CN105066869B - Lateral deviation double sensitive grid interdigitated metal strain gauge capable of measuring lateral deflection of surface strain - Google Patents

Abstract

A lateral deviation double sensitive grid interdigitated metal strain gauge capable of measuring the lateral deflection of surface strain, including a base and two sensitive grids, each of which is connected to a lead wire at both ends, and the two sensitive grids are fixed on the base ; Each sensitive grid includes a sensitive section and a transition section, and the axes of all sensitive sections are straight lines, arranged in parallel and in the same plane; in the plane determined by the axis of the sensitive section, along the axis direction of the sensitive section, that is, the axial direction, and The direction perpendicular to the axial direction is the transverse direction; the resistance of the two sensitive grids is the same, and the resistance change is the same under the same strain. They are respectively called the upper sensitive grid and the lower sensitive grid from top to bottom along the horizontal direction. On the plane determined by the axis of each sensitive section, The upper sensitive grid and the lower sensitive grid are interdigitated; the centers of the two sensitive grids have no deviation in the axial direction, but have deviations in the lateral direction. The invention can not only measure the strain, but also can effectively detect the transverse first-order partial derivative of the surface strain.

Description

The lateral deviation of the lateral deflection of the surface strain can be measured. The interdigitated metal strain of the double sensitive grid Variation

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:

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

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.

Contents of the invention

In order to overcome the deficiency that the existing metal strain gauges cannot detect the strain deflection, the present invention provides a lateral deviation double sensitive grid interdigitated type that can measure the strain and effectively detect the lateral deflection of the surface strain. Metal strain gauges.

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

A lateral deviation double-sensing grid interdigitated metal strain gauge capable of measuring surface strain lateral deflection, including a base, and the metal strain gauge also includes two sensitive grids, respectively a lower sensitive grid and an upper sensitive grid, each sensitive Two ends of the grid are respectively connected to a lead wire, and the two 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. The axis of the sensitive section is a straight line segment. The axes of the sensitive sections are parallel and located in the same plane. In the plane defined by the axes of the sensitive section, The direction is the axial direction, and the direction perpendicular to the axial direction is the transverse direction; the shape and size of all cross-sections of each 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 nominal mass point of each sensitive section, the centroid position formed by the nominal mass points of each sensitive section is the center of the sensitive grid;

The total resistance of the sensitive section of the two sensitive grids is consistent, and the total resistance change value of the sensitive section of the two sensitive grids is the same under the same strain, and the centers of the two sensitive grids are located on a straight line, which is perpendicular to the two sensitive grids. The two sensitive grids are called the upper sensitive grid and the lower sensitive grid from top to bottom along the line direction of any sensitive section axis of the grid; on the plane determined by the axes of each sensitive section, there is a fork between the upper sensitive grid and the lower sensitive grid. refers to the layout;

The centers of the two sensitive grids have no deviation in the axial direction, but have deviations in the lateral direction, and the distance between the center of the upper sensitive grid and the center of the lower sensitive grid is Δy.

In the present invention, the connecting line between the centers of the two sensitive grids should be perpendicular to the axial direction of any one of the sensitive sections of the two sensitive grids. Therefore, it is said that the two sensitive grids have a lateral deviation. The distance between the centers of the two sensitive grids is Δy, or the lateral deviation is Δy. Δy is generally smaller or even much smaller than the length of each sensitive section. The interdigital arrangement refers to that: 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 a direction perpendicular to the axes of the sensitive sections. There is no limitation on the order and times of the sensitive sections of the two sensitive gates appearing in this direction. Using the linear relationship between the resistance change value and strain of metal materials, on the one hand, it can be used to measure strain like ordinary strain gauges; on the other hand, the ratio of the resistance difference between the two sensitive grids and the distance between the centers of the two sensitive grids reflects Transverse deflector of strain.

In the process, care should be taken to keep the total resistance of the transition section of each sensitive gate and the change of the transition section resistance under external strain consistent to increase the measurement accuracy. If the resistance of the transition section and the change of resistance under strain cannot be ignored, it can also be used as a system error. Eliminated 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 two sensitive gates are arranged on the base up and down. Of course, other arrangements are also possible.

The beneficial effects of the invention are mainly manifested in that not only the surface strain of the workpiece can be measured, but also the lateral partial derivative of the surface strain can be effectively detected.

Description of drawings

Fig. 1 is a schematic diagram of a lateral deviation double-sensitive grid interdigitated metal strain gauge capable of measuring lateral deflection of surface strain.

Fig. 2 is a top view of a lateral deviation double-sensitive grid interdigitated metal strain gauge capable of measuring lateral deflection of surface strain.

