RU2133450C1 - Method studying movement of object - Google Patents

Abstract

FIELD: measurement technology. SUBSTANCE: given method studying movement of object includes irradiation of studied object with coherent radiation with wave length λ, formation of interference signals, their conversion to electric ones, separation of coherent radiation into two rays. Optical length of path of second ray is increased by (2n- 1)(2n-1)λ/4/4, where n=1, 2, 3,...,interference signals of both rays are formed and converted to electric signals, electric signal of first or second ray is differentiated, signal equal to relation of differentiated electric signal from one ray to electric signal from the other ray is found. Spectral characteristic of found signal is taken, amplitudes of spectral components of movement of studied object are determined by proposed relation. Form of movement of object is obtained in addition by determined amplitudes of spectral components of movement of studied object with the aid of inverse Fourier transform. Operation of inversion can be conducted in addition. Both differentiated signal till determination of found signal and found signal till spectral characteristics are taken can be inverted as well as either magnitudes of spectral components of found signal after their taking or magnitudes of amplitudes of spectral components of movement of studied object after their determination. EFFECT: expanded range of measured magnitudes with increased measurement accuracy. 4 cl, 8 dwg, 1 tbl

Description

 The invention relates to measuring technique and can be used to study movements in microelectronics and mechanical engineering.

 A known method of non-contact measurement of object vibrations (A.S.SSSR N262295. MKI: G 01 H 9/00), which consists in probing the object under investigation by ultrasonic vibrations, receiving a modulated signal reflected from this object, mixing the probing and reflected signals, and isolating two adjacent Doppler harmonics from the total signal, the amplitude of the oscillations is determined by the ratio of the powers of these harmonics, and the object's oscillation frequency by the difference of their frequencies.

 However, in the method it is not possible to determine any other form of motion, except for sinusoidal vibrations, as well as harmonic vibrations, the magnitude of the amplitude of the second harmonic, and limitations are placed on the accuracy of measurements of the amplitude of vibrations in connection with a sufficiently long wavelength.

There is also a method for determining the amplitude of mechanical vibrations (GDR patent N276989, MKI: G 01 H 9/00), which consists in the fact that a linearly polarized, monochromatic, coherent light beam is decomposed into two equal beams that pass mutually perpendicularly. In this case, one beam is sent to a mechanical object moving with an unknown amplitude, where it is reflected. The second beam is directed to a fixed surface, from which it is also reflected. Moreover, between two mutually perpendicular components of these beams provide a phase shift of 90 ^o . Both beams are laid one on top of the other and then processed.

 However, using this method it is impossible to control the parameters of inharmonic vibrations, as well as other forms of movement.

где σ = 4πξ/λ, ξ - амплитуда вибрации исследуемого объекта;
λ - длина волны излучения лазера.There is also a method of determining the amplitude of vibration of an object (Wei Jin, Li Ming Zang, Deepak Uttamchandam, Brian Culshaw, Appl.Opt., V.30, N31, p. 4496-4499,1991), which consists in the fact that the laser radiation is directed into the oscillation zone of the object and the reference mirror through the divider, from the rays reflected from them form an interference pattern, convert it into an electrical signal and take its spectrum. The method proposes to find the amplitudes of four harmonics with frequencies that are multiples of the fundamental vibration frequency of the object under study, with a coefficient n = 1,2,3,4. Calculate the amplitude of the oscillations of the object by the formula:

where σ = 4πξ / λ, ξ is the vibration amplitude of the object under study;
λ is the wavelength of the laser radiation.

The coefficients c ₁ , c ₂ , c ₃ , c _{4 are} calculated based on the synthesis of the decompositions of the signal at the output of the measuring system in the Fourier and Bessel series. Coefficients c _n can have both positive and negative values.

 However, the scope of this method is limited by harmonic oscillations.

 A known method of measuring the amplitude of harmonic oscillations (HADefferari, RA Darby, FAAndrews, J. Acoust. Soc. Am., V.42, N5, p.982-990, 1967), which consists in the fact that the radiation reflected from objects with a given and desired vibration amplitudes, form interference patterns, convert them into electrical signals, take the characteristics of the received signals, comparing them, they judge the amplitude of the studied object.

 However, this method is characterized by a limited range of measured values (up to λ / 2, λ is the laser radiation wavelength) and is intended to determine the amplitude of only harmonic vibrations.

 Closest to the proposed invention is a method for the study of harmonic oscillations (Russian patent N2060475, MKI: G 01 H 9/00), which consists in generating an interference signal from the object under study and converting it into an electrical signal, taking the signal characteristics and judging them about the amplitude of oscillations of the investigated object.

 However, the scope of this method is limited by harmonic oscillations.

 The objective of the present invention is to expand the range of measured values while increasing the accuracy of measurements.

