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Claims  |
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What we claim is:
1. A weighing method comprising the steps of:
(a) charging articles to be weighed into a plurality of weighing hoppers;
(b) measuring the weight of each batch of articles received in the
respective weighing hoppers;
(c) selecting, based on the measured weights, a combination of article
batches giving a total weight value closest to a target weight value
within preset limits; and
(d) discharging the selected article batches from the respective weighing
hoppers to obtain a collection of articles the weight of which corresponds
to the total weight value closest to the target weight value within preset
limits;
said step (a) including controlling the charging of the articles into the
weighing hoppers on the basis of a target charge quantity, obtained from
the number of weighing hoppers and the target weight value, which serves
as a target for the charging operation, said step (a) also including
charging the articles into each of the weighing hoppers with a weight
value of 2X/N serving as the target charge quantity when N is even, and
with a weight value of 2X/(N.+-.1) as the target charge quantity when N is
odd, where N is the number of weighing hoppers and X is the target weight
value.
2. The weighing method according to claim 1, wherein said step (a) includes
controlling dispersing feeders, which charge the articles into the
weighing hoppers, in such a manner that the quantity of articles charged
into each weighing hopper will conform to the target charge quantity.
3. The weighing method according to claim 2, wherein said step (a) includes
controlling vibration amplitude and vibration duration of the dispersing
feeders.
4. The weighing method according to claim 2, wherein said step (a) includes
computing the target charge quantity from the target weight value and
number of weighing hoppers, and controlling the dispersing feeders in such
a manner that the quantity of articles charge into each weighing hopper
conforms to the target charge quantity.
5. A weighing apparatus for obtaining a collection of articles, the total
weight of which substantially corresponds to a target value, by measuring
the weights of batches of articles, charged into a plurality of weighing
hoppers, using respective weight sensors, by selecting a combination of
article batches giving a total weight value closest to the target weight
value within preset limits based on the weights of the batches of articles
measured by the weight sensors, and by discharging the selected articles
from the weighing hoppers, said apparatus comprising:
at least one auxiliary weighing hopper;
an auxiliary weighing hopper weight sensor for measuring the weight of a
batch of articles received in said at least one auxiliary weighing hopper;
main control means for selecting a combination of article batches, which
gives a total weight closest to the target weight value within preset
limits, from the weight values measured by the weight sensors of the
respective weighing hoppers and said auxiliary weighing hopper weight
sensor, the selected combination including the batch of articles received
in said at least one auxiliary weighing hopper, said main control means
for discharging the batches of articles from the selected weighing hoppers
and from said at least one auxiliary weighing hopper, and for computing,
from the weights of batches of articles in weighing hoppers not
participating in the selected combination, a quantity of articles to be
charged into said at least one auxiliary weighing hopper; and
auxiliary feed control means for charging said at least one auxiliary
weighing hopper with a quantity of articles conforming to the computed
quantity.
6. The weighing apparatus according to claim 5 wherein said main control
means includes:
combination control means for selecting the combination and for discharging
the selected batches of articles; and
auxiliary feed arithmetic means for computing the quantity of articles to
be charged into said at least one auxiliary weighing hopper.
7. The weighing apparatus according to claim 6, wherein said combination
control means generates a combination selection signal and wherein said
auxiliary feed arithmetic means includes:
a first circuit for weighting each unselected batch of articles based on a
deviation between a target feed quantity for each of the weighing hoppers
and the weights of batches of articles in weighing hoppers which do not
participate in the selected combination, the latter being obtained on the
basis of the combination selection signal produced by said combination
control means; and
a second circuit, operatively connected to said first circuit, for
computing the quantity of articles to be charged into said at least one
auxiliary hopper, based on the weighting values determined for the
unselected batches of articles.
8. The weighing apparatus according to claim 7, wherein said first circuit
includes:
a comparator circuit for classifying the magnitude of the deviation into
plural ranks of predetermined scope; and
a weighting arithmetic circuit, operatively connected to said comparator
circuit, for counting, rank-by-rank, the number of classified batches of
articles, and for obtaining the weighting values by multiplying the
weights determined for the ranks by the counted values for each rank.
9. The weighing apparatus according to claim 8, wherein said second circuit
computes the quantity of articles based on the weighting values, the
weight values obtained from the unselected weighing hoppers, the number of
said at least one auxiliary weighing hopper and the target weight value.
10. The weighing apparatus according to claim 6, wherein said combination
control means includes means for selecting a combination of article
batches in the weighing hoppers giving a total weight value closest to a
differential weight value found by subtracting the weight value of an
article batch in said at least one auxiliary weighing hopper from the
target weight value.
11. The weighing apparatus according to claim 10, wherein said at least one
auxiliary weighing hopper comprises a pair of hoppers employed
alternately.
