matter 
contained in the above description or shown in the accompanying drawings 
shall be interpreted as illustrative and not in a limiting sense. 
It is also to be understood that the following claims are intended to cover 
all of the generic and specific features of the invention herein described 
and all statement so the scope of the invention which, as a matter of 
language may be said to fall therebetween.