JPH034090B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a vibration-type load measuring device that uses a vibration-type load converter to obtain highly accurate and highly stable measurement values.

Load transducers using vibrating strings, tuning fork vibrators, etc. have the advantage of not only having a simple structure but also not requiring an A/D converter because measured values are obtained as digital quantities called vibration frequencies. However, this type of transducer is extremely sensitive to disturbing vibrations and impact forces applied from the outside in addition to the measurement load, so the digitally displayed measured value tends to flicker.
It tends to become unstable and impede practical application.

FIG. 1 shows an example of a conventional load conversion tuning fork vibrator 1 that constitutes a part of a load converter, in which two vibrating pieces 1 are symmetrical and parallel to the central axis.
Both ends of the vibrator 1 composed of parts a and 1b are connected by U-shaped coupling parts 2a and 2b, and one of the coupling parts 2
By attaching the first and second piezoelectric elements 3a and 3b to both sides of b and connecting them to an external oscillation amplifier 4, the first piezoelectric element 3a is used for pickup and the second piezoelectric element 3b is excited. It can be used for any purpose.

In such a configuration, by appropriately selecting the gain and frequency characteristics of the oscillation amplifier 4, the vibrating pieces 1a and 1b oscillate at the fundamental frequency of the symmetric mode as shown by the broken line. In this state, when a load F is applied for measurement in the axial direction via the mounting parts 5a and 5b of the vibrator 1, the oscillation frequency changes, so this frequency is read by the frequency counter 6 and the load is measured. You can know F. However, if forces such as f1 and f2 in the axial direction or f3 and f4 in the direction perpendicular to the axis are applied as an external force accompanied by vibration or impact acceleration other than the measurement load F,
In addition to sudden and large changes in the vibration frequency, a phenomenon occurs in which a normal vibration state cannot be maintained and the faithful correspondence between the measured load F and the vibration frequency is temporarily lost.

Under such abnormal conditions, conventional methods such as inserting a filter into the input section of the frequency counter 6 or increasing the integration time using an integration method to indicate the average value within the integration period will not work. It becomes extremely difficult to perform accurate load measurements, and the reliability of the counted load as a load measurement value is completely lost, and the load indication value fluctuates so much due to disturbing vibrations that it becomes unreadable. Sometimes.

In view of the uniqueness of such a vibrating load converter, an object of the present invention is to provide a vibrating load measuring device that can accurately measure loads without being affected by external vibrations or impact forces. The gist is that in a load measuring device using a vibrating load transducer whose natural frequency changes according to the applied load, there is a means for detecting an abnormal state of excessive amplitude of the electrical output of the transducer, and In the case of the abnormal state, the frequency output from the converter within the period is discarded, and only the frequency output in the normal state is adopted as the measurement value.

The present invention will be explained in detail based on the embodiments shown in FIG. 2 and below.

FIG. 2 is a block diagram showing the circuit configuration of the first embodiment. Here, 11 is a load detector, for example, a tuning fork vibrator 1 as shown in FIG. 1 can be used, and the oscillation amplifier 4 is the same as that shown in FIG. The output of the oscillation amplifier 4 is input to the rectifier 12 and the frequency counter 6, and the output of the rectifier 12 is input to the comparator 13 as the output of the reference setter 14.
Compared to EO. The output of the comparator 13 is sent to a latch circuit 15, and the output of the latch circuit 15, together with the output of the frequency counter 6, is sent to a data processing circuit 16 using a microprocessor or the like, and further output to a display 17.

When the load F to be measured is applied to the load detector 11 and maintained as it is, for example, when there is no load,
The frequency of vibrator 1, which was vibrating at 2KHz, is now 2.2KHz.
will change and continue in that state. Therefore, based on the output of the oscillation amplifier 4, the frequency counter 6
By counting the changes in the frequency, the magnitude of the applied load F can be determined.

