RU2797150C1 - Strapdown inertial measurement unit - Google Patents

Abstract

FIELD: measuring technology and instrumentation.

SUBSTANCE: invention can be used in inertial systems of moving objects. The essence of the proposed strapdown inertial measuring unit is that the base for installing gyroscopes-accelerometers is made in the form of spherical belts rigidly fastened to each other perpendicular to each other at two points of their contact, on the outer surface of which there are substrates for mounting eight gyroscopes-accelerometers installed in points of conjugation of spherical belts with the vertices of the internal corners of a conditional cube and conditional tetrahedra.

EFFECT: reduced weight and size when redundant sensors, as well as increased reliability of the strapdown inertial measuring unit by increasing the probability of detection and identification of failures while improving measurement accuracy.

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Description

The field of technology.

The proposed solution relates to the field of measuring technology and instrumentation and can be used in inertial systems of moving objects, aircraft and vehicle safety systems.

The level of technology.

A block of mechanical quantity transducers in the form of linear acceleration or angular velocity is known (patent RU No. 2432548), in which six identical mechanical quantity transducers are used: accelerometers or angular velocity sensors (RSS), the measuring axes (MO) of which are oriented along a polyhedron (dodecahedron). On each of the six faces of the polyhedron, intended for the installation of transducers of a mechanical quantity, one transducer is installed.

The disadvantage of this configuration is the low accuracy, which is due to the presence of variable cross-links between the sensing elements. The change in connections occurs when the orientation of the axes of a single element relative to the axes of other separately installed sensitive elements is changed due to deformation of the object structure during movement.

A strapdown inertial measuring unit (patent RU 2162203) adopted as a prototype is also known, containing gyroscopes-accelerometers with electrodes for excitation of oscillations and retrieval of information from sensitive elements and a temperature sensor placed on a base fixed on a substrate on which service electronics assemblies are installed, in which the substrate is made in the form of a dielectric board, and the base is in the form of a regular hexagonal truncated pyramid, at least on three side faces of which there are sensitive elements of gyroscopes-accelerometers, and on the smaller end face - a temperature sensor, while the base is along the plane of the larger end face fixed in the central part of the substrate, and service electronics microassemblies are installed around the base along the periphery of the substrate. In this device, the number of sensitive elements of gyroscope-accelerometers is limited by the design of the base and is six, which is insufficient for the necessary redundancy.

However, improving the parameters by installing additional gyroscope-accelerometers on known bases can lead to a significant increase in weight and dimensions, as well as to the appearance of additional measurement errors that affect the final accuracy of the device.

The technical task of the proposed solution is to create a strapdown inertial unit, on the basis of which it is possible to install a larger number of additional sensitive elements of gyroscopes-accelerometers while reducing the weight and size characteristics.

The technical result of the proposed solution is to reduce the weight and size characteristics when redundant sensors, as well as increase the reliability of operation by increasing the probability of detection and identification of failures while improving the measurement accuracy.

Essence disclosure.

This technical result is achieved by the fact that the base for installing blocks of gyroscopes-accelerometers is made in the form of spherical belts rigidly fastened to each other perpendicular to each other at two points of their contact, on the outer surface of which there are substrates for mounting eight blocks of accelerometers and gyroscopes with electrodes for excitation of oscillations and retrieval of information, installed at the points of conjugation of spherical belts with the vertices of the internal corners of a conditional cube and conditional tetrahedra.

This design allows you to install a larger number of measuring devices and reduce navigation errors significantly lower than the errors of individual sensitive elements due to the use of a conditional cube and tetrahedra to improve the accuracy of determining the installation locations of gyroscopes-accelerometers on spherical belts. The accuracy of determining navigation parameters and attitude parameters is improved by reducing the random and systematic components and increasing the probability of detecting and identifying failures while improving measurement accuracy.

Brief description of the drawings.

Fig. 1 is a general view of the strapdown inertial measuring unit. Fig. 2 - layout of a conditional cube inside spherical belts. Fig. 3-scheme of arrangement of conditional tetrahedra in a conditional cube.

Fig. 4 is a block diagram of information processing from a strapdown inertial measuring unit.

Implementation.

On a movable object (not shown in the drawing) on a substrate 1, a base 3 is fixed by means of support elements 2 to accommodate eight sensitive elements (Fig. 1), which contain gyroscopes-accelerometers with electrodes for excitation of oscillations and retrieval of information from the sensitive elements and temperature sensors. The base 3 is made in the form of two spherical belts 4 and 5 rigidly fastened to each other by means of power tides 6 (or other type of fastening) perpendicular to each other at the points of their contact.

