CN105865321A - Axial-deviation three-sensitive-grid interdigital metal strain gauge capable of measuring outside axial partial derivative of bias sensitive grid - Google Patents

Abstract

An interdigitated metal strain gauge with three sensitive grids that can measure the axial deflection of the outer axial deflection of the offset sensitive grid, including a base and three sensitive grids fixed on it, each sensitive grid includes a sensitive section and a transition section, all The axis of the sensitive section is a straight line, arranged in parallel and in the same plane; in the plane determined by the axis of the sensitive section, the direction along the axis of the sensitive section is the axial direction, and the direction perpendicular to the axial direction is the transverse direction; the center of the three sensitive grids There is a deviation in the axial direction, but no deviation in the lateral direction; the three sensitive grids are called the left sensitive grid, the middle sensitive grid and the right sensitive grid from left to right along the axial direction according to the order of the center position of the sensitive grid; Sensitive gates are arranged as interdigitated fingers; the total resistance change value of the sensitive segments of the left sensitive gate, middle sensitive gate and right sensitive gate under the same strain is 3:8:5. The invention can detect the axial first-order partial derivative of the strain from the right outer side of the right sensitive grid to the center of the right sensitive grid equal to the center distance between the middle and right two sensitive grids.

Description

It can measure the axial deviation of the axial deflection of the outer axial deflection of the offset sensitive grid. Three sensitive grid interfinger gold Strain gauge

technical field

The invention relates to the field of sensors, in particular to a metal strain gauge.

Background technique

The working principle of the metal resistance strain gauge is the resistance strain effect, that is, when the metal wire is subjected to strain, its resistance changes correspondingly with the magnitude of the mechanical deformation (stretch or compression). The theoretical formula for the resistance strain effect is as follows:

$\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; \&rho;</span>}\frac{\mathrm{<span\; class="notranslate">\; L</span>}}{\mathrm{<span\; class="notranslate">\; S</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

Where R is its resistance value, ρ is the resistivity of the metal material, L is the length of the metal material, and S is the cross-sectional area of the metal material. During the process of mechanical deformation of the metal wire under strain, ρ, L, and S will all change, which will inevitably cause changes in the resistance value of the metal material. When the metal material is stretched, the length increases, the cross-sectional area decreases, and the resistance value increases; when it is compressed, the length decreases, the cross-sectional area increases, and the resistance value decreases. Therefore, as long as the change of the resistance value can be measured, the strain of the metal wire can be known. The formula for the resistance change rate of metal materials can be derived from formula (1) and related knowledge of material mechanics

$\frac{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; R</span>}}{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; K</span>}\frac{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; L</span>}}{\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; K</span>}\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

Among them, ΔR is the change in resistance, ΔL is the change in the length of the metal material in the direction of tension or pressure, ε is the strain in the same direction, often called axial strain, and K is the strain sensitivity coefficient of the metal material.

In practical applications, the metal resistance strain gauge is pasted on the surface of the elastic element of the sensor or the mechanical part to be tested. When the elastic element in the sensor or the mechanical part under test is subjected to force to generate strain, the strain gauge pasted on it will also undergo the same mechanical deformation, causing a corresponding change in the resistance of the strain gauge. At this time, the resistance strain gauge converts the mechanical quantity into the output of the change of resistance.

But sometimes we also need to know the partial derivative of the workpiece strain. For example, there are three occasions below, but not limited to these three. The partial derivative of the workpiece surface strain is needed:

First, due to the strain concentration near the sudden change in the shape of the workpiece, it is often the first place where the workpiece is damaged. Monitoring the partial strain derivative near the sudden change in shape can intuitively obtain the degree of strain concentration there.

Second, there are a large number of bending parts in buildings, bridges, and mechanical equipment. The knowledge of material mechanics tells us that the axial strain on the surface of a curved beam is proportional to the section bending moment, and the axial partial derivative of the section bending moment and the section shear strain become Proportional, that is, the cross-sectional shear strain can be obtained through the axial partial derivative of the surface axial strain, and the shear strain cannot be directly measured on the workpiece surface with a strain gauge;

Third, when using elastic mechanics to study workpiece strain, the internal strain is determined by partial differential equations, and the solution of the equation requires boundary conditions, and the partial derivative of workpiece surface strain is one of the boundary conditions, which cannot be provided by general strain gauges.

