JPH0450613A - Apparatus for measuring gradient angle - Google Patents

Abstract

PURPOSE:To improve detection sensitivity by placing two inclination sensors so that an output of one of the inclination sensors shows change reverse to that of an output of the other inclination sensor with respect to a gradient angle. CONSTITUTION:When oscillation frequency difference output from one inclination sensor 32 is FA and oscillation frequency difference output from the other inclination sensor 33 is FB, a pair of inclination sensors 31,32;34,35 are placed so that a change in differential frequency FA is reverse to a change in differential frequency FB with respect to a gradient angle theta. That is, one differential frequency FA increases at a rate of change +alpha while the other differential frequency FB decreases at a rate of change -alpha with respect to a change of the angle theta. However, influence on the differential frequencies FA,FB due to an ambient temperature causes changes in the same direction. By obtaining the difference (FA - FB) between the differential frequency outputs of the pair of inclinations sensors, a fluctuation component due to the temperature can be offset and a change component due to the angle can be doubled.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a tilt angle measuring device equipped with a tilt sensor that utilizes surface acoustic waves.

[Prior Art] Conventionally, as an external force sensor using surface acoustic waves, there is a sensor as shown in FIG. 4, for example.

In Fig. 4, 1 is a beam attached to the support part 2 in the form of a cantilever, and the beam 1 is made of a piezoelectric material, and when an external force acts on the beam 1, distortion occurs on the surface of the beam 1. do. 3.4 is a transmitting electrode that transmits surface acoustic waves;
5 and 6 are receiving electrodes that receive the surface acoustic waves, and 7.8 is a transmitting electrode 3.4 that amplifies the received signal of the receiving electrode 5.6.
These transmitting electrodes 3.4, receiving electrodes 5, 6, and amplifier 7.8 constitute a pair of front and back oscillators 9.10. The strain caused by the external force 11 changes the propagation time of the surface acoustic wave in the beam 1, and the change in the propagation time of the surface acoustic wave changes the oscillation frequencies of the oscillators 9 and 10. 12 is a mixer; mixer 12
performs signal processing on the oscillation frequencies Fl and F2 of the oscillators 9 and 1.0, and outputs a difference frequency component F. In order to prevent unnecessary reflected waves from entering the propagation course of the surface acoustic waves in the beam 10, an absorbent 13 is applied to the surface of the beam 1 where the surface acoustic waves are reflected.

Here, the oscillation frequencies of the oscillators 9 and 10 under no load are FIO and F20, respectively. When external force 11 acts,
A strain -ε due to tensile stress is generated on the upper surface of the beam 1, and a strain ε due to compressive stress is generated on the lower surface. At this time,
The oscillation frequencies Fl and F2 of the oscillators 9 and 10 are expressed by the following equations (1) and (2), considering only the strains ε and -ε caused by the external force 11.

F1=F10-2F10ε...(1)F2
=F20+2F20ε...(2) And,
The oscillation frequency difference F (F=lF2-Fll) is expressed by the following equation (3).

F'=l (F2G+2F20ε)-(F 10-2
F 1(lε)=l F20−F1G+2ε・(
F20+FIO) (3) When F20=F10, F becomes the following equation (4).

F=4εFIO...(4) On the other hand, the relationship between strain 1ε1 and external force 11 is as follows: external force 11 is Q1 cross-sectional thickness of beam 1 is 81 width is b1 Young's modulus is E1 from the free end of beam 1 to the center of the wave propagation path. Assuming that the distance from

x Eaz bQ-(5) ε = Therefore, the external force Q acting on the beam 1 can be detected from the output F of the mixer 12.

Here, when the external force sensor is used as a tilt sensor, it is sufficient to attach a weight of gravity W to the free end of the beam 1, and if the tilt angle with respect to the vertical axis is θ, the acting external force 11 becomes W sin θ. Therefore, the strain 1ε1 is expressed by the following equation (6), and the inclination angle θ can be obtained.

X e l = W sin# ,,,
(6) a2 b Specifically, from the previous equation (4) and equation (6), in the range where the angle θ is small, sin θ = θ, and F = θ・α, where ゛ 24xWF10 is calculated, and the difference output from the tilt sensor is Frequency F
There is a proportional relationship between and the inclination angle θ, and the inclination angle θ can be uniquely measured.

[Problems to be Solved by the Invention] However, in such a conventional tilt sensor, the strain generated in the beam is not only caused by external force but also by thermal expansion due to ambient temperature.

The output frequency F of the tilt sensor relative to the ambient temperature, which was obtained through experiments by the inventors of the present application, is expressed by a linear function of the tilt angle θ and the temperature T, as shown in the following equation (7).

