JP3036675B2 - Method for correcting nonlinearity of capacitance type acceleration 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 method for correcting non-linearity of an acceleration sensor using a change in capacitance capable of simultaneously detecting accelerations on two or more axes. The present invention relates to a method for correcting non-linearity of a capacitive acceleration sensor capable of realizing a three-axis acceleration sensor which is corrected so as not to cause interference between axes and not change due to temperature.

[0002]

2. Description of the Related Art For example, Japanese Patent Application Laid-Open Nos. 4-148833 and 4-33743 disclose capacitive acceleration sensors.
No. 1, Japanese Patent Application Laid-Open No. Hei 5-18879 discloses that a plurality of pairs of capacitance elements are provided on opposite surfaces of a fixed substrate and a flexible substrate and electrodes are attached to each other, and an XY parallel to the substrate surface is provided. A plane is set, and changes in acceleration in the three-dimensional directions of the X, Y, and Z axes of the Z axis orthogonal to the plane are calculated based on capacitance changes between a plurality of pairs of capacitance elements. There has been proposed a configuration for performing detection.

For example, as shown in a vertical section of FIG. 1B, a fixed substrate 11 diametrically arranged in a cylinder 10 and a flexible substrate 12 arranged in parallel at a predetermined interval to the fixed substrate 11 are provided. As shown in FIG. 1A showing the lower surface of the
To 5 to form the capacitance elements C _{1 to} C ₅ . An actuator 13 having an appropriate mass is provided on the lower surface of the flexible substrate 12.

In detail, here, four pairs of electrodes are provided on the outer peripheral portion between the opposing surfaces, and one pair of electrodes are provided
Configuration to form a ₁ -C _5, i.e., perpendicular with the electrode surface X, each two capacitances arranged on two axes of Y element C
And ₁ -C _4, consisting of construction of arranging the capacitive element C ₅ in the middle of the previous two axes. In the above-described configuration, when acceleration is applied in the X-axis direction, as shown in FIG.
Since the distance between each of the electrodes 1 to 5 between the surfaces facing the flexible substrate 12 and the flexible substrate 12 changes, the capacitance of each of the capacitance elements C _{1 to} C ₄ changes. Also, as shown in FIG. 2B, the capacitance of each of the capacitance elements C _{1 to} C ₄ similarly changes when acceleration is applied in the Z-axis direction.

The detection of each component of the acceleration based on the change in the capacitance is performed, for example, as an output with respect to the acceleration in the X-axis direction, a capacitance difference (C ₁ -C ₃ ) between the capacitance elements C ₁ and C ₃ , As outputs for the acceleration in the Y-axis direction, the capacitance elements C ₂ and C ₄
Is detected as the capacitance (C ₅ ) of the capacitance element C ₅ as an output with respect to the capacitance difference (C ₂ −C ₄ ) and acceleration in the Z-axis direction. With respect to the applied acceleration, the amounts of change d _{1 to} d _{5 of the} distances between the electrodes are proportional to the acceleration. That is, the capacitance change amount Cj can be expressed by the following equation. However,
ε = dielectric constant, S: electrode area, d ₀ ; initial value of electrode gap.

[0006]

(Equation 1)

[0007]

[SUMMARY OF THE INVENTION However, in the electrostatic capacitance type acceleration sensor having the above configuration, the capacitance element C ₁ -C ₅
The output of the X-, Y-, and Z-axes calculated with an electric signal proportional to the capacitance of the above has a problem in that it does not have strictly linearity with respect to acceleration. Further, in this case, there is a problem that the sensitivity of the X and Y axis outputs depends on the Z axis output. When the initial value d ₀ of the electrode gap changes due to a temperature change or the like, sensitivity shifts in the X, Y, and Z axes occur in addition to the zero point shift in the Z axis.
There is a problem.

Further, in the capacitance type acceleration sensor having the above-described structure, even when the calculation is performed using an electric signal inversely proportional to the capacitances C _{1 to} C ₅ , the stray capacitance other than the capacitance of the sensor cannot be ignored. Then, the various problems described above occur.

The present invention solves the above-mentioned problem of the conventional capacitance type acceleration sensor, corrects the nonlinearity of the output with respect to acceleration, eliminates interference between the X, Y, and Z axes, and reduces the temperature. It is an object of the present invention to provide a method for correcting non-linearity of a capacitance type acceleration sensor that can realize a three-axis acceleration sensor without change.

