JPH08178948A - Accelerometer - Google Patents

Abstract

PURPOSE: To accurately detect acceleration even when the acceleration or external force is small by calculating the acceleration based on the pulse interval of the pulses of first and second resonance frequencies. CONSTITUTION: The accelerometer is provided with resonance systems 20A and 20B for vibrating vibration parts 11A and 11B, and when the parts 11A and 11B are deformed by an external force A, the acceleration is obtained based on the difference Δf=f1 -f2 between resonance frequencies f1 and f2 of the systems 20A and 20B. At this time, a calculation part 41 receives an output signal of the system 20A within a specified measuring time ts and measures the pulse interval of the pulse of the frequency f1 by using the clock pulse of a clock signal generating part 45. Similarly, a calculation part 42 inputs an output signal of the system 20B and measures the pulse interval of the pulse of the frequency f2 by using a clock pulse 45. Then, a calculation part 43 calculates an acceleration from the pulse intervals of the frequencies f1 and f2 that are measured by the parts 41 and 42. Thus, even when an acceleration or external force is small, the acceleration can be detected accurately.

Description

Detailed Description of the Invention

[0001]

The present invention relates to surface acoustic waves (SURFACE AC
The present invention relates to a resonance type accelerometer suitable for application to an accelerometer using OUSTIC WAVE (SAW).

[0002]

2. Description of the Related Art Referring to FIG. 5, a conventional surface acoustic wave (SA
An example of an accelerometer using W) will be described. The accelerometer is an elastic body that is cantilevered on a fixed wall, for example, a beam 11 and a SAW resonance system 20 arranged above and below the beam 11.
A and 20B. The beam 11 is made of, for example, a piezoelectric single crystal of quartz, lithium niobate, lithium tantalate, or the like, and an ST cut quartz single crystal is used particularly when temperature characteristics are emphasized.

A support member 13 is mounted on the fixed side of the beam 11, and a weight 15 is mounted on the free end side. Upper SA
Since the W resonance system 20A and the lower SAW resonance system 20B have the same configuration, the upper SAW resonance system 20A will be described.

The upper SAW resonance system 20 A has a resonator 21 mounted on the upper surface 11 A of the beam 11, a power supply terminal 23 and an amplifier 25. The resonator 21 has an input electrode 21-1, an output electrode 21-2, and a reflector (not shown).
The resonator 21 is formed by, for example, a photolithography method. The SAW resonance system 20A constitutes a resonator for generating a surface acoustic wave on the upper surface 11A of the beam 11.

The accelerometer also includes two SAW resonance systems 20.
A buffer amplifier 27 for inputting the output signals of A and 20B,
27, a mixer 31, and a filter 33.

When power is supplied from the power supply terminal 23, vibration is applied to the upper surface 11A of the beam 11 via the input electrode 21-1. As a result, surface acoustic waves are generated on the upper surface 11A of the beam 11. Such surface acoustic wave is output to the output electrode 21-
2 and is supplied to the amplifier 25. The received signal amplified by the amplifier 25 is a buffer amplifier 27.
And is fed back to the input electrode 21-1 at the same time. The buffer amplifiers 27 and 27 function so that the vibration characteristics of the SAW resonance systems 20A and 20B are not affected by the load variation of the mixer 31.

The operation of the lower SAW resonance system 20B is similar. Therefore, the output signals of the two SAW resonance systems 20A and 20B are supplied to the mixer 31. Mixer 31 is each SA
The sum and difference of the oscillation frequencies output from the W resonance systems 20A and 20B are calculated. The output signal of the mixer 31 is the filter 33.
Is supplied to the filter 33 from the sum and difference of the oscillation frequencies,
Only the difference Δf in oscillation frequency represented by the following equation 1 is extracted.

[0008]

[Formula 1] Δf = f ₁ −f ₂

Where f ₁ is the upper SAW resonance system 20A
Is the oscillation frequency of the surface acoustic wave generated by, and f ₂ is the oscillation frequency of the surface acoustic wave generated by the lower SAW resonance system 20B. If the upper SAW resonance system 20A and the lower SAW resonance system 20B have the same configuration and the same resonance frequency, the difference Δf in oscillation frequency becomes zero when the acceleration A or the external force F does not act.

