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 more can effectively detect the horizontal local derviation of surface strain measure close interdigital metal strain plate, particularly measuring workpieces corner, edge etc. in cross direction profiles five sensitive grid of one-sided outer horizontal local derviation to foil gauge have size restriction site or other should not arrange the horizontal single order local derviation of foil gauge position.
The technical solution adopted for the present invention to solve the technical problems is:
A kind ofly measure close interdigital metal strain plate in cross direction profiles five sensitive grid of one-sided outer horizontal local derviation, comprise substrate, described metal strain plate also comprises five sensitive grids, and the two ends of each sensitive grid connect a pin respectively, described substrate is fixed described five 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 five 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;
Five sensitive grid center bias frees in the axial direction, have deviation in the horizontal; The order of sensitive grid center pressed by five sensitive grids, is transversely followed successively by thin sensitive grid, middle first sensitive grid, middle second sensitive grid, close first sensitive grid and close second sensitive grid from top to bottom.The spacing of dredging sensitive grid center and middle first sensitive grid center is Δ y
a, the spacing at middle first sensitive grid center and close first sensitive grid center is also Δ y
a; The spacing of dredging sensitive grid center and middle second sensitive grid center is Δ y
b, the spacing at middle second sensitive grid center and close second sensitive grid center is also Δ y
b, Δ y
b> Δ y
a; The distance at middle first sensitive grid center and middle second sensitive grid center is Δ y
1, the spacing at close first sensitive grid center and close second sensitive grid center is 2 Δ y
1, Δ y
1=Δ y
b-Δ y
a;
Each sensitive segment axis is determined in plane, is interdigital layout, in interdigital layout between bottom close first sensitive grid and close second sensitive grid, without the interdigital layout between other sensitive grids in middle part between first sensitive grid and middle second sensitive grid;
The sensitive segment all-in resistance of dredging sensitive grid, middle first sensitive grid, middle second sensitive grid, close first sensitive grid and close second sensitive grid is the proportionate relationship of 5:12:12:7:7, dredges the proportionate relationship that sensitive grid, middle first sensitive grid, middle second sensitive grid, close first sensitive grid and the all-in resistance changing value of sensitive segment sensitive segment under identical strain of close second sensitive grid are also 5:12:12:7:7.
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 thin sensitive grid, middle first sensitive grid, middle second sensitive grid, close first sensitive grid and close second sensitive grid is the proportionate relationship of 5:12:12:7:7.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.
Among five sensitive grids, except being interdigital layout between above-mentioned two pairs of sensitive grids, without the interdigital layout between other sensitive grids.Described interdigital layout refers to: in the plane, in the sensitive segment distribution straggly with two sensitive grids on sensitive segment axes normal direction, the order occur respectively the sensitive segment of two sensitive grids in the direction in which and number of times do not limit in each sensitive segment axis institute of two sensitive grids.
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 y direction first-order partial derivative of f (x, y) is as follows:
Wherein y
1=y
0+ h, y
2=y
1+ h, paying special attention to above formula is (x, y
2+ 2h) 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, dredge the resistance of sensitive grid and close first sensitive grid and deduct the resistance value of middle first sensitive grid, distance again divided by thin sensitive grid center and close first sensitive grid center is the horizontal single order numerical value local derviation strained, according to numerical differentiation theory, this is the horizontal single order numerical value local derviation of close first sensitive grid center to downside 2h distance, here h equals the half of thin sensitive grid center to the spacing at close first sensitive grid center certainly, to survey be generally horizontal single order local derviation outside foil gauge coboundary, equally, dredge the resistance of sensitive grid and close second sensitive grid and deduct the resistance value of middle second sensitive grid, distance again divided by thin sensitive grid center and close second sensitive grid center is the horizontal single order numerical value local derviation strained, according to numerical differentiation theory, this is the horizontal single order numerical value local derviation of close second sensitive grid center to downside 2h distance, here h equals the half of thin sensitive grid center to the spacing at close second sensitive grid center certainly, to survey be generally horizontal single order local derviation outside foil gauge coboundary.The horizontal single order local derviation of above-mentioned two positions, place is by almost measuring the time-sharing multiplex of thin sensitive grid simultaneously.Therefore the advantage of this foil gauge be to can be used on the downside of it general foil gauge such as measuring workpieces corner, edge due to size restriction cannot the horizontal single order local derviation of two place's close positions of measuring point.
