Combinatorial weighing method and apparatus

A combinatorial weighing method and apparatus wherein a value serving as a target for a combinatorial computation is set so that the mean weight value of batches of articles weighed out selectively by plural weighing cycles becomes equal to a preset weight value within preset allowable limits. Combinatorial computations are performed while diminishing the target weight value by a predetermined amount when the mean weight value is greater than the preset weight value, and increasing the target weight value by a predetermined amount when the mean weight value is less than the preset weight value.

CROSS REFERENCE TO RELATED APPLICATION 
This application is related to U.S. application Ser. No. 590,356 filed Mar. 
16, 1984, now U.S. Pat. No. 4,512,427, and assigned to the assignee of the 
subject application. 
BACKGROUND OF THE INVENTION 
This invention relates to a combinatorial weighing method and apparatus in 
an automatic weighing system of the combinatorial type. More particularly, 
the invention relates to a combinatorial weighing method and apparatus for 
measuring the weight of a batch of articles introduced into each of a 
plurality of weighing machines, forming the weight values provided by the 
weighing machines into combinations, selecting the combination of weighing 
machines whose articles have a total combined weight within a preset 
allowable range, and discharging the articles from the selected 
combination of weighing machines. 
According to a combinatorial weighing apparatus which is known in the art, 
combinatorial weighing is carried out by weighing batches of articles 
which have been introduced into a plurality of weighing machines, forming 
combinations of the weight values from the weighing machines, obtaining a 
combination (referred to as the "optimum combination") the total weight of 
which is equal to a preset weight value or closest to the preset weight 
value within preset allowable limits, discharging the articles from the 
machines belonging to the combination obtained, subsequently replenishing 
the weighing machines, which have discharged their articles, with articles 
in order to prepare for the next combination, and continuing automatic 
weighing by repeating the foregoing operations. 
In a combinatorial weighing apparatus of the foregoing type, a 
combinatorial weighing technique customarily employed is referred to as a 
so-called "minus-cut method" wherein the lower limit value of the preset 
allowable limits is so determined as to be equal to the preset weight 
value. The reason is that setting the lower limit value to one below the 
preset weight value can have the undesirable result of providing a batch 
of discharged articles the total weight of which is too low. With the 
minus-cut method, a mean weight value W.sub.m obtained over a plurality of 
weighing cycles always falls within a range between a preset weight value 
W.sub.s and an upper limit weight value W.sub.max, as shown in FIG. 1. 
Therefore, as a result of adopting the minus-cut method, the total weight 
of the combination obtained in every weighing cycle must be made greater 
than the preset weight value. This is a disadvantage in that it results in 
a lower yield on the producer's, or seller's, side. 
Accordingly, in some countries it is legally permitted to adopt a lower 
limit value W.sub.min, namely the lower limit of the aforementioned preset 
allowable limits, which is below the preset value W.sub.s. In other words, 
if the total weight of a combination resides within the limits of a 
predetermined precentage (e.g., 4.5%) about a central value which is the 
preset weight value, then shipment of the product is allowed even if the 
total weight of the combination is below the preset weight value. For 
consumer protection, however, the producer is obligated to adopt a mean 
weight value W.sub.m for shipment which is greater than the preset weight 
value W.sub.s, as shown in FIG. 2. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a combinatorial weighing 
method and apparatus through which the mean weight value of the total 
weight of a discharged combination of articles can be kept greater than a 
preset weight value even if the lower limit value of the preset allowable 
limits is below the preset weight value. 
Another object of the present invention is to provide a combinatorial 
weighing method and apparatus through which the mean weight value of the 
total weight of a discharged combination of articles can be brought 
extremely close to a preset weight value. 
According to the present invention, the foregoing objects are attained by 
providing a combinatorial weighing method, and an apparatus for practicing 
the method, in which there is provided a control unit adapted to perform 
combinatorial computations based on weight values produced as outputs by 
respective ones of a plurality of weighing machines which measure the 
weights of articles supplied thereto, to select a combination of weighing 
machines whose articles have a total combined weight value within preset 
allowable limits, and to discharge the articles from the weighing machines 
belonging to the selected combination. The method comprises the steps of 
calculating a mean weight value of total combined weight values selected 
by a plurality of weighing cycles, setting a target weight value, which 
serves as the target of a combinatorial computation, in such a manner that 
the mean weight value approaches a preset weight value which is within the 
preset limits, and performing combinatorial computation while diminishing 
the target weight value by a predetermined amount when the mean weight 
value is greater than the preset weight value, and increasing the target 
weight value by a predetermined amount when the mean weight value is less 
than the preset weight value. 
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.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Reference will now be had to the drawings to describe an embodiment of the 
present invention in detail. 
Illustrated in FIG. 3 is an example of a combinatorial weighing apparatus 
for practicing the combinatorial weighing method of the present invention. 
Numeral 10 denotes a dispersing table of vibratory conveyance-type, 
supported by a platform 3 disposed above the central portion of a base 2. 
Articles to be weighed are introduced onto the dispersing table 10 from 
chutes of a supply conveyor (not shown) and are imparted with vibratory 
motion for a predetermined length of time so as to be dispersed radially 
outward from the center of the table. Numerals 1, . . . 1 denote n-number 
of weighing stations which are arranged around the dispersing table 10 
along radially extending lines to receive the articles dispersed by the 
table. Each weighing station 1 includes a dispersing feeder 11, a pool 
hopper 12, a weighing machine 101 comprising a weighing hopper 13 and a 
weight sensor 14, and a hopper drive unit 15 for opening and closing a 
hopper gate 121 of the pool hopper 13 and a hopper gate 131 of the 
weighing hopper 13. 
The dispersing feeders 11 are arranged radially so as to surround the 
dispersing table 10, and each includes an electromagnetic vibrator 111 and 
a trough 112 supported by the platform 3. Articles supplied to the trough 
112 from the dispersing table 10 fall into the corresponding pool hopper 
12 from the end of the trough due to the linear reciprocating motion of 
the electromagnet 111. The pool hopper gate 121 is opened under the 
control of the hopper drive unit 15, whereupon the articles contained in 
the pool hopper 12 are released into the corresponding weighing hopper 13 
constituting the weighing machine 101. Each of the weight sensors 14 
attached to a respective one of the weighing hoppers 13 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 a combinatorial control unit, described below. The 
combinatorial control unit then obtains an optimum combination by 
performing processing for combinatorial weighing based on the weight 
values obtained from the weighing machines 101, and produces a discharge 
control command which is applied to the hopper drive units corresponding 
to the optimum combination. The hopper drive units 15 respond to the 
command by opening the hopper gates 131 on the weighing hoppers 12 of the 
corresponding weighing machines 101, whereby the articles contained in 
these weighing hoppers 13 are discharged. 
Designated at numeral 4 is a collecting chute disposed below the weighing 
hoppers 13 for collecting the articles released from the weighing hoppers 
13 and for supplying these articles to a packaging machine, (not shown). 
A block diagram of a weighing apparatus for practicing the combinatorial 
weighing method of the present invention is illustrated in FIG. 4. 
In FIG. 4, weight values Wi (i=1, 2, . . . n) produced by n-number of the 
aforementioned weighing machines 101-1, 101-2 . . . 101-n, are applied to 
a multiplexer 102, constituted by, e.g., an analog switch, which delivers 
the weight values in sequential fashion in response to a weight read 
signal WRS from a combinatorial control unit 104. An analog-to-digital 
(A/D) converter 103 converts each analog weight value Wi, delivered by the 
multiplexer 102, into a digital value. The digital output of the A/D 
converter 103 is applied to the combinatorial control unit 104, which has 
the construction of a microcomputer. The latter includes a processor 104a 
which receives the output of the A/D converter 103 for executing 
processing in accordance with a combinatorial processing program, a data 
memory 104b comprising a RAM (random-access memory), a memory 104c storing 
the combinatorial processing program, and a timer 104e. A weight setting 
unit 105 sets a preset weight value W.sub.s, which is applied to the 
processor 104a. Numeral 106 denotes an upper limit setting unit, and 107 a 
lower limit setting unit. The units 106, 107 are for establishing preset 
allowable limits (an upper limit value W.sub.max and a lower limit value 
W.sub.min) for the total weight value of a combination. It should be noted 
that the upper limit value W.sub.max, lower limit value W.sub.min and 
preset weight value W.sub.s are related by the inequality W.sub.min 
&lt;W.sub.s &lt;W.sub.max, as shown by FIG. 2. Numeral 108 denotes a display 
unit for displaying the total weight of a combination, the weighing 
machines selected, improper weights, etc. Numeral 109 denotes a discharge 
control unit. 
The weighing operation performed by the combinatorial weighing apparatus 
shown in FIG. 4 will now be described in conjunction with the flowcharts 
of FIGS. 5(A) and (B). We will assume that starting the weighing operation 
sets the mean weight value W.sub.m to a predetermined value (a binary 
number of all "1"s), sets a target weight value W.sub.t equal to the 
preset weight value W.sub.s, starts the timer 104e upon first clearing the 
timer to zero, and that the operations 0.fwdarw.N.sub.T, 0.fwdarw.W.sub.T 
are performed. 
(a) When a packaging machine (not shown) generates a start signal (timing 
signal) STS, the signal is read by the processor 104a. Upon detecting the 
generation of the start signal STS, the processor 104a (1) sets to zero a 
numerical value k stored in the data memory 104b, and (2) initially sets a 
minimum deviation value B to a predetermined number (a binary number of 
all "1"s). 
(b) Next, the processor 104a delivers the weight value read signal WRS to 
the multiplexer 102. The latter responds by successively applying the 
weight values Wi (i=1, 2 . . . n) to the AD converter 103, which proceeds 
to convert each weight value Wi into a digital quantity that the processor 
104a stores in the data memory 104b. 
(c) Thereafter, the processor 104a generates 2.sup.n -1 combination 
patterns, one after another, under the control of the combinatorial 
processing program. The 2.sup.n -1 combination patterns are generated in 
the following manner. Specifically, the processor 104a has an internal 
general-purpose register 104d. Correspondence is established between the 
first bit of the register 104a and the first weighing machine (weight 
value W1), the second bit and the second weighing machine (W2), and so on 
through the n-th bit, which corresponds to the n-th weighing machine 
(weight value Wn). Then, when the general-purpose register 104d has been 
counted up from 1 to 2.sup.n -1, the result will be the generation of 
2.sup.n -1 combination patterns 0000 . . . 001 through 1111 . . . 111. 
The processor 104a is adapted to add the weight values corresponding to the 
"1" bits in each of the combination patterns to calculate the total weight 
value X (=.SIGMA.Wi) of each and every combination. Accordingly, in 
response to generation of the first combination pattern 0000 . . . 001, 
the processor 104a calculates X (=W1) and stores this value in the data 
memory 104b. 
(d) The processor 104a then finds the difference A between the total weight 
value X and the target weight value W.sub.t by performing the following 
operation: 
EQU .vertline.X-W.sub.t .vertline..fwdarw.A (1) 
(e) Upon calculating the difference A, the processor 104a renders a 
decision concerning the magnitude of the mean weight value W.sub.m 
(initially all "1"s, i.e., 11 . . . 1) and the magnitude of the preset 
weight value W.sub.s. Since W.sub.m is initially equal to 11 . . . 1, the 
decision rendered is W.sub.m &gt;W.sub.s. 
(f) If W.sub.m &gt;W.sub.s is found to hold, the processor 104a determines 
whether the total weight X of the combination falls within certain limits, 
that is, whether the following relation holds: 
EQU W.sub.min .ltoreq.x.ltoreq.W.sub.max (2) 
If Eq. (2) is satisfied, then k is updated through the following operation: 
EQU k+1.fwdarw.k (3) 
(g) The processor 104a then compares the magnitude of the difference 
.vertline.A.vertline. and of a minimum deviation value B, which is stored 
in the data memory 104. If .vertline.A.vertline.&lt;B is found to hold, the 
difference .vertline.A.vertline. is made equal to the minimum deviation 
value B, i.e., the operation .vertline.A.vertline..fwdarw.B is performed, 
and the bit pattern 000 . . . 001 is stored in the data memory 104b as a 
combination pattern which, up to the present point in time, is the optimum 
combination. Note that .vertline.A.vertline.&lt;B will hold initially due to 
the fact that the initial value of B is the binary number 11 . . . 1 
consisting of all "1"s. 
(h) Thereafter, or where X does not satisfy Eq. (2), or where 
.vertline.A.vertline..gtoreq.B holds, the processor 104a determines 
whether all possible combination patterns have been generated. Where this 
is not the case, the general-purpose register 104d is incremented and the 
next combination pattern is generated. 
(i) From this point onward, the foregoing processing is repeated until all 
combination patterns are generated, thereby ending combinatorial 
processing. When this is accomplished, the processor 104a determines 
whether the following holds: 
EQU k.gtoreq.1 (4) 
If it does not, then the processor causes the display unit 108 to present 
an alarm indication, which signifies failure to obtain a combination the 
total weight value of which is within the preset allowable limits. Note 
that if k=0 holds, the processor 104a compares the magnitudes of the 
weight values W.sub.1, W.sub.2 , . . . W.sub.10, which are produced by the 
respective weighing machines and stored in the data memory 104, with the 
magnitude of a value given by, e.g., W.sub.s /8, and produces an enable 
signal to open the pool hoppers corresponding to those weighing machines 
that produce weight values which are less than the value W.sub.s /8. In 
this way these weighing machines are supplied with additional articles. 
Processing then returns to step (a). 
(j) If k.gtoreq.1 is found to hold in step (i), the processor 104a again 
enters the weight values W.sub.i and adds weight values Wi' corresponding 
to the "1" bits in the above-mentioned optimum combination pattern stored 
in the data memory 104b, thereby calculating the total weight value X' of 
this combination. When the total weight value X' of the combination has 
been calculated, the processor determines whether X' falls within the 
range given by: 
EQU W.sub.min .ltoreq.X'.ltoreq.W.sub.max (5) 
In other words, the processor 104a again determines whether X' lies within 
the preset allowable limits. Note that a combination of articles having a 
total weight outside the present allowable limits is prevented, by virtue 
of step (j), from being discharged even if the weight values W.sub.1 
through W.sub.10 used in steps (a) through (i) contain an error 
attributable to the effects of external vibration or the like. 
(k) If Eq. (5) is not satisfied, the processor 104a executes processing 
similar to that executed in step (i) for the case where k=0 was found to 
hold. 
(l) If Eq. (5) is satisfied, then the processor 104a determines whether a 
time T.sub.a measured by the timer 104e (FIG. 4) has attained a preset 
time T.sub.s (e.g., 30 sec or 1 hr). 
(m) If T.sub.a &lt;T.sub.s is found to hold, then the processor 104a performs 
the following operations: 
EQU N.sub.T +1.fwdarw.N.sub.T (6) 
EQU W.sub.T +X'.fwdarw.W.sub.T (7) 
to update N.sub.T, which is the total number of times articles have been 
discharged, and W.sub.T, which is the running total weight of articles 
discharged. 
(n) Thereafter, the processor 104a determines whether N.sub.T has attained 
a prescribed numerical value, e.g., a factor of five. If it has, then the 
processor 104a calculates the mean weight value W.sub.m. In other words, 
the mean weight value W.sub.m is calculated every five discharge cycles. 
(p) If N.sub.T is not a multiple of five, then the processor 104a delivers 
the obtained optimum combination pattern to the discharge control unit 
109, which responds by controlling the hopper drive units 15 in such a 
manner that the weighing hoppers 13 of the weighing machines 101 
corresponding to the "1" bits in the optimum combination pattern, 
discharge their articles. the processor 104a then controls the hopper 
drive units 15 in such a manner that these units cause the weighing 
hoppers 13 of the weighing machines which have discharged their articles 
to be resupplied by the overlying pool hoppers 12, after which the system 
awaits a start signal from the packaging machine. 
(q) If N.sub.T is a multiple of five, the processor 104a calculates the 
mean weight value W.sub.m by performing the following operation: 
EQU W.sub.T /N.sub.T .fwdarw.W.sub.m (8) 
(r) Thereafter, the processor 104a determines whether the mean weight value 
W.sub.m and the preset weight value W.sub.s are equal. If W.sub.m =W.sub.s 
holds, the target weight Wt is not updated and step (p) is performed to 
discharge the articles corresponding to the optimum combination and supply 
the corresponding weighing machines 101 with articles from the overlying 
pool hopper 12. The system then awaits a start signal from the packaging 
machine. 
(s) If the mean weight value W.sub.m and the preset weight value Ws are not 
equal, the processor 104a, through subsequent processing which is 
dependent upon the magnitude of these values, updates the target weight 
value W.sub.t in such a manner that the mean weight value approaches the 
preset weight value. More specifically, when W.sub.m &gt;W.sub.s holds, the 
target weight value W.sub.t is diminished so as to reduce the size of the 
mean weight value. However, since the minimum value of the target weight 
Wt is the lower limit value W.sub.min of the preset allowable limits, the 
processor 104a first determines whether W.sub.t =W.sub.min holds. When the 
condition W.sub.t =W.sub.min does hold, the processor clamps the target 
weight value W.sub.t to W.sub.min and executes the discharge and supply 
operations of step (p), with the system then being placed in the mode 
awaiting the start signal from the packaging machine. If W.sub.t 
=W.sub.min does not hold, on the other hand, that is, if W.sub.t 
&gt;W.sub.min holds, then the processor 104a diminishes the target weight 
value W.sub.t by a predetermined amount, say 0.1 g, and executes the 
discharge and supply operations of step (p), with the system then being 
placed in the mode awaiting the start signal from the packaging machine. 
(t) If the condition W.sub.m &lt;W.sub.s is found to hold when the average 
weight value W.sub.m and preset weight value W.sub.s are unequal, the 
processor 104a enlarges the target weight value W.sub.t so as to increase 
the mean weight value. However, since the maximum value of the target 
weight Wt is the upper limit value W.sub.max of the preset allowable 
limits, the processor 104a first determines whether W.sub.t =W.sub.max 
holds. When the condition W.sub.t =W.sub.max does hold, the processor 
clamps the target weight value W.sub.t to W.sub.max and executes the 
discharge and supply operations of step (p), with the system then being 
placed in the mode awaiting the start signal from the packaging machine. 
If W.sub.t =W.sub.max does not hold, on the other hand, that is, if 
W.sub.t &lt;W.sub.max holds, then the processor 104a enlarges the target 
weight value W.sub.t by a predetermined amount, say 0.1 g, and executes 
the discharge and supply operations of step (p), with the system then 
being placed in the mode awaiting the start signal from the packaging 
machine. 
(u) If the mean weight value W.sub.m is found to be less than the preset 
weight value W.sub.s in the decision step (e), the processor 104a 
determines whether the difference A obtained in step (d) is equal to or 
greater than zero. In other words, the processor determines whether the 
total weight value X of a combination is equal to or greater than the 
target weight value W.sub.t. If X.gtoreq.W.sub.t (A.gtoreq.0) is found to 
hold, step (f) is executed; if X&lt;W.sub.t (A&lt;0) holds, step (h) is 
executed. Thus, according to the present invention, when W.sub.m &lt;W.sub.s 
is found to hold, so-called minus-cut combinatorial processing is 
executed, namely processing wherein the lower limit value is used as the 
target weight value W.sub.t. This is helpful in bringing the mean weight 
value W.sub.m close to the set weight value W.sub.s. 
(v) When the time T.sub.a is found to be equal or greater than the preset 
time T.sub.s is step (l), the timer 104e is cleared to zero and then 
restarted by the processor 104a. The processor also executes the 
initialization process steps 0.fwdarw.N.sub.T, 0.fwdarw.W.sub.T, W.sub.s 
W.sub.t and then executes the discharge and supply control operations of 
step (p), after which the start signal STS from the packaging machine is 
awaited. 
In the foregoing description, it was assumed that the mean weight value 
initially has a binary value of all "1"s. However, all "0"s can be used as 
the initial value, in which case W.sub.m &lt;W.sub.s would initially hold in 
step (e), followed by execution of step (u). 
As many apparently widely different embodiments of the present invention 
can be made without departing from the spirit and scope thereof, it is to 
be understood that the invention is not limited to the specific 
embodiments thereof except as defined in the appended claims.