Patent Publication Number: US-2022236099-A1

Title: Quantitative dispensing system

Description:
The present application is a U.S. National Phase of PCT/JP2020/022092 filed on Jun. 4, 2020, claiming priority to Japanese Patent Application No. 2019-106755 filed on Jun. 7, 2019. The disclosure of the PCT Application is hereby incorporated by reference into the present Application. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to a quantitative dispensing system and, more particularly, to a quantitative dispensing system that includes a supply device and a weighing device and weighs out a fluid or powder and granular material in predetermined amounts. 
     BACKGROUND ART 
     Conventionally, there is known a quantitative dispensing apparatus that includes a pump as a supply unit that supplies a weighing object, a vessel as a holding unit that holds a weighing object, a weighing unit that weighs the weight of a weighing object, and a control unit that controls the operation of the supply unit based on a weighing result. This apparatus weighs out a predetermined amount of a weighing object by controlling to stop the supply unit when a predetermined supply target weight value is achieved. 
     Such a quantitative dispensing apparatus generates a stop signal to stop the supply unit when a weighed value reaches a target supply weighed value. So, a supply amount deviation occurs due to, for example, a response delay between the timing when a stop signal is generated and the timing when the supply of a weighing object actually stops. 
     The quantitative dispensing system disclosed in Patent Literature 1 calculates the supply amount deviation caused by a response delay until the supply of a weighing object stops based on a flow rate and a response delay time, sets, as a supply stop weight value, the value obtained by subtracting the deviation as a correction weight from a target weight value, and corrects the supply error caused in a weighed value by a response delay from when a stop signal is generated to when the supply of the weighing object actually stops. 
     CITATION LIST 
     Patent Literature 
     
         
         Patent Literature 1: Japanese Published Unexamined Patent Application No. 2007-003343 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     However, further examination has revealed that a supply amount deviation originates from not only a response delay from the timing of stop control to the timing of the actual stop of the supply unit but also the drop between the stop position of the supply unit and the holding unit, the filter setting in signal processing by a weighing device, a supply pressure at the time of supply from the supply unit to the holding unit, etc. Note that herein, a filter setting means the setting of a so-called response characteristic. 
     The quantitative dispensing system according to the Patent Literature 1 can handle an excessive supply amount deviation but does not handle an insufficient supply amount deviation. Accordingly, there is demand for a quantitative dispensing system that can more accurately dispense a predetermined amount in consideration of these supply amount deviations. 
     The present invention has been made in consideration of the above circumstances and has as its object to provide a quantitative dispensing system that can accurately weigh out a weighing object of a supply target weight in consideration of a filter setting in a weighing device and the supply pressure of the weighing object. 
     Solution to Problem 
     In order to achieve the above object, a quantitative dispensing system according to one aspect of the present invention includes a supply device configured to supply a weighing object, and a weighing device that includes a holding unit configured to hold the weighing object supplied from the supply device, a load sensor unit configured to detect a load of the weighing object supplied to the holding unit, and an arithmetic processing unit configured to sequentially calculate a weighed value of the weighing object from a detection result on the load and control an operation of the supply device. The arithmetic processing unit performs control to stop the supply device when a current weighed value becomes not less than a supply stop weight value calculated by subtracting a stop weighed value deviation from a supply target weight value. The stop weighed value deviation is calculated in consideration of a flow rate and a supply pressure at which the supply device supplies the weighing object and a filter setting in the weighing device. 
     In the above aspect, the weighing device may include a storage unit, the arithmetic processing unit may include a test mode executing unit configured to execute a test mode for changing a flow rate and a filter setting in a plurality of levels, measuring a stop weighed value deviation in each level, calculating a relationship between a flow rate, a filter setting in the weighing device, and a stop weighed value deviation, and storing the relationship in the storage unit, and the arithmetic processing unit may calculate a supply stop weight value based on the relationship between a flow rate calculated by the test mode executing unit, the filter setting, and the stop weighed value deviation when quantitative dispensing is executed. 
     In the above aspect, a relationship between the flow rate, the filter setting in the device, and the stop weighed value deviation may be stored as a function in the storage unit. 
     In the above aspect, a relationship between the flow rate, the filter setting in the device, and the stop weighed value deviation may be expressed by 
     
       
         
           
             
               δ 
               ⁡ 
               
                 ( 
                 Q 
                 ) 
               
             
             = 
             
               
                 a 
                 · 
                 
                   Q 
                   2 
                 
               
               + 
               
                 b 
                 · 
                 Q 
               
             
           