When the acceleration A or the external force F acts on the accelerometer along the direction of the arrow, the beam 11 bends and the two surfaces 11A and 11B.
One side extends and the other side contracts. Therefore, the upper surface 11A
Also, the oscillation frequency of the surface acoustic wave generated on the lower surface 11B changes due to elastic deformation. That is, the oscillation frequency output from each SAW resonance system 20A, 20B changes.
Therefore, the difference Δ in the oscillation frequency output from the filter 33
f changes. From this, it can be seen that the acceleration A or the external force F is a function of the difference Δf in oscillation frequency.

[0011]

## EQU2 ## A = K × (Δf−Δf _B )

Where A is acceleration, K is proportional constant, and Δf
_B is the bias frequency. The direction of acceleration can be determined by the sign ± of the acceleration A.

As described above, the upper SAW resonance system 20A
When the SAW resonance system 20B on the lower side and the lower SAW resonance system 20B have the same configuration and the resonance frequencies are matched, the difference Δf in the oscillation frequency becomes zero when the acceleration A or the external force F does not act. However,
In practice, as described below, a difference is set in advance between the two oscillation frequencies f ₁ and f ₂ so that the difference Δf between the oscillation frequencies does not become zero even when the acceleration A or the external force F is zero. There is. The difference Δf _B between the oscillation frequencies output from the filter 33 when the acceleration A or the external force F is zero is called the bias frequency.

The bias frequency Δf _B will be described with reference to FIG. If Figure 6A without the bias frequency Delta] f _B, i.e., when the bias frequency Delta] f _B = 0 and the acceleration A in the case of showing the relationship of the difference Delta] f of the oscillation frequency, FIG. 6B is to provide a bias frequency Delta] f _B, i.e., Delta] f The relationship between the acceleration A and the difference Δf between the oscillation frequencies when _B ≠ 0 is shown.

The operating range of the accelerometer is, for example, acceleration A
Is in the range of A _{1 to} A ₂ . In such a case, as shown in FIG. 6A, when the bias frequency Δf _B = 0, the difference Δf between the oscillation frequencies of the output signals is −Δf ₂ to + Δf ₁ (Δ
It is assumed that f ₂ > 0 and Δf ₁ > 0). However, as shown in FIG. 6B, when the bias frequency Δf _B ≠ 0, the difference Δf between the oscillation frequencies of the output signals is Δf _B.
It is −Δf _{2 to} Δf _B + Δf ₁ .

[0016] Therefore, the acceleration A is small, in the case of A ≒ 0, the bias frequency Delta] f _B = 0 in difference Delta] f of the oscillation frequency is the output signal is small, the bias frequency Delta] f _B ≠ 0
Then, the difference Δf in oscillation frequency is sufficiently large. Generally, providing the bias frequency Δf _B has the following effects.

(1) The direction of acceleration A or external force F can be determined. (2) Even if the value of the acceleration A or the external force F is small, the frequency region of the accelerometer can be set arbitrarily. (3) When the value of the acceleration A or the external force F is small, the values of the oscillation frequencies of the two SAW resonance systems are prevented from approaching each other to prevent the suction phenomenon (lock-in) from occurring.

[0018]

Conventional surface acoustic wave accelerometers generally have low sensitivity. Therefore, there is a drawback that the acceleration with the required accuracy cannot be obtained.

The sensitivity of the accelerometer is, for example, the ratio of the output frequency to the input acceleration, that is, 1 G (G is the gravitational acceleration).
It is represented as a frequency difference Δf per hit. Usually, the frequency difference Δf is obtained as a pulse signal, and the value of the frequency difference Δf is obtained by obtaining the number of pulses within a predetermined measurement time. Therefore, if the measurement time is lengthened, the number of pulses increases, so that the acceleration can be measured with high accuracy.

Thus, this type of accelerometer can be used when a sufficiently long measurement time can be secured, but cannot be used otherwise.

For example, in a strap-down type navigation device, it is necessary to continuously calculate the attitude, position and azimuth. Therefore, it is necessary to use an accelerometer that can output the required number of pulses every short time. For this reason,
There is a drawback that this type of accelerometer cannot be used in a strapdown navigation system.

