Background technology
The principle of work of metal resistance strain gauge is resistance strain effect, and namely tinsel is when being subject to effects of strain, and its resistance, along with the size of occurred mechanically deform (stretching or compression), corresponding change occurs.The theoretical formula of resistance strain effect is as follows:
Wherein R is its resistance value, and ρ is metal material resistivity, and L is metal material length, and S is metal material sectional area.Tinsel occurs in the process of mechanically deform bearing strain, and ρ, L, S three will change, thus will inevitably cause the change of metal material resistance value.When metal material is stretched, length increases, and sectional area reduces, and resistance value increases; When by compression, length reduces, and sectional area increases, and resistance value reduces.Therefore, as long as the change of resistance value can be measured, just known strained situation wiry.Metal material resistance change rate formula can be derived by relevant knowledges such as formula (1) and the mechanics of materials
Wherein Δ R is resistance variation amount, and Δ L is the variable quantity of metal material length on pulling force or pressure action direction, and ε is that the strain on same direction is usually called axial strain, and K is metal material ga(u)ge factor.
In actual applications, metal resistance strain gauge is pasted onto the surface of Sensor Elastic Element or tested mechanical component.When the flexible member in sensor or tested mechanical component produce strain by acting force, also there is identical mechanically deform in the foil gauge pasted thereon thereupon, causes foil gauge resistance that corresponding change occurs.At this moment, mechanical quantity is just converted to the variable quantity output of resistance by resistance strain gage.
But we also need the partial derivative understanding workpiece strain sometimes, such as have three kinds of occasions below, but are not limited thereto three, need to use surface of the work strain partial derivative:
The first, concentrate owing to there will be strain near workpiece shapes sudden change place, often become workpiece and first occur damaging part, the strain partial derivative near sudden change place of monitoring shape, this place strain intensity can be obtained intuitively.
Second, exist in a large number by comer pieces in building, bridge, plant equipment, mechanics of materials relevant knowledge tells us, bent beam surface axial strain is directly proportional to section turn moment, the axial partial derivative of section turn moment is directly proportional to cross section shearing strain, namely can know cross section shearing strain by the axial partial derivative of surperficial axial strain, and this shearing strain directly cannot measure at surface of the work with foil gauge;
3rd, during applied elasticity research workpiece strain, internal strain is decided by partial differential equation, and equation solution needs boundary condition, and surface of the work strain partial derivative is exactly one of boundary condition, and this is that general foil gauge cannot provide.
In addition, to some position of workpiece, the such as position such as the shaft shoulder, part edge place, due to the sudden change of geomery, it strains the change that often corresponding existence is larger.But, just due to the sudden change of geomery, make the foil gauge that the more difficult arrangement in this place is general, need a kind of energy inclined edge of monitor strain the sheet even product of edge outer fix instead of center position strain local derviation.So just can realize avoiding more difficult a distance, the target measured point layout foil gauge laying foil gauge, and finally measure the strain local derviation at this target measured point place.
Summary of the invention
The deficiency of strain local derviation cannot be detected in order to overcome existing metal strain plate, the invention provides a kind of can monitor strain axial distribution three the sensitive grid metal strain plate, particularly measuring workpieces corner, edge etc. that more effectively can detect the outer axial local derviation of the sheet measured of the axial local derviation of surface strain to foil gauge have size restriction site or other should not arrange the axial single order local derviation of foil gauge position.
The technical solution adopted for the present invention to solve the technical problems is:
Measure an axial distribution three sensitive grid metal strain plate for the outer axial local derviation of sheet, comprise substrate, described metal strain plate also comprises three sensitive grids, and the two ends of each sensitive grid connect a pin respectively, described substrate is fixed described three sensitive grids;
Each sensitive grid comprises sensitive segment and transition section, the two ends of described sensitive segment are transition section, described sensitive segment is elongated strip shaped, described transition section is tubbiness shape, the resistance of described sensitive segment is much larger than the resistance of described transition section, under same strain state, the increased resistance value of described sensitive segment is much larger than the increased resistance value of described transition section, and the increased resistance value of described transition section is close to 0;
All xsect centres of form of each sensitive segment form sensitive segment axis, this sensitive segment axis is straight line section, in described three sensitive grids each sensitive segment axis being parallel and be arranged in same plane, sensitive segment axis is determined in plane, along described sensitive segment axis direction namely axially, be laterally with axially vertical direction; Each sensitive segment exists the xsect that its both sides resistance value is equal, get this cross-section centroid position and with this sensitive segment resistance value for nominal mass is formed the nominal particle of place sensitive segment, the centroid position that the nominal particle of each sensitive segment is formed jointly is the center of sensitive grid;
There is deviation at three sensitive grid centers in the axial direction, bias free in the horizontal; The order of sensitive grid center pressed by three sensitive grids, is called left sensitive grid, middle sensitive grid and right sensitive grid vertically from left to right; The distance at left sensitive grid center and middle sensitive grid center is Δ x
1, the distance at middle sensitive grid center and right sensitive grid center is Δ x
1, sensitive grid center axial location height person among any two sensitive grids, on its each sensitive segment, the axial location of every bit is higher than the axial location of any point on the arbitrary sensitive segment of another sensitive grid;
The sensitive segment all-in resistance of left sensitive grid, middle sensitive grid and right sensitive grid is the proportionate relationship of 5:12:7, and left sensitive grid, middle sensitive grid and the all-in resistance changing value of sensitive segment sensitive segment under identical strain of right sensitive grid are also the proportionate relationship of 5:12:7.