         
       
     
     where δ is the stop weighed value deviation, Q is a flow rate, b is a coefficient associated with a filter setting, and a is a coefficient associated with a discharge pressure. 
     In the above aspect, the weighing device may include an analog control unit and the arithmetic processing unit may control the analog control unit to cause the weighing device to control the supply device by analog control. 
     Advantageous Effects of Invention 
     The quantitative dispensing system according to the above aspect can accurately weigh out a weighing object of a supply target weight in consideration of a filter setting in a weighing device and the supply pressure of the weighing object. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view illustrating the overall configuration of a quantitative dispensing system according to the first embodiment of the present invention. 
         FIG. 2  is a configuration block diagram of a weighing device of the same system. 
         FIG. 3  is a functional block diagram of the arithmetic processing unit of the weighing device of the same system. 
         FIG. 4  is a graph for explaining the behavior of a weighed value at the time of a supply device stopping in the same system. 
         FIG. 5  is a graph illustrating the relationship between stop weighed value deviation and flow rate in the same system. 
         FIG. 6  is a graph illustrating the relationship between stop weighed value deviation after approximation and flow rate in the same system. 
         FIG. 7  is a flowchart for flow rate function computation processing by the same system. 
         FIG. 8  is a flowchart for test mode processing by the same system. 
         FIG. 9  is a flowchart for quantitative dispensing processing by the same system. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. However, the present invention is not limited to them. 
     EMBODIMENT 
     Overall Configuration of System 
       FIG. 1  illustrates the overall configuration of a quantitative dispensing system (hereinafter simply referred to as “system”)  1  according to an embodiment of the present invention. The system  1  is embodied the present invention as a system that dispenses a liquid as a weighing object in predetermined amounts. 
     The system  1  includes a weighing device and a supply device that supplies a weighing object. In this embodiment, the weighing device is an electronic balance  10 . The supply device is a pump  50  that supplies a liquid at a predetermined flow rate. 
     As is apparent, the electronic balance  10  includes a holding unit  10   a  that holds the liquid supplied from the pump  50  and an electronic balance body  10   b . The electronic balance  10  is connected to the pump  50  via a cable  70  that can transmit analog signals and contact signals. The holding unit  10   a  includes a vessel  12  that contains a weighing object and a weighing pan  14  on which the vessel is placed. 
     The pump  50  is, for example, a tube type pump such as a peristatic pump, which operates to externally flatten an elastic tube with a roller so as to squeeze out the liquid inside the tube. One end  52   a  of a supply tube  52  of the pump  50  is placed inside the liquid retained in a tank  60 , and the other end  52   b  is placed above the holding unit  10   a . When the pump  50  operates, the liquid inside the tank  60  is supplied into the vessel  12  of the holding unit  10   a  at a set flow rate. The pump  50  is configured to enable external control of the flow rate by analog signals, with a current value serving as a controlled value. 
       FIG. 2  is a block diagram illustrating the internal structure of the electronic balance  10 . The electronic balance  10  includes a load sensor unit  21 , a clock unit  22 , an A/D conversion unit  23 , an arithmetic processing unit  24 , a storage unit  25 , a display unit  26 , an input unit  27 , and an analog control unit  28 . 
     The load sensor unit  21  is a load detection mechanism that includes the weighing pan  14  on which the vessel  12 , into which a weighing object is to be injected, is placed, and also includes, for example, an electromagnetic balance type sensor or load cell that detects the load of a weighing object. The load sensor unit  21  outputs an analog signal corresponding to a detected load. 
     The clock unit  22  is, for example, a clock generation circuit that includes a crystal oscillator. The clock unit  22  outputs reference time signals to the A/D conversion unit  23  and the arithmetic processing unit  24  at predetermined intervals. Note that when the A/D conversion unit  23  or the arithmetic processing unit  24  incorporates a unit equivalent to the clock unit  22 , there is no need to independently provide the clock unit  22 . 
     The A/D conversion unit  23  is an A/D converter that includes an A/D conversion circuit. The A/D conversion unit  23  digitally converts analog load signals output from the load sensor unit  21  at predetermined intervals based on reference time signals from the clock unit  22  to obtain load data. 
     The arithmetic processing unit  24  is, for example, a microprocessor (MPU). The basic operation of the arithmetic processing unit  24  is to convert the load data output from the A/D conversion unit  23  into a weighed value W (n)  to update the latest weighed value W (n)  at predetermined intervals based on reference time signals and cause the storage unit  25  to sequentially store the values. The storage unit  25  includes n storage areas and stores weighed values W (n) , W (n-1) , . . . W (2) , and W (1)  starting from the latest weighed value. When the weighed value W (n)  is updated, the oldest weighed value W (1)  is discarded, and W (n) , W (n-1) , . . . W (2) , and W (1)  are newly stored. 
