CN101876545A - Inclination angle sensor - Google Patents

Abstract

The invention provides an inclination angle sensor, comprising a ferromagnetic fluid measurement element, a displacement measurement coil unit and a deformation measurement coil unit. The ferromagnetic fluid measurement element comprises a sealed tube, non-magnetic carrier liquid encapsulated in the sealed tube, and ferromagnetic fluid soaked in the non-magnetic carrier liquid. The displacement measurement coil unit is convolved on the radical periphery of the middle part of the sealed tube for measuring the displacement of the magnetic fluid. The deformation measurement coil unit is convolved along the external part of the sealed tube for measuring the deformation of the ferromagnetic fluid. The inclination angle sensor can eliminate acceleration interference and measure inclination angle precisely; the inclination angle sensor has simple structure, and can improve the measurement precision greatly by improving the existing inclination angle sensor without increasing much cost.

Description

Obliquity sensor

Technical field

The present invention relates to a kind of obliquity sensor, particularly a kind of obliquity sensor that adopts ferrofluid.

Background technology

Usually need the angle of inclination of surveying work system in commercial production and the scientific research, so obliquity sensor there is purposes widely with respect to reference field.According to different principle of work, obliquity sensor can be divided into liquid pendulum-type, fixedly pendulum-type and gas pendulum.The obliquity sensor of liquid pendulum-type and most fixedly pendulum-type obliquity sensor can independently use, and steady-state behaviour is good.The obliquity sensor of gas pendulum is subjected to the influence of several factors, therefore seldom uses.

United States Patent (USP) 5908987 has provided a kind of ferrofluid obliquity sensor, and it has a glass tube, and glass tube is filled with the ferrofluid of non magnetic carrier fluid, minute bubbles peace treaty half container volume, and the outer radial periphery of glass tube is being twined inductive coil.When glass tube tilted, the ferrofluid in the pipe moved in the effect of gravity, and its periphery induction coil wound produces induction current.But this sensor can only induce ferrofluid along axial the moving of glass tube.In actual use, even without any inclination, work system is quickened or deceleration as prominent the chance, the inductive coil place of obliquity sensor also can produce and be similar to the induction current that produces because of inclination, therefore in dynamic case, the reason that this obliquity sensor can't be told ferrofluid displacement in the sensor is velocity variations or tilts that therefore the measurement result of this obliquity sensor is usually inaccurate.

In order accurately to measure the pitch angle of unstable state system, present measuring system adopts the mode of gyrostatic mode or dual sensor to measure usually.United States Patent (USP) 4282933 has utilized two obliquity sensors, and adopts certain algorithm, in the hope of getting rid of the influence of acceleration to angle of bank measurement.If also will measure acceleration, adopt the mode of multisensor combination usually, promptly in the module of an encapsulation, include two or more sensors of various types, to distinguish acceleration and angle of inclination, obtain good dynamic property.United States Patent (USP) 6691437 provides a kind of inclinator, has comprised a gyro obliquity sensor and an acceleration transducer, in the hope of obtaining pitch angle and accekeration.

Yet the complex structure of these obliquity sensors costs an arm and a leg, and be not easy to use in existing systems, and as long as any one sensor malfunctioning wherein will cause whole measuring system malfunctioning.

Summary of the invention

Therefore, the present invention aims to provide and a kind ofly can eliminate that acceleration disturbs, the high precision dip sensor, and this obliquity sensor is simple in structure, only needs transform slightly existing some obliquity sensor, can improve measuring accuracy greatly, and not have the anxiety that increases a lot of costs.

For achieving the above object, the invention provides a kind of obliquity sensor, it has: a ferrofluid measuring sensor, a displacement measurement coil unit and a deformation measurement coil unit.The ferrofluid measuring sensor comprises a sealed tube, is encapsulated in the non magnetic carrier fluid in the sealed tube and is immersed in a kind of magnetic fluid of non magnetic carrier fluid, and the density of ferrofluid is greater than the density of non magnetic sanction liquid.The displacement measurement coil unit is wrapped in the outer radial periphery at sealed tube middle part, in order to measure the displacement of ferrofluid; The deformation measurement coil unit then along the sealed tube external shaft to winding, in order to measure the deflection of ferrofluid.

In a kind of embodiment of the present invention, the deformation measurement coil unit is a sensing coil.

In another embodiment of the present invention, the displacement measurement coil unit is a sensing coil.