Further, all shape of cross section consistent size of each sensitive segment, get the axis point midway of each sensitive segment and with this sensitive segment resistance value for nominal mass is formed the nominal particle of place sensitive segment, the sensitive segment total length of described left sensitive grid, middle sensitive grid and right sensitive grid is the proportionate relationship of 5:12:7.The program is a kind of scheme that can select, as long as the position of nominal particle meets the equal xsect position of form center of its both sides resistance value, also can be other positions.
Further, two pins of right sensitive grid are all positioned at the left side of right sensitive grid.Object reduces the distance of right sensitive grid center to foil gauge right side edge.
Further again, sensitive grid relatively, the sensitive segment axial length of right sensitive grid can be shorter and cross direction profiles can be closeer.Object reduces the distance of right sensitive grid center to foil gauge right side edge.
Utilize the linear relationship between metal material increased resistance value and strain, this foil gauge may be used for monitor strain as common foil gauge.On the other hand, according to (" numerical computation method " 21 pages (1.4.11)-(1.4.14) formula as Yi Fengkang etc. compiles, National Defense Industry Press publishes in Dec, 1978 makes equidistant interpolation analysis) in numerical differentiation theory about the circular of single order local derviation, the numerical computation method of the x direction first-order partial derivative of f (x, y) is as follows:
Wherein x
1=x
0+ h, x
2=x
1+ h, paying special attention to above formula is (x
2+ 2h, y) the first-order partial derivative value formula of position, the truncation error of this formula is less is o (h
2) be the higher order indefinite small of step-length square.By the strain that formula (2) engineering be it is generally acknowledged sensitive grid resistance change direct ratio and sensitive grid center, in conjunction with the proportionate relationship of each sensitive grid resistance and the resistance change under same strain, resistance and the resistance value deducting middle sensitive grid of left sensitive grid and right sensitive grid, then be the axial single order numerical value local derviation strained divided by the distance at left sensitive grid center and right sensitive grid center; Especially, this is the axial single order numerical value local derviation of right sensitive grid center 2h distance to the right, here h equals the distance between right sensitive grid center to middle sensitive grid certainly, therefore the advantage of this foil gauge be measuring workpieces corner, edge etc. to foil gauge have size restriction site or other should not arrange the axial single order local derviation of foil gauge position.
Technique should be noted keep left sensitive grid, middle sensitive grid and right sensitive grid transition section all-in resistance and the variable quantity of transition section resistance under external strain to be that the numerical relation of 5:12:7 is to heighten measuring accuracy, if the resistance of transition section and the lower resistance change of strain be can not ignore, also can be eliminated when detecting as systematic error.
Further, described metal strain plate also comprises cover plate, and described cover plate is covered in described sensitive grid and substrate.
Further again, described sensitive grid is wire form, foil, diaphragm type or thick-film type sensitive grid.
Further, described substrate is glued membrane substrate, glass fabric substrates, asbestos substrate, metallic substrates or temporary substrate.
Described three sensitive grid left, center, right are arranged in substrate.Certainly, also can be other arrangement.
Beneficial effect of the present invention is mainly manifested in: can detect the strain axis at right outside side one place, right sensitive grid center to single order local derviation, transversely this place and right sensitive grid center bias free, axially the spacing at this place and right sensitive grid center equals the spacing at left sensitive grid center and right sensitive grid center.Therefore the present invention can measuring workpieces corner, edge etc. to foil gauge have size restriction site or other should not arrange the axial single order local derviation of foil gauge position.
Embodiment
Below in conjunction with accompanying drawing, the invention will be further described.