где c′(ν) - амплитуды спектральных составляющих найденного сигнала на частотах ν.
Кроме того, способ позволяет определить не только амплитуды спектральных составляющих движения исследуемого объекта, но и получить форму (траекторию) движения объекта. Для этого дополнительно проводят обратное преобразование Фурье для полученных значений амплитуд спектральных составляющих движения исследуемого объекта. Кроме того, в случае дифференцирования электрического сигнала первого луча и n - четного или в случае дифференцирования электрического сигнала второго луча и n - нечетного необходимо предварительно осуществить операцию инвертирования.The problem is solved in that in a method for studying the movement of an object, including irradiating the investigated object with coherent radiation with a wavelength of λ, the formation of interference signals, converting them into electrical signals, taking the spectral characteristics of the signals by which the motion parameters are determined, divide the coherent radiation into two beams , the first and second, increase the optical path length of the second beam by (2n-1) λ / 4, n = 1,2,3, .., form interference signals from both beams, convert them to electrical signals, differentiate the electric signal of the first or second beam, find a signal equal to the ratio of the differentiated electric signal of one beam to the electric signal from another beam, take the spectral characteristic of the found signal, the amplitudes of the spectral components of the motion of the object under study are determined from the relation

where c ′ (ν) are the amplitudes of the spectral components of the found signal at frequencies ν.
In addition, the method allows to determine not only the amplitudes of the spectral components of the motion of the investigated object, but also to obtain the shape (trajectory) of the movement of the object. For this, an inverse Fourier transform is additionally carried out for the obtained values of the amplitudes of the spectral components of the motion of the object under study. In addition, in the case of differentiation of the electric signal of the first beam and n - even, or in the case of differentiation of the electric signal of the second beam and n - odd, it is necessary to carry out the inversion operation first.

 Inversion is carried out at different stages of the method, and the object of inversion is chosen: a differentiated electric signal after it is taken or a found signal before taking its spectral characteristic or spectral characteristic of the found signal after it is taken or the amplitudes of the spectral components of the motion of the studied object after their determination.

 The originality of the proposed solution lies in the fact that two electrical signals are measured simultaneously taken from the output of the measuring system (from photodetectors), which correspond to two interference signals from the object under study, one of which has a certain phase delay; they create a new signal from the ratio of one differentiated signal to the value of another, in a special way, from the spectrum of the new signal, determine the spectrum of the original function that characterizes the movement of the object, and get it. Thus, the proposed method allows to obtain useful information for a wider class of object movements, without resorting to a significant complication of the experimental part of the method. A similar set of actions, successfully combining the experimental and calculated parts, entailing the ability to control the motion parameters of the object, is not known.

The invention is illustrated using the drawings of FIG. 1 - FIG. 8, as well as tables 1. In FIG. 1 shows a diagram of a device that implements a method where
1 - laser
2 - mirror
3 - a translucent mirror dividing the radiation into reference and objective waves,
4 - device for delaying part of the object wave (a special glass plate),
5 - the investigated object,
6 - piezoceramic plate,
7 - sound generator,
8 and 9 are photodetectors,
10 and 11 are amplifiers,
12 - computer
13 and 14 are analog-to-digital converters,
15 - differentiator,
16 - signal divider
17 - spectrum analyzer,
18 - signal divider.

 In FIG. 2 shows an interference signal converted to electrical form from a beam propagating without delay of a first beam; and in FIG. 3 - interference signal, converted into electrical form, from a beam propagating with a delay, the second beam; in FIG. 4 shows the derivative of the electrical signal of the first beam; in FIG. 5 shows the shape of a new signal constructed in relation to the derivative of the electric signal of the first beam to the value of the electric signal of the second beam; in FIG. 6 shows a spectrum of a new signal, and FIG. 7 - spectrum of an unknown function of the object; in FIG. Figure 8 shows the restored function of the object’s movement, Table 1 shows the values of the determined amplitudes of the spectral components of the motion of the object under study.

(1)

(2)
где θ - стационарный набег фазы в интерференционной системе,
t - время, f(t) - функция, описывающая продольное движение объекта.The inventive method consists in the following: coherent radiation from a laser 1 with a wavelength λ is directed to a translucent mirror 3 and divided into reference and objective waves to form interference signals; the reference wave reflected from the mirror 2 is directed to the photodetectors 8 and 9; the object wave is directed to the object under study 5, part of the object wave is covered with a special glass plate 4, which provides an increase in the optical path of the beam by (2n-1) λ / 4, n = 1, 2, 3, .., when passing part of the object beam to the object under study object 5 and back to the translucent mirror 3, which reflects this beam (II beam) to the photodetector 9. The other half of the object wave is sent without delay to object 5 and, after reflection from the object, this wave is sent by the translucent mirror 3 to photodetector 8 (I beam). These object beams together with the reference beam create interference patterns, which are recorded by photodetectors 8 and 9. Two voltages are removed from the output of photodetectors

(1)

(2)
where θ is the stationary phase incursion in the interference system,
t is time, f (t) is a function that describes the longitudinal movement of an object.

 These voltages are then amplified by amplifiers 10 and 11 and converted into digital form by analog-to-digital converters 13 and 14 for subsequent processing on a computer 12.

(3)
в случае записи неизвестной функции движения объекта f(t) в виде интеграла Фурье

(4)
Находят сигнал на выходе делителя сигналов 16 S(t)

(5)
где

(6)
Находят спектр сигнала S(t) с делителя 16 и определяют его спектр с помощью спектроанализатора 17, реализованного на основе быстрого преобразования Фурье в ЭВМ. Определяют спектр функции движения объекта с помощью делителя сигналов 18, реализующего формулу (7).Differentiate the first signal by differentiator 15 and determine the signal at its output, which can be represented as

(3)
in the case of writing an unknown object motion function f (t) in the form of the Fourier integral

(4)
Find the signal at the output of the signal splitter 16 S (t)

(5)
Where

(6)
Find the spectrum of the signal S (t) from the divider 16 and determine its spectrum using a spectrum analyzer 17, implemented on the basis of a fast Fourier transform in a computer. The spectrum of the object’s motion function is determined using a signal divider 18 that implements formula (7).

(7)
Вариант дифференцирования сигнала второго луча аналогичен рассмотренному выше.

(7)
The option of differentiating the signal of the second beam is similar to that considered above.

 Thus, the amplitudes of the spectral components of the object’s motion are determined. These amplitudes judge the nature of the movement of the object.

 The method allows in addition to the amplitudes of the spectral components of the movement of the object to accurately determine the shape (trajectory) of the movement of the object. For this, an inverse Fourier transform is additionally carried out for the obtained values of the amplitudes of the spectral components. In addition, in the case of differentiation of the first signal and n - even, or in the case of differentiation of the second signal and n - odd, inversion is necessary. Moreover, it can be carried out at different stages of the method, namely: after removing the differentiated signal from the differentiator 15, it is inverted or inverted by the found signal after receiving it from the divider 16. You can also invert the values of the spectral characteristics of the found signal taken from the spectrum analyzer 17, or invert the amplitude of the spectral components of the movement of the object after the divider 18.

 Inverting, if necessary, allows you to get the exact shape (trajectory) of the movement of the object, taking into account the direction of movement (approximation or removal).

 Example. As the object under study, a mirror was used, specially mounted on a piezoceramic plate 6, the movement of the plate and the mirror was excited by a sound generator 7 (GZ-56/1). A He-Ne laser (LGN-113) with a wavelength of 6328 A was used as a radiation source. Interference signals were recorded by photodetectors 8 and 9 of the FD-265 type, and then amplified by low-frequency amplifiers 10 and 11 U4-28 and sent to analog-digital a converter with two channels 13 and 14, located in the computer.

 The process of recovering an unknown function of the object’s movement is illustrated in FIG. 2 - FIG. 8. The values of the reconstructed amplitudes of the spectral components ξ of the unknown function, determined by formula (7), are shown in Table 1. The shape of the reconstructed complex motion of the object is shown in FIG. eight.

Claims (5)

1. A method for studying the motion of an object, which consists in irradiating the studied object with coherent radiation with a wavelength λ, forming interference signals, converting them into electrical signals and determining motion parameters, characterized in that the coherent radiation is divided into two beams - the first and second, while the optical path length of the second beam is increased by (2n-1) λ / 4, where n = 1, 2, 3 ..., interference signals are generated from both beams, which are converted into electrical signals, differentiate the electric si drove the first or second beam, find a signal equal to the ratio of the differentiated electric signal from one beam to the electric signal from another beam, take the spectral characteristic of the found signal, the amplitudes of the spectral components of the motion of the object under study are determined from the relation

where c ′ (ν) are the amplitudes of the spectral components of the found signal at frequencies ν,
the obtained spectrum judges the nature of the movement of the object.  2. The method according to claim 1, characterized in that according to the amplitudes of the spectral components of the motion of the investigated object as defined above, they additionally obtain the shape of the movement of the object; in the case of differentiation of the electric signal of the second beam and n-odd, an invert operation is additionally performed.  3. The method according to claim 2, characterized in that after removing the differentiated signal, it is inverted.  4. The method according to claim 2, characterized in that the found signal is inverted before the spectral characteristics or the spectral components of the found signal are taken after they are taken.  5. The method according to claim 2, characterized in that after determining the amplitudes of the spectral components of the motion of the investigated object, their values are inverted.

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