RU2829195C1 - Fibre-optic pressure sensor - Google Patents

Abstract

FIELD: measuring.

SUBSTANCE: invention relates to measurement equipment and can be used for measurement of low pressure in cavities with limited height. Fibre-optic pressure sensor comprises a housing, a membrane, input and output optical fibres, parallel to the common end of which an opaque shutter moves, on the other side of the shutter, a mirror surface is fixed perpendicular to the optical axis of the optical fibres at a distance from the shutter. Mirror surface is formed on a fixed insert installed in the housing. Opaque shutter is made on the inner end of the flat protrusion of the newly introduced receiving element with two cylindrical protrusions which are variable in diameter, the outer diameter of the receiving surface of which is greater than the diameter of the membrane. In the centre of the membrane there is a hollow cylindrical protrusion, the base of which the membrane is sealed on the first protrusion of the receiving element, and the inner surface of the cylinder is on the second protrusion of the receiving element, wherein inner diameter and height of membrane cylindrical protrusion are equal to diameter and height of second protrusion of the receiving element. Membrane is tightly connected along the outer contour to the lower part of the housing. Base is installed in the upper part of the housing, which is tightly connected along the contour to the upper part of the housing.

EFFECT: device makes it possible to reduce errors of interaction of measuring instrument with object of measurement at minimum weight-overall dimensions and provides possibility of application in narrow spaces on objects with uneven surfaces.

8 cl, 3 dwg

Description

The invention relates to measuring equipment and can be used to measure low pressures in medicine: in neonatology to measure the pressure of a newborn's tongue in the first days of its life, in dentistry to measure the pressure of the tongue on the palate at the initial stage of diagnosing a disease associated with congenital clefts of the upper lip and palate and other anomalies of the oral cavity, as well as other moving objects in cavities limited in height that have a non-linear surface profile, for example, in air and liquid tonometers (located between the rubber and leather shells of the cuff in the area of contact with the human body), in artificial lung ventilation devices.

A similar in its functional purpose fiber-optic sensor of the force (pressure) of the tongue on the palate is known, comprising two plates, between which an optical fiber is located, one end of which is connected to the radiation source, and the second to the radiation receiver, the upper plate is made in the form of an inverted glass, the lower plate is made flat, with a thickness close to the thickness of the bottom of the upper plate, and which is attached along the contour to the protrusion of the upper plate, the free space between the plate, the glass and the optical fibers is filled with a sealant, and the turns of the optical fiber are located between the plates either in the form of the letter "O", or in a spiral, or in the form of the letter "B", or the number "6", or in the form of two mutually perpendicular letters "P" [patent for invention of the Russian Federation 2741274 Fiber-optic sensor of the force of the muscles of the tongue - pressure of the tongue on the palate and the method for assembling it].

The disadvantages of this technical solution are as follows:

- the sensitivity of the optical signal conversion in the measurement zone is low for measuring the force (pressure) of the tongue, especially when it comes to a child,

- during long-term use, the integrity of the optical fiber may be compromised due to constant bending;

- a fairly complex sensor manufacturing technology;

- inaccurate positioning of the sensor relative to the palate due to uncertainty in the patient's palate profile;

- a large (up to 30%) component of instrumental error: the error in the interaction of the measuring instrument with the measurement object (the patient’s palate and tongue), caused by the complex profiles of both the patient’s palate and tongue.

A fiber-optic pressure sensor, which contains supply and return optical fibers, an opaque shutter fixed to a membrane moves parallel to the common end of which, on one side of the shutter, a mirror surface is fixedly installed perpendicular to the optical axis of the optical fibers, wherein the thickness and width of the shutter and the distance between the common end of the optical fibers and the mirror surface are determined by the parameters of the optical fiber and the distance between the optical axes of the optical fibers [RU Patent for Invention 2740538 IPC G01L 13/00. Method for converting a luminous flux and a fiber-optic pressure sensor implementing it / E.A. Badeeva, T.I. Murashkina, D.I. Serebryakov, A.V. Badeev // Published: 2021.01.15, Bulletin 2].

The disadvantages of this technical solution are as follows:

- a large (up to 30%) component of instrumental error: the error in the interaction of the measuring instrument with the object of measurement (the patient’s palate and tongue), caused by the complex profiles of both the patient’s palate and tongue, and the morphometric parameters of the human cavity are different for different people (different sexes, different ages, different pathologies of the oral cavity);

- a large (up to 10%) error in measuring the pressure of the tongue on the palate if the pressure is unevenly distributed over the surface of the membrane, for example, the main pressure is exerted on the peripheral part of the membrane, while the curtain can move at an angle relative to the ends of the optical fibers.

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

The technical result of the proposed invention is a reduction in the error of interaction between the measuring instrument and the measurement object (by 5...6 times) with minimal weight and dimensions (no more than the dimensions of the prototype), the possibility of use in narrow spaces on objects with uneven surfaces.

The specified technical result is achieved in that the fiber-optic pressure sensor, comprising a housing, a membrane, supply and discharge optical fibers, parallel to the common end of which an opaque shutter moves, on the other side of the shutter perpendicular to the optical axis of the optical fibers at a distance from it a mirror surface is fixedly mounted, is characterized in that

1) the mirror surface is formed on a fixed insert installed in the housing;

2) an opaque curtain is made on the inner end of the flat protrusion of the newly introduced sensing element with two cylindrical protrusions of variable diameter, the outer diameter of the sensing surface of which is greater than the diameter of the membrane;

3) in the center of the membrane there is a hollow cylindrical protrusion, the base of which the membrane is hermetically mounted on the first protrusion of the sensing element, and the inner surface of the cylinder is mounted on the second protrusion of the sensing element, wherein the inner diameter and height of the cylindrical protrusion of the membrane are equal to the diameter and height of the second protrusion of the sensing element;

4) the membrane is hermetically connected along the outer contour to the lower part of the housing;

5) a base is installed in the upper part of the body, hermetically connected along the contour to the upper part of the body.

The outer surface of the sensing element can be made flat and can repeat the profile of the surface of the object on which the sensor is installed.

The outer end of the base can be made flat, in the form of a mushroom - a hemisphere, or the profile of the outer end of the base can repeat the profile of the surface of the object on which the sensor is installed.

A protrusion can be made in the center of the outer end of the base, on the threaded part of which a part is fixed along the thread, the outer profile of which is made in the form of a mushroom - a hemisphere or repeating the profile of the surface of the object on which the sensor is installed.

Fig. 1 shows the design of a fiber-optic pressure sensor (FOPS), Fig. 2 shows geometric constructions explaining the transformations of optical signals in the measurement zone and the connection of optical fibers to the radiation source and receivers, Fig. 3 shows possible designs of a base with a protrusion.

The optical fiber detector comprises a membrane 1 fixed in a housing 2, a sensing element (SE) 3 in the form of a pyramid with two cylindrical projections of variable diameter, a base 4, an insert 5 with a mirror surface 6 fixedly installed in the housing 2 (for example, using screws or glue) (Fig. 1). On the inner end of the SE 3, a flat projection is formed - an opaque shutter 7 (screen, attenuator), the thickness of which is equal to (0.5...2)d _c , and the width exceeds the core diameter d _c of the optical fiber.

In the center of the membrane 1 there is a hollow cylindrical protrusion 8, the base of which the membrane 1 is hermetically (for example, by welding) installed on the first protrusion 9 of the sensing element 3, and the inner surface of the cylinder 8 is installed on the second protrusion 10 of the sensing element 3 (for example, by an interference fit), wherein the inner diameter and height of the cylindrical protrusion 8 of the membrane 1 are equal to the diameter and height of the second protrusion 10 of the sensing element 3.

The outer diameter of the receiving surface VE 3 is greater than the diameter of the membrane 1. The membrane 1 is hermetically (for example, by welding) connected along the outer contour to the lower part of the housing 2.

The base 4 is hermetically (for example, by welding) connected along the contour to the upper part of the body 2.

On one side of the shutter 7, at a distance l ₁ , there are a supply optical fiber (FOF) 11, a working diverting optical fiber ( _WDOF ) 12, and a compensating diverting optical fiber (CDOF _K ) 13. On the other side of the shutter 7, at a distance l _2, there is a fixed mirror surface 6. The common end of the _WDOF 12 and CDOF _K 13 is fixed at a distance X ₀ from the fixed mirror surface 6.

OOV _P 12 is located vertically above POV 11. OOV _K 13 can be located either vertically below POV 11 or with a circumferential offset in the lower half of the reflected spot (see Fig. 2).

The POV 11 is connected to the radiation source (RS) 14 (Fig. 2). The OOV _R 12 is connected to the working radiation receiver ( _WR ) 15, and the OOV _K 13 is connected to the compensation radiation receiver ( _CRR ) 16.

The newly introduced base 4 is in contact with the sky.

The outer surface of the VE 3 can be made flat and can repeat the profile of the surface of the object on which the sensor is installed.

The outer end of the base 4 can be made either flat or in the form of a mushroom-hemisphere, or the profile of the outer end of the base 4 can repeat the profile of the surface of the object on which the sensor is installed.

In the center of the outer end of the flat base 4, a projection 17 can be made, on the threaded part of which a part 18 is fixed along the thread, the outer profile of which is made either in the form of a mushroom - a hemisphere, or repeats the profile of the surface of the object on which the sensor is installed (Fig. 3). The height of the part 18 depends on the height of the measurement object (for example, on the height of the patient's palate).

The VOD works as follows.

The luminous flux Ф ₀ , formed by the radiation source 14, is transmitted via the POW 11 to the measurement zone in the direction of the mirror surface 6 (see Fig. 2). The light rays from the POW 11 in the form of a cone pass in the forward direction the distance Х ₀ to the mirror 6 and the distance Х ₀ in the opposite direction to the OOV _R 12 and OOV _K 13 at an aperture angle Θ _NA to the optical axis of the fiber. In this case, in the plane of the ends of the OOV _R 12 and OOV _K 13, an illuminated annular zone S _A-A of width h=2r _C is observed, the outer and inner radii of which are determined by the expressions:

where Θ _NA is the aperture angle of the optical fiber;

X ₀ = D/2tgΘ _NA ,

where D is the distance between the optical axes POV 11 and OOV _P 12.

In the neutral position at Z=0, shutter 7 is installed relative to the common end of the optical fibers in such a way that the illuminated annular zone S _AA completely or partially covers the surface S _OOB of the diverting optical fiber OOBr 12 (see Fig. 2).

Under the influence of the pressure P of the tongue, the base 4 rests against the palate, whereby the VE 13 rises upward and pulls the membrane 1 upward with it, which, when the pressure is removed, returns the VE 13 to its original neutral position. In this case, the shutter 7, located between the OOV _P 12 and the mirror surface 6 of the insert 7, shifts upward in the direction Z by the value Z=Z _i parallel to the common end of the optical fibers located in the same plane. In this case, only half of the light cone opposite the OOV _p 12 is blocked. Accordingly, the light signal at the input and output of the OOV _P 12 and the signal at the output of the PI _P 15 change depending on the measured pressure P.

The transformation function Ф(7) has the form: Ф(Z)=К(Z)Ф ₀ , where Ф ₀ is the luminous flux introduced into the measurement zone; К(Z) is the transmission coefficient of the path "POV 11 - mirror surface 6 - OOV _R 12''; К(Z)=ρS _PR /S _AA , where ρ is the reflection coefficient of the mirror surface 6; S _PR is the total area of the receiving ends of OOVr 12, illuminated by the luminous flux reflected from the mirror surface 6; S _AA =4πr _c (2X ₀ tgΘ _NA -r _c ).

In order to minimize the overall dimensions of the sensor, it is advisable to select the distance D equal to the diameter of the core of the optical fiber d _c =2r _C . In accordance with Fig. 2:

Finally:

The conversion coefficient K(Z) depends on the distance X ₀ from the end of the optical reflector 11 to the mirror reflective 6 surface and on the distance D between the optical axes of the optical reflector 11 and the optical reflector 12. By changing the parameters D, X _0, it is possible to achieve maximum conversion sensitivity with the maximum achievable linearity of the conversion function and modulation depth of the optical signal.

Taking into account expression (4), the transformation function of the optical system of the sensor will have the form:

In this case, Ф(Z)~Ф _Р.

The reflected light fluxes Ф _Р =ƒ(Р) and Ф _К =const via ООВ _Р 12 and ООВ _К 13 are fed to ПИР 15 and ПИК 16, where they are converted into electrical signals И _p (Р) and И _к (X ₀ =const), respectively.

The light signal at the input of OOV _K 13 and, accordingly, the signal at the output of PIK 16 remain unchanged.

When processing signals from the output of PI _R 15 and PI _K 16, in order to improve the metrological characteristics of the sensor, it is advisable to form the ratio of the difference in signals at the output of the first and second measuring channels to their sum:

[I _P (P) - I _K (X ₀ )]/[I _P (P) + I _K (X ₀ )].

In this case, there is a doubling of the conversion sensitivity, linearization of the output dependence, and a reduction in the influence of optical fiber bends, changes in the radiation power of the radiation source, and the sensitivity of the radiation receivers on the measurement accuracy.

We will establish the cause-and-effect relationship between the claimed features and the achieved technical effect in the following way.

The use of membrane 1 with cylindrical protrusion 8 ensures its rigid contact with VE 3, tightness of the sensor structure (for example, by welding) and return of VE 3 to the neutral position when the load is removed.

The presence of a high cylindrical protrusion 8 in the center of the membrane 1 makes it possible to reduce the measurement error caused by the displacement of the point of contact of the base 4 with the surface of the object (for example, with the sky), since it will not allow the curtain 7 to deviate from the vertical position.

The outer diameter of the receiving surface VE 3 is made larger than the diameter of the membrane 1 in order to reduce the influence of VE 3 on the accuracy of measuring the shape of the measurement object.

Sealed connections of membrane 1 with the lower part of housing 2 and VE 3 and base 4 with the upper part of housing 2 (for example, by welding) eliminate the occurrence of condensation in the optical system when the ambient temperature changes and, accordingly, reduce additional temperature error.

Moving the shutter 7 by the value Z allows changing the radiation intensity at the receiving ends of the optical _fiber 12 under the influence of pressure P and ensures compensatory signal conversion, since only one (working) half of the light cone is blocked.

The location of POV 11, OOV _R 12 and OOV _K 13 on one side of the curtain 7 ensures a reduction in the overall dimensions of the sensor in height.

The arrangement of a fixed insert 5 with a mirror surface 6 on the other side of the curtain 7 ensures a reduction in the overall dimensions of the sensor in height, and also allows for the implementation of compensatory conversion of optical signals, which reduces the influence of bends in the optical fiber, changes in the power of the radiation source with changes in temperature, etc., and accordingly leads to a reduction in sensor errors.

The possibility of locating the OOV _K 13 with a slight offset along the circumference reduces the requirements for the adjustment procedure.

The combination of features leads to an increase in the accuracy of positioning optical elements relative to each other, the manufacturability and tightness of the sensor design with high measurement accuracy due to a decrease in the error of interaction between the measuring instrument and the measurement object and the implementation of two-channel compensatory conversion of optical signals.

The technical result of the proposed invention is as follows.

The proposed fiber optic pressure sensor allows:

- implement compensatory transformation of optical signals directly in the zone of perception of measurement information;

- increase the sensitivity of optical signal conversion and the technological design of the sensor;

- reduce the mass and dimensions of the sensor, and accordingly place the sensor in a small volume, for example, in the patient’s mouth;

- reduce by 5...6 times the error in the interaction of the measuring instrument with the measurement object (the patient’s palate and tongue), caused by the complex profiles of both the patient’s palate and tongue;

- to increase the accuracy of measuring the pressure of the tongue on the palate due to the uniform distribution of pressure on the surface of the VE and the base and, accordingly, the vertical movement of the curtain relative to the ends of the optical fibers;

- eliminate electromagnetic radiation in the patient's oral cavity and any negative consequences of electromagnetic impact on the patient's health and on diagnostic results, since optical radiation with a power of no more than 10 μW is used.

Claims (8)

1. A fiber-optic pressure sensor comprising a housing, a membrane, supply and return optical fibers, parallel to the common end of which an opaque shutter moves, on the other side of the shutter perpendicular to the optical axis of the optical fibers at a distance from it, a stationary a mirror surface is installed, characterized in that the mirror surface is formed on a fixed insert installed in the housing; an opaque curtain is made on the inner end of the flat protrusion of the newly introduced sensing element with two cylindrical protrusions of variable diameter, the outer diameter of the sensing surface of which is greater than the diameter of the membrane; in the center of the membrane there is a hollow cylindrical protrusion, the base of which the membrane is hermetically mounted on the first protrusion of the sensing element, and with the inner surface of the cylinder - on the second protrusion of the sensing element, wherein the inner diameter and height of the cylindrical protrusion of the membrane are equal to the diameter and height of the second protrusion of the sensing element; the membrane is hermetically connected along the outer contour to the lower part of the housing; a base is installed in the upper part of the housing, hermetically connected along the contour to the upper part of the housing. 2. A fiber-optic sensor according to claim 1, characterized in that the outer surface of the sensing element is made flat. 3. A fiber-optic sensor according to claim 1, characterized in that the outer surface of the sensing element repeats the profile of the surface of the object on which the sensor is installed. 4. A fiber-optic sensor according to claim 1, characterized in that the outer end of the base is made flat. 5. A fiber-optic sensor according to item 1, characterized in that the outer end of the base is made in the form of a mushroom-shaped hemisphere. 6. A fiber-optic sensor according to claim 1, characterized in that the profile of the outer end of the base repeats the profile of the surface of the object on which the sensor is installed. 7. A fiber-optic sensor according to item 4, characterized in that in the center of the outer end of the base there is a protrusion, on the threaded part of which a part is secured along the thread, the outer profile of which is made in the form of a mushroom - a hemisphere. 8. A fiber-optic sensor according to item 4, characterized in that in the center of the outer end of the base there is a protrusion, on the threaded part of which a part is secured along the thread, the outer profile of which repeats the profile of the surface of the object on which the sensor is installed.