With reference to Fig. 1 ~ Fig. 3, measure an axial distribution three sensitive grid metal strain plate for the outer axial local derviation of sheet, comprise substrate, described metal strain plate also comprises three sensitive grids, the two ends of each sensitive grid connect a pin respectively, described substrate are fixed described three sensitive grids;
Each sensitive grid comprises sensitive segment and transition section, the two ends of described sensitive segment are transition section, described sensitive segment is elongated strip shaped, described transition section is tubbiness shape, the resistance of described sensitive segment is much larger than the resistance of described transition section, under same strain state, the increased resistance value of described sensitive segment is much larger than the increased resistance value of described transition section, and the increased resistance value of described transition section is close to 0;
All xsect centres of form of each sensitive segment form sensitive segment axis, this sensitive segment axis is straight line section, in described three sensitive grids each sensitive segment axis being parallel and be arranged in same plane, sensitive segment axis is determined in plane, along described sensitive segment axis direction namely axially, be laterally with axially vertical direction; Each sensitive segment exists the xsect that its both sides resistance value is equal, get this cross-section centroid position and with this sensitive segment resistance value for nominal mass is formed the nominal particle of place sensitive segment, the centroid position that the nominal particle of each sensitive segment is formed jointly is the center of sensitive grid;
There is deviation at three sensitive grid centers in the axial direction, bias free in the horizontal; The order of sensitive grid center pressed by three sensitive grids, is called left sensitive grid, middle sensitive grid and right sensitive grid vertically from left to right; The distance at left sensitive grid center and middle sensitive grid center is Δ x
1, the distance at middle sensitive grid center and right sensitive grid center is Δ x
1, sensitive grid center axial location height person among any two sensitive grids, on its each sensitive segment, the axial location of every bit is higher than the axial location of any point on the arbitrary sensitive segment of another sensitive grid.
The sensitive segment all-in resistance of left sensitive grid, middle sensitive grid and right sensitive grid is the proportionate relationship of 5:12:7, and left sensitive grid, middle sensitive grid and the all-in resistance changing value of sensitive segment sensitive segment under identical strain of right sensitive grid are also the proportionate relationship of 5:12:7.
Further, all shape of cross section consistent size of each sensitive segment, get the axis point midway of each sensitive segment and with this sensitive segment resistance value for nominal mass is formed the nominal particle of place sensitive segment, the sensitive segment total length of described left sensitive grid, middle sensitive grid and right sensitive grid is the proportionate relationship of 5:12:7.The program is a kind of scheme that can select, as long as the position of nominal particle meets the equal xsect position of form center of its both sides resistance value, also can be other positions.
Further, two pins of right sensitive grid are all positioned at the left side of right sensitive grid, and object reduces the distance of right sensitive grid center to foil gauge right side edge.
Further again, sensitive grid relatively, the sensitive segment axial length of right sensitive grid can be shorter and cross direction profiles can be closeer, and object reduces the distance of right sensitive grid center to foil gauge right side edge.
The axial distribution three sensitive grid metal strain plate of the outer axial local derviation of the sheet measured of the present embodiment, comprise substrate 1, described metal strain plate also comprises three sensitive grids, and the two ends of each sensitive grid connect a pin respectively, described substrate 1 is fixed described three sensitive grids.
Left sensitive grid 2, middle sensitive grid 3 and right sensitive grid 4 can be fixed on substrate 1, for keep each sensitive grid fixing shape, position and size; Substrate 1 is very thin, thus the strain of surface of test piece is delivered to left sensitive grid 2, middle sensitive grid 3 and right sensitive grid 4 exactly.Substrate 1 can be glued membrane substrate, glass fabric substrates, asbestos substrate, metallic substrates and temporary substrate.Usually with cohering, weld, substrate is fixed on the tested position of test block by the mode such as ceramic spraying.Substrate 1 also can be printed on the lines that some are located for foil gauge.
The materials such as cover plate paper using or glue are made, and are covered in left sensitive grid 2, middle sensitive grid 3, right sensitive grid 4 and substrate 1, play the protective seam of the effects such as protection against the tide, corrosion protection, loss prevention.
Pin 5 is for connecting sensitive grid and metering circuit, and left sensitive grid 2, middle sensitive grid 3 and right sensitive grid 4 respectively have two pins 5, to foil and membrane type foil gauge, the left sensitive grid 2 that pin 5 is connected with it, middle sensitive grid 3 and right sensitive grid 4 combine as a whole.Two pins of left sensitive grid 2 are 5-1 and 5-2, two pins of middle sensitive grid 3 are 5-3 and 5-4, two pins of right sensitive grid 4 are 5-5 and 5-6, and pin 5-5 and 5-6 is all positioned at the left side of right sensitive grid 4, and object reduces the distance of right sensitive grid 4 to foil gauge right side edge.
