JP2006118872A - Precision weight measuring instrument - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a weight measuring instrument capable of shortening a time from weight loading up to measurement, and capable of preventing lowering of precision, even in a place where disturbance vibration exists, in precision weight measurement. <P>SOLUTION: This instrument is constituted of a mechanism for exciting forcibly a balance, and a device for extracting data in a specified frequency area. The vibration generated in the weight loading is quickly damped by the forcible excitation/control to shorten the measuring time. The frequency area containing a data as to weight data are set in an area different from the frequency area of the disturbance vibration to impart resistance against disturbance. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a weight measuring apparatus that performs quick and precise weight measurement when measuring the weight of a powdered medicine or the like. In particular, the present invention is characterized in that the time required for the weight measuring device to reach an equilibrium state is short, so that the measurement time can be shortened when the weight is continuously measured. In addition, since the present invention uses only information relating to a specific frequency region, the present invention is suitable for applications in which precise weight measurement is performed in an environment where mechanical vibrations are received as disturbances.

  Conventional methods for accurately measuring the weight of powdered chemicals and the like are roughly classified into a static weight measurement method and a dynamic weight measurement method. Hereinafter, specific examples of these will be described.

  Static weight measurement is generally known as a method of measuring the weight of a measured object from the weight of the weight in an equilibrium state by placing a measured object and a weight on both ends of a fulcrum, such as a balance or a balance. It has been. It is known that an upper pan balance does not cause a deviation error due to a position where a measurement object / weight is placed by providing a mechanism called a Roverval mechanism in the heel portion of the balance.

  Moreover, in a platform balance, an electronic balance, etc., weight measurement is performed by utilizing the fact that the amount of displacement of the elastic body when a load is applied is uniquely determined with respect to the magnitude of the applied load. As the elastic body, a spring or a load cell is used, and is generally used as a precision weight measuring device.

  In any of the above cases, a static equilibrium must be reached in order to measure the weight. For this reason, there is a time for waiting for the vibration generated when a load is applied to the balance to be attenuated. In particular, in a balance for performing precise weight measurement, the period of vibration is long and much time is required for damping. Therefore, in the case where a certain amount of medicine is weighed, it is necessary to wait for the vibration to be attenuated at every adjustment, resulting in a large time loss.

  Next, the dynamic weight measurement method will be described. The dynamic weight measurement method is a method of measuring weight from a state of vibration generated when a load is applied. For example, the following methods are known.

  In the weight measuring device (Japanese Patent Laid-Open No. 56-117126), the characteristic frequency is changed by reading the value of the natural frequency using the characteristic that the natural frequency of the vibrator changes according to the load. Further, in the continuous measurement and classification method of the article weight (Japanese Patent Laid-Open No. 53-048768), the fact that a damped vibration output with an amplitude proportional to the mass size is generated at the arrival and passage of the article is used. The weight is measured by measuring the amplitude.

  When any of the above methods is used, it is necessary to observe the state of the damped vibration for a certain period. Therefore, the measurement time cannot be shortened with a precision balance or the like that originally has a long vibration cycle. In order to solve this problem, a method has been proposed in which the measurement time is shortened by applying an external force to forcibly stop.

In the force balance scale (Japanese Patent Laid-Open No. 2002-174545), control is performed so that the position of the scale is always maintained at a constant position, and weight measurement is performed by using the fact that the weight can be calculated from the magnitude of the force required when stationary. ing. By using this method, the vibration is quickly attenuated, and the weight measurement time can be shortened.
JP 56-117126 A JP-A-53-048768 JP 2002-174545 A

  However, in order to perform accurate weight measurement using these methods, it is a condition that there is no disturbance vibration such as floor vibration. This is because if there is disturbance vibration, the measured value vibrates in the same manner and a stable value cannot be obtained. For this reason, it is essential to take measures for seismic isolation such as installing on a seismic isolation table.

