JP5950449B2 - Accelerometer - Google Patents

Description

  The present invention relates to an accelerometer, and more particularly to an accelerometer that is used by being attached to the surface of a structure to be measured.

Conventionally, an accelerometer (also referred to as an acceleration transducer) configured with a strain gauge is used for the impact of a structure in a test process necessary for the safety design of a moving body such as an automobile or a structure such as an aircraft. It is often used to measure the intensity and analyze the generated acceleration waveform.
In addition, the resistance of the four sides constituting the Wheatstone bridge circuit by the strain gauge is formed by a foil material type, a wire material type, a sputter gauge type, a diffusion type semiconductor gauge type, and the like, and this is called a grid.
A general accelerometer consists of a fixed part (driven part), a strain generating part, and a weight (generally also referred to as a weight or weight). In some cases, a fixed part is attached to the structure side, and the weight, which is the free end, is displaced relative to the driven part to cause strain in the strain-generating part, which is composed of a strain gauge attached to the strain-generating part. A signal output from the Wheatstone bridge circuit is detected as an acceleration signal.

Regarding this type of acceleration transducer, the applicant of the present application previously described in Patent Document 1 (Japanese Patent Laid-Open No. 7-167886),
When a weight is supported via a flexible part on a driven part that moves integrally with the object to be measured and the driven part receives acceleration, the weight is relatively displaced with respect to the driven part. In an acceleration transducer of a type that detects the acceleration by converting strain into an electrical signal with a strain gauge,
By forming slits with a certain depth from both sides of the opposite side circumferential surface in the middle part of the beam having a rectangular cross section, a rigid follower on the proximal side and a rigid on the distal side A cantilever having a weight portion and a flexible portion having flexibility in the middle portion;
A pair of thin and flexible strain generating plates joined to the peripheral surfaces of the driven portion and the weight portion so as to straddle a pair of slits formed in the middle portion of the cantilever. When,
At least one pair of strain gauges attached so as to be able to detect strain on the slit side surface portion of the pair of strain generating plates;
The strain plate itself has a tensile / compressive strain that acts on the strain plate when the cantilever is deformed by the acceleration acting on the weight portion, and the acceleration that acts on the strain plate. The present invention has proposed an acceleration transducer configured to be detected by the pair of strain gauges by adding bending strain caused by deformation.

As another acceleration converter, the applicant of the present application disclosed in Patent Document 2 (Japanese Patent Laid-Open No. 8-5656).
When a weight is supported via a flexible part on a driven part that moves integrally with the object to be measured and the driven part receives acceleration, the weight is relatively displaced with respect to the driven part. In an acceleration transducer of a type that detects the acceleration by converting strain into an electrical signal with a strain gauge,
By forming slits of a certain depth from both sides of the opposite side peripheral surface in the middle part of the beam, a rigid follower part on the proximal side, a heavy weight part on the distal side, Cantilever beams each having a flexible portion having flexibility in the intermediate portion;
A pair of reinforcing films made of a flexible thin film joined to each of the peripheral surfaces of the driven portion and the weight portion so as to straddle a pair of slits formed in an intermediate portion of the cantilever When,
A pair of thin insulating films respectively attached to the anti-slit side surface portions of the pair of reinforcing films;
A strain gauge attached to the anti-slit side surface of the pair of insulating films;
Acceleration conversion configured to detect the tensile / compressive strain acting on the reinforcing film when the cantilever is deformed by the acceleration acting on the weight portion with the pair of strain gauges. Proposed a vessel.

Furthermore, in Patent Document 3 (Japanese Patent Laid-Open No. 2006-294899),
A fixing part made of a semiconductor material;
A displacement portion made of the semiconductor material, which receives an acceleration in a predetermined direction and is displaced with respect to the fixed portion;
A plurality of connecting portions made of the semiconductor material, each connecting the fixed portion and the displacement portion and arranged side by side in the predetermined direction, and perpendicular to the predetermined direction from the width in the predetermined direction A plurality of connecting portions having a cross-sectional shape having a large thickness in the direction;
A plurality of strain sensing elements arranged in the plurality of connecting portions;
A single-axis semiconductor acceleration sensor characterized by comprising:

JP-A-7-167886 JP-A-8-5656 JP 2006-294892 A

Inventors according to the present application, regarding the acceleration converter (acceleration sensor or accelerometer) of Patent Documents 1 to 3 described above, the acceleration output with respect to the original sensitive axis direction, that is, the weight portion of the strain-generating body exhibiting a beam shape. In addition to the output from the vertical acceleration component, acceleration output in the lateral direction of the strain body, that is, in the left-right direction and the front-rear direction of the strain body is generated, which becomes an error and the acceleration output in the original sensitive axis direction It has been found that there is a problem that the measurement accuracy of the true acceleration is lowered due to being mixed in as an error.
Conventionally, such a problem has been allowed only as an error in the specification.
However, as a result of earnestly searching for the cause of the problem, the inventor according to the present application has clarified that interference occurs due to the following causes.
That is, the cause will be described with reference to FIG. 12.
The accelerometer shown in FIG. 12 constitutes the basic configuration of the present invention.
For example, the accelerometer 50 is a beam body 51 having a rectangular cross section and extending in the longitudinal direction. The base end side of the beam body 51 attached to the object to be measured is a fixed portion 52, and is orthogonal to the longitudinal direction in the middle. A slit 53 penetrating in the direction to be formed is formed into a thin wall to form a pair of strain generating portions 54, and a distal end side is defined as a weight portion 55. A total of four strain gauges G1 to G4, two at a portion separated by a certain distance in the longitudinal direction and two at a portion separated by a certain distance in the direction orthogonal to the longitudinal direction, with the center of the slit 53 as a boundary. Will be described as being attached.