Left sensitive grid 2, middle sensitive grid 3 and right sensitive grid 4, according to the difference of its metal sensitive material and processing technology, can be wire form, foil, diaphragm type, thick-film type.No matter the thickness of which kind of left sensitive grid 2, middle sensitive grid 3 and right sensitive grid 4 is all very little, make the axial length of left sensitive grid 2, middle sensitive grid 3 and right sensitive grid 4 with it depend on the deformation of workpiece and change.The basic crucial part of the present invention is left sensitive grid 2, cooperation between middle sensitive grid 3 and right sensitive grid 4, has following main points:
The first, three sensitive grids are arranged in substrate, is called left sensitive grid 2, middle sensitive grid 3 and right sensitive grid 4.
The second, left sensitive grid 2, middle sensitive grid 3 and right sensitive grid 4 all can be divided into multiple sensitive segment 6 and multiple transition section 7, and each sensitive segment 6 is connected to form sensitive grid by each transition section 7.Comparatively speaking, sensitive segment 6 is in elongated shape, and resistance is comparatively large and its resistance is comparatively responsive to strain; Described transition section 7, substantially in tubbiness shape, makes the resistance of described transition section very little and insensitive to strain, and under duty, resistance variations is close to 0, and therefore the summation of sensitive segment resistance is the all-in resistance of single sensitive grid substantially.Fig. 2 has marked sensitive segment 6 and transition section 7 in more detail from angle more clearly.
3rd, the sensitive segment of each sensitive grid 6 is in elongated strip, and all xsect centres of form of each sensitive segment 6 form sensitive segment axis, and this sensitive segment 6 axis is straight line section, the axis being parallel of each sensitive segment 6 and be arranged in same plane.All xsects of each sensitive segment 6 are consistent along the projection of shape of sensitive segment axis direction.Get the axis point midway of each sensitive segment and with this sensitive segment resistance value for nominal mass is formed the nominal particle of place sensitive segment, the centroid position that the nominal particle of each sensitive segment is formed jointly is the center of sensitive grid.
4th, sensitive segment 6 total length of left sensitive grid 2, middle sensitive grid 3 and right sensitive grid 4 is the proportionate relationship of 5:12:7, sensitive segment 6 all-in resistance of left sensitive grid 2, middle sensitive grid 3 and right sensitive grid 4 is the proportionate relationship of 5:12:7, and left sensitive grid 2, middle sensitive grid 3 and the all-in resistance changing value of sensitive segment 6 sensitive segment under identical strain of right sensitive grid 4 are also the proportionate relationship of 5:12:7.
5th, overlook left sensitive grid 2, middle sensitive grid 3 and right sensitive grid 4, they all have axis of symmetry and axis of symmetry overlaps (x-axis in Fig. 2), left sensitive grid 2, middle sensitive grid 3 sensitive segment 6 respective with right sensitive grid 4 is all parallel with this axis of symmetry, and the sensitive segment 6 of each sensitive grid all distributes about this rotational symmetry.Therefore, left sensitive grid 2, middle sensitive grid 3 and right sensitive grid 4 are coaxial, namely detect equidirectional strain and the center of left sensitive grid 2, middle sensitive grid 3 and right sensitive grid 4 all in x-axis, there is axial deviation at their center without lateral deviation.According to the vertical view of foil gauge in Fig. 2, the sensitive segment 6 of left sensitive grid 2 has lateral symmetry axle y
l, the center of left sensitive grid 2 is at x-axis and y
lthe intersection point of axle, the sensitive segment 6 of middle sensitive grid 3 has lateral symmetry axle y
m, the center of middle sensitive grid 3 is at x-axis and y
mthe intersection point of axle, the sensitive segment 6 of right sensitive grid 4 has lateral symmetry axle y
r, the center of right sensitive grid 4 is at x-axis and y
rthe intersection point of axle.
6th, the distance at left sensitive grid 2 center and middle sensitive grid 3 center is Δ x
1, the distance at middle sensitive grid 3 center and right sensitive grid 4 center is Δ x
1, namely the line mid point at the center of left sensitive grid 2 and the center of right sensitive grid 4 is also x-axis and y
mthe intersection point of axle, as shown in Figure 2.By the forward of x-axis shown in Fig. 2, on any sensitive segment 6 of left sensitive grid 2 the x coordinate of arbitrfary point be less than middle sensitive grid 3 any sensitive segment 6 on the x coordinate of arbitrfary point, on any sensitive segment 6 of middle sensitive grid 3 the x coordinate of arbitrfary point be less than right sensitive grid 4 any sensitive segment 6 on the x coordinate of arbitrfary point.Because the relative position of left sensitive grid 2, middle sensitive grid 3 and right sensitive grid 4 is ensured quite accurately to be secured by foil gauge production technology, this is also that the present invention can detect the key one of of workpiece strain axis to partial derivative.
