Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02229237 2001-O1-17
TITLE: Weighing Scale for Moving Loads
BACKGROUND AND SUMMARY OF THE INVENTION
This invention pertains to a weighing mechanism designed to
provide a more accurate weight in less time than present systems.
Weighing systems for material suspended from a trolley rolling
on a standing rail are fairly common. That material consists
usually of meat carcasses, but may also include some other types of
material. The purpose is to roll the trolley along the rail by the
operation of a chain having a dog to engage the trolley to pull it
over a short section of suspended track separated from the rest of
the rail. The live track - that free section - is supported by
weighing cells of various types. These cells may be strain gage
type devices, thus a type of spring device, which provide for a
measured displacement or measurable displacement to indicate the
weight.
There are a number of problems with such a system. One of the
chief of these problems is the oscillation of the free track caused
by sudden loading of the spring-like devices which support that part
of the track. The carrying trolley typically has only a single
load-carrying wheel having linear contact with the track. Thus, any
transition from one part of the rail to another is very quick, going
from no load to full load almost instantaneously. Such a quick
bounce creates an oscillation in the weighing cells making necessary
an appreciable time for damping before the weight can be accurately
measured.
There is another factor entering into the same problem. That
factor is the motor force moving the trolley along the rail. In
most instances that force is provided by a chain pulling the trolley
along the rail through a dog on the chain engaging, either directly
or indirectly through an arm, the top of the trolley. This
engagement, particularly when the transition between the regular
rail and the live rail is reached, is somewhat jerky resulting in a
swinging load on the trolley. Such swinging also contributes to
objectionable oscillation in the scale. The contact with the chain
may also create a small component of vertical force creating a false
reading of the scale.
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The swinging problem is worsened by another system sometimes used to
advance the trolley. This other system utilizes a downward slope on the live
track to cause the trolley to roll. Trolleys in such a system must be freely
rolling (well lubricated). Here again, the transition from regular to live
rail is very quick so that the bouncing oscillation is enlarged. Swinging may
also be encouraged by the slight bump between the two portions of the rails.
It should also be noted that flat or out-of-round wheels can also
contribute to a bouncing oscillation.
It is the purpose of the present invention to avoid, so far as possible,
any bouncing or swinging of the load as it passes over the live track. This
is accomplished by use of a transitional rail to load the live rail more
gradually and a unique separate transporting system to move the trolley on the
live track. Thus, the bouncing is virtually eliminated and the swinging is
reduced. To avoid an uncertain tare weight, the transitional rail is normally
kept out of contact with the live rail.
BRIEF DESCRIPTIGN OF THE DRAWINGS
Fig 1 is a front elevational view of the system at the region of the
live track,
Fig 2 is a rear elevational view of the system,
Fig 3 is an elevational view axi<~lly of the track showing the end of the
system,
Fig 4 is a plan view from line 4--4 of Fig 2,
Fig 5 is a detailed elevational ~riew to an enlarged scale of the
transition rail and its surrounding parts.
Fig 6 is a top plan view of the parts shown in Fig 5,
Fig 7 is a sectional view from line 7-7 of Fig 5, and
Fig 8 is a view similar to Fig 5 showing the parts just before the
trolley is weighed.
DESCRIPTION
Briefly this invention comprises a unique system of transmitting a
trolley-suspended load from a fixed track to a live track for weighing the
load. More specifically and referring to the drawings, the system includes a
customary, basic, fixed track 10 on which trolleys 11 run. The trolleys
normally include a single wheel 12 journalled to a hanging strap 13 and ending
in a hook 14 from which the load is hung. The wheel 12 is grooved so that it
will stay on the track 10.
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The trolley 11 is moved along the track 10 by a moving chain 15 linked
to a series of arms 16. The arms 16 c=arry wheels 17 adapted to roll on a
second track 18 parallel to but dispo:red above the carrying track 10. To
maintain flexibility of use and free rolling for the trolleys 11, each arm 16
carries an engagement dog 19 at its lower end in position to engage each
single trolley 11. The arm 16 by engagement between the dog 19 and the
trolley 11 pushes the trolley along its track as required, but leaves the
trolley to roll freely where the push is not required. This feature makes
possible a feature of this invention which will be described later.
The weighing mechanism, for weighing each trolley and its load as the
trolley moves along the track, ordinarily includes a scale mechanism 20
mounted on a beam 23. The beam 23 is fixed to the track 10 so that a cut
track will still have both ends supported. The weighing mechanism is arranged
to support a short section 25 of the t=rack 10 which is cut from the track.
The support is from supports in the weighing mechanism which are carried by
springs or strain gage devices of various kinds well known in the art.
Normally, the section 25 is simply cut from the track and catches the
trolley wheel 12 from the fixed track 10 as the trolley rolls past. The
section 25 thus actuates the weighing mechanism. However, the actuation is
sudden and causes oscillating fluctuat=ion of readings of weight. The present
invention provides a vast improvement by alleviating that problem. Instead of
a simple cut in the track 10, a transitional piece 30 (Figs 1 and 2) is
fastened to the fixed track near the entry side of the split track piece 25 at
a pivot. The pivot 31 is formed simply by use of a spherical surface on top
of a block fixed to the track 10. Then transition rail 30 rests on the
spherical surface of the pivot 31 and thus is free to rock on that surface.