In addition, for some parts of the workpiece, such as the shaft shoulder and the edge of the part, due to the sudden change in shape and size, the strain often changes relatively greatly. However, due to the sudden change in shape and size, it is difficult to install ordinary strain gauges at this place, and a product that can measure the strain deflection of the strain gauge at the edge or even the outer side of the edge instead of the central position is needed. In this way, it can be realized that the strain gauges are arranged at a certain distance away from the target measured point where it is difficult to place the strain gauges, and finally the strain deflector at the target measured point is measured.

Contents of the invention

In order to overcome the deficiency that the existing metal strain gauges cannot detect the strain deflector, the present invention provides an axial deflector that can measure the axial deflection of the outer side of the bias sensitive grid, which can not only measure the strain but also effectively detect the axial deflector of the surface strain. The deviation three-sensitive grid cross refers to the metal strain gauge, especially for measuring the first-order axial deflection of the corners and edges of the workpiece that have size restrictions on the strain gauge or other axial first-order deflectors that are not suitable for the location of the strain gauge.

The technical solution adopted by the present invention to solve its technical problems is:

An interdigitated metal strain gauge with three sensitive grids that can measure the axial deflection of the outer axial deflection of the offset sensitive grid, including a base, and the metal strain gauge also includes three sensitive grids, and the two ends of each sensitive grid are respectively connected A pin, the three sensitive grids are fixed on the substrate;

Each sensitive grid includes a sensitive section and a transition section, the two ends of the sensitive section are transition sections, the sensitive section is in the shape of a long and thin strip, the transition section is in a thick and short shape, and the resistance of the sensitive section is much greater than the The resistance of the transition section, the resistance change value of the sensitive section under the same strain state is much greater than the resistance change value of the transition section, and the resistance change value of the transition section is close to 0;

All the centroids of the cross-sections of each sensitive section constitute the axis of the sensitive section, which is a straight line segment, and the axes of the sensitive sections in the three sensitive grids are parallel and located in the same plane, within the plane defined by the axes of the sensitive section , along the axial direction of the sensitive section, that is, the axial direction, and the direction perpendicular to the axial direction is the transverse direction; each sensitive section has a cross section with equal resistance values on both sides, and the centroid position of the section is taken as the resistance value of the sensitive section The value is the nominal mass point of the sensitive section where the nominal mass constitutes, and the centroid position formed by the nominal mass points of each sensitive section is the center of the sensitive grid;

The centers of the three sensitive grids have deviations in the axial direction and no deviations in the lateral direction; the three sensitive grids are called left sensitive grids, middle sensitive grids and right sensitive grids from left to right along the axial direction in the order of the center positions of the sensitive grids. grid; the distance between the center of the left sensitive grid and the center of the middle sensitive grid is Δx ₁ , the distance between the center of the middle sensitive grid and the center of the right sensitive grid is Δx ₁ , on the plane determined by the axes of each sensitive section, the left sensitive grid and the middle sensitive grid form a fork Finger arrangement, middle sensitive grid and right sensitive grid are interdigitated arrangement;

The total resistance of the sensitive section of the left sensitive grid, the middle sensitive grid and the right sensitive grid is in a ratio of 3:8:5, and the total resistance of the sensitive section of the left sensitive grid, the middle sensitive grid and the right sensitive grid is under the same strain. The change value is also in a ratio of 3:8:5.

Further, all cross-sectional shapes and sizes of each sensitive section are consistent, and the axis midpoint position of each sensitive section is taken and the nominal mass of the sensitive section is formed with the resistance value of the sensitive section. The left sensitive grid, the middle sensitive The total length of the sensitive section of the grid and the right sensitive grid is in a ratio of 3:8:5. This scheme is an optional scheme. The position of the nominal mass point only needs to conform to the centroid position of the cross-section with equal resistance values on both sides, or it can be other positions.

Furthermore, the left sensitive grid and the right sensitive grid are arranged in an interdigitated arrangement; of course, a non-interdigitated arrangement is also possible. The interdigital arrangement refers to: on the plane where the axes of the sensitive sections of the two sensitive grids are located, the sensitive sections of the two sensitive grids are distributed in a staggered direction perpendicular to the axes of the sensitive sections, and the sensitive sections of the two sensitive grids in this direction appear respectively The sequence and number of times are not limited.

