JP6028193B2 - Multi-axis gravity sensor - Google Patents

Description

  The present invention relates to a gravity sensor that detects a change in gravity acting on a piezoelectric piece as a change in the oscillation frequency of the piezoelectric piece, and in particular, a plurality of sensor units composed of piezoelectric pieces in a predetermined position on a common base. The present invention relates to a multi-axis gravitational sensor that can measure the relative change in gravitational acceleration with high accuracy.

  A high-sensitivity gravity sensor using MEMS technology is used as a means for detecting a change in gravitational acceleration on the earth or other planets and remotely searching for resources buried underground or under the seabed. For example, Patent Document 1 and Patent Document 2 disclose known techniques for remotely performing resource exploration using a gravity sensor.

  In this field, as a gravitational acceleration sensor, a mechanical type in which a weight is suspended by a coil spring or a leaf spring and a spring expansion / contraction amount corresponding to a change in gravity is widely used. Such a gravity sensor is large in size. The gravity sensor here detects not only the direction of gravity but also the total amount of change at a specific position (not only the deviation from the value at the level, but also the change between the target position and its surroundings). In this specification, the detection of gravity on the earth will be described as an example.

  Various methods are known for gravity measurement sensors other than the mechanical type described above, but the gravity measurement newly developed by the present inventors using the fact that the resonance frequency of piezoelectric materials changes due to the change of gravity. There are the following measuring devices similar to sensors.

  That is, Patent Document 3 discloses a QCM probe (quartz balance) that uses a piezoelectric substance such as a quartz piece and measures a mass change of the substance attached to the quartz piece by a change in vibration frequency. This QCM probe uses a sensor unit composed of a piezoelectric element (quartz piece) supported in a cantilever manner. The piezoelectric element is distorted by the gravity change due to the adhesion of the substance, and the change in mass (change) Value).

JP 2002-40155 A JP 2000-206266 A WO97 / 04314

  In the gravity sensor under development, as a gravity sensor using a piezoelectric material, a piezoelectric material typified by quartz is processed into a thin piece, and an appropriate electrode is provided on the front, front, back, or fixed member side, and one end thereof is a piece. The sensor unit is composed of a vibrating element that is held and supported, and is enclosed in a suitable container. This sensor unit is arranged at a predetermined angle with respect to the earth axis (straight line passing through the center of the earth), and the vibration output of the vibration element constituting the sensor unit according to gravity change is applied to an oscillator, and the oscillation frequency The frequency deviation based on the change is calculated by the data processing means, and the amount of change in gravity (change value) is detected from the calculation result.

However, in a so-called uniaxial gravity sensor using one sensor unit for gravity measurement using a piezoelectric piece, the limit is 5 mgal, and it is difficult to detect a change in gravity more precisely than that. In particular, it is difficult to measure a gravity change value with a high precision with a single digit accuracy, for example, a value of 0.1 mgal. In the configuration of the so-called multiaxial gravity sensor comprising a plurality of the sensor unit, arranged for each of the plurality of sensor units to the Earth's axis is placed accurately at a predetermined angle and a predetermined posture and at a predetermined positional relationship with each other There is a problem that it is not easy to do.

An object of the present invention is to provide a multi-axis gravity measuring sensor that can measure the relative value of gravity change with high accuracy of 0.1 mgal as described above, has design margin, is easy to manufacture, and is low in cost. is there. In addition, there is provided a multi-axis gravity measuring sensor in which each of a plurality of sensor units is easily installed with a predetermined angle and a predetermined attitude with respect to the earth axis and arranged in a predetermined positional relationship with each other. This is also an object of the present invention.