Technique should be noted keep thin sensitive grid, middle first sensitive grid, middle second sensitive grid, close first sensitive grid and close second 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 5:12:12:7:7 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 five sensitive grid upper, middle and lower are arranged in substrate.Certainly, also can be other arrangement.
Beneficial effect of the present invention is mainly manifested in: dredge sensitive grid by time-sharing multiplex, foil gauge almost can detect the horizontal single order local derviation at one place, outside under one place, outside and close second sensitive grid center under close first sensitive grid center simultaneously, wherein under close first sensitive grid center outside axially with close first sensitive grid center bias free, transversely the spacing at this place and close first sensitive grid center equals the spacing at thin sensitive grid center and close first sensitive grid center; Under close second sensitive grid center outside axially with close second sensitive grid center bias free, transversely the spacing at this place and close second sensitive grid center equals the spacing at thin sensitive grid center and close second sensitive grid center.Therefore can there be the horizontal single order local derviations of two place close positions of size restriction site the downside of foil gauge to foil gauge in measuring workpieces corner, edge etc.
Embodiment
Below in conjunction with accompanying drawing, the invention will be further described.
With reference to Fig. 1 ~ Fig. 4, measure a close interdigital metal strain plate in cross direction profiles five sensitive grid of one-sided outer horizontal local derviation, comprise substrate, described metal strain plate also comprises five sensitive grids, the two ends of each sensitive grid connect a pin respectively, described substrate are fixed described five 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 five 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;
Five sensitive grid center bias frees in the axial direction, have deviation in the horizontal; The order of sensitive grid center pressed by five sensitive grids, is transversely followed successively by thin sensitive grid, middle first sensitive grid, middle second sensitive grid, close first sensitive grid and close second sensitive grid from top to bottom.The spacing of dredging sensitive grid center and middle first sensitive grid center is Δ y
a, the spacing at middle first sensitive grid center and close first sensitive grid center is also Δ y
a; The spacing of dredging sensitive grid center and middle second sensitive grid center is Δ y
b, the spacing at middle second sensitive grid center and close second sensitive grid center is also Δ y
b, Δ y
b> Δ y
a; The distance at middle first sensitive grid center and middle second sensitive grid center is Δ y
1, the spacing at close first sensitive grid center and close second sensitive grid center is 2 Δ y
1, Δ y
1=Δ y
b-Δ y
a;
Each sensitive segment axis is determined in plane, is interdigital layout, in interdigital layout between bottom close first sensitive grid and close second sensitive grid, without the interdigital layout between other sensitive grids in middle part between first sensitive grid and middle second sensitive grid;
The sensitive segment all-in resistance of dredging sensitive grid, middle first sensitive grid, middle second sensitive grid, close first sensitive grid and close second sensitive grid is the proportionate relationship of 5:12:12:7:7, dredges the proportionate relationship that sensitive grid, middle first sensitive grid, middle second sensitive grid, close first sensitive grid and the all-in resistance changing value of sensitive segment sensitive segment under identical strain of close second sensitive grid are also 5:12:12:7:7.
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 thin sensitive grid, middle first sensitive grid, middle second sensitive grid, close first sensitive grid and close second sensitive grid is the proportionate relationship of 5:12:12:7:7.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.
Among five sensitive grids, except being interdigital layout between above-mentioned two pairs of sensitive grids, without the interdigital layout between other sensitive grids.Described interdigital layout refers to: in the plane, in the sensitive segment distribution straggly with two sensitive grids on sensitive segment axes normal direction, the order occur respectively the sensitive segment of two sensitive grids in the direction in which and number of times do not limit in each sensitive segment axis institute of two sensitive grids.
The present embodiment measure close interdigital metal strain plate in cross direction profiles five sensitive grid of one-sided outer horizontal local derviation, comprise substrate 1, described metal strain plate also comprises five sensitive grids, and the two ends of each sensitive grid connect a pin respectively, described substrate 1 is fixed described five sensitive grids.