In another kind of embodiment of the present invention, the deformation measurement coil unit is an excitation induced coil groups, and it can be made up of a difference inductive coil group and a drive coil.Difference inductive coil group is axially twined side by side along the sealed tube outside; Drive coil then is wrapped in the outside of difference inductive coil group.

In another embodiment of invention, the displacement measurement coil unit also is an excitation induced coil groups, and it can be made up of a difference inductive coil group and a drive coil.Difference inductive coil group is twined side by side along the radially outer of sealed tube; Drive coil then is wrapped in the outside of this difference inductive coil group.

Among the present invention, sealed tube can adopt glass tube, and the non magnetic carrier fluid of encapsulation can be water in the sealed tube.

In obliquity sensor of the present invention, owing to adopted two orthogonal slotted line coil units, measure the displacement and the deflection of ferrofluid in the sealed tube respectively, so both got rid of the incline measurement error that causes because of acceleration, improve the measuring accuracy at pitch angle, also attaching the measurement acceleration simultaneously.

Simultaneously, obliquity sensor of the present invention both need not to use a plurality of measuring tubes, more sensors of various types needn't be installed, just can improve the measuring accuracy at pitch angle greatly, make easy for installationly, have very high letter price ratio.

In an embodiment of concrete enforcement of the present invention, because displacement measurement coil unit and/or deformation measurement coil unit have adopted the excitation induced coil groups, the amplitude that changes the exciting current of drive coil can change the range of inclinator, the amplitude of exciting current increases, and the range of inclinator also increases accordingly.

In addition, two of being set to twine side by side of the inductive coil in the displacement measurement coil unit can adapt to different vergence directions better; And the inductive coil in the deformation measurement coil is set to twine side by side two, then both can increase the signal intensity of ferrofluid deformation measurement, make the service orientation of obliquity sensor have more dirigibility again.

Obliquity sensor of the present invention is compared with the obliquity sensor of existing fixed pendulum-type, does not have mechanical spring, and mechanical parts such as bearing just can not produce the mechanical wear that produces therefrom and mechanical fatigue etc. yet.

Description of drawings

The following drawings is only done the present invention and is schematically illustrated and explain, not delimit the scope of the invention.Wherein:

Fig. 1 is the structural representation of a kind of obliquity sensor embodiment of the present invention;

Fig. 2 is the structural representation of another embodiment of the present invention;

Fig. 3 is an obliquity sensor shown in Figure 2 synoptic diagram when being in obliquity;

Fig. 4 is an obliquity sensor shown in Figure 2 synoptic diagram when being in acceleration mode;

The distortion that produces when Fig. 5 has represented that ferrofluid shown in Figure 4 is steady state shearing stress fluid;

Fig. 6 is the schematic curve that concerns between the extensibility of ferrofluid shown in Figure 5 and the shear stress.

Embodiment

Understand for technical characterictic of the present invention, purpose and effect being had more clearly, now contrast description of drawings the specific embodiment of the present invention, identical label is represented same or similar part in each figure.

The present invention relates to a kind of astable high-precision tilt angle sensor that can be used for.Fig. 1 is the structural representation of a kind of embodiment of this obliquity sensor.As shown in the figure, this obliquity sensor has a ferrofluid measuring sensor, a displacement measurement coil unit 3 and a deformation measurement coil unit 4.Comprise at ferrofluid measuring sensor shown in Figure 1: be packaged with non magnetic carrier fluid and ferrofluid 2 in sealed tube 1, the sealed tube 1, ferrofluid 2 is immersed in the non magnetic carrier fluid of sealed tube 1.In the embodiment shown in fig. 1, displacement measurement coil unit 3 is a sensing coil, and deformation measurement coil unit 4 also is a sensing coil.

For ease of explanation, in this article, sealed tube 1 long direction is defined as axially, is defined as radially with this axially vertical direction.

In obliquity sensor of the present invention, sealed tube 1 can be by the made of the exhausted magnetic of any one insulation, glass for example, engineering plastics etc.; Be full of the non magnetic carrier fluid that does not merge mutually with ferrofluid 2 as water, isopropyl alcohol etc. in the sealed tube 1, or their potpourri, and the proportion of non magnetic carrier fluid is less than the proportion of ferrofluid 2, is submerged in the bottom of sealed tube to guarantee ferrofluid 2.