  In order to achieve the above object, the present invention provides a plurality of uniaxial gravity measuring sensor units installed at a predetermined angle and a predetermined attitude arbitrarily selected with respect to the ground axis, and the plurality of uniaxial gravity measuring sensors. A common base (hereinafter simply referred to as a base) that can fix the sensor unit accurately and reliably is used. As this base, a polygonal column, cylinder, with a fixed surface (facet: sensor unit fixed surface) on which an arbitrary number of uniaxial gravity measuring sensor units of three or more surfaces are installed and a base plane with respect to the ground axis, This is achieved by using a metal material (a metal block is preferable) that can be easily processed precisely for forming the sensor unit fixing surface and the reference surface. The metal material constituting the common base is preferably aluminum, copper, iron, nickel, or an alloy thereof having a low coefficient of thermal expansion, easy processing, and little deterioration due to the environment. Then, it is desirable to cut and form the metal block.

  The sensor unit fixing surface of the base on which a plurality of uniaxial gravity measuring sensor units are installed is precisely formed by metal processing. In other words, by using the above-mentioned metal that can be precisely machined in any shape as the base material, multiple sensor unit fixed surfaces have the same angle or accurate posture with respect to the reference surface, and multiple uniaxial gravity measurements It is possible to form the sensor units so as to be fixed at an arbitrary installation angle with respect to the ground axis accurately and at equal intervals. The reference plane with respect to the ground axis of the common base can also be formed by precise machining so as to be perpendicular to the ground axis (a direction parallel to the direction of gravity action).

  Precisely determine the resonance frequency of each uniaxial gravity measurement sensor by accurately setting the sensor unit fixing surface of the common base that fixes multiple uniaxial gravity measurement sensors at an arbitrary angle with respect to the ground axis. Thus, the resonance frequency of a plurality of uniaxial gravity sensors can be determined optimally. Therefore, it is possible to obtain a multi-axis gravity measuring sensor that can detect a change in gravity with high accuracy of the order of 0.1 mgal, for example.

It is a perspective view of the sensor unit which comprises the multi-axis type gravity sensor explaining Example 1 of this invention. It is a 4th page figure of the multi-axis type gravity sensor explaining Example 1 of the present invention. It is a 2nd page figure of the multi-axis type gravity sensor explaining Example 2 of the present invention. It is a 2nd page figure of the multi-axis type gravity sensor explaining Example 3 of the present invention. It is explanatory drawing of 1 structural example of the sensor unit which comprises the multiaxial gravity sensor of this invention. It is explanatory drawing of 1 structural example of the sensor unit which comprises the multiaxial gravity sensor of this invention. It is a schematic block diagram explaining an example of the gravity measurement circuit using the multi-axis type gravity sensor of this invention. It is explanatory drawing when the inclination angle (theta) is zero, ie, (theta) = 0deg, in the crystal piece of a sensor unit. It is explanatory drawing in case the crystal piece of a sensor unit has the value whose inclination | tilt angle (theta) is not zero. It is explanatory drawing in case the inclination angle (theta) is 90 degree | times, ie, (theta) = 90deg, in the crystal piece of a sensor unit. It is a figure explaining the change acceleration ((DELTA) G) with respect to the said change angle ((DELTA) (theta)) when making the sensitivity axis of a sensor unit in parallel with the gravity direction, and inclining +/- DELTA (theta) with respect to the initial angle (theta). When the sensitivity axis of the sensor unit is parallel to the direction of gravity and the initial angle θ is deviated, the change acceleration (ΔG) with respect to the change angle (Δθ) when tilted by ± Δθ with respect to the initial angle θ FIG. It is explanatory drawing of the acceleration change which generate | occur | produces when the inclination (0.0811 deg) equivalent to 0.1 mgal which assumed the initial inclination as an error is applied. The data before tilt correction of the tilt evaluator, the horizontal axis is time (seconds: sec), the vertical axis is the sensor output (μG), the state of the sensor unit installation angle + the unestablished value θ by the level of the tilt evaluator The sensor output when the inclination is 0.573 deg to the rear and the inclination is 0.573 deg to the left is shown. It is explanatory drawing of the result measured after correcting the initial inclination of an inclination evaluation machine.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings of the examples.