First, the cause of the first interference is that the strain gauges G1 and G3 on the fixed side and the strain gauges G2 and G4 on the weight part 56 side are separated as shown in FIG. G2 and G4 receive only the mass Ma of the weight part 56, whereas the strain gauges G1 and G3 attached to the fixed part 52 side are strain gauges G1 and G3 and a strain gauge in addition to the mass of the weight part 56. Since the amount of mass ma corresponding to the strain generating portion 54 existing between G2 and G4 is received as acceleration, these four strain gauges G1, G3, G2, and G4 are used as a Wheatstone bridge circuit (hereinafter, “ Even if a “bridge circuit” is assembled, the interference component in the Z-axis direction remains without being canceled.
In order cause the second interference, as shown in FIG. 12 (b), a moment is generated by the mass ma, subjected to distortion due to the moment, the strain amount is, that can not be canceled by the bridge circuit, This is an interference value.
The third cause of interference is that the weight 55 is bent by a load due to the mass Ma to generate a moment, and a new strain is generated due to the moment. This distortion shows a complicated behavior, and interference that is an apparent output in terms of a circuit cannot be eliminated.
Accordingly, a first object of the present invention is to provide a highly accurate accelerometer that realizes reduction or removal of the apparent component.
A second object of the present invention is to provide an accelerometer that is simple in structure and inexpensive without using complicated circuit means.
A third object of the present invention is to provide an ultra-compact accelerometer that can detect minute accelerations.

In order to achieve the first and second objects described above, an accelerometer according to claim 1
The base end side in the longitudinal direction of the strain-generating body exhibiting a beam shape is a fixed portion, and a pair of thin strain-generating portions formed by forming a slit penetrating in the direction perpendicular to the longitudinal direction in the middle, and the distal end side is It is an accelerometer formed by attaching a weight part and attaching at least four strain gauges to the strain generating part with each gauge axis directed in the longitudinal direction,
With the center of the slit as a boundary,
A plurality of first strain gauges connected to one side of the Wheatstone bridge circuit and a plurality of second strain gauges connected to the other side adjacent to the one side are placed at symmetrical positions on the strain generating portion. , Respectively,
The resistance values of the first strain gauge and the second strain gauge are all set equal, and the grid length of the second strain gauge is different from the grid length of the first strain gauge, and the Wheatstone The bridge circuit is characterized in that it is set so that the output in the main sensitivity direction of the grid can be increased and the output in the direction orthogonal to the main sensitivity direction can be canceled.

In order to achieve the first and second objects, an accelerometer according to claim 2 is provided.
The grid length of the second strain gauge is formed longer than the grid length of the first strain gauge.
According to a third aspect of the present invention, in order to achieve the first and second objects, the inner surface side of the strain generating portion is symmetrically formed in a semicircular cross section with a predetermined interval from the slit center. A plurality of the first strain gauges and the second strains are provided on the plane side corresponding to the symmetric semicircular arc thin portion from the center of the slit. It is characterized by attaching gauges.
In order to achieve the first and second objects, the accelerometer according to claim 4 is configured such that an up-down direction in which the weight portion is displaced in a main sensitivity direction with respect to the strain body is an X-axis direction,
When the direction displaced in the left-right direction is the Y-axis direction and the direction displaced in the front-rear direction is the Z-axis direction, when the weight is displaced in the X-axis direction, the first strain gauge and the second strain gauge are The first strain gauge and the first strain gauge are deformed so that one side is subjected to compressive strain and the other side is subjected to tensile strain to produce a large output at the output end of the Wheatstone bridge circuit, and the weight portion is displaced in the Y-axis direction. 2 strain gauges are similarly deformed to receive compressive strain or tensile strain, and cancel each other in the Wheatstone bridge circuit to provide no substantial output. When the weight portion is displaced in the Z-axis direction, The first strain gauge and the second strain gauge are similarly subjected to compressive strain or tensile strain, and the first strain gauge and the second strain gauge By varying the lid length so as to provide a small output is offset by the Wheatstone bridge circuit, it is characterized by being configured.

In the accelerometer according to claim 5, in order to achieve the first and second objects, the first strain gauge is formed in the double-arched fixed-side half formed at a predetermined interval. The center of the grid length of the first strain gauge is matched with the plane side position corresponding to the arcuate vertex,
The second strain gauge is attached in a state where the center of the grid length of the second strain gauge is aligned with the plane side position corresponding to the semicircular arc apex on the weight side of the double arch. It is characterized by.
In order to achieve the first and second objects, the accelerometer according to claim 6 is configured such that the grid length of the first strain gauge is x and the second degree of interference for reducing the interference degree in the Z direction is halved. When the upper limit allowable value of the grid length of the strain gauge is y ₁ and the lower limit allowable value is y ₂ , the allowable range y of the grid length of the second strain gauge is expressed by the following conditional expressions (1), ( 2), (3):
(1) y ₁ = 0.0007x ² + 0.5959x + 120.02
(2) y ₂ = 0.0005x ² + 0.723x + 61.218
(3) y ₂ <y <y ₁
It is characterized by satisfying.
The accelerometer according to claim 7 is characterized in that, in order to achieve the first to third objects, the grid length x of the first strain gauge is set in a range of 100 μm to 400 μm.

