JPH10267658A - Vibration-type angular velocity sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an accurate angular velocity signal by subtracting an offset error component that does not depend on coriolis force from the output signal value of two vibrators with a vibration mass part being arranged closely on a substrate by employing a specific expression. SOLUTION: A vibrator A8.2 with a mass of (m), and a vibrator B804 with a mass of Cm (c is a proportional constant) are driven by a drive circuit 801 at a frequency (f) and an amplitude (a). When the angular velocity at this time is set to Ω, the detection signal A (the output of A: Aout) and the detection signal B (the output of B: Bout) of each vibrator are expressed by expressions I and II, respectively, in which K1 is a proportional constant in the case of converting the coriolis force to an output electrical signal, and OF is an offset error (ω=2 πf). Therefore, by performing an operation of (Bout-C.Aout)/(1-C) by an operation circuit 806, an expression III is obtained, thus the inclination of a vibration surface being generated regardless of the coriolis fore, namely an offset can be calculated. Then, for example, by subtracting OF obtained by the expression III from Aout in the expression I, output K1 .2 maωΩ that is proportional to a true angular velocity Ω can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an angular velocity sensor and, more particularly, to a structure and signal processing of a vibration type angular velocity sensor suitable for reducing an output error of the sensor due to variations in manufacturing conditions, temperature change, and various disturbance factors. .

[0002]

2. Description of the Related Art For example, FIG. 7A is a plan view showing a conventional vibration type angular velocity sensor, and FIG.
A cross-sectional view shows “A Micromachined Comb-Drive Tunin
g ForkRate Gyroscope ”, IEEE Micro Eletro Mechanica
l Systems 1993 Proceedings pp. 143-148, in which a vibrating gyro was manufactured by micromachining the surface of a semiconductor substrate.

In FIGS. 7 (a) and 7 (b), the vibrating mass portions 103 and 104 are so-called floating shapes separated from the substrate 203 by a predetermined distance by beams 102 fixed to the substrate 203 by fixing portions 101. Is held in. Further, comb-shaped drive electrodes 105 arranged at minute intervals are provided between another fixed portion 106 and the vibrating mass portions 103 and 104, and by applying a voltage to the drive electrodes 105,
Due to the generated electrostatic force, the vibrating mass units 103 and 104
Vibration is performed in the axial direction, that is, in parallel with the substrate 203. Here, when an angular velocity ω ₁ around the y-axis is applied, Coriolis force Fc is generated in the vibrating mass units 103 and 104 in the z-axis direction. As a result, the substrate 203 is moved in the z-axis direction perpendicular to the x-axis direction. It will also vibrate in the direction. The displacement in the z-axis direction can detect the angular velocity ω ₁ by measuring the capacitance generated between the substrate 203 and the vibrating masses 103 and 104.

In this conventional example, when the vibrating mass sections 103 and 104 are driven in opposite directions on the xy plane and an angular velocity ω ₁ about the y-axis is applied thereto, the vibrating mass sections 103 and 104 are driven. Generates Coriolis forces Fc in opposite directions in the z-axis direction, and the gap between the lower electrodes 201 and 202 and the vibrating mass portions 103 and 104 changes. Thus, the differential signals of the vibrating mass units 103 and 104 are received and an angular velocity signal is output. External noise generated in the same phase by such a differential configuration, for example, while eliminating the influence of the acceleration in the z-axis direction, but also enhance the detection sensitivity of the angular velocity omega _1.

[0005]

The conventional vibration type angular velocity sensor has the following problems. The vibration type angular velocity sensor is measured based on the measured value of the Coriolis force, and the Coriolis force Fc generated by vibrating the vibrating mass portion of the mass m at the speed v is represented by Fc = 2 × m × v × ω,
The displacement of the vibrating mass due to the Coriolis force and the strain of the beam caused by the displacement are measured as a change in capacitance, a change in resistance of a strain gauge, and a change in voltage due to the piezoelectric effect.

