JP3017344B2 - Tilt sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tilt sensor for detecting a minute tilt angle with high accuracy by using SAW technology.

[0002]

2. Description of the Related Art Conventionally, as this kind of SAW tilt sensor, for example, the one shown in FIG. 3 is known. In FIG. 3, reference numeral 1 denotes a cantilever made of, for example, a quartz substrate. One end of the cantilever 1 is fixed to a fixed portion 2 such as a sensor housing, and the other end is free and a weight 3 is mounted.

[0005] On each of the upper and lower surfaces of a quartz substrate constituting the cantilever 1, electrode patterns constituting SAW resonators 4a and 4b are formed. The electrode patterns of the SAW resonators 4a and 4b include transmitting electrodes 5a and 5b and receiving electrodes 6a and 6b.
b are arranged, and an array pattern of the reflectors 8a, 9a and 8b, 9b is formed outside thereof. SAW resonators 4a, 4
b, the outputs of the receiving electrodes 6a and 6b are positively fed back to the transmitting electrodes 5a and 5b by the amplifiers 10 and 11, whereby the SA
The W oscillators 12a and 12b are configured to oscillate signals of frequencies f ₁ and f ₂ .

Oscillation signals from the SAW oscillators 12a and 12b are input to a mixer 14 where a frequency difference (f ₁ -f ₂ ) is detected and output through a band pass filter (BPF) 15 to remove unnecessary components. I do. FIG. 4 shows the actual arrangement of the cantilever 1 in the tilt sensor. That is, when the inclination angle θ is zero, the cantilever 1 is vertical,
When the tilt angle θ is generated as shown in the figure, the weight 3 causes an elongation distortion on the right surface of the cantilever 1 on which the SAW resonator 4a is formed, and at the same time generates a compression distortion on the left surface of the cantilever 1 on which the SAW resonator 4b is formed.

FIG. 5 shows an electrode pattern of the SAW resonator shown in FIG. 4 in which reflectors 8 and 9 using a delay line array pattern are arranged at symmetrical positions outside the transmission electrode 5 and the reception electrode 6. Have been. The resonance frequency f of the SAW resonator shown in FIG. 5 is as follows: f = m × V / (L _c + δ) (1) where m: a value of about one hundred and several tens of harmonics V ; SAW propagation velocity on the quartz substrate L _c ; distance between reflectors δ It is determined by the effective distance within the reflector.

Further, the resonance frequency f of the SAW resonator has a temperature dependency represented by the following equation. f = f ₀ ｛1−a (T−T ₀ ) ² ｝ (2) where f ₀ ; resonance frequency a at the vertex temperature T ₀ ; material constant is about 3 × 10 ^{-8 in} the case of quartz; ambient temperature T ₀ of; peak temperature T ₀ of the apex temperature the equation (2), as shown in FIG. 6, the resonance frequency f at a certain temperature is a peak value, at the before and after temperature decreases the resonance frequency f The frequency of the peak value is called f ₀ , and the temperature at the peak frequency f ₀ is called the peak temperature T ₀ .

Next, two SAWs are used to detect the inclination angle.
A method for making the oscillation frequencies f ₁ and f ₂ of the oscillators 12a and 12b different will be described. First, the SAW resonators 4a and 4b
When the peak temperature T _10, T _20, and since the vertex temperature T _10, T ₂₀ having a resonance frequency f _10, f _20, the oscillation frequency f _1, f _{2 is, f 1 = f 10 {1} -a ( T−T ₁₀ ) ² −bθ｝ (3) f ₂ = f ₂₀ ｛1−a (T−T ₂₀ ) ² + bθ｝ (4)

Note that θ in equations (3) and (4) is exactly sin
θ, but since the inclination angle θ is extremely small, sin
There is no problem if it is treated as θ = θ. Therefore, when ΔT is small,
In this case, the frequency difference F is given by: F = (f ₁ −f ₂ ) = Δf ｛1−at ² + 2a (f ₁₀ / Δf) ΔT · t｝ −b (f ₁₀ + f ₂₀ ) θ (5) where Δf = f ₁₀ −f ₂₀ ΔT; difference in peak temperature (T ₁₀ −T ₂₀ ) t; difference between actual temperature and peak temperature (T−T ₂₀ ). Here, b is: b = (9Wx / ED ² e) (6) where, W; weight of weight x; distance from center of weight to center of resonator E; Young's modulus of quartz D: thickness of quartz substrate e; given by the width of the quartz substrate.

