JPH08178949A - Accelerometer - Google Patents

Abstract

PURPOSE: To accurately detect acceleration even when a frequency difference is small by calculating frequency difference based on the pulse of a pulse signal indicating frequency difference and correcting it with a bias frequency. CONSTITUTION: The accelerometer is provided with resonance systems 20A and 20B for vibrating parts 11A and 11B, and when the parts 11A and 11B are deformed by an external force A, an acceleration is obtained based on a difference Δf0 =f1 -f2 between the resonance frequencies f1 and f2 of the systems 20A and 20B. At this time, a frequency calculation part 41 generates a pulse signal indicating the frequency difference Δf0 in a specified measuring time ts, and it measures its pulse interval based on the clock pulse of a clock signal generating part 45, then it calculates the frequency difference Δf0 based on the pulse interval. A bias correction calculation part 42 inputs the output from the part 41 and output signal ΔfB from a bias generation part 43 and corrects the frequency difference Δf0 with the bias frequency ΔfB so as to calculates an acceleration A. Thus, even when the frequency difference f0 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 oscillation frequency difference Δf ₀ represented by the following equation 1 is extracted.

[0008]

[Formula 1] Δf ₀ = 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. When the upper SAW resonance system 20A and the lower SAW resonance system 20B have the same structure and the same resonance frequency, the difference Δf ₀ between the oscillation frequencies 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 ₀ changes. From this, it can be seen that the acceleration A or the external force F is a function of the difference Δf ₀ between the oscillation frequencies.

Since the oscillation frequency difference Δf ₀ includes the bias frequency Δf _B , the oscillation frequency difference Δf ₀ is the sum of the bias frequency Δf _B and the change A / K due to the input acceleration A. Therefore, the following equation holds.

[0012]

## EQU2 ## A = K × (Δf ₀ −Δf _B )

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

As described above, the upper SAW resonance system 20A
And the lower SAW resonance system 20B have the same configuration,
If the wave numbers are matched, acceleration A or external force F does not act
When the difference in oscillation frequency Δf₀Is zero. But Naga
In fact, as described below, the acceleration A or the external force
Even if F is zero, the difference in oscillation frequency Δf₀Gaze
Two oscillation frequencies f in advance so that they do not become₁, F₂
There is a difference. When acceleration A or external force F is zero
Oscillation frequency difference Δf output from filter 33 _BThe
This is called the ear 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 ₀ of the oscillation frequency, FIG. 6B is to provide a bias frequency Delta] f _B, i.e., The relationship between the acceleration A and the difference Δf ₀ between the oscillation frequencies when Δf _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 ₀ between the oscillation frequencies of the output signals is −Δf ₂ to + Δf.
It is assumed that ₁ (Δf ₂ > 0, Δf ₁ > 0). However, as shown in FIG. 6B, the bias frequency Δf _B
When ≠ 0, the difference Δf ₀ between the oscillation frequencies of the output signals
Is Δf _B −Δf _{2 to} Δf _B + Δf ₁ .

Generally, providing the bias frequency Δf _B has the following effects. Therefore, the accelerometer is usually designed to have the bias frequency Δf _B.

(1) The direction of the acceleration A or the external force F can be discriminated. (2) Even when the value of the acceleration A or the external force F is small, it is possible to arbitrarily set the measurable frequency range of the accelerometer. (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.

[0019]

Even if the bias frequency Δf _B is provided in the conventional surface acoustic wave type accelerometer, the output signal, that is, the difference Δf ₀ between the oscillation frequencies is small depending on the magnitude of the acceleration A or the external force F. There were cases. Therefore, when the difference Δf ₀ between the oscillation frequencies is small, there is a drawback that the acceleration cannot be accurately obtained as described below.

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 expressed as a frequency difference Δf ₀ per hit. Usually, the frequency difference Δf ₀ is obtained as a pulse signal (rectangular wave signal), and the value of the frequency difference Δf ₀ is obtained by obtaining the number of pulses within a predetermined measurement time. Therefore, if the measurement time is lengthened, a predetermined number of pulses can be obtained. Therefore, there is a drawback that the measurement time must be lengthened in order to obtain acceleration with a predetermined accuracy.

Thus, this type of accelerometer can be used if 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 calculate the attitude, position and azimuth, for example, every 10 ms, and therefore a short time (for example, 10 ms).
It is necessary to use an accelerometer that can output the required number of pulses for. However, there is no accelerometer of this type that can measure the required number of pulses for each short time as described above, and it is not possible to use this type of accelerometer in a strapdown navigation device. There was a flaw.

Further, the output signal of the accelerometer, includes a bias frequency Delta] f _B, in order to obtain the input acceleration from the output signal of the accelerometer has a disadvantage that must subtract the bias frequency Delta] f _B .

In view of the above point, an object of the present invention is to provide an accelerometer capable of accurately detecting acceleration even when the output signal, that is, the difference Δf ₀ between the oscillation frequencies is small.

