CN1865877A - Mechanical stress measuring apparatus - Google Patents

Abstract

The disclosed mechanical stress measuring device comprises: a sensor with an exciting electrode with coil D and two measuring electrodes with coils (E1, E2) connected by vertical equal-distance wires, a sensor driver arranged both a gear box driven by a step motor to connect the a probe frame by its output shaft and a control circuit with a displacement/angle sensor to send measured signal into a main computer, and a measuring circuit. This invention has high sensitivity for both static and dynamic measurement with simple structure.

Description

A kind of mechanical stress measuring instrument

Technical field

The present invention relates to a kind of stress measurement device, particularly a kind of mechanical component to the ferromagnetic material manufacturing carries out the mechanical stress measuring instrument of stress measurement.

Background technology

In mechanical engineering, stress is very important physical quantity, and the accurate measurement of these physical quantitys is to guaranteeing equipment safety operation, realize control automatically and for the deviser provides rational designing and calculating foundation significance being arranged all.The strain gauge close with the present invention mainly is: strain ga(u)ge and piezomagnetic torque sensor.The principle of work of resistance strain gage is based on its strain effect.When using foil gauge to measure component stress or strain, resistance strain gage is pasted on tested component surface, foil gauge and part are out of shape together, because wire size and resistivity all change in the sheet, resistance value wiry also changes, and the variation of measuring resistance value by metering circuit (electric wire strain gauge) can be tried to achieve the size of strain or stress.Strain ga(u)ge is a common technology of measuring physical quantitys such as strain, loading, pulling force, pressure at present, but also have some shortcomings: conventional foil gauge is under big strain regime, the relation of resistance change rate and strain presents bigger non-linear, and semiconductor gauge is more remarkable.Conventional foil gauge output signal is less, and signal is connected lead will conscientiously be shielded..Foil gauge has the dimensions.So actual what measure is mean strain on a certain area, can not show the situation of stress gradient in the stress field fully.Be subjected to Temperature Influence bigger.Be not suitable for long-term work under rugged environment.Can not carry out non-cpntact measurement.

Adopt the structure of many piezomagnetic torque sensors mostly to be corssed core type at present, this sensor is developed by Sweden ASEA company the earliest.It is formed by having the sections core that exchanges field winding and having the sections core of measuring winding, wherein the field winding iron core is installed along shaft centerline, measure iron core and field core at an angle of 90 and symmetrically, with the line that guarantees each adjacent pole and mutual at 45 and 135 ° of angles of center line of measured axis.When rotating shaft was subjected to torsional interaction, because piezomagnetic effect, excitation pole and the magnetic permeability of measurement magnetic pole in rotating shaft changed, at this moment, and whole magnetic bridge balance, the axle distortion of field.Be in different magnetic potential following time and measuring in the coil and will induce and the directly proportional AC electromotive force of moment of torsion when measuring iron core.The major defect of this torque sensor is a complex structure, and measurement sensitivity is lower, can only be used to measure moment of torsion, when plane stress state, can not be used for differentiating the direction of definite principle stress and the measurement of principle stress.

Summary of the invention

The technical problem to be solved in the present invention is at the deficiencies in the prior art, proposed a kind of simple in structure, measure convenient and swift, the novel mechanical stress detector of applied range.

The technical problem to be solved in the present invention is achieved through the following technical solutions, a kind of mechanical stress measuring instrument, be characterized in: it comprises sensor, sensor drive mechanism and metering circuit, sensor is provided with sensor probe and the fixedly skeleton of popping one's head in, be provided with insulation course between probe and the skeleton, described probe is provided with an excitation pole and two measurement magnetic poles, measure magnetic pole and distance orthogonal for two and equate, be wound with field coil D on the excitation pole, measuring at two and be wound with measurement coil E on the magnetic poles respectively with the line between the excitation pole ₁And E ₂, sensor drive mechanism is provided with stepper motor driven transmission case, and skeleton joins the output shaft of transmission case with popping one's head in fixedly,

Metering circuit comprises sensor sensing signal processing circuit and sensor drive mechanism control circuit, the sensor sensing signal processing circuit is provided with main control computer and signal generator, signal generator inserts sensor circuit by power amplification circuit, and sensor circuit output is joined by pre-amplification circuit, detecting circuit, filtering circuit, voltage comparator circuit, low-frequency amplifier circuit, A/D analog to digital conversion circuit and main control computer successively.

