Powder weighing mixer and method thereof

A powder measuring device and powder measuring mixer in which powder is supplied from a supply hopper to a measuring hopper with its flow rate controlled by a flow regulator associated with the hopper. The weight of the measuring hopper is monitored. A controller compares the measured weight with a target rate to produce a deviation therebetween and a time variation of the deviation. The controller operates according to fuzzy inference to produce a desired flow rate for the next control cycle. This desired flow rate is then supplied to the flow regulator. Several supply hoppers with associated flow regulators can be used. Then the output of the controller is switched between the different flow regulators at different phases of the mixing measurement. Additionally, the measuring hopper can be movable between the different supply hoppers so as to avoid complicated piping.

BACKGROUND OF THE INVENTION 
1. Field Of the Invention 
This invention relates to a powder weighing method, and more specifically 
it relates to a powder weighing method which makes possible high accuracy, 
wide-ranging and short-duration weighing by varying the speed of flow of 
the powder supply of a following cycle by means of a fuzzy inference 
performed on the basis of a weighing setting and the actual weighing 
value. 
The present invention further relates to powder weighing mixers which 
produce new materials by mixing various kinds of powders after having 
weighed them. 
2. Background Art 
Conventionally, for weighing powders, there have been used scale systems 
which in the main make use of load cells. 
There are known control systems which regulate the time taken and the flow 
rate in a following weighing cycle by calculating the average flow from 
the time taken and the overall discharge weight of a body being weighed in 
the prior prescribed count weighing cycles. These systems then find the 
deviation from the target weight based on this average flow amount have 
been disclosed in Japanese Patent (OPI) Publication Nos. 148019/81 and 
155412/81. See also Japanese Patent (OPI) Publication No. 29114/82. 
Thus, to date, there have been no closed loop weighing control methods 
which sequentially alter the speed of flow in accordance with the actual 
weighing value weighed in the receiving container. 
Furthermore, when supplying powder from a plurality of supply containers 
(or tanks) to one receiving container in conventional powder weighing 
mixers, separate weighing equipment is attached to each of the supply 
containers. 
For example, for heavy weighings two pieces of weighing equipment are used 
for two powders, as shown in FIG. 1. For closed loop control (one of the 
features of this invention) of these separate pieces of equipment, a 
two-loop control function is required for the pre-estimation control of 
the flow amount. 
This is to say that it has not been possible to expect highly accurate 
weighings with a single control function because the powder flow varied as 
a result of the amount of powder remaining in the supply container, the 
target weight and the varying values of the physical properties of the 
powder. 
Furthermore, there are weighing methods for realizing high accuracy 
weighing which change over to a slower speed of flow near the set target 
weight by providing equipment which possesses the capability of changing 
over to fixed conditions of differing speeds of flow as disclosed, for 
example, in Laid-open Japanese Patent Application (OPI) No. 72015/82. 
Alternatively, flow regulators of differing speeds of flow may be arranged 
in series. However, here too a two-loop control is required for the 
control function. 
The reason for using the expression two-loop control function here is that 
when for example, dispersion-type control equipment is used, it is 
possible to compute the control functions with a single piece of control 
equipment so that two pieces of control equipment are, in fact, not 
required. However, it is still called two pieces of control equipment from 
the point of view of the software and the number of inputs and outputs. 
Again, in connection with the above-mentioned methods, there are some 
methods which anticipate the amount of inflow to the weighing vessel at 
the cessation of weighing and stop the flow slightly in advance. 
Because conventional weighing control methods have fixed weighing 
conditions within a prescribed range, either with a fixed speed of flow or 
dividing the speed of flow into two stages and changing over between them, 
as mentioned previously, they have the drawbacks mentioned below. 
(1) Weighing accuracy: There are times when the accuracy cannot be 
guaranteed because of disturbances and changes in the physical properties 
of the powder. 
Thus, the transfer equipment will differ with the physical properties of 
the powders. For example, dampers are used with granular powders because 
they have good flow characteristics and screw feeders are used with 
powders with poor flow characteristics. However, powder flow cannot be 
defined according to a single rule, and flow will vary with disturbances 
such as the consistency of the powder, the powder form and vibrations. 
The flow characteristics of hygroscopic powders and powders which readily 
form bridges in particular will vary with their storage conditions. Thus, 
in a system in which powder is also stored over long periods in its supply 
vessels, the flow characteristics of a powder will change with changing 
environmental conditions, for example temperatures humidity and vibrations 
caused by the attachments such as vibrators, air knockers, etc., used to 
accelerate the flow characteristics of the powder. Thus, weighing accuracy 
declines with changes in the conditions of supply flow. There are, 
therefore, imposed limitations on the amounts stored and limitations on 
the installation conditions for the equipment with their resultant 
increase in the initial cost and running costs for component parts. These 
limitations are necessary to maintain weighing accuracy. 
(2) The weighing range: The weighing range is narrow. 
The reason for this is that there is an amount of residual inflow caused by 
delays in the response of the system even after the flow at one part of 
the system has been stopped. Since the amount is determined by the speed 
of flow, when the speed of flow is fixed, a tolerable amount of inflow can 
be guaranteed by narrowing the weighing range. Accordingly, even when 
weighing the same powder, if the weighing settings greatly diverge, 
weighing equipment suitable to each weighing range will be necessary and 
the number of units of equipment will increase. 
(3) Weighing time: The weighing time is governed by the target weight. 
The weighing time is short when the target weight is small and long when it 
is large. Weighing equipment with a weighing time appropriate to the 
production cycle is required in accordance with the target weight and the 
number of units of equipment is thus increased. Moreover, if target 
weights are to differ for each starting powder when several powders are to 
be mixed to produce a new mixed powder, for example, the production 
capacity of the system is determined by raw materials which require the 
longest duration weighings. 
Furthermore, in conventional powder weighing mixers, many individually 
controlled units of weighing equipment are installed for each supply 
container for the above-mentioned reasons. Since they are installed for 
each optimal weighing time in order to increase the production capacity, 
the system is complicated and very many component parts are added to the 
weighing equipment. 
