Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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BACKGROUND OF THE INVENTION
This invention relates to mechanical equipment generally, and particularly
to index drives.
Index drives of the type in this invention are intended to produce step-by-
5 step ("indexed") rotary motion of a sprocket or ribbed pulley or the like, via an endlesschain or synchronous belt respectively. The sprocket or pulley may be connected in
any desired conventional fashion to produce whatever indexed motion is actually
required.
In the manufacturing of index drives, as in that of other mechanical
10 equipment, the general situation is, the better the performance, the higher the cost.
Despite numerous past solutions, there remains a need for an improved
index drives which is simple, robust, effective, and inexpensive. Existing index drives
tend to be too expensive, too ineffective, or both.
15 SUMMARY OF THE INVENTION
It is an object of the invention to provide an improved indexing
mechanism .
In the invention, effective indexing is carried out by a simple sequence of
steps, using inexpensive, readily-available components. An optimum balance point20 between performance and cost has thus been found.
The mechanism for producing rotary indexing of a primary sprocket or
pulley has sprocket or pulley locking means, operable to alternately lock or unlock the
primary sprocket or pulley, and an endless chain or synchronous belt passing around
the primary sprocket or pulley and past chain or synchronous belt locking means. The
25 chain or synchronous belt locking means is operable to alternately lock or unlock the
chain or synchronous belt at a locking location. The chain or synchronous belt has first
and second loops between the primary sprocket or pulley and the chain or synchronous
belt locking location, on opposite sides thereof. First and second secondary sprockets
or pulleys are mounted on the ends of the rods of first and second cylinders
30 respectively, each secondary sprocket having one of the loops passing over it. Control
means are provided for alternately locking and unlocking the sprocket or pulley and at
the same time unlocking and locking the chain or synchronous belt at its locking
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location, and for counter-actuating the first and second cylinders to increase the length
of chain or synchronous belt in one loop while decreasing the length of chain orsynchronous belt in the other loop by the same amount, so as to pull the chain or
synchronous belt to rotate the primary sprocket or pulley while the chain or synchronous
5 belt is locked at its locking location, and so as to return to a starting position when the
sprocket or pulley is locked.
In the preferred embodiment, a single locking bracket is used as the
sprocket or pulley locking means and the chain or synchronous belt locking means.
The locking bracket is operable via a third cylinder between two locking positions,
10 namely one in which only the sprocket or pulley is locked, and one in which only the
chain or synchronous belt is locked at its locking location.
The control means, from a starting position in which the locking bracket
is in the chain or synchronous belt locking position, the first cylinder is extended, and
the second cylinder is retracted, operates the mechanism in the following steps:a. with the chain or synchronous belt still locked, retracting the first cylinder,
whereby the chain or synchronous belt rotates the sprocket or pulley;
b. actuating the third cylinder to move the locking bracket to the sprocket or pulley locking position;
c. retracting the second cylinder to return the first and second cylinders to
their starting positions;
d. actuating the third cylinder to move the locking bracket back to the chain
or synchronous belt locking position; and
e. repeating steps a. to d. as desired, to produce indexed movement of the
sprocket or pulley.
Apart from solving the cost problem, this invention also greatly improves
interchangeability between different models, indexing stability, the size of the center
through hole, etc.. The invention is especially suitable for the manufacturing of index
drives in a wide range of light, medium and heavy duty designs.
In the preferred embodiment of the invention, an endless chain and
30 sprocket are used, although a synchronous belt and pulley could instead be used, by
direct analogy. For convenience, the following description will refer to the chain and
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sprocket version only, but it should be clearly understood that this is not intended to limit
the invention in any way to just chain and sprocket configurations.
It is much cheaper to buy the chain, sprocket and other components used
in the invention than to produce custom-made precision components like cams and
5 flanges in a typical cam mechanism as commonly used in the prior art. The sprocket
and chain perform well in either high or low load transmission. In most applications, the
sprocket can serve directly as an indexing component, rather than being connected to
other means, thus reducing the cost further. One limitation of the invention, however,
is that it cannot be used for applications involving weight lifting.
BRIEF DESCRIPTION OF THE DRAWINGS
In order that the invention may be more clearly understood, the preferred
embodiment will be described in detail below, with reference to the accompanyingdrawings thereof, in which:
Fig. 1 is a schematic view of the preferred embodiment in a first or
"starting" position of the indexing sequence;
Fig. 1A is an enlarged view of the locking bracket area in Fig. 1;
Fig. 2 is a more detailed view of the starting position;
Fig. 3 is a corresponding view of the first step in one cycle of the indexing
sequence after the starting position;
Fig. 4 is a corresponding view of the second step in one cycle of the
sequence;
Fig. 5 is a corresponding view of the third step in one cycle of the
sequence, the next step being a return to the starting position;
Fig. 6 is a corresponding view of the final step in one cycle of the
sequence, being a return to the starting position;
Fig. 7 is a close-up view of the locking bracket area showing the chain
locked and the sprocket unlocked;
Fig. 8 is a cross-section at 8-8 of Fig. 7;
Fig. 9 is a close-up view of the locking bracket area similar to Fig. 7, but
showing the chain unlocked and the sprocket locked; and
Fig. 10 is a cross-section at 10-10 of Fig. 9.