The sensor drive mechanism control circuit is provided with displacement transducer that detects output shaft axial displacement and the angular transducer that detects the output shaft corner, the detection signal of displacement transducer and angular transducer inserts above-mentioned main control computer, and main control computer joins by servo-driver and stepper motor.

The technical problem to be solved in the present invention can also come further to realize by the following technical programs, be provided with the driving shaft that joins with stepper motor in the transmission case of sensor drive mechanism, driving shaft joins by arrangement of clutch and output shaft, the driving shaft leading portion is provided with helical screw, output shaft is provided with the nut sleeve that matches with screw mandrel, is provided with circumferential stop means between output shaft and transmission case casing.

The technical problem to be solved in the present invention can also come further to realize by the following technical programs, the transmission case of sensor drive mechanism and a mount pad are hinged, mount pad is provided with a back shaft, be with support set by screw thread on the back shaft, the casing of described transmission case and the upper articulation of support set.

Measuring principle

The dynamometry principle of this sensor is based on piezomagnetic effect.So-called piezomagnetic effect is meant that after the stressed effect of tested ferromagnetic component that places magnetic field, the magnetic permeability in its surperficial certain depth will change.The magnetic field of setting up by exciting current makes the measured material surface magnetization.When magnetized measured material is subjected to stress, because magnetostrictive anisotropy, it is the parallel direction that positive material direction of magnetization turns to tension that tension will make λ s, also promptly increase (magnetic resistance reduces) with the magnetic permeability of tension parallel direction, and be difficult to magnetization with the tension vertical direction, also promptly reduce (magnetic resistance increase) with the magnetic permeability of tension vertical direction; The situation of compressive stress is then opposite.In whole magnetic circuit, have only the magnetic permeability of measured material section to change, this variation causes measuring and induces voltage on the coil.To zero stress state or etc. draw, isobaric plane stress state, the same basically in the magnetization of either direction.

According to magnetic circuit, the voltage output equation that can derive sensor is:

$U=\frac{2\mathrm{\&pi;ft}{N}_1{\mathrm{<figure-callout\; id="2"\; label="N"\; filenames="A20061008806200141.png,A20061008806200162.png"\; state="\{\{state\}\}">N</figure-callout>}}_2\mathrm{\&omega;}{I}_1}{({\mathrm{A\&delta;}}_o+\frac{B}{{\mathrm{\&mu;}}_{\mathrm{CD}}}+C)\sqrt{{\mathrm{<figure-callout\; id="2"\; label="r"\; filenames="A20061008806200141.png,A20061008806200162.png"\; state="\{\{state\}\}">r</figure-callout>}}_2^2+{\mathrm{<figure-callout\; id="2"\; label="X"\; filenames="A20061008806200141.png,A20061008806200162.png"\; state="\{\{state\}\}">X</figure-callout>}}_2^2}}\sqrt{1+\frac{A\frac{{\mathrm{d\&delta;}}_o}{\mathrm{dt}}\frac{B}{{\mathrm{\&mu;}}_{\mathrm{<figure-callout\; id="2"\; label="CD"\; filenames="A20061008806200141.png,A20061008806200162.png"\; state="\{\{state\}\}">CD</figure-callout>}}^2}\frac{{{\mathrm{d\&mu;}}_{\mathrm{<figure-callout\; id="2"\; label="CD"\; filenames="A20061008806200141.png,A20061008806200162.png"\; state="\{\{state\}\}">CD</figure-callout>}}}^2}{\mathrm{dt}}}{2({\mathrm{A\&delta;}}_o+\frac{B}{{\mathrm{\&mu;}}_{\mathrm{CD}}}+C)}}$

In the formula,

N ₁, N ₂Be respectively the number of turn of field coil and measurement coil;

I ₁Effective value for electric current in the field coil;

r ₂Virtual impedance for magnetic test coil;

X ₂The invalid impedance of magnetic test coil;

F is the frequency of exciting current,

T is the time;

A＝5/μ _oS _Mo，B＝l _CD/ha，C＝∑l _Mi/S _Mi；

μ _oBe the magnetic permeability of air,

S _MoEnd on projection area for corresponding field pole on the measured material surface;

l _CDBe corresponding two lengths of magnetic path that detect between magnetic pole on the measured material surface,

A is the mean breadth of measured material internal magnetic circuit,

H is that magnetic flux is in measured material surface penetration depth;

S _MiFor in the sensor magnetic core from excitation pole to detecting each section of magnetic pole area of section,

l _MiBe corresponding S in the sensor magnetic core _MiThe length of magnetic path of each section.

