RU2520949C1 - Method of measurement of angular rate and sensitive element of gyroscope based on it - Google Patents

Abstract

FIELD: instrumentation.

SUBSTANCE: method consists of measuring the phase difference resulting from differences in the distribution time of two waves, connected to change in their rates. Two waves with circular polarisation are created in opposite directions. Particles in these waves move along circular trajectories in opposite directions. The resultant phase difference is proportional to the rotation rate. The gyroscope sensitive element comprises two solid isotropic acoustic lines 1 and 3, the shape of which enables the distribution and the receiving of volume reception acoustic wave, for example of cylindrical shape, and the emitting piezoelectric transducer 2. The transducer consists of two cross-polarised piezoelectric plates, which polarisation are orthogonal to each other, and is the transducer of waves of circular polarisation. The acoustic lines are mounted on both surfaces of the emitting transducer.

EFFECT: reduction of sensitivity of the method to external factors and increase in interference immunity of the sensitive element.

4 cl, 2 dwg

Description

The invention relates to the field of instrumentation, namely to instruments of orientation, navigation and control systems for moving objects, and is intended for measuring angular velocity.

A known method of measuring angular velocity, implemented in devices based on surface acoustic waves [S.W. Lee “A micro rate gyroscope based on the SAW gyroscopic effect", Journ. of Micromech. & Microeng., No 17, 2007], where an informative signal is formed by changing the propagation velocity of a surface acoustic wave depending on the speed of rotation of the sound duct. The advantage of this method is the manufacturability of the design, the disadvantage is the low tuning rate associated with the presence of a high-quality delay line in the feedback circuit.

A known sensitive element of a gyroscope made on surface acoustic waves [RF Patent No. 2244966 "Gyroscope on surface acoustic waves"], containing a solid-state sound pipe emitting and receiving piezoelectric transducers. The advantage of such a sensitive element is resistance to loads, the disadvantage is sensitivity to mechanical stresses on the sound duct.

The closest analogue is a method of measuring angular velocity using volumetric acoustic waves [patent No. 2392625 "Method of measuring angular velocity", publ. 06/20/2010] and a sensitive element based on it [patent No. 2397445 "Sensitive element of the gyroscope", publ. 08/28/2010]. The method is based on the registration of the orthogonal component of the emitted linearly polarized transverse wave resulting from the action of the Coriolis force and proportional to the rotation speed. The sensitive element contains a solid-state sound duct, on one of the plane-parallel ends of which there is a piezoelectric transducer emitting transverse waves, and on the other a receiving transverse wave transducer, the polarization angle of which is chosen close to 90 ° relative to the emitted transverse wave. Thus, the receiving transducer receives the orthogonal components that arise in the emitted wave as it propagates in the sound duct under rotation conditions. The advantage of this method is resistance to mechanical stress. The disadvantage of this method is the use of the amplitude method of extracting an informative signal, which is characterized by weak noise immunity.

A common disadvantage of the described methods and devices is the sensitivity to external influences, such as mechanical, magnetic and other, causing amplitude interference.

The present invention is to develop a method and a sensitive element of a gyroscope based on it, not sensitive to external influences.

The problem is solved due to the fact that the proposed method for measuring angular velocity, as well as the known one, is based on the excitation and reception of a volume acoustic wave in a sound duct. In contrast to the known method, the angular velocity measurement method is based on the estimation of the phase difference arising due to the difference in the propagation times of two circularly polarized waves having circular polarization with opposite directions of particle motion. That is, the solution comes down to using not absolute values, but their differences as an informative parameter.

The technical result is a reduced sensitivity of the method of measuring rotation speed to external factors.