In view of the above point, the present invention has an object to provide an accelerometer capable of accurately detecting the acceleration even when the acceleration or the external force is small.

[0023]

According to the present invention, for example, as shown in FIG. 1, a first resonance system for vibrating a first vibrating portion and a second resonance system for vibrating a second vibrating portion. When the first and second vibrating parts are deformed by an external force, the difference Δf between the resonance frequency f _{1 of the first} resonance system and the resonance frequency f ₂ of the second resonance system. = f ₁ -f
_{In the} accelerometer configured to obtain the acceleration from _2, the output signal of the first resonance system is input within a predetermined measurement time t _S , and the pulse interval of the pulses of the _first resonance frequency f ₁ is set as a clock pulse. Is used to input the output signal of the second resonance system within a predetermined measurement time t _S , and the pulse interval of the pulses of the _second resonance frequency f ₂ is set as a clock pulse. A second arithmetic unit for use and measurement, and a first arithmetic unit counted by the first and second arithmetic units.
And a third calculation unit that calculates acceleration from the pulse interval of the pulses of the second resonance frequencies f ₁ and f ₂ .

According to the present invention, in the accelerometer, the first calculation unit inputs the output signal of the first resonance system within a predetermined measurement time t _S to indicate the first resonance frequency f ₁ . A pulse signal to be generated, and the pulse number N _{1 of the} pulse signal
And N ₁ counter for counting said clock pulses n in correspondence with the number of pulses N ₁ to the predetermined measurement time in t _{S
A first} register that counts ₁ and the second arithmetic unit inputs the output signal of the second resonance system within a predetermined measurement time t _S and outputs the second resonance frequency f ₂ generates a pulse signal for instructing the n ₂ counter for counting the number of pulses n ₂ of the pulse signal, the number of clock pulses n ₂ corresponding to the pulse number n ₂ within the predetermined measurement time t _S A second register for counting, and the third arithmetic unit,
It is characterized in that the acceleration is calculated by the following equation from the pulse numbers N ₁ , n ₁ , N ₂ , n ₂ and the constant K supplied from the first and second calculation sections. _{A = K (N 1 / n} 1 -N 2 / n 2)

According to the present invention, in the accelerometer, the N ₁ counter inputs the output signal of the first resonance system within a predetermined measurement time t _S , and every time the pulse of the _first resonance frequency f ₁ rises. The N ₂ counter receives the output signal of the second resonance system within a predetermined measurement time t _S and outputs the second resonance frequency f. It is characterized in that the pulse signal is generated by generating one pulse at each rising edge of the _second pulse.

According to the present invention, in the accelerometer, the vibrations generated in the first and second vibrating portions by the first and second resonance systems are surface acoustic waves.

[0027]

According to this example, as shown in FIG. 2A, output signals are taken out from the first and second resonance systems at a predetermined measurement time t _S , and the acceleration is calculated. As shown in FIG. 2B, the clock pulse having the period Δt is supplied during the measurement time t _S.

When the measurement time t _S is started, a pulse of the first resonance frequency f ₁ is input from the first resonance system as shown in FIG. 2C, and a rising pulse is generated as shown in FIG. 2D. This rising pulse is obtained by generating one pulse for each rising pulse of the oscillation frequency f ₁ .

As shown in FIG. 2D, the measurement time t _S, there are N ₁ pieces of rising pulse, the time from the start to the end of such N ₁ pieces of rising pulse is T _S1. That is, within the measurement time t _S , the net measurement time is T _S1
Therefore, the number of rising pulses is N ₁ .

Next, as shown in FIG. 2E, the net measurement time T _S1
Alternatively, the rising pulse number N ₁ is counted by the clock pulse having the period Δt. In this example, the net measurement time T _S1 or the number of rising pulses N ₁ corresponds to n ₁ clock pulses. Also for the second resonance system 20B, the first resonance system 20
It is calculated in the same manner as A.

Average oscillation frequency f within measurement time t _S
1 , ₁ and f ₂ are the net measurement times T, as is clear from FIG.
_It is obtained as the average frequency of the rising pulse within _S1 and T _S2 . Therefore, it can be obtained by the equation (3) described later. From this, the difference in resonance frequency Δf as shown in the equation (4)
Is obtained.

