Sheet feed tractor

A sheet-feed tractor is provided with raised land portions adjacent its drive and idler wheels. The raised land portions are positioned on the chassis of the tractor and shaped to form wall surfaces that are in radial registration with borders on a drive belt trained around the drive and idler wheels. The wall surfaces provide a positive means for preventing outward movement of the drive belt off the drive wheel and therefore prevent their disengagement.

BACKGROUND OF THE INVENTION 
The present invention relates to drive tractors for web material. It finds 
particular application in the type of sheet-feed tractor used to feed 
paper in high-speed printers. 
Paper is often fed to high-speed printers by tractors that have toothed 
belts that engage holes provided along either border of the paper sheet. 
The toothed belts are often trained around two wheels, a drive wheel and 
an idler wheel. It is important that the belts move synchronously and in 
tandem so that both edges of the paper are moved at the same rate and at 
the same time. For this reason, the drive wheels for both of the belts are 
typically driven by the same drive means so that equal simultaneous 
movement of the drive wheels is almost certainly assured. In many cases, 
this also assures equal simultaneous movement of the drive belts. 
The advancement of technology and the explosion of the data processing 
field have required increasingly fast printing of data on the paper 
sheets. As the speed of printing increases, so does the speed of 
advancement of the paper sheet, to the extent that the inertia of the 
paper sheet and the drive belt becomes significant. As a result, it is 
possible for the sudden jerking movements of the drive wheel to stretch 
the drive belt, possibly allowing it to deflect outward from its normal 
path of travel by an amount sufficient to allow the belt to disengage from 
the drive wheel. It is apparent that disengagement of one belt can at the 
very least cause the paper sheet to be bent or torn, and it could possibly 
result in jamming of the feeder. 
In order to avoid disengagement of the belt from the drive wheel, tension 
on the drive belt can of course be increased by various means. However, 
the amount of tension required to avoid most instances of disengagement 
increases as the required speed of motion increases, and this of course 
increases wear on the various moving parts. In addition, mere increase in 
tension does not provide a positive means for preventing the undesired 
disengagement. 
Accordingly, what is required is a positive means for preventing 
disengagement of the drive belt from the drive wheel that can be 
inexpensively provided and that does not significantly increase wear on 
the moving parts. 
SUMMARY OF THE INVENTION 
According to the present invention, a drive tractor for web material 
includes a chassis and a flexible endless belt mounted on the chassis. The 
belt has an inner driven surface and an outer driving surface and defines 
a closed path of travel. A belt driving means is mounted on the chassis 
and includes a rotatable member adapted to be rotated by a drive member, 
the rotatable member drivingly engaging the inner driven surface of the 
belt when the belt is in the path of travel. The chassis has wall means on 
it adjacent the rotatable member and extending transversely of the belt. 
The wall means is disposed outwardly of and closely adjacent the path of 
travel to limit the amount of deflection of the belt from the path and 
thereby prevent disengagement of the belt from the rotatable member. 
In the preferred embodiment, the belt has pin members extending outwardly 
from it. The pin members are spaced from the edges of the belt to leave 
borders on both edges of the belt that are uninterrupted by the pins. The 
wall means has at least two wall surfaces, at least one associated with 
each border, and each wall surface is spaced transversely from the pin 
members but positioned directly outward from and in radial registration 
with one of the borders. Limiting by the wall means of deflection of the 
belt is thereby possible without interference with the pin members. 
The chassis in one arrangement includes a chassis frame that has a planar 
web portion. The rotatable member includes a drive wheel rotatably mounted 
on the generally planar web portion of the chassis. The chassis further 
includes a chassis plate fastened to the chassis and positioned on the 
side of the wheel and the belt opposite the generally planar web portion 
of the chassis. The wall-forming means includes raised land portions on 
the chassis plate and on the generally planar web portion of the chassis, 
the raised land portions being positioned and shaped to form the wall 
surfaces in radial registration with the borders of the belt. 
An idler wheel may also be rotatably mounted on the generally planar web 
portion of the chassis frame between the chassis frame and the chassis 
plate. It would be spaced from the drive wheel and engage the inner driven 
surface of the belt, and the belt would be trained around the drive wheel 
and the idler wheel. Preferably, the chassis plate and the web portion of 
the chassis frame are spaced to prevent transverse movement of the belt 
off the drive wheel and the idler wheel. 