  For the above reasons, it is difficult for thorough seismic isolation with current precision weight measuring devices, such as weight measurement in places where there are many vibration sources (mechanical devices) such as factories, and built-in use as automation devices. Under the circumstances, there is a problem that precise weight measurement cannot be performed. This property is a problem that the precision weight measuring apparatus has in common with those other than the conventional examples.

  In view of this, the present invention proposes a precision weight measuring apparatus that can perform accurate weight measurement quickly even in an environment with disturbance vibrations.

  According to the present invention, in the weight measuring device according to claim 1, the balance pan is supported at one end of the balance supported by the fulcrum, the displacement sensor for detecting the displacement amount of the balance at the other end, and the balance is arbitrarily vibrated. -A drive power source that can be displaced, and a control system that controls the input signal to the drive power source so that the output of the displacement sensor has a sinusoidal profile with a constant period T and a constant amplitude A. Weight measurement characterized by comprising a signal processing device for extracting information at a specific frequency 1 / T of a signal, and an arithmetic device for calculating the weight of a measurement weight placed on the balance from the data processing information An apparatus is provided.

  In the above configuration, the control system using the displacement sensor and the driving power source has an effect of realizing early stabilization to a state where the weight can be measured.

  In addition, the signal processing device that extracts information at the specific frequency 1 / T has an effect of removing the influence of disturbance vibration.

  In addition, according to the present invention, there is provided a weight measuring device characterized in that the balance is configured by a Roverval mechanism.

  In the above configuration, the Robert mechanism has the effect of eliminating the occurrence of an offset error due to the position of the weight load on the balance pan.

  According to the present invention, there is provided a weight measuring device characterized in that the displacement sensor is constituted by an optical displacement sensor.

  According to the present invention, there is provided a weight measuring device characterized in that the displacement sensor is constituted by an eddy current displacement sensor.

  In addition, according to the present invention, there is provided a weight measuring device characterized in that the displacement sensor is constituted by a capacitance type displacement sensor.

  In addition, according to the present invention, there is provided a weight measuring device characterized in that the driving power source is composed of an electromagnet and a magnetized substance.

  In addition, according to the present invention, there is provided a weight measuring device characterized in that the driving power source is constituted by a direct acting motor.

  According to the present invention, there is provided a weight measuring device characterized in that the driving power source is constituted by a rotary motor.

  According to the present invention, the signal processing device includes a phase meter that reads phase information of the measurement signal, an oscillation device that generates a sinusoidal signal having the same phase as the measured phase information and a constant period T, and the measurement signal. There is provided a weight measuring device comprising: a multiplication calculator that multiplies the oscillated sinusoidal signal; and a low-pass filter that extracts only a direct current component from the multiplied signal.

  Further, according to the present invention, there is provided a weight measuring device, wherein the signal processing device is composed of a band-pass filter corresponding to a frequency of 2π / T and an AC voltmeter that reads the amplitude of the output signal. Is done.

  If the weight measuring device according to the present invention configured as described above is used, from the characteristic of actively controlling the vibration waveform of the balance, the state of the weight measuring device is stabilized from the moment of weight loading until the weight can be measured. It is possible to shorten the time.

  In addition, if the weight measuring device according to the present invention configured as described above is used, the influence of vibration noise having a frequency band other than the frequency 1 / T from the characteristic that only information at a specific frequency 1 / T is extracted and used. It is possible to measure the weight with a high S / N ratio from which the water is removed.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows the simplest configuration of the present invention. It is a figure showing the weight measuring apparatus using an optical displacement sensor for a displacement sensor, and using an electromagnet as a drive power source. The signal processing apparatus in this figure includes a phase meter, a phase shifter, a multiplication calculator, and a low-pass filter.

  FIG. 2 is a view showing a weight measuring apparatus having a robust mechanism in the balance portion, using an optical displacement sensor as a displacement sensor, and using an electromagnet as a driving power source in addition to the configuration in FIG. The signal processing apparatus in this figure includes a phase meter, a phase shifter, a multiplication calculator, and a low-pass filter.