  FIG. 1 is a perspective view of a multi-axis gravity sensor illustrating Embodiment 1 of the present invention. The multi-axis gravity sensor 1 includes three or more uniaxial shafts on a sensor base 10 made of a metal (for example, aluminum) having a hexagonal disk shape in which a portion near the top surface of a hexagonal column is cut out together with a part of the columnar portion. The sensor unit for gravity measurement (hereinafter also simply referred to as a sensor unit) is fixed. Hereinafter, for convenience of explanation, the sensor base 10 is simply referred to as a hexagonal prism. Three sensor units 4a, 4b, 4c are arranged on every other side of the six surfaces (six facets) formed on the top surface of the hexagonal column (long axis: a surface intersecting the height direction axis in the figure). It is fixed at equal intervals to three sensor unit fixing surfaces 3a, 3b, 3c which are located every other position. On the opposite side (rear surface) of the top surface of the hexagonal column that constitutes the base 10, the base portion 2 that constitutes a reference surface with respect to the ground axis is provided on the surface. The height of the base 2 is arbitrary, and the larger the height dimension (the longer the axial dimension), the more suitable the shape representation of the hexagonal column (suitable).

FIG. 2 is a four-side view of the multi-axis gravity sensor for explaining the first embodiment of the present invention. FIG. 2 (a) is a top view, FIG. 2 (b) is an arrow A in FIG. 2 (c) is a side view of FIG. 2 (a) viewed from the direction of arrow B, and FIG. 2 (d) is a bottom view. The same parts as those in FIG. 1 are denoted by the same reference numerals. The central axis C of the hexagonal prism constituting the base 10 of the multi-axis gravity sensor 1 passes through the vertex common to the six triangles, and the angle θ ₁ at the vertex of the sensor unit fixing surfaces 3a, 3b, 3c, θ ₂ and θ ₃ are θ ₁ = θ ₂ = θ ₃ . The corresponding angles at the vertices of the other three remaining faces are equal. Note that the angles at the apexes of the remaining three surfaces are not necessarily equal to the angles at the apexes of the sensor unit fixing surfaces 3a, 3b, 3c. Since Example 1 is an axially symmetric regular hexagonal prism, the angle at the vertex of the remaining three surfaces is equal to the angle at the vertex of the sensor unit fixing surfaces 3a, 3b, 3c.

  With respect to the multi-axis gravity sensor described in FIGS. 1 and 2, for example, the case where the sensor units are fixed at equal intervals on each of the three sensor unit fixing surfaces 3a, 3b, 3c of the regular six surfaces will be described. In this case, the inclination angle of the sensor unit fixing surfaces 3a, 3b, 3c with respect to a plane orthogonal to the long axis is set to 120 degrees. The sensor units 4a, 4b, 4c for uniaxial gravity measurement are fixed to the inclined surface with an adhesive. The Y plane shown in FIG. 2 (b) is perpendicular to the Z axis, which is the major axis of the hexagonal prism, parallel to a plane perpendicular to the major axis and perpendicular to a straight line passing through the center of the earth.

  Due to the viscosity of the adhesive that fixes the sensor units 4a, 4b, and 4c, the mounting error with the Y-plane installation mechanism, etc., the inclination of the sensor units 4a, 4b, and 4c for uniaxial gravity measurement is about ± 3 degrees. Error occurs. This error can be eliminated by prior calibration. In the case of each of the embodiments described below in which the inclination angle of the sensor unit fixing surfaces 3a, 3b, 3c is other than 120 degrees, the same level of error occurs. The calibration of this error will be described later with reference to FIG.

FIGS. 3A and 3B are two views of a multi-axis gravity sensor for explaining the second embodiment of the present invention. FIG. 3A is a top view, and FIG. 3B is an arrow A in FIG. It is the side view seen from the direction. 1 denote the same parts. In the second embodiment, sensor units 4a, 4b, and 4c for uniaxial gravity measurement are fixed at equal intervals on each of three surfaces (three facets) formed on the top surface of a triangular prism constituting the base. is there. The angles θ ₁ , θ ₂ , and θ ₃ at the vertex C of the three facets are θ ₁ = θ ₂ = θ ₃ . On the opposite side (rear surface) of the top surface of the triangular prism of the base 10, the surface has a base portion 2 that forms a reference surface with respect to the ground axis. The height of the base portion 2 (dimension in the Z-axis direction) is arbitrary, and the longer the height dimension, the better the shape representation of the triangular prism.

