JPH1019642A - Electronic balance - Google Patents

Abstract

(57) [Summary] [PROBLEMS] Even if the use environment or the use method of the balance changes, it automatically adapts to the change and performs control suitable for the use environment or the use method, and always has a favorable response and good response. Provide an electronic balance that can have stability. SOLUTION: A plurality of combinations of PID parameters used in PID calculation means 7 for digitally PID-calculating the displacement detection data of the balance mechanism are stored in a storage means 12, and among these, the latest specified number of displacement detection data is stored. The combination according to the time series information is selected by the parameter selecting unit 13.
And supplies the selected PID to the PID calculation means 7, so that the optimum P in accordance with the vibration situation of the use environment, the use purpose, etc.
The system is controlled based on the ID operation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic balance,
More specifically, the present invention relates to an electronic balance provided with a so-called digital PID type servo mechanism for performing digital PID calculation on displacement detection data of a balance beam.

[0002]

2. Description of the Related Art In electronic balances, generally, a coil is fixed to a balance mechanism such as a lever which is displaced by a load to be measured, and the coil is arranged in a static magnetic field, and a current flows through the coil. The electromagnetic force generated by this is opposed to the load to be measured, the current flowing through the coil is controlled so that both are balanced, and the magnitude of the load to be measured is obtained from the coil current in the balanced state.

The current flowing through the coil is detected by detecting the displacement of the balance mechanism by a displacement sensor, and feedback-controlled so that a current corresponding to the detection result flows through the coil.
That is, the coil current is controlled by a servo mechanism that keeps the displacement of the balance mechanism at zero.

In an electronic balance provided with such a servo mechanism, the output of a displacement sensor is usually subjected to PID (proportional, integral, differential) operation by a PID operation circuit, and then converted to a current signal and fed back to a coil. , P,
It is considered that the responsiveness and stability of the system can be obtained by appropriately setting the calculation parameters of I and D.

Here, the PID calculation of the displacement detection result by the displacement sensor has conventionally been generally performed by an analog calculation, but in recent years, a so-called digital PID method (PID calculation) in which a PID calculation process is performed by a digital calculation. Or, a system employing a system called digital servo system) has been put to practical use.

[0006]

By the way, in an electronic balance provided with a servo mechanism accompanied by PID calculation, by setting the parameters of each calculation optimally as described above, it is assumed that the parameters are set in a favorable environment or when setting the parameters. When used in an environment where it is used, responsiveness and stability as designed can be obtained, but when used in an environment where vibrations are large compared to the assumed environment, for example, apparent stability , There is a problem that the weighing display value fluctuates.

[0007] In addition to the method of using a balance, a method of placing a sample of unknown mass on a dish and measuring the mass of the sample,
For example, it is sometimes used for so-called weighing work, in which a liquid sample is gradually added on a plate and addition is stopped when the target mass has been reached. On the way, high-speed response rather than system stability is required. However, it is difficult to set each parameter of the PID so as to be suitable for any of these different use methods in the conventional electronic balance. is there.

An object of the present invention is to provide an electronic balance capable of automatically following a change in the use environment or the use method even if the use environment or the use method of the balance changes, and performing control more suitable for the use environment or the use method. Is to do.

[0009]

In order to achieve the above object, an electronic balance according to the present invention is a digital balance which calculates digital displacement data of a momentary displacement detection of a balance mechanism by a measured load.
ID calculation means, a servo mechanism for determining the magnitude of the current flowing through the coil of the electromagnetic force generator based on the calculation result to balance the balance mechanism, and a weighing value calculation for determining the weighing value using the PID calculation result Means for storing a plurality of sets of combinations of parameters P, I and D used in the PID calculation means, and parameters stored in the storage means based on time-series information of displacement detection data. And a parameter selection unit for selecting an optimum combination from the combinations and supplying the selected combination to the PID calculation unit.

Here, the time-series information of the latest specified number of displacement detection data in the present invention is, specifically, information representing a variation such as a standard deviation and a fluctuation width of the specified number of displacement detection data; Similarly, it refers to a temporal change pattern of the displacement detection data for the specified number.

According to the present invention, in a digital PID system in which a PID operation is performed by a digital operation, each operation parameter of P, I, and D can be changed at any time and arbitrarily by software, and time series information of displacement detection data can be obtained. This makes use of the fact that the environment in which the balance is placed and the method of use can be easily estimated.