[0010]

That is, the present invention provides:
An electrode is attached to each opposing surface of the fixed substrate and the flexible substrate, and a plurality of pairs of capacitance elements are provided opposite to each other.An XY plane parallel to the substrate surface is set, and a Z-axis X orthogonal to the plane is set. , Y, the change in acceleration in the three-dimensional direction of the Z-axis, in the capacitive acceleration sensor that detects each X, Y, Z-axis direction component based on the capacitance change between a plurality of pairs of capacitance elements, When calculating the difference between the electric signals of each capacitive element in the axial direction and detecting each of the X, Y, and Z components in the axial direction, the respective electric signals are subjected to acceleration by acceleration before the difference calculation. Change in distance between electrodes of capacitance element
This is a method for correcting non-linearity of a capacitance type acceleration sensor, wherein a correction operation is performed to a value proportional to an amount .

[0011] Further, according to the present invention, in the above structure,
An electrostatic capacitance type acceleration sensor is provided in which a plurality of pairs of capacitance elements are provided on the outer surface of the opposing surface and one pair is provided at the center of the opposing surface by mounting electrodes on the opposing surfaces of the fixed substrate and the flexible substrate. A non-linearity correction method for a certain capacitive acceleration sensor is also proposed. Further, in the above configuration, when there is a temperature change of the initial value d ₀ of the gap between the electrodes, the change is not affected by the acceleration and the change due to the temperature is a separate capacitance similar to the change of d _0. Non-linearity of an electrostatic capacitance type acceleration sensor, wherein a correction operation is performed using an element, and a correction operation is performed from a difference output of an electric signal of each capacitance element. Is also proposed.

[0012]

The present inventors have studied variously for the purpose of correcting non-linearity of a capacitive acceleration sensor that can realize a three-axis acceleration sensor without interference between X, Y, and Z axes and no change due to temperature. As a result, an electric signal of the capacitance element C ₁ -C ₅ described above (C
Before performing the difference calculation of 1-C3) and (C2-C4), the respective electric signals are corrected and calculated to a value proportional to the amount of change in the distance between the electrodes of each capacitance element due to acceleration, and then the difference calculation is performed. By doing so, it was found that the linearity of the output could be ensured, and the outputs of the X, Y, and Z axes could be completely separated, and the present invention was completed.

Further, the present inventors have found that when there is a temperature change of the initial value d ₀ of the electrode gap of the capacitance element, the change due to temperature is not affected by the acceleration, and the change due to temperature is the same as the change of d ₀ .
By using the capacitive element C ₆ of, Z-axis output can also linearity secured including, interference between the axes without no change with temperature was found that can be realized three-axis acceleration sensor. Further, a differential output of electric signals V _{1 to} V ₆ proportional to the capacitance elements C _{1 to} C ₆ , Vx = V ₁ −V ₃ , V _Y = V ₂ −
From V ₄ , V _Z = V ₅ -V ₆ , and V ′ _Z = V ₅ , it was found that an output with good linearity and no interference between axes and no temperature change was obtained.

The operation of the method of the present invention will be described in detail below along with the calculation formula. Here, the capacitance element C shown in FIG.
Description will be given of a configuration having ₁ -C _5. FIG. 3A shows the capacitance element gap distance d ₀ when no acceleration is applied at room temperature of the capacitance element. FIG. 3B shows the X axis and the Z axis direction when there is a change d _{t in the} capacitance element gap due to temperature. to show a state in which acceleration is applied, in FIG., the gap distance of the electrostatic capacitance element C ₂ is _{d 0 + d t + d z} -d x, gap distance of the electrostatic capacitance element C ₄ is d ₀ + d _t + D _z +
a d _x, the gap distance of the electrostatic capacitance element C ₅ is d ₀ + d _t
+ D _z . Hereinafter, when a temperature change and an acceleration are applied, this definition is used. The case of obtaining an electric signal V ₁ ~V ₅ in proportion to the capacitance of the capacitance element C ₁ -C ₅ below.

[0015]

(Equation 2)

D = d ₀ + d _t + d _z K = constant of CV conversion d ₀ = capacitance element gap distance when no acceleration is applied at room temperature d _t = change amount of capacitance gap distance due to temperature d _z = Z axis the amount of change in capacitance gap distance by the X-axis (Y-axis) direction acceleration change amount of the capacitance gap distance by direction acceleration d _j = capacitance _{C j {j = 1.2.3.4} d} 1 = -d 3 _{d 2 = -d 4 C 0 j} = parasitic capacitance a = ε × S (ε = dielectric constant, S = electrode area) where and rearranging the d _j of equation (1) becomes (2).

[0017]

(Equation 3)

By substituting equation (2) with equation (2 ′), appropriate α,
β is determined logically or from measured data. Obtained α
_The X-axis acceleration AX is obtained from Expression (3) using _j and β _j .

[0019]

(Equation 4)

[0020]

(Equation 5)

The Y-axis acceleration Ay is given by equation (4). By the way, from d ₁ + d ₃ = 0 and d ₂ + d ₄ = 0, d ₁ + d ₂ +
d ₃ + d ₄ = 0.