The outer radial periphery at sealed tube 1 middle part is wound with displacement measurement coil unit 3, in order to measure the displacement of ferrofluid because of tilting or quickening to produce; Then be wound with deformation measurement coil unit 4 in sealed tube 1 axial outside, in order to measure the deflection that ferrofluid 2 produces because of acceleration.

Figure 2 shows that another embodiment of the invention.In this embodiment, displacement measurement coil unit 3 is one group of excitation induced coil groups, and it comprises a difference inductive coil group and a drive coil 32.Difference inductive coil group comprises that two are wrapped in sealed tube 1 outer radial periphery and the identical inductive coil 31 of the number of turn, 32 outsides that are wrapped in inductive coil 31 of drive coil side by side.

In embodiment shown in Figure 2, deformation measurement coil unit 4 also is one group of excitation induced coil groups, and it comprises a difference inductive coil group and a drive coil 42.Difference inductive coil group comprises that two are wrapped in sealed tube 1 outer radial periphery and the identical inductive coil 41 of the number of turn, 42 outsides that are wrapped in inductive coil 41 of drive coil side by side.

When obliquity sensor was horizontal, ferrofluid 2 roughly was positioned at the middle part of displacement measurement coil 32, and the displacement according to ferrofluid 2 in the displacement measurement coil unit 3 is exported correspondent voltage.

When obliquity sensor produces as shown in Figure 3, ferrofluid 2 departs from its initial position, its displacement can make magnetic force that ferrofluid 2 is subjected to and its reach balance along sealed tube 1 axial weight component, the output voltage of displacement measurement coil unit 3 changes at this moment, and this output voltage is the function of sensor perturbations angle θ.

In order to simplify description to ferrofluid obliquity sensor performance, suppose that used ferrofluid 2 has viscosity and incompressible, the non magnetic carrier fluid of sealing up for safekeeping in the sealed tube 1 is a water, and the power that then acts on the ferrofluid 2 comprises magnetic force, water resistance and inertial force, and these power should keep balance.

According to law of physics, the magnetic force that acts on the paramagnetic material is:

$F_m=-\▿U=(B\·\▿)m+(m\·\▿)B---\left(1\right)$

Wherein: U=mB represents the magnetic energy of ferrofluid particle in the magnetic magnetic field,

M represents magnetic moment,

B represents magnetic flux density.

Magnetic moment m and magnetic field intensity H in the formula (1) are following linear relationship:

m＝Vx _mH (2)

Wherein: x _mExpression magnetic susceptibility,

V represents the volume of ferrofluid.

Then formula (1) can be reduced to:

$F_m={\mathrm{Vx}}_m(H\·\▿)B.---\left(3\right)$

If produced a magnetic field under the effect of drive coil, the magnetic force that is produced along the coil main shaft is:

$F_m\left(z\right)\&ap;C\&CenterDot;(\frac{l-z}{\sqrt{\left(r^2{(l-z)}^2\right)}}+\frac{l+z}{\sqrt{({\mathrm{<figure-callout\; id="2"\; label="r"\; filenames="H2009101358639E0000011.png,H2009101358639E0000012.png"\; state="\{\{state\}\}">r</figure-callout>}}^2+{(l+z)}^2)}})(\frac{-r^2}{{\left(({\mathrm{<figure-callout\; id="2"\; label="r"\; filenames="H2009101358639E0000011.png,H2009101358639E0000012.png"\; state="\{\{state\}\}">r</figure-callout>}}^2+{(l-z)}^2)\right)}^{\frac{3}{2}}}+\frac{r^2}{{\left(({\mathrm{<figure-callout\; id="2"\; label="r"\; filenames="H2009101358639E0000011.png,H2009101358639E0000012.png"\; state="\{\{state\}\}">r</figure-callout>}}^2+{(l+z)}^2)\right)}^{\frac{3}{2}}})---\left(4\right)$

Wherein: z represents the coordinate of the calculation level of power, represents that as z=0 the calculation level of power is positioned at the center of coil,

L represents half of drive coil length,

R is the radius of drive coil 32,

C represents the magnetic susceptibility x by ferrofluid _m, volume V, permeability μ ₀, exciting current I _DcWith the constant that drive coil number of turn n determines, it is expressed as:

$C=\frac{{\mathrm{\&mu;}}_0}{4}{n}^2{I}_{\mathrm{dc}}^2{x}_{m}V.---\left(5\right)$

Although the magnetic force F that drive coil 32 produces _mNon-and be linear with ferrofluid 2 along the axial displacement z of sealed tube 1, but in a bigger working range, exist linear trend, in having the scope of linear trend, magnetic force F _mCan be expressed as approx:

F _m≈k(I _dc)z (6)

Wherein: k represents elastic constant,

I _DcThe expression exciting current,

Z represents the displacement of ferrofluid 2 with respect to aclinal initial position.