According to the first aspect of the present invention, the base end side in the longitudinal direction of the strain-generating body exhibiting a beam shape is used as the fixed portion, and a slit penetrating in the direction perpendicular to the longitudinal direction is formed in the middle to make the wall thin. An accelerometer comprising a pair of strain-generating portions, a distal end side as a weight portion, and at least four strain gauges attached to the strain-generating portions with their gauge axes directed in the longitudinal direction,
With the center of the slit as a boundary,
A plurality of first strain gauges connected to one side of the Wheatstone bridge circuit and a plurality of second strain gauges connected to the other side adjacent to the one side are placed at symmetrical positions on the strain generating portion. , Respectively,
The resistance values of the first strain gauge and the second strain gauge are all set equal, and the grid length of the second strain gauge is different from the grid length of the first strain gauge, and the Wheatstone In the bridge circuit, the output in the main sensitivity direction of the grid is increased so that the output in the direction orthogonal to the main sensitivity direction can be canceled, thereby increasing the output in the main sensitivity direction and in the main sensitivity direction. It is possible to realize a significant improvement in the measurement accuracy of the acceleration by preventing the apparent output in the orthogonal direction, that is, the lateral front-rear direction as much as possible, and to provide an inexpensive accelerometer with a simple configuration.

According to the invention described in claim 2, the same effect as that of the invention described in claim 1 can be obtained by forming the grid length of the second strain gauge longer than the grid length of the first strain gauge. Can be provided.
According to a third aspect of the present invention, the double arch-shaped strain generation is further achieved by forming the inner surface side of the strain generation portion symmetrically in a semicircular arc shape with a predetermined interval from the slit center. A plurality of the first strain gauges and a plurality of the second strain gauges are respectively attached to the plane side corresponding to the thin semicircular arc-shaped thin portion symmetrical from the center of the slit. It is possible to provide an accelerometer capable of increasing the output in the sensitivity direction, further reducing the apparent output in the lateral direction and the front-rear direction orthogonal to the main sensitivity direction, and further improving the measurement accuracy of acceleration.

According to invention of Claim 4,
The vertical direction in which the weight portion is displaced in the main sensitivity direction with respect to the strain body is defined as the X-axis direction,
When the direction displaced in the left-right direction is the Y-axis direction and the direction displaced in the front-rear direction is the Z-axis direction, when the weight is displaced in the X-axis direction, the first strain gauge and the second strain gauge are The first strain gauge and the first strain gauge are deformed so that one side is subjected to compressive strain and the other side is subjected to tensile strain to produce a large output at the output end of the Wheatstone bridge circuit, and the weight portion is displaced in the Y-axis direction. 2 strain gauges are similarly deformed to receive compressive strain or tensile strain, and cancel each other in the Wheatstone bridge circuit to provide no substantial output. When the weight portion is displaced in the Z-axis direction, The first strain gauge and the second strain gauge are similarly subjected to compressive strain or tensile strain, and the first strain gauge and the second strain gauge By configuring different lid lengths, the Wheatstone bridge circuit cancels out in the Wheatstone bridge circuit so that a small output is generated. Therefore, the output in the lateral direction is canceled to make the apparent output zero, and in particular, the apparent in the front-rear direction. It is possible to provide an accelerometer that can greatly improve the measurement accuracy of acceleration by hardly outputting strain output.

According to the invention described in claim 5, the first strain gauge is in a plane side position corresponding to the semicircular arc apex of the fixed side of the double arch formed at a predetermined interval, Align the center of the grid length of the first strain gauge,
The second strain gauge is attached in a state where the center of the grid length of the second strain gauge is aligned with the plane side position corresponding to the semicircular arc apex on the weight side of the double arch. As a result, the output in the main sensitivity direction can be increased, the apparent output in the lateral direction and the front-rear direction orthogonal to the main sensitivity direction can be reduced more appropriately, and an accelerometer that can further improve the measurement accuracy of acceleration can be achieved. Can be provided.
According to the invention of claim 6,
The grid length of said first strain gauge and x, the grid length upper tolerance of the Z direction of the interference of the second strain gauge for halving the as y _1, a lower allowable value was y ₂ When the allowable range y of the grid length of the second strain gauge is the following conditional expressions (1), (2), (3):
(1) y ₁ = 0.0007x ² + 0.5959x + 120.02
(2) y ₂ = 0.0005x ² + 0.723x + 61.218
(3) y ₂ <y <y ₁
By satisfying the above, the relationship between the grid lengths of the first strain gauge and the second strain gauge that can reduce the interference degree in the Z direction to half or less can be set easily and accurately, and the output in the lateral direction is canceled. Thus, it is possible to provide an accelerometer capable of further greatly improving the measurement accuracy of acceleration by setting the apparent output to zero and, in particular, outputting almost no apparent distortion in the front-rear direction.

According to the invention of claim 7,
By setting the grid length of the first strain gauge in a range of 100 μm to 400 μm, in addition to the above effects, it is possible to detect a small acceleration and to provide a microminiature accelerometer.