[0025]

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. ₀ = f ₁ −
In the accelerometer configured to obtain the acceleration from f _2, a pulse signal indicating the frequency difference Δf ₀ is generated within a predetermined measurement time t _S , the pulse interval is measured by a clock pulse, and the pulse is measured. It is characterized in that it has a frequency calculation section for calculating the frequency difference Δf ₀ from the interval and a bias correction calculation section for correcting the frequency difference Δf ₀ by the bias frequency Δf _B.

According to the present invention, in the accelerometer, the frequency calculation unit counts the pulse number N of the pulse signal indicating the frequency difference Δf ₀ within the predetermined measurement time t _S , and the predetermined number. And a register for counting the clock pulse number n corresponding to the pulse number N within the measurement time t _S.

According to the present invention, in the accelerometer, the bias correction calculation unit calculates the acceleration by the following formula from the number of pulses N and n supplied from the frequency calculation unit, the period Δt of the clock pulse and the constant K. It is characterized in that it is configured to. A = K (N / nΔt−Δf _B )

According to the present invention, in the accelerometer, the counter is provided with the frequency difference Δf within a predetermined measurement time t _S.
It is characterized in that it is configured to generate a pulse signal instructing the frequency difference Δf ₀ by inputting a rectangular wave signal instructing ₀ and generating one pulse at each rising edge thereof.

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.

[0030]

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, as shown in FIG. 2C, the difference Δf ₀ = f between the frequencies f ₁ and f ₂ of the two resonance systems.
_{A 1-} f ₂ rectangular wave signal is input, and its rising pulse is generated as shown in FIG. 2D. This rising pulse is obtained by generating one pulse for each rising of the rectangular wave signal having the frequency difference Δf ₀ .

As shown in FIG. 2D, at the measurement time t _S , there are N rising pulses, and the time from the start to the end of these N rising pulses is T _S.
That is, within the measurement time t _S , the net measurement time is T _S and the number of rising pulses is N.

Next, as shown in FIG. 2E, the net measurement time T _S
Alternatively, the rising pulse number N is counted by the clock pulse having the period Δt. In this example, the net measurement time T _S or the number of rising pulses N corresponds to n clock pulses.

Frequency difference Δf ₀ within the measurement time t _S
As is clear from FIG. 2, the average value of
_It is obtained as the average frequency N / T _S of the rising pulse in _S. Therefore, it can be obtained by the equation (3).
From this, the acceleration A is obtained as shown in the equation (4).

Even when the bias frequency Δf _B is provided in the accelerometer, the output signal, that is, the difference Δf _{0 in the} oscillation frequency may be small when the value of the input acceleration A is small or depending on the direction of the input acceleration A. According to this example, the difference Δf ₀ between the oscillation frequencies can be accurately obtained, and the acceleration A can be accurately calculated from the difference Δf ₀ .

[0036]

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 an example of the configuration of the accelerometer according to this example. The accelerometer of this example is different from the accelerometer of FIG. 5 in that a frequency calculator 41, a bias correction calculator 42, a bias generator 43, and a clock signal generator 45 are arranged on the output side of the accelerometer. Is different. Therefore, the beam 11, which is an elastic body, the first and second SAW resonance systems 20A and 20B, the buffer amplifiers 27 and 27, the mixer 31 and the filter 33, which are provided above and below the beam 11, are shown in FIG. It may be the same as the conventional one shown.

According to this example, the accelerometer output signal Δf ₀
Is supplied to the frequency calculation unit 41 together with the output signals Δt and t _S of the clock signal generation unit 45.
The output signals N and n of are supplied to the bias correction calculator 43. The bias correction calculator 43 inputs the output signals N and n of the frequency calculator 41 and the output signal Δf _B of the bias generator 43 to calculate the acceleration A.

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 two SAW resonance systems 20A, 20.
Oscillation frequency f of B₁, F₂Difference Δf ₀= F₁-F₂The Pa
It is a loose signal (rectangular wave signal). Measurement time t_SWill start
Then, the difference Δf between the oscillation frequencies in FIG. 2C₀Figure from the square wave signal of
The rising pulse shown in 2D is generated. Rising
The pulse is the difference in oscillation frequency Δf₀Rising of square wave signal
It is obtained by generating one pulse for each bite.

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

Next, as shown in FIG. 2E, the net measurement time T _S
Alternatively, the rising pulse number N is counted by the clock pulse having the period Δt. In this example, the net measurement time T _S or the number of rising pulses N corresponds to n clock pulses.

According to this example, the average value of the oscillation frequency difference Δf ₀ within the measurement time t _S is obtained as the average frequency of the rising pulse within the net measurement time T _S , as is apparent from FIG. Therefore, it is obtained by the following formula.