The two SAW oscillators 12a and 12b shown in FIG.
In order to make the oscillation frequencies f ₁ and f ₂ of
As is apparent from the equation, SAW resonators 4a, may be changed reflector distance L _c in 4b. FIG. 7 shows a conventional SA
The electrode structure of the W resonators 4a and 4b is compared with each other. For example, the distance L _c2 between the reflectors of the SAW resonator 4b is slightly shorter than the distance L _c1 between the reflectors of the SAW resonator 4a. The resonance frequencies that determine the oscillation frequencies f ₁ and f ₂ are different. In this case the reflectors 8a and 8b, 9a and 9b
And the pitch d of each electrode array pattern is the same and does not change.

[0010]

However, in such a conventional SAW tilt sensor having a structure in which a SAW resonator is formed on both surfaces of one cantilever, two S
There is a problem that a large temperature drift occurs in the difference frequency F due to a difference in the temperature characteristics of the AW resonator, and a measurement error increases.

That is, the difference frequency F of the SAW tilt sensor is
As given by the above equation (5), [2a (f ₁₀ / Δ
f) ΔT] has a considerably large value. For example, when the actual temperature t and the t = 10 ° C., the value of the term of _{[2a (f 10 / Δf)} ΔT] with respect to the temperature difference [Delta] T of the peak temperature T ₁₀ and T _20, for example [Delta] T = 1 ° C. in [2a ( f ₁₀ /Δf)ΔT]=1.5×10 ^−3, and the measurement error increases due to the large temperature drift.

The present invention has been made in view of such a conventional problem, and an object of the present invention is to provide a tilt sensor using SAW technology which can suppress temperature drift and dramatically improve measurement accuracy. Aim.

[0013]

In order to achieve this object, the present invention is configured as follows. The reference numerals in the drawings are also shown. First, the present invention relates to a cantilever 1 made of a piezoelectric substrate having one end fixed and the other end free, and a weight 3 mounted thereon.
A pair of SAW resonators 4a and 4b having different resonance frequencies respectively formed on the front and back surfaces of the cantilever 1;
A pair of SAW oscillators 12a and 12b that oscillate signals of frequencies f ₁ and f ₂ that match the resonance frequency by positively feeding back the outputs of the resonators 4a and 4b, and a pair of SAW oscillators 12a and 1
Mixer 1 for detecting frequency difference F (= f ₁ −f ₂ ) of 2b
4 and a tilt sensor that detects the tilt angle θ of the cantilever 1 with respect to the vertical axis based on the frequency difference F output from the mixer 14 is symmetric.

In the tilt sensor according to the present invention, a pair of SAW resonators 4a and 4b are formed on a piezoelectric substrate by an electrode array of transmitting electrodes 5a and 5b and receiving electrodes 6a and 6b.
b, and the reflectors 8a, 8a, 5b,
It has a structure in which an array pattern of 8b and 9a, 9b is formed, and the distance between reflectors L _c1 , the effective distance in reflector δ ₁ and the array pitch d _{1 in one} SAW resonator 4a is _equal to the other SAW resonator. In FIG. 4b, the inter-reflector distance L _c2 , the effective distance δ ₂ in the reflector and the array pitch d ₂ are similar patterns having a dimensional ratio K at which a specified frequency difference F can be obtained, and the apex temperature T ₁₀ between a pair of SAW resonators , characterized in that suppressing a difference ΔT of T ₂₀ to zero or minimum.

Further, in the tilt sensor according to the present invention, the composition ratio (L _c / δ) between the distance L _c between the reflectors of the pair of SAW resonators 4a and 4b and the effective distance δ in the reflectors is determined by this configuration. Ratio L
_The inflection point at which the change in the vertex temperature T ₀ is minimized with respect to the change in _c / δ or a value near the inflection point is set.

