JPWO2015145489A1 - Acceleration sensor and acceleration or vibration detection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly accurate acceleration sensor. When a first sensor 11 detects acceleration in a positive Z-axis direction (β direction), a weight body 12 of the first sensor 11 moves in a direction away from the substrate 3, and a second sensor 21 is moved. The weight bodies 22 are arranged to face each other so as to move in a direction approaching the substrate 3. The differential value is calculated | required by the differential amplifier (not shown) for the value detected from two sensors. Capacitive triaxial acceleration is obtained by arranging two sensors facing each other so that the axis vectors of all the detection axes of XYZ are correlated with physical acceleration, and obtaining a differential value of the detected values. Eliminate problems arising from sensor imbalances. [Selection] Figure 4

Description

  The present invention relates to an acceleration sensor, and more particularly to improvement in accuracy.

  FIG. 1 shows a conceptual diagram of a capacitance type small acceleration sensor 100 manufactured by a MEMS process (semiconductor microfabrication). In the small acceleration sensor 100, the weight body 12 is held in a floating state on the pedestal 13 so that it can be displaced in the direction of acceleration when the acceleration acts. When the weight body 12 is displaced, the capacitances of the regions 111, 113, 114, 115, 116, and 117 change. By detecting these, accelerations in the three-axis directions of the X, Y, and Z axes are detected. Specifically, the capacity difference between the areas 111 and 113 is detected in the X-axis direction, the capacity difference between the areas 114 and 116 is detected in the Y-axis direction, and the capacity difference between the areas 115 and 117 is detected in the Z-axis direction. By detecting, the acceleration in the triaxial direction can be detected.

  Such a small acceleration sensor has an advantage that it can be miniaturized, but has a problem that accuracy is poor compared to a servo acceleration sensor.

  Japanese Unexamined Patent Application Publication No. 2013-7743 discloses a structure in which a plurality of electrodes are installed in the horizontal direction in order to improve accuracy.

  However, just as N sensors are multiplexed as in the above publication, the noise level is improved only by about 1 / √N.

  An object of the present invention is to solve the above problems and provide a highly accurate small acceleration sensor.

  (1) An acceleration sensor according to the present invention includes a first acceleration sensor, a second acceleration sensor arranged so that a detection axis direction faces the first acceleration sensor, and detection from the first acceleration sensor. A differential value detection unit that obtains a differential value between the value and a detection value from the second acceleration sensor. Therefore, it is possible to increase the detected acceleration while removing electrical noise that is in phase. Therefore, a highly accurate acceleration sensor can be provided.

  (2) In the acceleration sensor according to the present invention, two acceleration sensors having unbalanced detection characteristics in the displacement direction are used as the first and second acceleration sensors. Therefore, even if the acceleration sensor has an unbalanced detection characteristic in the vibration direction, it is possible to provide a highly accurate acceleration sensor as a whole.

  (3) In the acceleration sensor according to the present invention, the opposed axis is a Z-axis. Therefore, self-noise that has a high probability of being an in-phase signal can be canceled.

  (4) In the acceleration sensor according to the present invention, the first acceleration sensor and the second acceleration sensor are three-axis acceleration sensors, and the X-axis and the second axis of the first three-axis acceleration sensor. 90 degrees in the Z-axis direction so that the Y-axis of the three-axis acceleration sensor faces each other and the Y-axis of the first three-axis acceleration sensor faces the X-axis of the second three-axis acceleration sensor It is rotated and placed. Therefore, a highly accurate three-axis acceleration sensor can be provided.

  (5) In the acceleration or vibration detection method according to the present invention, the second acceleration sensor is arranged so that the detection axis direction faces the first acceleration sensor, and the detection value from the first acceleration sensor; A differential value with respect to a detection value from the second acceleration sensor is obtained. Therefore, the detected acceleration is increased while removing the electrical noise that is in phase. Therefore, highly accurate acceleration or vibration can be detected.

  In the present specification, “determining a differential value” means obtaining a difference between two detection values with the other detection value relatively in phase with respect to one detection value. In the present embodiment, this is realized by a differential circuit. However, any differential detection method may be used.

  Further, “the detection axis directions oppose” means that, as shown in the embodiment, the plus direction of one axis and the minus direction of the other axis are the same direction.

