Note: Descriptions are shown in the official language in which they were submitted.
DEVICE, NETHOD AND U~ OF THE ~ETHOD
FOR DE~RMINING A PROD~CTION FLO~
Technical Field 2 0 ~ 9 ~ 3 ~
The invention is directed to a device as well as a
method for determining a production flow with products
having unfavorable flow behavior, e.g. in a mill.
Background Art
In production plants which already have a high degree
of automation, e.g. mills as well as feedstuff mills, a
conflict of goals has recently developed in that an
inexpensive increase in quantity is impossible with existing
technical measuring means or is possible only at the cost of
qualitative parameters. Increasingly higher installed
throughput capacities with persistently strict demands on
quality, particularly on the consistency of the quality,
require a more precise controlling and monitoring of the
production flows. Both the processing quantity and the
instantaneous throughput must be constantly determined with
weighing precision.
However, accurate weighing involves repeated filling of
the weigher, measurement and emptying of the weigher,
insofar as accurate weighing is understood to mean weighing
by means of weighers which are calibrated by government
technicians, and results in an intermittent transporting of
the product. In order to overcome this disadvantage,
intermediate compensating bins must be used in addition, but
this necessitates additional costs. At present, belt
weighers are used almost exclusively for continuously
determining a production flow with respect to quantity with
materials having unfavorable flowing properties, e.g. flour,
flour mixtures, break, bran, etc., and for a continuous
transporting of the product. Belt weighers have the great
advantage that the problems of flow behavior of the product
to be weighed have virtually no influence. The product is
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continuously guided on the weighing belt, weighed and
discharged, likewise in a continuous manner. But this
solution is disadvantageous in two respects. A belt weigher
is less accurate than a classic hopper scale. While the
latter works easily within a tolerance of +/- 1 to 2 ~, this
value ranges from +/- 2 ~ to 1 ~ in belt weighers. The other
disadvantageous aspect consists in the cost for belt weighers
and particularly in the operating expense for maintenance,
cleaning, servicing, etc. Belt weighers are expensive and can
only be successful in the processing of very highly priced
products such as chemical substances. Not many belt weighers
are found in foodstuff and feedstuff plants for the
aforementioned reasons, but also because belt weighers require
relatively large horizontal dimensions. In past years, great
efforts have also been made to monitor the product flow with
entirely different measuring systems, but without greater
success.
Another special problem consists in the throughput
capacity, which regularly amounts to well over one ton per
hour in present-day milling operations; the usual amounts are
10...20...50 or more tons per hour for the respective
production flows to be measured.
Disclosure of the Invention
The object of the invention is to develop a new measuring
system for the measurement of a large product flow, also,
which measures the throughput with weighing precision, allows
a completely continuous product transfer as in belt weighers
and operates without disturbance and in an accurately weighing
manner particularly for product with heavy flow properties.
A solution, according to an embodiment of the invention,
is characterized in that it comprises an upright weighing
container, a variable-speed discharge screw with a
substantially horizontally directed discharge at the weighing
container, as well as a transition piece from the weighing
container to the discharge screw and differential weighing
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elements.
The basic idea of this embodiment consists in the use of
an upright weighing container, from which the product is
positively discharged by a controllable discharge screw. The
weight can be determined continuously in a manner known per se
by an upright weighing container by means of differential
weighing. The substantially horizontal discharge does not
influence the vertical weight signals. Accordingly, a
production flow can be measured with weighing precision with
the concept of differential weighing and can be constantly
monitored with a variable-speed discharge screw and a
completely continuous transfer of the product is guaranteed in
this way. A natural, constant product flow results from the
consistent filling of a weighing container, particularly a
tubular weighing container (tube weigher) and a transition
piece from the upright weighing container to the horizontal
discharge screw, all three of which together form a type of
knee piece, wherein the weighing container works like a build-
up space which empties continuously by means of the force of
gravity and only the horizontal discharge is effected in a
compulsory manner by mechanical means. In a preferred manner,
the upright weighing container, the transition piece, the
discharge screw which discharges on one side, and the
controllable drive motor which discharges on the opposite side
form a weighing unit and this weighing unit can be suspended,
for example, at three bending rods.