Based on the above-mentioned facts, the present invention intends to 
provide a powder weighing mixer with the great economic advantages of: 
(1) reducing the initial cost by reducing the number of units of equipment; 
(2) reducing the labor spent on maintenance by similarly reducing the 
number of units of equipment; 
(3) reducing breakdowns by improving reliability by reducing the number of 
units of equipment; and 
(4) reducing running costs as a result of reducing raw material losses. 
The weighing control equipment should not only produce high accuracy 
weighing unaffected by changes in the flow speed caused by disturbances 
and variations in the physical characteristics of the powder, but should 
also guarantee a wide range of weighing. It should effect weighing in a 
short time ungoverned by the size of the target weight. Thus, a system can 
be constructed which increases production capacity and simplifies 
component parts while reducing source material losses. 
SUMMARY OF THE INVENTION 
Based on the above-mentioned considerations, this invention intends to 
provide a powder weighing method which effects high accuracy weighings 
unaffected by changes in the flow rate caused by disturbances and 
variations in the physical properties of the powder and which secures a 
wide-ranging weighing range, and moreover, which effects short duration 
weighings not governed by the size of the target weight. 
The above-mentioned objects of this invention are further achieved by using 
powder weighing mixers which make use of weighing control equipment which 
makes the speed of flow variable from moment to moment by means of a 
closed loop control and a control based on fuzzy inference. Such mixing 
equipment can reduce the number of component parts in the aforementioned 
weighing control equipment. 
The powder weighing mixer of this invention is constructed using the basic 
construction given below. 
(1) Supply containers: containers which store the powder to be weighed. 
The capacity of the container should be of a scale appropriate for 
production. 
With this invention, there are no limitations on the amount of stock 
material remaining in the container. In theory, weighing may be carried 
out down to a zero remaining amount. Furthermore, any powder may be 
weighed down to an amount remaining of zero as long as the measuring is 
not affected by values of its physical properties (for example, grain 
size, etc.) and the powder is able to flow out. 
(2) Flow regulator: the number of flow regulators correspond to the number 
of supply containers. These control the flow by, for example, instructing 
the rotation count in a screw feeder. In an aperture damper, the flow is 
varied by changing the aperture using a position command. 
Furthermore, the flow characteristics of the screw feeder and the aperture 
damper are of a construction such that outflow does not occur when the 
rotation count rate and the aperture are slightly above zero and flow 
occurs from around 10% of maximum speed or opening. 
As an example, AC servo motors, or the like, can be used as the drivers. 
(3) Receiving containers: containers with a capacity appropriate for the 
scale of production. 
(4) Detectors: positioned on the receiving containers, these weigh the 
amount of powder received into the receiving container. In the case of 
mixable powders, they are capable of cumulative weighing in one receiving 
container. 
(5) Weighing control equipment: control equipment which operates with 
closed loop control and which changes the speed of flow. This control 
allows the speed of flow of powder in the flow regulator to vary using a 
control system using fuzzy inference. That is to say, the initial speed of 
powder transmission in the flow regulator is determined by the flow 
characteristics in the flow regulator and the weighing setting. 
Thereafter, the change in the transmission speed is determined by fuzzy 
control based on the actual weighing value and the weighing setting. 
(6) Change-over equipment: changes over its input from the weighing control 
equipment to one of several outputs connected to a prescribed flow 
regulator. 
(7) Moving equipment: moving equipment for conveying the receiving 
container. There are unmanned carriages and other conveyors which might be 
used as the method of conveying. Moreover, there will be occasions when 
the conveying function will be on the receptor container itself and 
occasions when it will be separate from the receiving container. 
The basic elements of this invention are given above. The invention further 
requires the use of closed loop weighing control equipment which varies 
the flow speed. In addition, the weighing control equipment performs the 
control based on fuzzy inference. 
The above-mentioned objects of this invention are achieved by means of a 
closed loop powder weighing method which varies the supply flow rate of 
powders by means of an arbitrarily set target setting and an actual 
weighing value when powders are supplied and weighed from a supply vessel 
to a receptor vessel. The speed of transfer is varied by performing a 
fuzzy inference using a target weight and the flow characteristic of a 
flow regulator which controls the speed of flow to determine the speed of 
transfer of the powder through the flow regulator prior to the beginning 
of weighing. Then, fuzzy control is carried out based on the target weight 
and the actual weighing value which is sequentially observed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
An embodiment of the invention is described below with reference to the 
figures. 
FIG. 2 illustrates powder weighing equipment which can appropriately be 
used as one embodiment of this invention. This embodiment shows an 
addition weighing where weighing is carried out in a receiving vessel. The 
powder is transferred to the receiving vessel which is placed on the 
downstream end. 
In the figure a storage hopper 1 acts as a supply vessel stocked with the 
powder to be weighed. A screw feeder 2 acts as a flow regulator which 
controls the speed of flow of the powder and is positioned at the outlet 
of the storage hopper 1. A shutter gate 3 can stop the flow. A weighing 
hopper 4 acts as a receiving vessel which has a weighing capability and is 
positioned on top of a load cell 5. A load cell amplifier 6 amplifies the 
output of the load cell 5. A weighing controller 7 controls the screw 
feeder 2 and the shutter gate 3. A servo driver 8 is controlled by the 
weighing controller 7 and in turn drives a servo motor 9 which drives the 
rotation of the screw feeder 2. 
The screw feeder 2 is able to vary the amount of supply powder flow over a 
wide range by varying its speed of rotation. 
The powder weighing method of this invention is now explained making use of 
both FIG. 2 and the control block diagram of FIG. 3. 
When a target weight of an arbitrary amount is entered in the weighing 
controller 7, the fuzzy control part 72 of the weighing controller 7 
calculates the initial rotational speed of the screw feeder 2 using fuzzy 
inference from the flow characteristics of the screw feeder 2 which are 
known beforehand. 
At the same time as the beginning of weighing, the weighing controller 7 
opens the shutter gate 3 and controls the servo driver 8 in such a way 
that the servo motor 9 of the screw feeder 2 rotates at this initial 
rotational speed. 
