CN109100074B - Six-dimensional force sensor irrelevant to patch direction and measuring method thereof - Google Patents
Six-dimensional force sensor irrelevant to patch direction and measuring method thereof Download PDFInfo
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- CN109100074B CN109100074B CN201810734086.9A CN201810734086A CN109100074B CN 109100074 B CN109100074 B CN 109100074B CN 201810734086 A CN201810734086 A CN 201810734086A CN 109100074 B CN109100074 B CN 109100074B
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- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L5/00—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes
- G01L5/16—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes for measuring several components of force
- G01L5/161—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes for measuring several components of force using variations in ohmic resistance
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Abstract
The invention discloses a six-dimensional force sensor irrelevant to the direction of a patch and a measuring method thereof, wherein the six-dimensional force sensor comprises two testing rings and connecting ends, the two testing rings are cylinders provided with inner holes, stop pin holes are formed in the two connecting ends, threaded holes are formed in the two connecting ends, two ends of each testing ring are respectively connected with one end of each connecting end, the other ends of the two connecting ends are connected with a structural member through the threaded holes and the stop pin holes, and the measuring method is obtained by forming an overdetermined equation set and using a least square method for inversion solution; the six-dimensional force sensor has the advantages of miniaturization, simple manufacture, high decoupling of force and couple in different directions, better noise resistance and no requirement on the direction of a patch for the decoupling degree.
Description
Technical Field
The invention relates to a sensor manufacturing and strain measurement technology, in particular to a six-dimensional force sensor irrelevant to a patch direction and a measurement method thereof.
Background
The six-dimensional force sensor plays an increasingly important role in the fields of modern national defense industry, robot manufacturing and the like. At present, the six-dimensional force sensor mainly has the following structure: three vertical ribs, four vertical ribs, eight vertical ribs, a cylindrical structure, a planar cross structure, a planar double cross structure, a double-ring type composite beam structure, an asymmetric planar three-beam structure, a double E-shaped thin film structure and the like. Chinese patent ZL201010577466.X discloses a double-cross beam high-sensitivity six-dimensional torque sensor, which has high requirements on part machining precision, assembly clearance and direction of a patch, and is difficult to implement. Chinese patent ZL201710340000.X discloses a non-coupling six-dimensional force sensor with a binocular structure, and the sensor is complex in structure and difficult to guarantee reliability. Some six-dimensional force sensors are designed based on a Steward parallel structure: the ball hinge is adopted, so that excessive noise is caused by assembly clearance when dynamic load is measured, and the ball hinge is not suitable for dynamic load measurement; the elastic ball hinge is adopted, and larger damping can be generated due to the deformation of the elastic ball hinge in the dynamic load measuring process, so that the elastic ball hinge is not suitable for dynamic load measurement. Some six-dimensional force sensors are too complex in structure; some six-dimensional force sensors have low force decoupling degrees in different directions; some six-dimensional force sensors have higher requirements on the direction of the patch, and have the problem of increased force coupling in each direction due to the direction error of the patch; some six-dimensional force sensors use quartz crystals, which are difficult to manufacture and have high manufacturing cost.
Disclosure of Invention
Aiming at the prior art, the invention aims to solve the problems that the strain type six-dimensional force sensor in the prior art uses a single-chip pasting method at pasting points and the decoupling degree of the six-dimensional force sensor is greatly influenced by the pasting direction, so that strain rosettes are pasted at all the pasting points, and the six-dimensional force sensor irrelevant to the pasting direction is provided, namely, the measuring precision of the force in each direction is not influenced by the pasting direction.
In order to achieve the purpose, the six-dimensional force sensor irrelevant to the patch direction comprises two testing rings and connecting ends, wherein the testing rings are cylinders provided with inner holes, stop pin holes are formed in the two connecting ends, threaded holes are formed in the two connecting ends, two ends of each testing ring are respectively connected with one end of each connecting end, and the other ends of the two connecting ends are connected with a structural member through the threaded holes and the stop pin holes.
Furthermore, the connecting end appearance structure is in a hexagon nut shape.
Furthermore, the number of the stop pin holes on each connecting end is two, and the two stop pin holes are on the same axis.
Further, the axis direction between the stop pin holes on the two connecting ends is the same.
Further, test ring and two link are integrated into one piece structure.