Further, the two pins of the right sensitive grid are located on the right side of the strain gauge or on the left side of the strain gauge. Arranging on the right side makes the lateral dimension of the strain gauge smaller, while arranging on the left side can reduce the distance from the center of the right sensitive grid to the right edge of the strain gauge.

Furthermore, compared with the middle sensitive grid, the axial length of the sensitive section of the right sensitive grid can be shorter and the lateral distribution can be denser. The purpose is to reduce the distance from the center of the right sensitive grid to the right edge of the strain gauge.

Utilizing the linear relationship between the resistance change value of the metal material and the strain, the strain gauge can be used to measure strain just like ordinary strain gauges. On the other hand, according to the numerical differential theory (such as according to Feng Kang et al., National Defense Industry Press published in December 1978 "Numerical Calculation Method" 21 pages (1.4.11) - (1.4.14) formula for equidistant interpolation Analysis) Regarding the specific calculation method of the first-order partial derivative, the numerical calculation method of the first-order partial derivative in the x direction of f(x,y) is as follows:

${\frac{<span\; class="notranslate">\; \&part;</span>\mathrm{<span\; class="notranslate">\; f</span>}}{<span\; class="notranslate">\; \&part;</span>\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; |</span>}_{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; \&ap;</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; h</span>}}<span\; class="notranslate">\; \&lsqb;</span>\mathrm{<span\; class="notranslate">\; 3</span>}\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 8</span>}\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 5</span>}\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&rsqb;</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

Among them, x ₁ ＝x ₀ +h, x ₂ ＝x ₁ +h, pay special attention to the above formula is the first-order partial derivative value formula at (x ₂ +h,y) position, the truncation error of this formula is smaller as o(h ² ) is the high-order infinitesimal quantity of the square of the step size. From the formula (2), it is generally believed that the change of the resistance of the sensitive grid is proportional to the strain of the center of the sensitive grid, combined with the proportional relationship between the resistance of each sensitive grid and the resistance change under the same strain, the resistance of the left sensitive grid and the right sensitive grid Subtract the resistance value of the middle sensitive grid, and then divide it by the distance between the center of the left sensitive grid and the center of the right sensitive grid to obtain the axial first-order numerical partial derivative of the strain; in particular, this is the distance h from the center of the right sensitive grid to the right Axial first-order numerical deflection, so the advantage of this strain gauge is to measure the axial first-order deflection of the workpiece corners, edges, etc. that have size restrictions on the strain gauge or other axial first-order deflectors that are not suitable for the location of the strain gauge.

In the process, care should be taken to keep the total resistance of the transition section of the left sensitive gate, the middle sensitive gate and the right sensitive gate, and the change of the resistance of the transition section under external strain in a numerical relationship of 3:8:5 to increase the measurement accuracy. If the transition section The resistance and the change in resistance under strain cannot be ignored, and can also be eliminated as a system error during detection.

Further, the metal strain gauge also includes a cover sheet, and the cover sheet covers the sensitive grid and the base.

Still further, the sensitive grid is a wire-type, foil-type, film-type or thick-film-type sensitive grid.

Furthermore, the base is an adhesive film base, a glass fiber base, an asbestos base, a metal base or a temporary base.

The three sensitive gates are arranged on the base at left, center and right. Of course, other arrangements are also possible.

The beneficial effects of the present invention are mainly manifested in: the axial first-order deflection of the strain at a place on the right outer side of the center of the right sensitive grid can be detected; The distance between the centers is equal to the distance between the center of the middle sensitive grid and the center of the right sensitive grid. Therefore, the present invention can measure the axial first-order deflection of the workpiece corners, edges, etc., where the size of the strain gauge is limited or other positions where the strain gauge is not suitable for arrangement.

Description of drawings

Fig. 1 is a schematic diagram of an interdigitated metal strain gauge of three sensitive grids capable of measuring the axial deviation of the axial deflection outside the offset sensitive grid.

Fig. 2 is a top view of the interdigitated metal strain gauge of three sensitive grids capable of measuring the axial deflection of the outer axial deflection of the offset sensitive grid.

Fig. 3 is a top view of the interdigitated metal strain gauge of the three sensitive grids with the pins of the right sensitive grid arranged on the left side which can measure the axial deflection of the outer axial deflection of the biased sensitive grid.

Figure 4 is a schematic diagram of the measuring bridge.

detailed description

The present invention will be further described below in conjunction with the accompanying drawings.