On the other hand, the different displacement z of relative ferrofluid, the fluid resistance that ferrofluid 2 is subjected to can be calculated by Stokes' law:

$F_h\left(z\right)=6\mathrm{\&pi;\&eta;R}\stackrel{\&CenterDot;}{z}\left(t\right)---\left(7\right)$

Wherein: η represents the viscosity of water,

R is the diameter of ferrofluid,

The speed of expression ferrofluid 2.

Ferrofluid 2 along sealed tube 1 axial weight component is:

F _g＝V(ρ _f-ρ _l)g?sin(θ) (8)

Wherein: V represents the volume of ferrofluid 2

ρ _fBe the density of ferrofluid 2,

ρ _lBe the density of water,

G represents acceleration of gravity,

θ is the pitch angle of obliquity sensor shown in Figure 3.

According to Newton second law, take all factors into consideration the power that acts on the ferrofluid 2, the displacement of ferrofluid 2 can be calculated by following formula:

${\mathrm{\&rho;}}_{f}V\stackrel{\&CenterDot;\&CenterDot;}{z}\left(t\right)=F_m+F_h+F_g---\left(9\right)$

If suppose initial position and speed be:

z(0)＝0； $\stackrel{\&CenterDot;}{z}\left(0\right)=0---\left(10\right)$

When obliquity sensor was in stable state, formula (9) can be reduced to:

F _m+F _g＝0 (11)

As shown in Figure 3, if this moment, the pitch angle was θ, when ferrofluid 2 is in as shown in the figure equilibrium position, utilize equation (6), (8) and (11) promptly can draw the tiltangle of obliquity sensor.

But in another case, if measurand does not tilt, and just has an acceleration, then as shown in Figure 4, ferrofluid 2 in the sealed tube 1 can depart from the middle part of displacement measurement coil unit 3 equally, this moment, ferrofluid 2 not only can produce the displacement when being similar to the stable state inclination, and the shape of ferrofluid 2 also can produce the distortion when being different from the stable state inclination.

Figure 5 shows that the three-dimensional mechanical model of a liquid spheres after the distortion.In order to reduce complexity to ferrofluid 2 deformation analyses, suppose that ferrofluid 2 is a kind of ferrofluids of Newtonian liquid that are, the initial sphere that is shaped as, and to establish the liquid that is packaged in the sealed tube 1 be shear stress liquid.According to the theory of Taylor and Cox, when measurand meets the situation of acceleration, act on spherical Newtonian liquid along the shearing force of X-axis, cause this liquid spheres to produce very big distortion, shear stress on it and extensibility can be calculated by following formula:

τ＝(σ/R)[(1+ε)/(1-k ₁ε) ²+(1+ε)/(1-k ₂ε) ²-2] (12)

${\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="H2009101358639E0000011.png,H2009101358639E0000022.png"\; state="\{\{state\}\}">k</figure-callout>}}_1=\frac{1}{6\&Element;{(\&Element;+1)}^3}[\sqrt[3]{-54{(\&Element;+1)}^8-1+3\sqrt{6}{(\&Element;+1)}^4\sqrt{54{(\&Element;+1)}^8+2}}+---\left(13\right)$

$\sqrt[3]{-54{(\&Element;+1)}^8-1-3\sqrt{6}{(\&Element;+1)}^4\sqrt{54{(\&Element;+1)}^8+2}}+6{(\&Element;+1)}^3-1]$

${\mathrm{<figure-callout\; id="2"\; label="k"\; filenames="H2009101358639E0000011.png,H2009101358639E0000012.png"\; state="\{\{state\}\}">k</figure-callout>}}_2=\frac{k_1(\&Element;+1)-1}{({\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="H2009101358639E0000011.png,H2009101358639E0000022.png"\; state="\{\{state\}\}">k</figure-callout>}}_1\&Element;-1)(\&Element;+1)}---\left(14\right)$

Wherein: τ express liquid ball is along the shear stress of X-axis,

ε express liquid ball is along the extensibility of X-axis,

Radius-of-curvature before R express liquid ball is not out of shape,

σ represents the interfacial tension coefficient of interfacial film

k ₁And k ₂Be contraction coefficient.