12. A weighing method comprising the steps of:
(a) charging articles to be weighed into a plurality of weighing hoppers;
(b) measuring the weight of each batch of articles received in the
respective weighing hoppers;
(c) selecting, based on the measured weights, a combination of article
batches giving a total weight value closest to a target weight value
within preset limits;
(d) discharging the selected article batches from the respective weighing
hoppers to obtain a collection of articles the weight of which corresponds
to the total weight value closest to the target weight value within preset
limits;
(e) computing a quantity of articles to be charged into an auxiliary
weighing hopper, based on the weights of unselected article batches in
weighing hoppers which do not participate in the selected combination
determined in said step (c); and
(f) charging the computed quantity of articles into the auxiliary weighing
hopper;
said step (a) including controlling the charging of the articles into the
weighing hoppers on the basis of a target charge quantity which is
obtained from the number of weighing hoppers, the number of auxiliary
weighing hoppers provided separately of the weighing hoppers, and the
target weight value;
said step (c) including selecting a batch of articles received in one of
the auxiliary weighing hoppers as an article batch included in the
selected combination;
said step (d) including discharging the article batch from the selected
auxiliary weighing hopper and the article batches from the selected
weighing hoppers to obtain the collection of the articles.
13. The weighing method according to claim 12, wherein said step (e)
includes the substeps of:
(e') weighting each unselected batch of articles based on the magnitude of
a deviation between the target charge quantity and the weight value of
each unselected batch of articles which does not participate in the
selected combination; and
(e") computing the weight of articles to be charged into the auxiliary
weighing hopper using the weighting values determined for each unselected
batch of articles.
14. The weighing method according to claim 13, wherein said substep (e')
includes classifying the magnitude of the deviation into plural ranks of
predetermined scope, and obtaining the weighting values by multiplying the
numbers of article batches classified by the ranks by predetermined
weighting factors for the ranks.
15. The weighing method according to claim 14, wherein said substep (e")
includes computing the weight of articles to be charged into the auxiliary
weighing hopper based on the weighting values, the weight values obtained
from the unselected weighing hoppers, the number of the auxiliary weighing
hoppers and the target weight value.
16. The weighing method according to claim 12, wherein said step (a)
includes a replenishment charging step of controlling the charging of the
articles into the weighing hoppers corresponding to the selected
combination, with the target charge quantity serving as a target for the
charging operation.
17. The weighing method according to claim 12, wherein said step (c)
includes selecting a combination of article batches in the weighing
hoppers giving a total weight value closest to a differential weight value
determined by subtracting the weight value of an article batch in the
auxiliary weighing hopper from the target weight value.
18. A weighing method for obtaining a collection of articles, comprising
the steps of:
(a) charging weighed batches of articles into hoppers;
(b) charging an auxiliary weighed batch of articles into an auxiliary
hopper;
(c) selecting, based on the weights of the weighed batches of articles and
the auxiliary weighed batch of articles, the auxiliary weighed batch of
articles and the combination of weighed batches of articles giving a total
weight value closest to a target weight value within preset limits;
(d) discharging the selected weighed batches of articles and the auxiliary
weighed batch of articles to obtain a collection of articles having a
total weight which corresponds to the total weight value closest to the
target weight value within preset limits; and
(e) computing a quantity of articles to be charged into the auxiliary
hopper, based on the weights of the unselected weighed batches of articles
in the hoppers which do not participate in the selected combination
determined in said step (c), said step (b) comprising charging the
computed quantity of articles into the auxiliary hopper;
said step (a) including controlling the charging of the weighed batches of
articles into the hoppers on the basis of a target charge quantity which
is obtained based on the number of hoppers, the number of auxiliary
hoppers, and the target weight value. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
This invention relates to a weighing method and apparatus for obtaining
articles of a weight closest to a target weight value. More particularly,
the invention relates to a weighing method and apparatus for weighing out
batches of articles with great accuracy wherein the articles in a batch
have unit weights which differ from one another, such articles being
agricultural products such as green peppers and potatoes, lifestock
foodstuffs such as meat and broilers, perishable foods, fruits and
fabricated parts.
According to a combinatorial weighing method which is known in the art,
combinatorial weighing is carried out by weighing articles which have been
introduced into a plurality of weighing hoppers, selecting the combination
of articles (referred to as the "optimum" combination) which gives a total
weight value closest to a target weight value, discharging only the
selected articles, subsequently replenishing the emptied weighing hoppers
with new articles to prepare for the next combination, and continuing
automatic weighing by thenceforth repeating the foregoing operations.