Referring to Figures 1 to 4, an interdigitated metal strain gauge with three sensitive grids that can measure the axial deflection of the outer axial deflection of the offset sensitive grid includes a base, and the metal strain gauge also includes three sensitive grids, each Two ends of the sensitive grid are respectively connected to a pin, and the three sensitive grids are fixed on the substrate;

Each sensitive grid includes a sensitive section and a transition section, the two ends of the sensitive section are transition sections, the sensitive section is in the shape of a long and thin strip, the transition section is in a thick and short shape, and the resistance of the sensitive section is much greater than the The resistance of the transition section, the resistance change value of the sensitive section under the same strain state is much greater than the resistance change value of the transition section, and the resistance change value of the transition section is close to 0;

All the centroids of the cross-sections of each sensitive section constitute the axis of the sensitive section, which is a straight line segment, and the axes of the sensitive sections in the three sensitive grids are parallel and located in the same plane, within the plane defined by the axes of the sensitive section , along the axial direction of the sensitive section, that is, the axial direction, and the direction perpendicular to the axial direction is the transverse direction; each sensitive section has a cross section with equal resistance values on both sides, and the centroid position of the section is taken as the resistance value of the sensitive section The value is the nominal mass point of the sensitive section where the nominal mass constitutes, and the centroid position formed by the nominal mass points of each sensitive section is the center of the sensitive grid;

The centers of the three sensitive grids have deviations in the axial direction and no deviations in the lateral direction; the three sensitive grids are called left sensitive grids, middle sensitive grids and right sensitive grids from left to right along the axial direction in the order of the center positions of the sensitive grids. grid; the distance between the center of the left sensitive grid and the center of the middle sensitive grid is Δx ₁ , the distance between the center of the middle sensitive grid and the center of the right sensitive grid is Δx ₁ , on the plane determined by the axes of each sensitive section, the left sensitive grid and the middle sensitive grid form a fork Finger arrangement, the middle sensitive grid and the right sensitive grid are interdigitated arrangement; the total resistance of the sensitive section of the left sensitive grid, the middle sensitive grid and the right sensitive grid is in a ratio of 3:8:5, the left sensitive grid, the middle sensitive grid and the right sensitive grid Under the same strain, the total resistance change value of the sensitive section of the sensitive grid is also in the ratio of 3:8:5.

Further, all cross-sectional shapes and sizes of each sensitive section are consistent, and the axis midpoint position of each sensitive section is taken and the nominal mass of the sensitive section is formed with the resistance value of the sensitive section. The left sensitive grid, the middle sensitive The total length of the sensitive section of the grid and the right sensitive grid is in a ratio of 3:8:5. This scheme is an optional scheme. The position of the nominal mass point only needs to conform to the centroid position of the cross-section with equal resistance values on both sides, or it can be other positions.

Furthermore, the left sensitive grid and the right sensitive grid are arranged in an interdigitated arrangement; of course, a non-interdigitated arrangement is also possible. The interdigital arrangement refers to: on the plane where the axes of the sensitive sections of the two sensitive grids are located, the sensitive sections of the two sensitive grids are distributed in a staggered direction perpendicular to the axes of the sensitive sections, and the sensitive sections of the two sensitive grids in this direction appear respectively The sequence and number of times are not limited.

Furthermore, the two pins of the right sensitive grid can be located on the right side of the strain gauge or on the left side of the strain gauge. Arranging on the right side makes the lateral dimension of the strain gauge smaller, while arranging on the left side can reduce the distance from the center of the right sensitive grid to the right edge of the strain gauge, as shown in Figure 4.

In this embodiment, the axial deviation of the axial deflection of the outer axial deflection of the offset sensitive grid can be measured. The three-sensitive grid interdigitated metal strain gauge includes a base 1, and the metal strain gauge also includes three sensitive grids, and two of each sensitive grid The terminals are respectively connected to a pin, and the three sensitive grids are fixed on the substrate 1 .

The left sensitive grid 2, the middle sensitive grid 3 and the right sensitive grid 4 can be fixed on the base 1 to maintain the fixed shape, position and size of each sensitive grid; the base 1 is very thin, so that the strain on the surface of the test piece can be accurately transmitted To the left sensitive gate 2, the middle sensitive gate 3 and the right sensitive gate 4. The substrate 1 can be an adhesive film substrate, a fiberglass substrate, an asbestos substrate, a metal substrate, and a temporary substrate. The substrate is usually fixed on the tested part of the test piece by means of bonding, welding, ceramic spraying and the like. Some lines for positioning the strain gauges can also be printed on the substrate 1 .

