Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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FIELD OF THE INVENTION
The invention relates to a sprocket drive drum, for driving sprockets
controlling a moving belt, and in particular, in which all but one of the
sprockets are slidable to and fro along the drum, to accommodate minor
misalignments of the belt.
BACKGROUND OF THE INVENTION
The use of cylindrical drums for driving sprocket driven belts has been
well known for many years. Recent examples are shown in U.S. Letters
Patents:
Patent No: 5,156,263
Title: MODULAR CONVEYOR BELT SEALED SPROCKET DRIVE
SYSTEM
Inventors: Brent A. Ledet, Kenner, La.
Issued: October 20, 1992
Patent No: 5,253,748
Title: MODULAR CONVEYOR BELT SEALED SPROCKET DRIVE
SYSTEM
Inventors: Brent A. Ledet, Kenner, La
Issued: October 19, 1993
The sprockets are required to drive belts carrying various kinds of
product, and the sprockets have teeth which engage the belt and drive it.
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In order to accommodate minor misalignments of the belt, it is
customary to key the sprockets onto the drum in such a way that they can
move somewhat from side to side, along the drum, while still transmitting
torque to the belt.
One early system for providing drive for sprockets on a drum, devised
by Van der Graaf, Inc. of Toronto, consisted simply of securing rectangular
bars to the exterior of the drum. In the case of the Van der Graaf units, the
drums were driven by internal motors and gear systems unique to Van der
Graaf.
In the two U.S. patents referred to, the keying of the sprockets on the
drive drum was proposed to be achieved by, for example, octagonal flat
surfaces formed on the surface of the drum and complimentary octagonal
surfaces formed in the sprockets. The patents also suggest other keying
systems.
However, most of these keying systems had certain disadvantages.
For various reasons the sprockets are made of plastic material while the
drums or rollers are made of steel. The keying systems used whether they
are octagonal surfaces or notches or teeth, are simply cut out of the plastic
material. The plastic material is engaged by the steel of the drive roller or
drum itself. There is continuous friction and eventually wear will take place,
requiring replacement or repair of the sprockets.
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Another factor in the design of these types of sprockets and drive
rollers, is the fact that the sprockets must necessarily move sideways to
accommodate minor misalignments of the belt steering operation. These
misalignments are inevitable, and are a natural function of the movement of
the belt over the drive sprockets. The sprockets are fitted on the drive drum
or roller somewhat loosely, so that this side to side movement can take place
without interfering with the action of the belt itself, and without causing
undue strains on the sprockets.
However, in all of these earlier designs there was contact between the
inner edge or surface of the sprocket, and the surface of the drive drum or
roller, around the full 360-degree extent. As a result, either the clearance
between the sprockets and the drum was sufficiently loose to allow free
sideways movement, in which case the sprockets might rapidly become
worn, or else, if there was insufficient clearance, these sprockets could not
move sideways, with the desired degree of freedom.
Clearly, it is desirable to provide a system in which the actual drive
could be transmitted from the drive drum to the sprocket by metal to metal
contact, and in which clearance space is provided between each sprocket
and the drum, so that there is less wear between the plastic fabric of the
sprocket, and the metal surface of the roller.
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BRIEF SUMMARY OF THE INVENTION
With a view to providing a roller drive sprocket system, wherein a
drive roller mounts a plurality of sprockets for driving a belt, and wherein
most of the sprockets are moveable to allow for minor misalignments of the
belt, the invention comprises a general cylindrical drive drum, a plurality of
grooves formed axially along the surface of the drive drum at spaced
intervals radially there around, a plurality of sprockets formed of plastic
material, said sprockets having a generally annular configuration, with
externally facing drive teeth at spaced intervals, for driving a belt, and
having
internal generally cylindrical surfaces, the cylindrical surfaces defining a
radius greater than the radius of the drive drum, and defining a clearance
space between the cylindrical inner surfaces of the sprockets and the outer
cylindrical surface of the drive drum, and, a plurality of metal keys,
embedded in said cylindrical inner surface of said sprockets, spaced radially
therearound, said plurality of keys corresponding to respective said grooves
in the surface of said cylindrical drive roller, and drive portions of said
keys
extending radially inwardly from said cylindrical inner surfaces of said
sprockets, whereby to interengage with respective said grooves, to provide a
positive metal-to-metal torque engagement between said drive drum and said
sprockets, while maintaining said cylindrical surfaces of said plastic
sprockets out of contact with said drive roller surface.