[0016]

According to the tilt sensor of the present invention having the above-mentioned structure, the SAW resonator electrode patterns provided on both sides of the piezoelectric substrate constituting the cantilever are replaced by one pattern, for example, K = with magnification of similar patterns, such as 0.9996, even changing the reflector distance L _c for varying the oscillation frequency, two S
Since the composition ratio ( _Lc / δ) of the AW resonator can be made the same, and if the composition ratio ( _Lc / δ) is the same, the vertex temperature becomes the same, the vertex temperature difference ΔT is set to zero or extreme. It can be a very small value.

As a result, the frequency difference F becomes: F = (f ₁ −f ₂ ) = Δf (1−at ² ) + b (f ₁₀ + f ₂₀ ) θ, and [2a (f ₁₀₎ / Δf) ΔT
t], the measurement error due to the difference in the temperature characteristics does not occur or can be minimized.
A detection accuracy of a tilt angle on the order of 1/100 degrees can be achieved.

In the actual manufacturing process, two S
Even if the AW resonator has a similar pattern, the thickness and width of the electrode will vary in the manufacturing process, making it difficult to make the peak temperature the same. So In the present invention, as the operating characteristics of the SAW resonator, a pair of SAW resonators 4a, 4b reflector distance L _c and the reflector in the effective distance δ and composition ratio of (L
_c / δ), the peak temperature hardly changes
Focusing on the fact that there is a point, and by setting the composition ratio (L _c / δ) to be a value at or near this point , even if dimensional variations occur in the shape of the electrode pattern during the manufacturing process, The change in the peak temperature is minimized, and as a result, a tilt sensor with extremely small temperature errors can be manufactured.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a cantilever of a SAW tilt sensor is used.
For example, a quartz substrate is adopted as a first embodiment. FIG. 1 is a configuration diagram of an embodiment showing the electrode arrangement of SAW resonators formed on both sides of the quartz substrate in comparison. In FIG. 1, reference numerals 4a and 4b denote SAW resonators. As shown in FIG. 3, one end of the cantilever 1 is supported by the fixed portion 2 and the other end is provided with a weight 3 and is made of a free quartz substrate. Formed on each of the two sides.

One SAW resonator 4a has a transmitting electrode 5a and a receiving electrode 6a arranged at a predetermined interval, and the transmitting electrode 5a
And reflectors 8a, 9a at symmetrical positions outside the receiving electrode 6a.
Is formed. Here, the reflector 8 of the SAW resonator 4a
The distance between the reflectors a and 9a is L _c1 , and the effective distance in the reflectors 8a and 9a is δ ₁ .

On the other hand, the other SAW formed on the opposite surface side
As for the resonator 4b, reflectors 8b and 9b are formed at symmetrical positions outside the transmission electrode 5b and the reception electrode 6b, and the distance between the reflectors 8b and 9b is _Lc2 . 8b, the reflectors within an effective distance in 9b is a [delta] _2. In the SAW resonators 4a and 4b of FIG. 1, both electrode patterns are similar patterns. That is, SA
Assuming that the pattern size of the W resonator 4a is P1, the other S
The pattern size P2 of the AW resonator 4b is equal to the pattern size P1.
Is multiplied by a magnification K that is slightly larger or slightly smaller than 1. The two have a dimensional relationship of P1 = K × P2, that is, both have a similar pattern.

More specifically, the distances L _c1 and L _c2 between the electrodes in the SAW resonators 4a and 4b, and the effective distances δ ₁ and δ in the reflectors.
₂ and the electrode pitches d ₁ and d ₂ , the following relational expression holds. L _c1 = K · L _c2 δ ₁ = K · δ ₂ (7) d ₁ = K · d ₂ By making the two SAW resonators 4a and 4b similar patterns, the peak temperatures T ₁₀ and T of the two SAW resonators 4a and 4b are obtained. ₂₀ can be made the same, and the temperature drift term 2a (f ₁₀ / Δf) ΔT in the equation (5) can be made zero.

FIG. 2 is a characteristic diagram showing the relationship between the peak ratio T ₀ and the composition ratio (L _c / δ) of the inter-reflector distance L _c and the effective distance δ in the reflector for the SAW resonator used in the present invention. It is. The characteristic diagram of FIG. 2 shows that the inventors of the present invention solve the problem of temperature drift in the SAW tilt sensor.
A simulator realizing the operation function of the SAW tilt sensor is created, and the composition ratio (L _c /
It was discovered when the variation of the peak temperature T ₀ was examined by changing δ), and further theoretical investigation was performed to confirm that the characteristics shown in FIG. 2 were obtained.