In general, in order to reduce the size of the angular velocity sensor, it is necessary to reduce the size of the vibrating mass and the beam supporting the vibrating mass. In particular, to detect a small angular velocity, a minute Coriolis force is detected. Must be able to do it. Therefore, an angular velocity sensor that detects displacement or distortion of the vibrating mass due to a small Coriolis force is required to have high sensitivity and high precision displacement detection performance.

FIG. 8 is a diagram showing the operation principle of the vibration type angular velocity sensor. For example, the oscillating mass shown in FIG.
0 μm × 200 μm × 10 μm single crystal silicon having a mass of about 1 μg. 600 μm length, 10 μm
A structure supported by two doubly supported beams made of single-crystal silicon having a width of 10 μm and a vibration mass portion having an amplitude of 10 μm
Vibration in the x-axis direction parallel to the substrate at pp, number of turns f = 20 kHz, angular velocity ω = 1 in the z-axis direction orthogonal to the x-axis
° / sec, the Q value is 1000, for example.
In this case, only a displacement of about 3 nm appears. This is only 0.3% when the angular velocity ω is 0 and the distance between the substrate and the vibrating mass part, that is, when the initial gap is 1 μm.
Is only the displacement of

Accordingly, in such a sensor requiring high sensitivity and high accuracy, an output may be generated even when the angular velocity ω is 0 due to a slight structural shift. In other words, when designing the structure of the angular velocity sensor, the structure is usually determined so that the output is 0 or a certain value is generated when the angular velocity ω is 0. Due to the non-uniformity of the force, the generation of thermal stress due to the temperature change, etc., the vibration does not always occur as designed, and there is a large possibility that the offset error varies from product to product. In particular, when designing a high-sensitivity, high-precision angular velocity sensor as described above, a measure against this variation becomes a serious problem.

FIG. 9 is a view showing the movement of the vibrating mass section of the prior art in which an offset has occurred. Mass part 1 shown in FIG.
Slight distortion of the support 102 supporting the 03 and 104,
Due to the non-uniformity of the electrostatic driving force and the distortion p caused by the thermal stress from the substrate 203, even a slight inclination of the vibrating surface results in a change in the gap with the substrate 203 and a zero angular velocity. However, an output signal is generated, and an offset is generated. Such an offset varies for each product, and in order to realize a high-accuracy angular velocity sensor, a state where a known angular velocity is applied to each product or an angular velocity ω = 0, Offset adjustment must be performed, which increases costs.

Even if such an offset adjustment is made during the manufacture of the product, the mechanical structure, for example, the spring constant of the beam supporting the vibrating mass portion, may change due to a change over time or a change in temperature during use of the product. It is also conceivable that the mechanical constant changes, and therefore the offset fluctuates.
In particular, in the case of using a signal from an angular velocity sensor to estimate the position of the own vehicle in a vehicle navigation system, it is necessary to obtain a low-offset angular velocity signal with high accuracy. It was difficult for the sensor to obtain a signal with low offset and low offset drift. The present invention has been made in view of such a problem of the related art, and has as its object to provide a highly accurate angular velocity sensor with extremely small offset.

[0011]

In order to achieve the above-mentioned object, the present invention has been made to solve the above problem by providing a vibrating mass having a vibrating mass disposed close to a substrate.
An offset error component independent of the Coriolis force may be calculated from the output signal values of the two vibrators, and an angular velocity signal obtained by subtracting the offset error component may be obtained. That is, a beam that connects the vibrating mass part and a fixing part that fixes the vibrating mass part, a drive electrode that vibrates the vibrating mass part,
A detection electrode for detecting the Coriolis force has the same mechanical specifications or characteristics, and calculates a signal output obtained by driving two vibrating mass units having different masses at the same amplitude and the same frequency. For example, as shown in FIG. 4, a vibrator A having a mass m vibrated at a frequency f and an amplitude a by a drive circuit 801.
The detection circuit A 803 and the detection circuit B 805 detect the change in the position of the vibrating surface that has been changed by receiving the Coriolis force generated by the vibrator B 804 due to the input of the angular velocity, and the two detected signals are calculated by the calculation circuit 806. An angular velocity sensor output is determined. From this output, calculate the offset error component that does not depend on the Coriolis force,
This is achieved by obtaining an angular velocity signal from which the offset error component has been subtracted.

