JP2000019009A - Measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable highly accurate measurement by canceling out the phase difference between a measuring signal of an object to be measured and a floor vibration detection signal, subtracting the floor vibration detection signal from the measuring signal, and outputting a floor vibration pre-corrected signal. SOLUTION: A measuring device is provided with a measuring cell 2 to measure an object to be measured, a floor vibration detecting cell 4 to detect the vibration of a floor F, a CPU 15, etc. A measuring signal of the object to be measured from the measuring cell 2 and a floor vibration detection signal from the floor vibration detecting cell 4 are each digitized by an A/D converter 9 via analog filers 5 and 6, an amplifier 7, and an anti-alias filter 8. At the CPU 15, the measuring signal is outputted as a pre-filtered measuring signal Ym via the first digital filter 10, and the floor vibration detection signal is outputted as a pre-filtered floor vibration signal Yc via the second digital filter 11 and a gain correcting means 12. A floor vibration correcting means 14 performs the processing of subtracting the pre-filtered floor vibration signal Yc from the pre-filtered measuring signal Ym and outputs a floor vibration pre-corrected signal Y in which floor vibration is corrected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a weighing device for removing, from a weighing signal output from a weighing cell, a weighing error caused by a vibration component of a floor on which the weighing cell is installed.

[0002]

2. Description of the Related Art Generally, when measuring an object to be weighed on a factory production line, the ground,
Low frequency (approx. 20H)
z or less), and these vibrations are superimposed on the weighing signal. Therefore, in the weighing device, a floor vibration detection cell that outputs a floor vibration detection signal on the same floor as the weighing cell near the weighing cell that outputs a weighing signal corresponding to the weight of the object to be weighed is output. There is a case where floor vibration compensation for removing a floor vibration component in the weighing signal is performed by installing and subtracting the floor vibration signal from the weighing signal.

In the weighing device for performing the floor vibration compensation,
When the weighing cell and the floor vibration detection cell are not the same size, such as when the floor vibration detection cell is downsized to save space, the output signal for the input signal on the weighing cell side and the floor vibration detection cell side Are different from each other, it is necessary to perform a gain correction for adjusting the output sensitivity of one of the cells to the other to adjust the output gain of both cells.

[0004]

However, when the dynamic characteristics of the weighing cell and the floor vibration detecting cell are not the same, that is, when the amplitude and phase delay (damping force) of the output signal with respect to the input signal (exciting force) are not the same. The phase difference occurs between the weighing signal and the floor vibration detection signal due to the difference in dynamic characteristics as well as the difference in gain described above.

Here, in the weighing cell and the floor vibration detecting cell having different dynamic characteristics, the weighing signal from the weighing cell is Y1, the floor vibration detecting signal from the floor vibration detecting cell is Y2, and the respective amplitudes are A1 and A2. Assuming that the phase difference is θ and the floor vibration frequency is ω, the weighing signal Y1 and the floor vibration detection signal Y2 are expressed by the following equations. Y1 = A1 · cosωt, Y2 = A2 · co
As described above, in the s (ωt + θ) floor vibration compensation, the coefficient C is set so that the amplitude A2 of the floor vibration detection signal Y2 becomes equal to the amplitude A1 of the weighing signal Y1 for the same excitation force (in this case, floor vibration). (That is, gain correction: A1 =
After C · A2), both signals are subtracted.

Y = Y1−C · Y2 = A1 · cosωt−C · A2 · cos (ωt + θ) = A1 (cosωt−cos (ωt + θ)) = A1 (cosωt−cosωt · cosθ + sinωt · sinθ) = A1 ((1− cosθ) cosωt + sinθ · sinωt) = A1√ (2-2cosθ) · cos (ωt + φ) where tanφ = sinθ / (1-cosθ)

Therefore, the original amplitude A1 becomes an amplitude of A1√ (2-2 cos θ) by floor vibration correction. If the phase difference θ is zero, the corrected amplitude becomes zero, and the floor vibration component is completely removed. However, if the phase difference θ exists, it is not completely removed. This phase difference is, for example, θ =
At the time of 1 °, ｃｏ (2-2 cos θ) = 0.0174
Therefore, 1.74% of the amplitude of the weighing cell remains without being removed, and when the amplitude of the weighing cell is large, even a small phase difference cannot be ignored. As described above, in a weighing device that performs high-precision weighing, there has been a problem that an error due to the phase difference reduces the accuracy of floor vibration compensation.