  FIG. 4 is a two-side view of a multi-axis gravity sensor for explaining the third embodiment of the present invention. FIG. 4 (a) is a top view, FIG. 4 (b) is FIG. It is the side view seen from the direction. 1 denote the same corresponding parts. In the third embodiment, the sensor unit fixing surface 3e on the top surface of the regular quadrangular prism constituting the base 10 and the sensor unit fixing surfaces 3a, 3b, 3c, and 3d on the side surfaces are respectively uniaxial gravity measuring sensor units 4e. , 4a, 4b, 4c, 4d are fixed. On the opposite side of the top surface of the quadrangular prism, which is a plane perpendicular to the long axis of the quadrangular prism (height direction in the figure: the central axis in the Z-axis direction), there is a base 2 that forms the reference surface on its lower surface Yes. The height of the base 2 in the Z-axis direction is arbitrary, and the longer the height dimension is, the more suitable the shape of the regular quadrangular prism is expressed.

  FIGS. 5A and 5B are two views of a multi-axis gravity sensor for explaining the fourth embodiment of the present invention. FIG. 5A is a top view, and FIG. 5B is FIG. It is the side view seen from the direction. 1 denote the same corresponding parts. In the fourth embodiment, the sensor units 4a, 4b, and 4c for uniaxial gravity measurement are fixed to the sensor unit fixing surfaces 3a, 3b, and 3c on the top surface of the column that constitutes the base 10, respectively. On the opposite side of the top surface of the edge column, which is a surface perpendicular to the long axis of the cylinder (the central axis in the height direction in the figure), there is a base 2 that forms the reference surface on its lower surface. The height of the base 2 is arbitrary, and the longer the height dimension, the more suitable for the shape expression of the edge column.

  The multi-axis gravity sensor is not limited to the one described in the first to fourth embodiments, but has a top surface of three or more prisms as a base 10 and a plurality of side surfaces formed at a plurality of equal intervals. If it is.

  FIGS. 6A and 6B are explanatory diagrams of one configuration example of the single-axis sensor unit constituting the multi-axis gravity sensor of the present invention, FIG. 6A is a cross-sectional view, and FIG. 6B is a plan view. This single-axis sensor unit 4 has a cantilever crystal piece 5 cantilevered and fixed with a conductive adhesive 43 at one location of a base 42 accommodated in a container 41a, filled with an inert gas inside, and covered with a lid 41b. It is sealed. One surface of the crystal piece 5 has an electrode (movable electrode) 5 a, and the pedestal 42 is provided with a fixed electrode 5 b on the inner surface corresponding to the movable electrode 5 a of the crystal piece 5. The operation of this sensor unit will be described later.

  An output terminal is provided for each of the fixed portion of the conductive adhesive 43 connected to the movable electrode 5a and the fixed electrode 5b provided on the base 42, and the input terminal of the gravity measuring circuit of FIG. Connected.

  FIG. 7 is a schematic block diagram for explaining an example of a gravity measuring circuit using the multi-axis gravity sensor of the present invention. This gravity measuring circuit supplies oscillation power to a plurality of uniaxial sensor units 4a, 4b, 4c,... Fixed to the above-mentioned base, and constitutes an oscillation circuit 7a, 7b, 7c,. ... Based on the oscillation outputs of the oscillation units 7a, 7b, 7c,..., The frequency deviation detection unit 8 that detects deviations at the resonance frequencies of the oscillation units and the frequency deviation value of the frequency deviation detection unit 8 are corrected and calculated. And a gravity deviation calculation unit 9 that performs correction for removing noise between the sensor units and outputs an accurate relative value of the gravity deviation.

  Next, calibration of the sensor unit mounting error described with reference to FIG. 6 will be described with reference to FIGS. 8 to 15, reference numeral 11 denotes a cantilever fixing portion of the crystal piece 5, 5 a is a movable electrode, 5 b is a fixed electrode, S is a sensitivity axis, and a is gravitational acceleration.