     The arithmetic processing unit  24  outputs control signals for controlling the pump  50  to the analog control unit  28 . The detailed function of the arithmetic processing unit  24  will be described later. 
     The storage unit  25  is, for example, a rewritable memory such as a RAM or flash memory and stores various types of data and calculation results such as weighed values which are used by the arithmetic processing unit  24 . Note that when the MPU incorporates a storage unit, there is no need to independently provide the storage unit  25 . 
     The display unit  26  is, for example, a liquid crystal display. The display unit  26  displays data such as weighing results, and other indications necessary for settings, etc. 
     The input unit  27  includes, for example, push buttons, a keyboard, and contact input switches. A measurer can input various types of settings such as a filter setting and a flow rate setting at the time of quantitative dispensing and operation instructions for quantitative dispensing via the input unit  27 . 
     Note that the display unit  26  and the input unit  27  may be integrated into one unit so as to be provided as a touch panel type input unit  27 . 
     The analog control unit  28  includes a D/A conversion circuit, a contact mechanism, and an output mechanism. The analog control unit  28  converts a control signal from the arithmetic processing unit  24  into a controlled value of a current value as an analog quantity and outputs the signal to the pump  50  via the cable  70 . More specifically, upon receiving a dispensing start signal from the arithmetic processing unit  24 , the analog control unit  28  starts the operation of the pump  50  by turning on the contact. Subsequently, the pump  50  outputs with a set controlled value. Upon receiving an instruction to stop the operation of the pump  50  from the arithmetic processing unit  24 , the analog control unit  28  stops the operation of the pump  50  by setting the output to 0. 
     The detailed function of the arithmetic processing unit  24  will be described below.  FIG. 3  is a functional block diagram of the arithmetic processing unit  24 . The arithmetic processing unit  24  includes a flow rate function computing unit  41 , a test mode executing unit  42 , and a quantitative dispensing executing unit  43 . Each functional unit may be implemented by a program or circuit. 
     The flow rate function computing unit  41  computes a function between the controlled value output from the analog control unit  28  and the flow rate of a weighing object supplied from the pump  50  and stores the function in the storage unit  25 . 
     The test mode executing unit  42  executes the test mode for changing a flow rate setting and a filter setting in a plurality of levels, measuring the deviation (hereinafter referred to as “stop weighed value deviation”) between a weighed value and a final weighed value at the time of stopping the pump  50  in each step, calculating the relationship between flow rate setting, a filter setting, and a stop weighed value deviation, and storing the relationship in the storage unit  25 . 
     The quantitative dispensing executing unit  43  weighs out a predetermined amount of a weighing object by controlling the operation of the pump  50  at a set flow rate, sequentially calculating the weighed value of the weighing object from the load detection result obtained by the load sensor unit  21 , and controlling the supply device to stop when the current weighed value becomes equal to or larger than the supply stop weight value calculated by subtracting a stop weighed value deviation from a supply target weighed value. 
     (Stop Weighed Value Deviation) 
     A stop weighed value deviation will be described prior to the description of the operation of the quantitative dispensing system  1 . As described above, causes for a stop weighed value deviation include the response delay of the supply device from stop control on the supply device to the actual stop of the supply device, the drop from the discharge unit of the supply device to the holding unit, the filter setting in the weighing device, and the supply pressure of a weighing object from the supply device to the holding unit. 
     Accordingly, the present inventors have examined in detail the influences of the filter setting in the electronic balance  10  and supply pressure. 
     The electronic balance  10  has a filter setting that changes display stability in accordance with a measurement environment. As indicated by Table 1, when the filter setting is strong (SLOW), the longer the time it takes to reach the final weighed value in a stable state. As a result, although the time it takes until the display of a measurement value is longer, weighed values do not easily vary and become stable regardless of being influenced by disturbance such as vibration. On the other hand, when the filter setting is weak (FAST), the time it takes for a weighed value to reach the final value shortens. This makes it possible to speed up the reading speed, but a weighed value is susceptible to the influence of disturbance and tends to become unstable. 
     Experiment 1 
       FIG. 4  illustrates the results obtained by measuring the behavior of a weighed value at the time of stopping the pump  50  by using the system  1  while the discharge port diameter of the supply tube  52  is changed in two levels as indicated by Table 2 with respect to each of the filter settings in two levels in Table 1. More specifically, the behavior of a weighed value after the stop of the supply device was measured at the time of stopping the supply device when the flow rate of the supply device was set to 100 g/min and the weighed value reached 20 g. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Characteristics of Filter Setting 
               
            
           
           
               
               
               
               
            
               
                   
                   
                 Measurement 
                   
               
               
                   
                 Filter Setting 
                 Response Speed 
                 Display Stability 
               
               
                   
                   
               
               
                   
                 Strong (SLOW) 
                 Low 
                 Strong 
               
               
                   
                 Weak (FAST) 
                 High 
                 Weak 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Inner Diameter of Discharge Distal End 
               
            
           
           
               
               
               
               
            
               
                   
                 Discharge  
                 Discharge Inner 
                   
               
               
                   
                 Distal End 
                 Diameter (mm) 
                 Actual Processing 
               
               
                   
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Standard (supply 
                 4 
                 Leaving tube intact 
               
               
                   
                 pressure: 
                   
                   
               
               
                   
                 standard) 
                   
                   
               
               
                   
                 Thin (supply  
                 0.52 
                 Connecting needle 
               
               
                   
                 pressure: high) 
                   
                 having inner diameter 
               
               
                   
                   
                   
                 of 0.52 mm to tube 
               
               
                   
                   
                   
                 distal end 
               
               
                   
                   
               
            
           
         
       
     
     Note that when the flow rate is constant, changing the discharge inner diameter, i.e., the sectional area of the discharge port, means to change the supply pressure when supplying a liquid to the vessel  12 . 
     Referring to  FIG. 4 , when the discharge distal end remains unchanged, a stronger filter setting increases the final value as an excessive amount. On the other hand, thinning the discharge distal end, thereby increasing the supply pressure, will reduce the final value after it temporarily becomes an excessive amount. If the filter setting is weak and the supply pressure is high, in particular, the final value becomes insufficient instead of being excessive. This indicates that a filter setting is associated with a stop weighed value deviation with respect to an excessive amount, whereas a supply pressure is associated with a stop weighed value deviation with respect to insufficiency. 
     Experiment 2 
     As in Experiment 1, final weighed values after the stop of the supply device at a target weighed value were measured by using the system  1  with respect to the filter settings and the discharge distal ends in the two levels each shown in Table 1 and Table 2 while the flow rate was changed from 40 g/min to 100 g/min. 
       FIG. 5  illustrates the results in Experiment 2. Referring to  FIG. 5 , the theoretical extreme point is assumed at a stop weighed value deviation of 0 when the flow rate is 0 g/min. 
     The results indicate that with the standard discharge distal end indicated by ∘ (white circle), i.e., the standard supply pressure, the final weighed values increase in proportion to the flow rates, whereas with the thin discharge distal end indicated by A (white triangle), i.e., the high supply pressure, the final weighed values tend to decrease in the form of quadratic curves with increases in flow rate. 
     Accordingly, a stop weighed value deviation δ (δ(Q)) can be approximated by a quadratic expression of a flow rate Q like equation (1) given below by using a coefficient a associated with a supply pressure and a coefficient b associated with a filter setting. 
     
       
         
           
             
               
                 
                   
                     δ 
                     ⁡ 
                     
                       ( 
                       0 
                       ) 
                     
                   
                   = 
                   
                     
                       a 
                       · 
                       
                         Q 
                         2 
                       
                     
                     + 
                     
                       b 
                       · 
                       Q 
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     In this case, the coefficients a and b are obtained from the results in  FIG. 5  as indicated by Table 3 and Table 4. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                 Discharge Distal End 
                 Coefficient a 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 Standard (standard supply 
                 0 
               
               
                   
                 pressure) 
                   
               
               
                   
                 Thin (high supply pressure) 
                 −1.36E−04 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
             
               
                   
                 TABLE 4 
               
               
                   
                   
               
               
                   
                 Filter Setting 
                 Coefficient b 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 Strong (SLOW) 
                 0.0188 
               
               
                   
                 Weak (FAST) 
                 0.0073 
               
               
                   
                   
               
            
           
         
       
     
     When the above coefficients are applied to equation (1), the stop weighed value deviation δ in the experiment in  FIG. 4  becomes that illustrated in  FIG. 6 , thus indicating that the deviation can be properly approximated. 
     The operation of the pump  50  is stopped to weigh out a weighing object of a final weighed value W e  from the stop weighed value deviation δ(Q), obtained in the manner described above, and the final weighed value W e . A supply stop weight value W s  can be obtained by equation (2) given below. 
     
       
         
           
             
               
                 
                   
                     W 
                     s 
                   
                   = 
                   
                     
                       W 
                       e 
                     
                     - 
                     
                       δ 
                       ⁡ 
                       
                         ( 
                         Q 
                         ) 
                       
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
     Operation of System  1   
     1. Computation of Flow Rate Function 
     The system  1  is configured to perform analog control on the flow rate of the pump  50  with a current value serving as a controlled value C 1 . Since the relationship between the controlled value C i  and a flow rate Q i  of the pump  50  changes depending on the device used as the pump  50  or the thickness of the tube, etc., the correlation function (hereinafter referred to as “flow rate function”) between the flow rate Q i  and the controlled value C i  needs to be obtained in advance.  FIG. 7  is a flowchart for flow rate function computation processing by the flow rate function computing unit  41 . The relationship between the flow rate and the controlled value for the pump based on the balance is obtained, and the relationship between the controlled value C i  for the pump and the flow rate Q i  is stored. 
     The following explanation is a specific example of obtaining flow rates Q 1  to Q 3  when the controlled value C i  is changed as a current value of an analog output in three levels, namely C 1  to C 3  indicated in Table 5 and storing the obtained flow rates as a function. 
     
       
         
           
               
             
               
                 TABLE 5 
               
             
            
               
                   
               
               
                 Relationship between Controlled Value  
               
               
                 and Current Value 
               
            
           
           
               
               
               
            
               
                   
                 Controlled Value C i   
                 Current Value (mA) 
               
               
                   
                   
               
            
           
           
               
               
               
            
               
                   
                 C 1   
                 10 
               
               
                   
                 C 2   
                 16 
               
               
                   
                 C 3   
                 20 
               
               
                   
                   
               
            
           
         
       
     
     When the processing starts, the flow rate function computing unit  41  sets i=1 in step S 101 . In step S 102 , the flow rate function computing unit  41  starts the operation of the pump  50  and sets the controlled value to C i . 
     Next, in step S 103 , the flow rate function computing unit  41  determines whether the weighed value is updated and repeats the processing until the weighed value is updated. If the weighed value is updated (Yes), the flow rate function computing unit  41  stores the latest weighed value W (n)  in the storage unit  25  in step S 104 . 
     Next, in step S 105 , the flow rate function computing unit  41  calculates a flow rate value Q (n)  according to equation (3) given below. 
     
