JP2587235B2 - Liquid weighing method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a liquid measuring method, and more specifically, performs a fuzzy inference based on an observation amount obtained during the measurement,
The present invention relates to a liquid measuring method for improving a measuring accuracy, expanding a measuring range, and realizing a short-time measuring by sequentially changing a flow velocity of an object to be measured.

(Prior Art) In liquid measurement, there are various detection methods such as a weight type (load cell or the like), a pressure type (differential pressure transmitter or the like), a positive displacement type (oval flow meter or the like), and the like.

However, in any of the methods, a constant flow rate is assumed as the measurement control, and there is no closed-loop measurement control method that continuously varies the flow rate.

Conventionally, the following technology has been implemented as a method for improving the measurement accuracy.

Divide the flow rate into two stages, and in the vicinity of the weighing setting,
Technology for weighing by switching to the slow flow side (for example,
-148019).

Specific Example 1) Two types of devices having different flow velocities are installed, and switching is performed when a deviation between a set measurement value and an actual measurement value reaches a certain condition value.

2) A single device having a function of switching the flow velocity between two fixed conditions is installed, and when the deviation reaches a certain condition value as in 1), the switching is performed.

3) In the contents of 1) and 2), a learning function is added as a software function, and a condition value for instructing switching is corrected from the previous actual measurement value.

As a weighing stop condition, there is an inflow amount (also referred to as a head amount), and a technique of predicting this amount and stopping the weighing in advance to perform weighing (for example, JP-A-57-29114).

Specific example 1) When the deviation between the weighing set value and the actual weighed value reaches a certain condition, the weighing is stopped.

2) Same as -3), except that the condition value for instructing the stop of the measurement is corrected by calculating from the previous actual measurement value.

(Problems to be Solved by the Invention) However, in the conventional metering control, the flow rate is fixed, or as described above, the flow rate is divided into two stages and switched, but the measurement is fixed within a certain range. There are drawbacks.

Measurement accuracy: Accuracy is not guaranteed due to flow velocity fluctuations due to disturbances and flow velocity fluctuations due to differences in liquid physical properties (viscosity, etc.).

For example, in the case of gravity transfer, the flow rate fluctuation occurs in the outflowing weighing object due to the remaining amount of the weighing object in the upstream container (hereinafter, this remaining amount is referred to as a head difference in the present specification). If the change in the difference is large, the flow velocity goes out of a certain condition range, and the accuracy deteriorates. In addition, this results in a limitation on the change width of the head of the upstream container, and in order to maintain the head difference within a predetermined range, stop the measurement or supply the raw material to the upstream container appropriately. Preparing raw materials that are equal to or greater than the weighed value leads to a secondary loss of raw materials.

Measuring range: Since the flow rate is restricted, the ratio of the minimum weighing value and the maximum weighing value that can be measured is usually about 1: 5.

 Even with a two-stage flow velocity setting type, the maximum is about 1:10.

The reason for the narrow measurement range is that even if measurement is stopped, there is an inflow due to the response delay of the system, and this amount is determined by the flow velocity. Range, which limits the weighing range.

In a manufacturing plant that can handle a wide variety of products, there is a maximum measuring range of about 1: 100 even for the same raw material, and it is necessary to select a measuring device in a measuring set value range.

Weighing time: The weighing time depends on the weighing set value.

When the weighing set value is small, the weighing time is short, and when it is large, the weighing time is long.

When the weighing set value is small, the operation time of the system varies, which makes it impossible to guarantee the weighing accuracy and narrows the weighing range.

Furthermore, from the point of view of the entire system for producing a new variety by mixing a plurality of types of weighed objects, the production capacity is dependent on the individual weighing times, and these weighing times are particularly affected by the production of a pipeless moving method. In the system, the transport capacity is limited.

(Object of the Invention) The object of the present invention is based on the above circumstances, and realizes high-precision weighing that is not affected by flow velocity fluctuations due to disturbance, secures a wide-range weighing range, and sets weighing set values. It is an object of the present invention to provide a liquid measuring method for realizing a short time measuring regardless of the size of the liquid.

Further, another object of the present invention is to provide a liquid measuring method which achieves high accuracy, wide range, and short time measurement by only easy adjustment without being influenced by the system configuration, valve flow characteristics and liquid physical properties (viscosity, etc.). Is to do.

That is, the present invention is intended to realize more accurate measurement limited to the measurement of the liquid, the control method in the conventional metering device, the opening adjustment valve, the detector for measuring the flow rate of the object to be measured, etc. It is to eliminate the following disadvantages.

In the conventional metering control, it is assumed that the flow rate is constant. However, the flow rate characteristics of the valve change due to a head difference, liquid physical properties, and the like, thereby deteriorating the metering accuracy.

Due to the dynamic characteristics of the detector, the observed quantity has an apparent fluctuation range, which deteriorates the measurement accuracy.

It is difficult to make the flow characteristics of the valves linear and have the same characteristics. The flow characteristics vary from one valve to another, and the flow characteristics also differ depending on the system configuration. Therefore, in order to ensure high-precision weighing, adjustment is required for each configuration.