Generally, the sensitivity of the accelerometer is low, which means that the frequency of the pulse representing the difference Δf in oscillation frequency is small. Similarly, when the value of the acceleration A is small,
The frequency of the pulse representing the difference Δf in oscillation frequency is small. However, in either case, the respective oscillation frequencies f ₁ and f
Frequency of the pulses represent the ₂ is sufficiently large as shown in FIG. 2C. According to this example, the oscillation frequencies f ₁ and f ₂ can be accurately obtained, and the difference Δf between the oscillation frequencies can be calculated from the oscillation frequencies f ₁ and f ₂ , so that the oscillation frequencies f ₁ and f ₂ of the two resonance systems 20A and 20B can be calculated. The difference Δf is not directly obtained.

[0033]

Embodiments of the present invention will be described below with reference to FIGS. 1 to 4, corresponding parts in FIG. 5 are designated by the same reference numerals, and detailed description thereof will be omitted.

FIG. 1 shows a configuration example of the accelerometer according to this example. The accelerometer of this example is different from the accelerometer of FIG.
2 and the third arithmetic units 41, 42, 43 and the clock signal generating unit 45 are arranged. Therefore, the beam 11 which is an elastic body, the first and second SAW resonance systems 20A and 20B and the buffer amplifiers 27 and 27 provided on the upper side and the lower side of the beam 11 are the same as the conventional one shown in FIG. May be

According to this example, the buffer amplifiers 27, 27
Output signals of the first and second calculation units 41 and 42, respectively.
And the output signals of the two arithmetic units 41 and 42 are supplied to the third arithmetic unit 43. The output signal of the accelerometer is output from the third arithmetic unit.

Next, the operation of the accelerometer according to the present invention will be described with reference to FIG. FIG. 2A shows a measurement time pulse signal indicating the measurement time t _S , and FIG. 2B shows a clock pulse signal having a period Δt at the measurement time t _S. As shown in FIG. 2B, a clock pulse having a period Δt is supplied during the measurement time t _S.

FIG. 2C shows an output signal of the first SAW resonance system 20A, that is, a pulse signal having an oscillation frequency f ₁ . When the measurement time t _S starts, the rising pulse shown in FIG. 2D is generated from the pulse signal having the oscillation frequency f ₁ shown in FIG. 2C. The rising pulse is obtained by generating one pulse for each rising of the pulse having the oscillation frequency f ₁ .

Next, the number of rising pulses is measured. In this example, as shown in FIG. 2D, there are N ₁ pieces of rising pulse, the time from the start to the end of such N ₁ pieces of rising pulse is T _S1. That is, the net measurement time is T _S1 and the number of rising pulses is N ₁ within the measurement time t _S.

Next, as shown in FIG. 2E, the net measurement time T _S1
Alternatively, the rising pulse number N ₁ is counted by the clock pulse having the period Δt. In this example, the net measurement time T _S1 or the number of rising pulses N ₁ corresponds to n ₁ clock pulses. Although FIG. 2 shows each pulse signal in the first SAW resonance system 20A, the same can be obtained for the second SAW resonance system 20B.

According to this example, the average oscillation frequencies f ₁ and f ₂ within the measurement time t _S are as shown in FIG.
It is obtained as the average frequency of the rising pulse within the net measurement times T _S1 and T _S2 . Therefore, it is obtained by the following formula.

[0041]

## EQU3 ## f ₁ = (N ₁ / n ₁ ) (1 / Δt) f ₂ = (N ₂ / n ₂ ) (1 / Δt)

Here, f ₁ and f ₂ are average oscillation frequencies within the measurement time t _S , N ₁ and N ₂ are rising pulse numbers, and n ₁ and n ₂ are clock pulses within the net measurement times T _S1 and T _S2 . The number, Δt, is the period of the clock pulse.

Therefore, the frequency difference Δf is as follows.

[0044]

Δf = f ₁ −f ₂ = [(N ₁ / n ₁ ) − (N ₂
/ N ₂ )] (1 / Δt)

The acceleration A is calculated from the frequency difference Δf as follows.

[0046]

## EQU5 ## A = K × Δf = [(N ₁ / n ₁ ) − (N ₂ / n
₂ )] (K / Δt)

K is a proportional constant. As is clear from the comparison between the equations (5) and (2), the bias frequency Δf _{B is set} to zero in this example.