The transition piece from the weighing container to the
discharge screw preferably remains constant in cross section,
at least approximately, wherein in the case of a circular
cross section of the weighing container, the shape of the
transition piece passes from circular to rectangular. A
positive, uniform product flow having a very great degree of
consistency as a result of a corresponding programming of a
weigher control unit accompanied by controllable feed
accordingly results within the entire weighing unit. When the
feed cannot be influenced, the product discharge even has a
greater uniformity than the feed if fluctuations of the feed
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are only brief. An exact measurement is effected in this way;
the production flow remains constant or can even be calmed.
Further, it is possible to let the weighing system idle prior
to every interruption or for a change of product. In
addition, the entire weighing unit can be suspended and/or
supported on a platform construction. When particularly
strict demands are made with respect to purity, a travel-out
rail can be arranged in the lower area of the weighing unit
and the discharge screw with the drive motor can move out on
this travel-out rail for cleaning purposes.
In all cases of application in which the feed cannot be
switched off, it is suggested that a build-up bin with a
controllable base flap be arranged above the tube weigher.
The preliminary bin will preferably comprehend 30~ to 90~ of
the tube weigher, wherein a cycle time can be in the range of
several seconds to thirty seconds.
The invention is further directed to a method and
consists of a method for determining the instantaneous
discharge amount per unit time and/or a summed throughput of a
product flow of products having unfavorable flow properties in
a production installation, the method using an apparatus
including a differential weigher and a discharge device, the
method comprising the steps of: directing the product flow
during intermittent filling intervals of a few seconds
duration into the differential weigher, wherein a cycle time
between successive fillings is less than 30 seconds;
discharging the product continuously and substantially
horizontally from the differential weigher using the discharge
device; and measuring the discharged product flow during
weighing intervals occurring between the filling intervals,
the measuring of product flow being correlated with rotational
speed of the discharge screw.
Surprisingly, the very valuable concept of differential
weighing has accordingly been successfully transferred from
metering technology to production monitoring contrary to
prejudices of technical circles. Although it was previously
assumed that the differential measuring system loses much of
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its appeal with large outputs. Various reasons have been
cited for this: large outputs call for extensive hoppers and
containers in order to reduce the refilling time in that the
metering means is compelled to work in a volumetric manner
in each instance. Problems relating to space can then also
occur with the refilling device. In fact, the space
requirement is much more critical for differential metering
means with great output than is the case in belt metering
devices. It can be assumed as a general rule that a
differential metering means should not work in a volumetric
manner for more than 1% of the operating time, i.e. the
refilling device would have to have enormous dimensions at
high outputs.
Finally, in addition, the accuracy of a differential
metering means has been placed in doubt when the throughput
exceeds one to two tons per hour.
With the new invention, the product can be delivered in
a continuous manner to the next processing stage after exact
weighing with minimum time delays of seconds. The results
are even more accurate because a very short cycle time is
used in a very deliberate manner and the evaluation is
calculated by means of statistical methods.
In a further development of the inventive idea,
differential weight values are measured in the weighing
container when the feed has stopped and the corresponding
speeds of the discharge screw are determined for the
calculation of the instantaneous discharge quantity per time
unit and/or a summed throughput of the production flow over
an allowed time period.
But the particular advantage consists in that the
product always remains in movement in the weighing container
from which material is constantly removed, and most products
with heavy flow properties, such as occur in a milling
operation for foodstuff or feedstuff, can accordingly be
determined with respect to throughput with the new solution.
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In the normal operating state, no product stoppage occurs in
the weigher, so that the problem of monitoring the calming
friction into the movement friction within the weighing
container can be avoided. Depending on the application, the
feed can be stopped by means of controlling the feed or by
means of forming a small preliminary bin. In the
preliminary bin, which can be locked e.g. via controllable
base flaps, a temporary build-up of the product for several
seconds is taken into account. However, since the
preliminary bin is not a weighing part, simple mechanical
movement means can easily be used in this instance, if
necessary, for supporting the discharge without disturbing
the measuring accuracy, but nevertheless preventing a
stoppage at the location.