FIGS. 1 and 2 are views useful in explaining a combinatorial weighing
apparatus for practicing the foregoing weighing method, in which FIG. 1 is
a schematic view showing the general features of the apparatus, and FIG. 2
is a block diagram of a combination control unit. Numeral 11 in FIG. 1
denotes a main feeder of vibratory conveyance type. Articles to be weighed
are introduced into the main feeder 11 and imparted with vibratory motion
for a predetermined length of time so as to be dispersed radially outward
from the center of the main feeder. Numerals 12, 12 . . . denote n-number
of weighing stations which are arranged around the main feeder 11 along
radially extending lines to receive the articles dispersed by the main
feeder. Each weighing station 12 includes a dispersing feeder 12a, a pool
hopper 12b, a pool hopper gate 12c, a weighing hopper 12d, a weight sensor
12e, and a weighing hopper gate 12f. The dispersing feeder 12a comprises
an independently vibratable conveyance device for feeding the articles by
means of vibration, or an independently operable shutter. In either case,
each dispersing feeder 12a is so arranged that the designated amount of
articles received from the centrally located main feeder 11 can be
introduced into the corresponding pool hopper 12b disposed below it. The
pool hopper gate 12c is provided on each pool hopper 12b in such a manner
that the articles received in the pool hopper 12b are released into the
weighing hopper 12d when the pool hopper gate 12c is opened. Each weighing
hopper 12d is provided with a weight sensor 12e of its own. The weight
sensor 12e is operable to measure the weight of the articles introduced
into the corresponding weighing hopper, and to apply an electrical signal
indicative of the measured weight to the combination control unit 20 shown
in FIG. 2. The combination control unit then selects the combination of
articles (the "optimum" combination) which gives a total weight closest to
the target weight value, as will be described below in further detail.
Each weighing hopper 12d is provided with its own weighing hopper gate
12f. A drive control unit 30, shown in FIG. 2, upon receiving the signals
from each of the weight sensors, produces a signal to open only the
weighing hopper gates 12f of those weighing hoppers 12d that give the
optimum combination, these gates 12f discharging the articles from the
corresponding weighing hoppers 12d into a common chute 13 where they are
collected together. The collecting chute 13 has the shape of a funnel and
is so arranged as to receive the articles from any of the circularly
arrayed weighing hoppers 12d via the hopper gates 12f, which are located
above the funnel substantially along its outer rim. The articles received
by the collecting chute 13 are collected at the centrally located lower
end thereof by falling under their own weight or by being forcibly shifted
along the inclined wall of the funnel by a mechanical scraper or the like,
which is not shown. The collecting chute 13 is provided with a timing
hopper 14 at the lower end thereof for temporarily holding the collected
articles. The arrival of an externally applied signal from a packaging
machine or the like causes the timing hopper 14 to release the retained
articles from the system.
Reference will now be had to the block diagram of FIG. 2 for a description
of the combination control unit. Numeral 20 denotes the combination
control unit which includes an n-bit (n=10) counter 21 for counting timing
pulses TP of a predetermined frequency, and for generating all
combinations of n-number of the weighing hoppers. These combinations will
also be referred to as "combination patterns" where appropriate.
Specifically, for n-number of weighing hoppers, n combinations are
possible when each combination is composed of one weighing hopper from the
total of n weighing hoppers, n(n-1)/2! combinations are possible when each
combination is composed of two weighing hoppers selected from said total,
and, in general, n(n-1)(n-2) . . . (n-r+1)/r! combinations are possible
when each combination is composed of r-number of weighing hoppers selected
from said total of n weighing hoppers. Accordingly, when the n-bit binary
counter 21 has counted 2.sup.n -1 timing pulses TP, a total of 2.sup.n -1
different bit patterns, from 000 . . . 001 to 111 . . . 111, will have
been generated. Therefore, if correlation is established between the first
bit and the first weighing hopper, between the second bit and the second
weighing hopper, and between third through n-th bits and the third through
n-th weighing hoppers, then the generated bit pattern will be an
indication of the above-mentioned combination pattern.
A multiplexer 22, in accordance with the output bit pattern of the counter
21, provides an arithmetic unit 24 with read values (indicative of the
weight of the article batches) from the weight sensors 12e of
predetermined weighing hoppers. For instance, if the value of the count
(the bit pattern) in counter 21 is 1000101011 when n=10, then the
arithmetic unit 24 will receive the weight value outputs W1, W2, W4, W6,
W10 from the weight sensors 12e attached to the first, second, fourth,
sixth and tenth weighing hoppers, respectively. A target weight register
23, for storing a target weight value W.sub.a, is connected to the
arithmetic unit 24 to apply W.sub.a thereto. The arithmetic unit 24
computes, and delivers the absloute value of the difference between the
total weight .SIGMA.W.sub.i, delivered by multiplexer 22, and the target
weight value W.sub.a. More specifically, the arithmetic unit 24 performs
the operation:
.vertline..SIGMA.W.sub.i -W.sub.a .vertline.=A (1)
and produces A, representing the difference (hereafter referred to simply
as the "deviation") between the total weight .SIGMA.W.sub.i of the
combination and the target weight value W.sub.a. Numeral 25 denotes a
minimum deviation register whose initially set value is the target weight
value W.sub.a, but whose content is thenceforth updated in a manner to be
described later. An optimum combination memory for storing the optimum
combination pattern is designated at numeral 26. Numerals 27, 28 denote
gates, and 29 a comparator which compares the magnitude deviation A,
namely the output of the arithmetic unit 24, with the magnitude of the
minimum deviation, denoted by B, stored in the minimum deviation register
25. When the inequality A<B holds, the output of comparator 29 is such
that the deviation value A is delivered for storage to the minimum
deviation register 25 through the gate 27, and the content (combination
pattern) of counter 20a is delivered for storage to the optimum
combination memory 26.