       
         
           
             
               
                 
                   
                     Q 
                     
                       ( 
                       n 
                       ) 
                     
                   
                   = 
                   
                     
                       
                         [ 
                         
                           
                             W 
                             
                               ( 
                               n 
                               ) 
                             
                           
                           ⁢ 
                           
                               
                           
                           - 
                           
                             W 
                             
                               ( 
                               
                                 n 
                                 - 
                                 X 
                               
                               ) 
                             
                           
                         
                         ] 
                       
                       / 
                       Δ 
                     
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     T 
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
     (where W (n)  is the latest weighed value, W (n-X)  is the Xth weighed value before the latest weighed value, and ΔT is the time interval between the latest weighed value and the Xth weighed value before the latest weighed value.) 
     Next, in step S 106 , the flow rate function computing unit  41  stores the latest flow rate value Q (n)  in the storage unit  25 . 
     Next, in step S 107 , the flow rate function computing unit  41  determines whether a predetermined time that allows proper calculation of a flow rate has elapsed since the start of the operation of the pump  50  with the controlled value C i . If the predetermined time has not elapsed (No), the process returns to step S 103  to repeat steps S 103  to S 107  until the elapse of the predetermined time. In this manner, w (n)  W (n-1)  W n-2 , . . . and Q (n) , Q (n-1) , Q (n-2) , . . . are sequentially stored in the storage unit  25 . 
     On the other hand, if the flow rate function computing unit  41  determined in step S 107  that the predetermined time has elapsed (Yes), the process shifts to step S 108 , in which the flow rate function computing unit  41  determines whether the flow rate values Q (n) , Q (n-1) , Q (n-2) , . . . are stabilized. Whether flow rate values are stabilized may be determined by determining whether the difference between the flow rate value Q (n)  and the immediately preceding flow rate value Q (n-1)  is equal to or less than a predetermined value, etc. 
     If the flow rate function computing unit  41  determines in step S 108  that the flow rate values are not stabilized (No), the process returns to step S 103 . On the other hand, upon determining that the flow rate values are stabilized (Yes), the flow rate function computing unit  41  causes the storage unit  25  to store Q (n)  as the flow rate Q i  at the controlled value C i  in step S 109 . 
     Next, in step S 110 , the flow rate function computing unit  41  stops the operation of the pump  50 . 
     Next, in step S 111 , the flow rate function computing unit  41  increments according to i=i+1. In step S 112 , the flow rate function computing unit  41  determines whether i=i max +1. In this case, the flow rate function computing unit  41  determines whether i=4. If not i=i max +1 (No), the process returns to step S 102 . 
     On the other hand, upon determining in step S 112  that i=i max +1 (Yes), the flow rate function computing unit  41  obtains a relational expression (function) between the controlled value C i  and the flow rate Q i  from the controlled value C i  and the flow rate Q i  at that time in the following manner and causes the storage unit  25  to store equation (5) in step S 113 . 
     The relationship between an arbitrary controlled value C x  and a corresponding flow rate Q x  can be theoretically obtained in the form of a linear expression. In practice, however, as the controlled value C x  is increased to increase the rotation speed of the pump, the response at the time of flattening/releasing the tube deteriorates. For this reason, the above relationship is approximated by a quadratic expression as equation (4) given below. 
     
       
         
           
             
               
                 
                   
                     Q 
                     x 
                   
                   = 
                   
                     
                       α 
                       · 
                       
                         c 
                         x 
                         2 
                       
                     
                     + 
                     
                       β 
                       · 
                       
                         c 
                         x 
                       
                     
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
     This makes it possible to calculate a controlled value C R  to achieve a desired flow rate Q R  according to equation (5) given below by obtaining flow rates Q i  corresponding to two or more controlled values C i  and obtaining α and β from the obtained flow rates. 
     
       
         
           
             
               
                 
                   
                     [ 
                     
                       Math 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       1 
                     
                     ] 
                   
                   ⁢ 
                   
                       
                   
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     C 
                     R 
                   
                   = 
                   
                     
                       
                         - 
                         β 
                       
                       + 
                       
                         
                           
                             β 
                             2 
                           
                           + 
                           
                             4 
                             · 
                             α 
                             · 
                             
                               Q 
                               R 
                             
                           
                         
                       
                     
                     
                       2 
                       · 
                       α 
                     
                   
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
           
         
       
     
     2. Test Mode 
     Next, the test mode will be described. As described above, the stop weighed value deviation δ is expressed as a function of the flow rate Q. In the test mode, before actual quantitative dispensing, the relationship between the stop weighed value deviations δ and the flow rates Q is measured with respect to a plurality of filter settings F p  and a plurality of flow rates Q y  and the relationship is stored.  FIG. 8  is a flow chart for processing in the test mode. 
     The following explanation is a specific example of obtaining the relationship between a filter setting F p , a stop weighed value deviation δ py , and a flow rate Q y  by measuring flow rates in the three steps in Table 7 with respect to the filter settings in the three levels in Table 6. 
     