The present invention solves the above-mentioned problems, and enables a highly accurate weighing device even if a phase difference occurs between the two signals due to a difference in dynamic characteristics between the weighing cell and the floor vibration detecting cell. It is intended to provide.

[0009]

In order to achieve the above object, an object of the present invention is to provide a weighing cell for weighing an object to be weighed and outputting a weighing signal corresponding to the weight thereof, and A floor vibration detection cell that detects the vibration of the installed floor and outputs a floor vibration detection signal, and at least one of the two signals so as to cancel the phase difference between the two signals due to the difference in the dynamic characteristics of the two cells. Phase adjustment means for adjusting the phase of the signal, the floor vibration detection signal is subtracted from the weighing signal in a state where the phase difference is cancelled, and the floor vibration corrected signal compensated for the error of the weighing signal caused by the floor vibration. Floor vibration compensating means for outputting. According to the above configuration, the phase adjustment unit adjusts the phase difference between the two signals due to the difference in the dynamic characteristics between the two cells, and cancels the phase difference between the two signals. Therefore,
The accuracy of floor vibration compensation for subtracting the floor vibration detection signal from the weighing signal can be improved.

According to a second aspect of the present invention, in the first aspect, a first analog filter for removing noise from the analog weighing signal output by the weighing cell, and an analog floor vibration detection output by the floor vibration detecting cell. A second analog filter that removes noise from the signal; and the phase adjustment unit includes the first analog filter and a second analog filter having a filter characteristic different from that of the first analog filter. According to the above configuration, the phase adjustment unit changes the filter characteristic of the analog filter in accordance with the phase difference between the two signals, so that the phase difference between the two signals can be easily canceled by the filtering.

According to a third aspect of the present invention, in the first aspect, there is further provided an A / D converter for digitally converting the weighing signal from the weighing cell and the floor vibration detection signal from the floor vibration detecting cell. A first digital filter for filtering the weighing signal, and a second digital filter for filtering the digitally-converted floor vibration detection signal, wherein the phase adjusting means includes: the first digital filter; And a second digital filter having different filter characteristics. According to the above configuration, the phase adjustment unit changes the filter characteristic of the digital filter according to the phase difference between the two signals, so that the phase difference between the two signals can be easily canceled by the filtering.

According to a fourth aspect of the present invention, in the first aspect, the phase adjusting means attaches a damping force adjusting member for adjusting a vibration damping force to at least one of the weighing cell and the floor vibration detecting cell. This is to cancel the phase difference between the two signals output from the cell. According to the above configuration, the phase adjustment unit changes the amount of the damping force adjustment member to be applied in accordance with the phase difference between the two signals, so that the phase difference between the two signals can be easily canceled.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a configuration of a weighing device according to a first embodiment of the present invention. This weighing device measures a weighing object and outputs an analog weighing signal corresponding to the weight of the weighing object, and a floor F on which the weighing cell 2 is installed.
Is provided with a floor vibration detection cell 4 that detects an analog floor vibration and outputs an analog floor vibration detection signal. Flexure element K of measuring cell 2
1, a weighing dish D1 is supported, and a weight D2 is provided on a strain body K2 of the floor vibration detection cell 4, and strain gauges G are attached to four places on the upper and lower surfaces where a large amount of strain is generated. ing.

The weighing apparatus further includes a first analog (low-pass) filter 5 for removing noise from the analog weighing signal, a second analog (low-pass) filter 6 for removing noise from the analog floor vibration detection signal, It comprises an amplifier 7 for amplifying signals, an anti-aliasing filter 8 for removing signals of a certain frequency or higher for each analog signal, an A / D converter 9 for digitally converting each analog signal, a CPU (microcomputer) 15, and a phase adjusting means 18. ing. This phase adjusting means 18
Is to adjust the phase of at least one of the two signals so as to cancel the phase difference between the two signals due to the difference in dynamic characteristics caused by the difference in the shape, material, size, etc. of the two cells 2 and 4.

The CPU 15 includes an A / D converter 9,
9, first and second digital filters 10 and 11 for filtering a weighing signal and a floor vibration detection signal which are digitally converted and outputting a filtered weighing signal and a filtered floor vibration detection signal. Gain correcting means 12 for correcting the gain based on the output sensitivity ratio of both cells; and floor vibration for outputting the floor vibration corrected signal y by subtracting the gain corrected filtered floor vibration detection signal yc from the filtered weighing signal ym. Compensation means 14 is provided.

As shown in FIG. 2, a bridge circuit B is formed by four strain gauges G of the weighing cell 2 and the floor vibration detecting cell 4, respectively, and analog weighing signals and analog floor vibration detection are provided from output terminals O1 and O2. The signal has been extracted. The first and second analog filters 5, 6
Has a capacitor H, which is a capacitor. The strain gauge G of the measuring cell 2 and the floor vibration detecting cell 4 and the capacitor H
Form a first-order filter. Phase adjusting means 18
Is composed of first and second analog filters 5 and 6, and the filter characteristics of the analog filters 5 and 6 are set to be different from each other, unlike the conventional one. This setting is made by making the capacitances of the capacitors H of the analog filters 5 and 6 different.

Hereinafter, the operation of the present weighing device will be described. First, the weighing signal of the object to be weighed detected from the weighing cell 2 shown in FIG. 1 and the floor vibration detection signal detected from the floor vibration detection cell 4 are noise-removed by the analog filters 5 and 6, respectively. , And a certain frequency or more is removed by the anti-aliasing filter 8, and the digital signal is converted by the A / D converter 9. Next, in the CPU 15, the weighing signal is filtered by the first digital filter 10 and output as a filtered weighing signal ym. Further, the floor vibration detection signal is filtered by the second digital filter 11, and the gain is corrected by the gain correction means 12 based on the output sensitivity ratio of the cells 2 and 4. After matching the gains, it is output as a filtered floor vibration detection signal yc. Then, the floor vibration compensating means 20 performs a subtraction process of subtracting the gain-corrected filtered floor vibration detection signal yc from the filtered weighing signal ym, and outputs a floor vibration corrected signal y in which the floor vibration is corrected. As a result, a floor vibration corrected weighing signal y in which the error of the weighing signal caused by the floor vibration is compensated is obtained.

FIG. 3A shows an example of the frequency-phase characteristics of the measuring cell 2 and the floor vibration detecting cell 4. The horizontal axis represents the frequency (Hz) of the floor vibration, and the vertical axis represents the phase shift (degree) between the floor vibration and the analog output signals from the cells 2 and 4. here,
When the dynamic characteristics of both cells 2 and 4 are not the same, FIG.
As shown in (a), a phase difference occurs between the weighing signal output from the weighing cell 2 and the floor vibration detection signal output from the floor vibration detection cell 4. In this figure, the phase of the weighing signal lags behind the floor vibration detection signal. The characteristic shown in FIG. 3A is obtained, for example, by applying floor vibration to both cells 2 and 4 in FIG. 1 without placing an object to be weighed, inputting a signal from an amplifier 7 to an external signal analyzer, Is measured.

When the phase of the weighing signal from the weighing cell 2 is relatively delayed from the floor vibration detection signal, the first and second analog signals are so advanced that the phase of the weighing signal is advanced by the amount of the delay. The filter characteristics of the filters 5 and 6 are changed. FIG. 4 shows frequency-phase characteristics of the analog filters 5 and 6 when the capacitance of the capacitor H is changed. As shown in this figure, as the capacitance decreases, the phase relatively advances. FIG. 3 (b)
9A shows the frequency-phase characteristics of the analog filters 5 and 6 in which the filter characteristics are changed such that the phase of the weighing signal is relatively advanced in accordance with the delay phase of the weighing signal in FIG.

FIG. 3 (c) shows the result of filtering both signals by the analog filters 5 and 6 having the changed filter characteristics of FIG. 3 (b). As shown in this figure, the phase difference between the two signals becomes almost zero in the frequency range of the floor vibration of about 20 Hz or less, and the phase difference is canceled.

The operation of the phase adjusting means 18 will be described with reference to an arithmetic expression of a transfer function. First, analog filter 5,
The transfer function indicating the relationship between the input and output of No. 6 is represented by 1 / (1 + jω (RC / 2)), where R is the resistance of the strain gauge G and C is the capacitance of the capacitor H. The transfer functions G ₁ (jω) and G ₂ (jω) of the filters 5 and 6 are set so as to cancel the phase difference according to the phase difference between the two signals.
This is after the filter characteristics have been changed by changing the capacitance C (FIG. 3B). The transfer function G ₁₁ (jω) of the weighing cell 2 and the transfer function G ₀₀ (j
ω) depends on the dynamic characteristics of both cells 2 and 4 (FIG. 3).
(A)). Since the signals from the cells 2 and 4 are filtered by the analog filters 5 and 6 having different filter characteristics, the transfer function of the combination of the cells 2 and 4 and the analog filters 5 and 6 is expressed by the following equation. (FIG. 3C). G ₁₁ (jω) G ₁ (jω) Floor vibration detection cell 4 side G ₀₀ (jω) G ₂ (jω) Both signals output with a phase difference from the measurement cell 2 and floor vibration detection cell 4 The phase difference becomes almost zero due to the filtering of the analog filters 5 and 6 set to the above filter characteristics.

In this example, both the capacitances C of the analog filters 5 and 6 are changed, but only one of the capacitances C may be changed. Also,
Instead of changing the capacitance C of the analog filters 5 and 6, another capacitor may be connected in parallel with the capacitor H.

By changing the filter characteristics of the analog filters 5 and 6, the gain characteristics of the filters also change. However, since the cutoff frequency of the filters 5 and 6 is in a range considerably higher than the floor vibration frequency, the gain characteristics are low. It hardly affects the gain in the frequency domain. In order to correct more accurately, the gain may be adjusted again after the phase adjustment.

As described above, according to the present weighing device, the analog filters 5 and 6 for removing noise convert both signals into two signals in accordance with the phase difference between the two signals caused by the difference in dynamic characteristics between the weighing cell 2 and the floor vibration detecting cell 4. Since the phase difference in the opposite direction is given, and the filtering cancels the phase difference between both signals,
The phase difference between the two signals is eliminated, and the accuracy of floor vibration compensation for subtracting the floor vibration detection signal from the weighing signal can be improved. In addition, the existing analog filters 5, 6
Is used to cancel the phase difference between the two signals, so that high-precision weighing can be achieved easily at low cost. Further, by preparing the cells 2 and 4 and the analog filters 5 and 6 whose phases have been adjusted in advance as one set, the cells 2 and 4 are prepared.
It is not necessary to adjust the circuit in the subsequent stage for phase adjustment at the time of replacement, and only one set is replaced, so that maintenance and inspection are facilitated.

As shown in FIG. 1, instead of providing the A / D converter 9 on each of the measuring cell 2 and the floor vibration detecting cell 4, a multiplexer is provided.
The / D converter 9 may be single. Each signal is sent to a weighing cell 2 or a floor vibration detecting cell 4 by a multiplexer.
, Through the analog filters 5 and 6, the amplifier 7, and the anti-aliasing filter 8, selectively converted into digital signals by a single A / D converter 9, and then demultiplexed by a demultiplexer means. 10 and 11 are selectively input. Even when there are a plurality of cells, the number of A / D converters 9 may be single, so that cost reduction can be achieved.

FIG. 5 shows a configuration diagram of a weighing device according to the second embodiment. In the second embodiment, the analog filters 5 and
In addition to the first phase adjusting means 18 using the filter 6, a second phase adjusting means 28 comprising a first digital filter 10 and a second digital filter 11 having a filter characteristic different from that of the filter 10 is provided. ing. The second phase adjusting unit 28 is used as a fine adjusting unit that roughly cancels the phase difference by the first phase adjusting unit 18 and then cancels the remaining slight phase difference. The digital filters 10 and 11 include ordinary FIR (Finite Impull
In addition to the se Response) type filter, for phase correction, for example, an IIR (Infinite Impulse Response
e) Shape is used.

The filter characteristics of the digital filters 10 and 11 are set to be different from each other, unlike the conventional one. In other words, according to the phase difference between the two signals from the A / D converters 9 and 9, the filter characteristics of the digital filters 10 and 11 are changed so that a phase difference in the opposite direction to this phase difference is given to cancel the phase difference. . Changing the filter characteristics changes the cutoff frequency. For example, lowering the cutoff frequency increases the phase delay. If the phase of the weighing signal output from the A / D converter 9 on the weighing cell 2 side is delayed, the floor vibration detection cell 6 output from the A / D converter 9 is delayed by the delay. So that the phase of the floor vibration detection signal is delayed.
The filter characteristics of 0 and 11 will be manually changed.

As a result, the second phase adjusting means 28
The phase difference between the two signals can be sufficiently canceled.

In the CPU 15, means for detecting the phase difference between the weighing signal and the floor vibration detection signal and means for changing the filter characteristics of the digital filters 10 and 11 are provided. Eleven filter characteristics may be automatically changed.

In this embodiment, the filter characteristics of both digital filters 10 and 11 are changed, but either one of the filter characteristics may be changed. When the difference between the dynamic characteristics of the cells 2 and 4 is small and the phase difference between the analog signals output from the cells 2 and 4 is small, the first phase adjusting means 18 is omitted, that is, the analog The filter characteristics of the filters 5 and 6 may be made the same, and the phase difference may be canceled by the second phase adjusting means 28 alone.

Next, a weighing device according to a third embodiment will be described. This measuring device differs from the first embodiment in that FIG.
The transfer function itself of the floor vibration detection cell 4a (or the weighing cell 2a) is changed to cancel the phase difference between the two signals. The phase adjusting means 38 of the present weighing device includes the weighing cell 2a
And a damping force adjusting member attached to at least one of the floor vibration detecting cells 4a to adjust the vibration damping force. The damping force adjusting member 38 allows the two signals 2a and 4a to generate both signals due to a difference in dynamic characteristics. Cancel the phase difference. The damping force adjusting member 38 has a function of suppressing the peak value at the natural frequency of the load cell and expanding the usable dynamic range of the load cell. According to the present invention, the damping force adjusting member 38 outputs the output from the load cell. It is noted that it has an effect of also causing a phase shift of a signal to be generated. The circuit configuration of the signal processing is the same as that of FIG. 1 except that the filter characteristics of the analog filters 5 and 6 in FIG. 1 are the same.

The damping force adjusting member 38 is made of, for example, butyl rubber. The floor vibration detection cell 4a includes a fixed portion 32 supported on the floor F, a thin stainless steel substrate 34 forming upper and lower beam portions, and a movable portion (weight) supported by the fixed portion 32 via these substrates 34. And a stopper screw 37 which is a stopper member attached to the fixed portion 32 and restricting the movable portion 33 from moving up and down. A notch 36 is provided on the surface of the stainless steel plate 34, and a strain gauge G is formed on the back surface of the stainless steel plate 34 at a position facing the notch 36, for example, by sputtering. A butyl rubber 38 is adhered to the surfaces of the stainless steel plate 34 and the strain gauge G by the adhesive force.

Hereinafter, the damping force adjusting member (butyl rubber)
The operation of 38 will be described. First, as in the case of the first embodiment, the phase difference between the weighing signal and the floor vibration detection signal is measured by the signal analyzer in a state where the object to be weighed is not placed, and the characteristic shown in FIG. According to the obtained phase difference between the two signals, the amount of the butyl rubber 38 to be attached to the floor vibration detection cell 4a in FIG. 6 is set so as to cancel the phase difference between the two signals. At this time, the transfer function G ₀₁ (jω) of the floor vibration detection cell 4a to which the butyl rubber 38 is attached is represented by the following equation, where m is the mass of the movable portion 33, c is the damping constant, and k is the spring constant.

G ₀₁ (jω) = − m / (m (jω) ² + c (jω) + k) = 1 / ((ω ² −k / m) −jω · c / m) When the butyl rubber 38 (constant mass) is used, the amount (number of sheets) of the butyl rubber 38 to be applied and the attenuation constant c
And the spring constant k, as shown in Table 1, has a certain correlation. Therefore, the amount of the butyl rubber 38 to be stuck to the floor vibration detection cell 4a, that is, the number of sheets, is set based on the values in Table 1 so that the transfer function G ₀₁ (jω) cancels the phase difference between the two signals.