Figure 3 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 3, a lateral deviation double-sensing grid interdigitated metal strain gauge capable of measuring the lateral deflection of surface strain includes a base, and the metal strain gauge also includes two sensitive grids, which are the lower sensitive grid and the lower sensitive grid respectively. An upper sensitive grid, the two ends of each sensitive grid are respectively connected to a lead wire, and the two 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. The axis of the sensitive section is a straight line segment. The axes of the sensitive sections are parallel and located in the same plane. In the plane defined by the axes of the sensitive section, The direction is the axial direction, and the direction perpendicular to the axial direction is the transverse direction; the shape and size of all cross-sections of each 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 nominal mass point of each sensitive section, the centroid position formed by the nominal mass points of each sensitive section is the center of the sensitive grid;

The total resistance of the sensitive section of the two sensitive grids is consistent, and the total resistance change value of the sensitive section of the two sensitive grids is the same under the same strain, and the centers of the two sensitive grids are located on a straight line, which is perpendicular to the two sensitive grids. The two sensitive grids are called the upper sensitive grid and the lower sensitive grid from top to bottom along the line direction of any sensitive section axis of the grid; on the plane determined by the axes of each sensitive section, there is a fork between the upper sensitive grid and the lower sensitive grid. refers to the layout;

The centers of the two sensitive grids have no deviation in the axial direction, but have deviations in the lateral direction, and the distance between the center of the upper sensitive grid and the center of the lower sensitive grid is Δy.

The double-sensing grid interdigitated metal strain gauge capable of measuring the lateral deviation of the lateral deflection of the surface strain in this embodiment includes a substrate 1, and the metal strain gauge also includes two sensitive grids, each of which is connected to a The two sensitive grids are fixed on the base 1.

The lower sensitive grid 2 and the upper sensitive grid 3 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 lower sensitive grid 2 And upper sensitive gate 3. 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, covering the lower sensitive grid 2, the upper sensitive grid 3 and the base 1, and serves as a protective layer for moisture-proof, corrosion-proof, damage-proof and other functions.

The lead wire 4 is used to connect the sensitive grid and the measurement circuit. The lower sensitive grid 2 or the upper sensitive grid 3 each has two lead wires 4. For foil and film strain gauges, the lower sensitive grid 2 or the upper sensitive grid connected with the lead wire 4 The grid 3 is connected as one.

The lower sensitive grid 2 and the upper sensitive grid 3 can be wire type, foil type, thin film type, thick film type according to their metal sensitive materials and processing technology. The thickness of the lower sensitive grid 2 or the upper sensitive grid 3 is very small, so that the axial lengths of the lower sensitive grid 2 and the upper sensitive grid 3 vary with the deformation of the workpiece to which they are attached. The basic innovation of the present invention lies in the cooperation between the lower sensitive grid 2 and the upper sensitive grid 3, which has the following main points:

First, two sensitive gates are arranged on the substrate, which are respectively called the lower sensitive gate 2 and the upper sensitive gate 5 .

Second, both the lower sensitive gate 2 and the upper sensitive gate 3 can be divided into a plurality of sensitive sections 5 and a plurality of transition sections 6, and each transition section 6 connects the sensitive sections 5 to form a sensitive gate. In comparison, the sensitive section 5 is elongated, has a large resistance and its resistance is more sensitive to strain; the transition section 6 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 grid. Figure 2 marks the sensitive section 5 and the transition section 6 in more detail for a clearer perspective.

Third, the cross-sectional shapes of the sensitive sections 5 of the lower sensitive grid 2 and the upper sensitive grid 3 are the same, and the sum of the lengths of the sensitive sections 5 of the lower sensitive grid 2 and the upper sensitive grid 3 is the same. Neglecting the resistance of the transition section 6, the total resistances of the lower left sensitive grid 2 and the upper sensitive grid 3 are equal, and the total resistance change of the sensitive section of the two sensitive grids should be consistent under the same strain.

Fourth, the sensitive section 5 of each sensitive grid is in the shape of a long and thin strip, and all the cross-sectional centroids of each sensitive section 5 constitute the axis of the sensitive section, the axis of the sensitive section 5 is a straight line segment, and the axes of each sensitive section 5 are parallel and lie in the same plane. The projection shapes of all cross sections of each sensitive section 5 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.

The 5th, overlooking all sensitive sections 5 of lower sensitive grid 2 and upper sensitive grid 3, they all have symmetry axis and symmetry axis coincides (y-axis in Fig. 2), the respective sensitive segments of lower sensitive grid 2 and upper sensitive grid 3 5 are all perpendicular to the axis of symmetry, and the sensitive segments 5 of each sensitive grid are distributed symmetrically about this axis, and the starting and ending positions of each sensitive segment 5 in the lower sensitive grid 2 and the upper sensitive grid 3 along the x-axis direction are the same. Therefore, it can be said that the lower sensitive grid 2 and the upper sensitive grid 3 have no axial deviation but only lateral deviation, and the center positions of the lower sensitive grid 2 and the upper sensitive grid 3 are both on the y-axis. According to the top view of the strain gauge in Fig. 2, the center of the lower sensitive grid 2 is at the intersection of the y axis and the x _L axis, and the center of the upper sensitive grid 3 is at the intersection of the y axis and the x _U axis. The midpoint of the line connecting the center of the lower sensitive grid 2 and the center of the upper sensitive grid 3 is the intersection of the x-axis and the y-axis.