A measuring method of a six-dimensional force sensor independent of the direction of a patch is realized by the following steps:
firstly, a numerical control method is used for processing and manufacturing the six-dimensional force sensor, the middle of the six-dimensional force sensor is provided with a test ring, the two sides of the six-dimensional force sensor are provided with connecting ends, the connecting ends are provided with threaded holes and stop pin holes, and the whole structure is manufactured integrally;
secondly, 4 strain flowers are pasted at the middle end (namely the A _ A section) of the test ring at equal intervals along the ring direction in a counterclockwise direction and are respectively pasted at four positions, namely a strain flower upper pasting point, a strain flower left pasting point, a strain flower lower pasting point and a strain flower right pasting point, and the pasting direction of the strain flowers is not required;
③ sequentially calibrating axial force (F)z) Bending moment (M)x,My) Shear force (F)x,Fy) Torque (T)z) And the transfer relation between the strains tested by each strain gauge and forming a transfer coefficient matrix K;
fourthly, loading the six-dimensional force sensor to obtain the corresponding strain on the strain gauge;
fifthly, the transfer coefficient matrix K and the strain are transformed into an over-determined equation set, the equation set is solved by using a least square method, and the force and the couple in each direction are obtained.
The invention has the beneficial effects that: the invention can miniaturize the six-dimensional force sensor,the reliability of the sensor is improved, the sensor has higher torsional rigidity and bending rigidity, and the test range of torque and bending moment is enlarged. The force-sensitive element is designed as a thin circular ring, and 4 strain patterns are pasted on the outer side of the circular ring at equal intervals along the circular ring direction, so that the axial force (F) is greatly improvedz) Bending moment (M)x,My) Shear force (F)x,Fy) Torque (T)z) And a transfer relation matrix K between the strains tested by each strain gauge, so that the transfer relation matrix K becomes a good state matrix. A least squares solution may be used for the good state matrix and for the over-defined matrix.
The invention does not require the direction of the patch, and different transfer coefficient matrixes can be obtained in different patch directions, but as long as the pasting points of the 4 strain flowers are unchanged, the condition numbers of the different transfer coefficient matrixes can be kept unchanged when the coordinates of the strain tensor are transformed in a Cartesian rectangular coordinate system. Therefore, as long as the transfer coefficient matrix between the load and the strain state of the 4 points is a good state matrix, the property state of the transfer coefficient matrix cannot be changed in any pasting direction of the strain, so that the least square inversion can still be adopted for solving, and the solution is not changed. According to the invention, the thin circular ring and the strain rosettes with 4 patch directions are used, and the transfer coefficient matrix between the strain and the load is directly calculated by combining the least square algorithm, so that the complex design of a strain gauge bridge assembly is omitted (the force coupling between different directions after the bridge assembly is still large, and high-precision decoupling can not be realized), and the high-precision decoupling effect and the good anti-noise effect are obtained.
The six-dimensional force sensor is miniaturized, the six-dimensional force sensor is simple to manufacture, the six-dimensional force sensor is enabled to highly decouple forces and couples in different directions, the six-dimensional force sensor is enabled to have better anti-noise performance, and the decoupling degree of the six-dimensional force sensor does not make a requirement on the direction of a patch.
Drawings
FIG. 1 is a schematic diagram of a six-dimensional force sensor according to the present invention;
FIG. 2 is a front view of a six-dimensional force sensor of the present invention;
FIG. 3 is a cross-sectional view taken along line A-A of the present invention;
FIG. 4 is a cross-sectional view of the invention taken along line B-B.
Wherein: the test ring is 1, the stop pin hole is 2, the threaded hole is 3, the connecting end is 4, the strain flower upper pasting point is 11, the strain flower left pasting point is 12, the strain flower lower pasting point is 13, and the strain flower right pasting point is 14.
Detailed Description
The following further description of the embodiments of the present invention will be made with reference to the drawings and finite element calculations, it being understood that the embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.
As shown in fig. 1 to 4, the invention provides a six-dimensional force sensor irrelevant to a patch direction, which comprises a test ring 1 and two connecting ends 4, wherein the test ring 1 is a cylinder provided with an inner hole, the two connecting ends 4 are provided with stop pin holes 2, a threaded hole 3 is arranged inside the test ring, two ends of the test ring 1 are respectively connected with one end of the connecting end 4, and the other ends of the two connecting ends 4 are connected with a structural member through the threaded hole 3 and the stop pin holes 2.