By this means, the powder is transferred from the storage hopper 1 to the 
weighing hopper 4 and the actual weight is measured using the weighing 
hopper 4. At this time, the weighing hopper 4 is being used to observe the 
actual weight which changes from moment to moment in a prescribed control 
cycle. The actual weight is weighed by the load cell 5 and is fed back to 
the weighing controller 7 via the load cell amplifier 6. 
As well as calculating the deviation and the change in the deviation over 
time between the preset target weight setting and the actual fed back 
weight, a filter computing part 71 in the weighing controller 7 also 
performs a low pass filtering process on both these amounts. 
The fuzzy control part 72 alters the speed of flow by performing a fuzzy 
inference based on this filtered observed amount and calculates the speed 
of rotation of the screw feeder 2 in the next control cycle. 
Fuzzy inference will now be described. Fuzzy inference, used in a fuzzy 
control system, is intended to emulate control by a human operator. If the 
operator observes that the deviation between a target value and a measured 
value is large and a time rate variation of this deviation is small, then 
he would increase the flow rate which decreases the deviation more 
quickly. On the other hand, if he observes that the deviation is small but 
the time rate variation is somewhat large, then he would slightly decrease 
the flow rate. Fuzzy control is discussed by E. H. Mamdani in a technical 
article entitled "Application of Fuzzy Algorithms for Control of a Simple 
Dynamic Plant" appearing in the Proceedings of IEEE, vol. 121. 1974 at 
pages 1585-1588 and by L. A. Zadeh in a memorandum entitled "Theory of 
Fuzzy Sets". Memo No. ERL-M502. Electronic Research Lab., University of 
California, Berkeley (1975). 
In FIG. 4 is plotted the deviation e (here the difference between the 
target weight and the actual measured weight) as a function of the time 
variation .delta.e (here the difference of the deviation e between the 
present and the past measuring cycles). If the measured deviation e and 
the measured time variation .delta.e fall within a balance zone, then the 
current flow rate is appropriate in view of the current deviation so that 
the valve opening or the like is not required to be changed. Rather than 
performing an exact arithmetic computation, however, the variables are 
designated by "vague" variables such as very small, small, medium, large 
and very large. 
If the variables are designated by these vague variables and by membership 
functions and if a control method is defined by "if-then" rules, fuzzy 
measurement control becomes possible. A fuzzy rule is generally expressed 
in the form of: if e is A and .delta.e is B, then .delta.u is C. In the 
present invention, e is the deviation. .delta.e is the time variation of 
the deviation and .delta.u is the time variation (between control cycles) 
of a quantity controlling the flow, such as the amount of opening of the 
control valve. The variables A, B and C in the rules are likewise defined 
by the vague variables, very small, small, etc. 
The membership functions are defined for each of the deviation e, the time 
variation of the deviation .delta.e and the time variation of the control 
quantity .delta.u. Such a membership function for the deviation e (in 
units of grams) is plotted in FIG. 5. The vertical axis is the membership 
value, function varying between 0 and 1. If the measured deviation is 3, 
then the deviation at the current measuring cycle is determined to be 
"small". Similar membership functions must be created for .delta.e and 
.delta.u. 
The membership functions for the measured values (namely, the deviation e 
and the time variation of the deviation .delta.e) should be divided along 
the measured value axis such that the intervals become increasingly 
smaller for smaller measured values. This variation is apparent from the 
semilog plot of e versus its membership function in FIG. 5 in which the 
control vague values have equal widths when expressed logarithmically. 
This type of variation is required if improvements in weighing accuracy and 
short duration weighings are both desired. When the deviation is large, 
there is no need for fine controllability, while when the deviation is 
small, there is a need to improve the control accuracy. This same idea 
also applies to the low pass filter processing. When the deviation or 
similar quantity is small, the output of the low pass filtering of these 
quantities is used to improve the weighing accuracy by attenuating the 
short term movement of the weighing detector (load cell). 
For fuzzy control, a number of fuzzy rules are defined beforehand. For 
example, a first rule is that if e is small and .delta.e is large, then 
.delta.u is negative large; and a second rule is that if e is small and 
.delta.e is medium, then .delta.u is negative medium. A further set of 
rules can be derived from FIG. 4, such as if e and .delta.e are small, 
then .delta.u is zero. Other rules become apparent from FIG. 4. When each 
of e and .delta.e falls in only one zone of the vague variables, then a 
single fuzzy rule using those vague variables is used to obtain the 
operation quantity .delta.u. If, however, the observed quantity falls in 
two zones of vague variables, two fuzzy rules for the observed quantity 
must be used with the membership values acting as weights in combining the 
"then" values of the operation quantities .delta.u. For instance. FIG. 6 
is a diagram used for obtaining the control quantity .delta.u. Providing 
that e has a membership value 0.8 in small zone, and .delta.e has a 
membership value 0.6 in large zone and value 0.7 in medium zone. Further, 
providing that fuzzy rules are (1) e is small and .delta.e is large, then 
.delta.u is negative large and (2) e is small and .delta.e is medium, then 
.delta.u is negative medium. In this case, a membership value of .delta.u 
is determined to be smaller one of values of e and .delta.e (other 
selection is possible). Accordingly, the membership value of .delta.u is 
0.6 when rule (1) is used, and 0.7 when rule (2) is used. From the 
membership values, .delta.u is obtained by calculating, for example, the 
center of gravity of the area hatched in FIG. 6. 
The initial setting of the flow is also performed with a form of fuzzy 
inference based upon the target weight and the flow rate characteristics 
of the flow regulator. Membership values and fuzzy inference rules need to 
be defined for the variables. One result is that the target weights have 
membership values in the range of zero to one which are formed in discrete 
steps and the flow regulator is controlled accordingly. 