The technical result is achieved due to the fact that, to isolate the informative component, it is not the amplitude method that is used, but the phase one, which is more noise-resistant. Two body waves of circular polarization propagate along the axis around which rotation occurs, but in opposite directions. These waves have circular polarization with opposite directions of particle motion. That is, in one wave the direction of motion of the particles coincides with the direction of rotation, and in the other it does not. When the direction of rotation and particle motion coincide, the wave velocity decreases, since the medium becomes less rigid, and when moving in opposite directions, the velocity increases due to the rigidity of the medium. This follows from the fact that in more rigid media the wave velocity is greater than in less rigid ones. From the difference in speeds it follows that the travel time by the waves of the same path will be different.

The invention is illustrated in figure 1, which schematically shows the movement of particles in two waves of circular polarization, propagating in opposite directions. In wave 1, particles oscillate in a clockwise direction at a speed of V, and the wave propagates in a direction opposite to the Y axis. In wave 2, particles oscillate in a counterclockwise direction, and the wave propagates in the direction of the Y axis. When the medium in which they propagate waves, with an angular velocity Ω, in wave 1, the direction of particle oscillation coincides with the direction of rotation and the wave velocity becomes V (1-W). And in wave 2, particle oscillations and rotation are oppositely directed, as a result of which the wave velocity will be V (1 + W).

The problem is solved due to the fact that the proposed sensitive element of the gyroscope, as well as the known one, contains emitting and receiving piezoelectric transducers and a solid-state sound duct and operates on the basis of volumetric acoustic waves. But, unlike the known device, both surfaces of a piezoelectric transducer, which is a circular polarization wave transducer consisting of two transversely polarized piezoelectric plates whose polarizations are orthogonal to each other, are in acoustic contact with two identical isotropic sound conductors symmetrically mounted on the piezoelectric transducer, containing at the free ends of the receiving transducers of acoustic waves. In such a device, the absolute value of the wave parameter is not informative, but the parameter difference is the phase difference of two waves propagating under the same conditions, arising from the difference in the wave propagation times from the emitting to the receiving transducers.

The technical result is to increase the noise immunity of the sensitive element.

The technical result is achieved due to the fact that the design allows to determine the speed of rotation by the phase difference of the two waves. The movement of particles in the waves emitted on both sides of the transducer occurs along circular paths in opposite directions. In the absence of rotation, waves in identical sound ducts will be received simultaneously by the receiving transducer. When rotating in one of the sound ducts, the rotation of the wave coincides with the rotation of the sound duct, but not in the second. When the direction of rotation of the sound duct coincides with the direction of motion of the particles, the wave velocity decreases, since the medium becomes less rigid, and when moving in opposite directions, the speed increases due to the stiffness of the medium. This is due to the fact that in more rigid media the wave velocity is greater than in less rigid ones. From the difference in speeds it follows that the propagation times of waves in sound ducts under rotation conditions will be different. Since both sound ducts are in the same external conditions, this time difference does not depend on changes in external influences and carries information about the speed of rotation.

Using as an informative parameter the time difference, rather than absolute values, allows to achieve accuracy under the influence of external factors, as well as to obtain the maximum informative signal.

The set of features described in claims 3 and 4 of the claims characterize the sensitive element of the gyroscope according to claim 2, characterized in that a transversely polarized piezoelectric transducer or a piezoelectric transducer of circular polarized waves is used as a receiving transducer. The authors found that both of these types of piezoelectric transducers can be used as receiving ones, however, the reception efficiency of a circularly polarized wave transducer is 1.4 times greater than that of a linearly polarized transducer.

The invention is illustrated in figure 2, which shows the design of the sensitive element of the gyroscope using body waves of circular polarization, consisting of two solid-state isotropic sound conductors 1 and 3, for example a cylindrical shape, and a radiating piezoelectric transducer 2. The transducer consists of two transversely polarized piezoelectric plates whose polarizations are orthogonal to each other. Sound ducts are installed on both surfaces of the radiating transducer, generating a circular polarized body wave in them. Acoustic waves are received by piezoelectric transducers 4 and 5 at the free ends of the sound ducts. In the absence of rotation, the waves arrive at the transducer at the same time, and in the presence of rotation, the arrival time of the waves is different.

We give calculations showing the difference in the propagation times of waves in cases where the direction of oscillation of the particles of the wave coincides with the direction of rotation and their differences.

It was shown [patent No. 2392625 "Method for measuring the angular velocity"] that the speed of particles in the wave varies under rotation. Wave propagation time when the directions of rotation of the particles in the wave and the sound duct coincide

, $${\tau }_{\mathrm{one}}=\frac{L_{\mathrm{one}}}{V(\mathrm{one}-W)}$$

,

- относительная частота вращения, Ω - угловая частота вращения, ω - угловая частота ультразвуковой волны.where L ₁ is the length of the sound duct, V is the velocity of particles in the wave at rest, $$W=\frac{\Omega }{\omega }$$

is the relative frequency of rotation, Ω is the angular frequency of rotation, ω is the angular frequency of the ultrasonic wave.

For the case of rotation in opposite directions, the propagation time will be equal to

. $${\mathrm{<figure-callout\; id="2"\; label="\tau "\; filenames="00000007.png"\; state="\{\{state\}\}">\tau </figure-callout>}}_2=\frac{L_2}{V(\mathrm{one}+W)}$$

.

Then the time difference:

$$\Delta \tau ={\tau }_{\mathrm{one}}-{\mathrm{<figure-callout\; id="2"\; label="\tau "\; filenames="00000007.png"\; state="\{\{state\}\}">\tau </figure-callout>}}_2=\frac{L_{\mathrm{one}}}{V(\mathrm{one}-W)}-\frac{L_2}{V(\mathrm{one}+W)}$$

Since the paths traveled by the wave are the same (L ₁ = L ₂ = L), and the value of W is small and W ² → 0, after transformations we get:

, $$\Delta \tau =\frac{2L}{V}W$$

,

From the obtained expression it follows that the difference in the propagation time of waves in a sound pipe, causing a phase shift of the waves, depends on the speed of rotation of the particles in the wave and the speed of rotation of the sound pipe.

The possibility of using such a device for measuring rotation speed on a structure in which one piezoelectric transducer operates as a radiating and receiving one was experimentally confirmed. For the manufacture of the model, quartz Y-slice plates and sound ducts made of glass in the form of cylinders were used. Qualitative results were obtained of the dependence of the informative parameter on the rotation speed, confirming their linear relationship.

The description of the invention indicates that a new sensitive element of a gyroscope based on volumetric acoustic waves is proposed, which is based on the new principle of measuring angular velocity, based on the propagation of circularly polarized waves. The technical result is achieved - improving the accuracy of measuring the speed of rotation and stability in conditions of changing external influences. In this case, an increase in the measurement accuracy is achieved by obtaining an informative parameter by the phase method, which leads to the independence of the result from external factors, for example, mechanical, magnetic, and others, causing amplitude noise.

Claims (4)

1. A method of measuring angular velocity by exciting and receiving a volumetric acoustic wave in a sound guide, characterized in that two waves are excited in opposite directions, having circular polarization with opposite directions of particle motion, and the phase difference is used as a measured characteristic proportional to the speed of rotation, resulting from the difference in the propagation times of these two waves, associated with a change in their velocities. 2. A sensitive element of the gyroscope containing an acoustic piezoelectric transducer and a sound pipe, the shape of which provides the propagation and reception of a volume acoustic wave, characterized in that both surfaces of the piezoelectric transducer of circular polarization waves, consisting of two transversely polarized piezoelectric plates, the polarizations of which are orthogonal to each other, are in acoustic contact with two identical symmetrically mounted on a piezoelectric transducer from otropny sound ducts containing at their free ends receiving transducers of acoustic waves. 3. The sensitive element of the gyroscope according to claim 2, characterized in that a transverse-polarized piezoelectric transducer is used as a receiving transducer. 4. The sensitive element of the gyroscope according to claim 2, characterized in that a piezoelectric transducer of circular polarization waves is used as a receiving transducer.

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