(Summary of the Invention) The present invention relates to a closed-loop liquid metering method in which a flow rate is changed by an arbitrarily set metering set value and an actual metering value fed back, and a flow rate characteristic of an opening control valve for limiting a liquid flow rate. Fuzzy inference based on the measured value and the measured set value, determines the initial opening of the valve before the start of weighing, and after the start of weighing, the deviation between the actual measured value and the weighed set value that are sequentially observed, and the time variation of the deviation Is the observable, the area of the deviation and the temporal change of the deviation is expressed as a membership function, and the division of the axis corresponding to the observable is expressed so that the section with a small observable is fine. A liquid measuring method characterized by expressing the transition relation of the expressed region by fuzzy rules, performing fuzzy inference from these, and changing the valve opening of the opening degree adjustment valve based on the result of the fuzzy inference. is there .

(Embodiments) Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a liquid metering apparatus applied to one embodiment of the present invention. In this embodiment, description will be made based on subtraction-type metering for observing the amount of liquid flowing out of a metering tank.

In the figure, 1 is a weighing control device, 2 is a load cell for measuring the weight of the raw material focused on the weighing tank 8, 3 is a weigh scale amplifier, 4 is a servo driver controlled by the weighing control device 1, and 5 is a servo driver 4. , A servo motor that moves an opening adjustment valve, which will be described later, 6 is an opening adjustment valve that adjusts the amount of effluent from the measuring tank 8, and 7 is controlled by the measurement control device 1 to stop the outflow of the liquid. It is a stop valve. In addition, the opening adjustment valve 6 has respective flow characteristics as shown in FIG. 3 (1).

Next, the liquid measuring method of the present invention will be described. Second
The figure shows a control process according to the weighing method of the present invention.

In FIG. 1 and FIG. 2, when a weighing set value is given to the weighing control device 1, the flow rate of the valve shown in FIG. The initial opening of the valve is calculated from the characteristics by fuzzy inference. At this time, as shown in FIG. 8, the membership function assigns a function of the initial opening degree of the opening degree adjustment valve to the measurement set value. For example, if the set value is 1000 g, , The coefficient of the initial opening is × 0.5. The initial opening obtained in this manner is the valve opening at the weighing time zero in FIGS. 7A and 7B. The metering control device 1 instructs the servo motor 5 of the opening adjustment valve 6 through the servo driver 4 with the initial opening set value at the same time as the start of the measurement. As a result, the liquid flows out of the measuring tank 8, and the actual weight value of the load cell 2 changes. Also, the weighing control device 1 repeatedly measures the actual weight value from the weight amplifier 3 at a predetermined control cycle, and the fuzzy operation unit (reference numeral 1-1 in FIG. 2) in the weighing control device 1 When the deviation between the weighing set value and the actual weight value and the amount of change in the deviation over time are calculated, and the amount of observation obtained by applying a low-pass filter process to these amounts is calculated, the fuzzy control unit 1-2 sets the fuzzy rule to the determined fuzzy rule. In other words, the deviation and the temporal change of the deviation are expressed in a membership function, and fuzzy inference for obtaining the change of the valve opening degree is performed in accordance with fuzzy rules that define conditions for shifting to the respective balance regions. At this time, the membership function based on fuzzy inference, the division of the axis corresponding to each physical quantity of the deviation amount and the deviation time change amount made the section where the physical quantity is small finer,
For example, it has a semi-logarithmic shape as shown in FIGS. This is for the purpose of improving weighing accuracy and short-time weighing. If the deviation amount is large, it is not necessary to have good control accuracy, and if the deviation amount is small, it is necessary to improve control accuracy. Because there is. This also applies to the primary filter processing function. When the deviation amount or the like is small, the deviation amount or the like of the primary filter is used to relax the dynamic characteristics of the weighing detector and improve the weighing accuracy.

FIG. 9 shows a balance area of the deviation and the time variation of the deviation corresponding to each section of the membership function, and the balance point in the figure indicates that the valve opening degree needs to be changed in each area. And not.

After the start of the weighing, fuzzy inference is performed according to the fuzzy rules that define the conditions for shifting to the respective balance areas in accordance with where the observation quantity is located in FIG. 9, and the opening adjustment valve 6 is appropriately determined based on the result. The degree of opening is controlled so that the opening degree of the opening degree adjustment valve 6 gradually narrows as the measurement deviation gradually decreases, and the flow velocity decreases. At this time, if the opening degree regulating valve 6 has the flow characteristic shown in FIG. 3, the valve opening degree is about 10% near the deviation 0.
A transition is made to a degree area, that is, a dead zone based on a fuzzy inference operation. In the dead zone, there is no flow in a predetermined range of the valve opening. Therefore, even if there is mechanical backlash of the valve or the like, the adverse effect of the backlash or the like is absorbed by the small fluctuation of the valve opening degree by the dead zone and the fuzzy control method, and the measurement can be performed with high accuracy.