The displacement sensor may be an eddy current displacement sensor as described in claim 4 or a capacitance displacement sensor as described in claim 5 instead of the optical displacement sensor. Further, as the drive power source, a direct acting motor may be used as described in claim 7. (FIG. 3) Further, as described in claim 8, a rotary motor may be used for the fulcrum portion. (Fig. 4)
In the weight measuring device according to the first aspect, since the balance is vibrated with a constant period T, the force F + F ₀ can be applied from the driving power source. At this time, the control system performs control so that the output from the displacement sensor draws a sine wave waveform. When this control is stabilized, the balance of forces acting on the balance is expressed by the following equation (1).

  Here, a represents the distance between the operating point of the driving power F and the balance fulcrum, and b represents the distance between the operating point of the weight m on the balance pan side and the balance fulcrum. Θ represents the magnitude of the angle between the balance and the horizontal reference, and θ is the magnitude of the vibration amplitude.

  Considering the case where the magnitude of the vibration amplitude θ is very small, the balance equation (1) is approximated as the equation (3). Here, ω = 2π / T.

  At this time,

となるようにすれば、釣り合いの式は式（４）のようになる。

Then, the balance equation is as shown in equation (4).

  Here, when a weighing object having a weight of Δm is loaded on the balance pan, the balance of force is expressed as in Equation (5).

  At this time, the input signal to the drive power source is

だけ増加するため、この値の大きさがわかれば、重量Δmを算出することができる。

Therefore, if the magnitude of this value is known, the weight Δm can be calculated.

  Next, consider the case where vibration noise Ν (t) from the outside is added to the stable vibration state. When Ν (t) is expressed by Fourier series expansion, the balance equation is as shown in Equation (6).

The vibration noise considered at this time is (1) the resonance frequency ω _{around the} surrounding vibration source, (2) white noise, and (3) the resonance frequency ω _libra of the balance. Therefore, when the input signal to the drive power supply is Fourier transformed, a strong spectrum appears at frequencies ω, ω _libra and ω _around . Among these, the measurement weight information is included in the spectrum of the frequency ω. Therefore, by setting ω to a value different from ω _libra and ω _around , information corresponding to the frequency ω can be separated in the Fourier space.

  As a specific method for performing the separation, there is a method using the signal processing device configuration according to claim 9. FIG. 5 shows the configuration of the signal processing apparatus at this time.

  First, the phase meter 501 reads the phase φ of the input signal to the drive power source. This phase φ is a phase lag generated by the control system. Next, a sine wave signal Dsin (ωt + φ) corrected by the phase shifter 503 corresponding to the phase φ is created. When the sine wave signal and the input signal to the driving power source are multiplied by the multiplier 505, the equation (7) is obtained.

  At this time, in order to extract only the DC component, when the multiplied signal is filtered by the low-pass filter 506, Expression (8) is obtained.

C _i is a spectrum corresponding to the frequency ω of the disturbance vibration noise. Therefore, if the vibration frequency omega _around-the frequency omega of the resonance frequency omega _libra · external vibration source of the balance does not match, C _i is the weak signal.

  Similar signal processing can be similarly realized by the apparatus configuration according to claim 10 in which an input signal to the driving power source is directly filtered by a band-pass filter corresponding to the frequency ω.

  In order to calculate the target load weight Δm from the signal obtained as described above, there is a method described below. One is a method of calculating the weight based on a function between the voltage value obtained by the signal processing device and the load weight. There is also a method of obtaining the weight by holding data with the voltage value obtained from the signal processing device at zero load as zero point and measuring the potential difference from the output voltage at heavy load. Whichever method is used, the weight data can be derived from the output voltage value.

  From the above properties, according to the present invention, a weight measuring device having excellent resistance to external vibration noise is provided.

  Specific embodiments of the present invention are described below. The configuration of the most basic embodiment in the present invention is shown in FIG.

  A balance 603 equipped with a Roberval mechanism is installed on the column 602 in the figure. At this time, it is necessary to realize a smooth rotational motion at the contact point between the Roverval mechanism and the support column 602 and at the contact portion of each component constituting the Roverval mechanism. Therefore, it is desirable that each contact portion uses a bearing represented by a ball bearing. There is only one axis of rotation, and the axial direction is perpendicular to the drawing.

  At the right end of the balance, a balance pan 601 is installed on the vertical side of the Roverval mechanism as shown. Similarly, a beam 604 is installed on the vertical side at the left end of the balance. A displacement sensor 605 for measuring a displacement amount is installed on the left end beam.

  An optical displacement sensor was used as the displacement sensor. The optical displacement sensor used here preferably has a high response frequency in order to measure the vibration state. For example, in this case, an optical heterodyne type minute displacement measuring instrument was used. It is also a preferable example to use a laser Doppler micro displacement measuring instrument. It is also a preferable example to use a triangulation type displacement measuring instrument.

  Further, in order to keep the measurement accuracy good, a flat mirror 606 was installed at the laser irradiation part = measurement point. An aluminum flat mirror was used to prevent unnecessary laser interference.

  On the left end beam, an electromagnet 607 was installed at a position as shown in the figure as a driving power source. At this time, a steel member 608 is added to the beam in order to sufficiently apply the force from the electromagnet to the beam.

  With reference to the displacement amount data from the displacement sensor, the output of the electromagnet is controlled using the control system 609 so that the displacement becomes a sine wave having an amplitude A and a period T. This control system is required to have a performance capable of controlling a high-frequency sine wave having a small vibration amplitude A and a short period T. Therefore, in this control system, it is desirable to use a control system in which a gain in a high frequency region (10 KHz or more) is obtained at −3 db (70%) or more and stability is compensated.

  In addition, a sine wave signal was input from the function generator 610 as a reference signal for control to this control system. The frequency of the sine wave input at this time is different from the resonance frequency of the balance.

  With the apparatus configuration as described above, a system for applying forced vibration to the balance is realized. Hereinafter, an embodiment of a signal processing system for extracting a signal including weight information from an output signal to the electromagnet 607 given by the control system will be described.

  It is the amplitude component of the output signal that contains information about the weight. In order to prevent the control system from being affected when signal processing is performed, a signal for signal processing is separately output from the control system. The signal at this time is exactly the same value as the output signal to the electromagnet.

  In order to extract the weight information = vibration amplitude amount from this signal, as described above, the output signal is multiplied by another sine wave signal by the multiplication calculator 611, and the DC component is extracted using the low-pass filter 612. I do. As the sine wave signal used at this time, the sine wave signal output from the function generator 610 is used. At this time, as the phase difference between the two signals increases, the magnitude of the direct current component decreases and the S / N ratio of the measurement improves. Therefore, in this embodiment, a system for matching and correcting the phase difference is provided.

  First, the phase of the output signal is measured using a phase meter 613. In order to match the phases of the two signals, the phase of the sine wave signal is shifted by the phase measured by the phase shifter 614. Thereby, the phases of the two signals to be multiplied can be matched.

  Also, in order to detect minute changes in weight sensitively, a large signal amplification factor is required. The amplification factor of this signal is proportional to the magnitude of the amplitude of the sine wave signal to be multiplied. Therefore, the amplifier 615 is used to amplify the amplitude of the sine wave signal.

The signal is passed through a low-pass filter 612 to extract a direct current component from the multiplication signal thus obtained. The low pass filter used at this time has a cutoff frequency of 0.1 mHz. By using such a filter with a low cut-off frequency, the signal processing system can obtain properties as a high-Q bandpass filter with respect to the excitation frequency 1 / T. For example, when the excitation frequency is 1 kHz, the characteristics are the same as those of a band-pass filter having a Q value of about 10 ⁷ . Therefore, the obtained DC component represents the amplitude information of the specific frequency 1 / T extracted by the band-pass filter having a high Q value, and a high S / N signal amplitude measurement is realized.

  By using the signal processing system as described above, it is possible to extract the amplitude information of the specific frequency 1 / T including the weight information. Hereinafter, an embodiment of an information processing system that extracts weight information from the amplitude information will be described.

  The amplitude information extracted by the signal processing system described above is expressed by Equation (9).