In the conventional example, since the frequency difference Δf is detected and the acceleration A is obtained from it, it is necessary to directly detect the frequency difference Δf with high accuracy. Further, it is necessary to introduce the bias frequency Δf _B in order to determine the direction of the acceleration A.

However, in this example, the acceleration is obtained from the oscillation frequencies f ₁ and f ₂ without directly obtaining the frequency difference Δf. That is, the net rising pulse numbers N ₁ and N ₂ and the corresponding clock pulse numbers n ₁ and n ₂ are detected, and the acceleration A is obtained from the equation 5 by the following equation:
It is only necessary to accurately detect the number of pulses N ₁ , N ₂ , n ₁ , and n ₂ , and therefore, it is not necessary to introduce the bias frequency Δf _B to increase the value of the frequency difference Δf.

The operation of the first arithmetic unit 41 will be described with reference to FIG. The first calculation unit 41 includes a first counter 41-1.
And a first register 41-2, an N ₁ counter 41-3 and a first discriminating circuit 41-4, and the clock signal generator 4
Measured time pulse (Fig. 2A) and period Δ
A clock pulse of t (FIG. 2B) is input and pulse count values N ₁ and n ₁ are output.

The first counter 41-1 inputs the measurement pulse of the cycle t _S (FIG. 2A) and counts the clock pulse of the cycle Δt (FIG. 2B). According to the operation timing, the first counter 41-1 clears the content of each measurement time pulse (FIG. 2A), and the first determination circuit 41-
When the start signal is supplied from 4, the clock pulse (FIG. 2B) having the period Δt is counted.

The first register 41-2 integrates clock pulses having a period Δt within the net measurement time T _S1 . According to the operation timing, the first register 41-2 clears the content of each measurement time pulse (FIG. 2A), and counts by the first counter 41-1 when the rising pulse (FIG. 2D) is generated. The pulse number n ₁ of the clock pulse having the cycle Δt is stored. Therefore, the first register 41-
2 is the pulse number n ₁ accumulated for each rising pulse
Is remembered.

N₁Counter 41-3 is a measurement time pulse
(Fig. 2A) Clear the contents every time, and start up
When a pulse (Fig. 2D) is generated, the number of pulses N₁To
Count. The first determination circuit 41-4 is the first register
Count n stored in 41-2 ₁= 0 and N₁Mosquito
Count N stored in the counter 41-3₁Start when = 1
A signal is generated and supplied to the first counter 41-1. So
Thereby, the first counter 41-1 starts counting.
It

When the measurement time pulse (FIG. 2A) is generated again, the number of pulses n ₁ stored in the first register 41-2
And the pulse number N ₁ stored in the N ₁ counter 41-3 is output.

The second arithmetic unit 42 has the same structure and operation as the first arithmetic unit 41. The third calculation unit 43 receives the count value N ₁ output from the first and second calculation units 41 and 42,
Input N ₂ , n ₁ and n ₂ and calculate the acceleration A by the formula
Is calculated.

The configuration and operation of the clock signal generator 45 of this example will be described with reference to FIG. According to this example, the clock signal generation unit 45 includes a reference clock 45-1 for generating a reference clock signal, a frequency divider 45-2 for dividing the reference clock signal, and one pulse at the start and end of the period t _S. And a one-shot circuit 45-3 for generating

The pulse signals output from the reference clock 45-1 and the one-shot circuit 45-3 are supplied to the first and second arithmetic units 41 and 42.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-mentioned embodiments, and it is apparent to those skilled in the art that various other configurations can be adopted without departing from the gist of the present invention. Easy to understand.

In the above description, the case where the present invention is applied to the surface acoustic wave type accelerometer has been described, but the present invention is not limited thereto. The above discussion is applicable to all resonant accelerometers. As an accelerometer to which the present invention can be applied, for example, there is an accelerometer utilizing lateral vibration of beams, vibration of strings, and the like.

[0060]

According to the present invention, in a resonance type accelerometer, there is an advantage that acceleration can be measured with high resolution even if the measurement time is short.

According to the present invention, in the resonance type accelerometer, there is an advantage that accurate acceleration can be continuously output even if the measurement time is short.

