JPH054013B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a vibratory load measuring device that can perform highly accurate load measurement.

"Prior Art" In recent years, vibrating load measuring devices that measure loads with high accuracy using strings, tuning fork vibrators, etc. have been developed (see Japanese Patent Publication No. 56422/1983). This device utilizes the fact that the natural frequency of the vibrator changes depending on the load applied to the vibrator, and an example of its configuration is shown in FIG. In this figure, 1 is a tuning fork vibrator, 2 is a piezoelectric element (excitation means) for exciting the tuning fork vibrator 1, 3 is a piezoelectric element (detection means) for detecting the vibration of the vibrator 1, and 4 is a piezoelectric element. This is an excitation circuit that amplifies the output of 3 and outputs it to the piezoelectric element 2.
The excitation circuit 4 constitutes a self-excited oscillation circuit 5 that oscillates at the natural frequency of the vibrator 1. 6 is a counting circuit that counts the output signal of the oscillation circuit 5, 7 is an arithmetic control circuit that calculates the load W (see Figure 2) applied to the vibrator 1 based on the output of the counting circuit 6, and 8 is a calculation circuit. This is an indicator that displays the applied load W.

The device configured as described above measures the load W by converting a change in the natural frequency of the vibrator 1 due to the load W into a change in the oscillation frequency of the oscillation circuit 5. Therefore, in order to perform load measurement with high precision and stability, in addition to the mechanical configuration that applies the load W to the vibrator 1, it is necessary to An important requirement is to oscillate accurately and stably at this frequency.

"Problems to be Solved by the Invention" By the way, in the excitation circuit 4 described above, in order to improve the stability and quick response of the system, there is a filter that passes only signals with frequencies near the natural frequency of the vibrator 1. A circuit is provided. This eliminates the influence of external vibrations by cutting off frequencies lower than frequencies near the natural frequency, and prevents oscillations at higher harmonics by cutting off high-frequency frequencies. This is to make the oscillation frequency of the oscillation circuit 5 quickly and stably follow the changed frequency when the natural frequency changes due to the application. However, in a filter circuit having such frequency characteristics, the phase slope (change in phase characteristics) becomes large near the natural frequency, which causes the following problem.

That is, for example, ceramic piezoelectric elements 2 and 3
is used, when the phase difference between the output signal S11 of the excitation circuit 4 and the output signal S12 of the piezoelectric element 3 is 90°, the level of the signal S11 becomes the highest, and
Oscillation is also stable. In FIG. 3, the signal S1
1, the phase difference of S12 (curve L1) and the signal S11
(curve L2). On the other hand, the more the phase difference between the signals S11 and S12 deviates from 90 degrees, the more unstable the oscillation becomes and the larger the measurement error becomes. Therefore, the filter circuit in the excitation circuit 4 controls the signal S1 according to the oscillation frequency.
If the phase difference between S1 and S12 changes, unstable oscillation occurs and measurement errors occur.
For this reason, if an attempt is made to measure the load using a range with a small phase difference, the frequency change (hereinafter referred to as span) with respect to the maximum rated load cannot be made large, resulting in a decrease in measurement accuracy. Further, the characteristics of a filter circuit usually change depending on the ambient temperature, and therefore the oscillation frequency also changes depending on the ambient temperature, resulting in poor reproducibility.

In order to solve this problem, if the phase characteristics of the excitation circuit 4 are flattened over a predetermined range, the stability and responsiveness of the system will decrease, and the measurement accuracy will also deteriorate.

This invention was made in view of the above-mentioned circumstances, and without reducing the stability and rapid response of the system,
Moreover, the signal S1 applied to the excitation means (piezoelectric element 2) and the output signal S2 of the detection means (piezoelectric element 3)
The object of the present invention is to provide a vibratory load measuring device that can always maintain a constant phase difference (for example, 90°).

"Means for Solving the Problem" This invention provides a vibrator whose natural frequency changes according to an applied load, an excitation means for vibrating the vibrator, and a detector for detecting the vibration of the vibrator. In the vibratory load measuring device, the self-excited oscillation circuit comprises a self-excited oscillation circuit configured with a means and an amplifying means in a closed loop, and measures a load based on the frequency of the vibrator, wherein the self-excited oscillation circuit a phase difference detecting means for detecting a phase difference between a signal applied to the excitation means and an output signal of the detecting means; and a phase difference detecting means inserted in the closed loop in series with the amplifying means, and having a frequency near the natural frequency of the vibrator. a filter circuit that is inserted in the closed loop in series with the amplification means and the filter circuit, and applies a signal to the excitation means based on the detection result of the phase difference detection means, and the detection means. It is characterized by having a phase adjustment circuit that adjusts the phase so that the phase difference with the output signal of the output signal is always constant.

"Embodiment" Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. In this figure, 1
1 is a tuning fork vibrator, 2 and 3 are ceramic piezoelectric elements, and 11 is an excitation circuit. These tuning fork vibrator 1, piezoelectric elements 2 and 3, and excitation circuit 4 constitute a self-excited oscillation circuit 12. ing. Further, 6 is a counting circuit, 7 is an arithmetic control circuit, and 8 is a display.