       
         
           
               
             
               
                 TABLE 6 
               
             
            
               
                   
               
               
                 Filter Setting 
               
            
           
           
               
               
               
            
               
                   
                 Filter Setting (F p ) 
                 Response Speed 
               
               
                   
                   
               
               
                   
                 F 1   
                 fast 
               
               
                   
                 F 2   
                 standard 
               
               
                   
                 F 3   
                 Slow 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 7 
               
             
            
               
                   
               
               
                 Flow Rate 
               
            
           
           
               
               
               
            
               
                   
                 Flow Rate (Q y ) 
                 Flow Rate (ml/min) 
               
               
                   
                   
               
            
           
           
               
               
               
            
               
                   
                 Q 1   
                 1 
               
               
                   
                 Q 2   
                 6 
               
               
                   
                 Q 3   
                 12 
               
               
                   
                   
               
            
           
         
       
     
     When the test mode is started, the test mode executing unit  42  sets a filter setting parameter p to p=1 in step S 201  and sets a flow rate setting parameter y to y=1 in step S 202 . 
     Next, in step S 203 , the test mode executing unit  42  sets the filter setting F p  in accordance with the set filter setting parameter p. In step S 204 , the controlled value C y  corresponding to the flow rate Q y  according to the set flow rate setting parameter y is calculated by using the flow rate function calculated by the flow rate function computing unit  41 , and the operation of the pump  50  is started with the controlled value C y . 
     Next, in step S 205 , the test mode executing unit  42  determines whether the weighed value is updated and repeats the processing until the weighed value is updated. If the weighed value is updated (Yes), the latest weighed value W (n)  is stored in the storage unit  25  in step S 206 . 
     Next, in step S 207 , the test mode executing unit  42  calculates the flow rate value Q (n)  according to equation (3). 
     
       
         
           
             
               
                 
                   
                     Q 
                     
                       ( 
                       n 
                       ) 
                     
                   
                   = 
                   
                     
                       
                         [ 
                         
                           
                             W 
                             
                               ( 
                               n 
                               ) 
                             
                           
                           ⁢ 
                           
                               
                           
                           - 
                           
                             W 
                             
                               ( 
                               
                                 n 
                                 - 
                                 X 
                               
                               ) 
                             
                           
                         
                         ] 
                       
                       / 
                       Δ 
                     
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     T 
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
     (where W (n)  is the latest weighed value, W (n-X)  is the Xth weighed value before the latest weighed value, and ΔT is e.) 
     Next, in step S 208 , the test mode executing unit  42  stores the latest flow rate value Q (n)  in the storage unit  25 . 
     Next, in step S 209 , the test mode executing unit  42  determines whether a predetermined time that allows proper calculation of a flow rate has elapsed since the start of the operation of the pump  50  with the controlled value C i . If the predetermined time has not elapsed (No), the process returns to step S 205 . In this manner, w (n) , W (n-1) , W (n-2) , . . . and Q (n) , Q (1) , Q (n-2) , . . . are sequentially stored in the storage unit  25 . 
     On the other hand, if the predetermined time has elapsed (Yes) in step S 209 , the process shifts to step S 210 , in which the test mode executing unit  42  determines whether the flow rate values Q (n) , Q (n-1) , Q (n-2) , . . . are stabilized. Whether flow rate values are stabilized may be determined by, for example, determining whether the difference between the flow rate value Q (n)  and the immediately preceding flow rate value Q (n-1)  is equal to or less than a predetermined value, etc. 
     If the flow rate values are not stabilized (No) in step S 210 , the process returns to step S 205 . If the flow rate values are stabilized (Yes), the process shifts to step S 211 , in which the test mode executing unit  42  causes the storage unit  25  to store the latest weighed value W (n)  as the supply stop weight value W s . At the same time, in step S 212 , the test mode executing unit  42  stops the operation of the pump  50  by setting the controlled value to 0. 
     Next, in step S 213 , the test mode executing unit  42  determines whether the weighed value is updated and repeats the processing until the weighed value is updated. If the weighed value is updated (Yes), the latest weighed value W (n)  is stored in the storage unit  25  in step S 214 . 
     Next, in step S 215 , the test mode executing unit  42  determines whether a predetermined time has elapsed since the start of the operation of the pump  50 . If the predetermined time has not elapsed (No), the process returns to step S 213 . In this manner, the weighed values W (n) , W (n-1) , W (n-2) , . . . are sequentially stored in the storage unit  25 . 
     On the other hand, upon determining in step S 215  that the predetermined time has elapsed (Yes), the test mode executing unit  42  determines in step S 216  whether the weighed values W (n) , W (n-1) , W (n-2) , . . . are stabilized. Whether weighed values are stabilized may be determined by, for example, determining whether the difference between the weighed value W (n)  and the immediately preceding weighed value W (n-1)  is equal to or less than a predetermined value. 
     If the weighed values are not stabilized (No) in step S 216 , the process returns to step S 213 . On the other hand, if the weighed values are stabilized in step S 216  (Yes), the test mode executing unit  42  causes the storage unit  25  to store the latest weighed value W (n)  as the final weighed value W e  in step S 217 . 
     Next, in step S 218 , the test mode executing unit  42  calculates the stop weighed value deviation δ py  by using equation (6). 
     