It is a conceptual diagram of the capacitance-type acceleration sensor produced by the conventional MEMS process. 1 is a diagram illustrating a structure of an acceleration sensor 1. FIG. 2 is a conceptual diagram showing a structure of a first sensor 11. FIG. It is a figure which shows the state arrange | positioned facing Z-axis direction. It is a functional block diagram which performs detection in an XYZ axis. It is a figure which shows the detection state of the acceleration of a X-axis direction. It is a comparative graph of noise resistance between the acceleration sensor 1 and a conventional acceleration sensor.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 2 shows an acceleration sensor 1 according to one embodiment of the present invention. The acceleration sensor 1 is an acceleration sensor that detects acceleration in XYZ triaxial directions, and includes a first sensor 11, a second sensor 21, and a signal processing unit 31.

The signal processing unit 31 obtains a differential value between the acceleration value detected by the first sensor 11 and the acceleration value detected by the second sensor 21. Specifically, it has three differential amplifiers and three filters for obtaining respective differential values for each acceleration in the XYZ directions detected by the first sensor 11 and the second sensor 21. Details will be described later.

  The structure of the first sensor will be described with reference to FIG. The first sensor 11 is a capacitance-type acceleration sensor that detects acceleration in three axial directions based on the variation in capacitance due to the relative acceleration of the mover with respect to the stator, as in the past.

  In FIG. 3, the conceptual diagram for demonstrating the acceleration detection method in the 1st sensor 11 is shown. The weight body 12, which is a mover, is held in a floating state on a pedestal 13, which is a stator, so that it can be displaced in the direction of acceleration when an acceleration acts. When the position of the weight body 12 is displaced, the capacitances 14, 15, and 16 formed by the weight body 12 and the pedestal 13 change. A displacement measuring unit (not shown) detects such a change in capacitance, and thereby detects acceleration in the XYZ axis directions.

  The structure of the second sensor 21 is the same as that of the first sensor 11, and similarly the acceleration in the XYZ axis directions is detected.

  The arrangement relationship between the first sensor 11 and the second sensor 21 will be described with reference to FIG. As shown in FIG. 3, the first sensor 11 is arranged so as to coincide with the XYZ axes of the substrate 3. In FIG. 2, only the capacitors 11X1 and 11X2 in the X-axis direction and the capacitors 11Y1 and 11Y2 in the Y-axis direction are schematically shown by broken lines. FIG. 2B is an arrow view from the direction of arrow α in FIG. 2A. An arrangement procedure of the second sensor 21 will be described with reference to FIG. 2C. First, the second sensor 21 is arranged in the same manner as the first sensor 11, this is inverted about the Y axis, and is further rotated by −90 degrees around the center 21 </ b> C of the second sensor 21. This is disposed on the back side of the substrate 3. As a result, as shown in FIG. 4, the first sensor 11 and the second sensor 21 face each other with the substrate 3 interposed therebetween, that is, the first sensor 11 increases the acceleration in the Z-axis plus direction (FIG. 4, β direction). When detecting, the weight body 12 of the first sensor 11 moves in a direction away from the substrate 3, and the weight body 22 of the second sensor 21 moves in a direction approaching the substrate 3.

  With reference to FIG. 5A, the signal processing unit 31 for obtaining the differential value of the detection values of the two sensors in the Z-axis direction will be described. The first sensor measurement unit of the first sensor 11 is based on the difference between the capacitance 11Z1 and the reference capacitance 11Z2 shown in FIG. 4, and the second sensor measurement unit of the second sensor 21 is based on the difference between the capacitance 21Z1 and the reference capacitance 21Z2. , The acceleration in the Z-axis direction is detected. The differential amplifier 31SZ shown in FIG. 5A determines the differential value of the detected acceleration. The filter 31FZ cuts a predetermined high frequency among the obtained differential values and outputs a Z-axis signal. That is, when the acceleration sensor 1 detects the acceleration in the β direction or the γ direction in FIG. 4, the acceleration sensor 1 outputs a Z-axis signal as shown in FIG. 5A.

  Similarly, for the detection in the X-axis direction and the Y-axis direction, the differential value of the values detected from the two sensors is obtained by a differential amplifier (see FIGS. 5B and 5C). The relationship between the two sensors is as follows. The arrangement of the capacitors for detecting the X-axis direction and the Y-axis direction is such that the capacitor 21X2 of the second sensor 21 and the capacitor 11Y1 of the first sensor 11 are the second sensor 21 when viewed from the upper surface direction of the substrate in FIG. The capacitance 21Y1 of the first sensor 11, the capacitance 11X2 of the first sensor 11, the capacitance 21X1 of the second sensor 21, the capacitance 11Y2 of the first sensor 11, and the capacitance 21Y2 of the second sensor 21 and the capacitance 11X1 of the first sensor 11 They are arranged so as to face each other.