When adopting this sensor dynamometry, as required, sensor probe contacts or does not contact with tested component surface, and the gap during contact measurement should be less than 0.2～0.3mm.

The present invention can realize the mechanical component with the ferromagnetic material manufacturing, the measurement of stress when unidirectional, two-way and twisting states by adopting the measuring instrument of particular design; Not only can static measurement, but also can carry out non-contacting kinetic measurement.It is simple in structure, is convenient to make and use; Measure convenient and swiftly, and can realize automatically measuring; Can measure the stress of multiple stress form, applied range; When adopting differential connection, measure highly sensitive.In addition,, can determine principle stress ground action direction exactly, make surveying work become convenient and swift owing to adopt computer aided measurement and control.

Description of drawings

Fig. 1 is a structure diagram of the present invention.

Fig. 2 is the sensor construction cut-open view.

Fig. 3 is the vertical view of Fig. 2.

Fig. 4 is the sensor probe structural drawing.

Fig. 5 is the metering circuit theory diagram.

Embodiment

A kind of mechanical stress measuring instrument, it comprises sensor 1, sensor drive mechanism and metering circuit, sensor 1 is provided with sensor probe 14 and the fixedly skeleton 15 of popping one's head in, be provided with insulation course 16 between probe 14 and the skeleton 15, described probe 14 is provided with an excitation pole 17 and two measurement magnetic poles 18,19, measure magnetic pole 18,19 and distance orthogonal for two and equate, be wound with field coil D on the excitation pole 17, on two measurement magnetic poles 18,19, be wound with measurement coil E respectively with the line between the excitation pole 17 ₁And E ₂, sensor drive mechanism is provided with the transmission case 10 that stepper motor 9 drives, and skeleton 15 joins the output shaft 2 of transmission case 10 with popping one's head in fixedly,

Metering circuit comprises sensor sensing signal processing circuit and sensor drive mechanism control circuit, the sensor sensing signal processing circuit is provided with main control computer 26 and signal generator 28, signal generator 28 inserts in sensor 1 circuit by power amplification circuit 27, and the output of sensor 1 circuit is joined with main control computer 26 by pre-amplification circuit 20, detecting circuit 21, filtering circuit 22, voltage comparator circuit 23, low-frequency amplifier circuit 24, A/D analog to digital conversion circuit 25 successively.

The sensor drive mechanism control circuit is provided with displacement transducer 4 that detects output shaft axial displacement and the angular transducer 8 that detects the output shaft corner, displacement transducer 4 inserts above-mentioned main control computer 26 with the detection signal of angular transducer 8, and main control computer 26 joins by servo-driver 29 and stepper motor 9.

Be provided with the driving shaft 7 that joins with stepper motor in the transmission case 10 of sensor drive mechanism, driving shaft 7 joins by arrangement of clutch 6 and output shaft 2, driving shaft 7 leading portions are provided with helical screw 5, output shaft 2 is provided with the nut sleeve 13 that matches with screw mandrel 5, is provided with circumferential stop means 3 between output shaft 2 and transmission case 10 casings.The transmission case 10 of sensor drive mechanism and a mount pad are hinged, and mount pad is provided with a back shaft 12, is with support set 11 by screw thread on the back shaft 12, the upper articulation of the casing of described transmission case 10 and support set 11.When needs sensor rotation calibration, stepping motor drives driving shaft 7 rotations, by manual clutch 6 driving shaft 7 and output shaft 3 is become one on the driving shaft 7, driving sensor 1 calibration; Manual clutch 6 is installed with the sliding sleeve of being with the tooth embedding at the input shaft upper spline, under the effect of shift fork, and slip cap and the fixedly tooth embedding engagement that drives on the output shaft.When needs sensor 1 straight line moves, clutch coupling 6 separates, rotatablely moving of driving shaft 7 passed on the output shaft 2 by helical screw mechanism, at this moment, circumferentially the sliding sleeve of the band female spline in the stop means 3 will link together with the fixed muffle of male splines, and fixed muffle is fixing on output shaft by flat key, fixed muffle by screw retention on housing, so output shaft can not rotate, and can only move by straight line.Linear displacement transducer 4 and angular transducer 8 detect the straight-line displacement and the anglec of rotation of output shaft 2 respectively, so that the direction of the measurement clearance of control sensor and measurement principle stress.Sensor drive mechanism promptly can move up and down in vertical plane and pitch rotation, also can rotate 360 ° in surface level, to satisfy the measurement requirement on the different directions.