Although in theory, shear stress τ and extensibility ε are not linear relationships, but Fig. 6 shows, in a bigger working range, in the solid line part of curve shown in Figure 6, be tending towards linear relationship between the two especially, therefore in this interval, acceleration a is the function of shear stress τ, promptly is the function of extensibility ε.Therefore can draw the relation between acceleration a and the extensibility ε.

As shown in Figure 4, when obliquity sensor is in level, make obliquity sensor be in acceleration mode, ferrofluid 2 had both produced displacement, also can under the effect of shear stress, produce with this acceleration and be out of shape accordingly, can produce the output signal that embodies this deflection this moment on deformation measurement coil unit 4, also can produce output signal because of displacement on the simultaneous displacement slotted line coil unit 3.

At the beginning of obliquity sensor uses, but Using such method is proofreaied and correct obliquity sensor: determine under the situation without any the pitch angle, the relation of the output of deformation measurement coil unit 4 and acceleration a, and then the relation of definite acceleration a ferrofluid 2 displacements when do not have.

When actual measurement, ferrofluid 2 along sealed tube 1 axial total displacement is:

z _tol＝z _ac(ε)+z _ti(θ) (15)

Wherein: z _TolThe displacement of the ferrofluid that expression is measured by displacement measurement coil 2,

z _Ac(ε) be the displacement of the ferrofluid 2 that causes because of acceleration,

z _Ti(θ) be the displacement of the ferrofluid 2 that only causes because of inclination.

In obliquity sensor measuring process of the present invention, determine the displacement z that ferrofluid 2 is total according to the output signal of displacement measurement coil unit 3 _Tol, deducting does not have the displacement z that tilts only to have ferrofluid 2 when quickening _Ac(ε), can calculate only displacement z of ferrofluid 2 according to equation (16) because of tilting to produce _Ti(θ), can obtain tiltangle accurately by equation (6), (8) and (11) according to this value.

Owing in obliquity sensor of the present invention, have two orthogonal measurement coils, measure the displacement and the deflection of the middle ferrofluid 2 of sealed tube 1 respectively, therefore, it both can get rid of the error that produces because of acceleration when measuring the pitch angle, accurately measure the pitch angle of unstable state system, also can measure the acceleration of determining system as required in the lump.

Obliquity sensor of the present invention only passes the accurate measurement that measuring sensor just can be implemented in various state angle of declinations with a ferrofluid, and needn't use a plurality of ferrofluid measuring sensors simultaneously, or use several sensors of various types, the measuring error that promptly can eliminate under the unsteady state to be caused, under the situation that does not roll up cost and sensor complex, but improved measuring accuracy greatly.

Above listed a series of detailed description only is specifying at feasibility embodiment of the present invention; they are not in order to restriction protection scope of the present invention, allly do not break away from equivalent embodiment or the change that skill spirit of the present invention done and all should be included within protection scope of the present invention.

Claims (6)

1. obliquity sensor has:

A ferrofluid measuring sensor, it comprises:

A sealed tube,

A kind of riddle in this sealed tube non magnetic carrier fluid and

A kind of ferrofluid that is immersed in the described non magnetic carrier fluid, the density of this ferrofluid is greater than the density of described non magnetic sanction liquid;

A displacement measurement coil unit that is wound in described sealed tube middle part outer radial periphery is in order to measure the displacement of described ferrofluid;

Wherein, described obliquity sensor also comprises:

One along the deformation measurement coil unit of sealed tube external shaft to winding, in order to measure the deflection of described ferrofluid.

2. obliquity sensor as claimed in claim 1, wherein, described deformation measurement coil unit is a sensing coil.

3. obliquity sensor as claimed in claim 1 or 2, wherein, described displacement measurement coil unit is a sensing coil.

4. obliquity sensor as claimed in claim 1, wherein, described deformation measurement coil unit is an excitation induced coil groups, this coil groups comprise one be wrapped in side by side described sealed tube external shaft to difference inductive coil group and a drive coil that is wrapped in outside this difference inductive coil group.

5. as claim 1 or 4 described obliquity sensors, wherein, described displacement measurement coil unit is an excitation induced coil groups, this coil groups comprises the difference inductive coil group and the drive coil that is wrapped in outside this difference inductive coil that are wrapped in described sealed tube outer radial periphery side by side.

6. obliquity sensor as claimed in claim 5, wherein, described sealed tube is a glass tube, described non magnetic carrier fluid is a water.

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