BRIEF DESCRIPTION OF THE DRAWINGS The structure of the principal part of the accelerometer which concerns on the 1st Embodiment of this invention is shown, Fig.1 (a) is a perspective view which shows the external appearance structure of an accelerometer, FIG.1 (b) is an accelerometer. 1 is a circuit diagram illustrating a circuit configuration of a Wheatstone bridge (hereinafter, simply referred to as “bridge”) that constitutes a part of the Wheatstone bridge. FIG. 2A shows a configuration of a main part of the accelerometer shown in FIG. 1, FIG. 2A is a plan view, and FIG. 2B is a left side view. FIG. 3A is an explanatory diagram exaggeratingly illustrating a state in which the shape of the accelerometer according to the first embodiment of the present invention is deformed in the direction of acceleration applied in a three-dimensional space, and FIG. 3B, the acceleration in the Y-axis direction (left-right direction), and the acceleration in the Z-axis direction (front-back direction) in FIG. 3C are applied, respectively. It is the perspective view, top view, and left view which show the deformation | transformation state. FIG. 4A shows a main part of the accelerometer according to the first embodiment of the present invention. FIG. 4A is a left side view illustrating the entire strain generating body, and FIG. It is a partial expanded side view formed by drawing the upper half part of the distortion part which is a part. Interference with the rated output of the accelerometer when the grid length of the first strain gauge installed on the fixed side is fixed to 200 μm and the grid length of the second strain gauge installed on the weight side is changed between 200 μm and 300 μm. It is a graph which shows the relationship with an output. Relationship between rated output and interference output when the second strain grid length installed on the weight side is fixed to 200 μm and the grid length of the first strain gauge installed on the fixed portion side is changed between 100 μm and 200 μm. It is a graph which shows. 6 is a graph showing the characteristics of strain output on the center line of the strain generating portion [line A in FIG. 2A] when 1000 G acceleration is applied from the X direction to the accelerometer according to one embodiment of the present invention. is there. The characteristic of the strain output on the center line [the line A in FIG. 2 (a)] of the strain generation part when the acceleration of 1000G is applied to the accelerometer which concerns on the form of one Example of this invention from a Z direction is shown. It is a graph. The graph which shows the characteristic of the strain output on the centerline [the line A in FIG. 2 (a)] of the strain generation part in case the acceleration of 1000G is applied to the accelerometer which concerns on other embodiment of this invention from a X direction. The grid length of the first strain gauge and the second strain gauge attached to the strain generating portion is different from the graph of FIG. The graph which shows the characteristic of the strain output on the centerline [line A in FIG. 2 (a)] of the strain generation part in case the acceleration of 1000G is applied to the accelerometer which concerns on other embodiment of this invention from a Z direction. The grid length of the first strain gauge and the second strain gauge attached to the strain generating portion is different from the graph of FIG. In an accelerometer according to still another embodiment of the present invention, when an acceleration of 1000 G is applied from the Z direction, the interference degree is + 0.09% and −0.09% centering on 0%. 5 is a graph continuously showing examples of combinations of grid lengths of a fixed-side strain gauge and a weight-side strain gauge capable of achieving the above. FIG. 12 is an explanatory diagram for analyzing the cause of mixing in the X-axis direction component when acceleration is applied to the accelerometer in the Z-axis direction that is the front-rear direction orthogonal to the X-axis direction that is the main sensitivity direction; a) is a side view for explaining the cause of interference due to the difference in mass applied between the fixed-side strain gauge installation position and the weight-side strain gauge installation position, and FIG. FIG. 12 (c) is a side view for explaining the cause of interference caused by the generation of moment by the mass ma existing between the gauge and the weight side strain gauge. FIG. 12 (c) shows the moment when the weight portion is bent by the mass Ma of the weight portion. FIG. 6 is a side view for explaining the cause of interference caused by the moment.

Hereinafter, embodiments of an accelerometer according to the present invention will be described in detail with reference to the drawings.
FIG. 1 shows a schematic configuration of a main part of an accelerometer according to a first embodiment of the present invention, and FIG. 1 (a) is a perspective view showing an external configuration of the accelerometer. FIG. 1B is a circuit diagram showing a circuit configuration of a Wheatstone bridge constituting a part of the accelerometer. 2A and 2B show a specific configuration of the accelerometer shown in FIG. 1A. FIG. 2A is a plan view and FIG. 2B is a left side view.
FIG. 3 is an explanatory view showing a state in which the shape of the accelerometer according to the first embodiment of the present invention is deformed in the direction of acceleration applied in the three-dimensional space, and among these, FIG. ) Is the acceleration in the X-axis direction which is the main sensitivity direction, FIG. 3B is the acceleration in the Y-axis direction (left-right direction), and FIG. 3C is the acceleration in the Z-axis direction (front-back direction). It is the perspective view, the top view, and the left view which exaggerate and show the deformation state of the accelerometer when applied, respectively.
FIG. 4 is an enlarged partial left side view showing the configuration of the upper strain generating portion of the accelerometer according to the first embodiment of the present invention.

1, 2, 3, and 4, reference numeral 2 denotes a strain generating body having a rectangular beam shape in cross section, and a base end side in the longitudinal direction (the left-right direction in FIGS. 1 to 4) of the strain generating body 2. (Left end side in FIGS. 1 to 4) is a fixed portion 3, and a rectangular slit 5 penetrating in the direction perpendicular to the longitudinal direction (direction perpendicular to the paper surface in FIGS. 1 to 4) is formed in the middle and thin. Thus, a pair of strain generating portions 4 is formed, and a tip end side (right end side in FIGS. 1 to 4) is a weight portion 6, and one of the pair of strain generating portions 4 and 4 (upper part in FIG. 5) The accelerometer 1 is configured by attaching four strain gauges G1, G2, G3, and G4 with their gauge axes in the longitudinal direction.
The semicircular arc sections 5b and 5c are formed on the inner surface side of the strain generating section 4 with a predetermined interval (0.6 mm in this example) with respect to the center line 5a of the slit 5 of the strain generating body 2. Thus, the double arch-shaped strain generating portion 4 is provided leaving the protruding portion 5d in the middle.
As a direction acting on the accelerometer 1, for example, in FIG. 3A, the vertical direction in which the weight 6 is displaced in the main sensitivity direction is defined as the X-axis direction, and the direction in which the weight 6 is displaced in the left-right direction orthogonal to the X-axis direction Is the Y-axis direction, and the direction displaced in the front-rear direction perpendicular to both the X-axis direction and the Y-axis direction is the Z-axis direction.