Method for measuring stress

The essence of piezomagnetic effect is that strain influences magnetized complexity, therefore, will determine the action direction of principle stress before measuring, because principal direction of stress is exactly the principal strain method.To uniaxial stressed state, strain is maximum and be positive direction easy magnetization, and its vertical direction is easy magnetization not; To two-way plane stress state, the direction easy magnetization that strain is big, the difficult magnetization of the direction that should diminish.Based on above-mentioned principle, rotation sensor is popped one's head in, and determines the direction of principle stress (principal strain) according to the power of sensor output induced voltage.During measurement, earlier sensor probe is slowly moved to measured surface by sensor drive mechanism, after touching measured surface, driving mechanism stops automatically, utilizes the rotation calibration function of sensor drive mechanism then, and sensor probe is rotated once automatically every 0.5 °, and judge the size of each measuring voltage value, after 360 ° of rotations, measure maximum inductive voltage value, to the direction that should be worth the direction of principle stress.The direction of principle stress and the angle between benchmark are by the angular transducer record in the sensor drive mechanism.When non-cpntact measurement, in order to obtain maximum induced voltage, accurately control the gap between sensor probe and measured surface, and this function realizes by the linear displacement transducer in the sensor drive mechanism.

After principal direction of stress is determined, just can measure according to stress state.

1. measurement uniaxial stress

When measuring uniaxial stress, measure coil E ₁And E ₂Separate output.When surveying stress, make the action direction of principle stress and the D-E of sensor ₁(or D-E ₂) line is parallel.According to piezomagnetic effect, no matter be tension or compressive stress, as shown in Figure 3, sensor one side probe (D-E ₁Or D-E ₂) the measured material surface magnetic resistance that contacted will change, and demarcate by the uniaxial stress to the measured material test specimen, just can draw the relation between induced voltage and the stress, promptly

σ＝K _μU

σ in the formula---stress;

K μ---sensitivity coefficient;

U---induced voltage.

2. measurement biaxial stress

When measuring biaxial stress, measure coil E ₁And E ₂Separate output also can oppositely be connected in series.When the pure shear state, two measure coils can oppositely be connected in series, and the measuring method of this moment is identical during with the measurement moment of torsion.When general two-dimensional state of stress, two measure coils exports separately.During measurement, determine the direction of principle stress by the rotation sensor probe earlier, and then measure two induced voltages on the principal direction of stress respectively.Try to achieve stress by existing mathematical model again after obtaining the induction on the both direction.

Under two-dimensional state of stress, the variation of stress causes the variation of material surface magnetic permeability tensor, that is to say, in the variation of a certain direction upper stress, can cause the variation of magnetic permeability on the both direction, makes the biaxial stress measurement more complicated that becomes.

In fact under the measuring condition of determining, stress σ _xAnd σ _yAnd there is certain functional relation between magnetic survey voltage U x and the Uy:

$\left\{\begin{array}{c}{\mathrm{\&sigma;}}_x=F_x(U_x,U_y)\\ {\mathrm{\&sigma;}}_y=F_y(U_y,U_x)\end{array}\right.$

Demarcate by biaxial stress, adopt the method for nonlinear multivariable regretional analysis, determine several (at least 4) equation coefficients, thereby can obtain σ the measured material test specimen _xAnd σ _yThe system of equations that unique solution is arranged.