[0024] As apparent from the characteristics of FIG. 2, the reflector distance L _c indicated on the horizontal axis reflector the effective distance δ configuration ratio (L
_c / δ), it was found that the vertex temperature T ₀ changes periodically so as to have a substantially sinusoidal curve. This figure 2
The following can be seen from the characteristics of First, in order to in the conventional pattern shown in FIG. 7, not changing the reflector effective distance [delta] by changing only the reflector distance L _c, the composition ratio (L _c / δ)
Differs for each SAW resonator, resulting in a difference in peak temperature.

On the other hand, in the present invention, as shown in FIG. 1, the two SAW resonators 4a and 4b are formed in a similar pattern so that the distance between the reflectors is different from L _c1 and L _c2. The composition ratio between the effective distances δ ₁ and δ ₂ in the reflector (L _c1 / δ
₁ ) and (L _c2 / δ ₂ ) are equal, and the position of the horizontal axis in FIG. 2 does not change. Therefore, in the SAW resonator 4a, 4b of the present invention shown in FIG. 1, determines the peak temperature at any one point on the characteristic curve of FIG. 2, naturally peak temperature T ₁₀
= The T _20.

As described above, if the peak temperatures T ₁₀ and T _{20 of the} two SAW resonators 4a and 4b are equal by a similar pattern, the peak temperature difference ΔT = 0, and therefore the above (5)
The equation is F = Δf (1−at ² ) + b (f ₁₀ + f ₂₀ ) θ (8), and the temperature drift term 2a (f ₁₀ / Δf) ΔT can be eliminated.

Next, a second embodiment of the present invention will be described. In the second embodiment of the present invention, as shown in FIG. 1, the two SAW resonators 4a and 4b have a similar pattern, and at the same time, the composition ratio of the distance between the reflectors and the effective recording distance in the reflector ( The value of (L _c / δ) is a value at or near point A at the peak, or a value at or near point B at the valley in the characteristic curve of FIG.

At points A and B in the characteristic curve and in the vicinity thereof, it is apparent that the shift amount of the peak temperature is small with respect to the fluctuation of the composition ratio (L _c / δ). Thus, the composition ratio (L _c /) of the inter-reflector distance and the effective distance in the reflector
By determining δ) to be a value at or near points A and B, dimensional variations such as thickness and width that occur when manufacturing the electrode patterns of the SAW resonators 4a and 4b shown in FIG. it is possible to minimize the difference ΔT of the peak temperature T _10, T ₂₀ by.

That is, the same composition ratio (L _c / δ) in the design stage
Even when the dimensions of similar patterns are obtained, the thickness, width, etc. of the electrodes must be adjusted due to various factors in the manufacturing stage of forming the respective electrode patterns shown in FIG. 1 on both sides of the quartz substrate. Variations occur. If the dimensional relationship of the electrode patterns varies as described above, the similarity of the patterns is broken, and as a result, a temperature difference ΔT occurs between the apex temperatures T ₁₀ and T ₂₀ , and the temperature drift term cannot be removed or reduced. .

On the other hand, the distance between the reflectors, the effective distance in the reflector, and the electrode pitch are determined so that the composition ratio (L _c / δ) of the points A and B in FIG. Therefore, even if the thickness and width of the electrode pattern are varied in the manufacturing stage, as is apparent from the characteristics of FIG. 2, the peak temperature is not so large even when the composition ratio (L _c / δ) changes at points A and B and in the vicinity thereof. Does not shift, the peak temperature difference ΔT due to manufacturing variations is minimized, and as a result, the temperature drift term 2a (f ₁₀ / Δf) ΔT in the above equation (3) is set to a very small value to reduce the inclination angle. Measurement accuracy can be improved.