Sixth, the lower sensitive grid 2 and the upper sensitive grid 3 are interdigitated, and the centers of the two sensitive grids are on the same symmetry axis y-axis. It can be noticed that the direct result of the interdigitation arrangement is that the center of the lower sensitive grid 2 is relatively close to the center of the upper sensitive grid 3 with a lateral distance of Δy, as shown in FIG. 2 . Since the relative positions of the lower sensitive grid 2 and the upper sensitive grid 3 are ensured to be fairly accurately fixed 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 lower sensitive grid 2 and the upper sensitive grid 3 of the present invention are equal in size, the axial distance between the sensitive grid centers is 0, and the lateral distance is very close to Δy.

In the free state, the resistance of the lower sensitive gate 2 is R _L0 , and the resistance of the upper sensitive gate 3 is R _R0 , so R _L0 =R _R0 =R ₀ . When the strain gauge of the present invention is placed on a strained surface, the resistance of the lower sensitive grid 2 is R ₀ +ΔR _L , and the resistance of the upper sensitive grid 3 is R ₀ +ΔR _U ; on the other hand, the lower sensitive grid 2 and the upper sensitive grid The centers of 3 are respectively located at the intersections of the y-axis and xL and the intersections of the _y -axis and _xU in Figure 2, and the distance between the centers of the two sensitive grids is Δy in the transverse direction, and the transverse direction is the x-axis. The difference in stress at the center of the lower sensitive grid 2 and the upper sensitive grid 3 results in the difference in resistance between the lower sensitive grid 2 and the upper sensitive grid 3 . The relationship between the sensitive grid resistance and the surface strain is:

in ε _L is the strain at the center of the lower sensitive grid 2 , and ε _U is the strain at the center of the upper sensitive grid 3 . This is the principle of the present invention to measure the lateral deflection of surface strain.

This embodiment can be used to measure strain and strain transverse deflection by combining this embodiment with an electric bridge. Assuming that the input voltage of the electric bridge is u _i and the output voltage is u _o , the schematic diagram of the measuring electric bridge is shown in FIG. 3 . 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

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 , (5)

Because, first, when the condition (5) is satisfied, the sensitivity of the strain gauge is the highest according to the relevant theory; second, the method of measuring the strain or the lateral deflection of the strain requires the condition (5) 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

Since ΔR _i << R _i (i=1,2,3,4) the first ≈, the second ≈negligible part ΔR ₁ ΔR ₃ -ΔR ₂ ΔR ₄ is also very small, and can be used in engineering It is much smaller than the more reserved part. Generally, the voltage obtained by formula (6) can be used to measure the strain; for the strain transverse deflector, formula (3) and formula (6) can be combined to rationally design and arrange the sensitive grid and resistance of each bridge arm to obtain a linear relationship with the strain transverse deflector The voltage value u _o is a weak signal that needs to be amplified.

Claims (5)

1. A lateral deviation double-sensitive grid interdigitated metal strain gauge capable of measuring surface strain lateral deflection, including a base, is characterized in that: the metal strain gauge also includes two sensitive grids, which are respectively a lower sensitive grid and an upper sensitive grid. Sensitive grids, two ends of each sensitive grid are respectively connected to a lead wire, and the two 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. The axis of the sensitive section is a straight line segment. The axes of the sensitive sections are parallel and located in the same plane. In the plane defined by the axes of the sensitive section, The direction is the axial direction, and the direction perpendicular to the axial direction is the transverse direction; the shape and size of all cross-sections of each 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 nominal mass point of each sensitive section, the centroid position formed by the nominal mass points of each sensitive section is the center of the sensitive grid; The total resistance of the sensitive section of the two sensitive grids is consistent, and the total resistance change value of the sensitive section of the two sensitive grids is the same under the same strain, and the centers of the two sensitive grids are located on a straight line, which is perpendicular to the two sensitive grids. The two sensitive grids are called the upper sensitive grid and the lower sensitive grid from top to bottom along the line direction of any sensitive section axis of the grid; on the plane determined by the axes of each sensitive section, there is a fork between the upper sensitive grid and the lower sensitive grid. refers to the layout; The centers of the two sensitive grids have no deviation in the axial direction, but have deviations in the lateral direction, and the distance between the center of the upper sensitive grid and the center of the lower sensitive grid is Δy. 2. The lateral deviation double-sensitive gate interdigitated metal strain gauge capable of measuring lateral deflection of surface strain according to claim 1, characterized in that: the metal strain gauge also includes a cover sheet, and the cover sheet covers the the sensitive grid and the substrate. 3. The lateral deviation double-sensitive grid interdigitated metal strain gauge capable of measuring lateral deflection of surface strain as claimed in claim 1 or 2, characterized in that: the sensitive grid is wire type, foil type, film type or thick Membrane sensitive grid. 4. The lateral deviation double-sensitive grid interdigitated metal strain gauge capable of measuring lateral deflection of surface strain according to claim 1 or 2, characterized in that: the substrate is an adhesive film substrate, a glass fiber substrate, an asbestos substrate, Metal base or temporary base. 5. The interdigitated metal strain gauge with double sensitive grids capable of measuring the lateral deviation of lateral deflection of surface strain according to claim 1 or 2, characterized in that: the two sensitive grids are arranged up and down on the substrate.