The cover sheet is made of materials such as paper or glue, and covers the left sensitive grid 2, the middle sensitive grid 3, the right sensitive grid 4 and the base 1, and serves as a protective layer for moisture-proof, corrosion-proof, and damage-proof functions.

Pin 5 is used to connect the sensitive grid and the measurement circuit, the left sensitive grid 2, the middle sensitive grid 3 and the right sensitive grid 4 each have two pins 5, for foil and film strain gauges, pin 5 is connected to the The left sensitive grid 2, the middle sensitive grid 3 and the right sensitive grid 4 are integrated into one. The two pins of the left sensitive grid 2 are 5-1 and 5-2, the two pins of the middle sensitive grid 3 are 5-3 and 5-4, and the two pins of the right sensitive grid 4 are 5-5 and 5-6; pins 5-5 and 5-6 can be arranged on the right side of the strain gauge, as shown in Figure 1 and Figure 2, to obtain a smaller lateral dimension of the strain gauge; pins 5-5 and 5-6 are also It can be arranged on the left side of the strain gauge, see Figure 3, the purpose is to reduce the distance from the right sensitive grid 4 to the right edge of the strain gauge.

The left sensitive grid 2, the middle sensitive grid 3 and the right sensitive grid 4 can be wire type, foil type, thin film type, thick film type according to their metal sensitive materials and processing technology. Regardless of the thickness of the left sensitive grid 2, the middle sensitive grid 3 and the right sensitive grid 4, the thicknesses are very small, so that the axial lengths of the left sensitive grid 2, the middle sensitive grid 3 and the right sensitive grid 4 vary with the deformation of the workpiece they are attached to. Variety. The basic key point of the present invention is the cooperation between the left sensitive grid 2, the middle sensitive grid 3 and the right sensitive grid 4, which has the following main points:

First, three sensitive gates are arranged on the substrate, which are respectively called left sensitive gate 2 , middle sensitive gate 3 and right sensitive gate 4 .

Second, the left sensitive gate 2, the middle sensitive gate 3 and the right sensitive gate 4 can be divided into a plurality of sensitive sections 6 and a plurality of transition sections 7, and each transition section 7 connects the sensitive sections 6 to form a sensitive gate. In comparison, the sensitive section 6 is elongated, has a large resistance and its resistance is more sensitive to strain; the transition section 7 is basically thick and short, so that the resistance of the transition section is small and insensitive to strain, In the working state, the resistance change is close to 0, so the sum of the resistance of the sensitive section is basically the total resistance of a single sensitive gate. Figure 2 marks the sensitive section 6 and the transition section 7 in more detail for a clearer perspective.

Third, the sensitive section 6 of each sensitive grid is in the shape of an elongated strip, and the centroids of all the cross-sections of each sensitive section 6 form the axis of the sensitive section. The axis of the sensitive section 6 is a straight line segment, and the axes of each sensitive section 6 are parallel and lie in the same plane. The projection shapes of all the cross sections of each sensitive section 6 along the axis direction of the sensitive section are consistent. Take the midpoint position of the axis of each sensitive section and use the resistance value of the sensitive section to form the nominal mass of the sensitive section. The centroid position formed by the nominal mass points of each sensitive section is the center of the sensitive grid.

Fourth, the total length of the sensitive section 6 of the left sensitive grid 2, the middle sensitive grid 3 and the right sensitive grid 4 is in a ratio of 3:8:5, and the sensitive sections of the left sensitive grid 2, the middle sensitive grid 3 and the right sensitive grid 4 6 The total resistance is in a ratio of 3:8:5, and the total resistance change value of the sensitive section 6 of the left sensitive grid 2, the middle sensitive grid 3 and the right sensitive grid 4 is also 3:8:5 under the same strain proportional relationship.