Thin sensitive grid 2, middle first sensitive grid 3, middle second sensitive grid 4, close first sensitive grid 5 and close second sensitive grid 6 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 exactly thin sensitive grid 2, middle first sensitive grid 3, middle second sensitive grid 4, close first sensitive grid 5 and close second sensitive grid 6.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 thin sensitive grid 2, middle first sensitive grid 3, middle second sensitive grid 4, close first sensitive grid 5, close second sensitive grid 6 and substrate 1, play the protective seam of the effects such as protection against the tide, corrosion protection, loss prevention.
Pin 7 is for connecting sensitive grid and metering circuit, dredge sensitive grid 2, middle first sensitive grid 3, middle second sensitive grid 4, close first sensitive grid 5 and close second sensitive grid 6 and respectively have two pins 7, to with foil and membrane type foil gauge, the thin sensitive grid 2 that pin 7 is connected with it, middle first sensitive grid 3, middle second sensitive grid 4, close first sensitive grid 5 and close second sensitive grid 6 combine as a whole.Two pins dredging sensitive grid 2 are 7-1 and 7-2, two pins of middle first sensitive grid 3 are 7-3 and 7-4, two pins of middle second sensitive grid 4 are 7-5 and 7-6, and two pins of close first sensitive grid 5 are 7-7 and 7-8, and two pins of close second sensitive grid 6 are 7-9 and 7-10.
Dredging sensitive grid 2, middle first sensitive grid 3, middle second sensitive grid 4, close first sensitive grid 5 and close second sensitive grid 6 difference according to its metal sensitive material and processing technology, can be wire form, foil, diaphragm type, thick-film type.No matter which kind of to dredge the thickness of sensitive grid 2, middle first sensitive grid 3, middle second sensitive grid 4, close first sensitive grid 5 and close second sensitive grid 6 all very little, make the axial length of thin sensitive grid 2, middle first sensitive grid 3, middle second sensitive grid 4, close first sensitive grid 5 and close second sensitive grid 6 with it depend on the deformation of workpiece and change.The basic crucial part of the present invention is thin sensitive grid 2, middle first sensitive grid 3, middle second sensitive grid 4, cooperation between close first sensitive grid 5 and close second sensitive grid 6, has following main points:
The first, five sensitive grids are arranged in substrate, is called thin sensitive grid 2, middle first sensitive grid 3, middle second sensitive grid 4, close first sensitive grid 5 and close second sensitive grid 6.
The second, dredge sensitive grid 2, middle first sensitive grid 3, middle second sensitive grid 4, close first sensitive grid 5 and close second sensitive grid 6 and all can be divided into multiple sensitive segment 8 and multiple transition section 9, each sensitive segment 8 is connected to form sensitive grid by each transition section 9.Comparatively speaking, sensitive segment 8 is in elongated shape, and resistance is comparatively large and its resistance is comparatively responsive to strain; Described transition section 9, 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 8 and transition section 9 in more detail from angle more clearly.
3rd, the sensitive segment of each sensitive grid 8 is in elongated strip, and all xsect centres of form of each sensitive segment 8 form sensitive segment axis, and this sensitive segment 8 axis is straight line section, the axis being parallel of each sensitive segment 8 and be arranged in same plane.All xsects of each sensitive segment 8 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, dredging the proportionate relationship that the sensitive segment total length of sensitive grid 2, middle first sensitive grid 3, middle second sensitive grid 4, close first sensitive grid 5 and close second sensitive grid 6 be 5:12:12:7:7, about how realizing this length ratio relation to see below the method for composition graphs 4 explanation; The sensitive segment all-in resistance of dredging sensitive grid 2, middle first sensitive grid 3, middle second sensitive grid 4, close first sensitive grid 5 and close second sensitive grid 6 is the proportionate relationship of 5:12:12:7:7; Dredge the proportionate relationship that sensitive grid 2, middle first sensitive grid 3, middle second sensitive grid 4, close first sensitive grid 5 and the all-in resistance changing value of sensitive segment sensitive segment under identical strain of close second sensitive grid 6 are also 5:12:12:7:7.