After the beginning of weighing, the screw feeder 2 is controlled in such a 
way that it assumes an appropriate rotational speed. The rotational speed 
gradually tends to slow with the gradual lessening in the weighing 
deviation and thus the flow rate decreases. When the weighing deviation 
falls below a certain value with the decrease of the weighing deviation 
and the time rate variation of the weighing deviation, the weighing stops 
so that the shutter gate 3 closes, the rotational count rate of the screw 
feeder 2 is set to zero and rotation ceases. At this time, the speed of 
flow is extremely small and the amount of residual inflow is thus, 
extremely small. As a result, the action of the screw feeder 2 changes in 
the weighing range due to the target weight and the processing system. 
Thus, the weighing range is increased and weighing is possible in a single 
piece of weighing equipment irrespective of the size of the target, 
although the static accuracy of the detector must be observed. 
Moreover, the action of the shutter gate 3 varies even within the weighing 
time and weighing is possible in an almost equally short weighing time 
irrespective of the size of the target weight. 
As has been described above, the weighing method of this invention controls 
the speed of flow as a result of fuzzy control of the rotation count rate 
of a screw feeder using closed loop control (FIG. 3) with a fixed control 
cycle based on the actual weight observed by the load cell 5. 
In the above embodiment, a screw feeder was given as the flow regulator 
which can vary the speed of flow. However, the flow regulator may be a 
rotary system which is able to vary the flow by means of a rotation count 
command in the same way as the screw feeder. Furthermore, the drive 
equipment is not limited to servo motors but inverter motors may also be 
used and any equipment which can vary its rotational count or position is 
possible. 
EXAMPLE 
Test results based on this invention will now be explained. 
These tests were performed on the weighing equipment shown in FIG. 2. 
The weighing equipment which produced the results was capable of a maximum 
weighing of 5 kg. The accuracy of the load cell was 1/2500. The screw 
feeder had its rotational rate controlled by the inverter motor, a 
rotational count command (voltage output) being outputted from the 
weighing command equipment. 
FIG. 7 shows the characteristics for the average value of flow rate as a 
function of the inverter input voltage (rotation signal) for two kinds of 
powders. These two kinds of powder had the following characteristics. 
Powder A was a granular powder with an apparent density of 0.5 and powder 
B was a wheatflour-like powder with strong adhesion and an apparent 
density of 0.5. These two kinds of powders were weighed using the system 
of FIG. 2 with no changes whatsoever being made to the respective control 
system and the like. 
FIG. 8 shows the weighing results for 1 kg of powder A and FIG. 9 shows the 
weighing results for 1 kg of powder B. As FIGS. 8 and 9 make clear, it was 
possible to obtain highly accurate weighing results in about the same 
weighing time even though the action pattern for the rotation of the screw 
feeder varied. 
Furthermore, the flow characteristics were different because of different 
flow properties, by making the storage hopper vibrate and by compressing 
the powders. However, although the action pattern of the screw feeder as a 
result varied, the same results were obtained for both the weighing time 
and the weighing accuracy. 
A process used for obtaining the result of measurement shown in FIG. 9 will 
be described in more detail in terms of fuzzy control. 
An initial rotation signal of the flow regulator is determined by a 
membership function as shown in FIG. 6A. For example, when the set value 
(target weight) is 1000 g, a membership value corresponding to the set 
value is 0.1 from FIG. 6A. The maximum rotation signal of the regulator is 
set at 5 v based on the flow-rate characteristics of the regulator, so 
that the initial rotation signal of the regulator is set at 
5.times.0.1=0.5 v. The fuzzy control is not conducted for a while (wastful 
time). Since it takes a time to transfer the liquid from a supply tank 
(storage hopper) to a measurement tank (weighing hopper) as shown in FIG. 
2, if the fuzzy control is conducted immediately after initiating the 
measurement, the rotation signal of the regulator may be increased 
excessively. Accordingly, the fuzzy control is not conducted for the 
wastful time, which is within 0-9.9 seconds. 
In the measurement, fuzzy rules used are as follows: 
(1) If e is very large and .delta.e is medium, then .delta.u is positive 
medium, 
(2) If e is very large and .delta.e is large, then .delta.u is positive 
small, 
(3) If e is very large and .delta.e is very large, then .delta.u is zero, 
(4) If e is large and .delta.e is very large, then .delta.u is negative 
small, 
(5) If e is medium and .delta.e is very large, then .delta.u is negative 
medium, 
(6) If e is medium and .delta.e is large, then .delta.u is negative small, 
(7) If e is large and .delta.e is large, then .delta.u is zero, 
(8) If e is large and .delta.e is medium, then .delta.u is positive small, 
and so on. 
At point A in FIG. 9 or FIG. 4, fuzzy rule (1) is used so that .delta.u is 
increased. At point A.sub.1 in FIG. 4, fuzzy rules (1) and (2) are used so 
that the opening degree further increases. At point A.sub.z in FIG. 4, 
fuzzy rule (2) is used. At point A.sub.3 in FIG. 4, fuzzy rules (2) and 
(3) are used. At point B in FIG. 9 or FIG. 4, fuzzy rule (3) is used so 
that the opening degree of the valve is not varied. At point C in FIG. 9 
or 4, fuzzy rules (3) and (4) are used so that the rotation signal of the 
regulator is decreased. Between points C and D in FIG. 9 or 4, some fuzzy 
rules are used as between points A and B. At point D in FIG. 9 or 4, fuzzy 
rule (8) is used so that the rotation signal of the regulator is 
increased. In the similar way, the fuzzy control is conducted so that the 
result of measurement shown in FIG. 9 was obtained. In this experiment, 
powder was measured, which is apt to flow discontinuously, so that small 
fluctuations occurred between points B and C. A low pass filter may be 
used for e and .delta.e to reduce the fluctuations. 
Table 1 shows the relationship between the weighing time and the weighing 
accuracy as a function of target weight. To obtain the weighing accuracy, 
the powder outflow was measured with a separate approved gravimeter. The 5 
kg weighing was limited by the maximum rotational speed of the inverter 
motor used in this test and thus, the extended weighing time was extended. 
Nonetheless, the weighing accuracy was .+-.2 g. It would be possible to 
reduce the weighing time if the capacity of the inverter motor were 
increased. FIG. 10 shows the weighing results for 5 kg of powder B and 
makes clear that the flow was at the maximum rotational speed and that if 
the flow rate were improved, the time would be even shorter. 