Preferably, the connecting end 4 is in a hexagon nut shape.
Preferably, the number of the stop pin holes 2 on each connecting end 4 is two, and the two stop pin holes 2 are on the same axis.
Preferably, the axial direction between the stop pin holes 2 on the two connecting ends 4 is the same.
Preferably, the test ring 1 and the two connecting ends 4 are of an integrally formed structure.
A measuring method of a six-dimensional force sensor independent of the direction of a patch is realized by the following steps:
firstly, the structural model of the sensor is shown in figure 1, the whole structure is processed and manufactured by a numerical control method, the middle of the structure is provided with a test ring 1, the two sides of the structure are provided with connecting ends 4, the two connecting ends 4 are provided with a threaded hole 3 and a stop pin hole 2, the threaded hole 3 and the stop pin hole 2 are used for being connected with other structural parts, and the stop pin hole 2 is used for transmitting torque; the whole structure is integrally made of the same material (such as steel);
secondly, as shown in fig. 3, 4 strain roses are respectively pasted on a strain rosette upper pasting point 11, a strain rosette left pasting point 12, a strain rosette lower pasting point 13 and a strain rosette right pasting point 14 at the middle end (namely, a _ a section) of the test ring along the ring direction at equal intervals in a counterclockwise direction, the 4 pasting points are distributed at equal intervals in the ring direction in the counterclockwise direction, and no requirement is made on the pasting direction of the strain rosettes;
③ the sensor will be subjected to 6 forces, respectively, one axial force F z2 bending moment Mx，M y2 shear forces Fx，FyAnd a torque Tz(ii) a Now consider each load individually, to the axle force FzComprises the following steps:
to bending moment MxComprises the following steps:
to bending moment MyComprises the following steps:
pair shear force FxComprises the following steps:
pair shear force FyComprises the following steps:
for torque TzComprises the following steps:
in the formula: is strain;
④ in the range of linear elasticity, step-by-step loading FzA total of 8 stages, corresponding to 8 available11A value of (1) in FzIs a transverse axis,11Linearly regressing the tested data as vertical axis to obtain linear regression proportionality coefficient, which is k11Sequentially calibrating coefficients k by the same method21，…，k12,1Then respectively to Mx，My，Fx，Fy，TzCalibrating by the same method;
⑤ in turn according to Fz，Mx，My，Fx，Fy，TzThe transfer coefficient matrix K obtained by the sequential arrangement calibration is shown in a formula (7),
⑥ for a combined unknown force State F'z，M′x，M′y，F′x，F′y，T′zCorresponding to the strain on the strain gauge on the sensor are'1,′2,…,′12Then, there are:
written in matrix form as:
′12×1＝K12×6F′6×1(9)；
the formula (9) is an over-determined equation set, and because the structural form and the patch mode of the invention enable the transfer coefficient matrix K to be non-pathological, and the property of the transfer coefficient matrix K is irrelevant to the pasting direction of the strain flower, the formula (9) is solved by inversion by using a least square method, and then the following equation sets are obtained:
finite element example demonstration:
establishing a finite element model, and sequentially applying a load Fz，Mx，My，Fx，Fy，TzCalibrating a transfer coefficient matrix K12×6. Then, as shown in the second row of Table 1, applying a precise solution (i.e., load) to the six-dimensional force sensor, the strain of each strain flower can be obtained'12×1Then straining the strained flower'12×1And a transfer coefficient matrix K12×6Substituting equation (10) results in a least squares solution.
The six-dimensional force sensor has good noise resistance because the number of strain gauges is greater than the number of loads. From the comparison between the least squares solution and the exact solution, it can be seen that the error between the least squares solution and the exact solution is less than 1% without noise, which indicates that the design of the ring, the use of the strain foil patch, and the combination of the least squares algorithm of the invention almost eliminate the coupling between the forces in different directions. Strain of test in Table 1'12×1The least square calculation results of random noise with the levels of 1%, 2%, 5% and even 10% are respectively given, and the six-dimensional force calculated by the method is not sensitive to the noise. It can be seen from Table 1 that when the noise level is 5%, the error of the sensor is substantially less than 1% (where M isx-1.0843%), which shows that the sensor is able to suppress random noise during measurement very well.