Of these, Δm represents the measured weight. C _i D / 2 corresponds to the frequency 1 / T component of disturbance vibration, and its power level decreases as the Q value of the signal processing system increases. In this embodiment, the Q value of the signal processing system is as high as about 10 ⁷ , and the noise level is reduced to 0.1% or less of the original level. Therefore, it can be ignored in this case.

  Therefore, if the value F of the no-load state is known, the remaining value is a known value, so that the measured weight Δm can be specified. Since this value F is nothing but a measured value when there is no weight, the measured value when there is no load may be stored and held in advance as a zero point. Therefore, the information processing system according to the present embodiment includes a recording device 616 that holds a measurement value at no load. The measurement weight Δm is extracted by providing a differential amplifier 617 that extracts the difference between the measured value at the zero point recorded by the recording device 616 and the measured value at the time of measurement weight loading.

  By using the weight measuring device having the above configuration, a precise weight measuring device capable of measuring the weight with a rising speed of 100 ms or less and a minimum weight resolution of 0.01 mg is provided even in a place where anti-vibration measures are not taken. The In the following, a precision weight measuring apparatus having the above-described configuration will be prototyped, and an example of a weighing experiment using this apparatus will be described.

  The same sample was weighed with a precision weight measuring apparatus according to the present invention and an analytical balance AW220 (AW220 is a trade name) manufactured by Shimadzu Corporation, and a comparative experiment was performed on the measurement results. The sample used for weighing was 1 mg of ultra-precision grade standard weight manufactured by Shimadzu Corporation. As a result of changing the sample weight from 1 to 20 mg in increments of 1 mg and measuring, it was confirmed that the weighing results were in the range of ± 0.5 mg. From the above examples, it can be seen that by using the precision weight measuring apparatus according to the present invention, the weight can be measured with an accuracy of ± 0.5 mg.

  Next, after loading a measurement weight, a measurement experiment of response speed until measurement was possible was performed. The experimental method measures the time until the weight measurement value converges to a width of ± 0.5 mg after adding the measurement weight. The size of ± 0.5 mg represents the measurement accuracy of the weight measuring device in the present embodiment. Moreover, the loaded measurement weight is 200 mg of an ultra-precision standard weight. As a result of conducting this experiment a plurality of times and measuring the average required time, it was confirmed that the convergence of the measured value was achieved in 0.1 s or less. From the above examples, it can be seen that the precision weight measuring apparatus according to the present invention has a high-speed response performance of 0.1 s or less.

  Next, a verification experiment was conducted on the stability when disturbance vibration was applied to the precision gravimetric measurement apparatus in this example. The experiment was conducted for two cases: (1) when an impulse was applied to the weight measuring device, and (2) when a constant vibration was applied to the weight measuring device.

  The verification experiment related to (1) measures the time until the measured value converges to a width of ± 0.5 mg when an impact is applied to the balance column of the precision weight measuring apparatus with a metal rod. As a result of conducting this experiment a plurality of times and measuring the average required time, it was confirmed that the convergence of the measured value was achieved in 0.1 s or less.

  The verification experiment related to (2) is a weight measurement experiment when a stationary vibration source is installed in the vicinity of the precision weight measurement device. A vacuum pump was placed in the vicinity as a vibration source. This pump is constantly oscillating at 50 Hz. In such a state, the precision weight measuring apparatus according to the present invention was used to weigh the ultra-precision standard weight. As a result of measuring by changing the sample weight from 1 to 20 mg in increments of 1 mg, it was confirmed that the measurement was performed in the range of ± 0.5 mg as in the case of the measurement result without the vibration source. From the above examples, it was confirmed that by using the precision weight measuring apparatus according to the present invention, it is possible to perform weight measurement with an accuracy of ± 0.5 mg even in an environment with disturbance vibration.