Of the four strain gauges G1 to G4, a pair of first strain gauges connected to one opposite side of a Wheatstone bridge circuit (hereinafter sometimes abbreviated as “bridge circuit”) shown in FIG. The strain gauges G1 and G3 are attached to the fixed portion 3 side by means of adhesion, sputtering, vapor deposition, etc. symmetrically with respect to the line A with the center line 5a (see FIGS. 2 and 4) of the slit 5 as a boundary. Yes.
On the other hand, the strain gauges G2 and G4 as a pair of second strain gauges connected to the other opposite side adjacent to one opposite side of the bridge circuit are symmetrical positions on the weight part 6 side with the center line of the slit 5 as a boundary. In addition, they are similarly attached to the line A at symmetrical positions.
In the accelerometer 1 according to the first embodiment, the first strain gauges G1 and G3 and the second strain gauges G2 and G4 are at the same distance with the center line 5a of the slit 5 as a boundary. Although installed, the second strain gauges G2 and G4 are set longer by a predetermined length than the grid length of the grids of the first strain gauges G1 and G3.
However, the resistance value R1 of the strain gauge G1, the resistance value R2 of the strain gauge G2, the resistance value R3 of the strain gauge G3, and the resistance value R4 of the strain gauge G4 forming the bridge circuit are all set equal.
In the present specification, it is referred to as grid length, but is generally referred to as gauge length, gauge length, strain gauge length, or the like, and is described as such in the accompanying drawings. In some cases.

One end of the grid of the strain gauge G1 is connected to a gauge tab 9R which is a + side input end via a wiring pattern, and the other end is connected to a gauge tab 9W which is a − side output end via a wiring pattern. ing.
One end of the grid of the strain gauge G2 is connected to a gauge tab 9B that is a negative input end via a wiring pattern, and the other end is connected to a gauge tab 9W that is a negative output end via a wiring pattern. .
One end of the grid of the strain gauge G3 is connected to a gauge tab 9B which is a negative input end via a wiring pattern, and the other end is connected to a gauge tab 9G which is a positive output end via a wiring pattern. ing.
One end of the grid of the strain gauge G4 is connected to a gauge tab 9R which is a + side input end via a wiring pattern, and the other end is connected to a gauge tab 9G which is a + side output end via a wiring pattern. .
With such a configuration, a bridge circuit as shown in FIG. 1B is formed.
That is, when a + bridge voltage Ein is applied to the gauge tab 9R and a − bridge voltage is applied to the gauge tab 9B, the strain gauges G1 to G4 constituting the bridge circuit are subjected to strain based on the acceleration, and the respective resistance values R1 to R1 are applied. R4 changes, and the output voltage Eout based on the change is output from the grid 9G (+ terminal) and the grid 9W (−terminal).

Here, the pair of strain gauges G1 and G3 as the first strain gauges are arranged on a line A (see FIG. 2A) in parallel at a predetermined distance from the center line 5a of the slit 5 on the fixed portion 3 side. As shown in FIG. 3 (a), when the weight portion 6 is relatively displaced due to acceleration in the X-axis direction and receives tensile strain, the resistance values R1 and R3 are both Will increase.
Further, the pair of strain gauges G2 and G4 as the second strain gauges are installed in parallel at the symmetrical position on the weight part 6 side from the center line 5a of the slit 5, as shown in FIG. When the weight portion 6 is relatively displaced by the acceleration in the X-axis direction and is subjected to a compressive strain, both the resistance values R2 and R4 decrease.
As described above, the first strain gauges G1 and G3 are connected to one side of the bridge circuit, and the second strain gauges G2 and G4 are connected to the other side adjacent to the one side. Since they are connected, a large strain output corresponding to the applied acceleration can be obtained from between the gauge tabs 9G and 9W which are the output ends of the bridge circuit.