Alternatively, said beam, said drive electrode, and said detection electrode have the same mechanical specifications or characteristics;
A signal output obtained by driving two vibrating mass units having the same mass at the same amplitude and different frequencies may be calculated, and an angular error signal may be obtained by subtracting an offset error component from the output. The angular velocity detecting means according to the first and second aspects includes, for example, the detecting circuit A and the detecting circuit B in FIG. 4 or FIG. 6, and the calculating means corresponds to the calculating circuit in FIG. 4 or FIG. Is what you do.

[0013]

By calculating the signal output from the two angular velocity detecting means, an offset error component irrelevant to Coriolis force caused by disturbance, temperature change, temporal change, etc. can be separated from the angular velocity signal. Thus, a highly accurate angular velocity signal can be obtained. Further, in addition to the above-mentioned common effects, as described later, the present embodiment also has effects unique to the first and second embodiments. That is, in the first embodiment, since the driving is performed by the vibrating mass unit using the same driving frequency and the same amplitude, the driving circuit can be shared. In the second embodiment, the two angular velocity detecting units are: Since exactly the same structure is applied, the structure can be simplified in comparison with the first embodiment.

[0014]

Embodiments of the present invention will be described with reference to the drawings. <First Embodiment> FIG. 1 is a plan view showing a first embodiment of the present invention. As shown in the drawing, the outer shape has a structure substantially similar to that of the conventional angular velocity sensor shown in FIG.
There is a difference between the masses of the two mass parts 503, 504. That is, the mechanical dimensions and characteristics of the sensor are exactly the same. In particular, when two structures having minute dimensions are formed adjacently on the same substrate by using a semiconductor manufacturing technique, it is possible to make the mechanical specifications, characteristics, and the like equal. .

FIGS. 2A and 2B are plan views illustrating the vibrating mass portions 601 and 602 having the same outer dimensions and different masses. The vibrating mass parts 601 and 602 have exactly the same thickness and outer dimensions, but 603 and 604 indicate holes, and the number of holes 603 of the vibrating mass part 601 is larger than the number of holes 604 of the vibrating mass part 602. The mass of the portion 601 is smaller than the mass of the vibrating mass portion 602. In this embodiment, it is assumed that a microstructure is formed by a surface micromachining manufacturing technique using a so-called sacrifice layer. The holes 603 and 604 have a free standing structure by removing the sacrifice layer by etching. It can also be used as an etching hole for forming.

FIGS. 3A and 3B show other vibrating mass portions 701 and 702 having the same outer dimensions and different masses.
FIG. This shows another structural example in which only the mass is changed without changing the external dimensions, and various structures other than FIGS. 2 and 3 are conceivable. For example, FIG.
In this example, a new weight 704 is added to the vibrating mass part, or only the mass is changed without changing the external dimensions without adding the weight. In any case, it is possible to change only the mass without affecting mechanical properties such as the spring constant for the beam supporting the vibrating mass.

Here, in FIGS. 2 and 3, the external dimensions of the mass part are equal or at least as equal as possible, but this is because the mechanical specifications of the two angular velocity sensors are close to each other. However, this is because the accuracy of calculating the offset error performed by the signal embedding means described later increases, but a slight difference in mechanical dimensions is allowed depending on the situation. Thus, the main object of the present invention is to provide two angular velocity detecting means having substantially the same external dimensions and differing only in the mass of the vibrating mass part, and to drive and detect the two angular velocity sensors as follows. Detection of an angular velocity with a small offset error can be performed.

FIG. 4 is a block diagram of the first embodiment of the present invention, illustrating drive, detection, and signal processing. A drive circuit 801 drives two vibrators having different masses, that is, a vibrator A 802 having a mass m and a vibrator B 804 (C is a proportional constant) having a mass Cm at a frequency f and an amplitude a. In this example, the drive frequency, that is, the detection frequency uses a frequency different from the resonance frequency of the vibrator A 802 and the vibrator B 804 in the detection direction (the direction in which the Coriolis force is generated). Driven vibrator A802, vibrator B804
The vibrating surface changes its position due to Coriolis force generated by inputting an angular velocity. This change is detected by the detection circuit A8.
03. The two signals detected and detected by the detection circuit B 805 are calculated by the calculation circuit 806, and finally the output of the angular velocity sensor is obtained.

