JPH0943034A - Electronic balance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an electronic balance of full digital type which has less error of quantization and high resolution by providing an absolute value circuit, etc., for converting a displacement detection signal of a balance stem into a signal with single polarity. SOLUTION: The rotational displacement of a balance stem 1 due to a load W to be measured is detected by a displacement detector 4, and an absolute circuit converts the displacement detection signal into a signal with single polarity. A single-polarity function converting circuit perfroms a specified function- computation by means of the output of the absolute value circuit as parameter and the output is digitized through an A/D converter. A digital computing section perfroms a conversion approximately reverse to the single-polarity function converting circuit by using the digital converted data as parameter. Then, it is converted into a data that is given a polarity corresponding to the judgment of the polarity of displacement detection signal, and the level of a feedback current to be supplied to a solenoid coil 2 is determined through a PID (proportion, integration, differentiation) computation. Thus, a highly accurate weighing result can be obtained by using a comparatively low-resolution A/D converter.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electromagnetic force balance type electronic balance, and more specifically, it performs digital conversion of the displacement detection result of a balance rod and performs feedback using an operation using the digital data. The present invention relates to a so-called fully digital electronic balance that determines a current value.

[0002]

2. Description of the Related Art In an electronic balance of the electromagnetic force balance type,
Generally, the displacement detector detects the deviation from the balance point of the balance rod caused by the load to be measured, and the current according to the detection result is applied to the coil (electromagnetic coil) placed in the static magnetic field. Thus, a servo system that balances the balance rod by generating an electromagnetic force corresponding to the load to be measured is provided, and the size of the load to be measured is obtained from the amount of current flowing through the electromagnetic coil in the balanced state. The actual measurement display value is obtained by performing data processing such as averaging processing on the measurement result of the coil current every moment. In such a servo system, normally, the feedback current value to be passed through the electromagnetic coil is P based on the displacement detection result.
It is determined by performing ID (proportional / integral / derivative) calculation.

In such an electromagnetic force balance type electronic balance, a so-called full digital system in which PID calculation is performed by digital calculation after A-D conversion of the displacement detection result of the balance rod has been conventionally available on the market. Basically, the feedback value is determined by the analog PID calculation, and the data used in the data processing unit for performing the averaging process is the signal obtained by converting the feedback current into a voltage or the analog PID calculation result by A-D. It is obtained by digitizing with a converter.

[0004]

In the electronic balance having the servo system using the analog PID arithmetic processing as described above and the A-D converter for digitizing the feedback value, the servo system and the A-D converter are used. Both of these require high stability, and it is difficult to obtain all of resolution, responsiveness, and stability at the same time.

By the way, the main reason why the full digital electronic balance has not been put to practical use is that it is difficult to reduce the quantization error caused by the A-D conversion. Such a quantization error not only lowers the measurement accuracy but also causes a dead zone or hysteresis in the servo system.

That is, when the displacement detection signal is digitized by the AD converter, even if the signal changes below the quantization level of the AD converter, it is not reflected in the digital signal.
PID calculation is performed using such a digital signal,
When the feedback value is determined based on the result of the calculation, a non-digitized level deviation remains, and a dead zone and hysteresis occur in the servo system. In order to solve or reduce such a problem, it is necessary to use an A / D converter having a wide input range and a high resolution, but such a high resolution and a wide dynamic range. Not only is the A-D converter having the above description extremely expensive, but there is a problem that the conversion time becomes long and the responsiveness deteriorates.

Here, in the field of general servo control, conventionally, when the deviation is detected and the detected signal is amplified, a non-linear function conversion is performed, so that the gain of the signal in the required level range is changed to the signal of another level. It is commonly used to be larger than. If such a technique is applied to a full digital electromagnetic force balance type electronic balance, in order to effectively use the resolution of the AD converter, the deviation,
In other words, the displacement detection value of the balance rod is guided to the function conversion circuit, and the function conversion circuit increases the amplification gain as the displacement detection value becomes closer to 0, and then leads it to the AD converter to be digitized and then digitally calculated. A method is conceivable in which a high-resolution feedback current value is obtained by performing a required calculation by processing.