F (θ, T) = F (0, I]) 10KF (0,0
)・T+αθ (7) where: 24×F10 Therefore, the inclination angle θ is obtained by the following equation (8).

F (θ, T) −F(0,0) K@F(
fl, 0)θ=
Tα
As is clear from equation α(8), there is a problem in that the inclination angle θ detected by the inclination sensor is affected by the ambient temperature T.

In addition, at a small inclination angle θ, for example, 1° or less,
The resolution of the tilt sensor is determined by α, and by increasing α (then,
There is also the problem that increasing X or W lowers the resonant frequency of the beam and deteriorates detection sensitivity.

The present invention has been made in view of these conventional problems, and provides a device equipped with a tilt sensor that uses surface acoustic waves to output a tilt angle as a difference between a pair of oscillation frequencies. It is an object of the present invention to provide an inclination angle measuring device that can reduce the influence of the above and improve the detection sensitivity.

[Means for Solving the Problems] In order to achieve this object, the present invention has one end fixed to the device casing side and a weight provided at the other end, and which is deformed by the load of the weight depending on the inclination angle and the ambient temperature. to the beam that produces,
A pair of tilt sensors are arranged so that a change in the oscillation frequency difference outputted by one tilt sensor with respect to the tilt angle is opposite to a change in the oscillation frequency difference outputted by the other tilt sensor,
A differential extraction means is provided which inputs each output of a pair of tilt sensors and outputs a difference frequency component between the two.

[Function] In the present invention, the oscillation frequency difference output from one tilt sensor is FA, the oscillation frequency difference output from the other tilt sensor is FB, and the change in the difference frequency FA and the difference frequency FB are calculated with respect to the tilt angle θ. A pair of inclination sensors are arranged so that the changes in are reversed. That is, as the angle θ changes, one difference frequency FA increases at a rate of change +α, and the other difference frequency FB decreases at a rate of change −α. However, the influence of ambient temperature on the difference frequencies FA and Fil results in changes in the same direction. Therefore, by determining the difference (FA-FB) between the differential frequency outputs of the pair of tilt angle sensors, the variation due to temperature is canceled out, and the variation due to angle is doubled.

Here, the difference frequency output FA of one tilt sensor is (9
), the difference frequency output FB of the other tilt sensor is (10)
The inclination angle θ is determined by the equation (11).

FA (θ, T) = FA (scold 0) + K FA
(I], 0) T+αθ...(9) FB(θ, T)=FB(I), l])+KFB(0,0
)T-αθ...(lO) ■ θ = U[IFB(0,11)-FA(mouth, 0))(F
B(θ, T)-FA(θ, Ta1l Formula (12) and (
13) Comparing equations, F A
(0,0), F B Fo, 0) is at no load (angle θ
−〇°), and K F A (I]
, 0)TlK F B (0,0) Similarly, T indicates the frequency change with respect to the ambient temperature T at no-load.

Difference frequency FA (0,
If 0) and F B (f], 0) can be matched, the effect of ambient temperature can be canceled from equation (11), but in reality, it is necessary to take into account variations in the difference frequency of the tilt sensor during no-load. For example, if FB(0,I])=1.2F^(0,0), then (
The temperature coefficient of the present invention given by formula (11) is given by formula (12), and the conventional temperature coefficient given by formula (8) is given by formula (13).

...(12) I understand.

Therefore, in the present invention, the influence of ambient temperature can be significantly reduced. In addition, by finally determining the difference in the tilt angle output frequency, the amount of change in the difference frequency with respect to the change in tilt angle is doubled compared to the case of one tilt sensor, increasing the resolution for the tilt angle and improving detection accuracy. can be improved.

[Example] Embodiments of the present invention will be described below based on the drawings.

FIG. 1A is a diagram showing an embodiment of the present invention.

First, to explain the configuration, in FIG. 1A, 21 is a beam made of piezoelectric material. One end of this beam 21 is attached in a cantilever shape to a support part 22 on the device housing side, and a weight is attached to the other end. 23 is attached. beam 2
When the load of the weight 23 acts on the beam 21, a tensile strain is generated on one surface of the beam 21, and a compressive strain is generated on the opposite surface, and this strain changes the propagation time of the surface acoustic wave of the beam 21. .

Note that 51 in the figure indicates the measurement direction in which a load is applied as the inclination angle θ increases.