According to the present invention, in the resonance type accelerometer, the output signals of the first and second resonance systems are respectively measured by the clock pulse. Therefore, even if a low acceleration is inputted, the acceleration can be measured with high accuracy. There is an advantage that can be.

According to the present invention, in the resonance type accelerometer, the output signals of the first and second resonance systems are respectively measured by the clock pulse, so that high accuracy is achieved even if the difference between the output signals of the two resonance systems is small. There is an advantage that acceleration can be measured at.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration example of an accelerometer according to the present invention.

FIG. 2 is an explanatory diagram for explaining the operation of the accelerometer according to the present invention.

FIG. 3 is an explanatory diagram for explaining a configuration and an operation of a first arithmetic unit of the accelerometer according to the present invention.

FIG. 4 is a diagram showing a configuration example of a clock signal generator.

FIG. 5 is a diagram showing a configuration example of a conventional accelerometer.

FIG. 6 is a diagram showing a relationship between an acceleration and an output signal of a conventional accelerometer.

[Explanation of symbols]

 11 Elastic body, beam 11A Upper surface 11B Lower surface 13 Supporting member 15 Weight 20A, 20B Resonance system 21 Resonator 21-1 Input electrode 21-2 Output electrode 23 Power supply terminal 25 Amplifier 27 Buffer amplifier 31 Mixer 33 Filter 41 First computing unit 42 second calculation unit 43 third calculation unit 45 clock signal generation unit

Claims (4)

[Claims] 1. A first resonance system for vibrating a first vibrating section and a second resonance system for vibrating a second vibrating section, wherein the first and second vibrating sections are driven by an external force. when the vibrating portion is deformed, the first resonance system of the resonance frequency f ₁ and the second resonance system difference Delta] f = f ₁ -f accelerometer configured to determine the acceleration from the _second resonance frequency f ₂ of In the first calculation unit, the output signal of the first resonance system is input within a predetermined measurement time t _S , and the pulse interval of the pulses of the _first resonance frequency f ₁ is measured using a clock pulse. A second arithmetic unit for inputting the output signal of the second resonance system within a predetermined measurement time t _S and measuring the pulse interval of the pulse of the _second resonance frequency f ₂ using a clock pulse, The first and second resonance frequencies f ₁ and f ₂ counted by the first and second arithmetic units An accelerometer, comprising: a third calculation unit that calculates acceleration from the pulse interval of the pulse. 2. The accelerometer according to claim 1, wherein the first arithmetic unit is configured to perform the first operation within a predetermined measurement time t _S.
And of generating a first pulse signal indicating a resonance frequency f ₁ of the output signal of the resonance system, and N ₁ counter for counting the number of pulses N ₁ of said pulse signal, said predetermined measurement time t
_A first register that counts the number of clock pulses n ₁ corresponding to the number of pulses N ₁ in _S , and the second computing unit is configured to perform the second calculation within a predetermined measurement time t _S.
And generating a pulse signal for instructing the second resonant frequency f ₂ receives the output signal of the resonance system, and N ₂ counter for counting the number of pulses N ₂ of the pulse signal, the predetermined measurement time t
_A second register that counts the number of clock pulses n ₂ corresponding to the number of pulses N ₂ in _S , and the third arithmetic unit is supplied from the first and second arithmetic units. An accelerometer characterized in that it is configured to calculate an acceleration according to the following formula from the number of pulses N ₁ , n ₁ , N ₂ , N ₂ and a constant K that have been applied. _{A = K (N 1 / n} 1 -N 2 / n 2) 3. The accelerometer according to claim 2, wherein the N ₁ counter inputs the output signal of the first resonance system within a predetermined measurement time t _S to generate a pulse having a _first resonance frequency f ₁ . The pulse signal is generated by generating one pulse at each rising edge, and the N ₂ counter inputs the output signal of the second resonance system within a predetermined measurement time t _S to generate the second resonance. An accelerometer, which is configured to generate the pulse signal by generating one pulse at each rising edge of a pulse of frequency f ₂ . 4. The accelerometer according to claim 1, wherein the vibrations generated in the first and second vibrating sections by the first and second resonance systems are surface acoustic waves. An accelerometer characterized by: