RU2016406C1 - Acoustoelectronic method of determining displacements of objects - Google Patents

Abstract

FIELD: measurement technology. SUBSTANCE: method involves the steps of: delaying a reference signal at an initial frequency by an additional small delay and recording the difference in phase of received and reference signals, excluding the additional delay of reference signal and recording the second phase difference, varying the initial frequency up to a value at which the initial phase difference of received and reference signals is recovered, finally determining displacements with regard to frequencies f₁, f₂, predetermined delay τ, propagation velocity V of surface acoustic waves. The method is characterized in that the reference signal is delay by receiving surface acoustic waves propagation over a piezoelectric plate at a fixed distance from an irradiator which is taken into account in determining displacements of an object so as to exclude the influence of environment upon surface acoustic wave propagation velocity. EFFECT: enhanced measurement accuracy due to maximum compression of ultrasonic oscillation frequency tuning range and due to excluded influence of the environment upon ultrasonic oscillation propagation velocity. 2 cl, 2 dwg

Description

 The invention relates to measuring technique and can be used to determine the position of an object moving in a wide range of displacement values.

где К-1 - изменение количества длин волн ультразвуковых колебаний, укладывающихся между излучателем и приемником, при изменении частоты колебаний от f₁ до f_к;
V - скорость распространения ультразвуковых колебаний;
ε - поправка, зависящая от расстояния между излучателем и приемником (акустической базы) и направленности излучения.A known method for determining the displacement of an object [1], based on the conversion of electrical vibrations to ultrasonic vibrations at the first frequency f ₁ , the emission of ultrasonic vibrations in the direction of the controlled object, the reception of reflected ultrasonic vibrations by a receiver with a known acoustic base in relation to the emitter, measuring the phase difference between the received and radiated oscillations, oscillation frequency changes _to f until the value at which the phase difference is changed to 2 (K-1) π, and determining displacement of an object Fur Ole
L =

where K-1 is the change in the number of wavelengths of ultrasonic vibrations that fit between the emitter and the receiver, with a change in the oscillation frequency from f ₁ to f _k ;
V is the propagation velocity of ultrasonic vibrations;
ε is the correction depending on the distance between the emitter and receiver (acoustic base) and the directivity of the radiation.

)^·

Наиболее близким к изобретению является известный акустоэлектронный способ определения перемещений объекта, заключающийся в том, что в неподвижной пьезоэлектрической пластине излучающим встречно-штыревым преобразователем возбуждают поверхностную акустическую волну (ПАВ), принимают ее приемным встречно-штыревым преобразователем, установленным на подвижной пьезоэлектрической пластине, предназначенной для связи с перемещаемым объектом, измеряют разность фаз между принятым и опорным сигналами и используют ее при определении перемещения объекта [2].If in the process of changing the frequency the number of wavelengths changes by one wavelength, then the phase difference changes only by 2 π and the formula takes the form
^{L =}

) ^·

Closest to the invention is a known acoustoelectronic method for determining object movements, which consists in the fact that a surface acoustic wave (SAW) is excited by a radiating interdigital transducer in a stationary piezoelectric plate, it is received by a receiving interdigital transducer mounted on a movable piezoelectric plate designed for communication with the moving object, measure the phase difference between the received and reference signals and use it when determining the displacement the object [2].

 The disadvantage of this method is the low accuracy of determining displacement due to the impossibility of measuring an integer number of phase cycles and the dependence of the result on changes in the speed of propagation of surfactants when changing external conditions.

 The aim of the invention is to improve the accuracy of determining the movements of the object.

The goal is achieved by the fact that according to the acoustoelectronic method for determining the displacements of an object, consisting in the fact that surfactants are excited by a radiating interdigital transducer in a stationary piezoelectric plate, they are received by a receiving interdigital transducer mounted on a movable piezoelectric plate intended for communication with a moving object, measure the phase difference between the received and reference signals and use it to determine the movement of the object, the measurement of the phase difference is carried out at f ₁ simplicity synchronism interdigital transducers with a delay τ << 1 / f ₁ of the reference signal and the reference signal without delay, change signal at the second frequency measurement to a frequency f _2, at which the phase difference signal corresponding to a phase difference between the first measurement and displacement the object is determined taking into account the frequencies f ₁ , f _{2 of the} excited signals, the selected delay τ and the propagation velocity V of the surfactant.

The goal is also achieved by the fact that the delay of the reference signal is carried out by receiving a surfactant on a stationary piezoelectric plate with an additional interdigital transducer installed from the radiating one at a distance of Z _o = τ V, taking into account which the desired parameter is determined.

 In FIG. 1 and 2 show variants of a device for measuring displacements.

 A device for measuring the displacements of an object comprises a dielectric plate 1 on which a piezoelectric plate 2 is located, a radiating interdigital transducer 3 and end absorbers 4, 5 of a surfactant mounted on it, a movable interdigital transducer 6 located above the surface of the plate 2 at a distance commensurate with a surfactant length, and intended to be connected by a rigid mechanical connection with a controlled object (not shown in the figures), and a fixed capacitive current collector connected in series 7, located above the movable interdigital converter 6 of the SAW, the first amplifier 8 and the phase meter 9, the second input of which through the second amplifier 10 is connected to the output of the switch 11, the first input of which is through the delay line 12, and the second input through the attenuator 13 is connected to the frequency counter 14 and an adjustable frequency generator 15, and an additional fixed interdigital interdigital transducer 16 of the SAW located on the plate 2 at a fixed distance from the radiating interdigital transducer 3.

 The method is as follows.

The generator 15 is tuned to the synchronism frequency f _{о of the} interdigital gratings of the SAW emitter and receiver, which is measured by the frequency counter 14. An electric signal with a frequency f ₁ = f _о from the generator 15 (Fig. 1) is supplied to the emitter 3, by means of which it excites in the plate 2 Surfactant. The electric field accompanying the surfactant and propagating along the plate 2, indicates an alternating signal of the same frequency f ₁ in the interdigital transducer 6.

The output signal can be represented as
a = Ae ^{j (2πf} 1 ^{t + Ψ} o ^{+ Ψ} z ⁾ , (1) where A is the signal amplitude, depending on the magnitude of the displacement of the receiving transducer and its distance from the plate surface;
Ψ _o - the initial phase of the signal, depending on the monitored parameters, the frequency detuning and the initial position of the receiving transducer;
Ψ _z is the phase increment of the output signal due to the movement of the receiving transducer along the plate.

Z=

f₁Z= 2Π(k+n), (2) где λ - длина ПАВ на частоте f₁;
V - скорость распространения ПАВ;
К - целое число фазовых циклов в 2 π;
n - дробное число последнего фазового цикла.When the receiving transducer is moved a distance Z from the radiator, the phase increment
Ψ _Z =

Z =

f ₁ Z = 2Π (k + n), (2) where λ is the length of the surfactant at a frequency f ₁ ;
V is the speed of propagation of surfactants;
K is the integer number of phase cycles in 2 π;
n is the fractional number of the last phase cycle.

 The output signal of the converter 6 is transmitted to a capacitive current collector 7, from which it passes through an amplifier 8 to one input of the phase meter 9. To the other input of the phase meter through an amplifier 10, a switch 11, initially set to the upper position, and a delay line 12 receives a reference signal directly from the generator 15 Thus, the reference signal is additionally delayed by line 12 relative to the signal received from the receiving transducer 6, the delay of which is determined by its position relative to the plate 2.

f₁Z-2Πf₁τ , (3) где τ - дополнительная задержка в цепи опорного сигнала.Depending on the movement Z of the receiving transducer 6 relative to the radiating transducer 3, the phase difference of the compared signals
ΔΨ _Z = Ψ _o +

f ₁ Z-2Πf ₁ τ, (3) where τ is the additional delay in the reference signal circuit.

 The phasometer 9 measures the fractional part of the last phase cycle, i.e.

= 2Πn′=

+

f₁Z-2Πf₁τ-2Πk , (4) где Ψ _о - начальная фаза сигнала на частоте f₁.

= 2Πn ′ =

+

f ₁ Z-2Πf ₁ τ-2Πk, (4) where Ψ _о is the initial phase of the signal at a frequency f ₁ .

=2Πn″=

+

f₁Z-2Πk . (6)
Далее изменяют частоту генератора 15 до значения f₂, при котором восстанавливается первоначальная разность фаз принятого и опорного сигналов

, (7) где Ψ_o'' - начальная фаза сигнала на частоте f₂.An additional delay τ is chosen from the condition
τ << 1 / f ₁ . (5)
The switch 11 eliminates the additional delay from the reference signal by introducing an attenuator 13 with a attenuation equal to the attenuation of the delay line 12. Since condition (5) is fulfilled, the integer k of phase cycles in relation (2) is not violated. Therefore, the phase meter 9 fixes the second phase difference within the same phase cycle

= 2Πn ″ =

+

f ₁ Z-2Πk. (6)
Next, the frequency of the oscillator 15 is changed to a value of f ₂ , at which the initial phase difference of the received and reference signals is restored

, (7) where Ψ _o '' is the initial phase of the signal at a frequency f ₂ .

The frequency value f _{2 is} measured by a frequency counter 14.

+

f₁Z-2Πf₁τ=

+

f₂Z. (8)
Поскольку дополнительная задержка τ << 1/f₁, то второе значение частоты f₂ мало отличается от первоначального значения частоты f₁, т.е.Equating expressions (7) and (4), get

+

f ₁ Z-2Πf ₁ τ =

+

f ₂ Z. (8)
Since the additional delay τ << 1 / f ₁ , the second value of the frequency f ₂ differs little from the initial value of the frequency f ₁ , i.e.

Z-f₁τ=

Z (10)
Решив уравнение (10) относительно перемещения Z, получают
Z=

V (11)
Таким образом, по двум значениям частоты f₁ и f₂, дополнительной задержке τ опорного сигнала и скорости V распространения ПАВ в звукопроводе можно определить перемещение объекта Z. Так как результат вычислений не зависит от количества фазовых циклов k (длин ПАВ) в определяемом перемещении, то положение объекта можно контролировать без реверсивного счета количества фазовых циклов от начального положения, т.е. исключается неоднозначность фазовых измерений.f ₁ - f ₂ << f ₁ . (9)
In view of condition (9), we can assume that Ψ _o '= Ψ _o ''. Then equation (8) can be represented in a simpler form:

Zf ₁ τ =

Z (10)
Solving equation (10) regarding the displacement Z, get
Z =

V (11)
Thus, according to two values of the frequency f ₁ and f ₂ , the additional delay τ of the reference signal and the propagation velocity V of the surfactant in the sound duct, the movement of the object Z can be determined. Since the calculation result does not depend on the number of phase cycles k (surfactant lengths) in the determined displacement, then the position of the object can be controlled without reversing the count of the number of phase cycles from the initial position, i.e. the ambiguity of phase measurements is eliminated.

. (12) где Δ f₁ - изменение частоты, вызывающее изменение разности фаз сравниваемых сигналов на 2 π (360^о).Compared with the prototype, a significant reduction in the frequency tuning range was achieved. So, according to the prototype method, the minimum frequency change when measuring the displacement Z is determined by the expression
Δf ₁ = f ₁ -f ₂ =

. (12) where Δ f ₁ is the change in frequency, causing a change in the phase difference of the compared signals by 2 π (360 ^о ).

V . (13)
Уменьшение диапазона перестройки частоты можно оценить коэффициентом сжатия частот
q=

=

=

. (14) где Δφ=2πf₁τ - дополнительный фазовый сдвиг, вносимый элементом задержки на частоте f₁.According to the proposed method, to determine the same value of displacement Z according to expression (11), a change in frequency is sufficient:
Δf ₂ = f ₁ -f ₂ =

V. (thirteen)
The decrease in the frequency tuning range can be estimated by the frequency compression coefficient
q =

=

=

. (14) where Δφ = 2πf ₁ τ is the additional phase shift introduced by the delay element at the frequency f ₁ .

 It can be seen from expression (14) that the smaller the delay τ introduced into the reference signal and, consequently, the corresponding phase shift Δτ, the greater the compression coefficient q.

= 3600....1800
Таким образом, по сравнению с прототипом минимальный диапазон изменения частоты за счет новых операций еще уменьшен по крайней мере в 1000 раз, что практически исключает влияние дополнительных фазовых сдвигов в цепи излучатель - приемник из-за частотной расстройки встречно-штыревых возбуждающих и принимающих преобразователей. Приведенный расчет подтверждает правомочность условия (9) и, как следствие, справедливость равенства начальных фаз сигнала Ψ'_o=Ψ''_o при столь малом изменении частоты ПАВ. Последнее обеспечивает повышение точности определения перемещений. При длине ПАВ λ = 20 мкм разрешающая способность по перемещению с учетом разрешающей способности цифровых фазометров составляет 0,001-0,002 мкм.The minimum value of the delay τ is determined by the possibility of detecting small displacements, i.e. resolution of the used phase meter. Modern digital phase meters (F2-28, F2-34, etc.) have a resolution at the level of Δφ _about = 0.01-0.02 ^about . If we assume that the additional phase shift Δφ = 10 Δφ _о , then the real value of the compression ratio
q =

= 3600 .... 1800
Thus, in comparison with the prototype, the minimum frequency range due to new operations is still reduced by at least 1000 times, which virtually eliminates the effect of additional phase shifts in the emitter-receiver circuit due to the frequency detuning of interdigital exciting and receiving transducers. The above calculation confirms the validity of condition (9) and, as a consequence, the equality of the initial phases of the signal Ψ ' _o = Ψ'' _o with such a small change in the frequency of the surfactant. The latter provides increased accuracy in determining movements. With a surfactant length of λ = 20 μm, the resolving power with respect to the resolution of digital phase meters is 0.001-0.002 μm.

Z_o=

, (16)
где γ = (f₁ - f₂)/f₁ - относительная частотная расстройка, необходимая для исключения неоднозначности.To exclude the influence of the external environment on the speed of propagation of the surfactant in the sound duct, the same sound duct 2 is used as an additional delay element in the section Z _o (Fig. 2), in which the surfactant from the radiating transducer 3 propagates in the direction of the absorber 4 and is received by the additional stationary receiving transducer 16 . At a fixed distance Z _o = const the delay time of the surfactant is determined by the ratio
τ = Z _o / V. (fifteen)
Substituting the delay value from expression (15) into expression (11), we obtain
Z =

Z _o =

, (sixteen)
where γ = (f ₁ - f ₂ ) / f ₁ is the relative frequency detuning necessary to eliminate ambiguity.

From the obtained expression (16), it can be seen that the measured displacement Z is determined by a fixed distance Z _о measured by the frequency detuning γ and does not depend on the propagation velocity of the surfactant in the sound duct.

 The use of the invention allows to increase the accuracy of measuring displacements both due to the maximum compression of the tuning range of the frequency of the surfactant, and to eliminate the influence of inconstancy in the speed of propagation of the surfactant from changing environmental parameters.

Claims (2)

1. ACOUSTOELECTRONIC METHOD FOR DETERMINING OBJECT MOVEMENTS, which consists in the fact that a surface acoustic wave is excited by a radiating interdigital transducer in a stationary piezoelectric plate, receive it by a receiving interdigital transducer mounted on a movable piezoelectric plate, intended for communication with the object, intended for communication with phases between the received and reference signals and use it when determining the movement of an object, characterized in that, in order to increase ochnosti, phase difference measurement is carried out at a frequency f ₁ synchronism interdigital transducers with a delay τ <<<< 1 / f ₁ of the reference signal and the reference signal without delay, change signal at the second frequency measurement to a frequency f _2, at which the phase difference signal corresponds to the phase difference during the first measurement, and the movement of the object is determined taking into account the frequencies f ₁ , f _{2 of the} excited signals, the selected delay τ and the propagation velocity v of the surface acoustic wave in the piezoelectric plate. 2. The method according to claim 1, characterized in that the delay of the reference signal is carried out by receiving a surface acoustic wave on a stationary piezoelectric plate with an additional interdigital transducer installed from the radiating one at a distance z _o = τ v, taking into account which the desired parameter is determined.

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