In an embodiment in which a second rotatable member is rotatably mounted on 
the chassis, the second rotatable member engages the inner driven surface 
of the belt when the belt is in the path of travel, the second rotatable 
member is spaced from the first rotatable member, and the belt is trained 
around the first and second rotatable members. Second wall means are 
provided on the chassis adjacent the second rotatable member, extending 
transversely of the belt, and disposed outwardly of and closely adjacent 
to the path to limit the amount of deflection of the belt from the path 
and thereby prevent disengagement of the belt from the second rotatable 
member. Again, each wall surface would be spaced transversely from the pin 
members but positioned directly outward from and in radial registration 
with the borders of the belt.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 shows, in exploded view, a drive tractor, generally indicated at 10 
including a base member 12 and a chassis 14. Base member 12 has a 
generally U-shaped configuration. The various components are assembled as 
indicated by the dot-dash lines in FIG. 1. Base member 12 is comprised of 
guide means comprising a pair of parallel spaced apart shaft elements 16, 
16' each of which is generally rectangular in cross section but having 
somewhat rounded corners. Each shaft element 16, 16' has a central bore 
18, 18' formed therein and extending longitudinally of shaft elements 16, 
16' and passing completely therethrough from front faces 20, 20', which 
comprise the forward end of base member 12, to rear faces, not visible in 
the drawings, which comprise the trailing end of base member 12. Shaft 
elements 16, 16' are joined at the trailing end of base member 12 by a 
connecting web portion that terminates at its upper end in a hinge block 
26 of generally triangular shape. The connecting web portion has an 
arch-shaped opening formed therein which is undercut to provide an 
inverted U-shaped lip 30 therearound to seat a rotatable threaded member 
162. 
Hinge block 26 has a bore formed therein extending in a direction 
perpendicular to the longitudinal axes of shaft elements 16, 16' to 
receive therein a lock hinge pin. An elongated locking tab 34 is of 
generally planar construction having a central cutout portion (unnumbered) 
sized to fit over hinge block 26 and having bores extending longitudinally 
adjacent the hinged portions thereof to receive opposite end segments of 
the lock hinge pin. 
Chassis 14 is of elongated construction and includes a chassis plate 90 and 
a chassis frame 42, which has a first sidewall portion 44 of planar 
configuration extending from feed end 46 to discharge end 48 of tractor 
10. 
Chassis frame 42 is seen to be of generally beam-like construction having a 
web portion generally indicated at 50 from which a flange-like feed end 
shoulder 52 and a discharge end shoulder 54 project laterally to the upper 
left of FIG. 1. Planar first sidewall portion 44 is provided by the side 
of web portion 50 opposite that from which shoulders 52, 54 project. An 
idler wheel bearing 56 projects outwardly of first sidewall portion 44. 
Idler wheel bearing 56 is in the form of a hollow cylinder having a 
stepped outer surface so that the outer diameter of the cylinder is larger 
at the base 56A projecting from first sidewall portion 44 than it is at 
the top 56B. A drive sprocket bearing 58 in the form of a simple hollow 
cylinder is provided at the end of chassis frame 42 adjacent feed end 
shoulder 52. Extending longitudinally between idler wheel bearing 56 and 
drive sprocket wheel bearing 58 is a belt support means 60 comprising a 
belt drive support element 62 and a belt return guide element 64. Support 
elements 62 and 64 are spaced apart from each other sidewise of chassis 
frame 42, element 64 having an assembly pin 64A projecting laterally from 
its side edge. 
A toothed idler wheel 66 has an inner bearing portion 68 adapted to fit 
over idler wheel bearing 56 to be rotatably mounted thereon. 
A toothed drive sprocket wheel 70 has a central cylindrical portion on 
which is formed a ring 74 having the sprocket teeth formed therein. 
Cylindrical portion 72 projects beyond opposite sides of ring 74 and 
cylindrical outer surface 72A is sized to be rotatably received within 
inner bearing portion 76 of sprocket wheel bearing 58. A shaftway 78 of 
square cross section extends longitudinally through cylindrical portion 72 
from one end thereof to the other. Thus, idler wheel 66 is adapted to be 
mounted for rotation on bearing 56 and sprocket wheel 70 is adapted to be 
mounted for rotation on bearing 58. 
An endless belt 80 is made of a flexible material and is adapted to be 
trained over wheels 66 and 70 in a loop. Belt 80 has an outer driving 
surface 82 from which a plurality of web engaging means conprising pins 84 
project. Pins 84 are spaced apart along the length of belt 80 and project 
perpendicularly outwardly of driving surface 82 thereof. Pins 84 are 
centered on the longitudinal center line of driving surface 82 and are 
spaced apart equally along the length thereof. They are transversely 
spaced from the edges of the belt to leave longitudinal borders 
unobstructed by the teeth. Inner driven surface 86 of belt 80 has a 
plurality of belt teeth spaced apart along the length thereof and 
extending transversely across surface 86. Inner driven surface 86 is 
adapted to mesh with the teeth of wheels 66 and 70 to drive belt 80. 