Opposite the pivot 31 on the transitional rail 30, a projection 32 is arranged
to engage an opposite projection 33 on the weighing track section 25. Thus,
any vertical pressure on the transitional rail 30 will be shared between the
pivot 31 and the projections 32 and 33. A bolt 34 extending through an
enlarged hole 35 may be used to keep t=he transitional piece from tipping
laterally. However, the piece must be free to tilt about the pivot 31.
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It will now be apparent that as the wheel 12 of a trolley transitions
from the track 10 onto the transitional track 30, the weight on that wheel
will shift from being largely supported by the pivot 31 of the transitional
track to being almost totally supported by the projections 32 and 33. This is
true because of the leverage caused by pivoting one end of the transitional
track 30. Because of this relatively gradual shift of weight rather than the
nearly instantaneous change, the oscillation is greatly reduced, and becomes
nearly non-existent, with the result of much easier and quicker weighing which
is also much more accurate.
Although it is not essential to the operation of the weighing, a
modification shown in Figs 5-B is desirable for the sake of accuracy. Because
the pivot line 31 is located either directly below or to the permanent track
side of the division between the permanent track 10 and the transitional
piece 30, there is a small component of the weight of that transitional piece
which will normally press onto the projection 33 of the weighing section 25.
To avoid what amounts to added tare weight on the scale, and because that
weight might be somewhat variable, a way has been devised to keep that weight
off the projection 33 of the weighing section 25.
To accomplish the relief, the plate 36 which also supports the pivot
piece 37 includes a small shelf 38. The transition piece 30 also carries a
corresponding shelf 39. A compression spring 50 which may be relatively soft
extends between these shelves. The spring must be strong enough to raise the
transition piece 30 from the projection 33 on the weighing section 25 but
should not be much stronger than that. For example, it should not be strong
enough to interfere more than minimal:Ly with the pressing down of the piece
30
as it is loaded by the wheel 12 of the trolley.
In this way, any adjustment of the tare weight because of the weight of
the transition piece 30 is avoided. Also, the weight on the scale will not be
interfered with as the wheel 12 runs ~~nto the weight section. Any effect on
the effectiveness of the transition piece in the gradual transition of weight
onto the weighing section 25 of the track will be reduced to a minimum because
of the proportions of the spring 50.
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Additional advantages in accura~~y may be gained from an auxiliary
transport system adapted to move the trolleys 11 over the weighing section 25
of track. This transit means includes a motor 40 which runs continuously. An
electrically operated clutch 41 controls the engagement between the motor 40
and an operating shaft 42. The engage=_ment of the normally disengaged clutch
may be controlled by any well known means for triggering an electrical device.
That trigger might be a contact device arranged to be contacted by a strap 13
or an arm 16, or it could be a pressure switch triggered by the weight of the
wheel 12. The preferred device may be an electric eye switch actuated by the
straps 13 breaking a beam in passing. The switch when actuated operates to
engage the clutch to drive the shaft 42.
A sprocket 43 on the shaft 42 drives an auxiliary chain 44 (Fig 3) which
in turn drives a finger chain 45 in a horizontal plane. This chain follows an
elongated path between a driven sprocket at one end and an idler sprocket at
the other end of the path, leaving a relatively straight run parallel to and
relatively close to the underside of the weighing section 25 of the track 10.
In the preferred embodiment, the chain carries two fingers 46 equally spaced
on the finger chain 45. These fingers are adapted to engage the strap 13 of
the trolley to move it along the weighing section 25 of the track 10, thus
providing an auxiliary drive mechanism at this stage of the movement of the
trolley. It will be noted that at an~r instant, the auxiliary drive will be
engaged with only a single trolley.
In operation, as the trolley 11 approaches the scale mechanism along the
track 10, it first triggers the electric engagement of the clutch drive 41 to
cause the motor 40 to drive the finger_ chain 45. The proportions of the gears
and sprockets is such that the lineal speed of the finger chain 45 is slightly
greater than that of the main chain 1!i so that upon engagement of a finger 46
with the strap 13, the trolley is advanced ahead of and out of contact with
the dog 19 that had been providing propulsion. Because the finger 46 is
supported by the chain 45 and indirect=ly, therefore, by the rail 25 and is
far
closer to the wheel 12 than is the main chain 15, there is no chance that
there will be any resultant vertical component of force on the trolley 11,
transmitted to the sides. Therefore, there is less opportunity for the
CA 02229237 1998-02-11
introduction of error into the individual weight on the scales. Also the
auxiliary device will be more steady because only a single trolley is
propelled instead of the multiplicity of trolleys being moved by the main
chain. This added steadiness helps also to avoid the swinging and related
oscillating movement existing in prior scale systems.
As the trolley 11 passes over t:he weighing section 25, it is released by
the finger 46 to coast a short way do~~rn the track 10 and then is again
picked
up by the dog 19 to be moved to the unloading area.
Thus, this invention provides a comparatively highly accurate and
relatively fast system of weighing the moving trolleys and their load.
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