RU2538929C2 - Polarisation-optical accelerometer - Google Patents

Abstract

FIELD: instrument.

SUBSTANCE: accelerometer comprises a cell of two polarisers set in parallel with the sensor element between them, made of transparent strain-sensitive material - polyurethane having a wedge shape. The force on the strain-sensitive element from the inertial element is transmitted by double lever system consisting of cargo under the action of the measured micro-acceleration, the leverage resting on the supports and the sites acting on the sensor element. To determine the number of interference fringes the web camera is used, mounted on one side of the cell, on the other side of which the highlighter of opal glass and LED light source is mounted for uniform illumination, at that a spring is mounted to protect the system from overload in the area of cargo under the action of the measured micro-acceleration.

EFFECT: increase in sensitivity and accuracy of measurement, the ability to conduct measurements under conditions of a space station.

2 cl, 1 dwg

Description

Technical field

The invention relates to instrumentation, namely to accelerometers designed to measure small (and micro) accelerations.

State of the art

Existing designs based on the Hele-Shaw cell [Seismic receiver based on the Hele-Shaw cell / Babushkin IA, Glukhov AF, 134-140.] Or convection sensor "Dacon-2" [I.A. Babushkin, Yu.P. Herzen, A.F. Glukhov, E.A. Zilberman, G.F. Putin, V.A. Sinkin, S.A. Nikitin, V.I. Polezhaev, M.Yu. Belyaev, D.A. Zavalishin, V.V. Sazonov, A.I. Ivanov, M.M. Maksimova. The space experiment “Investigation of convective flows in microgravity (Dacon-M)”] is based on the measurement of convective flows. To be included in the work, they need time to establish a stationary thermal regime (for “Dacon-2” - at least half an hour, and for a Hele-Shaw cell - tens of seconds.

Also known are devices containing an inertial sensing element [a.c. CCCP No. 79224, NKI 42o, 17, publ. 1962 g, a.s. USSR No. 80902, IPC G01P 15/03, publ. 01/01/49, a.c. CCCP No. 1080087, IPC G01P 15/03, publ. 03/15/84]] (self-recording, with a damper). An accelerometer with a liquid electrolytic pendulum is also proposed, in which the role of the inertial element is played by a glass ampoule with contacts welded into it [No. 281922, Liquid electrolytic pendulum. Declared June 25, 1970 IPC 01P 15 / 06-3, publ. September 14, 70]. A liquid electrolyte at certain acceleration values bridges the contacts and thereby gives a signal that the specified acceleration value has been reached.

The inertial sensing element also contains an accelerometer [Pendulum compensation accelerometer, SU No. 1840663 A1. Declared 01.01.1975, IPC 01H 5/08, publ. 09/20/08] based on the tunnel effect and an acceleration sensor for the transport of dangerous goods [Acceleration sensor. RU 2192645 C2. IPC 01P 15/135, Declared May 12, 1999, publ. November 10, 02]] The disadvantages of the above analogues is the lack of sensitivity.

The closest in technical essence and the achieved result to the proposed technical solution is an optical accelerometer (US Pat. RF No. 2156979, IPC G01P 15/03, publ. 09/27/2000), which contains a radiation source, two optical fibers, a photodetector. The input and output optical amplitude modulators operating in the optical key mode, an optical amplifier are introduced into the accelerometer. An annular waveguide formed by two optical fibers with different refractive indices, a control device, a delay element, an optical combiner. The output of the radiation source is connected to the first optical input of the input optical amplitude modulator and the first input of the optical combiner. The output of the input optical amplitude modulator is connected to the input of the optical amplifier. The output of the optical amplifier through the connection of the first fiber of the ring waveguide with the second fiber of the ring waveguide is connected to the input of the output optical amplitude modulator, the first output of which is connected through the connection of the second fiber of the ring waveguide with the first fiber of the ring waveguide to the second input of the input optical amplitude modulator. The control input of the output optical amplitude modulator through the delay element and the control input of the input optical modulator are connected to the output of the control device. The second output of the output optical amplitude modulator is connected to the second input of the optical combiner. The output of the optical combiner is connected to the input of the photodetector, the output of which is the output of the device.

The disadvantage of the prototype device is that in it the product of acceleration by the length of the fiber is negligible compared to ² , the circuit bypass time weakly depends on acceleration, therefore the slightest vibration impairs the measurement accuracy.

The objective of the invention is to develop an accelerometer design with higher sensitivity and measurement accuracy, suitable for space research.

The problem is solved using the signs specified in the 1st claim, such as a polarization-optical accelerometer, containing a cell of two parallel mounted polaroids with a sensitive element between them, made of a transparent strain-sensitive material - wedge-shaped polyurethane, while the force on the strain-sensitive element from the inertial element is transmitted using a double lever system consisting of a load under the action of the measured microacceleration, lever systems based on supports and platforms acting on the sensor, and to determine the number of interference fringes, use a web camera mounted on one side of the cell, on the other side of which for uniform illumination a backlight made of frosted glass and an LED light source is installed, while To protect the system from overload in the area of the cargo under the influence of the measured microacceleration, a spring is installed.

According to claim 2, the signal from the webcam is fed to the input of a computer (laptop) for further processing using a computer program that allows you to determine the number of interference fringes on a sensitive element and thus record the force created on it, which is proportional to the acceleration acting in the system,

The technical result of the above set of essential features is an increase in the range, sensitivity and accuracy of measurements, the possibility of measurements in a space station.

The invention is illustrated by the following embodiment and the drawing, which shows a diagram of the device.

The polarization-optical accelerometer contains a cell of two parallel-mounted polaroids 1, 2 with a sensitive element 3 between them, made of a transparent strain-sensitive material - a wedge-shaped polyurethane. The force on the strain-sensing element 3 from the inertial element 4 is transmitted using a double lever system consisting of a load 5, which is under the influence of the measured microacceleration, a system of levers 6, 7, based on the supports 8 and the platform 9, acting on the sensitive element 3. To determine the number interference fringes 10 use a webcam 11 mounted on one side of the cell, on the other side of which for uniform illumination a backlight of frosted glass 12 and an LED light source 13 is installed, while for System overload protection in the cargo area 5 under the action of the measured microaccelerations a spring 14.

Device operation

The polarization-optical accelerometer (see drawing) includes a measuring cell formed by two polaroids A (1) and B (2) crossed at an angle of 90 °. Between the polaroids there is a load-sensitive element C (3) of polyurethane made in the form of a wedge. This form provides a variable load along the height of the wedge, which gives in its narrow part an increase in the number of interference fringes and increases the sensitivity of the device.

It should be noted that for calibration of a polyurethane wedge according to the method [Alexandrov A.Ya., Akhmetzyanov M.X. The main edition of the physical and mathematical literature. “Science”, 1973, 576 pp.], It is required to select the minimum load at which the first dark band appears in the interference pattern, thereby determining the so-called STRIP PRICE σ ^1.0

Subsequently, the number of strips on the wedge is multiplied by the measured “strip price” and, thus, it becomes possible to calculate the load on the sensitive element (3).

For the first dark band to appear on the wedge, as shown by measurements, it is necessary to apply a force of 5 g of weight (this is under the conditions of usual acceleration of gravity g _З = 9.81 m / s ^{2. The} equality of the moments of forces on the load G and on the stop C gives the relation leverage lengths of levers l ₁ and l ₂

$$M_G\cdot g*\cdot l_{\mathrm{one}}=m*\cdot g_s\cdot l_2(\mathrm{one})$$

Here M _G is the mass of the cargo G, kg; g * is the acceleration of gravity in the measured system, m / s ² ; l ₁ - shoulder of the lever GC (in case there is only one lever), m * - mass used during calibration of the sensor, kg; g _s - acceleration of gravity under Earth conditions (with calibration). Calculations by the formula (1) show that the condition m * · g _s / (M _G · g *) ≈5000 must be satisfied.

This means that if we make levers with a shoulder ratio l ₁ : l ₂ equal to 100, then the cargo mass G needs to be taken 50 kg, which complicates its use in space (lifting one kilogram of cargo into space costs about $ 30,000), in addition, even with the lever length l ₂ 5 mm, the lever l ₁ must have a length of 500 mm, which makes the device cumbersome and also unrealistic in space flight conditions.

The load on the sensing element (3) can be created by a double lever system (6, 7) with the ratio of the lengths of the shoulders of each l ₁ : l ₂ ≅√5000 = 70. If you make short shoulders equal to 3 mm, then long shoulders will be required l ₂ = 210 mm, which is quite compact. Then the double lever system will consist of a load G under the action of the measured microacceleration, supports FF 'and С-С', a system of levers GF and CE, the last of which rests on the support O (8) and the platform С (9) acting on sensitive element C (3).

Behind the polaroids A (1) and B (2) there is a frosted glass backlight (12) and an LED light source (13) that gives a uniformly illuminated field. The interference pattern is recorded by a Web camera (11), the signal from which is fed to the input of a computer (laptop) (not shown) for further processing.

The computer program “MathLab” determines the number of interference fringes and, based on a pre-calibration, calculates the load applied to the sensor, which can easily be converted into actual microacceleration.

If the acceleration is approaching the usual Earth's acceleration of gravity, then in this case the load is held by the spring 14.

This description and example implementation are considered as material illustrating the invention, the essence of which and the scope of patent claims are defined in the following claims, a combination of essential features and their equivalents.

Claims (2)

1. The polarization-optical accelerometer, characterized in that it contains a cell of two parallel-mounted polaroids with a sensitive element between them, made of a transparent strain-sensitive material - wedge-shaped polyurethane, while the force on the strain-sensitive element from the inertial element is transmitted using a double lever a system consisting of a load under the influence of measurable microacceleration, a system of levers based on supports and platforms acting on a sensitive element, moreover, to determine the number of interference fringes, use a web camera mounted on one side of the cell, on the other side of which illumination of frosted glass and an LED light source is installed for uniform illumination, while protecting the system from overload in the area of cargo under influence measured microacceleration, spring installed. 2. The accelerometer according to claim 1, characterized in that the signal from the webcam is fed to the input of the computer (laptop) for further processing using a computer program that allows you to determine the number of interference fringes on the sensing element and thus record the force generated on it, proportional to the acceleration acting in the system.