That is, the strain output output from the bridge circuit when acceleration is applied in the X-axis direction (main sensitivity direction) is Eout (X), and the resistance values of the strain gauges G1, G2, G3, and G4 when no load is applied. , R1, R2, R3, R4, and the output Eout (X) of the accelerometer 1 when ΔR1, ΔR2, ΔR3, ΔR4 are the resistance value changes when acceleration is applied, It can be expressed by an expression.
Eout (X) = 1/4 (ΔR1 / R1−ΔR2 / R2 + ΔR3 / R3−ΔR4 / R4) Ein (1)
Further, with respect to the Y-axis direction (left-right direction) rotated by 90 degrees with respect to the X-axis direction, strain gauges G1 and G3 and strain gauge R2 with respect to the center of gravity of the weight portion 6 as shown in FIG. And R4 are symmetrical with each other, and their resistance value changes ΔR1 and ΔR3 and ΔR2 and ΔR4 cancel each other on the bridge circuit, so that no apparent acceleration is detected. That is, the strain output Eout (Y) in this case is expressed by the following equation (2).
Eout (Y) = 1/4 (ΔR1 / R1−ΔR2 / R2 + (− ΔR1 / R1) − (− ΔR2 / R2)) Ein = 0 (2)
Further, when acceleration is applied in the Z-axis direction (FIG. 3C) rotated by 90 degrees with respect to the X-axis direction and the Y-axis direction, as described with reference to FIG. The output Eout (Z) is obtained by detecting the acceleration corresponding to the mass Ma of the weight part 6 and the mass ma of the strain generating part 4 by the strain gauge R1 and the strain gauge R (more specifically, The apparent acceleration is the resistance value change α corresponding to the acceleration corresponding to the mass ma) of the strain generating portion 4 between the first strain gauges G1 and G3 and the second strain gauges G2 and G4. Detected as That is, the strain output Eout (Z) in this case is expressed by the following equation (3).

Eout (Z) = 1/4 (ΔR1 / R1 + α / R1−ΔR1 / R1 + ΔR1 / R1 + α / R1−ΔR1 / R1)) Ein
= 1/4 (2α / R1) Ein (3)
However, when an acceleration is applied in the Z-axis direction, as described with reference to FIG. 12A, the above equation (3) is an interference output when the mass Ma and the mass ma act as load components. It only responds.
That is, as an interference when acceleration is applied in the Z-axis direction, as shown in FIG. 12B, a moment is generated by the mass ma and not only a distortion component due to the moment exists as a cause of interference, but also Further, as shown in FIG. 12C, a moment is generated by the weight 55 of the mass Ma, and a strain component due to the moment is also mixed as a cause of interference.
That is, as the strain output with respect to the acceleration in the first embodiment, as shown in FIG. 3A, the output Eout (X) when the acceleration is applied in the X-axis direction (main sensitivity direction) is the X-axis. A large output corresponding to the acceleration applied in the direction can be obtained.
Further, the main force Eout (Y) when acceleration is applied in the Y-axis direction orthogonal to the main sensitivity direction as shown in FIG. 3B is canceled by the bridge circuit, and the output becomes 0, and the Y-axis direction The apparent acceleration is not detected.

However, as shown in FIG. 3C, the output Eout (Z) when acceleration is applied in the Z-axis direction that is orthogonal to the X-axis direction that is the main sensitivity direction and also orthogonal to the Y-axis direction is In the bridge circuit, unless any countermeasure is taken, it is detected as an apparent acceleration, which is mixed in as an error of a strain output corresponding to the acceleration, thereby reducing the detection accuracy.
Here, a specific numerical example 1 will be described.
As shown in FIG. 2, the total length (Z-axis direction) of the strain body 2 is 10 mm, the total height (X-axis direction) is 5 mm, the depth (Y-axis direction) is 5 mm, and the width of the slit 5 is 1.4 mm (at the four corners). The radius of the arc is 0.2 mm), the plate thickness of the strain generating portion 4 is 0.2 mm, the distance from the base end (left end) of the fixed portion 3 to the center line 5a of the slit 5 is 6.5 mm, The material is stainless steel (SUS630-H900).
Such strain gauges G1 and G3 and G2 and G4 are respectively set at target positions separated by 0.6 mm from the center line 5a of the slit 5 of the strain generating part 4 to the fixed part 3 side and the weight part 6 side. In this case, the amount of deviation from the target position of the sputter gauge is set to zero.

Table 1 below shows that the grid lengths of the first strain gauges G1 and G3 on the fixed part 3 side are fixed to 200 μm and the grid lengths of the second strain gauges G2 and G4 on the weight part 6 side in the above numerical example. An accelerometer when changing from 10 μm to 300 μm, rated output (1/4 · KEin × 10 ⁻⁶ strain) when 1000 G acceleration is applied in the X direction, and 1000 G acceleration in the Z direction Interference output (1/4 · KEin × 10 ⁻⁶ strain), interference degree (%), strain amounts ε1 and ε3 detected by the first strain gauges G1 and G3, and second The strain amounts detected by the strain gauges G2 and G4 are shown as values of ε2 and ε3.

FIG. 5 shows the relationship between the rated output and the interference output based on the values obtained from Table 1.
As can be seen from FIG. 5, as a setting condition in which the rated output does not decrease so much and the interference output becomes 0, the grid length of the first strain gauges G1 and G3 is 200 μm, and the second strain gauges G2 and G4 This is when the grid length is 245 μm, and interference is completely prevented.
However, even if the interference is not 0, for example, the first strain gauges G1 and G3 on the fixed part 3 side and the second strain gauges G2 and G4 on the weight part 6 side have the same grid length (both 200 μm). When the interference degree is −0.20, the grid length of the second strain gauges G2 and G4 is in the range of 230 μm to 260 μm when there is no practical problem even with an interference degree of 50% of this interference degree. If you use something, it will be good.
In the second embodiment, the grid lengths of the second strain gauges G2 and G4 on the weight part 6 side are fixed, and the grid lengths of the first strain gauges G1 and G3 on the fixed part 3 side are changed and adjusted. A numerical example 2 will be described.
Table 2 below shows that the grid lengths of the second strain gauges G2 and G4 on the weight part 6 side of the accelerometer are constant, and the grid lengths of the first strain gauges G1 and G3 on the fixed part 3 side are in the range of 100 μm to 200 μm. Over 10 μm, rated output when 1000 G acceleration is applied in the X direction (1/4 · KEin × 10 ⁻⁶ strain) and interference output when 1000 G acceleration is applied in the Z direction (1 / 4 · KEin × 10 ⁻⁶ strain), the degree of interference (%), and the output strains ε1 and ε3 (× 10 ⁶ strain) of the first strain gauges G1 and G4.