Here, the maximum speed v _{A in} the driving direction of the vibrator A802 is given by: v _A = aω (1) where a is given by the drive amplitude and ω = 2πf is given by the drive frequency, where Then, a Coriolis force Fc shown in (Equation 2) is generated in the direction of the outer product of the velocity and the angular velocity vector.

Fc _A = 2 maΩΩ (Equation 2) The vibrating surface is tilted by the Coriolis force, and the change is converted into an electric signal by capacitance, distortion, or the like. At this time, as described above, it is expected that the vibrating surface slightly changes irrespective of the Coriolis force due to temperature change, disturbance, and the like.
This becomes an error offset signal of the sensor, and cannot be distinguished from the true angular velocity.

In this state, the detection signal A (output of A: Aou
t) can be represented as _{Aout = k 1 · 2maωΩ + OF} ... ( Equation 3).

Here, k ₁ is a proportionality constant when converting the Coriolis force into an output electric signal, and OF is an offset error.

On the other hand, since the vibrator B 804 having the mass Cm is also driven at the frequency f and the amplitude a, when the angular velocity Ω is input, a Coriolis force of Fc _B = 2 CmaωΩ is generated similarly to the vibrator A 802. At this time, it is expected that the vibrating surface slightly changes irrespective of the Coriolis force due to a temperature change, disturbance, or the like. However, the vibrator B804 is disposed close to the vibrator A802 on the same substrate. Since the mechanical specifications are almost the same, it is considered that a change in the vibrating surface due to a temperature change, a disturbance, or the like causes an offset error substantially equal to that of the vibrator A802, and the detection signal B (output of B: B
out) it is expressed as _{Bout = k 1 · 2CmaωΩ + OF} .

Therefore, (Bout-C)
· Aout) / (by computing 1-C), _{[(k 1 · 2CmaωΩ + OF)} -C (k 1 · 2maωΩ + OF) ] / (1-C) = OF ... ( Equation 4), and the temperature change, disturbance Thus, the inclination of the vibrating surface, that is, the offset generated independently of the Coriolis force can be calculated. And for example, if subtracted OF obtained in the Aout (Equation 4) (Equation 3), output proportional to the true angular velocity Omega, i.e., k ₁ · 2maωΩ is obtained. In the actual calculation, a method using analog electronic circuits,
Various methods such as a digital signal processing method are conceivable, but it suffices if Expression 4 is obtained as a result.

<Second Embodiment> FIG. 5 is a plan view showing a second embodiment of the present invention, and FIG. 6 is a block diagram of signal processing according to the second embodiment. It is an example. In Embodiment 1, only the mass is different 2
Although two vibrators A100 are used in the present embodiment, the two vibrators A100 have substantially the same mechanical structure and the same mass.
2. The transducers B1005 have the same amplitude and
By driving at different frequencies f and Cf and calculating two outputs, an angular velocity sensor capable of obtaining an angular velocity with a small offset error is realized. FIG. 5 shows the structure of the vibrator, and the mechanical structure conforms to the conventional example of FIG.
Description is omitted.

As in the first embodiment, the vibrator A1002,
The driving frequency of the vibrator B1005 is changed so that the vibrator B1005 is in a non-resonant state in the detection direction.
Set to C times 002. (Output of A: Aout) detection signal A of the transducer A1002 is represented by _{Aout = k 1 · 2ma · 2πf} · Ω + OF ... ( Equation 5), the output of the detection signal B (B of the oscillator B 1005:
Bout) is the drive frequency because C times as is represented by _{Bout = k 1 · 2ma · 2πCf} · Ω + OF ... ( Equation 6).