Fifth, looking down at the left sensitive grid 2, the middle sensitive grid 3 and the right sensitive grid 4, they all have symmetrical axes and the symmetrical axes coincide (x-axis in Figure 2), the left sensitive grid 2, the middle sensitive grid 3 and the right sensitive grid All the sensitive sections 6 of 4 are all parallel to the axis of symmetry, and the sensitive sections 6 of each sensitive grid are symmetrically distributed about this axis. Therefore, it can be said that the left sensitive grid 2, the middle sensitive grid 3 and the right sensitive grid 4 are coaxial, that is, the strain in the same direction is detected and the center positions of the left sensitive grid 2, the middle sensitive grid 3 and the right sensitive grid 4 are all on the x-axis , their centers have axial deviation and no lateral deviation. According to the top view of the strain gauge in Fig. 2, the sensitive section 6 of the left sensitive grid 2 has a transverse axis of symmetry y _L , the center of the left sensitive grid 2 is at the intersection of the x axis and the y _L axis, and the sensitive section 6 of the middle sensitive grid 3 has a transverse axis Symmetry axis y _M , the center of the middle sensitive grid 3 is at the intersection of the x axis and the y _M axis, the sensitive section 6 of the right sensitive grid 4 has a transverse symmetry axis y _R , and the center of the right sensitive grid 4 is at the intersection of the x axis and the y _R axis intersection.

Sixth, the distance between the center of the left sensitive grid 2 and the center of the middle sensitive grid 3 is Δx ₁ , the distance between the center of the middle sensitive grid 3 and the center of the right sensitive grid 4 is Δx ₁ , that is, the distance between the center of the left sensitive grid 2 and the right sensitive grid 4 The midpoint of the connecting line at the center is also the intersection point of the x-axis and the y- _M axis, as shown in FIG. 2 . According to Figure 2, on the plane determined by the axes of each sensitive section 6, the left sensitive grid 2 and the middle sensitive grid 3 are interdigitated, the middle sensitive grid 3 and the right sensitive grid 4 are interdigitated, and the left sensitive grid 2 and the right sensitive grid are interdigitated. 4. It can be interdigitated or vice versa; said interdigitated arrangement refers to: on the plane where the axes of the sensitive sections of the two sensitive grids are located, the sensitive sections of the two sensitive grids are staggered in the direction perpendicular to the axes of the sensitive sections. There is no limit to the order and times of the sensitive sections of the two sensitive gates in the direction.

Since the relative positions of the left sensitive grid 2, the middle sensitive grid 3 and the right sensitive grid 4 are fixed quite accurately by the strain gauge production process, this is also one of the keys for the invention to detect the axial partial derivative of workpiece strain.

In summary, the resistance change value of the left sensitive grid 2, the middle sensitive grid 3 and the right sensitive grid 4 of the present invention has a ratio of 3:8:5 under the same strain, and the center of each sensitive grid has no lateral deviation and axial deviation, The distance from the center of the left sensitive grid 2 to the center of the middle sensitive grid 3 is equal to the distance from the center of the middle sensitive grid 3 to the right sensitive grid 4 .

Let the resistance of the left sensitive grid 2 be R _L0 , the resistance of the middle sensitive grid 3 be R _M0 , and the resistance of the right sensitive grid 4 be R _R0 in the free state, and R _L0 +R _R0 = _RM0 =R ₀ . When the strain gauge of the present invention is placed on a surface with strain, the resistance of the left sensitive grid 2 is R ₀ +ΔR _L , the resistance of the middle sensitive grid 3 is R ₀ +ΔR _M0 , and the resistance of the right sensitive grid 3 is R ₀ +ΔR _R ; On the other hand, the centers of the left sensitive grid 2 and the right sensitive grid 4 are respectively located at the intersections of the x-axis and y _L and the intersections of the x-axis and y _R in FIG. 2 , with an axial distance of 2Δx ₁ . Assume It is Δx ₁ on the right side of the center of the right sensitive grid 4, that is, the intersection of the x-axis and y _O in Figure 2, using the relationship between the sensitive grid resistance and surface strain and the formula (3) for numerical differentiation:

${\frac{<span\; class="notranslate">\; \&part;</span>\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}{<span\; class="notranslate">\; \&part;</span>\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; |</span>}_{\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; x</span>}}}<span\; class="notranslate">\; \&ap;</span>\frac{\mathrm{<span\; class="notranslate">\; 3</span>}{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 8</span>}{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 5</span>}{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; \&Delta;x</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; \&ap;</span>\frac{\mathrm{<span\; class="notranslate">\; K</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&Delta;R</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&Delta;R</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&Delta;R</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; \&Delta;x</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; .</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

