RU2515339C2 - Method to measure linear movements - Google Patents

Abstract

FIELD: measurement equipment.

SUBSTANCE: method consists in generation of a light radiation flow supplied to the surface of the investigated object, registration of reflected light in the fixed point and its conversion into an electric signal, the value of which is used to determine distance from the surface of the investigated object in accordance with the following formula: $$\Delta x=x_0-\sqrt{\frac{x_0^2{U}_0}{U}},$$

where x₀ - initial distance from the light-reflecting surface of the investigated object to a photodetector; U₀ - amplitude of an output signal from a photodetector corresponding to x₀; U - amplitude of an output signal from a photodetector corresponding to Δx.

EFFECT: possibility to determine movement at any moment of time due to measurement of level of an output signal from a photodetector.

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Description

The invention relates to measuring equipment and is intended for measuring linear displacements.

A known method of measuring linear displacements ("Fiber-optic measuring transducers of speed and pressure", M., Energoatomizdat, 1987, p. 15), which consists in directing radiation to an object, measuring the reflected radiation flux and the magnitude of this flux judge about moving.

The disadvantage of this method is the relatively low accuracy of the measurements and the insufficient range of measured movements.

There is also known a method of measuring linear displacements, implemented by the device described in A.S. No. 1767327, IPC G01B 21/00, publ. 10/07/1992, under the name "Optical displacement sensor", selected as a prototype and including the formation of a stream of light radiation supplied to the surface of the object under study, registration at a fixed point of reflected light, converting it into an electrical signal, the value of which is used to determine the distance from the surface the investigated object.

The disadvantages of this technical solution include the small range of measured displacements, the solutions are designed to measure displacements near the surface to be monitored, where the amplitude of the output signal from the photodetector is proportional to the distance to the surface of the object under study.

The aim of the invention is to expand the range of measurements of linear displacements.

This is achieved by the fact that in the method of measuring linear displacements, which consists in generating a stream of light radiation supplied to the surface of the object under study, registering the reflected light at a fixed point, converting it into an electrical signal, the magnitude of which is used to determine the displacement of the controlled surface Δx, according to the invention, this displacement determined by the formula:

$$\Delta x=x_0-\sqrt{\frac{x_0^{2}U{}_0}{U}}\text{, (one)}$$

where x ₀ is the initial distance from the surface of the investigated object to the photodetector;

U ₀ is the amplitude of the output signal from the photodetector corresponding to x ₀ ;

U is the amplitude of the output signal from the photodetector corresponding to Δx.

The technical result consists in the fact that it was possible to determine the movement of the controlled surface at any time using the derived formula, for this it is only necessary to measure the level of the output signal U from the PMT using an oscilloscope, applying a pulse from the generator to the LED.

The presence in the claimed invention features that distinguish it from the prototype, allows us to consider it appropriate to the condition of "novelty."

New features (the definition of linear displacement, carried out by the formula:

$$\Delta x=x_0-\sqrt{\frac{x_0^{2}U{}_0}{U}},$$

where x ₀ is the initial distance from the surface of the investigated object to the photodetector;

U ₀ is the amplitude of the output signal from the photodetector corresponding to x ₀ ;

U is the amplitude of the output signal from the photodetector, corresponding to Δx) not detected in technical solutions of a similar purpose. On this basis, we can conclude that the claimed invention meets the condition of "inventive step".

Figure 1 presents a block diagram of a device with which this method is implemented;

Figure 2 presents the General dependence of the voltage from the photodetector on the distance to the surface of the investigated object.

The proposed method for measuring linear displacements is carried out using a device consisting of a radiation source in a pulsed circuit, including a pulse generator 1 and a pulsed LED 2, a light guide 3 and a receiving light guide 4 associated with a pulsed LED 2 and a photodetector 7, designed to operate in a pulsed mode and having a wide range of linearity of the light characteristic in the pulse, the surface of the investigated object 5, the interference filter 6, the photodetector 7 and the recording device VA 8 (e.g., oscilloscope).

The method is carried out using the described device as follows.

A rectangular electric pulse from a pulse generator 1 is supplied to a pulsed LED 2. Radiation from the LED 2 through the light guide 3 is supplied to illuminate the surface of the test object 5. The signal reflected from the test surface 5 is transmitted to the photodetector 7 through the receiving fiber 4, the electric signal from which is recorded by the oscilloscope 8. The shape of the pulse registered by the oscilloscope 8 is also rectangular. To reduce the parasitic external signal arriving at the photodetector 7, an interference filter 6 can be installed in the line of the optical fiber 4, the transmission maximum of which coincides with the wavelength of the maximum radiation of the LED

It is assumed that during the measurement process, the reflection coefficient of the surface of the investigated object 5 does not change. The general dependence of the voltage from the photodetector on the distance to the surface of the studied object 5 has the form shown in Fig. 2, here: OA is the plot of dependence where the signal level is proportional to the distance to the surface of the studied object 5 - the considered analogues work on this section; AB - dependence plot with a transient response; BC - plot of dependence, on which the signal level is inversely proportional to the square of the distance to the surface of the investigated object 5 - the described device for implementing the method works in this plot.

If we consider the surface of the studied object as a secondary emitter, then in this case the following relation is true:

$$\Phi =\tau \times \frac{L\times A_{\mathrm{and}-\mathrm{to}\mathrm{but}}\times A_{\mathrm{at}x}}{x^2},\text{(2)}$$

where f is the flux incident on the photodetector;

τ is the transmittance of the receiving fiber;

L is the brightness of the radiation source - the surface of the investigated object;

A _i-ka is the area of the radiation source;

A _I - the area of the receiving fiber;

x is the distance from the surface to the receiving fiber.

Secondary source brightness

$$L=E\times k,\text{(3)}$$

where E is the illumination of the probed area;

k is the coefficient taking into account the law of radiation for the surface [1 / sr]. So for a source emitting according to Lambert's law, k = 1 / π.

Illumination of a given section

$$E=F_{\mathrm{and}sl}/\mathrm{BUT},\text{(four)}$$

where Ф _izl is the radiation flux at the output of the light guide — a value that, in a first approximation, depends only on the power of the primary emitter and the transmittance of the light guide;

A is the area of the illuminated surface of the investigated object, in this case, this area is equal to the area of the secondary radiation source A = A _and-ka .

Substitution of the obtained data in the formula (2) gives the following expression

$$F={\tau }_{\mathrm{about}\mathrm{from}}\times k\times \frac{F_{\mathrm{and}sl}\times {\mathrm{BUT}}_{\mathrm{at}x}}{x^2}.\text{(5)}$$

From (5) it follows that for constant power primary emitter F _rad, constant parameters of the optical system of τ and A _Rin and at constant optical characteristics of the surface of the object (reflection coefficient ρ and coefficient reflecting radiation law k) flux incident on photodetector, depends only on the square of the distance from the emitter to the receiver.

In turn, the amplitude of the output electric signal from the photodetector is also inversely proportional to x ² (in the region of linearity of the light characteristic of the photodetector), because is the response of the photodetector to a given stream and depends only on the sensitivity of the receiver

$$U=F\times S,\text{(6)}$$

where f is the flux incident on the photodetector; S is the sensitivity of the photodetector.

In the case of a linear displacement of the surface of the investigated object 5 in a direction parallel to the optical axis of the system, the distance from the surface of the studied object 5 to the ends of the optical fibers 3 and 4 at each time will be calculated by the formula:

$$x=\sqrt{\frac{x_0^2}{\Delta U},}\text{(7)}\text{,}$$

where x ₀ is the initial distance from the surface of the investigated object 5 to the ends of the optical fibers 3 and 4; ΔU = U / U ₀ - the ratio of the amplitudes of the output signals from the photodetector 7, corresponding to the desired and initial time t ₀ .

The distance traveled by the surface of the investigated object 5

$$\Delta x=x_0-x=x_0-\sqrt{\frac{x_0^2{U}_0}{U}}.\text{(8)}$$

Before taking measurements using measuring tools (for example, a ruler, caliper, tiles), the initial distance x ₀ from the surface of the object 5 to the ends of the receiving and lighting optical fibers 3, 4 is determined. Using an oscilloscope 8, the output signal level U ₀ with PMT 7 is determined, corresponding to a given distance x _0.

When taking measurements at any time, the displacement of the surface of the studied object 5 can be determined by the formula (1), it is only necessary to measure the level of the output signal U with a PMT 7 using an oscilloscope 8, by applying a pulse from the generator 1 to LED 2.

Laboratory studies were performed that showed the operability of the method of measuring linear displacements.

The composition of the laboratory setup shown in figure 1:

- Tabor Electonics 8551 pulse generator, pulse parameters: U = 3 B, τ = 50 μs;

- blue LED λ _max = 450 nm, Ф _λmax = 40 mW;

- optical quartz-polymer fibers, conductors = 0.65 mm, N _a = 0.3;

- PMT SNFT-3, linearity of the impulse response 1.5 A (R _H = 75 Ohm);

- Tektronix TDS 2024 oscilloscope.

The installation was assembled on a stand that has an independent reading scale in millimeters and allows you to control the distance from the surface of the investigated object 5 to the ends of the optical fibers 3 and 4.

The ends of the lighting and receiving optical fibers 3 and 4 were placed at a distance from the surface of the investigated object 5, equal to 30 mm In the process of research, the distance between the optical fibers 3 and 4 and the surface of the investigated object 5 was successively reduced. Using the scale, the distance from the surface of the object under study 5 to the optical fibers 3 and 4 was measured. The output voltage level with the PMT corresponding to this distance was measured with an oscilloscope 8.

The surface displacement of the investigated object 5 Δx was determined in two ways:

- using a scale located on the stand Δx _stand ;

- according to the formula (1) Δx _calculation .

The measurement error Δ was calculated by the formula

$$\Delta =|\; |\; |\frac{\Delta x_{\mathrm{from}tend}-\Delta x_{R\mathrm{but}\mathrm{from}het}}{\Delta x_{\mathrm{from}tend}}|\; |\; |\times \mathrm{one\; hundred}\%.$$

In the field of operation of the device (section BC in figure 2), the differences in the measurement of displacements by the absolute method (using the scale) from the proposed calculation method (according to formula (1)) did not exceed 3%.

The inventive method has allowed to expand the range of measured displacements due to the new calculation algorithm and the use of a pulsed measurement system.

For the claimed invention in the form described in the claims, the possibility of implementing a method of measuring linear displacements and the ability to achieve the technical result perceived by the applicant is confirmed. Therefore, the claimed invention meets the condition of "industrial applicability".

Claims (1)

A method of measuring linear displacements, which consists in forming a stream of light radiation supplied to the surface of the object under study, registering the reflected light at a fixed point, converting it into an electrical signal, the value of which is used to determine the distance from the surface of the object under study, characterized in that this distance is determined by the formula :
$$\Delta x=x_0-\sqrt{\frac{x_0^{2}U{}_0}{U}},$$

where x ₀ is the initial distance from the reflective surface of the investigated object to the photodetector;
U ₀ is the amplitude of the output signal from the photodetector corresponding to x _0;
U is the amplitude of the output signal from the photodetector corresponding to Δx.

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