Since a load cell of an accuracy of 1/2500 was used in this test, with a 50 
g weighing, there is an accuracy of .+-.2 g, which is the equivalent of 
the static accuracy of the load cell. It is, therefore, evident that if a 
load cell with an accuracy of 1/5000 were used an accuracy of .+-.1.0% can 
be obtained in a weighing range of 1:100. Moreover, an inverter motor was 
used in this test, and the range of its rotational speed (the ratio of the 
minimum speed and the maximum speed) was 1:10. If this motor were replaced 
with a servo motor, the range of the rotational speed will be widened and 
higher accuracy weighings will be possible in the same weighing time in a 
1:100 weighing range. 
TABLE 1 
______________________________________ 
Powder A, n = 3 
Powder B, n = 3 
Weighing Weighing 
Target weight 
Error time Error time 
______________________________________ 
5 kg .+-.2 g 116 sec .+-.2 g 
145 sec 
1 kg .+-.2 g 32 .+-.2 g 
48 
500 g .+-.2 g 28 .+-.1 g 
38 
100 g .+-.2 g 39 .+-.0 g 
54 
50 g .+-.2 g 27 .+-.2 g 
30 
______________________________________ 
The following effects can be obtained with the same membership functions 
and fuzzy rules without relying on the flow characteristics of the flow 
regulator or the construction of the weighing system. etc., using a powder 
weighing of this invention as described above. 
(1) High accuracy weighings can be effected regardless of changes in the 
speed of flow due to disturbances and variations in the physical 
properties of the powder. 
(2) A wide range of weighings can be effected with a wide range of target 
weight settings. 
(3) Short duration weighings which do not rely on the size of the target 
weights can be effected. 
Furthermore, weighing control equipment can be easily produced using a low 
capacity memory and equipment can be reduced. 
Two embodiments of the weighing mixer with multiple supply containers and a 
fixed receiving container will now be explained. 
The first embodiment, illustrated in FIG. 11, is a weighing mixer for N 
types of powder. That is, this embodiment produces mixed powders by 
stocking raw materials into N storage hoppers 102 positioned as supply 
containers at the head of flow, supplying powder into a single weighing 
hopper 104 positioned as a receiving container downstream from the supply 
hoppers 102 and, after cumulatively weighing the weights of the N types of 
powders in the weighing hopper 104, transfers them into a preparation tank 
106. 
The outlets of the N storage hoppers 102 are connected with N shutter gates 
108 via N screw feeders 110 driven by N servo motors 112. The outputs from 
these gates 108 are led through piping or ductwork with a construction 
such that no powder is left in the piping but all travels into the 
weighing hopper 104. 
The screw feeders 110 have a variable rotation count rate and so are able 
to vary the powder transmission speeds over a wide range. 
The weighing hopper 104 is positioned on a load cell 114 which is the 
detector, in order to measure the weight of powder transferred from each 
of the storage hoppers 102. The load cell 114 is connected through a load 
cell amplifier 116 to a weighing controller 118. The weighing controller 
118 is connected via a servo driver 120 to a change-over device 122. 
The change-over device 122 changes its input to different outputs in 
accordance with commands from the weighing controller 118 to select one of 
the several powder supply systems. It transmits the rotation drive command 
and the aperture position command from the weighing controller 118 to the 
selected servo motor 112 and shutter gate 108. 
Furthermore, the weighing hopper 104 has pipes leading through a discharge 
gate 124 into the preparation tank 106 and is further fitted with 
equipment such as a vibrator or air knocker to dispel powder left inside 
the weighing hopper 104. The preparation tank 106 is fitted with a 
stirring apparatus 126 and a bottom valve 128 at its outlet. 
Next, a powder weighing mixing process usable in the above powder weighing 
mixer will be explained in conjunction with FIG. 12 which is a control 
block diagram. 
First, the weighing and mixing criteria such as the specification of the 
storage hoppers to supply the stock powders for mixing and the weighing 
sequence of the storage hoppers involved are specified by the weighing 
controller 118. 
A target weight is established by the weighing controller 118 and when the 
start of weighing for one of the powders is indicated, first of all, the 
supply system is selected by the change-over device. In this example, it 
is assumed that it is the first of the N supply systems which is selected 
so that the first shutter gate 108 opens. A rotation count command is 
transmitted to the servo driver 120 from the weighing controller 118 so 
that the first screw feeder 110 will transfer powder at a predetermined 
rotational count. The first servo motor 112 is set in drive and the screw 
feeder is rotated at the indicated rotational count so that the flow of 
raw material begins. At this time, the initial speed of rotation of the 
first screw feeder 110 is calculated by a fuzzy control part 130 of the 
weighing controller based on a fuzzy inference using the flow 
characteristics and the target weight of the selected screw feeder 110. 
Using this, the raw material in the first supply hopper 102 begins to be 
transferred to the weighing hopper 104. The load cell 114 of the weighing 
hopper 104 detects the weight of the raw material which has been 
transferred thereto and feeds the value back to the weighing controller 
118 through the load cell amplifier 116. 
In the weighing controller 118, a filter computing part 132 calculates the 
deviation between the target weight and the actual fed back measured 
weight and the change in this deviation over time and also calculates an 
apparent weight produced by a low pass filtering process performed on 
these weights. 
The fuzzy control part 130 performs a fuzzy inference based on this 
apparent value of the weight, and calculates the rotational count for the 
selected screw feeder 110 in the next control cycle to change the speed of 
flow. 
As illustrated in FIG. 5 the proportions of the horizontal axes of the 
membership function used for the fuzzy inference corresponding to the 
respective physical quantities of the deviation and the time variation of 
the deviation are divided,for example, in equal semilogarithmic intervals 
so that the intervals for small physical amounts are more detailed. This 
division allows both the improved weighing accuracy and shortened weighing 
times. When the amount of deviation is large, there is no need for fine 
controllability, while when the amount of deviation is small, there is a 
need to improve the control accuracy. This is also true for the low pass 
filtering process. When the amount of deviation etc. is small, the 
deviation output of the low pass filter is used, and weighing accuracy is 
improved by softening the movement characteristics of the weighing 
detector (load cell). 