However, it goes without saying that a high-precision function conversion circuit is required to adopt such a system, but a high-precision function conversion circuit is complicated, and moreover, the input value has positive and negative polarities. On the other hand, it is necessary to devise to have symmetrical properties, and there is a problem that it becomes expensive including the development cost.

The present invention has been made in view of the above circumstances, and a simple function conversion circuit is used to increase the amplification gain of the detection signal as the displacement amount of the balance rod becomes closer to 0. It is an object of the present invention to provide a fully digital electronic balance that can be led to a converter and thus has a relatively low resolution AD converter and a high resolution electronic balance with a small quantization error.

[0010]

In order to achieve the above object, the electronic balance of the present invention, as illustrated in FIG. 1, detects the rotational displacement of the balance rod 1 due to the load W to be measured as a displacement detector 4.
The servo system 10 for balancing the balance rod 1 by generating an electromagnetic force corresponding to the load W to be measured by controlling the magnitude of the feedback current flowing through the electromagnetic coil 2 according to the displacement detection result. The measured load W from the current value flowing in the electromagnetic coil 2 in the balance state
In an electronic balance that seeks the size of
Is an input of the absolute value circuit 12 for inputting the displacement detection signal from the displacement detector 4 and converting it into a unipolar signal and the polarity determining means (12) for the displacement detection signal, and the output of the absolute value circuit 12. , A unipolar function conversion circuit 13 that performs a predetermined function operation using the input signal as a parameter, and an AD converter 14 that digitizes the output of the unipolar function conversion circuit 13.
And the polarity determination result of the digital conversion data and the displacement detection signal from the A / D converter 14 are input, the conversion is performed approximately reverse to that of the unipolar function conversion circuit 13 using the digital conversion data as a parameter, and the polarity determination is performed. It is characterized by including a digital operation means 15 for converting the data to which the polarity is added according to the result and then determining the magnitude of the feedback current to be supplied to the electromagnetic coil 2 by using the converted data. .

Here, the operation for determining the magnitude of the feedback current using the data after the inverse conversion and the polarity application by the digital operation means 15 can adopt, for example, a normal PID operation.

[0012]

According to the present invention, a unipolar function conversion circuit can be obtained with high precision under a simple circuit configuration, and since it is unipolar, the symmetry in both positive and negative polarities is It is not necessary to convert the output of the displacement detector 4 into a function as it is by utilizing the fact that there is no need to consider it at all. Function conversion is performed, and the unipolar analog signal after the conversion is digitized by the AD converter 14. Then, the A-D output is subjected to a function conversion, which is almost the reverse of that of the unipolar function conversion circuit 13 by digital calculation, and is converted into data to which a polarity is given according to the polarity determination result of the displacement detection signal.

The digital data obtained in this manner is subjected to a unipolar function conversion circuit 13 so that the required level of the displacement detection result is made higher in gain than the other levels, so that the digital data has a relatively high resolution. After being A-D converted, it is returned by substantially reverse conversion so as to match the output characteristic of the displacement detector 4,
Moreover, the data is given the original polarity. Therefore, if the feedback current is determined by using such data, a minute displacement of the balance rod 1, that is,
Servo control is performed after relatively improving the -D conversion resolution, and therefore, using an AD converter with a relatively low resolution, high-precision and smooth balanced operation,
It is possible to obtain a high-resolution metric with a small quantization error. Further, since the A / D converter 14 only has to digitize a unipolar analog signal, the input voltage width becomes 1/2 as compared with the case where it is normally used, and the number of bits thereof is substantially 1. It can be regarded as increasing by a bit.

[0014]

1 is a block diagram schematically showing an overall configuration of an embodiment of the present invention, and FIG. 2 is a graph showing an input / output characteristic of each part thereof.

The measuring dish 1a on which the load W to be measured is loaded is
It is supported on one end of a balance rod 1 which is rotatable around a fulcrum 1b. An electromagnetic coil 2 is wound around the other end of the balance rod 1 via a winding frame 2a. The electromagnetic coil 2 includes a magnetic circuit 3 mainly composed of a permanent magnet 3a.
It is placed in the static magnetic field created by, and generates an electromagnetic force according to the magnitude of the current flowing there.

At the tip of the other end of the balance rod 1, there is arranged a displacement detector 4 for detecting the rotational angle displacement θ of the balance rod 1 by optical means, for example, in a non-contact manner. Is introduced into the displacement conversion circuit 11 and converted into a voltage signal E (θ) proportional to the rotational angle displacement θ of the balance rod 1 (see FIG. 2A).

The output E (θ) of the displacement conversion circuit 11 is guided to the absolute value circuit 12, and a unipolar analog signal A (E) = |
E (θ) | = E (| θ |) (see FIG. 2 (B)), and at the same time, the polarity determination signal of the input signal E (θ),
That is, based on E (θ) / | E (θ) |, for example, E> 0
Then, a signal of P = 0 is obtained with P = 1 and E <0.

The output E (| θ |) of the absolute value circuit 12 is introduced into the unipolar function conversion circuit 13 and converted into a required function output G {| θ |} with | θ | as a variable. The unipolar function conversion circuit 13 has a gain ∂G / ∂θ in a portion where θ is small.
Is larger and θ is larger, the gain ∂G / ∂θ is smaller. Therefore, a polygonal line function as illustrated in FIG. 2C can be adopted.

The absolute value circuit 12 and the unipolar function conversion circuit 13
FIG. 3 shows an example of a concrete circuit configuration of the above, and FIG. 4 shows a time chart showing an example of the signal waveform of each part thereof. As shown in FIG. 3, the absolute value circuit 12 is a known circuit composed of two differential amplifiers and a diode, and the unipolar function conversion circuit 13 is a relatively simple circuit called a row select circuit. Moreover, it is possible to perform highly accurate polygonal line function conversion. In addition, the absolute value circuit 12 of FIG.
In the figure, a signal for easily discriminating the polarity of the input signal E _in can be taken out from the connection point between the differential amplifier at the preceding stage and each diode shown by E _AO in the figure.

Now, the output G of the unipolar function conversion circuit 13
{| Θ |} is introduced into the A / D converter 14 and digitized, and a digital signal G {| θ |} with | θ | as a variable is used.
_{Get DIG} .

This digital signal G { _│θ│ } _DIG is taken into the digital arithmetic processing section 15 together with the polarity discriminating signal P from the absolute value circuit 12. Digital arithmetic processing unit 1
5 is a digital signal G {| θ |} _DIG and a polarity discrimination signal P
As a parameter, the unipolar function conversion circuit 13 described above is used.
The function conversion opposite to that is performed, and P
And a digital function conversion unit 15a for obtaining data H (θ) _DIG with polarity according to
PID (proportional, to data H (θ) _DIG from a
Digital PID calculation unit 1 that obtains a digital feedback value F (θ) _DIG by _performing integral (differential) calculation
5b and a weighing value calculation unit 15c for determining a weighing display value from the feedback value F (θ) _DIG every moment. In addition, this digital arithmetic processing unit 1
In FIG. 1, 5 is shown as a block diagram for each function, but actually it is constituted by a microcomputer having a program that achieves these functions.

Here, in the function conversion in the digital function conversion section 15a, as shown in FIG. 2D, the displacement amount θ of the balance rod 1 is obtained by the function conversion reverse to the function conversion by the unipolar function conversion circuit 13. Is obtained, the output characteristic of the data H (θ) _DIG with respect to θ is substantially returned to the output characteristic of the displacement conversion circuit 11. At this time, θ has a certain value. It is desirable that the gain be sharply reduced and the output be saturated when the value exceeds.

The digital feedback value F (θ) _DIG from the digital PID calculator 15b is the DA converter 16
After being analogized by the voltage / current conversion circuit 17
Is converted into a current value by the electromagnetic wave, and is fed as a feedback current to the electromagnetic coil 2. Further, this digital feedback value F (θ) _DIG is guided to the measurement value calculation unit 15c,
In this measurement value calculation unit 15c, the feedback value F is changed every moment.
(Θ) Calculate the measured value by averaging _DIG .

According to the above configuration, the displacement θ of the balance rod 1
The detection result of A is converted into a function so that the closer the value is to 0, the higher the gain becomes, and then A / D converted. The digital conversion data is inversely converted by digital calculation and used for PID calculation. Therefore, A-D for small deviations
The feedback value is determined with the conversion resolution relatively improved, and the A / D converter 14 is substantially used.
, The quantization error is reduced, and even if the resolution of the AD converter 14 is low, a highly accurate and smooth balanced operation can be obtained, and a high-resolution metric value can be obtained. And
Since the function conversion of the displacement detection signal is performed by the unipolar function conversion circuit 13 after being converted into the unipolar signal by the absolute value circuit 12, it is possible to perform highly accurate function conversion based on a simple circuit configuration. Become.