FIG. 8 shows a case where the crystal piece of the sensor unit has an inclination angle θ of zero, that is, θ = 0 deg. This is a case where the crystal piece 5 of the sensor unit is installed in parallel to a plane perpendicular to the ground axis. In this state, since cos θ = 0, the gravitational acceleration a applied to the sensitivity axis S is
a = 9.8 (m / sec ² ) × cos θ
= 9.8 (m / sec ² )
It becomes.

FIG. 9 shows a case where the crystal piece of the sensor unit has a value where the inclination angle θ is not 0, that is, θ = Δdeg. When the crystal piece 5 of the sensor unit is tilted by Δθdeg from a plane perpendicular to the ground axis, the gravitational acceleration a applied to the sensitivity axis S at cos θ = Δθdeg is
a = 9.8 (m / sec ² ) × cos Δθ
It becomes.

FIG. 10 shows a case where the crystal piece of the sensor unit is at an inclination angle θ90 degrees, that is, θ = 90 deg. This is a case where the crystal piece 5 of the sensor unit is installed parallel to the ground axis. In this state, since cos θ = 0, the gravitational acceleration a applied to the sensitivity axis S is
a = 9.8 (m / sec ² ) × cos θ
= 0
It becomes.

And the output of this sensor unit can be shown as follows.
V _out1 = k × cos θ (1)
V _out2 = k × cos (θ + Δθ) (2)
Here, k is a sensitivity coefficient of the sensor unit. Note that V _out1 is a reference gravitational acceleration, and V _out2 is a gravitational acceleration when changed.

The applied gravity change ΔG is:
ΔG = (cos θ−cos Δθ) × 9.8 (m / sec ² ) (3)

The output ΔV _out of the sensor unit when the applied gravitational acceleration ΔG changes is
ΔV _out = V _out1 -V _out2 (4)

The sensitivity of the sensor unit when tilted by Δθ when the angle θ = 0 deg perpendicular to the direction of gravity (horizontal to the ground) is
V _out1 −V _out2 = k × (1−cos Δθ) (5)

  Since this sensor unit is intended to measure gravity, a sensitivity axis is arranged in the direction of gravitational acceleration, and the state is set to zero. Therefore, it is necessary to evaluate the output change from 0 deg or a preset angle, and set the sensitivity axis to an angle accurately determined with respect to the sensitivity axis of the sensor unit.

FIG. 11 is a diagram for explaining a change acceleration (ΔG) with respect to the change angle (Δθ) when the sensitivity axis of the sensor unit is parallel to the direction of gravity and tilted by ± Δθ with respect to the initial angle θ. As shown in FIG. 10, when the initial inclination angle is inclined to both sides of ± Δθ with respect to 0 deg, the change acceleration (ΔG) with respect to the change angle (Δθ) is the left (−) and right ( +) Direction,
ΔG = 1−cos (± Δθ) (6)
Therefore, the amount of change between the two coincides, and the change ΔG in the gravitational acceleration applied is determined by equation (6).

FIG. 12 shows the change with respect to the change angle (Δθ) when the sensitivity axis of the sensor unit is parallel to the gravitational direction and the initial angle θ is deviated from the initial angle θ by ±± θ. It is a figure explaining acceleration (ΔG). As shown in FIG. 12, when the initial inclination angle is inclined to both sides of ± Δθ with respect to 0 deg, the change acceleration (ΔG) with respect to the change angle (Δθ) is − on the left side and + on the right side. , On the left side (ΔG ₁ ) and right side (ΔG ₂ ),
ΔG ₁ = cos θ−cos (θ−Δθ) (7)
ΔG ₂ = cos θ−cos (θ + Δθ) (8)
Since the initial angle (θ) is not a known value, the measurement accuracy of the applied gravitational acceleration is significantly reduced.

  FIG. 13 is an explanatory diagram of an acceleration change that occurs when, for example, an inclination equivalent to 0.1 mgal (0.0811 deg) with the initial inclination regarded as an error is applied. When a 1 mgal sensitivity evaluation is performed on a tilt evaluator or sensor with an initial tilt of 0.1 deg, the actual change in acceleration applied is 5 mgal, and when the initial tilt is not an existing value, the accuracy is high with a 500% error. It is not a sensor evaluation.