The output of the optimum combination memory 26 is applied to a drive
control unit 30 which, in accordance with the optimum combination bit
pattern received from memory 26, opens the specified weighing hopper gates
12f (FIG. 1), causing the corresponding weighing hoppers 12d to discharge
their articles into the chute 13 and, concurrently, causing the
corresponding pool hopper gates 12c to open to supply the emptied weighing
hoppers 12d with articles afresh.
The operation of the weighing apparatus will now be described. At the
beginning, each of the pool hoppers 12b and weighing hoppers 12d contains
a supply of the articles. The weight sensors 12e provided on the
corresponding weighing hoppers 12d measure the weights of the articles
within the respective weighing hoppers and produce the weight values W1
through W10 which are sent to the combination control unit 20. The n-bit
(n=10) counter 21 counts the timing pulses TP having the predetermined
frequency to produce 2.sup.n -1 combination patterns. Thus, when the first
timing pulse TP arrives and is counted, the content of counter 21 becomes
0000000001. As a result, the multiplexer 22 sends the first weight value
signal W1, from the weight sensor 12e-1 provided on the first weighing
hopper, to the arithmetic unit 24, which responds by performing the
operation specified by equation (1) above, thereby producing the signal
indicative of the deviation A (=.vertline.W1-W.sub.a) between the total
weight of the combination and W.sub.a. Next, the comparator 29 compares A
with the content B of the minimum deviation register 25 (the initial value
of B being the target weight value W.sub.a). Since the inequality A<B
naturally holds, the gates 27, 28 are opened that the deviation value A is
transferred to and stored in the minimum deviation register 25, and the
content (the combination pattern 0000000001) of n-bit counter 21 is stored
in the optimum combination memory 26. Thenceforth, when the second timing
pulse TP is generated, the pulse is counted by counter 21, whose content
(combination pattern) is incremented to 0000000010. Consequently, the
weight value output W2 of the weight sensor 12e provided on the second
weighing hopper is delivered to the arithmetic unit 24 which then performs
the operation of equation (1) to produce the signal indicative of the
deviation value A (=.vertline.W.sub.2 -W.sub.a). The comparator 24
compares the deviation value A with the content B (=.vertline.W.sub.1
-W.sub.a .vertline.) of the minimum deviation register 25. If the relation
A.ltoreq.B holds, then neither the register 25 nor the optimum combination
memory 26 is updated; if A<B holds, the deviation value A is transferred
to and stored in the minimum deviation register 25, and the content of
counter 21 is transferred to and stored in optimum combination memory 26.
The operation described above is repeated until all 2.sup.n -1
combinations have been generated. At such time, the content of the minimum
deviation register 25 will be the minimum deviation value obtained from
the 2.sup.n -1 combinations, and the content of the optimum combination
memory 26 will be the combination pattern that gave said minimum value.
The optimum combination is thus selected from the total of 2.sup.n -1
possible combination patterns.
The optimum combination pattern selected in the above manner is applied to
the drive control unit 30 which opens the weighing hopper gates 12f of the
weighing hoppers corresponding to the "1" bits in the optimum combination
pattern, whereby these weighing hoppers release their articles into the
chute 13, this batch of articles making up the optimum combination of
articles. This will leave the selected weighing hoppers 12d empty.
Subsequently, therefore, the pool hopper gates 12c corresponding to the
empty weighing hoppers 12d are opened to introduce a fresh supply of the
articles from the respective pool hoppers into said weighing hoppers 12d,
leaving these pool hoppers empty. Accordingly, the dispersing feeders 12a
which correspond to the empty pool hoppers 12b, are vibrated for a
predetermined period of time to deliver a fresh supply of the articles to
these pool hoppers. This restores the weighing apparatus to the initial
state to permit resumption of the control operation for selecting the best
weight combinations in the manner described. Thus, weighing by the
combinatorial weighing apparatus may proceed in continuous fashion by
repeating the foregoing steps.
With the conventional weighing method as described above, weighing errors
can be held below the unit weight of the articles being weighed even when
the articles have unit weights differing widely from one to another. Green
peppers, for example, vary greatly from one to another in their unit
weight. The same is true of potatoes and other agricultural products,
livestock foodstuffs such as meats and broilers, and articles in general
that cannot be shaped artificially. When weighing candies, snack foods and
fabricated metal parts, moreover, the conventional method makes it
possible to diminish the average weighing error.
When weighing out a target weight over and over with the prior-art method,
however, the weighing error differs with each weighing operation, with the
possibility that, ultimately, the total weight of a combination will no
longer exist in the neighborhood of the target weight. For example, let us
assume that from several dozen to several thousand articles having a
comparatively small unit weight of about 5 g or less are to be gathered
together and weighed out to a predetermined weight. The weighing error not
only frequently exceeds the unit weight in such case, but is known to grow
as large as 20 to 30 g. When a combined weight no longer exists near the
target weight value, the conventional practice is to charge additional
articles into each of the weighing stations to alter the weight in each
station, followed by recomputing combinations. With such method, however,
too large a value is likely to be weighed out owing to an excessive supply
of the articles, thereby leading to a much greater weighing error.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a weighing
method and apparatus, based on a combinatorial scale, for executing a
highly accurate weighing operation in which weighing error is greatly
reduced.
Another object of the present invention is to provide a weighing method and
apparatus so adapted that a target weight can be obtained from
combinations which are large in number.
Still another object of the present invention is to provide a weighing
method and apparatus for executing highly accurate weighing in which
weighing error is greatly reduced, even when weighing out the same target
weight repeatedly.
Yet another object of the present invention is to provide a weighing method
and apparatus for executing highly accurate weighing, so adapted that
articles will not remain in weighing hoppers for an extended period of
time because the weighing hoppers containing these articles are repeatedly
unselected for participation in an optimum combination.
A further object of the present invention is to provide a weighing method
and apparatus capable of minimizing article batches of a weight which
tends not to be selected for participation in optimum combinations.
According to the present invention, these and other objects are attained by
provided a weighing method and apparatus wherein each of a plurality of
weighing hoppers is supplied with articles having a mean weight of 2X/N
(when N is even) or 2X/(N.+-.1) (when N is odd), where the number of
weighing hoppers is N and the target weight value is X. This makes it
possible to perform highly accurate weighing by reducing weighing error.
According to another feature of the invention, articles will not reside in
the weighing hoppers for a prolonged period of time even when their
weighing hoppers are not selected for participation in an optimum
combination. This is accomplished by monitoring the tendency exhibited by
the weights of the remaining article batches. For example, if the weight
of a remaining article batch inclines toward the negative side or positive
side with respect to the value 2X/N, this is monitored so that a new feed
quantity may be introduced to cancel the particular inclination. Articles
therefore will not remain in any of the weighing hoppers for a prolonged
period of time.
Other features and advantages of the present invention will be apparent
from the following description taken in conjunction with the accompanying
drawings, in which like reference characters designate the same or similar
parts throughout the figures thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view of the general construction of a weighing
apparatus useful in describing a weighing method according to the prior
art;
FIG. 2 is a block diagram of a combination control unit in a weighing
apparatus, used for describing a weighing method according to the prior
art;
FIG. 3 is a distribution curve indicative of the weights of article batches
charged into weighing stations, and is useful in describing the principle
of the present invention;
FIG. 4 is a schematic view of the general construction of a weighing
apparatus embodying the present invention;
FIG. 5 is a block diagram of the weighing apparatus embodying the present
invention;
FIG. 6 is a graph of deviation ranks for describing the operation of the
apparatus shown in FIG. 5; and
FIG. 7 is a block diagram of an essential portion of the arrangement shown
in FIG. 5.
DESCRIPTION OF THE PREFERRED EMBODIMENT
According to the present invention, the weight of the articles introduced
into each of the weighing stations is controlled in a manner which will
now be described. Let us examine a case where X grams are to be weighed
out in a combinatorial scale having N-number of weighing stations. The
target weight value will therefore be X grams. To obtain the target
weight, the amount of articles fed to each weighing station should be
adjusted to have a mean value of 2X/N grams when N is even, and
2X/(N.+-.1) grams when N is odd. The reason is as follows. The number of
combinations that can be computed by a combinatorial scale composed of N
weighing stations, where a combination may be made up of only one weighing
machine or up to all N of the weighing machines, is 2.sup.N -1. When N is
even, combinations composed of N/2 weighing machines will be the largest
in number among said 2N-1 combinations. When N is odd, combinations
composed of (N.+-.1)/2 weighing machines will be the largest in number
among said 2.sup.N -1 combinations. Thus, if it can be arranged to obtain
the target weight with the combinations that select the largest number of
weighing stations, then the possibility of achieving an accurate weighing
operation will improve correspondingly. Accordingly, when N is even, N/2
times the mean weight W.sub.m of the articles introduced into each
weighing station should be equivalent to the target weight of X grams.
When N is odd, (N.+-.1)/2 times the mean weight W.sub.m of the articles
introduced into each weighing station should be equivalent to the target
weight of X grams. In accordance with the present invention, therefore,
control is effected so that the mean weight of the articles introduced
into each weighing station will be equivalent to 2X/N grams when N is
even, and 2X/(N.+-.1) grams when N is odd.