[0044]

## EQU3 ## Δf ₀ = (N / n) (1 / Δt)

Here, Δf ₀ is the average value of the difference between the oscillation frequencies within the measurement time t _S , N is the number of rising pulses within the net measurement time T _S , n is the number of clock pulses within the net measurement time T _S , and Δt Is the period of the clock pulse. It should be noted that the difference Δ in the oscillation frequency expressed by the equation 3
f ₀ includes the bias frequency Δf _B.

The acceleration A is calculated by substituting the oscillation frequency difference Δf ₀ into the equation (2), and the result is as follows.

[0047]

Equation 4] _{A = K (Δf 0 -Δf B} ) = K [(N / n) (1 / Δt) -Δf B ] = K (N / nΔt-Δf B)

K is a proportional constant and Δf _B is a bias frequency.

In this example, the frequency calculator 41 inputs the input rectangular wave signal representing the oscillation frequency difference Δf ₀ to detect the pulse numbers N and n, and the bias generator 43 generates the bias frequency Δf _B. Then, the bias correction calculator 42 calculates
Since the acceleration A is obtained by the equation, the acceleration A can be obtained accurately.

The bias frequency Δf _B generated by the bias generator 43 may be arbitrary, and is set so as not to exceed the output frequency difference Δf ₀ even when the maximum acceleration is input, for example.

The operation of the frequency calculator 41 will be described with reference to FIG. The frequency calculation unit 41 includes a counter 41-1, a register 41-2, an N counter 41-3, and a discrimination circuit 41-.
4 and inputs the measurement time pulse (FIG. 2A) and the clock pulse of the period Δt (FIG. 2B) supplied from the clock signal generator 45, and outputs the pulse count values N and n.

The 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 its operation timing,
The counter 41-1 clears the content of each measurement time pulse (FIG. 2A), and when the start signal is supplied from the determination circuit 41-4, counts the clock pulse of the period Δt (FIG. 2B).

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

The N counter 41-3 clears the content of each measured time pulse (FIG. 2A), and counts the number N of rising pulses (FIG. 2D) when they occur. The determination circuit 41-4 generates a start signal when the count n = 0 stored in the register 41-2 and the count N = 1 stored in the N counter 41-3, and the counter 41- Supply to 1. Thereby counter 4
1-1 starts counting.

When the measurement time pulse (FIG. 2A) is generated again, the pulse number n stored in the register 41-2 and the pulse number N stored in the N counter 41-3 are output.

The bias correction calculation unit 42 is the frequency calculation unit 4
The count values N and n output from 1 and the bias frequency Δf _B output from the bias generator 43 are input,
And the equation (4) are calculated.

The configuration and operation of the clock signal generator 45 of this example will be described with reference to FIG. According to the present example, the clock signal generator 45 includes a reference clock 45-1 for generating a reference clock signal with a period Δt, 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 the frequency calculation unit 41.
Is supplied to.

Although the embodiments of the present invention have been described in detail above, those skilled in the art will understand that the present invention is not limited to the above-mentioned embodiments and 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 a 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.

[0061]

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, since the difference between the output signals of the first and second resonance systems is measured by the clock pulse, the acceleration can be accurately performed even if the difference between the output signals is small. There is an advantage that it can be measured.

[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 bias calculation 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 support member 15 weights 20A, 20B resonant 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 frequency operation unit 42 bias Correction calculation unit 43 Bias generation unit 45 Clock signal generation unit

Claims (5)

[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 difference in the resonance frequency f ₂ of the first resonance frequency f ₁ and the second resonance system of the resonance system Delta] f ₀ = f ₁ -f ₂
In an accelerometer configured to obtain more acceleration, a pulse signal indicating the frequency difference Δf ₀ is generated within a predetermined measurement time t _S , the pulse interval is measured by a clock pulse, and the pulse interval is calculated from the pulse interval. Difference in frequency Δ
The frequency calculation unit that calculates f ₀ and the frequency difference Δf ₀
Accelerometer and having a bias correction calculation unit which corrects the bias frequency Delta] f _B, the. 2. The accelerometer according to claim 1, wherein the frequency calculation unit counts a pulse number N of a pulse signal indicating the frequency difference Δf ₀ within a predetermined measurement time t _S , and the counter. An accelerometer, comprising: a register that counts the clock pulse number n corresponding to the pulse number N within a predetermined measurement time t _S. 3. The accelerometer according to claim 1 or 2, wherein the bias correction calculation unit includes the number of pulses N and n supplied from the frequency calculation unit and the period Δt of the clock pulse.
An accelerometer which is configured to calculate the acceleration from the constant K and the following equation. A = K (N / nΔt−Δf _B ) 4. The accelerometer according to claim 2, wherein the counter inputs a rectangular wave signal indicating the frequency difference Δf ₀ within a predetermined measurement time t _S and generates one pulse at each rising edge. The frequency difference Δf
An accelerometer configured to generate a pulse signal indicating ₀ . 5. 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: