RU2290605C1 - Fiber-optic converter of movements - Google Patents

Abstract

FIELD: measuring technique.

SUBSTANCE: fiber-optic converter of movements comprises axially aligned nontransparent shield with opening and cords of input and output optical fibers. The distance between the input optical fibers and shield and the distance between the input and output optical fibers are determined from the equations presented. The receiving face of the cord of output fibers receives the section of fiber that is coaxial to the input optical fiber and opening in the shield. The receiving faces of the output optical fibers are arranged around the fiber section.

EFFECT: enhanced accuracy of measurements and simplified structure.

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Description

The invention relates to measuring equipment and can be used in sensors of physical quantities (pressure, displacement, acceleration, fluid level, vibration parameters, etc.) in various sectors of the economy and, first of all, for measuring physical quantities in conditions the impact of external destabilizing factors on the products of rocket and space technology.

Fiber optic pressure sensors (VODD) are known, containing optical fiber bundles installed at a fixed distance from a reflective metal membrane, the pressure measurement process in which is carried out by recording changes in the intensity of the reflected light flux depending on the deflection of the membrane under pressure (Zhilin V.G. Fiber-optic measuring transducers of speed and pressure. - M .: Energoatomizdat, 1987. - S.11-12; Avdoshin ES. Fiber optics in military equipment of the USA // Foreign electronic onika, 1989. - No. 11. - P.98-99; a.s. 1631329, G 01 L 11/00. Pressure sensor; Busurin VI, Nosov Yu.R. Fiber-optic sensors: Physical fundamentals, questions of calculation and application. - M .: Energoatomizdat, 1990. - P.40-41).

The disadvantages of these sensors are:

- low conversion sensitivity due to significant losses of light flux when reflected from the mirror surface of the membrane within the aperture angle of the optical fibers,

- high temperature error due to a change in the geometric parameters of the sensor,

- error from uninformative bending of optical fibers during the assembly, testing and operation of sensors.

Closer in technical essence to the present invention is a device in which, under the influence of an alternating acoustic field, the light is modulated by a thin curtain of titanium foil attached to a flexible membrane. The light from the LED enters through the splitter through the fiber into the cavity where the shutter is located, the modulated light through another fiber is sent to the photodiode [Light guide sensors / B. A. Krasyuk, O. G. Semenov, A. G. Sheremetev, etc. - M .: Engineering, 1990. - P.15].

The disadvantages of this device are the low conversion sensitivity, due to significant loss of optical power in the splitters, due to the loss of light flux during transmission from optical fiber to the optical fiber within the aperture angle of the optical fibers, as well as high error due to uninformative bends of optical fibers when exposed to external mechanical factors, for example, during the assembly of sensors, during tests, during operation, which lead to significant uninformative loss of the optical signal as it passes through optical fibers.

In addition, this device requires a very accurate alignment of the optical fibers relative to each other and the curtain, which greatly complicates the technology of their manufacture and, accordingly, increases its cost.

Thus, the prototype does not achieve a technical result, expressed in high accuracy of measurement due to the low sensitivity of the conversion, the impact on the measurement result of changes in the power of the radiation source, bends of the fiber optic cable.

A new design of the fiber optic displacement transducer is proposed, devoid of the above disadvantages.

The specified technical result is achieved by the fact that in the known fiber-optic displacement transducer containing coaxially located opaque curtain with an aperture, bundles of supply and discharge optical fibers, the distance between the supply optical fibers and the curtain is determined by the expressions

l ₁ > d _c / 2tgΘ _NA ,

the radius of the hole in the curtain R ₀ expression

R ₀ = (l ₁ + t _PCS) tgΘ _NA,

the distance between the input and output optical fibers is determined by the expression

where d _c , d _OB , Θ _NA are the core diameter, outer diameter and aperture angle of the optical fiber, respectively;

t _SH - the thickness of the curtain;

in the receiving end of the bundle of exhaust fibers coaxially with the supplying optical fiber and the hole in the curtain, there is a segment of the technological fiber, around which there are receiving ends of the output optical fibers, divided into two equal in number of fiber groups, symmetrically located one above the other in the direction of movement of the curtain.

As a result of a search by sources of patent and technical information, no devices were found with a combination of essential features that coincide with the invention and provide the claimed technical result.

Thus, the present invention is a technical solution to the problem, which is a new, industrially applicable and inventive step, i.e. the present invention meets the criteria of patentability.

The figure 1 shows a structural diagram of the proposed displacement transducer, figure 2 - design and structural diagram of the displacement transducer, figure 3 is a simplified structural diagram of one of the options for a differential fiber-optic pressure sensor, including the proposed displacement transducer.

The fiber-optic displacement transducer comprises a supply optical fiber POV 1 coaxially located with it (in the neutral position: at the initial value of the input physical quantity) a shutter 2 with an aperture of thickness t, the optical fibers OOV 3 of the first measuring channel, the optical fibers OOV 4 of the second a measuring channel, a piece of technological fiber or a cylindrical part 5. The shutter 2 is located at a distance l ₁ relative to the end face of POV 1 (figure 1). The ends of OOB 3 and 4 of the first and second measuring channels, respectively, are located at a distance L from POV 1. Technological optical fiber 5 is necessary for the symmetrization of optical fibers 3 and 4. Around the technological fiber 5 are the receiving ends of the outlet optical fibers 3 and 4, divided into two equal according to the number of fibers of the group, symmetrically located one above the other in the Z direction of movement of the curtain 2. The number of optical fibers in the first and second measuring channels is equal, moreover, in the recommended var Iante it is equal to three.

Fiber optic displacement transducer operates as follows.

The luminous flux Ф ₀ from the output of POV 1 at an aperture angle Θ _NA falls on the curtain 2, passes through it, and enters the receiving ends OOB 3 and 4. Under pressure, the curtain 2 moves to the Z value relative to OOB 3 and 4, which leads to a change in the intensity of the light fluxes Φ ₁ (Z) and Φ ₂ (Z), coming further through the discharge fibers to the photosensitive areas of the radiation receivers (photodiodes) of the first and second measuring channels, respectively.

The radiation receivers convert the optical signals into electrical I ₁ and I ₂ received at the input of the information conversion unit (BPI). In the BPI, the operation of dividing the signals I ₁ and I _{2 is} performed, which allows you to compensate for changes in the radiation power of the LED and uninformative loss of light flux during bending of optical fibers, since their ratio does not depend on these factors. To increase the sensitivity of the conversion, it is possible to form the ratio of the difference of the signals I ₁ and I ₂ to their sum.

The main task of calculating the optical system is to determine a number of design parameters that ensure efficient input of radiation from POV 1 to OOB 3 and 4, the maximum depth of modulation of the optical signal, a uniform distribution of illumination in the plane of the OOB ends, and the minimum overall dimensions of the measuring transducer. The initial data for the calculation are:

1) the type of optical fibers used, characterized by the following reference data: aperture angle θ _NA ; core radius r _c (core diameter d _c );

2) the maximum movement of the curtain along the Z axis;

3) the distance of beam formation L _Ф = d _C / 2tgΘ _NA ;

4. The location of the plane AA, in which the receiving ends of the OOB are located, where the distribution of illumination is uniform.

As a result of the calculation, the following parameters should be determined: radius of the hole in the curtain R _O ; the distance from the radiating end of the POW to the curtain l ₁ ; the distance from the curtain to the receiving end OOB l ₂ ; the distance from the emitting end face of the POW to the receiving end OOB L; curtain thickness t _pcs .

Since the sensor design uses a differential luminous flux control circuit, in which at Z _i = 0, when the center of the image coincides with the axis of the receiving ends of the OOB, the upper half of the OOB of the first measuring channel and the lower half of the OOB of the second measuring channel are open. Moreover, in order for the fluxes Ф ₁ and Ф ₂ entering the OOB of each channel to be equal, it is important that the surface of the curtain 2 and OOB 3 and 4 be illuminated uniformly. This is achieved by the location of the curtain at a distance l ₁ > L _Ф and the location of OOB at a distance L> l ₁ + t _PC .

From the triangle MNF (see figure 1)

From the OVS triangle:

The shutter thickness t _PC is selected from the following considerations: it should be as thin as possible to reduce light loss, at the same time it should be reliable and not bend when exposed to mechanical stress. Recommended values of curtain thickness 0.2 ... 0.3 mm.

From equation (2), the distance from the radiating end of the POW to the curtain l _{1 is} determined as follows:

The most optimal location of OOB in the plane AA, when the image of the radiating end of the POW will be a ring with an area of S _AA . In the neutral position at Z _i = 0, the ring overlaps the core of all optical fibers. The inner R _OUT and the outer R _OUT radii of the ring are defined by the following expressions:

R _VNUT = d _OB -r _C ,

R _EXT = d _OB + r _C ,

Then

As an example, to calculate the optical system of the sensor, the parameters of the optical fiber ТХО.735.123 ТУ were used: optical fiber diameter d _OB = 500 μm, d _c = 200 μm, aperture angle θ _NA = 12 °. The thickness of the curtain is selected t _PC = 0.25 mm. In accordance with the graphic construction adopted l ₁ = 1,57 mm In this case (section AA), the diameter of zone 1 is equal to the diameter of the core d _c and the illumination of zone 2 is uniform.

Then R ₀ = (1.57 + 0.25) 0.19 = 0.34 mm;

A significant modulation depth of the optical signal (up to 30%) can be achieved by moving the shutter along the Z axis up or down relative to the OB by approximately 0.5d _c . Thus, at d _c = 200 μm, the displacement along the Z axis will be 100 μm.

In the proposed VOP movement, the optical signal is modulated by blocking part of the luminous flux with a moving opaque screen.

The conversion function Ф (Z) of one measuring channel has the form:

where K _about - coefficient characterizing the distribution of illumination in the measurement zone;

K _pcs (Z) - transmission coefficient of the path "supply optical fiber POV - curtain - output optical fiber OOB";

F _about - the initial light flux at the output of the POV.

For targeted control of the behavior of the conversion function, it is necessary that the coefficient K _o be equal to 1. Obviously, when K _o = 1, the behavior of the transformation function Ф (Z) will be evaluated by the behavior of the transmission function of the optical path, i.e., the coefficient K _pc (Z).

The calculation scheme of the measuring transducer of the sensor when controlling the luminous flux using a curtain with a circular hole moving along the Z axis is shown in figure 2.

With coaxial arrangement of POB and OOB

where n is the number of OOB;

S _Zi - illuminated part of the cross section of the core OOB;

S _c is the cross-sectional area of the core of OM;

S _AA is the cross-sectional area of the light flux in the plane AA of the location of the receiving ends OOB.

In accordance with figure 2:

S _AA = (Ltgθ _NA + r _c ) ² ,

where L is the distance between the radiating end face of the SOW and the plane in which the receiving ends of OOB are located, L = d _OB / tgθ _NA ;

respectively

that is, determined by the parameters of the selected optical fiber.

The cross-sectional area S _Z depends on the displacement of the curtain in the Z direction.

Let us find S _Z for OOB3 as an example:

Area S _Z3 is the sum of the areas of two circular sectors S ₁₃ and S ₂₃ formed by the mutual intersection of two circles: a radius r _c equal to the radius of the core OB and a radius R _cn equal to the radius of the light flux passing through the hole in the curtain in the plane of the receiving ends OOB. Moreover

The distance L is chosen so that the luminous flux in the AA plane completely overlaps the ends of the OOB in the neutral position of the curtain (at Z = 0).

In accordance with FIG. 2

But

Respectively

Then, taking into account expressions (10) - (13) for S _Z3 we get:

By analogy with S _Z3 we find S _Z1, we have:

where i = 1 ... n,

where n is the number of tapping optical fibers.

As can be seen from expressions (14), (15) they differ in the parameters a _i .

Find the parameters a _i . As an example, we find a ₃ (I) of the third OOB of the first measuring channel OOB3 (I) (the fibers are located on your Y axis).

From triangle A ₃ O ₃ (I) O _Z

where D ₃ = O ₃ (I) O _Z

From the triangle O ₂ (I) O ₃ (I) O _Z

where Z _i is the shift of the curtain along the Z axis;

γ = 360 ° / n

By analogy with a ₃ and D ₃ we find a _i and D _i , where i = 1 ... n, where n is the number of output optical fibers, we have:

In the General case, when there are n OOB located at the same distance relative to the optical axis, the distance D _i (I) of the first measuring channel for fibers located above the Y axis (see figure 2) is calculated by the formula (18), and for fibers of the second measuring channel located below the Y axis according to formula (19).

For a special case, when we have six OOBs located at the same distance relative to the optical axis (the seventh technological fiber is located in the center, which ensures the symmetry of the cable structure), formulas (18) and (19) take the form:

Taking into account expressions (6) - (8), (19), expression (5) for one measuring channel (for example, the first) is rewritten as follows:

where a _i , D _{i are} defined by expressions (17) - (19); R _cn - expression (10).