24.25 is a pair of front and back transmitting electrodes that transmit surface acoustic waves, 26.27 is a receiving electrode that receives surface acoustic waves, and 28.29 amplifies and transmits the received signals of the receiving electrodes 26.27. an amplifier that feeds back to the electrodes 24, 25, respectively, and these transmitting electrodes 24;
, 25, receiving electrodes 26, 27, and amplifiers 28, 29 collectively constitute a pair of front and back oscillators 30, 31.

Here, assuming that the oscillation frequency of one oscillator 30 is Fl and the oscillation frequency of the other oscillator 31 is F2, it is set so that F2 > Fl. The outputs of the oscillators 30 and 31 are input to the mixer 43, and the difference frequency FA is FA = F2-
Detected as Fl.

A pair of oscillators 30 and 31 constitute one tilt sensor 32.

33 is the other tilt sensor;
The difference frequency FB output by the tilt sensor 32 is arranged so as to change in the opposite direction to the difference frequency FA output by one of the tilt sensors 32 with respect to the tilt angle.

That is, the tilt sensor 33 is composed of a pair of front and back oscillators 34, 35, a pair of front and back transmitting electrodes 36, 37 that respectively transmit surface acoustic waves, and a pair of front and back transmitting electrodes 36, 37 that respectively receive surface acoustic waves. receiving electrodes 38,3
9 and receiving electrodes 38, 39, and feeds the amplified signals back to transmitting electrodes 36, 37, respectively.

The oscillation frequency F3 of one oscillator 34 of the tilt sensor 33 and the oscillation frequency F4 of the other oscillator 35 are set so that F3 > FA. That is, the oscillation frequencies Fl and F of the oscillators 30 and 31 constituting one of the tilt sensors 32
2, the oscillation frequency F3.2 of the oscillator 34.35 forming the other tilt sensor 33. The magnitude relationship of F4 is set to be an inverse magnitude relationship with respect to the position of the beam surface. Specifically, in the tilt sensor 32, Fl on the front surface of the beam is smaller than F2 on the back surface, and the other tilt sensor 33
is set to have an inverse magnitude relationship such that F3 on the front surface of the beam is larger than FA on the back surface.

The output F3. of the oscillator 34.35 provided in the tilt sensor 33.
F4 is input to the mixer 44, and the difference frequency FB between the two is determined as FB=F3-F4.

45 is a differential extraction means, which processes the output FA of one tilt sensor 32 and the output FB of the other tilt sensor 33 and outputs a difference frequency component (FB-FA).

The differential extraction means may be a mixer or a CPU.

FIG. 2 shows a specific circuit configuration of mixers 43 and 44 shown in FIG. 1A.

In FIG. 2, the mixer includes a capacitor 46, a bias resistor 47, a detection diode 48, and a diode load 4.
9, and a low-pass filter 50, add the different oscillation frequencies of the pair of oscillators 30, 31, or 34.35, extract the sum frequency and the difference frequency from them, and then The sum component is removed by a low-pass filter 50, and only the difference frequency component is extracted and filtered.

Next, the effect will be explained.

As mentioned above, the output of one tilt sensor 32 is converted to FA (
=F2-Fl), and the output of the other tilt sensor 33 is FE(
=F3-F4), and the pair of tilt sensors 32 and 33 are arranged so that FB changes inversely to FA with respect to the tilt angle θ.

For example, the difference frequency output FA with respect to the inclination angle θ of one inclination sensor 32 has a positive inclination of +α, as shown in FIG.
The difference frequency output FB has a negative slope of −α, as shown in FIG.

For this purpose, the oscillation frequencies Fl, F2 and F3 . The relationship of FA is expressed by equation (14), (
15) This can be achieved by setting the following equation.

F2 > Fl ・
...(14) F3 > FA
(15) For example, as the inclination angle θ increases, the load increases in the direction shown by the arrow 51 of the weight 23 in FIG. Adds distortion. The oscillation frequencies of the oscillators 30.31 and 34.35 decrease with tensile strain, and increase with compressive strain.

Therefore, if we pay attention to the oscillators 30 and 31 of one inclination sensor 32, we can see that the oscillation frequency F
1 decreases, increasing the oscillation frequency F2 of the oscillator 31 which is subjected to compressive strain. Here, since Fl<F2, Fl
For a decrease in F2 and an increase in F2, the difference frequency FA = F2 - F
l will increase, and as a result, the characteristics shown in FIG. 1B (a) will be obtained.

On the other hand, in the oscillators 34 and 35 of the other tilt sensor 33, the oscillation frequency F3 of the oscillator 34 on the front surface of the beam decreases due to tensile strain, and the oscillation frequency F4 of the oscillator 35 on the back surface of the beam decreases.
increases with compression strain, and since F3>FA, the difference frequency F
B=F3-F4 decreases, and the characteristic shown in FIG. 1B (b) is obtained.