After the start of weighing, the screw feeder 110 is controlled to an 
appropriate speed of rotation. As the weighing deviation gradually 
lessens, the speed of rotation also gradually slows and the flow rate 
decreases. The weighing deviation and the time variation of the deviation 
time lessen. When the deviation falls below a certain value, the 
measurement stops, the shutter gates 108 closes, the rotational speed of 
the screw feeder 110 reaches zero and rotation stops. Then the flow rate 
and the amount of inflow are both very small. Accordingly, the amount of 
inflow after cessation of weighing is small and the weighing accuracy can 
be improved without relying on changes in the flow rate. 
Because of the flow characteristics of the screw feeder 110, illustrated in 
FIG. 7, there is a dead-zone for flow below about 10% of the maximum 
rotation rate. For the fuzzy inference operation, this dead-zone is all 
considered as zero deviation. Thus, even when rotational irregularities in 
the screw feeder, mechanical play, etc. occur, their adverse influence is 
allowed for by the dead-zone and the fuzzy control system and high 
accuracy weighing is possible. Moreover, within the weighing range the 
operation of the screw feeder 110 changes owing to the target weight and 
the processing system and weighing can be carried out with one unit of 
weighing equipment regardless of the size of the target weight and the 
weighing range is expanded. However the static accuracy of the detector 
must be observed. 
Furthermore, the shutter gate 108 can be activated even within the weighing 
time and almost equally short duration weighings are possible regardless 
of the size of the target weight. 
Next, in the weighing and mixing process, there is a switch to weighing the 
powder in second supply hopper 102 selected in the same way. The 
change-over device 122 changes over to the second screw feeder 110 
associated with the second supply hopper 102. The target weight is 
predetermined and weighing is performed using the same type of control as 
that described above following the weighing start indication. That is to 
say, the control function within the control equipment is the same except 
that the output signals to the second shutter gate 108 and the second 
screw feeder 110 (the operational devices) have been changed over by the 
change-over equipment 122. 
Moreover, the flow characteristics of the second screw feeder 110 need not 
necessarily be the same as those of the previously first screw feeder 110. 
However, the characteristics are similar around the dead-zone. As a result 
of this, although the changes in speeds of transmission after the start of 
weighing are different, the speed of transmission immediately before the 
end of weighing is roughly the same and it is possible to weigh with the 
same membership functions and fuzzy rules. Accordingly, high accuracy, 
wide range, short duration weighing which does not rely upon differences 
in the system structure, the flow characteristics of a flow regulator, 
etc., can be achieved. 
When cumulative weighing of the various types of powders has been completed 
in the weighing hopper 104, the discharge gate 124 in the weighing hopper 
104 opens and the powders are introduced into the preparation tank 106. 
Moreover, when performing the discharge from the weighing hopper, the 
entire amount of powder is discharged by means of auxiliary equipment 134 
such as a vibrator. As well as adding desired liquid chemicals, mixing is 
carried out with the stirring apparatus 126 being rotated in the 
preparation tank 106. With the completion of stirring, the bottom valve 
128 opens and the mixed powders are discharged. 
Next, results of a trial carried out on the basis of this invention are the 
same as those described with reference to FIGS. 7, 8 and 9. 
In the embodiment described immediately above, a case was described in 
which cumulative weighings of N kinds of powder were performed in one 
weighing hopper. There were no limitation on the number of kinds of powder 
to be weighed and mixed. However, from the point of view of the system, 
the optimum number of screw feeders controlled by the same weighing 
equipment is approximately eight. 
FIG. 13 shows an alternative example of this measuring mixer of the 
invention. 
In this alternative example, a negative weighing system is combined with 
previously described positive weighing system. The negative system weighs 
the amount of powder flowing out of the supply hopper by providing a 
detector in the supply hopper. 
Thus, first the (N-1) storage hoppers, the powder supply system and the 
weighing mixing system in this figure have the same construction as in the 
previous embodiment. Accordingly, their explanation is abbreviated by 
using the same reference numerals. In this example, the N-th storage 
hopper 102 has its weight measured by a load cell 140 associated therewith 
and the amount of powder flowing out of the N-th hopper 102 is thereby 
weighed. Furthermore an aperture damper 142 is attached at the outlet from 
the N-th supply hopper 102 and the amount of outflow is controlled by the 
variable aperture of the damper 142. Moreover, in the figure, although an 
aperture damper is shown as the operational point of the subtraction 
weighing, this flow rate control is also possible through other means, a 
screw feeder, for example. 
FIG. 14 shows a block diagram of the control of the above-mentioned 
alternative example. The amount of outflow of the powder which has been 
charged in the N-th storage hopper 102 is subtractively weighed by means 
of the load cell 140. Also, when the same powder is transferred to the 
weighing hopper 104, it is weighed cumulatively by means of the load cell 
114 with the powders which have already been transferred from the first 
(N-1) storage hoppers 102. In this way, the actual weighing values 
obtained by the negative weighing system and the positive weighing system 
respectively are fed back to a corresponding negative system weighing 
controller 144 and a positive system weighing controller 146. The weighing 
controllers 144 and 146 calculate the deviation and the change in 
deviation over time with their respective set target weights. Both output 
control values by means of fuzzy control. These control values then pass 
through a control system change-over device 148. The value from the 
negative system is converted to a value showing the aperture of the 
aperture damper 142 by a position command converter 150 and they are 
transmitted together with the rotation count of the screw feeder obtained 
by the addition system to the servo driver 120, after being changed over 
and output by change-over device 122. 
Using a construction such as that mentioned above, it is possible to 
perform weighings in an even wider weighing range by performing fine 
weighings by negative weighing and large target weight weighings by 
positive weighing. 
It is also possible to provide a movable preparation tank as an alternative 
example of this invention. With such a construction, it is possible to 
simplify the distribution system and receive only the desired powders by 
moving the preparation tank to under the discharge gates corresponding to 
those of the various kinds of powders to be supplied to the preparation 
tank at the time of stirring or reaction, for example. 
In the aforementioned embodiments, screw feeders were given as the flow 
controls which varied the speed of flow, however, they could be 
rotary-type, varying the flow with a rotation count, command in the same 
way as a screw feeder. Furthermore, if the powder has good flow 
characteristics, an aperture damper which alters the flow by varying the 
aperture with a positional command can also be employed. 
As described above, with the powder weighing mixers of this invention, it 
is possible to: 
(1) reduce the number of weighing units: 
(2) reduce the loss of raw materials by making use of weighing equipment 
which is not governed by the target weight, the amount of powder 
remaining, the physical properties of the powder. Thus the following 
economic effects can be obtained: 
(a) a reduction in the initial cost owing to the reduction in the number of 
units; 
(b) a reduction in maintenance owing to the reduction in the number of 
units; 
(c) a reduction in breakdowns owing to the improvement in reliability 
caused by the reduction in the number of units; and 
(d) a reduction in running costs owing to the reduction in the losses of 
raw material. 
With a batch production process using a plurality of powders, there are 
many occasions when it is impossible to perform a cumulative weighing in 
one receiving hopper since the physical properties of the powders are 
different. Accordingly, a production system may be adopted which has a 
plurality of receiving or weighing hoppers 104 and 150, each equipped with 
weighing equipment, as shown in FIG. 4. Thereby the mixable kinds of 
powders are weighed in the first weighing hopper 104, and the non-mixable 
kinds of powders are weighed in the separate weighing hopper 150. The 
downstream preparation tank 106 is required for reacting and preparing the 
different sets of powders, thus complicating the system. 
When several kinds of product are to be prepared in a production system 
where the preparation tank 106 is fixed, there will be a need to fit the 
equipment in accordance with the desired constituents of the products and, 
as outlined previously, there will be a need for a large number of 
weighing hoppers, preparation tanks and weighing equipment, control 
equipment, and valves to fit to them particularly for high accuracy 
weighings. In this instance, the equipment will be such that components 
will be used for some product types but not for others, which is a very 
wasteful system and one which increases the initial cost of components. 
Furthermore, there has recently been a need for a production system with 
many applications, but with a fixed production system. Modifications are 
needed to the piping system of this fixed system and to other attachments 
which would make for a very complicated production system. 
A mobile batch production system in which the receiving containers, the 
preparation tank, etc. are able to move has, therefore, been recently 
proposed. 
However, when such systems have been adopted in conventional weighing 
equipment, the weighing time differs depending on the size of the target 
weight. The weighing takes longer when the target weight is large, 
imposing a limit on the conveying time for the containers in a mobile 
production system. Thus, the requisite number of weighing equipment units 
are provided in conventional production systems so that no constraints are 
placed on the conveying time. However, this cancels out the benefit of a 
mobile production system. The length of stay at a station is also extended 
in such a system. Also, a very large number of weighing equipment units 
are required because of the range of the target weights, the limits on 
weighing time, weighing accuracy conditions, etc. For this reason, the 
operating time for piping connectors is increased. 
In production processes for photographic materials, since these are 
light-sensitive materials which are being dealt with, there is a need to 
maintain light exclusion. Any complication of the system owing to an 
increase in connecting parts or change in the conveyance cycle will affect 
the product performance. 
By providing moving equipment for the receiving hopper, it becomes possible 
to receive powders from all the powder supply hoppers because the weighing 
hopper is able to move. Flexibility in the components is also possible, 
reducing the number of weighing hoppers since the powder which has been 
weighed is distributed to all the preparation tank without any fixed 
piping. Accordingly, it is possible to avoid idleness in the components of 
the weighing hoppers when producing many kinds of products. Changes in the 
method of treatment can be undertaken with an extremely reduced increase 
in equipment. Furthermore, variations in time can be kept small with small 
scale manufacture since the weighing cycle can be made quicker by means of 
the movement of the weighing hopper. A stirring apparatus can be attached 
to the weighing hopper for the powder from the powder supply hoppers and 
it can be used itself as a preparation tank. 
A movable embodiment of this invention will be described now in more 
detail. 
Considering an instance in which there are N powder substances, as shown in 
FIG. 16, it is assumed that a plurality of product types will be produced, 
but that with any product type the overall number of substances used will 
be less than N. In conventional production systems, the weighing equipment 
and the powder supply hopper for the substance will be required for the 
sole use of the product type because of the restraints of the weighing 
range, weighing time and weighing accuracy even when the equipment is of 
the same type. This multiplicity is required irrespective of whether the 
system is moving or fixed and more than N units of equipment are used. 
However, in the present invention, since closed loop weighing control 
equipment for variable flow speed is adopted and the weighing control 
equipment utilizes fuzzy control, the weighing range, weighing time and 
weighing accuracy need cause ho concern. N units of powder supply hoppers 
are sufficient and a very small number of weighing units determined by the 
conveying capacity are sufficient. provided there are no problems of 
powder contamination. 
Here, one unit of weighing equipment 114 (load cell) is assumed. A number N 
of powder supply hoppers 102 is sufficient, but since the number of 
weighing units 114 is determined by the production time, the production 
scale of the product type, there will be occasions when a number of 
weighing units greater than this will be required. 
Each unit of weighing equipment possesses a weighing controller 154 capable 
of implementing the control diagram shown in FIG. 17. The output from the 
weighing controller 154 is selected and output to a plurality of flow 
regulators, for instance the N screw feeders 110, by switching performed 
in a change-over device 156. This is to say, the weighing of a plurality 
of substances (1 to N) is carried out in the same weighing hopper 104 
equipped with the load cell 114 using the same control algorithm. 
Since the rotational count of the screw feeders 110 is variable, the powder 
flow speed can vary over a wide range. 