Here, if the calculation of (Bout−C · Aout) / (1−C) is performed by the calculation circuit 1007 in the same manner as in the first embodiment, [(k _{1 2} CmaωΩ + OF−C · (k ₁ 2maωΩ + OF) ] / (1-C) = OF (Equation 7), and it is possible to calculate the inclination of the vibrating surface, that is, the offset generated independently of the Coriolis force due to temperature change, disturbance, etc. For example, (Equation 5) ) Is subtracted from the offset error OF obtained by (Equation 7), an output proportional to the true angular velocity Ω, that is, k ₁ · 2
maωΩ is required.

[Brief description of the drawings]

FIG. 1 is a plan view showing a vibration type angular velocity sensor according to a first embodiment of the present invention.

FIG. 2 is a plan view illustrating a vibrating mass part according to the present invention having masses having the same external dimensions and different sizes.

FIG. 3 is a plan view illustrating another vibrating mass portion according to the present invention, which has a mass whose outer dimensions are equal and different.

FIG. 4 is a block diagram of a vibration type angular velocity sensor according to a first embodiment of the present invention.

FIG. 5 is a plan view showing a vibration type angular velocity sensor according to a second embodiment of the present invention.

FIG. 6 is a block diagram of a vibration type angular velocity sensor according to a second embodiment of the present invention.

7A is a plan view showing a conventional vibration type angular velocity sensor, and FIG. 7B is a sectional view taken along line AA of FIG.

FIG. 8 is a diagram illustrating an operation principle of the vibration type angular velocity sensor.

FIG. 9 illustrates the movement of a prior art mass with an offset.

[Explanation of symbols]

101, 106, 501, 506, 901, 906: Fixed part 102, 502, 902: Beam 103, 104, 503, 504, 903, 904: Vibrating mass part 105, 505, 905: Driving electrode 201, 202: Lower electrode 203: substrate 801, 1001, 1004 ... drive circuit 802, 804, 1002, 1005 ... vibrator 803, 805, 1003, 1006 ... detection circuit 806, 1007 ... arithmetic circuit

Claims (3)

[Claims] 1. A vibrating type for measuring the angular velocity by detecting a displacement of the vibrating mass or a displacement of a support for supporting the vibrating mass from a Coriolis force generated in a predetermined vibrating mass by application of an angular velocity. In the angular velocity sensor, two oscillating masses which are provided close to each other on the same substrate and have different masses; a beam connecting the oscillating masses and a fixing unit for fixing the oscillating masses; A drive electrode to be vibrated, and two angular velocity detecting means having a detection electrode for detecting the Coriolis force, wherein the beam, the drive electrode, and the detection electrode all have equivalent mechanical specifications or characteristics, The two angular velocity detecting means drive the respective vibrating mass sections with the same amplitude and at mutually equal frequencies other than the resonance frequency in the Coriolis force detection direction of the vibrating mass section. Detecting the velocity output, the vibration type angular velocity sensor this from the angular velocity output and calculates an offset error component that is independent of the Coriolis force, characterized by having a calculating means for obtaining an angular velocity signal obtained by subtracting the offset error component. 2. A vibration type for measuring the angular velocity by detecting a displacement of the vibrating mass section or a displacement of a support supporting the vibrating mass section from Coriolis force generated in a predetermined vibrating mass section by applying an angular velocity. In the angular velocity sensor, two vibrating mass portions provided close to each other on the same substrate and having the same mass, a beam connecting the vibrating mass portion and a fixing portion fixing the vibrating mass portion, and vibrating the vibrating mass A drive electrode to be driven, and two angular velocity detection means having a detection electrode for detecting the Coriolis force, wherein the beam, the drive electrode, and the detection electrode each have equivalent mechanical specifications or characteristics; The two angular velocity detecting means drive the respective vibrating mass sections at the same amplitude and at different frequencies other than the resonance frequency in the Coriolis force detection direction of the vibrating mass section, and drive the respective angular mass sections. Detecting a degree output, the vibration type angular velocity sensor this from the angular velocity output and calculates an offset error component that is independent of the Coriolis force, characterized by having a calculating means for obtaining an angular velocity signal obtained by subtracting the offset error component. 3. The vibration type angular velocity sensor according to claim 1, wherein the substrate is made of a semiconductor crystal.