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The invention is particularly applicable to cylindrical drive rollers having
internal motors and gear reduction drive, although the invention is not
exclusively restricted thereto.
Usually in the practice of the invention there will be three or more
sprockets on one such roller. In this case, the central or one of the
intermediate sprockets will be secured to the drive roller, so that it is non-
slidable relative thereto, while the remaining said sprockets may slide, with
their respective metallic keys sliding in respective grooves of the metallic
drive drum.
The invention further provides that the plastic sprockets will be formed
with recesses at spaced intervals, for receiving said keys therein, and said
recesses defining inwardly directed openings, whereby portions of said keys
are exposed inwardly for interengagement with said respective grooves.
The keys are preferably held in their respective cylindrical recesses by
means of set screws in threaded recesses. One of the set screws maybe
made of greater length than the others, so that it extends right through the
key, and enters into the cylindrical groove, so that the set screw maybe
tightened down thereby locking the one sprocket in position on the roller.
In one embodiment of the invention, the set screws may be used in
pairs, so that there is an inner set screw, which enters first into the
threaded
recess, and a second set screw is then threaded into the recess behind the
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first set screw, and is tightened up so as to lock the first set screw in
position.
The various features of novelty which characterize the invention are
pointed out with more particularity in the claims annexed to and forming a
part of this disclosure. For a better understanding of the invention, its
operating advantages and specific objects attained by its use, reference
should be made to the accompanying drawings and descriptive matter in
which there are illustrated and described preferred embodiments of the
invention.
IN THE DRAWINGS
Figure 1 is a perspective illustration of a drive roller in accordance with
the invention, showing two sprockets thereon, and a third sprocket being
shown in phantom;
Figure 2 is a section along the line 2-2 of Figure 1;
Figure 2A is a section along line 2A-2A of Figure 2;
Figure 3 is an exploded perspective illustration of the portion of the
sprocket containing the key, and also showing the key and the set;
Figure 4 is a partially cut away perspective of the internal motor drive
of the preferred form of drive roller;
Figure 5 is an exploded perspective illustration of an alternate
embodiment of the invention using a pair of set screws; and,
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Figure 6 is a sectional illustration corresponding to Figure 2A, showing
an alternate embodiment.
DESCRIPTION OF A SPECIFIED EMBODIMENT
As already explained, the invention relates to sprockets for driving
belts, in which the sprockets are mounted on drive rollers, The driver rollers
may driven by internal as illustrated in Figure 4, or may be driven by other
means, depending upon the particular application.
As illustrated in Figure 1, the drive roller will consist of a cylindrical
steel drum 10, having end plates 12, and any suitable shaft means (not
shown) extending from either end, by means of which it may be mounted in
suitable bearings (not shown).
Sprockets, in this case three such sprockets, are indicated generally as
14A, 14B, and 14C. Such sprockets typically are formed with external teeth
16, for engaging suitable link portions of a bolt (not shown) such as is well
known in the art.
As best shown in Figure 1, and also in Figure 2, the drum 10 is formed
with, in this case, four semi-cylindrical grooves 18A, 18B, 18C and 18D
along its length. As shown in Figure 1, the grooves are discontinuous
at each end of the drum, for reasons to be described.
The sprockets 14, are formed in the particular case, typically of
thermoplastic material, and having a predetermined thickness. Collars 20 are
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formed integrally with sprockets 14 and having a width greater than the
thickness of said sprockets 14, and extend laterally on either side of
sprocket
14, and define opposite ends..
The collars 20 define cylindrical interior surfaces 22.