As the characteristics of the SAW resonators 4a and 4b used in the SAW sensor of the present invention shown in FIG. 1, for example, the 196 MHz band is used as the oscillation frequencies f ₁ and f ₂ , and the difference frequency between the two is F = 80 kHz. In the case, the distance L between the reflectors
L _c1 = 0.9996 × L _c2 L _c2 = 1991 μm between _{c 1} and L _c2 . When a SAW resonator having this similar pattern was prepared and the peak temperatures T ₁₀ and T ₂₀ were obtained, T ₁₀ = 2.98 ° C.
T ₂₀ = 2.88 ° C., and the peak temperature difference ΔT was suppressed to 0.1 ° C.

[0032]

As described above, according to the present invention, the two SAW resonators have similar patterns so that the two SAW resonators have the same apex temperature, thereby eliminating or minimizing the temperature drift in multi-frequency detection. It is possible to improve the measurement accuracy of the inclination angle while suppressing the inclination. Further, by setting the composition ratio of the inter-reflector distance and the effective distance in the reflector in the electrode pattern to a value at or near a point where the peak temperature does not fluctuate much, the electrode pattern generated at the stage of manufacturing a SAW sensor having a similar pattern is obtained. The temperature difference between the vertices is minimized with respect to variations in thickness and width, and the yield at the manufacturing stage of forming a fine similar electrode pattern can be greatly improved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention by comparing electrode patterns of two SAW resonators.

FIG. 2 is a characteristic diagram showing a relationship between a shift ratio of a vertex temperature and a composition ratio of an inter-reflection distance and an effective distance in a reflector according to a principle of the present invention.

FIG. 3 is a structural explanatory view of a tilt sensor.

FIG. 4 is an explanatory view showing an attached state of a cantilever used for an inclination sensor.

FIG. 5 is an explanatory diagram of an electrode pattern of a SAW resonator used for a tilt sensor.

FIG. 6 is a characteristic diagram showing a relationship between a resonance frequency and a temperature of the SAW resonator.

FIG. 7 is an explanatory diagram showing a dimensional relationship for changing a resonance frequency in a conventional SAW resonator.

[Explanation of symbols]

 1: cantilever (quartz substrate) 2: fixed part 3: weight 4a, 4b: SAW resonator 5a, 5b: transmitting electrode 6a, 6b: receiving electrode 8a, 8b, 9a, 9b: reflector 10, 11: amplifier 12a, 12b: SAW oscillator 14: Mixer

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Hideki Ouchi 2-16-46 Minami Kamata, Ota-ku, Tokyo Tokimec Co., Ltd. (56) References JP-A-63-184071 (JP, A) Hei 3-222511 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01C 9/00-9/36 G01B 7/30

Claims (2)

(57) [Claims] 1. A cantilever made of a piezoelectric substrate having one end fixed and the other end free and mounted with a weight, a pair of SAW resonators having different resonance frequencies respectively formed on the front and back surfaces of the cantilever, A pair of SAW oscillators that oscillate signals of frequencies (f ₁ , f ₂ ) matching the resonance frequency by positively feeding back the output of the SAW resonator, and a frequency difference (F) between the oscillation signals of the pair of SAW oscillators. A mixer for detecting,
Based on the frequency difference (F) output from the mixer,
In the tilt sensor for detecting the tilt angle θ of the cantilever, the pair of SAW resonators has a transmission electrode array and a reception electrode array arranged on the piezoelectric substrate and a reflector array outside the transmission electrodes and the reception electrodes. Is formed, and the distance between the reflectors (L _c1 ) in one SAW resonance is
For the effective distance (δ ₁ ) and the array pitch (d ₁ ) in the reflector, the distance (L _c2 ), the effective distance (δ ₂ ) in the reflector and the array pitch (d ₂ ) in the other SAW resonator are calculated. A similar pattern having a dimensional ratio (K) at which a specified frequency difference (F) can be obtained, and a difference (ΔT) in apex temperatures (T ₁₀ , T ₂₀ ) between a pair of SAW resonators is suppressed to zero or a minimum. A tilt sensor characterized by the above-mentioned. 2. A tilt sensor according to claim 1, wherein a ratio (L _c / δ) of a distance (L _c ) between the pair of SAW resonators and an effective distance (δ) in the reflector. Is set to a value at or near an inflection point at which the change in the apex temperature (T ₀ ) is minimized with respect to the change in the composition ratio (L _c / δ).