If the signals from the output of OOB 3 and 4 are fed to radiation receivers, and then to a subtractor, then a signal proportional to the difference in the radiation fluxes is observed at its output:

I ~ (Ф ₁ -ΔФ) - (Ф ₂ + ΔФ) = 2ΔФ.

Thus, (Φ _{1 -} Φ ₂ ) = f (Z). In this case, a doubling of the conversion sensitivity and linearization of the output dependence Φ = f (Z) are observed.

If the signals from the OOB output are fed to a dividing device, then a signal proportional to the ratio of the radiation fluxes is observed at its output

I (Z) ~ (Ф ₁ -ΔФ) / (Ф ₂ + ΔФ).

Thus, Φ _1i / Φ _2i = f (Z). In this case, the influence on the measurement accuracy of non-informative bends of the EQA, changes in the radiation power of the radiation source is reduced.

When processing VODD signals to improve metrological characteristics, it is advisable to form the ratio (F ₁ -F ₂ ) / (F ₁ + F ₂ ). In this case, there is a doubling of the conversion sensitivity and linearization of the output dependence, and the influence on the measurement accuracy of non-informative bends of the EQA, changes in the radiation power of the radiation source and the sensitivity of the radiation receiver is reduced. In this case, a signal is generated at the sensor output, which is determined by the following expression:

[I ₁ (P) -I ₂ (P)] / [I ₁ (P) + I ₂ (P)].

An example of a specific application of a fiber optic transducer in a fiber optic pressure sensor is shown in figure 3.

The membrane 1 is rigidly connected to the fitting 2 (for example, by welding) or is part of it. In the center of the membrane, a shutter 3 is rigidly fixed (for example, by welding) with a hole at distances l ₁ and l ₂ relative to the emitting end of the supply optical fiber POB 4 and the receiving ends of the output optical fibers OOB 5 of the first and second measuring channels, respectively. POV 4 and OOB 5 are rigidly fixed in the housing 6. Alignment of the fibers relative to the holes in the curtain 3 is carried out using a metal strip 7, the thickness of which is selected during the configuration of the sensor.

The sensor operates as follows (see figure 3). Part of the luminous flux Φ _{0 of the} radiation source II 8 is supplied to the measurement zone through the STI 4, passes through the hole in the curtain 3 to OOB 5. Under the influence of the measured pressure P, the membrane 1 bends, and accordingly shifts in the Z direction of the curtain 3. Part of the optical radiation F ₁ ( P) passes through the opening in the curtain, enters the OOB of the first measuring channel, the other part of the light flux Ф ₂ (P) - into the OOB of the second measuring channel. According to OOB 5 of the first and second measuring channels, the light fluxes are directed to PI 9 and PI 10, respectively. The radiation receivers PI 9 and PI 10 convert the optical signals F ₁ (P) and F ₂ (P) into electrical signals I ₁ (P) and I ₂ (P), respectively, which are then fed to the input of the information conversion unit.

The technical result of the invention is as follows.

The proposed converter design provides differential control of the luminous flux in the measurement zone, which achieves a more linear conversion function, higher measurement accuracy of physical quantities (pressure, acceleration, force, vibration parameters, etc.) under the influence of external factors. The influence on the measurement accuracy of non-informative parameters of the external environment and the bends of the fiber optic cable is significantly reduced, errors due to changes in the power of the radiation sources, inaccurate alignment of the optical fibers and the blind relative to each other are reduced, since these factors cause proportional changes in the signals in both measuring channels, which do not entail changes in their attitude.

The use of three or more outlet fibers and the optimal arrangement of the individual elements of the optical path relative to each other can increase the conversion sensitivity.

Claims (1)

Fiber-optic displacement transducer containing coaxially located opaque curtain with a hole, bundles of optical fiber inlet and outlet, characterized in that the distance between the optical fiber inlet and the curtain is determined by the expressions l ₁ > d _c / 2tgΘ _NA ,

and the distance between the input and output optical fibers is determined by the expression

where d _c , d _0c , Θ _NA is the core diameter, outer diameter and aperture angle of the optical fiber, respectively; t _pcs - curtain thickness; R ₀ is the radius of the hole in the curtain, in the receiving end of the bundle of exhaust fibers coaxially with the supplying optical fiber and the hole in the curtain, there is a segment of the technological fiber, around which there are receiving ends of the output optical fibers, divided into two equal in number of fiber groups, symmetrically located one above the other in the direction of movement of the curtain.

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