As can be seen from Table 2, when the grid lengths of the second strain gauges G2 and G4 are 200 μm and the grid lengths of the first strain gauges G1 and G3 are 148 μm, the interference degree is 0%. This means that an accelerometer can be obtained.
FIG. 6 is a graph showing the relationship between the interference output and the rated output when the grid length of the first strain gauges G1 and G3 on the fixed portion 3 side is changed based on the data in Table 2 above.
As can be seen from Table 2 and FIG. 6, if the grid length of the strain gauge on the fixed portion 3 side is adjusted to 120 μm to 170 μm, the interference output can be halved compared to when the grid length is 200 μm.
Thus, even when the grid length of the strain gauges G2 and G3 on the weight part 6 side is an arbitrary length, the interference output can be obtained by changing and adjusting the grid length of the strain gauges G1 and G3 on the fixed part 3 side. It can be eliminated as described above.
Next, the basis of the fact that the interference output can be reduced or eliminated by adjusting the grid length of the strain gauge will be discussed below.

FIG. 7 shows a reference point 0 for the center line 5a of the slit 5 on the line A [see FIG. 2 (a)] of the strain generating portion 4 when an acceleration of 1000 G is applied to the accelerometer according to the present invention from the X direction. Is a graph showing a strain distribution in a range of -0.7 mm to +0.7 mm.
FIG. 8 shows a range of −0.7 mm to +0.7 mm with the center line 5a of the slit 5 on the line A of the strain generating part 4 when a 1000 G acceleration is applied to the accelerometer from the Z direction as a reference point. It is a graph which shows strain distribution in.
In FIGS. 7 and 8, the centers of the first strain gauges G1 and G3 having a grid length of 200 μm on the fixed portion 3 side are attached to a portion of −0.3 mm from the reference position, while the weight portion 6 side has the center. Second strain gauges G2 and G4 having a grid length of 245 μm are attached to a portion +0.3 mm from the reference position. This is based on the grid length of 245 μm obtained from the calculation result of Table 1.
In this numerical example, the strain outputs ε1, ε3 of the first strain gauges G1, G3, the strain outputs ε2, ε4 of the second strain gauges G2, G4, and the value of strain at the time of X-direction acceleration, that is, ε1- The values of ε2 + ε3-ε4 are listed in Table 3 below, and it can be seen that high strain, that is, 426.71 × 10 ⁻⁶ strain, is detected during acceleration in the X direction.

FIG. 8 shows the strain in the range of −0.7 mm to +0.7 mm with the center line 5a of the slit 5 on the line A of the strain generating part 4 when the acceleration of 1000 G is applied to the accelerometer from the Z direction. It is a graph which shows distribution.
As shown in FIG. 8, the strains ε1 and ε3 of the first strain gauges G1 and G3, the strains ε2 and ε4 of the second strain gauges G2 and G4, and the total strain ε1 when an acceleration of 1000 G is applied in the Z direction. The values of -ε2 + ε3-ε4 are as shown in Table 4.

It can be seen from Table 4 that the value of the total strain ε1−ε2 + ε3−ε4 is as small as −0.01, and only interference is output.
This is because the grid length of the second strain gauges G2 and G4 is 245 μm and the grid length of the first strain gauges G1 and G3 is 200 μm, so the strain in the region longer than the first strain gauges G1 and G3 is larger. By averaging, the acceleration component in the Z direction is canceled and interference output is hardly output.
Similarly, FIG. 9 and FIG. 10 show the slit center line 5a on the line A [see FIG. 2 (a)] of the strain generating portion 4 when 1000 G acceleration is applied to the accelerometer from the X direction and the Z direction. It is a graph which shows the strain distribution in the range of -0.7 mm-+0.7 mm as a reference point (0 point).
In FIGS. 9 and 10, the center of the first strain gauges G1 and G3 on the grid length 148 μm fixing portion 3 side is attached to a portion −0.3 mm from the reference position, while the grid length on the weight portion 6 side is attached. 200 μm second strain gauges G2 and G4 are attached to a portion 0.3 mm from the reference position.

This is the grid length of 148 μm obtained from the calculation result of Table 2, that is, the grid lengths of the strain gauges G1 and G3 on the fixed portion 3 side are shorter than the grid length of 200 μm on the strain gauges G2 and G4 on the weight portion 6 side. It is set.
As a result, as shown in Table 5, a large strain output of ε1−ε2 + ε3−ε4 = 436.89 is obtained as the strain when the acceleration of 1000 G is applied in the X direction, that is, the total strain.

In contrast, as shown in Table 6, the strain during acceleration in the Z direction when 1000 G acceleration is applied in the Z direction is as shown in Table 6.
ε1-ε2 + ε3-ε4 = 0.00
And the interference becomes zero.

This also means that the strain detections of the strain gauges G1 and G3 on the fixed part 3 side of the grid length 148 μm and the strain gauges G2 and G4 on the weight part 6 side of the grid length of 200 μm are averaged and canceled to cancel the interference. Conceivable.
For the strain gauge grid length in the range of 100 μm to 400 μm, adjust the grid length of each strain gauge on the fixed part 3 side and the weight part 6 side, and the combination example in which the interference degree is 0% and the grid length When the combination of the grid lengths of 100 μm is −0.186%, the interference degree that halves this interference degree is −0.09% and the interference degree is 0.09%. Table 7 shows examples of combinations.