Where ε _L is the strain at the center of the left sensitive grid 2, ε _M is the strain at the center of the middle sensitive grid 3, and ε _R is the strain at the center of the right sensitive grid 4. This is the principle of measuring the axial deflection of surface strain in this embodiment. In particular, the numerical differential calculated by the above formula is the first-order partial derivative of the strain axis at the position Δx ₁ outside the center of the right sensitive grid 4, and this position can be located at the right part, right edge, Even the outside of the edge, so it has the advantage of being convenient to measure the axial first-order deflection of the corners and edges of the workpiece where the size of the strain gauge is limited. The pins 5-5 and 5-6 of the right sensitive grid 4 can be arranged on the left side of the strain gauge according to Fig. 3, the purpose of which is to minimize the distance from the center of the right sensitive grid 4 to the right edge of the strain gauge, so as to further develop the above-mentioned Advantage.

This embodiment can be used to measure the strain and the axial first-order partial derivative of the strain by using the bridge. Assuming that the input voltage of the bridge is u _i and the output voltage is u _o , the schematic diagram of the measuring bridge is shown in FIG. 4 . When there is no workpiece strain, the resistances of the bridge arms of the bridge are respectively marked as R ₁ , R ₂ , R ₃ , and R ₄ in the clockwise direction, and these symbols are also used to mark the bridge where the resistance is located if there is no confusion. Sensitive gates or resistors of strain gauges can be placed on each bridge. Same as the general arrangement of strain gauges, if sensitive grids are installed on multiple bridge arms, there are qualitative requirements for the order and strain of each installation position. When there is no workpiece strain, the output voltage formula of the bridge is

${\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; ;</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

At this time, it is required that the bridge balance is u _o = 0, so the so-called bridge balance condition R ₁ R ₃ -R ₂ R ₄ = 0 must be satisfied, and the bridge used further satisfies

R ₁ =R ₂ =R ₃ =R ₄ , (6)

Because, first, when the condition (6) is satisfied, according to the relevant theory, the sensitivity of the strain gauge is the highest; second, the method of measuring the strain or the axial deflection of the strain requires the condition (6) to be established. When the strain gage also strains with the external strain, the above bridge equilibrium condition is generally no longer valid, at this time

$\begin{array}{c}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}<span\; class="notranslate">\; =</span>\frac{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&Delta;R</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&Delta;R</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&Delta;R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&Delta;R</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; )</span>}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&Delta;R</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&Delta;R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&Delta;R</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&Delta;R</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}\\ <span\; class="notranslate">\; \&ap;</span>\frac{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; \&Delta;R</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Delta;R</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}{\mathrm{<span\; class="notranslate">\; \&Delta;R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; \&Delta;R</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&Delta;R</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Delta;R</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&Delta;R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; \&Delta;R</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}\\ <span\; class="notranslate">\; \&ap;</span>\frac{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&Delta;R</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&Delta;R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&Delta;R</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&Delta;R</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; 4</span>}{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}\end{array}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 7</span>}<span\; class="notranslate">\; )</span>$

Since ΔR _i << R _i (i=1,2,3,4), the first ≈ holds true, and the second ≈ when ΔR ₁ -ΔR ₂ has the same or different sign as ΔR ₃ -ΔR ₄ but |ΔR ₁ -ΔR ₂ | is not very close to |ΔR ₃ -ΔR ₄ |, and it can be realized by selecting the location of the strain gauge reasonably in engineering. Generally, the voltage measured by the formula (7) can be used to measure the strain; the axial deflection of the strain can be combined with the formula (4) and formula (7), and the sensitive grid and resistance _of each bridge arm can be reasonably designed and arranged. Grid 3, bridge arm R ₂ arrange left sensitive grid 2 and right sensitive grid 4 in series, and the remaining bridge arms are equipped with resistances equivalent to bridge arm R ₁ , so that the axial strain at the position Δx ₁ outside the center of right sensitive grid 4 can be obtained The voltage value u _o of which the first-order partial derivative is linearly related, and this voltage needs to be amplified for weak signals.