In addition to chassis frame 42, the chassis 14 also includes a chassis 
plate 90. The chassis plate is of elongated generally planar construction 
and, as shown in FIG. 1A, has an inner side thereof comprising a planar 
second sidewall portion 92 in which is formed an aperture 64B which is 
adapted to lockingly engage assembly pin 64A so as to securely mount 
chassis plate 90 upon chassis frame 42. Still referring to FIG. 1A, a 
raised land portion 94 of generally square periphery is seen to be formed 
on second sidewall portion 92 and projects laterally outwardly thereof. 
Land portion 94 has a bore 96 (FIG. 1) of circular cross section extending 
therethrough and through chassis plate 90. Spaced longitudinally apart on 
either side of land portion 94 are a pair of passage openings 98, 98' 
(FIG. 1) of generally rectangular cross section but having rounded or 
fillet corners. Passage openings 98, 98' are dimensioned and configured to 
receive therein for easy sliding passage therethrough shaft elements 16, 
16'. Longitudinally spaced apart on opposite sides of openings 98, 98' are 
sprocket wheel opening 100 and idler bearing opening plate 102. Wheel 
opening 100 is circular in shape and is adapted to receive rotatably 
therein outer surface 72B of center cylindrical portion 72 of sprocket 
wheel 70. Similarly, idler bearing opening 102 is circular in shape and is 
adapted to rotatably receive therein outer surface 56B, the reduced 
diameter portion of idler wheel bearing 56. The cylindrical outer surface 
56A of the large diameter portion of bearing 56 is adapted to receive 
idler wheel 66 rotatably thereon as indicated above. 
Further raised land areas 210 and 216 are formed on the ends of the second 
sidewall 92. These land areas 210 and 216 are wall-forming members that 
form arcuate wall surfaces 212 and 214. Wall-forming members 210 and 216 
are positioned opposite corresponding wall-forming members 208 and 202, 
respectively, which are raised land areas on the web portion 50 of the 
chassis frame 42. When assembled, corresponding wall-forming members are 
laterally spaced enough to permit teeth 84 to pass between them, but they 
are close enough to register radially with the border regions of the belt. 
Chassis plate 90 has a parting arm 104 (FIG. 1) formed at its end thereof 
which is adapted to be positioned adjacent to discharge end shoulder 54 of 
chassis frame 42. Parting arm 104, as best seen in FIG. 1A, is triangular 
in cross section and, when chassis plate 90 is mounted upon chassis frame 
42, extends entirely across the gap provided between plate 90 and frame 42 
as described more fully hereinbelow. Outside wall 106 of chassis 90 is 
disposed opposite to second sidewall portion 92. 
A pair of hinges 112, 112' are formed atop chassis frame 42, on 
respectively, the top surfaces of shoulders 52, 54. Hinges 112, 112' are 
longitudinally spaced apart along the longitudinal or first dimension of 
chassis frame 42. Hinges 112, 112' each contain a bore (unnumbered) 
passing therethrough parallel to the longitudinal axis of chassis frame 
42. A cover plate 114 is generally rectangular in shape and has a central, 
longitudinal slot 116. 
Cover plate 114 has formed on the underside thereof longitudinally 
extending bearing surfaces 118, 118' extending along opposite edges of 
slot 116. A longitudinally extending bore 120 extends through cover plate 
114 parallel to and adjacent hinge edge 114A and is aligned with the bores 
formed in hinges 112, 112' so that cover plate hinge pins 122, 122' may be 
inserted therein to mount cover plate 114 for hinged rotation about 
chassis frame 42. A torsion spring 124 encircles cover plate hinge pin 122 
and is received within a torsion spring retaining compartment 126 formed 
in cover plate 114 to spring bias cover plate 114 towards its open 
position in which it is rotated 90.degree. counterclockwise from the 
position shown in FIG. 1. 
A cover latch 128 has a catch portion 130 having a lip 132 formed at the 
lower portion thereof. A central bearing retainer socket 134 of circular 
cross section is formed in body portion 136. At the lower end of cover 
latch 128 a compression spring retaining compartment 138 is formed to 
receive therein one end of a compression spring 140. A washer 142 and a 
bearing nut 144 are employed to mount cover latch 128 on chassis frame 42. 
Fastening means are provided by the combination of a threaded shaft 156 and 
a nut 162. Shaft 156 has a threaded shank 158 and an enlarged head 160 
which is adapted to be seated within counterbored passage opening 96. 
To assemble a drive tractor from its component parts it is necessary only 
to slip idler wheel 66 and drive sprocket wheel 70 over their respective 
bearings 56, 58 and train belt 80 over wheels 66 and 70 with belt teeth 88 
meshed with the teeth on wheels 66 and 70. Chassis plate 90 is then 
mounted upon chassis frame 42 by engagement of assembly pin 64A with its 
respective aperture 64B. Cover plate 114 mounted to chassis frame 42 by 
means of cover plate hinge pins 122, 122' which are passed, respectively, 
through bore 120 and the bores (unnumbered) in hinges 112,112'. Torsion 
spring 124 is emplaced and the opposite legs thereof seat, respectively, 
against cover plate 114 and hinge 112. Cover latch 128 is mounted on 
chassis frame 42 with compression spring 140 having one end received 
within its retaining compartment 138 and its opposite end abutted against 
a flange not seen in the drawings that projects from the unseen side of 
chassis frame 42. Compression spring 140 is thus compressed between the 
flange and retaining compartment 138, and a retaining pin not shown serves 
to provide a stop for pivoting movement of latch 128 about the cylindrical 
bearing portion 148 of nut 144. 
Chassis frame 42 is provided with frame passage openings 99, 99' that are 
of substantially identical configuration as corresponding passage openings 
98, 98' of chassis plate 90. With chassis plate 90 mounted to chassis 
frame 42 passages 98, 99 and 98', 99' are in axial alignment and together 
cooperate to provide a pair of passages. Shaft 156 is threaded through 
chassis frame 42 and plate 90. 
Body portion 12 is mounted upon chassis 14 by passing shaft elements 16, 
16', respectively, through the passages 99 and 99' and 98 and 98' for 
sliding movement therein. The outer surfaces of shaft elements 16, 16' are 
configured to closely but slideably pass within the passages and to be 
constrained for linear sliding movement therein. 
Threaded shaft 156 is then passed through bore 96, bore 154 and extends 
between shaft elements 16 and 16', as may best be seen in FIG. 5 with 
respect to tractor 10 thereof. Nut 162, internally threaded to receive 
shaft 156, is seated upon lip 30, and the end of threaded shaft 156 
opposite its head 160 is threadably engaged with nut 162. 
As is indicated in Applicant's prior United States patent application Ser. 
No. 847,236, now U.S. Pat. No. 4,159,794 and more fully explained in it, 
the assembled tractor 10 is used in conjunction with a complementary 
tractor that is the mirror image of the one shown in FIG. 1 and is spaced 
from it so that holes on one side of suitably perforated paper can be 
engaged by teeth 84 on the tractor in FIG. 1, and corresponding teeth in 
the complementary tractor can engage holes on the other side of the 
perforated paper. The paper is advanced through the operation of the 
tractors. 
Attention is now invited to the wall means that include the land areas 202 
and 208 on the chassis frame and 210 and 216 on the chassis plate. FIG. 2 
is a side elevation, greatly simplified, of the chassis frame of FIG. 1. 
There it is seen that an arcuate wall surface 206 is formed by raised land 
area 208. This surface 206 matches a corresponding surface 212 (FIG. 3), 
which is provided by the land area 210 formed on the feed end of the 
chassis plate 90. Similar matching wall surfaces 204 and 214 are present 
at the discharge ends of the chassis frame and chassis plate, 
respectively. 
As is best seen in FIGS. 4 and 5, the raised land areas 208 and 210 extend 
transversely of the belt and are disposed outwardly of but very closely 
adjacent to it. The wall surfaces are transversely spaced from the teeth 
84, but they are positioned in radial registration with the borders left 
by the teeth 84 on either edge of the belt. 
FIGS. 6 and 7 are the best views for observing the outward spacing of the 
wall means. As FIGS. 6 and 7 show, the raised land area 208 is closely 
adjacent to the path of travel of the belt 80 so that it limits the amount 
of deflection of the belt from the path that it is intended to take. FIG. 
6 also shows raised land area 216 providing the limiting function at the 
position of the other wheel 66. 
In operation, appropriate drive means not shown apply torque to drive wheel 
70, causing it to rotate, thereby driving belt 80. Teeth 84 on belt 80 
engage holes provided for that purpose on the borders of the paper sheet 
to be fed. The paper accordingly moves along with drive belt 80. This 
feeding is effected through the tandem operation of both complementary 
tractors, so it is important that the tractor drive belts remain 
synchronized. However, it is conceivable in some prior-art arrangements 
for one of the belts to stretch, momentarily disengaging itself from the 
drive wheel. The resultant misalignment of the belts on the complementary 
tractors would cause the paper to be creased or torn. 
With the arrangement shown in FIGS. 1 through 7, however, the drive belts 
always remain aligned as long as the drive wheels are in alignment. This 
is because the raised land areas 208 and 210 positively prevent the belt 
from being deflected outwardly from the intended path by enough to allow 
the belt 80 to come out of engagement with the drive wheel 66. Raised land 
areas 202 and 216 perform the same function with respect to the idler 
wheel 66. Accordingly, a sheet-feed tractor provided with the wall means 
described above provides significant advantages over prior-art tractors 
without significant increase in tractor cost.