The weighing controller 154 is constructed from a low pass filter section 
158, a fuzzy controller 160, a drive controller 162 and the change-over 
device 156. As far as the flow characteristics of the N screw feeders 110 
are concerned, fuzzy control is carried out based on the target weight and 
the weighing value obtained from the load cell 114. The rotational count 
of the N screw feeders N is thereby controlled. 
Moreover, when aperture dampers are used for the flow regulators, the angle 
of the damper is controlled by a positional command. 
The operational process of the powder weighing mixer of the invention is 
now described. 
An indication is sent out from the host production control equipment to the 
free-standing movable type weighing hopper 104 to move the weighing hopper 
104 beneath a desired powder storage hopper 102. The change-over device 
156 is changed over by means of a system selection signal and the screw 
feeder 110 of the selected storage hopper 102. The first stop valve or 
shutter gate 108 so selected can be controlled by means of the weighing 
controller 154. 
Furthermore, an indication is sent out from the host production control 
equipment so that a coupler 164 corresponding to the first powder supply 
hopper 102 connects with a matching coupler 166 of the weighing hopper 
104. When the weighing preparation state has been confirmed, the weighing 
start indication is sent out from the host via this sort of initial 
setting. By means of the weighing start command, the supply system first 
selected by the change-over device 156, in this instance the first powder 
supply system, is selected, the first shutter gate 108 opens, the 
associated drive motor 112 is driven and rotates in such a way that the 
first screw feeder 110 transfers powder at a predetermined rotational 
count using the rotational command from the drive controller 162 of the 
weighing controller 156, to thereby start the flow of the source material. 
At this time, the rotational count of the first screw feeder 110 is 
calculated by the fuzzy controller 160 using the target weight and the 
flow characteristics of the screw feeder 110. Thus, the raw material in 
the first storage hopper 102 start to be transferred to the weighing 
hopper 104. The weighing load cell of the weighing hopper 104 detects the 
weight of the raw material transmitted and feeds the value back to the 
weighing controller 154. 
The filter section 158 of the weighing controller 154 carries out an 
operation on the deviation from the target weight on the time rate of 
change of deviation from the supply powder weighing values which have been 
fed back. It calculates a value in which a low pass filter operation has 
been carried out on these amounts. The aforementioned fuzzy controller 160 
performs an inference operation based on fuzzy rules on the basis of this 
calculated value and it calculates the revolution count for the screw 
feeder 110 to take on an appropriate flow rate in the next control cycle. 
After this start of weighing, the screw feeder 110 reduces its rotational 
count as the weighing deviation grows smaller until it takes on a very 
small flow rate. The weighing deviation and the time rate of change 
thereof grow less. When the weighing deviation falls below a certain 
value, the first shutter gate 108 moves to fully closed. At this time, the 
flow speed is very small and the amount of inflow is very small. As a 
result, the amount of inflow after the cessation of weighing is small and 
the weighing accuracy improves without relying on changes in the flow 
speed. Furthermore, as a result of possessing the general flow 
characteristics shown in FIG. 18, the screw feeder 110 has a dead-zone in 
the lower 10% of its allowed rotational rate range. This dead-zone is 
treated as zero in the fuzzy inference operation. Thus, even if there are 
rotational irregularities in the screw feeder or mechanical play, the 
adverse influence of play is absorbed by means of this dead-zone. Thereby, 
fuzzy control and high accuracy weighing become possible. Furthermore, the 
action of the flow regulator will vary as a result of the target weights 
and the process system and weighings with the same weighing equipment are 
possible regardless of the size of the target weight. Also, the weighing 
range is expanded. Again, the action pattern of the aforementioned flow 
regulator varies during the weighing time, and almost equally short 
duration weighings are possible regardless of the size of the target 
weight. The operation of the form mentioned above is put into effect in 
accordance with the constituents of the product type. When all the desired 
substances for a product type are weighed, the process shifts to an 
operation which transfers the powder to a preparation tank for a process 
downstream. 
This preparation tank 168 also moves and connects its coupler 170 to the 
lower part of a piping link coupler 172. After the connection has been 
confirmed, the bottom valve 124 of the weighing hopper 104 is controlled 
by the conveying control equipment and opens and the powder is transferred 
through the piping link coupler 172 to the preparation tank 168. 
In FIG. 16, the load cell 114 is positioned at the weighing hopper 104. 
Also, the moving equipment of the weighing hopper 104 is of a 
free-standing/running type, and may be a form which weighs at a desired 
position and is conveyed with the unmanned carriage. Moreover, 
electrically based linking equipment such as position sensors, etc., in 
every connecting position are necessary as attachments. 
When a rotation blade is attached to the weighing hopper 104 and it is made 
to assume a mixing function and is positioned as a preparation tank, the 
system becomes all the more effective. 
In the previously mentioned embodiment, a load cell 114 was given as an 
example of the weighing equipment, but there is no difference if another 
tank weighing detector is used. 
The moving device may be an unmanned carriage which lifts the weighing 
hopper 104 for transport between stations or may be wheels attached to the 
weighing hopper 104. 
By using the powder weighing mixer of this invention, a powder weighing 
mixer cumulatively weighs powders from a plurality of powder supply 
hoppers, receives them in a receiving hopper and mixes them. Weighing 
control equipment is fitted with a change-over device and operates with 
closed loop control in which supply powder the weighing control equipment 
varies the flow through various flow regulators by means of fuzzy 
inference based on various supply powder target weights. The powder supply 
hoppers each possess the flow regulators in series with powder supply 
piping. The weighing equipment for the powder supplied from the powder 
supply hoppers is positioned beside the receiving hopper. The invention is 
further characterized in that is possesses moving equipment for the 
receiving container. In a system which uses the control equipment of this 
invention short duration and fast weighing times are possible even over a 
wide range of weights. Accurate weighings can be effected without being 
influenced by changes in the flow rate due to disturbances and variation 
in the physical properties of the powders, even with large scale 
components. The production capacity increases with simplification of the 
components and a reduction in the number of units of weighing equipment. 
It is possible to effect reductions in raw material losses and 
improvements in production quality by means of large scale preparation. 
Thus, initial costs, maintenance costs and running costs can be reduced 
and reliability increased.