[0022]

(Equation 6)

[0023]

(Equation 7)

If there is no change d _t due to temperature, L ₃ d
_{Since 0} is a constant, the Z-axis acceleration Az can be obtained from equation (5). Assuming that the change due to temperature is the sixth capacitance C ₆ that changes the same as _dt , equation (6) is obtained. Next, the expression (6) is substituted into the expression (5) to obtain the expression (7) of the Z-axis acceleration Az.
Equation (7) is an output that is not affected by temperature. Where L
_{1, L 2, L 3,} L 4 is a proportionality constant.

[0025]

(Equation 8)

Hereinafter, a case where electric signals V _{1 to} V ₅ proportional to the reciprocals of the capacitances of the capacitance elements C _{1 to} C ₅ will be described.

[0027]

(Equation 9)

Here, D = d ₀ + d _t + d _z d ₀ = capacitance element gap distance when no acceleration is applied at room temperature d _t = change in capacitance gap distance due to temperature d _z = capacity gap due to Z-axis acceleration Distance change amount _dj = Capacitance C _j {j = 1,2,3,4} Change amount of capacitance gap distance due to acceleration in the X-axis (Y-axis) direction d ₁ = −d ₃ d ₂ = −d ₄ C _oj = parasitic capacitance A = ε × S (ε = dielectric constant, S = electrode area) K = constant of electric circuit

Since d _j is proportional to the acceleration in the j direction, G _j = M _dj . (M is a constant) (9) Expression (8 ′) is obtained from Expression (8), and Expression (8 ′) is converted to (8 ″).
Appropriate α and β are obtained logically or from actual measurement data by using equations. Using the obtained α _j and β _j , the X-axis acceleration Ax is given by the following equation (10).

[0030]

(Equation 10)

[0031]

[Equation 11]

The Y-axis acceleration A _Y is obtained by equation (11).
By the way, from d ₁ + d ₃ = 0 d ₂ + d ₄ = 0, d ₁ + d ₃ = 0
d ₂ + d ₃ + d ₄ = 0.

[0033]

(Equation 12)

[0034]

(Equation 13)

[0035] When the change with temperature is not the electrode gap, A _Z is obtained by so L ₃ d ₀ is a constant (12). Assuming that the change due to the temperature is the sixth capacitance C ₆ that changes the same as _dt , d _t + d ₀ is given by the following equation (13).

[0036]

[Equation 14]

Then, by substituting equation (13) into equation (12), the Z-axis acceleration _AZ can be obtained from equation (14). Equation (14) is an output that is not affected by temperature. Where L ₁ ,
L ₂ , L ₃ and L ₄ are proportional constants.

[0038]

(Equation 15)

When the differential output of the electric signals V _{1 to} V ₆ proportional to the capacitance elements C _{1 to} C ₆ is expressed by the following equation (15), the following equation (1) is obtained.
Equations 6) and (17) are obtained.

[0040]

(Equation 16)

[0041] Next When _{d t = 0 d z = V} 5 output V _'5 in which V ₅ output was adjusted to be 0 when the 0,
When the equation (18) is obtained and the equation (18) is modified, the equation (19) is obtained.

[0042]

[Equation 17]

By substituting the equation (19) into the equation (15) and rearranging the quantity d _x proportional to the acceleration, if D ₂ 2d _x ² can be considered, the equations (15) and (16) are approximated. Equation (2
Expressions (0) and (21) can be used instead.

[0044]

(Equation 18)

Substituting equation (19) into equation (20) and equation (21) and equation (12) into equation (17), d _x , d _y , and d _z , respectively.
Is solved, the equations (22), (23) and (24) are obtained.

[0046]

[Equation 19]

Therefore, from theoretically and actually measured data, α,
Using β, the accelerations A _X , A _Y , and A _Z in the X, Y, and Z axes are
Expressions (25), (26), and (27) are obtained.

[0048]

(Equation 20)

If d ₀ ² ≫d _x ² cannot be considered, (1
Substituting equation (19) into equations (5) and (16), dx, dy,
Solving for dz gives equations (28) and (29), and an exact solution can be obtained.

[0050]

(Equation 21)

[0051]

(Equation 22)

When there is no change due to the temperature or when it can be ignored, d _t = 0 and V _Z = V ′ ₅
(25), (26), (27), (28),
An equation in which V ′ ₅ = V _Z is substituted for the equation (29) may be used.

[0053]

【Example】

Example 1 A capacitance type three-axis acceleration sensor having the configuration shown in FIG. 1 was manufactured, the nonlinearity of the output voltage was confirmed, and a correction operation according to the present invention was performed. As the CV conversion of the signal processing circuit, one that outputs a voltage proportional to the amount of change in capacitance was used. FIG. 4 shows how the gravitational acceleration is detected when the acceleration sensor is rotated about the X axis.
X, Y and Z axis output voltages (V _X = V ₁ −V ₃ , V _Y = V ₂ −
V ₄ , V _Z = V ₅ ) and a rotation angle. The X-axis output is indicated by □, the Y-axis output is indicated by +, and the Z-axis output is indicated by Δ.
When the rotation angle is 0 degrees, -1 G is added in the Z-axis direction and 0 G is added in the X and Y-axis directions. Acceleration is always applied at 0G in the X-axis direction, sin in the Y-axis direction, and -cos in the Z-axis direction.