~
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The interior surfaces 22 define a radius which is slightly greater than
the radius of the surface of the roller 10, so as to provide a slack clearance
between the collar 20 and the drum 10.
At spaced intervals around the collar 20, there are formed
generally cylindrical recesses 24. The cylindrical recesses 24 which extend
around about 220 to 270 degrees define inwardly open gaps 26 spaced apart
by a distance less than the diameter of the cylindrical recess 24. Recesses 24
extend through the collar from one end to the other of each collar, and are
open at each end of the collar.
Within each of the recesses 24, thee is provided a cylindrical steel
key 28. The key 28 makes a snug fit in the cylindrical recess 24, and a
segment of the key 28 extends out through the gap or slot 26 (Figure 3) into
a respective groove 18.
A threaded inwardly directed opening 30 is formed in the collar 20 of
each sprocket 14, registering and communicating at right angles with the
cylindrical recess 24 for the key 28.
A set screw 32 is threadedly received in the threaded recess 30, and is
received in a corresponding recess 34 in the key 28.
In this way, the keys 28 can be slid endwise, along one of grooves 18
into their respective recesses 24, from one open end of a recess and then can
be securely engaged and held in the recesses, by means of the said screws so
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that the keys 28 cannot escape.
As is well known, thee is a tendency on this type of belt drive for the
belt to wander or move sideways and misalign itself slightly. It is desirable
to allow for a minor degree of misalignment. For this reason, the two
sprockets 14A and 14C, can slide to a minor extent, sideways. The
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keys 28 will ride in their corresponding grooves 18, and allow a sliding
movement while maintaining a good metal-to-metal torque.
The central sprocket 14B however is secured in position so as to
prevent any major misalignment of the belt. This securing of the central
sprocket 14B is achieved by providing a set screw 36 (Figure 2A) which is
longer than the rest of the set screws. In this case, the recess 34 in the key
28 extends all the way through the key. The set screw 36 is then simply
tightened down until it securely engages the semi-cylindrical groove, and in
this way, the sprocket 14B cannot slide to and fro.
A further embodiment is shown in Figures 5 and 6. In this case, the
single set screw 36 of the embodiments of Figures 1 through 4 is replaced
by pairs of set screws. In the Figure 5 embodiment pairs of set screws 32A
and 32B are used, to hold the key 28 in position. The inner set screw 32B is
inserted first into the recess 30, and the second set screw 32A is then
inserted behind the set screw 32B and is tightened up against it so as to
prevent it from becoming loosened.
In the Figure 6 embodiment, a pair of set screws 36A and 36B are
shown. The set screw 36B enters completely through the pin 28, and
engages the roller 10.
The second set screw 36A is then inserted and tightened up behind it
so as to prevent it from becoming dislodged.
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The manufacturer of the cylindrical sprocket and semi-cylindrical
grooves is relatively easy to carry out with a great degree of precision. The
use of the blind ends on the grooves 18 prevents the sprockets 14 from
sliding off one end of the roller.
Assembly of the sprockets on the roller is simple to achieve, since
they can simply be slid onto the roller, without their keys 28 in position.
Once on the roller, the keys 28 can simply be inserted into their recesses 24
and the set screws 32 tightened up.
All of these numerous manufacturing and assembly advantages lead to
a greatly improved drive roller for such belts, which is both easier and more
economical to make, and at the same time has a greatly increased working
life, since all torque is carried through metal to metal contact without
friction
as between plastic and metal, as was the case in other such drives.
While reference has been made herein to cylindrical sockets and
cylindrical keys 28, it will of course be appreciated that the sockets may be
of any desired shape, and that the metal keys while preferably being
cylindrical for ease of manufacture, may, in fact, be of any appropriate
shape, preferably an arcuate shape, without departing from the scope of the
invention.
The foregoing is a description of a preferred embodiment of the
invention which is given here by way of example only. The invention is not
to be taken as limited to any of the specific features as described, but
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comprehends all such variations thereof as come within the scope of the
appended claims.
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