JPS61212737A - Power detector - Google Patents

Abstract

PURPOSE:To simplify the construction, by correcting variations in the resonanse frequency with changes in the density of a power detection vibrator by the resonance frequency of a crystal resonator. CONSTITUTION:A power detection vibrator 10 is so arranged that two beam- shaped plates 11a and 11b are provided parallel in symmetry, formed in a shape of a square with a connection 12 and then, connected to a support 14 through a flexure 13. An exciting element 15a and a vibration detecting element 15b are mounted on the side of the connection 12 and each connected to an amplifier 16 to construct a first exciting means 17. Then, a second exciting means 21 is made up of a crystal resonator 22, an inverter 23, a resistance 24 and a capacitor 25. The outputs of the means 17 and 21 are inputted into a signal processing section 20 with which the rate of change in the resonance frequency with variations in the density of the power detection vibrator 10 is corrected by the resonance frequency of the crystal resonator 22. This can produce a highly accurate power detector at a low cost with a simple construction.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Application of the Invention The present invention relates to a force detection device that outputs a frequency signal corresponding to a force to be measured, and more particularly to a force detection device that performs density correction.

<Prior Art> FIG. 4 is a configuration explanatory diagram showing an example of a conventionally known device of this type, which is described in Japanese Patent Laid-Open No. 56-79221. This device includes a diaphragm 1 that receives measurement pressure (force), a flat force detection vibrator 3 whose one end is fixed to the inner shell of a housing 2 and the other end to the diaphragm 1, and this flat force detection vibrator. The signal processing means 4 detects the natural frequency of 3. An apparatus having such a configuration has high pressure sensitivity and can obtain a signal corresponding to pressure as a digital signal that is highly compatible with a computer.

<Problems to be Solved by the Invention> However, in such a force detection device, since the sensitivity of the force detection vibrator is high, there is a problem that the resonance frequency is affected by the density of the surrounding gas, and the zero point fluctuates.

Means for Solving the Problems> The present invention has been made in view of the above problems, and an object of the present invention is to provide a force detection device that corrects the influence of the resonance frequency due to changes in the density of surrounding gas. Its configuration is characterized by a force detection vibrator to which the input to be converted is applied in the axial direction, a first excitation means J5 that causes this force detection vibrator to resonate at its natural frequency, and an imaging device for the force detection vibrator. , a crystal resonator, and a second excitation means for exciting the crystal resonator, the resonant frequency of the crystal resonator is input to the signal processing means, and density correction is performed. This is how it was done.

When a force to be measured is applied to the force detection device, which vibrates at a resonant frequency corresponding to the horn, the force detection device is affected by the density of the surrounding gas in which the device is placed (the resonant frequency changes due to On the other hand, the resonant frequency of the crystal oscillator also fluctuates, but the output from this crystal oscillator is input to the signal processing circuit of the force detection device to correct the fluctuation of the resonant frequency due to the density change. Example 1 The figure is a block diagram showing one embodiment of a force detection device according to the present invention.

In the figure, 17 is the first excitation means. 1Ω- is a force detection sensor, which consists of two beam-shaped plates 11a and 11b.
are provided symmetrically and in parallel, are formed into a mouth shape by the connecting portion 12, and are connected to the support portion 14 via a flexure 13. 15a and 15b are piezoelectric elements attached to the side surfaces of the joint, for example, 15a is an excitation element;
b is a vibration detection element, and each element is connected to an externally provided amplifier 16 to constitute a first excitation means 17. 2o is a signal processing section that processes the output from the first excitation means 17. 21 is a second excitation means, which includes a crystal resonator 22 and an inverter 23 . Resistance 24. This second excitation means 21 is constituted by a capacitor 25.
The output from is input to the signal processing section 20. The crystal oscillator 22 is manufactured with judicial precision using photography technology.

For example, a crystal tuning fork vibrator for watches with uniform density sensitivity is desirable. Such a crystal oscillation circuit 21 is extremely inexpensive because it only requires one inverter and one crystal m-driver.

The resonance frequency including the surrounding gas density of the force detection vibrator 10 having the above configuration can be determined by the following equation.

f m p = f m o / r c] - 1 c)
(1) Here, fmo: Resonant frequency of the force detection sensor in vacuum A: Constant Also, the resonant frequency including the surrounding gas density of the crystal resonator can be determined by the following equation.

f Q D 7 f Q o / FrT■7- (2
>Here, fqo: Resonant frequency of the crystal resonator in vacuum B: Constant Figure 2 shows the rate of change of the resonant frequency with respect to the density determined by the above calculation formula and experimental values. According to the figure, the rate of change of the force detection vibrator 10 is such that the density is 2 m Q /
It can be seen that the rate of change of the crystal resonator 22 is approximately 0.03%, compared to approximately 0.32% when cm 3 .

(σ-1,2~2.4mg/cm' is 1 atm~2
From the above equation (2) (corresponding to atmospheric pressure), the density at that point can be determined by the following equation.

ρ-1/B ((fQo /fqρM-1))...<
3) The frequency of the power detection sensor to be corrected can be determined from the density at that point determined by the formula (3) using the following formula.

Δfm-fmo/r-TW bottom'f m o ・” (4
) Figure 3 shows the results of correcting the rate of frequency change with respect to the density of the second force detection sensor by performing the calculations shown in the above formulas in the signal processing unit 20 shown in Figure 1, with the horizontal axis representing the density and the vertical axis representing the density. The axis is shown as the frequency change rate. According to the figure, the rate of frequency change with respect to density change is less than 0.001%, and by making corrections using the crystal oscillator, the rate of frequency change is improved by more than two orders of magnitude compared to the case of only a force-detecting camera element. I understand.

<Effects of the Invention> As specifically explained above in conjunction with the embodiments, according to the present invention, fluctuations in the resonant frequency due to changes in the density of the force detection resonator are corrected by the resonant frequency of the crystal resonator. A force detection device can be realized at low cost with a simple configuration.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the force detection device according to the present invention, and Fig. 2 shows the rate of change in the resonant frequency of the force detection oscillator and the crystal oscillator with respect to the density determined by calculation formulas and experimental values. FIG. 3 is a diagram showing the result of correcting the frequency change rate with respect to the density of the force detection vibrator, and FIG. 4 is a configuration explanatory diagram showing a conventional example. 10...force detection vibrator, 15a...excitation element, 15
b...detection element, 17...first excitation means, 20.
...Signal processing unit, 21...Second excitation means, 22...
·Crystal oscillator. Figure 3 Figure 4 Figure 2 f [mg/d]

Claims (1)

[Claims] a force detection oscillator to which a force to be converted is applied in the axial direction; a first excitation means for resonating the force detection oscillator at a natural frequency; and a signal processing means for detecting vibrations of the force detection oscillator; It has a crystal resonator and a second excitation means for exciting the crystal resonator, and the resonant frequency of the crystal resonator is input to the signal processing means to perform density correction. Force detection device.