  Therefore, when acceleration is applied to the weight body 12 as shown in FIG. 6, the acceleration in the X direction detected by the difference between the capacitance 11X1 and the capacitance 11X2 of the first sensor 11 is It is detected by the difference between 21Y1 and the capacity 21Y2. In FIG. 6, the substrate 3 is omitted.

  As shown in FIG. 5B, the acceleration in the X-axis direction detected by the difference between the capacitance 11X1 and the capacitance 11X2 in the first sensor 11 and the difference between the capacitance 21Y1 and the capacitance 21Y2 of the second sensor 21 are used. In addition, detection values from the first sensor measurement unit and the second sensor measurement unit are obtained, and a differential value thereof is obtained as a differential value in the X-axis direction.

  The same applies to the Y-axis direction.

  In this way, the acceleration sensor 1 detects acceleration in the XYZ axis directions (three axes) using the two sensors. FIG. 7 shows a comparison graph of dark noise when only the first sensor 11 is used and when two first sensors 11 and two second sensors 21 are used. Compared to one case, the noise resistance is clearly improved.

  Although the reason why the noise resistance is improved is not clear, the inventor considered as follows. In general, as shown in FIG. 4, the capacitance type acceleration sensor has an operation fulcrum 11g and a gravity center 12g shifted from each other. As described above, there is a risk that a component due to self-microvibration may be detected because the center of gravity on the operation fulcrum is shifted from the center of gravity of the weight. Further, in the Z-axis direction, the detection characteristics are unbalanced in the upward direction and the downward direction. On the other hand, in the acceleration sensor 1, the two sensors are arranged so that the XYZ detection axis directions face each other. As a result, the vibration signal is output as an opposite phase signal by the two sensors. Such an antiphase signal also has the above detection characteristics reversed. Therefore, the detection accuracy is improved as compared with a case where a plurality of sensors are simply arranged in parallel. In addition, the sensor output for subtracting the opposite phase is twice that of the original sensor being used, and the electrical noise has a high probability of being an in-phase signal, and is reduced by subtraction in the differential circuit. Therefore, noise resistance is also improved.

  As described above, the two vectors are arranged opposite to each other in a state in which the axis vectors of all the detection axes of XYZ have a correlation with the physical acceleration, and the above-mentioned unbalance is obtained by obtaining the differential value of the detection values. The problem that arises from the problem can be solved.

  In addition, the XY axis of the representative capacitance type triaxial acceleration sensor shown this time uses the left and right capacitance difference, but the Z axis is the difference from the reference capacitance. Therefore, the noise component can be canceled.

  In addition, the capacitance type acceleration sensor has problems such as a large DC drift due to temperature influence. With respect to these problems, the components generated in the same phase can be canceled by obtaining the differential value, and stable vibration measurement can be performed with low noise.

(2. Other embodiments)
In the present embodiment, the case where the present invention is applied to a capacitance type triaxial acceleration sensor has been described. However, if the acceleration sensor is deviated from the center of gravity of the holding mechanism, the capacitance sensor is not limited to the capacitance type. Even if it is a piezoelectric type etc., it is applicable similarly.

  In the present embodiment, the case of three axes has been described, but the present invention can be similarly applied to a uniaxial acceleration sensor.

  In the present embodiment, the case where the present invention is applied to a general capacitive three-axis acceleration sensor has been described, but the present invention can also be applied to a comb electrode capacitive acceleration sensor.

11 First Sensor 21 Second Sensor 31 Signal Processing Unit 31SZ Differential Amplifier 31SX Differential Amplifier 31SY Differential Amplifier

Claims (5)

A first acceleration sensor;
A second acceleration sensor arranged so that a detection axis direction faces the first acceleration sensor;
A differential value detection unit for obtaining a differential value between a detection value from the first acceleration sensor and a detection value from the second acceleration sensor;
Accelerometer with The acceleration sensor according to claim 1.
Two acceleration sensors having unbalanced detection characteristics in the displacement direction are used as the first and second acceleration sensors.
Acceleration sensor featuring The acceleration sensor according to claim 1 or 2,
The opposing axis is the Z axis;
Acceleration sensor featuring In the acceleration sensor in any one of Claims 1-3,
The first acceleration sensor and the second acceleration sensor are three-axis acceleration sensors, the X-axis of the first acceleration sensor and the Y-axis of the second acceleration sensor are opposed to each other, and the first Rotating at 90 degrees in the Z-axis direction so that the Y-axis of one acceleration sensor and the X-axis of the second acceleration sensor face each other,
Acceleration sensor featuring The second acceleration sensor is arranged so that the detection axis direction faces the first acceleration sensor,
Obtaining a differential value between a detection value from the first acceleration sensor and a detection value from the second acceleration sensor;
An acceleration or vibration detection method characterized by the above.