Further, the present invention is applied to a plurality of tanks 11, 1 shown in FIG.
When the object to be weighed supplied from 2 is mixed into one weighing tank 16 and applied to the cumulative weighing system for weighing with the load cell 15, the opening adjustment valves 1 attached to the upstream tanks 11 and 12 respectively.
If the characteristics near the dead zone shown in FIG. 3 do not change so much even if the flow characteristics of 3, 14 are different, the behavior of the opening adjustment valve after the start of the measurement is different, but the behavior immediately before the end of the measurement is almost the same. They are equivalent and can be measured with the same membership function and fuzzy rules.

Therefore, high accuracy, wide range, and short time measurement can be easily achieved regardless of differences in system configuration, valve characteristics, liquid physical properties, and the like.

Next, the results of experiments performed based on the present invention will be described.

This experiment was performed using the weighing device shown in FIG.

The resulting weighing device can weigh up to 10 kg and the accuracy of the load cell is 1/5000. The position of the FCV (opening adjustment valve) is controlled by a servomotor, and a position command is output from the metering control device.

FIG. 6 shows the flow characteristics of the two types of opening adjustment valves. These two types of opening adjustment valves were sequentially installed in the system shown in FIG. 1, and the measurement was performed without any change in the control method or the like.

FIG. 7 shows the 1000 g weighing result at that time. Fig. 7-a
Is the result of the opening degree adjustment valve having the flow rate characteristic of FIG.
FIG. 7-b is the result of FIG. 6-b.

As is clear from FIG. 7, the operation pattern of the opening degree of the opening adjustment valve naturally changes, but a highly accurate weighing result was obtained in almost the same weighing time.

In addition, in the present measuring system, as shown in FIG. 6, even if the opening degree is the same, the flow rate,
That is, the flow rates are different. And although the operation pattern of the valve opening was different, the same result was obtained in both the measuring time and the measuring accuracy. As for the measuring range, the accuracy within ± 1.0 g was guaranteed in the range of 1: 100.

In the above embodiment, a load cell is used as a weighing detector, but any detector may be used instead of the load cell as long as a weighing value such as a differential pressure transmitter or a liquid level gauge can be observed.

In addition, although a servomotor has been described as an example of a driving device of the opening adjustment valve, any device that can control the position can be realized.

(Effects of the Invention) As described above, the following effects can be obtained by the present invention.

The following effects can be obtained with the same membership function and fuzzy rules without depending on the flow rate characteristics of the opening adjustment valve, the configuration of the metering system, and the like.

Realization of high-precision weighing that is not affected by flow velocity fluctuations due to disturbance Realization of wide-range weighing with a wide range of weighing set values Realization of short-time weighing independent of the magnitude of weighing set values It can be easily manufactured with a memory, and the cost of the device can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a liquid metering device applied to one embodiment of the present invention, FIG. 2 is a block diagram illustrating a control process in the device of FIG. 1, and FIG. 3 is a flow rate of an opening adjustment valve. FIG. 4 is a diagram illustrating a membership function of fuzzy control, FIG. 5 is a diagram illustrating a cumulative weighing device to which the present invention is applied, and FIG. It is a figure which shows the flow-rate characteristic diagram of the opening degree adjustment valve applied to the measuring device of a figure, (a) shows the type | mold of the high flow velocity, (b) the type of the low flow velocity, respectively, and FIG. 7 shows an experiment. 7A and 7B are diagrams showing the measurement results obtained by (a) and (b).
FIG. 8 is a diagram corresponding to that of FIG. 8, FIG. 8 is a diagram for explaining a membership function for determining the initial value of the valve opening, and FIG. 9 is a diagram illustrating a membership function for determining the valve opening from the deviation and the time variation of the deviation. FIG. DESCRIPTION OF SYMBOLS 1 ... Measurement control device, 2,15 ... Load cell, 3 ... Weigh scale amplifier, 4 ... Servo driver, 5 ... Servo motor, 6,13,14 ... Opening adjustment valve, 7 ... Stop valve , 8 ... tank, 16 ... measuring tank

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Tadashi Kobayashi 210 Nakanuma, Minamiashigara Fuji Photo Film Co., Ltd. (56) References JP-A-51-147356 (JP, A) JP-A-59-202504 (JP) JP-A-60-185826 (JP, A) JP-A-59-56118 (JP, A) JP-A-51-223049 (JP, U) Transactions of the Society of Instrument and Control Engineers, Vol. 8, August 1984, p. 720 to 726, see automatic learning fuzzy controller

Claims (1)

(57) [Claims] In a closed-loop liquid metering method for changing a flow rate by an arbitrarily set metering value and an actual metering value fed back, a flow rate characteristic and a metering set value of an opening control valve for limiting a liquid flow rate. The fuzzy inference is performed according to and the initial opening of the valve before the start of weighing is determined, and after the start of weighing, the deviation between the actual weighing value and the weighing set value that are sequentially observed and the amount of temporal change in the deviation are taken as the observed amount. , The area of the deviation and the temporal change of the deviation are represented by a membership function, and the division of the axis corresponding to the observable is expressed so that the section with a small amount of the observable is fine, and the area expressed by this membership function The liquid transfer method is characterized in that the transition relation of the above is expressed by fuzzy rules, fuzzy inference is performed from them, and the valve opening of the opening adjustment valve is changed based on the result of the fuzzy inference.