That is, the magnitude and frequency of vibration of the environment in which the balance is placed are estimated from the time-series information of the latest specified number of displacement detection data, ie, the magnitude and variation pattern of the variation, or the occurrence of convection. Can be estimated. Once the magnitude or frequency of vibration in the environment in which the balance is used, or the presence or absence of convection, is determined, the system can be configured based on the response appropriate for the environment by combining the PID parameters accordingly. Can be controlled.

On the basis of the time-series information of the displacement detection data, for example, if the time-dependent change of the data tends to increase monotonously irrespective of the operation of the servo mechanism, the sample is gradually placed on the plate. In other words, it is possible to determine that a weighing operation is being performed. In this case, a PID that emphasizes responsiveness over system stability is used.
By selecting a combination of parameters, control suitable for the purpose of use of the balance can be performed.

In the configuration of the present invention, the storage means stores in advance a plurality of types of vibration conditions of the balance use environment or a combination of PID parameters suitable for a plurality of use purposes. A combination of a plurality of parameters stored in the storage means is selectively selected by the parameter selection means in accordance with the time series information of the latest specified number of pieces of displacement detection data and supplied to the PID calculation means. Thus, the parameters P, I, and D used in the PID calculation means are appropriately determined according to the vibration condition of the use environment of the balance, the presence or absence of convection, the use purpose of the balance (how to apply the load to be measured), and the like. And the system is always controlled under a more suitable PID operation.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an overall configuration diagram of an embodiment of the present invention, in which a schematic diagram showing a mechanical configuration and a block diagram showing an electrical configuration are shown together.

A plate 1 for applying a load to be measured is supported on one end of a lever 2 which is rotatable about a fulcrum 2a. A displacement sensor 3 is provided at the other end of the lever 2, and the displacement sensor 3 detects a rotational displacement of the lever 2. Further, a force coil 4a is fixed to the lever 2 on the opposite side of the plate 1 with respect to the fulcrum 2a, and the force coil 4a is arranged in a static magnetic field created by the magnetic circuit 4b. The generator 4 is constituted. That is, an electromagnetic force is generated by passing a current through the force coil 4a, and the electromagnetic force acts to return the displacement of the lever 2 to zero against the load to be measured.

A displacement detection signal of the lever 2 by the displacement sensor 3 is taken into the PID calculation unit 7 every minute for about several milliseconds as digital displacement detection data via the amplifier 5 and the A / D converter 6. Digital arithmetic processing is performed for proportional (P), integral (I), and derivative (D) operations. Then, the PID output is supplied to the pulse width modulator 8 and the weighing value calculator 9.

The pulse width modulation section 8 includes a pulse duty conversion section 8a for forming a duty signal in which the ratio of H and L changes within a predetermined period based on the magnitude of the PID output from the PID calculation section 7, It comprises an electronic switch 8b that opens and closes according to a duty signal from the duty conversion section 8a.
By b, the output current from the constant current generation circuit 10 is chopped, and is supplied to the force coil 4a as a pulse current. In other words, a pulse current having a constant peak value whose duty changes at regular intervals according to the PID calculation result of the displacement detection data of the lever 2 by the displacement sensor 3 flows through the force coil 4a. , The displacement of the lever 2 is always controlled to be zero.

The PID output from the PID calculation unit 7 is transmitted to the force coil 4a to balance the lever 2.
Therefore, the weighing value calculation unit 9 calculates the magnitude of the load to be measured on the plate 1 using the PID output, that is, the weighing value, and displays it on the display 11. .

In the PID calculation unit 7, when performing the respective calculations of P, I, and D on the displacement detection data, the respective parameters are not fixed, and a plurality of sets of parameters stored in the memory 12 are used. The combination selected by the parameter selection unit 13 from the combinations is used.

That is, the memory 12 stores P, P in advance in accordance with time-series information of displacement detection data described later.
A plurality of combinations of each parameter of I and D are written, and the parameter selection unit 13 selects an optimum combination from the combinations by a method exemplified below and supplies it to the PID calculation unit 7.

The parameter selection unit 13 captures displacement detection data output from the A / D converter 6 every moment, and a predetermined period of time from the time when the latest specified number of displacement detection data has been captured, ie, one displacement detection data. Using the minute displacement detection data, the time series information is obtained by a preset operation. In this example, the time-series information includes the standard deviation of the displacement detection data for the number of pieces, and the time-dependent change pattern of the displacement detection data for the number of pieces, specifically, the oscillation cycle and the monotonic increase of the displacement detection data. Or not. When the displacement detection data is not monotonically increasing, the parameter selection unit 13 determines which of the plurality of levels the calculation results of the standard deviation and the vibration cycle are at.