5th, overlook thin sensitive grid 2, middle first sensitive grid 3, middle second sensitive grid 4, close first sensitive grid 5 and close second sensitive grid 6, they respectively have the sensitive segment that two kinds of length are different with axial starting point, terminal is identical, the two hop count is identical, above-mentioned each sensitive grid center can all be configured in y-axis by both choose reasonable length, and concrete grammar sees below the explanation of composition graphs 4.Dredge the center of sensitive grid 2, middle first sensitive grid 3, middle second sensitive grid 4, close first sensitive grid 5 and close second sensitive grid 6 all in y-axis, there is lateral deviation at their center without axial deviation.According to the vertical view of foil gauge in Fig. 2, the sensitive segment 8 dredging sensitive grid 2 has axial axis of symmetry x
s, dredge the center of sensitive grid 2 at y-axis and x
sthe intersection point of axle, the sensitive segment 8 of middle first sensitive grid 3 has axial axis of symmetry x
mA, the center of middle first sensitive grid 3 is at y-axis and x
mAthe intersection point of axle, the sensitive segment 8 of middle second sensitive grid 4 has axial axis of symmetry x
mB, the center of middle second sensitive grid 4 is at y-axis and x
mBthe intersection point of axle, the sensitive segment 8 of close first sensitive grid 5 has axial axis of symmetry x
dA, the center of close first sensitive grid 5 is at y-axis and x
dAthe intersection point of axle, the sensitive segment 8 of close second sensitive grid 6 has axial axis of symmetry x
dB, the center of close second sensitive grid 6 is at y-axis and x
dBthe intersection point of axle.
6th, the spacing of dredging the center of sensitive grid 2 and the center of middle first sensitive grid 3 is Δ y
a, the spacing at the center of middle first sensitive grid 3 and the center of close first sensitive grid 5 is also Δ y
a; The spacing of dredging the center of sensitive grid 2 and the center of middle second sensitive grid 4 is Δ y
b, the spacing at the center of middle second sensitive grid 4 and the center of close second sensitive grid 6 is also Δ y
b, Δ y
b> Δ y
a; The distance at the center of middle first sensitive grid 3 and the center of middle second sensitive grid 4 is Δ y
1, the spacing at the center of close first sensitive grid 5 and the center of close second sensitive grid 6 is 2 Δ y
1, Δ y
1=Δ y
b-Δ y
a, as shown in Figure 2.Shown in Fig. 2, each sensitive segment axis is determined in plane, is interdigital layout, in interdigital layout between bottom close first sensitive grid 5 and close second sensitive grid 6, without the interdigital layout between other sensitive grids in middle part between first sensitive grid 3 and middle second sensitive grid 4.Described interdigital layout refers to: in the plane, in the sensitive segment distribution straggly with two sensitive grids on sensitive segment axes normal direction, the order occur respectively the sensitive segment of two sensitive grids in the direction in which and number of times do not limit in each sensitive segment 8 axis of two sensitive grids institute.Because the relative position of thin sensitive grid 2, middle first sensitive grid 3, middle second sensitive grid 4, close first sensitive grid 5 and close second sensitive grid 6 is ensured quite accurately to be secured by foil gauge production technology, this is also that the present invention can detect workpiece and strains one of key of horizontal partial derivative.
In sum, the present invention dredges the proportionate relationship that sensitive grid 2, middle first sensitive grid 3, middle second sensitive grid 4, close first sensitive grid 5 and the all-in resistance changing value of sensitive segment sensitive segment under identical strain of close second sensitive grid 6 are also 5:12:12:7:7, each sensitive grid central shaft is to bias free, laterally have deviation, the spacing of dredging the center of sensitive grid 2 and the center of middle first sensitive grid 3 is Δ y
a, the spacing at the center of middle first sensitive grid 3 and the center of close first sensitive grid 5 is also Δ y
a; The spacing of dredging the center of sensitive grid 2 and the center of middle second sensitive grid 4 is Δ y
b, the spacing at the center of middle second sensitive grid 4 and the center of close second sensitive grid 6 is also Δ y
b, Δ y
b> Δ y
a; The distance at the center of middle first sensitive grid 3 and the center of middle second sensitive grid 4 is Δ y
1, the spacing at the center of close first sensitive grid 5 and the center of close second sensitive grid 6 is 2 Δ y
1, Δ y
1=Δ y
b-Δ y
a.