The throughput of the production flow can be measured
based on the continuous volumetric discharge from the
weighing container with a cyclical correction of the
volumetric value by means of the differential weighing
weight value. In a particularly preferred manner, the ratio
of throughput to speed of a metering discharge screw or lock
determined by the differential weighing is determined,
stored and predetermined for subsequent presetting of a
volumetric metering output of a like or similar product.
If the production flow has greater fluctuations which
cannot be influenced directly, per se, or if the production
flow is known only within larger limiting values, one or
more filling cycles of constant duration are advantageously
predetermined over a selectable first time interval, wherein
the differential weighing begins with a delay of constant
duration and the product is discharged with predetermined
volumetric reference values during the first time interval.
It is advantageous if the filling cycle time for a
following time interval is changed due to the weight
differences at the beginning of the respective differential
weighing. It is particularly preferred that the production
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flows be measured by means of differential weighing before
and after milling in a mill, which values are used for
determining the yield and determining other parameters for
controlling the mill.
However, the new invention also makes it possible for
the first time, in the case of a continuously slightly
fluctuating production flow resulting from the processing
process, to accurately measure the weight of this production
flow in a continuous manner and to mix other components into
the continuous production flow, e.g. different specific
flour into a main flour in order to change the quality of
the main flour. This is effected in that a master weigher
is provided for mixing two or more product flows and each
additional differential weigher begins cyclically with the
master weigher with predetermined speed reference values,
and the regulating of the metering output of each additional
differential weigher is effected corresponding to the actual
value of the measured weight values of the master weigher.
It is very advantageous if the new invention is used in
such a way that the production flow in a mill is determined
via a cyclical, volumetric-gravimetric measurement for the
control and/or monitoring of the working process prior to
wetting and/or as mill input capacity and/or for monitoring
in the milling process and/or for the flour weigher.
The invention is explained in more detail in the
following with reference to several embodiment examples:
Fig. 1 shows a flow measuring device, according to the
lnvention;
Fig. 2 shows the measuring device of Figure 1 during the
differential weighing phase;
Fig. 3 shows an analogous measuring device during the
volumetric discharge phase;
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Fig. 4 shows a classic diagram of differential metering
weighing;
Fig. S shows the curve of the weight indication in the
weighing container over time;
Fig. 6 shows uses of the new invention in a milling diagram.
Reference is made to Figure 1 in the following. The
production flow P1 enters vertically into a flow measuring
device 1 at the top and leaves the latter again at the
bottom as P2. The flow measuring device comprises a feed
head 2 which is securely connected with a platform 3 via
brackets 4 and is supported on the base 5. A feed tube 6
and a diverting tube 7 are stationary. The weighing part 8
is connected to the feed head 2 and the diverting tube 7 via
a flexible rubber sleeve 9 in each instance so as to be
tight against dust relative to them. The weighing part 8
comprises an upright weighing container 10 whose lower part
comprises a slight conically tapered portion 10'. The
weighing container 10 and the conically tapered portion are
constructed as a circular tube shape. A transition piece 12
is arranged between the weighing container 10 and a
discharge screw 11 and ensures the transition from the
upright tubular shape of the weighing container 10 into a
horizontal tubular shape of the discharge screw 11 in an
optimal manner with respect to production flow technology.
In Figure 1, the transition piece 12 has an approximately
constant cross section from top to bottom and has a shape
passing from circular to rectangular in the embodiment
example. The weighing part 8 is suspended in the
circumferential direction at e.g. three weight measurement
value receivers 13 at the platform 3. Especially
interesting is the suspension of the entire weighing part 8,
including a drive motor 14, so that the drive motor 14 and
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the discharge screw 11 project out over the weighing part 8
in opposite directions and balance one another within a
certain circumference with respect to a center axis 15. A
preliminary bin 16 is situated directly at the feed tube 6,
which preliminary bin 16 is controllable by a pneumatic
cylinder 17 and a base flap 18 via an electronic control
unit 19 or a pneumatic signal transformer 20, respectively,
according to a selectable program, wherein reference values
for the product discharge are obtained by an external
computer 21 and the actual value weight signals are obtained
by the weight measurement value receivers 13.