Thus, control is performed in such a manner that the dispersing feeders
load articles into the corresponding weighing hoppers with 2X/N as the
target for each weighing hopper when N is even, and with 2X/(N.+-.1) as
the target when N is even. Since the dispersing feeders are arranged in
such a manner that the amount of articles charged into the weighing
hoppers is decided by the amplitude and duration of vibration, the desired
results may be obtained by finding the above-mentioned mean weight W.sub.m
from the target weight value X and the number N of weighing stations,
computing the vibration amplitude and duration corresponding to the mean
weight W.sub.m, and driving the dispersing feeders at the computed
vibration amplitude for the computed period of time. By effecting control
in this fashion, the weight of the batch of articles received in each of
the weighing hoppers will not be uniformly equivalent to the mean weight
W.sub.m, but the mean value of these weights will be approximately
equivalent to the mean weight W.sub.m.
Next, as will be described in further detail below, there is a tendency for
certain weighing hoppers not to be selected in a combinatorial weighing
operation, making it progressively more difficult to obtain on optimum
combination close to the target weight. According to another feature of
the invention, therefore, a monitoring operation is carried out during
combinatorial weighing to determine what trends are exhibited by the
weights of the articles remaining in the unselected weighing hoppers. The
control operation proceeds in a manner which will now be described.
Assume that articles are being introduced at a regular distribution where
the mean weight introduced into N-number of weighing stations is L grams
and the standard deviation from L is .sigma. grams (see FIG. 3). N shall
be an even number.
Though the desired relation is L=2X/N, over supply and under supply tend to
occur, so that the actual condition which prevails is given by:
L=(2X/N)+.sigma.
With the articles being supplied in this manner, those article batches
exhibiting a deviation near -3.sigma. are likely to be selected, while
those having a deviation near +3.sigma. are not. The reason is that
articles are not present for cancelling or offsetting the deviation of
+3.sigma.. When the weighing cycle is repeated again and again in the
automatic weighing operation, therefore, the article batches with the
deviation in the vicinity of +3.sigma. continue to remain unselected and
make up a large part of the N number of article batches. Under such
conditions, the result is a larger weighing error so that desirable
combinations fail to appear.
According to the invention, therefore, control is executed by monitoring
the trend exhibited by the weights of the article batches remaining in the
unselected weighing hoppers, such as by monitoring whether the weight of
each remaining batch of articles is inclining toward the positive side or
negative side with respect to 2X/N, and creating a new article charge
quantity in such fashion as to cancel the particular inclination, so that
articles will not reside in the weighing hoppers for a prolonged period of
time.
Reference will now be had to FIGS. 4 and 5 illustrating a weighing
apparatus for practicing the weighing method of the present invention, in
which FIG. 4 is a schematic view of the mechanical features of the
apparatus, and FIG. 5 is a block diagram of the associated circuitry.
Referring first to FIG. 4, it will be seen that the apparatus is
distinguishable over the prior-art arrangement of FIG. 1 in that there are
provided auxiliary weighing stations 41, 42, and in that (N-1)-number of
weighing stations 12 are provided. Other portions which are similar to
those shown in FIG. 1 are designated by like reference characters and are
not described in detail again.
The auxiliary weighing stations 41, 42 include respective auxiliary
dispersing feeders 41a, 42a, auxiliary pool hoppers 41b, 42b, auxiliary
pool hopper gates 41c, 42c, pool hopper weight sensors 41d, 42d for
measuring the weights of articles charged in the auxiliary pool hoppers
41b, 42b, respectively, auxiliary weighing hoppers 41e, 42e, auxiliary
weight sensors 41f, 42f, and auxiliary weighing hopper gates 41g, 42g. The
auxiliary weighing stations 41, 42 correspond to the weighing stations 12
(serving as the main weighing stations). The auxiliary dispersing feeders
41a, 42a, auxiliary pool hoppers 41b, 42b, auxiliary weighing gates 41c,
42c, pool hopper hoppers 41e, 42e, auxiliary weight sensors 41f, 42f and
auxiliary hopper gates 41g, 42g correspond to, and have the same
construction as, the dispersing feeders 12a, pool hoppers 12b, pool hopper
gates 12c, weighing hoppers 12d, weight sensors 12e and weighing hopper
gates 12f. The pool hopper weight sensors 41d, 42d sense the weights of
articles introduced into the pool hoppers 41b, 42b, respectively, and
deliver signals indicative of the sensed weight values to an auxiliary
dispersing feed control unit, which will be described below with reference
to FIG. 7. Control is effected by the control unit in such a manner that
the weight of the articles introduced into auxiliary pool hopper 41b or
42b will be equivalent to an auxiliary feed quantity (weight value)
W.sub.s computed in an auxiliary feed arithmetic unit, described below.