FIG. 11 is a graph showing a combination example of Table 7.
In FIG. 11, the horizontal axis represents the grid length (μm) of the fixed portion 6 side strain gauge, and the vertical axis represents the strain gauge grid length (μm) on the weight portion 6 side. As a center, a line segment having an interference degree of -0.09% and a line segment having an interference degree of 0.09% are displayed together.
Here, the grid length of the first strain gauge and x, the second strain upper tolerance of the grid length gauge for halving the interference of the Z-axis direction and y _1, a lower allowable value y ₂ Then, the allowable range y of the grid length of the second strain gauge is the following conditional expressions (1), (2), (3):
(1) y ₁ = 0.0007x ² + 0.5959x + 120.02
(2) y ₂ = 0.0005x ² + 0.723x + 61.218
(3) y ₂ <y <y ₁
Should be satisfied.
In this way, by setting the combination of the grid length of the first strain gauge and the grid length of the second strain gauge, an accelerometer that can reduce the interference degree to 0% or reduce the interference degree by half is appropriately provided. can do.

In the present embodiment, the grid length x of the first strain gauge is exemplified as the range of 100 μm to 400 μm, but is not limited to this range, and more or more based on the same basis. The following grid lengths are applicable.
The present invention is not limited to the above-described and illustrated embodiments, and can be implemented with various modifications.

DESCRIPTION OF SYMBOLS 1 Accelerometer 2 Strain body 3 Fixed part 4 Strain part 5 Slit 5a Slit center line 6 Weight part 9R, 9W, 9B, 9G Gauge tab 5b, 5c Semicircular arc part 5d Protrusion part G1, G2, G3, G4 Gauge R1 , R2, R3, R4 Resistance value

Claims (7)

The base end side in the longitudinal direction of the strain-generating body exhibiting a beam shape is a fixed portion, and a pair of thin strain-generating portions formed by forming a slit penetrating in the direction perpendicular to the longitudinal direction in the middle, and the distal end side is It is an accelerometer formed by attaching a weight part and attaching at least four strain gauges to the strain generating part with each gauge axis directed in the longitudinal direction,
With the center of the slit as a boundary,
A plurality of first strain gauges connected to one side of the Wheatstone bridge circuit and a plurality of second strain gauges connected to the other side adjacent to the one side are placed at symmetrical positions on the strain generating portion. , Respectively,
The resistance values of the first strain gauge and the second strain gauge are all set equal, and the grid length of the second strain gauge is different from the grid length of the first strain gauge, and the Wheatstone In the bridge circuit, an accelerometer is set so that the output in the main sensitivity direction of the grid can be increased and the output in the direction orthogonal to the main sensitivity direction can be canceled.   The accelerometer according to claim 1, wherein the grid length of the second strain gauge is formed longer than the grid length of the first strain gauge.   A double arch-shaped strain-generating portion is provided by symmetrically forming the inner surface side of the strain-generating portion into a semicircular cross-section with a predetermined interval from the slit center, and is symmetrical from the center of the slit. The plurality of the first strain gauges and the plurality of the second strain gauges are respectively attached to the plane side corresponding to the semicircular arc thin portion. Accelerometer. The vertical direction in which the weight portion is displaced in the main sensitivity direction with respect to the strain body is defined as the X-axis direction,
When the direction displaced in the left-right direction is the Y-axis direction and the direction displaced in the front-rear direction is the Z-axis direction, when the weight is displaced in the X-axis direction, the first strain gauge and the second strain gauge are The first strain gauge and the first strain gauge are deformed so that one side is subjected to compressive strain and the other side is subjected to tensile strain to produce a large output at the output end of the Wheatstone bridge circuit, and the weight portion is displaced in the Y-axis direction. 2 strain gauges are similarly deformed to receive compressive strain or tensile strain, and cancel each other in the Wheatstone bridge circuit to provide no substantial output. When the weight portion is displaced in the Z-axis direction, The first strain gauge and the second strain gauge are similarly subjected to compressive strain or tensile strain, and the first strain gauge and the second strain gauge By varying the lid length, the Wheatstone bridge as circuit is offset by results in small output, accelerometer according to any one of claims 1 to 3, characterized by being configured. The first strain gauge has a grid length of the first strain gauge at a plane side position corresponding to the semicircular arc apex of the fixed side of the double arch formed at a predetermined interval. Match the center,
The second strain gauge is attached in a state where the center of the grid length of the second strain gauge is aligned with the plane side position corresponding to the semicircular arc apex on the weight side of the double arch. The accelerometer according to any one of claims 1 to 4, wherein The grid length of said first strain gauge and x, the grid length upper tolerance of the Z direction of the interference of the second strain gauge for halving the as y _1, a lower allowable value was y ₂ When the allowable range y of the grid length of the second strain gauge is the following conditional expressions (1), (2), (3):
(1) y ₁ = 0.0007x ² + 0.5959x + 120.02
(2) y ₂ = 0.0005x ² + 0.723x + 61.218
(3) y ₂ <y <y ₁
The accelerometer according to any one of claims 1 to 5, wherein:   The accelerometer according to claim 6, wherein the grid length x of the first strain gauge is set in a range of 100 μm to 400 μm.