Here, one inclination sensor 3 takes into consideration the influence of ambient temperature.
2 output FA, and the output FB of the other tilt sensor 33
can be expressed by a linear equation as shown in the following equations (9) and (10).

FA (θ, T) = FA (+], [l) + KFA ([1,
[1) T + a e...(9) Fit(θ, T) = FB((1,(])+KF[1
(11, IIJT-αθ...(10) Note that FA([1, [l), F B (11, Q) indicates the difference frequency output at no load (when the tilt angle θ=0°).

Therefore, the inclination angle θ can be determined by the following equation (11).

θ=Ding [fF B fO, [1] −F A fO,
[1)) - (F [l (θ, T) - FA (θ, T))] If F A (0, I]) = F 1l (0, 0), (11) The second term (temperature class) on the right side of the equation is eliminated and is not affected by the ambient temperature T at all. This case is an ideal case (FIG. 1B (C)).

FIG. 3 is a diagram showing another embodiment of the present invention.

This embodiment is an example in which a pair of beams are provided, one beam is provided with one tilt sensor, and the other beam is provided with the other tilt sensor.

In FIG. 3, 21A is one beam, and this one beam 21A has a support part 22 with one end facing the device housing side.
It is supported in a cantilevered manner, and a weight 23A is attached to the other end. One beam 21A is provided with one tilt sensor 32 similar to the embodiment shown in FIG. 1A, of which eight sensors are FA (=F2-Fl). Reference numeral 21B denotes the other beam, and this other beam 21B is supported in a cantilevered manner by the support portion 22 with one end facing the device casing, and a weight 23B is attached to the other end. The other beam 21B is provided with another tilt sensor 33 similar to the embodiment of FIG. 1A, the output of which is Fil (=F3-FA). Therefore, the inclination angle θ is determined by the above equation (11).

The two tilt sensors may be housed in the same case or in separate cases.

It goes without saying that the same effects as those of the previous embodiment can be obtained in this embodiment as well.

[Effects of the Invention] As explained above, according to the present invention, two tilt sensors are arranged such that the output of one tilt sensor changes inversely to the output of the other tilt sensor with respect to the tilt angle. Because of this arrangement, the influence of ambient temperature can be significantly reduced, and the resolution for the inclination angle can be doubled, making it possible to improve detection sensitivity.

[Brief explanation of drawings]

FIG. 1A is a diagram showing one embodiment of the present invention, and FIG. 1B is a diagram showing an embodiment of the present invention.
Figure A is an explanatory diagram showing the output characteristics of a pair of tilt sensors and their composite characteristics, Figure 2 is a configuration diagram of a mixer, Figure 3 is a diagram showing another embodiment of the present invention, and Figure 4 is a conventional example. FIG. In the figure, 21.21A, 21B... Beam, 22... Support part, 23.23A, 23B... Weight, 24.25, 36.37... Transmission electrode, 26.27,
38.39...Receiving electrode, 8.29.41.42...
・Amplifier, 0,31.34.35...Oscillator, 2.33...Inclination sensor, 3.44...Mixer 5...Differential oil 8 means, 6...Capacitor, 7...・Bias resistor, 8...Detection diode, 9...Diode load, 0...Low pass filter.

Claims (3)

[Claims] (1) In a tilt angle measurement device equipped with a tilt sensor that uses surface acoustic waves to output the tilt angle as the difference between the oscillation frequencies of a pair of oscillators, one end is fixed to the device housing and a weight is attached to the other end. The change in the oscillation frequency difference output by one tilt sensor with respect to the tilt angle is the oscillation frequency difference output by the other tilt sensor. A pair of tilt sensors are arranged so as to be opposite to the change in the tilt angle, and differential extraction means is provided for inputting each output of the pair of tilt sensors and extracting a difference frequency component between the two. measuring device. (2) Each of the pair of tilt sensors has a pair of oscillators in which a positive feedback circuit is provided with a propagation path for surface acoustic waves formed on each of the opposing beam surfaces of the beam, and the tilt angle becomes zero. In this state, the oscillation frequencies of the pair of oscillators of one tilt sensor are made to have a predetermined difference, and the pair of oscillators of the other tilt sensor are set in a positional relationship such that the beam plane is opposite to that of the first tilt sensor. The inclination angle measuring device according to claim 1, characterized in that the oscillation frequencies have the same difference. (3) The inclination angle measuring device according to claim 1, characterized in that two beams are provided, one of the beams is provided with the one inclination sensor, and the other beam is provided with the other inclination sensor.