Next, reference will be had to the block diagram of FIG. 5 to describe the
electrical system for practicing the weighing method of the invention.
Portions similar to those shown in the conventional arrangement of FIG. 2
are designated by like reference characters and need not be described
again. In FIG. 5, the blocks indicated at numeral 12e are the weight
sensors provided on the corresponding weighing hoppers. As in FIG. 2,
numeral 20 denotes the combination control unit, and 30 the drive control
unit. The blocks indicated at numerals 41f, 42f are the auxiliary weight
sensors provided on the corresponding auxiliary weighing hoppers 41e, 42e.
Signals from the auxiliary weight sensors 41f, 42f, indicative of the
weights measured thereby, are applied to a multiplexer 51 which, in
response to a switching signal ES from the auxiliary feed control unit,
described below, alternatingly applies one of the outputs received from
the auxiliary weight sensors 41f, 42f to the arithmetic unit 24 of the
combination control unit 20 as a signal W.sub.s indicative of the measured
weight. The combination control unit 20 selects the optimum combination
through a control operation substantially the same as that described above
in connection with FIG. 2. In this case, however, the arithmetic unit 24
also receives the weight value output W.sub.s from the multiplexer 51 and
performs the following arithmetic operation instead of that given by Eq.
(1) above:
.vertline..SIGMA.W.sub.i +W.sub.s -W.sub.a .vertline.=A (2)
Thus, the combination control unit 20 always selects the weight of the
articles from one of the auxiliary weighing hoppers 41e, 42e as one
constituent of the optimum combination, and selects the other constituents
of the optimum combination from the (N-1)-number of weighing hoppers 12d.
Designated at 52 is the auxiliary feed arithmetic unit, and at 53 the
auxiliary feed control unit, referred to above. The auxiliary feed
arithmetic unit 52 includes NOT gates 52a, AND gates 52b, a sequential
switching circuit 52c, and a multiplexer 52d. The inputs to the NOT gates
52a are single bits in the optimum combination pattern stored in the
optimum combination memory 26. Since the bits corresponding to the
weighing hoppers not selected for participation in an optimum combination
are "0" bits, only the outputs of NOT gates 52a corresponding to the
unselected weighing hoppers will be logical "1". The sequential switching
circuit 52c is adapted to produce "1" signals sequentially on lines
l.sub.1, l.sub.2, . . . , l.sub.n at a predetermined period. As a result,
the AND gates 52b corresponding to weighing hoppers which do not
participate in an optimum combination deliver logical "1" signals
sequentially to the multiplexer 52d, the latter functioning to provide a
comparator circuit 52g with the weight W.sub.i of the articles contained
in each of the unselected weighing hoppers.
In order to rank the batches of articles in the weighing hoppers in
accordance with the magnitude of the deviation between the mean weight
W.sub.m (=2X/N) of the introduced articles and the actual weight of the
articles in each hopper, the auxiliary feed arithmetic unit 52 is provided
with registers 52e.sub.1, 52e.sub.2, . . . 52e.sub.i for storing rank
boundary values. Thus, numeral 52e.sub.1 denotes a first rank boundary
value register, 52e.sub.2 a second rank boundary value register and, in
general, 52e.sub.i an i-th rank boundary value register. Letting (N-M) be
the number of weighing hoppers 12d (where M is the number of auxiliary
weighing hoppers) and W.sub.a the target weight, and assuming that N is an
even number, the mean weight W.sub.m of the articles introduced into each
of the weighing hoppers 12d will be given by:
W.sub.m =2X/N
As illustrated in FIG. 6, in accordance with the preferred embodiment, the
ranks of the measured article weight values are divided into first through
fifth ranks about a central value which is the mean weight W.sub.m. The
first rank indicates article weights of less than y.sub.1 grams, the
second rank article weights of between y.sub.1 and y.sub.2 grams, the
third rank article weights of between y.sub.2 and y.sub.3 grams, the
fourth rank article weights of between y.sub.3 and y.sub.4 grams, and the
fifth rank article weight of above y.sub.4 grams. The first rank is
furthest from the mean weight W.sub.m on the negative side, and the fifth
rank is furthest from the mean weight W.sub.m on the positive side.
The auxiliary feed arithmetic unit 52 further includes a sequential
switching circuit 52f for sequentially selecting, at a predetermined
period, the rank boundary values stored in the first through i-th rank
boundary value registers 52e.sub.1 through 52e.sub.i, the selected values
being delivered to the comparator circuit 52g. The latter is adapted to
compare the weight values W.sub.i of the unselected article batches,
received sequentially from the multiplexer 52d, with the data stored in
each of the rank boundary value registers, and to determine the rank of
each unselected batch of articles, a signal indicative of the latter being
applied to a ranking counter unit 52h. The ranking counter unit 52h
includes counters for respective ones of the five ranks mentioned above
for counting the number of article batches belonging to each rank. The
counter outputs are applied to constant multipliers 52i provided for
respective ones of the five ranks. The constant multipliers 52i are
so-called weighing circuits for weighting the first rank with 2w, the
second rank with w, the third rank with 0, the fourth rank with -w, and
the fifth rank with -2w. For example, letting m.sub.i (i=1,2, . . . , 5)
be the number of article batches belonging to the i-th rank (i=1,2, . . .