Dredging sensitive grid 2 resistance under making free state is R
u0, middle second sensitive grid 4 resistance is R
m0, close second sensitive grid 6 resistance is R
l0, should R be had
u0+ R
l0=R
m0=R
0.Foil gauge of the present invention is placed in certain when having a surface strain, dredging sensitive grid 2 resistance is R
0+ Δ R
u, middle second sensitive grid 4 resistance is R
0+ Δ R
m0, close second sensitive grid 6 resistance is R
0+ Δ R
l; On the other hand, the center of dredging sensitive grid 2 and close second sensitive grid 6 lays respectively at y-axis and x in Fig. 2
sintersection point and y-axis and x
dBintersection point, transversely at a distance of 2 Δ y
b.The formula of the relation of sensitive grid resistance and surface strain and numerical differentiation (3) is utilized to have:
Wherein
for outside 2 Δ y under close second sensitive grid 6 center deviation
bplace, namely y-axis and x in Fig. 2
oBintersection point, ε
ufor the strain of thin sensitive grid 2 center, ε
mfor the strain of middle second sensitive grid 4 center, ε
lfor the strain of close second sensitive grid 6 center.Namely this is the principle that the present embodiment measured surface strains horizontal local derviation.Pay special attention to, the numerical differentiation that above formula calculates is outside 2 Δ y under close second sensitive grid 6 center deviation
bthe horizontal single order local derviation of strain of position, this position is outside foil gauge lower limb, therefore has and is convenient to there are the horizontal single order local derviation of size restriction site in measuring workpieces corner, edge etc. advantage to foil gauge.Equally, dredge sensitive grid 2, middle first sensitive grid 3 and close first sensitive grid 5 can coordinate and calculate outside 2 Δ y under close first sensitive grid 5 center deviation
aposition, namely y-axis and x in Fig. 2
oAthe intersection point of axle, the horizontal first-order partial derivative of strain, this position is outside foil gauge lower limb.Outside 2 Δ y under above-mentioned close second sensitive grid 6 center deviation
boutside 2 Δ y under the horizontal single order local derviation of the strain of position and close first sensitive grid 5 center deviation
athe horizontal first-order partial derivative of strain of position is by realizing almost measuring to the time-sharing multiplex of thin sensitive grid 2 simultaneously.
Coordinated by the present embodiment electric bridge to can be used for monitor strain, strain horizontal 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,(5)
Because, the first, satisfy condition (5) time, the highest according to relevant theoretical foil gauge sensitivity; The second, monitor strain or strain horizontal local derviation the equal requirement condition of method (5) set up.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 (6) obtains; Can convolution (3) and formula (6) to the horizontal local derviation of strain, reasonable design arranges each brachium pontis sensitive grid and resistance, such as brachium pontis R
1second sensitive grid 4 in layout, brachium pontis R
2arranged in series close second sensitive grid 6 and thin sensitive grid 2, all the other brachium pontis configuration substitutional resistance, can obtain and outside 2 Δ y under close second sensitive grid 6 center deviation
bthe magnitude of voltage u that place's horizontal single order local derviation of strain is linear
o, this voltage is that feeble signal need be amplified.
Composition graphs 4, illustrates each sensitive grid how in design drawing 2.In Fig. 2, each sensitive grid is furnished with the sensitive segment that two kinds of length are different with axial starting point, terminal is identical, and its fundamental purpose is the center of two interdigital each other sensitive grids can be configured in the y-axis in Fig. 2, and principle is shown in Fig. 4.Have the local of two sensitive grid A and B in Fig. 4, A has A1 and A2 two kinds of sensitive segments, and B has B1 and B2 two kinds of sensitive segments.Each size is shown in Fig. 4, and wherein d is the size that technique determines, thinks definite value; L=2l-x is the overall length of A1 and A2, in design drawing 2 during each sensitive grid, according to resistance ratio and sensitive segment number, can determine its value, therefore also thinks in Fig. 4 that L determines; The amount determined is needed to be l and x in Fig. 4.Because A only has A1 and A2 two kinds of sensitive segments, and the hop count of the two is identical, as long as therefore be configured in the y-axis in Fig. 4 by the common center of one section of A1 and section A2.Linear relationship in conjunction with resistance value and length obviously has following system of equations:
Wherein first formula left side
refer to the distance of the off-centring y-axis of A1, the right
it is then the distance of the off-centring y-axis of A2.According to symmetry, l and x that can solve from above-mentioned formula is equally applicable to B1 and B2.And then l and x of each sensitive grid first can first determine L combined process length d and being solved by formula (7) again by the sensitive grid length in earlier stage determined, proportionate relationship, sensitive segment hop count etc. in foil gauge.