In sum, the left sensitive grid of the present invention 2, middle sensitive grid 3 and right sensitive grid 4 increased resistance value under same strain is the proportionate relationship of 5:12:7, and each sensitive grid central cross bias free axially has deviation, left sensitive grid 2 center equal to the distance of right sensitive grid 4 with middle sensitive grid 3 center to the distance at middle sensitive grid 3 center.
Free state bottom left sensitive grid 2 resistance is made to be R
l0, middle sensitive grid 3 resistance is R
m0, right sensitive grid 4 resistance is R
r0, should R be had
l0+ R
r0=R
m0=R
0.Foil gauge of the present invention is placed in certain when having a surface strain, left sensitive grid 2 resistance is R
0+ Δ R
l, middle sensitive grid 3 resistance is R
0+ Δ R
m0, right sensitive grid 4 resistance is R
0+ Δ R
r; On the other hand, the center of left sensitive grid 2 and right sensitive grid 4 lays respectively at x-axis and y in Fig. 2
lintersection point and x-axis and y
rintersection point, axially at a distance of 2 Δ x
1.If
for right sensitive grid 4 central right 2 Δ x
1place, namely x-axis and y in Fig. 2
ointersection point, utilize the formula of the relation of sensitive grid resistance and surface strain and numerical differentiation (3) to have:
Wherein ε
lfor the strain of left sensitive grid 2 center, ε
mfor the strain of middle sensitive grid 3 center, ε
rfor the strain of right sensitive grid 4 center.Namely this is the principle of the present embodiment measured surface strain axis to local derviation.Pay special attention to, the numerical differentiation that above formula calculates is 2 Δ x outside right sensitive grid 4 center deviation
1the strain axis of position to single order local derviation, this position be foil gauge right side edge very outside, therefore have and be convenient to there are the axial single order local derviation of size restriction site in measuring workpieces corner, edge etc. advantage to foil gauge.Composition graphs 2, notices that pin 5-5 and 5-6 of right sensitive grid 4 is arranged on the left of right sensitive grid 4, and its object is all to reduce the distance of right sensitive grid 4 center to foil gauge right side edge as far as possible, so that play above-mentioned advantage further.
Coordinated by the present embodiment electric bridge to can be used for monitor strain, strain axis to single order local derviation, suppose that bridge input voltage is u
i, output voltage is u
o, Fig. 3 is shown in by the schematic diagram of measuring bridge.When without workpiece effects of strain, each arm resistance of electric bridge is labeled as R respectively according to clockwise direction
1, R
2, R
3, R
4, when obscuring also with these sign flag resistance place electric bridges.Each electric bridge can be laid sensitive grid or the resistance of foil gauge.Arrange identical with general foil gauge, if settle sensitive grid on multiple brachium pontis, to the order of each installation position, the requirement of strain difinite quality.During without workpiece effects of strain, the Output Voltage Formula of electric bridge is
Now, bridge balance i.e. u is required
o=0, so so-called bridge balance condition R must be met
1r
3-R
2r
4=0, the electric bridge of employing meets further
R
1=R
2=R
3=R
4,(6)
Because, the first, satisfy condition (6) time, the highest according to relevant theoretical foil gauge sensitivity; The second, monitor strain or strain axis are set up to the equal requirement condition of method (6) of local derviation.When foil gauge, with external world's strain, strain also occurs, above-mentioned bridge balance condition is generally no longer set up, now
Due to Δ R
i< < R
i(i=1,2,3,4) event first ≈ sets up, and second ≈ is as Δ R
1-Δ R
2with Δ R
3-Δ R
4jack per line or contrary sign but | Δ R
1-Δ R
2| with | Δ R
3-Δ R
4| not very close to time set up, in engineering, choose reasonable foil gauge installation position can realize completely.The voltage measurement strain that general available formula (7) obtains; Can convolution (4) and formula (7) to the axial local derviation of strain, reasonable design arranges each brachium pontis sensitive grid and resistance, such as brachium pontis R
1sensitive grid 3 in layout, brachium pontis R
2the left sensitive grid of arranged in series 2 and right sensitive grid 4, the configuration of all the other brachium pontis and brachium pontis R
1equivalent resistance, can obtain and right sensitive grid 4 center deviation right outside side 2 Δ x
1position strain axis is to the linear magnitude of voltage u of single order local derviation
o, this voltage is that feeble signal need be amplified.