5), the constant multipliers 52i will deliver the following weighted
values, respectively: +2w.multidot.m.sub.l, +w.multidot.m.sub.2, 0,
-w.multidot.m.sub.4, -2w.multidot.m.sub.5. As for the value of w, this can
be set to .sigma. assuming that the width of each of the second, third and
fourth ranks is .sigma.. The auxiliary feed arithmetic unit 52 also has a
multiplier 52m for multiplying the target weight W.sub.a by 2/(N+1), and
an adding circuit 52n. The latter adds together the outputs from each of
the constant multipliers 52i and the output of the multiplier 52m to
produce an auxiliary feed signal W.sub.s indicating the weight of
articles to be introduced into one of the pool hoppers 41b, 42b.
Thus, the auxiliary feed arithmetic unit 52 functions to determine whether
the weight of each article batch which does not participate in an optimum
combination is inclining toward the positive or negative side of the mean
weight 2X/N. The unit 52 also computes the auxiliary feed quantity W.sub.s
indicating the weight of the articles to be charged into the auxiliary
weighing hoppers 41e, 42e (FIG. 4), based on said determination, in such
fashion as to cancel the particular inclination or, in other words, to
assure that articles will not reside in any of the weighing hoppers for a
prolonged period of time.
The auxiliary feed control unit 53, as shown in greater detail in the block
diagram of FIG. 7, comprises a controller 53a; feed storage registers 53b,
53c set alternately to the auxiliary feed quantity W.sub.s which enters
from the auxiliary feed arithmetic unit 52 (FIG. 6) a gating circuit 53d
for applying the auxiliary feed quantity W.sub.s to the feed storage
registers 53b, 53c alternately, and comparators 53e, 53f for comparing the
auxiliary feed quantity, denoted W.sub.s1 and W.sub.s2 when stored in the
registers 53b, 53c, respectively, with output values W.sub.T1, W.sub.T2
from the pool hopper weight sensors 41d, 42d. The comparators 53a, 53f
deliver logical "1" on line L.sub.11 when W.sub.s1 >W.sub.T1 holds or on
line L.sub.21 when W.sub.s2 >W.sub.T2 holds, a coincidence signal
COI.sub.1 on line L.sub.12 when W.sub.s1 =W.sub.T1 or a coincidence signal
COI.sub.2 on line L22 when W.sub.s2 =W.sub.T2. The lines L.sub.11,
L.sub.21 are connected to the input side of AND gates 53g, 53h,
respectively.
The weighing method of the present invention will now be described in
detail with reference to FIGS. 4, 5 and 7.
For starting conditions, assume that batches of articles to be weighed have
been introduced into the N-number of weighing hoppers 12d and pool hoppers
12b and into the auxiliary weighing hopper 41e and auxiliary pool hopper
42b, that the auxiliary weighing hopper 42e is empty, and that the
auxiliary pool hopper 41b contains only a small amount of the articles.
The situation is as illustrated in FIG. 4, where the accumulations of the
articles in the various hoppers are shown, with auxiliary weighing hopper
42g being shown empty. We will also assume that the multiplexer 51 (FIG.
5) responds to the switching signal ES from the auxiliary feed control
unit 53 by applying the output (weight value) W.sub.s from the auxiliary
weight sensor 41f to the arithmetic unit 24 of the combination controller
20.
The weight sensors 12e provided on the corresponding weighing hoppers 12d
measure the weights of the article batches contained in these hoppers, and
provide the combination control unit 20 with signals indicative of the
measured weight values W.sub.1 through W.sub.n. The n-bit counter 21
counts the timing pulses TP of the predetermined period, sequentially
producing 2.sup.n -1 different combination patterns. Each time a new
combination pattern is generated, the arithmetic unit 23 performs the
operation of Eq. (2) to produce the deviation value A, and the comparator
29 compares A with the content B of the minimum deviation register 25.
When A.gtoreq.B holds, neither the register 25 nor the optimum combination
memory 26 is updated. When A<B holds, the deviation value A is transferred
to and stored in the minimum deviation register 25, and the content of
counter 21 is transferred to and stored in optimum combination memory 26.
The operation described above is repeated until all 2.sup.n -1
combinations have been generated. At such time the content of the minimum
deviation register 25 will be the minimum deviation value obtained from
the 2.sup.n -1 combinations, and the content of the optimum combination
memory 26 will be the combination pattern that gave said minimum value.
The optimum combination is thus selected from the total of 2.sup.n -1
possible combination patterns, thereby ending this cycle of combin | | |