[0035]

[Table 1]

FIG. 7 shows the frequency-phase characteristics of the floor vibration detecting cell 4a when the number of the butyl rubbers 38 applied to the floor vibration detecting cell 4a is changed. As shown in this figure, the phase is delayed as the number of butyl rubbers 38 is increased. If the phase of the weighing signal is delayed, the number of butyl rubbers 38 to be affixed to the floor vibration detection cell 4a is set so that the phase of the floor vibration detection signal is also delayed by the delay.

As a result, the phase adjusting means 38 of the third embodiment gives a phase difference between the two signals in the opposite direction according to the phase difference between the two signals, so that the phase difference between the two signals can be easily canceled. .

In this embodiment, the butyl rubber 38 is attached to the stainless steel plate 34 of the floor vibration detecting cell 4a and the front and back surfaces of the strain gauge G, but may be attached to only one of the surfaces. Further, the butyl rubber 38 is stuck only to the floor vibration detecting cell 4a, but may be stuck only to the measuring cell 2a or may be stuck to both cells.

Further, the adjustment by the filter characteristics of the analog filters 5 and 6 of the first embodiment and the adjustment by the damping force adjusting member of the third embodiment may be combined to cancel the phase difference between the two signals. .

[0040]

According to the present invention, the phase adjusting means cancels the phase difference between the two signals due to the difference in the dynamic characteristics between the two cells. Therefore, it is possible to improve the accuracy of floor vibration compensation for subtracting the floor vibration detection signal from the weighing signal.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a weighing device according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a phase adjusting unit of the first embodiment.

FIG. 3 is a characteristic diagram showing an operation of the phase adjusting means.

FIG. 4 is a characteristic diagram showing frequency-phase characteristics of an analog filter.

FIG. 5 is a configuration diagram illustrating a weighing device according to a second embodiment.

FIG. 6 is a side view showing a floor vibration detection cell of a weighing device according to a third embodiment.

FIG. 7 is a characteristic diagram showing frequency-phase characteristics of the floor vibration detection cell.

[Explanation of symbols]

2 ... weighing cell, 4 ... floor vibration detection cell, 5 ... first analog filter, 6 ... second analog filter, 9 ... A / D
Converter, 10 ... first digital filter, 11 ... second
Digital filter of 14, floor vibration compensation means, 18,
28, 38: phase adjusting means.

Claims (4)

[Claims] 1. A weighing cell that weighs an object to be weighed and outputs a weighing signal corresponding to its weight, and a floor that detects vibration of a floor on which the weighing cell is installed and outputs a floor vibration detection signal. A vibration detection cell, phase adjusting means for adjusting the phase of at least one of the two signals so as to cancel a phase difference between the two signals caused by a difference in dynamic characteristics between the two cells, and a state in which the phase difference is canceled. A floor vibration compensating means for subtracting the floor vibration detection signal from the weighing signal and outputting a floor vibration corrected signal in which an error of the weighing signal caused by the floor vibration is compensated. 2. The apparatus according to claim 1, further comprising: a first analog filter configured to remove noise from the analog weighing signal output from the weighing cell; and a noise removing unit configured to remove noise from the analog floor vibration detection signal output from the floor vibration detecting cell. A second analog filter, wherein the phase adjusting means comprises: a first analog filter;
A weighing device comprising the filter and a second analog filter having different filter characteristics. 3. An A / D converter for digitally converting a weighing signal from the weighing cell and a floor vibration detection signal from a floor vibration detection cell, and filtering the digitally converted weighing signal. A first digital filter for filtering the floor vibration detection signal that has been digitally converted, and a second digital filter for filtering the digitally converted floor vibration detection signal. A weighing device comprising a second digital filter. 4. The phase adjusting device according to claim 1, wherein the phase adjusting unit is configured to affix a damping force adjusting member that adjusts a vibration damping force to at least one of the weighing cell and the floor vibration detecting cell, to thereby determine a phase difference between the two signals. A weighing device that negates.