It can be seen from the graph of FIG. 4 that the nonlinearity shown in equation (1) actually appears. Y-axis output is Z
The shape is shifted from sin due to the influence of the axial acceleration. Graph of uncorrected (+ sign) of FIG. 5 is the relationship between acceleration and Y-axis output V _Y are applied to the calculated from the rotation angle Y-axis direction. From this graph, it can be seen that Y
It can be seen that the linearity of the shaft output has been lost.

Embodiment 2 FIG. 5 shows the correction coefficients α of the equations (25), (26) and (27) using the differential outputs V _X , V _Y and V _Z of the electric signals V _{1 to} V ₅ . After obtaining β and correcting the Y-axis output when performing the correction (□
Mark). The effect of the Z-axis acceleration was eliminated, and the characteristics became almost completely linear with respect to the acceleration.

[0056]

According to the present invention, in a capacitance type acceleration sensor, the electric signal difference of one set of elements in the X-axis direction and the electric signal difference of one set of elements in the Y-axis direction are obtained from the electric signals of a plurality of capacitance elements. When calculating the electrical signal difference, the linearity of the output is ensured by correcting each electrical signal to a value proportional to the acceleration and then performing the difference operation, thereby ensuring the linearity of the output. The linearity with respect to the acceleration can be obtained also when dealing with or when the influence of the parasitic capacitance cannot be ignored.

Further, according to the present invention, even in the above case, the sensitivity of the XY axis output does not depend on the Z axis output.
Even if the initial value of the gap distance changes due to temperature change, etc.,
There is an advantage that zero point shift and sensitivity shift can be eliminated, there is no interference between axes, and there is no change due to temperature.
An axial acceleration sensor can be realized.

[Brief description of the drawings]

FIG. 1A is an explanatory view showing a lower surface of a fixed substrate of a capacitive acceleration sensor, and FIG. 1B is a longitudinal sectional view of the capacitive acceleration sensor.

FIG. 2A is a vertical cross-sectional view of a capacitive acceleration sensor showing a state in which acceleration in the X-axis direction is applied; FIG. 2B is a longitudinal sectional view of the capacitive acceleration sensor showing a state in which acceleration in the Z-axis direction is applied; FIG.

FIG. 3A is an explanatory diagram showing a capacitance element gap distance d ₀ when no acceleration is applied at room temperature of the capacitance element;
B is an explanatory diagram showing a state where acceleration is applied in the X-axis and the Z-axis directions when there is a change _{dt in the} capacitance element gap due to temperature.

FIG. 4 is a graph showing a relationship between a rotation angle and an output showing a state of detecting a gravitational acceleration when the acceleration sensor is rotated around the X axis.

FIG. 5 is a graph showing a relationship between acceleration and output before and after correction.

[Explanation of symbols]

1,2,3,4,5 electrode 10 cylindrical 11 fixed substrate 12 flexible substrate 13 operating element C ₁ -C ₅ capacitive element

Claims (4)

(57) [Claims] A plurality of pairs of capacitance elements which are provided opposite to each other by providing electrodes on opposite surfaces of the fixed substrate and the flexible substrate,
Set the XY plane parallel to the substrate surface and set the Z axis
A capacitive acceleration sensor that detects changes in acceleration in the three-dimensional X, Y, and Z axes based on changes in capacitance between a plurality of pairs of capacitive elements. Calculate the difference between the electric signals of each capacitive element in the axial
When detecting the X-, Y-, and Z-axis components, each of the electric signals is converted to the electric power of each capacitance element by acceleration before calculating the difference.
A method for correcting non-linearity of a capacitance type acceleration sensor, wherein a correction operation is performed to a value proportional to a change amount of a gap distance . 2. An electrostatic capacitor comprising: a plurality of pairs of capacitance elements provided on opposite surfaces of a fixed substrate and a flexible substrate, each of which is provided with an electrode; 2. The method for correcting nonlinearity of a capacitive acceleration sensor according to claim 1, wherein the capacitive acceleration sensor is a capacitive acceleration sensor. 3. The method of claim 2, when there is a temperature change in the initial value d ₀ of the gap between the electrodes is not affected by the acceleration, additional capacitance device similar to the change in the change with temperature d ₀ A method for correcting non-linearity of a capacitance type acceleration sensor, wherein the correction calculation is performed using 4. The method according to claim 3, wherein a correction operation is performed from a difference output of an electric signal of each capacitance element.