However, as mentioned above, for example, f1 to f4
When disturbing external vibrations or shocks from the various directions and transmission paths shown in are applied to the vibrator 1, the vibration frequency and amplitude suddenly change significantly, and in particular, the peak value of the wave height increases abnormally. After this abnormal voltage is rectified by a rectifier 12, a reference voltage EO is set to an appropriate level by a reference setting device 14 according to the usage environment and purpose of use of the load detector 11.
A comparison is made in the comparator 13. Rectifier 12
During the abnormal period when the output of is greater than the reference voltage EO,
By activating the latch circuit 15, the determination result is transmitted to the data processing circuit 16, the count value of the frequency counter 6 that is counting the output of the oscillation amplifier 4 is discarded, and only the count value of the frequency counter 6 in the normal state is used. It is transmitted to the display 17 and displayed as a load measurement value.

Figure 3 shows each part of this embodiment, in which the vibration output is discarded when the vibration condition of the vibrator 1 becomes abnormal due to the influence of external vibration, etc., and only the vibration output under normal conditions is used as the measured value. FIG. 2 is a simplified explanatory diagram of a pulse waveform. The vibration output waveform obtained from the oscillation amplifier 4 is as shown in FIG. 3A, for example, and in sections A, B, and C, the vibration frequency is significantly disturbed in the waveform due to the influence of external vibration. After this is rectified by the rectifier 12, the output exceeds the reference voltage EO set by the reference setting device 14, as shown in b. Then, as shown in c, the output of the latch circuit 15 changes from OFF to ON and a latch signal is output, and during abnormal periods A, B, and C, data processing is performed so that the vibration output count value is excluded from the measured value. Circuit 16 commands.

Various methods can be considered for specifically discarding and removing the signal during the abnormal state from the measured value, but for example, as shown in Fig. 3, there is a method of counting and displaying the frequency at each predetermined integral time TO. and the third
In the first section shown in Figure a, the vibration output signal is completely normal, so the vibration frequency during the predetermined TO is counted and displayed as a measured value. In the second section, the frequency was counted again from zero in the first normal signal section T21, and since the frequency shifted to abnormal section A before T21 reached TO, counting was temporarily stopped or the counted value was discarded. Do not add it to the measured value, restart counting at the end of abnormal section A, and end the second counting when the sum of the counting time T22 after restarting and the first counting time T21 becomes TO. do. The third counting starts in the interval at the end of the second counting, but during the interval B and C
Since there are two abnormal sections, the effective counting time in the section is T31 + T32 + T33 = TO.

FIG. 4 is a block diagram showing the circuit configuration of the second embodiment, in which a phase comparator 2 is provided after the oscillation amplifier 4.
0, a loop filter 21, and a voltage controlled oscillator 22. The output of the oscillation amplifier 4 is input to a phase comparator 20, and the output thereof is sent to a rectifier 12 and is also input to a voltage controlled oscillator 22 via a loop filter 21. The output of the voltage controlled oscillator 22 is sent to the frequency counter 6, and at the same time a portion is sent back to the phase comparator 2.
Negative feedback is given to 0.

The configuration and functions of such a PLL circuit 23 are well known, so a detailed explanation will be omitted, but the point is that it is a phase synchronized circuit that follows the phase of the input AC signal. Generally, S/
If an AC signal with improved N ratio is obtained as output, or if it follows a steady input signal, but the input signal frequency changes rapidly or if large noise is added, Phase difference/waveform difference/
It is used for applications such as utilizing the difference signal voltage generated depending on frequency differences, etc., and in practical use.
A single element integrated into an IC can be used as the PLL circuit 23.

With the PLL circuit 23 connected in this way, if the load F is constant or changes over time but the rate of change is slow, this
Since the PLL circuit 23 adequately follows and responds to the frequency of the vibrator 1 and its changes, the output of the oscillation amplifier 4, that is, the input of the phase comparator 20, and the voltage controlled oscillator 2
The output of 2 is equal in both phase and frequency. Then, the input of the phase comparator 20 and the voltage controlled oscillator 22
The result of the comparison with the output of the phase comparator 20 appears as the output of the phase comparator 20, and the difference signal voltage becomes zero. The actual phase difference in such a steady state is 90°, but for the sake of simplicity, the following description will be made assuming that 90° is the reference value of zero.