       
         
           
             
               
                 
                   
                     δ 
                     
                       p 
                       ⁢ 
                       y 
                     
                   
                   = 
                   
                     
                       W 
                       e 
                     
                     - 
                     
                       W 
                       s 
                     
                   
                 
               
               
                 
                   ( 
                   6 
                   ) 
                 
               
             
           
         
       
     
     Accordingly, since the final weighed value W e  means a supply target weight value W a , the supply stop weight value W s  for weighing out the weighing object of the supply target weight value W a  can be calculated by using equation (7) given below. 
     
       
         
           
             
               
                 
                   
                     W 
                     s 
                   
                   = 
                   
                     
                       W 
                       a 
                     
                     - 
                     
                       δ 
                       
                         p 
                         ⁢ 
                         y 
                       
                     
                   
                 
               
               
                 
                   ( 
                   7 
                   ) 
                 
               
             
           
         
       
     
     Next, in step S 219 , the test mode executing unit  42  associates and stores the filter setting F p , the flow rate Q y , and the stop weighed value deviation δ py  in the storage unit  25 . 
     Next, in step S 220 , the test mode executing unit  42  increments the flow rate setting parameter y according to y=y+1. In step S 221 , the test mode executing unit  42  determines whether y=y max +1. In this specific example, the test mode executing unit  42  determines whether y=4. 
     If the flow rate setting parameter y is not y=y max +1 (No), the process returns to step S 203 . On the other hand, if the flow rate setting parameter y is y=y max +1 (Yes), the process shifts to step S 222 . In step S 222 , the test mode executing unit  42  increments the filter setting parameter p according to p=p+1. In step S 223 , the test mode executing unit  42  determines whether p=p max +1, that is, p=4 in a specific example. 
     If the filter setting parameter p is not p=p max +1 (No), the process returns to step S 202 . On the other hand, if the filter setting parameter p is p=p max +1 (Yes), the test mode executing unit  42  calculates an approximation expression for calculating the stop weighed value deviation δ x  from the flow rate Q x  with each filter setting from the measurement result of the stop weighed value deviation δ with respect to the flow rate Q according to equation (1) and stores the approximation expression in the storage unit  25  in step S 224 . The test mode executing unit  42  then terminates the processing. In this manner, the relationship between the flow rate Q and the stop weighed value deviation δ with each filter setting is stored in the storage unit  25 . 
     3. Quantitative Dispensing 
     Next, quantitative dispensing processing using the system  1  will be described with reference to  FIG. 9 . Assume that the computation of the above flow rate function and the test mode have been executed before quantitative dispensing. 
     When starting quantitative dispensing, the user inputs the supply target weight value W a  and the desired flow rate setting Q y  to the system  1 . In this case, the flow rate setting parameter y is set to y=1. The user can input an instruction by selection from a drop-down list or inputting an arbitrary value, etc. In addition, the filter setting Fp is set to, for example, p=m in advance in accordance with the installation environment (the influences of vibration and wind) of the balance. 
     Upon starting quantitative dispensing, the quantitative dispensing executing unit  43  sets the flow rate setting parameter y to y=1 based on an instruction from the user in step S 301 . 
     Next, in step S 302 , the quantitative dispensing executing unit  43  reads out a filter setting F m  set in advance. 
     Next, in step S 303 , the quantitative dispensing executing unit  43  sets a flow rate Q 1  in accordance with the flow rate parameter p set in step S 301 , converts the flow rate Q 1  into a controlled value C 1  by using the flow rate function obtained by the flow rate function computing unit  41 , and starts the operation of the pump  50  with the controlled value C 1 . 
     Next, in step S 304 , the quantitative dispensing executing unit  43  determines whether the weighed value is updated. If the weighed value is not updated (No), step S 304  is repeated again. If the weighed value is updated (Yes), the quantitative dispensing executing unit  43  stores the latest weighed value W (n)  in the storage unit  25  in step S 305 . 
     Next, in step S 306 , the quantitative dispensing executing unit  43  calculates the stop weighed value deviation δ py  at the time of p=m and y=1 according to the relational expression between the flow rate Q y  and the stop weighed value deviation δ py  acquired by the test mode executing unit  42  and compares the latest weighed value W (n)  with the value obtained by subtracting a stop weighed value deviation δ m1  from the supply target weight value W a , i.e., the supply stop weight value W s . 
     If the latest weighed value W (n)  is smaller than the supply stop weight value W s  (No), the process returns to step S 304 . On the other hand, if the latest weighed value W (n)  is equal to or more than the supply stop weight value W s  in step S 306 , the quantitative dispensing executing unit  43  stops the operation of the pump  50  in step S 307  and terminates the processing. In this manner, a weighing object of the supply target weight value W a  can be precisely dispensed. 