Next, the excitation circuit 11 will be explained in detail. first,
Reference numeral 13 denotes an in-phase amplifier, which amplifies the output of the piezoelectric element 3 and outputs it as a signal S1 to the gain adjustment circuit 14 and the phase difference detection circuit 15. Note that this amplifier 13 has a phase difference between input and output that is almost negligible. The gain adjustment circuit 14 is constituted by an amplifier whose gain changes according to the output signal S2 of the control signal generation circuit 16, and its output signal S3
is supplied to the phase adjustment circuit 17. The phase adjustment circuit 17 changes the phase of the output signal S3 of the gain adjustment circuit 14 according to the output signal S4 of the phase difference detection circuit 15, and outputs the same. That is, when the output signal S4 of the phase difference detection circuit 15 is at a predetermined constant voltage V1, the output signal S3 of the gain adjustment circuit 14 is directly passed to the filter circuit 1 as the signal S5.
8, and when the same constant voltage is higher than V1, (S4
−V1), the phase of signal 3 is advanced by an amount corresponding to
The phase of the signal S3 is delayed by an amount corresponding to S4) and output. The filter circuit 18 includes a tuning fork vibrator 1
The piezoelectric element 2 is driven by the output signal S6. The phase difference detection circuit 15 is a circuit that detects the phase difference between the output signal S1 of the amplifier 13 and the output signal S6 of the filter circuit 18.
When the phase of signal S1 is exactly 90 degrees ahead of the phase of signal S6, the aforementioned constant voltage V1 is output as signal S4, and the phase of signal S1 is ahead of the phase of signal S6.
When it has advanced by 90 degrees or more, a signal S4 with a higher level than the voltage V1 is output, and the signal S with respect to the signal S6 is output.
When the phase advance amount of 1 is 90 degrees or less, a signal S4 at a level lower than the voltage V1 is output. Control signal generation circuit 16 supplies signal S2 corresponding to the level of signal S6 to gain adjustment circuit 14. The oscillation abnormality detection circuit 19 is a circuit that detects an abnormal oscillation state such as a sudden change in the oscillation frequency of the oscillation circuit 12. That is, when the oscillation circuit 12 causes an abnormal oscillation state, the phase difference between the signals S1 and S6 greatly deviates from 90 degrees. Therefore, the oscillation abnormality detection circuit 19
The level of signal S4 is detected, and the same level is V1±
When the voltage is within V2 (V2; the voltage set in the circuit 19), an L level signal S7 is output to the arithmetic control circuit 7, and when it is outside V1±V2, an H level signal S7 is output to the arithmetic control circuit 7. The arithmetic control circuit 7 calculates the load only when the signal S7 is at the L level, and does not calculate the load when the signal S7 is at the H level.

According to the above configuration, the phase difference between the signals S1 and S6 is determined by the functions of the phase difference detection circuit 15 and the phase adjustment circuit 17, in other words, the signal applied to the piezoelectric element 2 and the output signal of the piezoelectric element 3. The phase difference is always kept at a constant value (90°). In addition, if an abnormal oscillation occurs and accurate load measurement is impossible, the arithmetic and control circuit 7 will stop calculating the load, and therefore an incorrect value may be displayed on the display 8. do not have.

Note that the vibrator 1 is not limited to a tuning fork vibrator, but may be a single plate, a cylinder, a string, or the like. Furthermore, any method may be used to convert a change in frequency into a load. For example, a method may be used in which the period of the oscillation waveform is measured using a reference pulse. Further, the arithmetic control circuit 7 is usually constituted by a microcomputer.

"Effects of the Invention" As explained above, according to the present invention, the signal applied to the excitation means (piezoelectric element 2) and the output signal of the detection means (piezoelectric element 3) are independent of the phase characteristics of the filter circuit. The phase difference can be kept constant at all times. As a result, stable oscillation can be performed, and since the span can be increased, highly accurate load measurement can be performed.
Furthermore, the slope of the filter characteristic can be made steeper than before, and measurement accuracy can also be improved thereby.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention, FIG. 2 is a block diagram illustrating the configuration of a conventional vibration type load measuring device, and FIG.
It is a figure which shows the relationship between the phase difference of signals S11 and S12 in a figure, and an oscillation output. DESCRIPTION OF SYMBOLS 1... Tuning fork vibrator, 2... Piezoelectric element (excitation means), 3... Piezoelectric element (detection means), 11... Excitation circuit, 15... Phase difference detection circuit, 17... Phase adjustment circuit (phase control circuit).

Claims (1)

[Claims] 1. (a) A vibrator whose natural frequency changes according to an applied load; (b) Excitation means for vibrating with the vibrator; (c) Detecting the vibration of the vibrator. (d) a self-excited oscillation circuit configured with an amplification means in a closed loop, and (e) a vibratory load measuring device that measures a load based on the frequency of the vibrator, (f) the self-excited oscillation circuit includes: (g) phase difference detection means for detecting a phase difference between the signal applied to the excitation means and the output signal of the detection means; and (h) the self-excitation means in series with the amplification means. (i) a filter circuit inserted in the closed loop in series with the amplifying means and the filter circuit, and passing only a signal having a frequency near the natural frequency of the vibrator; A vibrating type characterized by having a phase adjustment circuit that adjusts the phase based on the detection result of the detection means so that the phase difference between the signal applied to the excitation means and the output signal of the detection means is always constant. Load measuring device.