When a disturbing external vibration or shock is applied to the resonator 1, its frequency suddenly changes significantly, causing the PLL
The circuit 23 cannot follow the significant change, and the phase comparator 2
The zero difference signal output voltage temporarily increases significantly to an abnormal value. After this abnormal voltage is rectified by the rectifier 12, it is connected to the reference voltage EO of the reference setter 14 and the comparator 1.
3, the comparison is made. Hereinafter, as in the first embodiment, during an abnormal period when the output of the rectifier 12 is higher than the reference voltage EO, the latch circuit 15 is activated and the determination result is transmitted to the data processing circuit 16, and the output of the voltage controlled oscillator 22 is The count value of the frequency counter 6 that is counting is discarded, and only the count value of the frequency counter 6 in the normal state is used to display the display 17.
to communicate.

FIG. 5 is an explanatory diagram of the signal waveform of each part. The vibration output waveform obtained from the oscillation amplifier 4 is as shown in FIG. 5a, for example, and in sections A, B, and C, the vibration frequency is The waveform is noticeably distorted. Under such an abnormal state of the vibration waveform, b
The output of the phase comparator 20 increases as shown in FIG.
After rectifying this with the rectifier 12, the output is the reference voltage set by the reference setting device 14, as shown in c.
Exceeded EO. Then, as shown in d, the output of the latch circuit 15 changes from OFF to ON and a latch signal is output, and during the abnormal periods A, B, and C, the vibration output count value is discarded from the measured value.

According to repeated experimental studies, the influence of external vibrations and impact forces applied to the vibrator 1 is extremely large, and as a countermeasure, various mechanical vibration damping structures such as the mounting parts 5a and 5b of the vibrator 1 have been devised, and the above-mentioned Even though circuit compensation efforts such as inserting filters and extending the integration time were not effective, the effects of adopting the circuit configurations of the first and second embodiments were extremely significant. In particular, the measurement accuracy of the second example is
It has become possible to put into practical use a highly accurate load measuring device that can reach 0.001%.

As explained above, although the vibration type load measuring device according to the present invention has a simple configuration, it discards the signal caused by abnormal operation of the vibrator and adopts only the signal generated during normal operation as the measured value, so it is effectively A vibrating load transducer can be used to quickly and accurately set loads without being affected by external vibrations or impact forces.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of a tuning fork vibrator for load conversion, Figure 2
The following figures show an embodiment of the vibrating load measuring device according to the present invention. Fig. 2 is a block circuit configuration diagram of the first embodiment, Fig. 3 is a waveform and operation explanation diagram of each part, and Fig. 4 The figure is a block circuit configuration diagram of the second embodiment, and FIG. 5 is a diagram showing waveforms and operation of each part thereof. 1 is a vibrator, 3a and 3b are piezoelectric elements, 4 is an oscillation amplifier, 6 is a frequency counter, 11 is a load detector, 12 is a rectifier, 13 is a comparator, 14 is a reference setter, 15 is a latch circuit, 16 1 is a data processing circuit, 17 is a display, 20 is a phase comparator, 21 is a loop filter, 22 is a voltage controlled oscillator, and 23 is a
It is a PLL circuit.

Claims (1)

[Scope of Claims] 1. In a load measuring device using a vibrating load transducer whose natural frequency changes depending on the applied load, means for detecting an abnormal state of excessive amplitude of the electrical output of the transducer; , means for discarding the frequency output from the transducer within the period when the vibration is in the abnormal state and adopting only the frequency output in the normal state as the measurement value. Device. 2. The vibration type load measuring device according to claim 1, wherein the means for detecting the abnormal state utilizes a phase difference signal between the output of the converter and the output of a voltage controlled oscillator based on the output. 3. The vibratory load measuring device according to claim 1, wherein the measured load is displayed every time the counting period in the normal state reaches a predetermined time.