Claims (9)

1. A three-sensitive-grid interdigitated metal strain gauge capable of measuring the axial deflection of the outer axial deflection of the offset sensitive grid, including a base, characterized in that: the metal strain gauge also includes three sensitive grids, each sensitive Two ends of the grid are respectively connected to a pin, and the three sensitive grids are fixed on the substrate; Each sensitive grid includes a sensitive section and a transition section, the two ends of the sensitive section are transition sections, the sensitive section is in the shape of a long and thin strip, the transition section is in a thick and short shape, and the resistance of the sensitive section is much greater than the The resistance of the transition section, the resistance change value of the sensitive section under the same strain state is much greater than the resistance change value of the transition section, and the resistance change value of the transition section is close to 0; All the centroids of the cross-sections of each sensitive section constitute the axis of the sensitive section, which is a straight line segment, and the axes of the sensitive sections in the three sensitive grids are parallel and located in the same plane, within the plane defined by the axes of the sensitive section , along the axial direction of the sensitive section, that is, the axial direction, and the direction perpendicular to the axial direction is the transverse direction; each sensitive section has a cross-section with equal resistance values on both sides, and the centroid position of the section is taken and the resistance of the sensitive section is The value is the nominal mass point of the sensitive section where the nominal mass constitutes, and the centroid position formed by the nominal mass points of each sensitive section is the center of the sensitive grid; The centers of the three sensitive grids have deviations in the axial direction and no deviations in the lateral direction; the three sensitive grids are called left sensitive grids, middle sensitive grids and right sensitive grids from left to right along the axial direction in the order of the center positions of the sensitive grids. grid; the distance between the center of the left sensitive grid and the center of the middle sensitive grid is Δx ₁ , the distance between the center of the middle sensitive grid and the center of the right sensitive grid is Δx ₁ , on the plane determined by the axes of each sensitive section, the left sensitive grid and the middle sensitive grid form a fork Finger arrangement, middle sensitive grid and right sensitive grid are interdigitated arrangement; The total resistance of the sensitive section of the left sensitive grid, the middle sensitive grid and the right sensitive grid is in a ratio of 3:8:5, and the total resistance of the sensitive section of the left sensitive grid, the middle sensitive grid and the right sensitive grid is under the same strain. The change value is also in a ratio of 3:8:5. 2. As claimed in claim 1, the axial deviation of the three-sensitive grid interdigitated metal strain gauge capable of measuring the axial deflection of the outer axial deflection of the offset sensitive grid is characterized in that: all cross-sectional shapes and sizes of each sensitive section are consistent, and take The position of the midpoint of the axis of each sensitive section and the nominal mass of the sensitive section constitutes the nominal mass of the sensitive section. The total length of the sensitive section of the left sensitive grid, the middle sensitive grid and the right sensitive grid is 3:8: 5 proportional relationship. 3. As claimed in claim 1 or 2, the axial deviation of the axial deflection of the outer axial deflection of the offset sensitive grid can be measured. The three-sensitive grid interdigitated metal strain gauge is characterized in that: the left sensitive grid and the right sensitive grid are forked Refers to the layout. 4. As claimed in claim 1 or 2, the axial deviation of the axial deflection of the outer axial deflection of the offset sensitive grid can be measured, and the interdigitated metal strain gauge of the three sensitive grids is characterized in that: the two pins of the right sensitive grid are located in the strain gauge Right side or left side of strain gauge. 5. As claimed in claim 1 or 2, the axial deviation of the axial deflection of the outer axial deflection of the offset sensitive grid can be measured, and the interdigitated metal strain gauge of the three sensitive grids is characterized in that: the sensitive section of the right sensitive grid is opposite to the middle sensitive grid The axial length can be shorter and the lateral distribution can be denser. 6. As claimed in claim 1 or 2, the axial deviation of the three-sensitive grid interdigitated metal strain gauge capable of measuring the axial deflection of the outer axial deflection of the offset sensitive grid is characterized in that: the metal strain gauge also includes a cover plate, the The cover sheet is covered on the sensitive grid and the base. 7. As claimed in claim 1 or 2, the axial deviation of the axial deflection of the outer axial deflection of the offset sensitive grid can be measured, and the interdigitated metal strain gauge of the three sensitive grids is characterized in that: the sensitive grid is wire type, foil type, Thin film or thick film sensitive gate. 8. As claimed in claim 1 or 2, the axial deviation of the three-sensitive grid interdigitated metal strain gauge capable of measuring the axial deflection of the outer axial deflection of the offset sensitive grid is characterized in that: the base is an adhesive film base, a glass fiber base , asbestos substrates, metal substrates or temporary substrates. 9. As claimed in claim 1 or 2, the axial deviation of the axial deflection of the outer axial deflection of the offset sensitive grid can be measured. The three sensitive grid interdigitated metal strain gauges are characterized in that: the three sensitive grids are left, middle and right placed on the base.