     In conventional quantitative dispensing apparatuses, a supply stop weight value has been set in consideration of a weighed value error based on the response delay from stop control on the supply device to the actual stop of the device and the drop of the supply tube. However, no consideration has been given to a stop weighed value deviation caused by the response delay of the measurement system which occurs in accordance with the filter setting of the balance and a supply pressure. In particular, in the quantitative dispensing system  1  according to the present embodiment, the stop weighed value deviation δ is obtained in consideration of the response delay of the measurement system and a supply pressure, thereby more accurately weighing out a predetermined amount. 
     Using the stop weighed value deviation δ in accordance with a flow rate and a filter setting makes it necessary to obtain the stop weighed value deviation δ every time the flow rate and the filter setting change, even if the pump to be used remains the same. The quantitative dispensing system according to the present embodiment includes the test mode for measuring the relationship between the stop weighed value deviation δ and the flow rate Q with respect to the plurality of filter settings F p  and the plurality of flow rates Q y  and storing the measured relationship and is configured to be able to calculate the stop weighed value deviation δ from a flow rate and a filter setting by using the relational expression obtained by the test mode. This makes it unnecessary for the user to calculate and set a stop weighed value deviation again every time a flow rate setting and a filter setting are performed, thereby the user can eliminate the trouble of performing setting. 
     In this test mode, in particular, since the relationship between the stop weighed value deviation δ and the flow rate Q is stored as a function, it is possible to handle control such as continuously changing the flow rate Q, thus providing an advantageous effect. 
     The quantitative dispensing system  1  according to the present embodiment is also configured to provide the electronic balance as the weighing device with the analog control unit that can perform contact output/analog output, and hence can perform analog control on the start/stop of the operation and the flow rate of the pump as the supply device without going through any external control unit. When a supply device is configured to directly perform digital control from the control unit of an electronic balance, the device is often additionally provided with an external control device that can perform digital/analog conversion. Many of the relatively compact supply devices of a tube pump type operate under analog control. Additionally providing an external control device for such a supply device will make the devices relatively expensive. Accordingly, the system  1  need not use any external control unit or can use an inexpensive analog control type supply device, and hence can achieve overall cost reduction. 
     Modification 
     Note that the above embodiment has exemplified the case in which the weighing device controls the supply device by using analog output with a current value serving as a controlled value. However, the supply device is not limited to one that is controlled by analog output and may be one that is controlled by digital signals. 
     As in the above embodiment, when the supply device is to be controlled by analog output, the device is not limited to one that is controlled by a current value as a controlled value and may be one that is controlled by a voltage value as a controlled value. 
     The above embodiment is configured to stop the supply device when the latest weighed value W (n)  becomes equal to or more than the supply stop weighed value W s . However, a threshold for changing a flow rate may be provided for the difference between the latest weighed value W (n)  and the supply stop weighed value W s  to perform control such that if the difference between the latest weighed value W (n)  and the supply stop weighed value W s  is sufficiently large, the controlled value to be output is increased and the flow rate is increased, whereas if the difference between the latest weighed value W (n)  and the supply stop weighed value W s  approaches the stop weighed value deviation to some extent, the controlled value to be output is reduced and the flow rate is reduced. In addition, if the difference between the latest weighed value W (n)  and the supply stop weighed value W s  becomes equal to or less than the stop weighed value deviation S (the latest weighed value W (n)  becomes equal to or more than the supply stop weighed value W s ), the operation of the supply device is stopped. As described above, the time required for quantitative dispensing can be shortened by changing the flow rate, i.e., the controlled value, based on the difference between the latest weighed value W (n)  and the supply stop weighed value W s . 
     The above embodiment has exemplified the case in which the present invention is configured as the system that dispenses a liquid as a weighing object in predetermined amounts. However, a weighing object is not limited to a liquid and may be a powder and granular material. 
     Although the preferred embodiments of the present invention have been described, the above embodiments are examples of the present invention. These embodiments can be combined based on the knowledge of a person skilled in the art. Such combined embodiments are also incorporated in the scope of the present invention. 
     REFERENCE SIGNS LIST 
     
         
           1 : Quantitative dispensing system 
           10 : Electronic balance (Weighing device) 
           10   a : Holding unit 
           21 : Load sensor unit 
           24 : Arithmetic processing unit 
           28 : Analog control unit 
           41 : Flow rate function computing unit 
           42 : Test mode executing unit 
           43 : Quantitative dispensing executing unit 
           50 : Pump (Supply device)