The memory 12 described above corresponds to each of the time series information, as schematically shown in FIG. 2, when the displacement detection data is monotonically increasing and when the displacement detection data is not, the oscillation period of the oscillation detection data is not. Optimum combinations of P, I, and D parameters are preliminarily written as a table in accordance with the length and the level of the standard deviation. Then, from these combinations, the combination according to the calculation / determination result of the time series information of the displacement detection data by the parameter selection unit 13 is selected and supplied to the PID calculation unit 7.

Here, the specific values of the parameters in FIG. 2 are determined by experiments or calculations, respectively. The tendency is that when the displacement detection data is monotonically increasing, Since it is estimated that the weighing operation is being performed, the parameter of I is decreased and the parameter of P is increased in order to increase the responsiveness of the system. In addition, in the case of non-monotonic increase, the parameter of I is increased as the standard deviation is increased, and the parameter of I is increased and the parameter of P is decreased as the oscillation period is shorter. When the vibration period is the longest, the parameter of D is additionally increased.

As described above, according to the time series information of the displacement detection data, P, I,
As a result, the optimum parameters are selected from the combinations in the memory 12 for each parameter of D. As a result, the servo system has an optimal response in accordance with the magnitude and cycle of the vibration or the presence or absence of convection in the use environment of the electronic balance. And controlled based on stability. Also, in the weighing operation, even in the same usage environment, the system responds faster than during normal measurement, and the weighing display value changes quickly accordingly,
The weighing operation can be performed based on good workability.

In the above embodiment, the PID calculation unit 7, the pulse duty conversion unit 8a, the weighing value calculation unit 9, the memory 12, and the parameter selection unit 13 are shown in FIG.
Although these are shown as block diagrams showing the respective functions, they are actually constituted by a microcomputer mainly composed of a CPU, a ROM, and a RAM and peripheral devices.

In the above embodiment, the time series information of the displacement detection data includes the standard deviation, the vibration cycle,
In addition, three types of information, that is, whether or not the information is monotonically increasing, are used. However, it may be configured to select a combination of parameters using only one or any two of them.
Instead of the standard deviation, a variation width (difference between the maximum value and the minimum value) of the specified number of pieces of displacement detection data may be used.

Further, in the above embodiment, the digital P
Although a pulse current having a pulse duty was passed through the force coil 4a based on the ID calculation result, the digital PID
A direct current whose value changes based on the calculation result may be passed. In other words, the present invention can of course be equally applied to an electronic balance in which PID calculation is performed by digital calculation.

[0029]

As described above, according to the present invention, in an electronic balance having a servo system for performing PID processing of displacement detection data by digital operation, based on the time series information of the latest specified number of displacement detection data. Since the optimum combination is automatically selected from a plurality of combinations of the parameters P, I, and D stored in advance and is used for digital PID calculation of the displacement detection data, The servo system is always controlled based on the optimum PID calculation according to the conditions of vibration and convection, or the purpose of use such as weighing work, so that the system always has optimal stability and responsiveness. In other words, compared to the conventional electronic balance in which each parameter of the PID is fixed, a more versatile electronic balance can be obtained, such as a reduced use environment condition.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of an embodiment of the present invention, showing a schematic diagram illustrating a mechanical configuration and a block diagram illustrating an electrical configuration.

FIG. 2 is a schematic explanatory view of a table written in a memory 12.

[Explanation of symbols]

 Reference Signs List 1 plate 2 lever 3 displacement sensor 4 electromagnetic force generator 6 A / D converter 7 PID calculation unit 8 pulse width modulation unit 9 weighing value calculation unit 10 constant current generation circuit 11 display 12 memory 13 parameter selection unit

Claims (1)

[Claims] 1. A PID calculating means for performing digital PID calculation of instantaneous displacement detection data of a balance mechanism due to a measured load, and a magnitude of a current flowing through a coil of an electromagnetic force generator is determined based on a result of the calculation. In an electronic balance having a servo mechanism for balancing a balance mechanism and a weighing value calculating means for determining a weighing value using the PID calculation result, a plurality of sets of combinations of parameters P, I, and D used in the PID calculating means are provided. An optimal combination selected from a combination of parameters stored in the storage means based on the latest prescribed number of pieces of time-series information of the displacement detection data.
An electronic balance comprising parameter selection means for supplying to a calculation means.