3. stress measurement during the pure shear state

When transmission shaft is subjected to moment of torsion, its stressed pure shear stress state that belongs in surface.At this moment, will measure coil E ₁And E ₂Oppositely serial connection forms differential connection.According to the mechanics of materials, when axle is subjected to torsional interaction, act on maximum tension stress and maximum crushing stress respectively along 45 ° and 135 ° on its surface.Therefore, E ₁With D line and E ₂With the D line respectively along 45 ° and 135 °, as shown in Figure 2.When not having torsional interaction, axle surface each section magnetic resistance is equal, and is equal by the magnetic flux of each magnetic test coil, because coil E ₁And E ₂Oppositely be connected in series, so magnetic flux is cancelled out each other, sensor is output as zero; When on the axle during action torque, 45 ° and 135 ° directions generation tensions and compressive stress on its surface.According to the piezomagnetic effect of ferromagnetic material, when the magnetostriction coefficient λ of ferrous materials s＞0, then the magnetoelastic energy in the tension direction is minimum, is direction of easy axis, and promptly magnetic permeability increases, and magnetic resistance reduces; And in the compressive stress direction, magnetic permeability reduces, and magnetic resistance increases.Therefore,  ₂＞ ₁, then sensor has induced voltage output.By sensor is demarcated, just can draw the relation between induced voltage and the moment of torsion.

If along principle stress σ _MaxDirection test, the variation of this direction magnetic permeability not only with σ _MaxRelevant, and with vertical with it principle stress σ _MinRelevant.According to the mechanics of materials, for isotropic material, by σ _MinThe transverse stress that causes is υ σ _Min, υ is the Poisson's ratio of material.

Be located at σ _MaxThe total stress of direction is σ

σ=σ then _Max+ υ σ _Min

And σ _Max=σ _Min

So σ=σ _Max+ υ σ _Min=σ _Max+ υ σ _Max=σ _Max(1+ υ)

Therefore, to the pure shear stress state,, just can reflect fully that the magnetic characteristic of measurement point changes only along an orientation measurement.Demarcate by uniaxial stress, just can draw the relation between induced voltage and the stress, promptly the measured material test specimen

σ _max＝K _μU。

Claims (3)

1. mechanical stress measuring instrument, it is characterized in that: it comprises sensor (1), sensor drive mechanism and metering circuit, sensor (1) is provided with sensor probe (14) and the fixedly skeleton (15) of popping one's head in, be provided with insulation course (16) between probe (14) and the skeleton (15), described probe (14) is provided with an excitation pole (17) and two measurement magnetic poles (18,19), measure magnetic pole (18 for two, 19) with excitation pole (17) between line orthogonal and the distance equate, on excitation pole (17), be wound with field coil D, measure magnetic pole (18 at two, 19) be wound with respectively on and measure coil E1 and E2, sensor drive mechanism is provided with the transmission case (10) that stepper motor (9) drives, skeleton (15) joins the output shaft (2) of transmission case (10) with popping one's head in fixedly

Metering circuit comprises sensor sensing signal processing circuit and sensor drive mechanism control circuit, the sensor sensing signal processing circuit is provided with main control computer (26) and signal generator (28), signal generator (28) inserts sensor (1) by power amplification circuit (27), sensor (1) output is successively by pre-amplification circuit (20), detecting circuit (21), filtering circuit (22), voltage comparator circuit (23), low-frequency amplifier circuit (24), A/D analog to digital conversion circuit (25) joins with main control computer (26)

The sensor drive mechanism control circuit is provided with displacement transducer (4) that detects output shaft axial displacement and the angular transducer (8) that detects the output shaft corner, displacement transducer (4) inserts above-mentioned main control computer (26) with the detection signal of angular transducer (8), and main control computer (26) joins by servo-driver (29) and stepper motor (9).

2. mechanical stress measuring instrument according to claim 1, it is characterized in that: be provided with the driving shaft (7) that joins with stepper motor (9) in the transmission case of sensor drive mechanism (10), driving shaft (7) joins by arrangement of clutch (6) and output shaft (2), driving shaft (7) leading portion is provided with helical screw (5), output shaft (2) is provided with the nut sleeve (13) that matches with screw mandrel (5), is provided with circumferential stop means (3) between output shaft (2) and transmission case (10) casing.

3. mechanical stress measuring instrument according to claim 1, it is characterized in that: the transmission case of sensor drive mechanism (10) is hinged with a mount pad, mount pad is provided with a back shaft (12), back shaft (12) is gone up and is with support set (11) by screw thread, the upper articulation of the casing of described transmission case (10) and support set (11).

Images