JPS5957166A - Acceleration sensor - Google Patents

Abstract

PURPOSE:To obtain a small acceleration sensor with limited power consumption while serving as telemeter by providing a comb-shaped electrode on the surface of a piezo-electric substrate to form a surface acoustic wave element and arranging a load appyling means so that a load is applied on the element as uniform stress with an acceleration to be measured. CONSTITUTION:A bomb-shaped electrode 2, an input terminal 3 and an output terminal 4 are provided on a piezo-electric substrate 1 to form a surface acoustic wave (SAW) element. A SAW generated on the surface of the substrate 1 by a signal from the input terminal 3 is reflected sequentially with the comb-shaped electrode 2 and an output appears at the output terminal 4. When a bending load is applied to an SAW element 10, the series resonance frequency, parallel resonance frequency and passage characteristic changes due to a pitch variation and hence, acts as acceleration sensor. An acceleration generating mass 11 is mounted closer to both ends of the SAW element 10 supported at both ends thereof and a 4-point bending method is used to apply a uniform stress thereon. This provides a small acceleration sensor with limited power consumption while serving as telemeter.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an acceleration sensor using a surface acoustic wave (abbreviated as SAW) element.

As acceleration sensors (vibration sensors), there are already established technologies such as resistance wire strain meters and piezo elements.

The present invention uses SAW probes to achieve smaller size and lower cost than these sensors.

The present invention aims to provide an acceleration sensor that can also be used as an oscillation element with the same wave number as the carrier wave of a telemeter.

For example, to detect tool damage and worker wear during cutting, a vibration sensor that is as small and reliable as possible is required. Desirably, the acceleration sensor of the present invention is not only effective for detecting tool damage, etc., but is also effective for general vibration measurement, particularly for field tests and vibration monitoring of various rotating equipment. be.

In the acceleration sensor of the present invention, comb-shaped electrodes are installed on the surface of the piezoelectric substrate, and surface waves generated on the piezoelectric substrate by input signals to the electrodes from the input terminals are sequentially reflected by the comb-shaped electrodes. According to Kanehaya, a surface acoustic wave element whose accompanying output is applied to the output terminal is used, and a load loading means is provided to the element so that the load associated with the acceleration to be measured becomes a substantially uniform stress. be.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Misfire ψノ acceleration section/? The SAW element used in
"lNh"3 + L,, "tto3 + "a"t0
3 + (3) hTlo3 A comb-shaped electrode is installed on the surface of a piezoelectric substrate to generate surface waves, and it is generally used as a quilter in TV circuits, etc.

Figure 1 shows the configuration of this SAW element, and 1t
Also, a piezoelectric substrate, 2 is a comb-shaped 'Jt pole (150 to 200 pieces), 3 is an input terminal, and 4 is an output terminal.

In this SAW cable, input terminals 3 and 1. (Table +ro generated on the surface of the piezoelectric substrate 1 due to No. ii)
The u sentence moves left and right, but the jl
↓Then, it is reflected and the output is sent to output terminal 4.

At this time, the comb-shaped electric MI! , 2 is half the wavelength of the surface wave, and when it matches 2, the wave is almost completely reflected, and the full output is output to the output terminal 4. This is a -glaze series resonant element, and its equivalent circuit is as shown in FIG. Q of resonance
There are thousands of people on the enemy's side. In addition, in Figure 2, C
12 is the capacitance between the output terminals 3 and 4.

Therefore, in the SAW cable shown in FIG. 1, L t 'I'a03 (sound a' = 3250
”/s) and when the pinch P is set to about 21 μm,
77.4hLjH2 of wave force) is oscillated.

When a bending load is applied to a SAW element like 2, the pitch P expands and contracts due to the stress, so the series resonance frequency f, ? ,
Parallel resonance frequency fP1 passage characteristics etc. change. This effect is the same even with a load due to acceleration, so it can be operated as an acceleration sensor.

Figures 6 and 4 show the SAW as shown in those figures.
This shows the change in characteristics when a bending load is applied to the element by 6-point bending.The actual frequency change was determined from the expansion and contraction of the pitch P (thicker than j-4, that is, the resistance Ivil strain As in case 1, there is a gauge no after.In the case of the bending load (2) caused by this six-point bending, the gauge factor is approximately 4% compared to the average stress since the force acting on the piezoelectric substrate 1 is uneven. , :(It was 3.

In addition, in the 6-point bending method, the series resonance approximation wave number f,
The changes are tedious and have poor linearity. This is caused by the deterioration of the passage characteristics due to the load m#j (addition).Such an effect is thought to be due to the disturbance of the coherence of the surface wave radiation due to the non-uniformity of the pitch P accompanying the non-uniform distortion. It will be done.

Therefore, in the present invention, the load associated with the constant acceleration of the 11 is applied to the SAW element by the load λ method which produces a uniform stress on the SAW element as a negative M L , and therefore a load applying means as illustrated in FIG. 5 is adopted. . This load applying means attaches acceleration generating masses 11 at positions close to both ends of the SAW resistor 10 supported at both ends, adopts a four-point bending method instead of the six-point bending method described above, and generates vibration acceleration. The force caused by the force is made to act on the SAW element 10 as a substantially uniform force.

FIG. 6 shows changes in characteristics in this four-point bending method, and both linearity and passing characteristics are good. Note that the gauge factor in this case was approximately 1.8.

Further, FIGS. 7A to 7C show a circuit configuration when the above-mentioned SAW element is also used for oscillating the carrier frequency of a telemeter 17 or the like.

As is clear from the detailed description above, according to the present invention, it is possible to obtain an acceleration sensor that is small, inexpensive, consumes little power, and can also be configured as a telemeter.

[Brief explanation of drawings]

FIG. 1 is a plan view of the SAW device used in the present invention, FIG. 2 is an explanatory diagram regarding the equivalent circuit of the above SAW device, and FIG.
4 and 4 are diagrams showing changes in characteristics due to loads in the 6-point bending method of the SAW element, FIG. The diagrams shown in FIGS. 7A to 7C are circuit configuration diagrams when the above-mentioned SAW resistor is used as an oscillation element of a carrier frequency. l・07j: Electrical substrate, 0 comb-shaped electrode, 3...
・Input terminal, 4...Output terminal, 10...SA
W element, 11...mass. Designated Agent Figure 1 Figure 2 Figure 3! 114WI Q 50 10G +50 load East (Hook 1$5vA O 6th E GiΣ Tsudori; 0 100 200 300 10fl
After Son *r5)

Claims (1)

[Claims] 1. A comb-shaped electrode is installed on the surface of the piezoelectric substrate, and the surface wave generated on the piezoelectric substrate by the input signal from the input terminal to the electrode is forwardly reflected by the comb-shaped electrode, and the resulting output is sent to the output terminal. What is claimed is: 1. An acceleration sensor comprising: a surface acoustic wave element having a surface acoustic wave element, and a load applying means for applying a load to the element due to a constant acceleration of the trout to a substantially uniform stress.