TABLE 1 comparison of inverse and exact solutions
The invention adopts the threaded connection joints with stronger structures at two sides and the force-sensitive element in the form of a thin circular ring in the middle, the strain rosette is pasted on the force-sensitive element, the direction of the strain rosette paster is random, the property of the transfer coefficient matrix can be greatly improved based on the structure and the paster mode, the condition number of the transfer coefficient matrix is not changed in different pasting directions of the strain rosette, and the transfer coefficient matrix is a good state matrix no matter what paster direction. The structure, the patch mode and the calculation mode of the invention can be used simultaneously to achieve the effect of the invention.
Finally, it should be noted that: the above examples are only for illustrating the technical solutions of the present invention and not for limiting the same, and although the present invention is described in detail with reference to the foregoing examples, those of ordinary skill in the art should understand that: modifications of the technical solutions described in the embodiments or equivalent replacements of some technical features may be carried out. And the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.
Claims (4)
1. A measuring method of a six-dimensional force sensor irrelevant to the direction of a patch is characterized in that: the measuring method is realized by the following steps:
the whole structure of the sensor structure model is processed and manufactured by a numerical control method, the structure comprises a test ring (1) and connecting ends (4), the test ring (1) is arranged in the middle of the structure, the connecting ends (4) are arranged at two sides of the structure, the test ring (1) is a cylinder provided with an inner hole, the connecting ends (4) are in a hexagonal nut shape in appearance, threaded holes (3) and stop pin holes (2) are respectively arranged on the two connecting ends (4), two stop pin holes (2) are arranged on each connecting end (4), the two stop pin holes (2) are arranged on the same axis, the axis directions between the stop pin holes (2) on the two connecting ends (4) are the same, the threaded holes (3) and the stop pin holes (2) are used for being connected with a structural part, and the test ring (1) and the two connecting ends (4) are of an integrally formed structure;
respectively sticking 4 strain flowers to an upper strain flower sticking point (11), a left strain flower sticking point (12), a lower strain flower sticking point (13) and a right strain flower sticking point (14) in the middle of the test ring (1);
③ the sensor will be subjected to 6 forces, respectively, one axial force Fz2 bending moment MxAnd My2 shear forces FxAnd FyAnd a torque Tz(ii) a Considering each load-to-shaft force F separatelyzComprises the following steps:
to bending moment MxComprises the following steps:
to bending moment MyComprises the following steps:
pair shear force FxComprises the following steps:
pair shear force FyComprises the following steps:
for torque TzComprises the following steps:
in the formula: strain;
④ in the range of linear elasticity, step-by-step loading FzA total of 8 stages, 8 obtained11A value of (1) in FzIs a transverse axis,11Linearly regressing the tested data as a vertical axis to obtain a proportional coefficient k of the linear regression11Sequentially calibrating coefficients k by the same method21，…，k12，1Then respectively to Mx，My，Fx，Fy，TzCalibrating by the same method;
⑤ in turn according to Fz，Mx，My，Fx，Fy，TzThe transfer coefficient matrix K obtained by calibration is arranged in sequence to obtain a formula (7),
⑥ for a combined unknown force State F'z，M′x，M′y，F′x，F′y，T′zCorresponding to the strain on the strain gauge on the sensor are'1,′2,…,′12Then, there are:
written in matrix form as:
′12×1＝K12×6F′6×1(9)；
the formula (9) is an over-determined equation set, and because the structural form and the patch mode of the invention enable the transfer coefficient matrix K to be non-pathological, and the property of the transfer coefficient matrix K is irrelevant to the pasting direction of the strain flower, the formula (9) is solved by inversion by using a least square method, and then the following equation sets are obtained:
2. the method of measuring a six-dimensional force sensor independent of patch orientation of claim 1, wherein: and 4 pasting points in the step II are distributed along the middle of the test ring (1) in an annular and anticlockwise equal interval mode.
3. The method of measuring a six-dimensional force sensor independent of patch orientation of claim 1, wherein: the stop pin hole (2) in the step (r) is used for transmitting torque.
4. The method of measuring a six-dimensional force sensor independent of patch orientation of claim 1, wherein: the measuring method is suitable for a patch mode with a structure that the two sides are threads and the middle is a circular ring and the strain flower patch direction is random, and by combining the structure, the patch mode and the measuring method, the transmission coefficient matrix can be improved, and the decoupling precision is improved.
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