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to the drawings, the basic configuration of the preferred
embodiment of the invention is as follows.
A large primary sprocket 25 is fixed on a hollow shaft 34 which is co-axial
5with a fixed shaft 30, which has a center through hole 31. The center through hole 31
can serve different applications with a wide range of diameters.
The large primary sprocket 25 is the target for indexing, i.e. it is the
component which is rotated in step-wise or "indexed" fashion. The sprocket can be
used to directly drive something requiring indexing in some applications, or can be
10connected in any conventional fashion to any other means requiring indexed motion.
The end use for the indexed motion of the sprocket is not relevant to the invention; the
invention relates simply to the production of the indexed motion of the sprocket, and
what that sprocket is then connected to is immaterial.
An endless chain 24 passes around the large sprocket 25 and all of the
15other sprockets as illustrated and as will be described, i.e. from sprocket 25, around
sprockets 10 and 8, along a guide block 20, around sprockets 7 and 9, and back to
sprocket 25.
On a locking bracket 23, which is movable towards and away from the
sprocket 25, there are a few locking teeth which can be engaged with the chain 24 to
20lock the chain against movement at that location. On the same locking bracket are
locking pins 22 which can be engaged with the tooth gaps of the sprocket 25, to lock
it against rotation. The locking bracket is actuated via the piston rod 6 of double-acting
cylinder 3, which moves block 19 which in turn moves the locking bracket 23 via a direct
connection through the guide rods 21. While the locking teeth on bracket 23 are
25engaged in the chain 24, the chain 24 is locked at that location, and at the same time
the sprocket 25 is unlocked. On the other hand, when the cylinder 3 has its piston rod
6 extended, so that locking pins 22 are engaged in the sprocket 25, the sprocket is
locked in position, and at the same time the chain is unlocked at its locking location.
Thus, at the locking bracket location, either one or the other of the chain and the
30sprocket is locked, but not both.
The indexed motion of the sprocket is achieved by alternating between
locking of the chain and the sprocket, while operating cylinders 1 and 2 to move the
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sprockets 10 and 9 back and forth in the manner explained in more detail below.
Cylinders 1 and 2 preferably work on their head chambers only (i.e. the chamber with
the piston rod). The bore of cylinder 1 is typically larger than that of cylinder 2, as
shown in the drawings, although they could be of equal size if desired. Cylinder 2 is
5 constantly connected to a source of compressed air (or hydraulic fluid, in cases where
the invention is hydraulically operated instead of pneumatically operated).
The small secondary sprocket 10 is fixed on shaft 28, which is connected
with bearings on a fork 12. The fork 12 connects the piston rod 4 of cylinder 1 through
a threaded rod 15, locked by lock nuts 13 and 14. They move togetherwith the piston
10 rod 4.
Similarly, the small secondary sprocket 9 is fixed on shaft 29 which is
connected with bearings on a fork 11. The fork 11 connects piston rod 5 of cylinder 2
through a threaded rod 18, locked by lock nuts 16 and 17. They move together with
piston rod 5.
The sprocket 8 is fixed on shaft 27, which like the guide block 20 is
bearing-mounted in a fixed position. Similarly, the sprocket 7 is fixed on shaft 26, which
is also in a fixed position. These fixed-position sprockets (or pulleys where
synchronous belts are used) are positioned wherever required to change the direction
of the chain. In other embodiments, i.e. where the configuration is different from the
20 configuration as illustrated, these fixed-position sprockets are located wherever
necessary to ensure the correct routing of the chain or synchronous belt.
Control means, such as preferably a computer or programmable logic
controller (PLC), not illustrated, are provided to implement the following operating
sequence:
Operating Sequence
1. Starting position
As shown in Figs.1 and 2, piston rod 6 of cylinder 3 is at the right end
of its stroke, making the locking teeth on bracket 23 lock the chain 24 at that location,
30 the locking pins 22 therefore being retracted from the sprocket 25. The head chamber
of cylinder 3 (i.e. the chamber with the piston rod) is now filled with compressed air and
the cap chamber of cylinder 3 (i.e. the chamber without the piston rod) is exhausted.
-5-
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The chamber of cylinder 2 is filled with compressed air constantly.
Cylinder 1 is now exhausted. Under the action of cylinder 2, piston rod 5 with its
connected parts is now at the right end of its stroke and piston rod 4 with its connected
parts is at the left end of its stroke.
2. Working process and functions
A. Input compressed air into the head chamber of cylinder 1:
As shown in Fig. 3, piston rod 4 and its connected parts move towards the
right, making the sprocket 25 turn clockwise as shown in the drawing as power
is transmitted from cylinder 1 to sprocket 25.
Simultaneously, piston rod 5 of cylinder 2 and its connected parts move
towards the left under the action of cylinder 1. When the piston of cylinder 2
comes to the end of its cushioning stroke (or fork 11 is stopped by shock
absorber 33 in case it is employed), the equal strokes of cylinders 1 and 2 are
ended, and sprocket 25 stops turning. Different degrees of rotation can be
achieved by selecting different length strokes of cylinders 1 and 2. Threaded
rods 15 and 18 can be used for stroke adjusting and finding the starting point of
sprocket 25.