Configuration of basic weight measuring apparatus according to the present invention Configuration of a weight measuring device with a robust mechanism in the balance Configuration of a weight measuring device using a direct-acting motor as a power source for driving the balance Configuration of weight measuring device using rotary motor as power source for driving balance Configuration of a signal processing device that extracts information in a specific frequency region Configuration of an embodiment of a weight measuring apparatus according to the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Balance pan 102 Balance strut 103 Balance scale 104 Displacement sensor 105 Electromagnet 106 Control system 107 Phase meter 108 Phase shifter 109 Function generator 110 Multiplier 111 Low pass filter 112 Voltmeter 201 Balance pan 202 Roval mechanism 203 Displacement sensor 204 Electromagnet 205 Control system 206 Phase meter 207 Phase shifter 208 Function generator 209 Low-pass filter 210 Voltmeter 301 Balance pan 302 Roval mechanism 303 Displacement sensor 304 Direct acting motor 305 Control system 306 Phase meter 307 Phase shifter 308 Function generator 309 Multiplier 310 Low pass filter 311 Voltage Total 401 Weighing pan 402 Roverval mechanism 403 Displacement sensor 40 Rotation type motor 405 Control system 406 Phase meter 407 Phase shifter 408 Function generator 409 Low pass filter 410 Voltmeter 501 Phase meter 502 Function generator 503 Phase shifter 504 Gain 505 Multiplier 506 Low pass filter 601 Balance pan 602 Column 603 Beam mechanism 60 Displacement sensor 606 Flat mirror 607 Electromagnet 608 Steel member 609 Control system 610 Function generator 611 Multiplier 612 Low pass filter 613 Phase meter 614 Phase shifter 615 Amplifier 616 Recording device 617 Difference amplifier

Claims (10)

A balance pan 4 is provided at one end 3 of the balance 2 supported by the fulcrum 1,
A displacement sensor 6 for measuring the amount of movement of the balance 2 at the other end 5 of the balance 2;
A driving power source 7 for driving the balance 2;
A control system 8 for controlling the input signal of the drive power source 7 so that the displacement obtained from the displacement sensor 6 has a sinusoidal profile with a constant period T and a constant amplitude A;
A measuring device 9 for monitoring the magnitude of an input value to the driving power source 7;
A signal processing device 10 for extracting only information corresponding to the frequency 1 / T from the input signal monitored by the measuring device 9;
A weight measuring apparatus comprising: an arithmetic unit that calculates a weight of the measurement weight loaded on the weighing pan from the output information of the signal processing apparatus. The balance 2 according to claim 1 is:
The weight measuring device according to claim 1, wherein the weight measuring device is configured by a Roverval mechanism 13. The displacement sensor 6 according to claim 1 is:
The weight measuring device according to claim 1, wherein the weight measuring device comprises an optical displacement sensor. The displacement sensor 6 according to claim 1 is:
The weight measuring device according to claim 1, wherein the weight measuring device comprises an eddy current displacement sensor 15. The displacement sensor 6 according to claim 1 is:
The weight measuring device according to claim 1, wherein the weight measuring device comprises a capacitance type displacement sensor 16. The drive power source 7 according to claim 1 is:
The weight measuring device according to claim 1, comprising an electromagnet 17 and a magnetized material 18. The drive power source 7 according to claim 1 is:
The weight measuring device according to claim 1, wherein the weight measuring device comprises a direct acting motor. The drive power source 7 according to claim 1 is:
The weight measuring device according to claim 1, wherein the weight measuring device comprises a rotary motor. The signal processing device 11 according to claim 1 comprises:
A phase meter 21 for reading out phase information of a measurement signal by the measuring device 9 according to claim 1;
An oscillating device 22 for generating a sinusoidal signal having the same phase and a constant period T as the phase information measured by the phase meter 21;
A multiplier 23 for multiplying a measurement signal from the measurement device 9 in claim 1 by a sinusoidal signal oscillated from the oscillation device 22;
The weight measuring device according to claim 1, wherein the weight measuring device comprises a low-pass filter that extracts only a direct current component from an output signal from the multiplier. The signal processing device 11 according to claim 1 comprises:
The weight measuring device according to claim 1, wherein the weight measuring device comprises a bandpass filter 25 corresponding to a specific frequency of 2π / T.

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