The preliminary bin comprises less than 50~ of the
maximum volumetric capacity of the weighing container 10,
preferably approximately 30% to 90%. However, a course is
accordingly taken in this instance in a very deliberate
manner which diverges from the conventional use of a
differential weigher, since only a portion can be pre-stored
for the filling of the weighing container, so that the feed
can likewise be determined with weighing technology, which
is important for determining a production flow if additional
regulating devices are not taken into account for the feed.
The height of the weighing container is approximately
twice its diameter, wherein the diameter can amount to 0.3
to 0.6 m. For this purpose, the tube screw conveyor has a
diameter of 0.100 to 0.250 m, so that the average ratio of
the weighing container cross section to the tube screw
conveyor is approximately 1 : 10.
A further particularly interesting construction idea is
shown in Figure 1 in that the drive motor 14, with or
without flanged on discharge screw shaft 22, can be pulled
out in the direction of the axis 24 of the discharge screw
11 in the manner of a drawer via pull-out means 23. This
makes it possible to service the device quickly at any time
while imposing particularly strict demands on the device
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with respect to the cleanliness of the product path of the
production flow.
As the product falls in the upright weighing container
10 constantly in the vertical direction, it is guided
directly into the front feed of the discharge screw shaft
22, discharged horizontally from the weighing container 10,
and delivered in turn in a continuous manner vertically via
the diverting tube 7 so as to be monitored once again with
the use of technical measuring means.
Figure 2 shows the same device as in Figure 1 during
the gravimetric weighing phase with closed base flap 18.
Differential weighing takes place in this instance during
the production discharge, or the constantly discharged
product is measured by means of the corresponding reduction
of weight in the weighing container 10.
Figure 3 shows an arrangement similar to that in Figure
2, but without a preliminary container. The phase of
volumetric discharge metering takes place here. Figure 4
shows the classic curve, known per se, of a differential
metering weigher. The latter is characterized by an
extremely short filling time and a very long gravimetric
weighing, which is ultimately the purpose of differential
metering.
Figure 5, which shows two weighing cycles, according to
the new invention, is referred to in the following. A is
the beginning of the filling of a differential weigher with
a more or less regular product feed. At B, the product feed
is stopped and the product discharge from the weigher begins
simultaneously with differential weighing, which consists
particularly in that the weight which is reduced per unit of
time is determined at the weigher which is no longer
disturbed by the feed. Point A' is the end of the
differential weighing. The product which has built up in
the feed area from 8 to A' is left in the differential
weigher until point C. A regular product feed is effected
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briefly until the product guidance is interrupted again at
point D. The second differential weighing is performed from
D to A'.
In the following two cases:
- change in the discharge quantity from the differential
weigher when the feed quantity cannot be influenced or
- change in the feed quantity at desired discharge reference
value,
it is important with respect to regulation that a constant
time (cycle time~ be selected for at least two weighing
cycles. As a result, there is a difference between the feed
weigher and the metering output which must be influenced.
tl = gravimetric weighing time
t2 = refilling time
t3 = time for regulating
t = cycle time
The regulating can be effected according to the
following equation:
y - (a) y - > (b)
Qreference (Xg/sec) = Qactual + + 0.5
t t
An entire mill is shown schematically in Figure 6.
This concerns a mill cleaning 30, tempering and milling
preparation 31 as upper left-hand block. At the top right-
hand corner is a flour silo 32, the mill 33 with plansifters
and semolina cleaning machines is at the bottom left-hand
corner, and a flour mixing 34 is indicated at the lower
right-hand corner. The use of the new invention is marked
by a circle in the diagram. A control passage, e.g. the
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ratio of sieve tailings to sieve throughs after Bl is
designated by B and a corresponding key passage at the
reduction passages for a continuous monitoring of the
production flow is designated by C.