20 B. Input compressed air into the cap chamber of cylinder 3 with the head side
exhausted:
As shown in Fig. 4, piston rod 6 of cylinder 3 moves towards the left, thus
moving block 19, guide rods 21, and locking bracket 23. This moves the locking
pins 22 towards the sprocket 25, and the locking teeth away from the chain 24.
When the locking pins 22 touch the tooth gaps of the sprocket 25, the sprocket
is finally positioned and locked in place accurately. At the same time, the chain
24 is unlocked. Cylinder 3 holds the locking as soon as its cap chamber is
energized.
The index motion of the chain and power transmission have now been
achieved, and it remains to reset the positions so that these steps can be
repeated.
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C. Exhaust head chamber of cylinder 1:
As shown in Fig. 5, both cylinders 2 and 1 reverse their stroke under the
action of cylinder 2. Because sprocket 25 is still locked by the locking pins 22,
piston rod 5 pulls from the other side of the chain locking section the same
length of chain as was used to advance the sprocket 25. The strokes of both
cylinders 1 and 2 are ended when the piston of cylinder 1 comes to the end of
its cushioning stroke (or fork 12 is stopped by shock absorber 32 in case it is
employed) .
10 D. Reverse the stroke of cylinder 3:
As shown in Fig. 6, the chain 24 is again locked at its locking location by
the locking teeth on bracket 23, and the sprocket 25 is unlocked at the same
time. Cylinder 3 holds the locking as soon as its head chamber is energized.
This completes the cycle, i.e. everything is returned to the starting position. The
sequence can be repeated endlessly to continuously index the sprocket.
Several further points should be noted in relation to the invention. First
of all, it should be noted that by changing the places of cylinders 1 and 2 with each
other, the indexing direction can be reversed.
Secondly, it should be noted that different numbers of stops per revolution
can be obtained simply by changing the strokes of cylinders 1 and 2 and the length of
the endless chain, i.e. the degree of indexing can be varied, as mentioned above.
Thirdly, by using a pneumatic-high pressure hydraulic tandem cylinder in
place of cylinder 2, an emergency stop function can be obtained through a simplehydraulic circuit.
Fourthly, by keeping the chain 24 locked at its locking location and moving
piston rod 4 of cylinder 1 back and forth, an oscillating function can be obtained if
desired .
Advantages of the Invention
The invention offers a number of advantages, some of which have already
been mentioned. These advantages include:
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1. Low cost with excellent performance.
2. A wide range of capacities - torque can range from 0.5 in-lb. up to
possibly 1 million in-lb.
3. A large center through-hole, with less limitation on available space.
4. Constant torque due to constant cylinder force and constant sprocket
radlus.
5. Better interchangeability. In different models with the same torque but a
different number of stops per revolution, the only thing to change is the
stroke of the cylinders and the length of the endless chain. In the case of
a small stroke difference, the same cylinders can even be used.
6. Changeable turning direction, by switching the driving cylinder with the
other one.
7. Oscillating function, simply by readjusting the control sequences.
8. Control of holding torque. Different holding torque can be obtained by
selecting different cylinder bores when it is needed, as in some
applications.
9. Emergency stop. There is a positive solution for it when it is needed, as
in some applications.
20Variations
It should be appreciated that the above description relates to the preferred
embodiment by way of example only. Many variations may be possible without
departing from the scope of the invention, including the following:
1. Different cylinder layouts with the same working principle as described
above.
2. Pneumatic or hydraulic cylinders.
3. Another part can be fixed on the same shaft with sprocket 25 to perform
positioning and locking, if necessary or desirable. That is, if sprocket 25
is viewed as the indexing output means, there could be a different
sprocket or other type of positioning disc, co-axial with sprocket 25, on
which the locking bar acts. That sprocket or other form of positioning disc
would not necessarily have the same pitch of teeth or other positioning
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elements as the sprocket 25. It could be much finer, for example, to
provide more precise final positioning.
4. Unlike the different sizes shown in the drawings, the bores of cylinders 1
and 2 could be equal.
5. The shaft 34 could be a solid output shaft.
6. Instead of a single locking bracket 23 to carry out the locking of the
sprocket or pulley and the chain or synchronous belt, separate brackets
or other locking means could be used for each, with suitable controls.
7. Layouts other than as illustrated clearly could be employed. As one
example, the cylinders could be positioned at ninety degrees to their
illustrated positions, with minimal adaptation.
The most significant possible variation is that the invention clearly could
be readily adapted to be used with a synchronous belt instead of a chain. Instead of
locking teeth, locking bars would be on the locking bracket 23. A ribbed pulley would
15 take the place of a sprocket, and locking bars would be used instead of locking pins.
Clearly, the principles are directly transferrable to such an embodiment, with only
minimal and purely routine adaptation. The claims which follow therefore contemplate
not only the use of a chain, but alternatively the use of a synchronous belt.