  A method for correcting the error as described in FIG. 14 will be described below. As a method for adjusting the tilt of the sensor to 0 deg, there is a method in which the sensor output is tilted while measuring and the angle at which the output becomes maximum is θ = 0 deg. However, since the output change in the vicinity of cos (0 deg) is slight, correction is difficult. Therefore, by applying ± Δθ in the state of the unexplained value θ, and calculating and correcting the initial inclination angle θ from the sensor output at that time, high accuracy evaluation becomes possible.

In FIG.
cos (θ−Δθ) = cos θ · cos Δθ−sin θ · sin Δθ
= ΔG ₁ (9)
cos (θ + Δθ) = cos θ · cos Δθ + sin θ · sin Δθ
= ΔG ₂ (10)
ΔG ₁ and ΔG ₂ are accelerations normalized from the output when about 1 G is applied to the sensor.
From the equations (1) and (2), the initial inclination angle θ is
θ = sin ⁻¹ [(ΔG ₁ −ΔG ₂ ) / 2 · sin Δθ] (11)
It becomes. The correction state in equation (10) is shown in the graphs of FIGS.

  FIG. 14 shows data before tilt correction of the tilt evaluator, the horizontal axis is time (seconds: sec), the vertical axis is sensor output (μG), and the sensor unit installation angle + tilt evaluator level In the state of the value θ, the sensor output when the inclination is 0.573 deg to the rear and the inclination is 0.573 deg to the left is shown.

  FIG. 15 shows the measurement results after correcting the initial tilt of the tilt evaluator. The measurement result is substituted into equation (3), and the measurement result is shown again after correcting the tilt evaluator to the left with the obtained correction angle of 0.56 deg. The unit (μG) on the vertical axis is almost equivalent to (mgal). The inclination sensor (level) at this time confirmed the correction method using LS-40C "high sensitivity acceleration sensor" by Rion Co., Ltd.

  The measurement error of each sensor unit 3 is corrected by the calibration as described above. A multi-axis gravity sensor that can measure relative changes in gravitational acceleration with high accuracy by fixing multiple modified sensor units to a common metal base (pedestal) to form a multi-axis gravity sensor. Can be obtained.

  DESCRIPTION OF SYMBOLS 1 ... Multi-axis gravity sensor, 2 ... Base, 3 (3a, 3b, 3c, 3d, 3e) ... Sensor unit fixed surface, 4 (4a, 4b, 4c, 4d, 4e) ... Sensor unit, 41a ... container, 41b ... lid, 42 ... pedestal, 43 ... conductive adhesive, 5 ... crystal piece, 5a ... movable electrode, 5b ... fixed Electrode, 7 (7a, 7b, 7c,...) ... oscillator, 8 ... frequency deviation detector, 9 ... gravity deviation calculator, 10 ... common base, 11 ... piece Holding part.

Claims (1)

A metal common base having a top surface, a side surface and a back surface intersecting the central axis, and three or more uniaxial sensor units are fixed to the top surface of the common base, and the back surface with respect to the ground axis A multi-axis gravity sensor with a right reference plane,
The metal common base has a surface cut by a plane perpendicular to the central axis of a 3 m prism having 3 m (m is a natural number of 2 or more) side surfaces as the back surface,
The top surface has a sensor unit fixing surface having three or more identical shapes that have the central axis as an apex and are inclined so as to approach the back surface as the distance from the central axis increases.
The sensor unit fixing surface on the top surface has a boundary between the 3m side surfaces and the top surface as a bottom, and a shared distance between two adjacent sides gradually becomes narrower toward the central axis. And an inclined surface located at an equiangular angle around the central axis, of the 3m triangular inclined surfaces having the same vertex at each other.
A multi-axis gravity sensor, wherein the uniaxial sensor unit is fixed around the central axis on each of the sensor unit fixing surfaces.

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