Further, since only a unipolar analog signal is always input to the A / D converter 14, the input voltage width becomes 1/2 as compared with the case of normal use. This means that when the same AD converter is used, the number of bits is substantially increased by 1 bit as compared with the conventional usage.

In the above embodiment, the unipolar function conversion circuit 13 is a polygonal function conversion circuit. However, the present invention is not limited to this, and for example, logarithmic conversion, the smaller the input signal, the higher the gain. Any function can be used as long as it performs such a function conversion.

Further, in the digital arithmetic processing section 15,
In order to calculate the feedback value using the data that has passed through the digital function conversion unit, an example in which the PID calculation is performed has been shown in the above-described embodiment, but the present invention is not limited to this, and a certain conventional method is used. Needless to say, the feedback value may be calculated by, for example, PI calculation or PD calculation as used in the electronic balance.

[0028]

As described above, according to the present invention,
After the displacement detection signal of the balance rod 1 is converted into a unipolar signal by the absolute value circuit, the required function conversion is performed by the unipolar function conversion circuit that can perform highly accurate function conversion with a simple circuit configuration. The subsequent analog signal is digitized by an A / D converter, and digital displacement information is obtained together with the polarity determination result of the displacement detection signal. Therefore, by adding a simple circuit, A / D conversion with a relatively low resolution is performed. It is possible to obtain a fully digital electronic balance that can obtain a smooth equilibrium operation and highly accurate weighing results using a measuring instrument. Here, since the displacement detection signal is function-converted by the absolute value circuit and the unipolar function conversion circuit, the obtained conversion output is necessarily symmetrical with respect to the polarity of the deviation, which is also advantageous in this respect.

Further, since the unipolar analog signal is always input to the A / D converter, the input voltage width is 1/2 that of the conventional one, and the number of bits is substantially larger by one bit. You can get the same effect as using one.

[Brief description of drawings]

FIG. 1 is a block diagram schematically showing an overall configuration of an embodiment of the present invention.

FIG. 2 is a graph showing the input / output signal characteristics of each part.

FIG. 3 is a circuit configuration diagram showing specific examples of an absolute value circuit 12 and a unipolar function conversion circuit 13.

FIG. 4 is a time chart showing an example of signal waveforms of respective parts in FIG.

[Explanation of symbols]

 1 Balance Rod 1a Measuring Plate 1b Support Point 2 Electromagnetic Coil 3 Magnetic Circuit 4 Displacement Detector 11 Displacement Conversion Circuit 12 Absolute Value Circuit 13 Unipolar Function Conversion Circuit 14 A-D Converter 15 Digital Operation Processor 15a Digital Function Converter 15b Digital PID calculation unit 15c Weighted value calculation unit 16 DA converter 17 Voltage / current conversion circuit

Claims (1)

[Claims] 1. A load to be measured is detected by detecting a rotational displacement of a balance rod due to a load to be measured by a displacement detector and controlling a magnitude of a feedback current flowing through an electromagnetic coil according to the displacement detection result. In an electronic balance that is provided with a servo system that generates an electromagnetic force to balance the balance rod, and in which the magnitude of the load to be measured is obtained from the value of the current flowing in the electromagnetic coil in the balanced state, the servo system includes the displacement detector. The absolute value circuit for inputting the displacement detection signal by and converting it into a unipolar signal and the polarity determining means for the displacement detection signal, and the output of the absolute value circuit are input,
A unipolar function conversion circuit that performs a predetermined function operation using an input signal as a parameter, an AD converter that digitizes the output of the unipolar function conversion circuit, digital conversion data from the AD converter, and the above After inputting the polarity determination result of the displacement detection signal, the digital conversion data is used as a parameter to perform a conversion substantially opposite to that of the unipolar function conversion circuit, and after conversion to data with a polarity according to the polarity determination result, the An electronic balance comprising: a digital arithmetic means for determining the magnitude of a feedback current to be supplied to the electromagnetic coil using the converted data.