On the outer surfaces of the spherical belts 4 and 5, eight substrates 7 are fixed, on which eight gyroscope-accelerometers 8 are fixed with temperature sensors and other necessary devices (not shown in the drawing) to compensate for temperature errors with double-sided wiring and in a protective standard housing with electrical circuit leads service electronics (not shown in the drawing). Substrates 7 and gyroscopes-accelerometers 8 are fixed at the conjugation points 9 (Fig. 2) of spherical belts 4 and 5 with the vertices of the internal corners of the conventional cube 10 and conventional tetrahedra 11 (Fig. 3). To determine the installation locations of eight gyroscopes-accelerometers 8 on substrates 7 at interface points 9, laser modeling was used.

In many industries, incl. and with the development of the abilities of technical design and modeling (Matveeva T.F., https://urok.lsept.ru/articles/530955), laser modeling is used, with which to improve the accuracy of the location of eight gyroscopes-accelerometers 8 on spherical belts 4 and 5, the authors inscribed a conditional cube 10 into them, and conditional tetrahedra 11 into it (Figs. 2 and 3), determined the points of their conjugation 9 with spherical belts 4 and 5, and after fixing eight gyroscopes-accelerometers 8 at these conjugation points 9, the initial exhibition was held, while the sensitivity vector (not shown in the drawing) of each of the eight gyroscopes-accelerometers 8 are located along the axes coinciding with the corresponding diagonals of the conditional cube 10, and one of the diagonals of this cube coincides with the line of direction of movement or flight ( not shown in the drawing).

(при значении ребра куба равной единице) и величины диагонали самого условного куба 10, где одна из величин кратна

Одинаковость сторон условных тетраэдров 11 и вертикальность их высот к их основаниям обеспечивает постоянность диагоналей сторон условного куба 10. Для повышения точности диагоналей условного куба 10 из каждой его вершины располагают восемь условных тетраэдров 11 по схеме, показанной на фиг. 3In a conditional cube 10, the angles of intersection of the diagonals are constant, but cannot be accurately calculated due to the irrational values of the diagonal of the face of the conditional cube 10, which includes a factor equal to

(with the value of the edge of the cube equal to one) and the value of the diagonal of the conditional cube itself is 10, where one of the values is a multiple of

The similarity of the sides of the conditional tetrahedra 11 and the verticality of their heights to their bases ensures that the diagonals of the sides of the conditional cube 10 are constant. 3

The block diagram of information processing is shown in Fig. 4.

Work strapdown inertial measuring unit is as follows.

When moving, each of the eight gyroscopes-accelerometers 8 of the strapdown inertial measuring unit 12 under the influence of the generators of the angle sensor 13 and the excitation system 14, the voltage regulators of the excitation system 15, the temperature sensor amplifier 16, the synchronous detector unit 17, the gyroscope filter unit 18, the accelerometer filter unit 19 and the block of quality factors 20 measures the corresponding projection of the linear acceleration of the object (angular velocity) on the sensitivity axis and outputs the measurement results.

The received output signals are filtered and the navigation parameters are calculated.

The proposed layout (selection of locations) of inertial elements increases their accuracy and reliability due to a larger number of mutually oriented sensors, the resulting output parameters of which complement each other, are easier to process and give a more accurate averaged result, and the failure of any of the sensors does not lead to significant distortion of output measuring parameters. In a conditional cube 10, the angles of intersection of the diagonals are constant, as are the diagonals of the sides, which ensure the sameness of both the conditional tetrahedra 11 themselves and the verticality of the heights of the conditional tetrahedra 11 to their bases, but the existence and inevitability of technological errors requires the calculation and determination of the angles of inclination with an accuracy not worse than ²³ arc seconds, as well as the measurement of the linear values of the conditional cube 10 and spherical belts 4 and 5 should be no more than 0.2 mm, while due to the "averaging" of the obtained values and the possibility of redundancy, the resulting accuracy indicators are minimized.

The positive effect of the implementation of the proposed solution was verified by the authors experimentally, when prototyping the proposed base design with the installation of eight gyroscopes-accelerometers 8 on spherical belts 4 and 5. As a result, the accuracy of determining the total signal was increased by more than four times.

To confirm the performance of the proposed strapdown measuring unit, the authors created a prototype using microelectronics technologies, where micromechanical gyroscopes (MMGs) were used as gyroscopes.

MMG electromechanical units are formed from non-metallic materials (single-crystal silicon, fused quartz, silicon carbide, etc.) by photolithography and isotropic or anisotropic etching methods together with excitation electronics elements, useful signal pickup and conversion sensors, feedback formation elements.

MMG production is large-scale, sensitive elements are created (“printed”) on silicon wafers in hundreds of pieces at once. After cutting, individual operations of control by parameters, fixing in cases, welding of electrodes, casing, evacuation, sealing of cases, etc. are carried out. The technological process includes dozens of stages. Ultra-high requirements are imposed on the purity and accuracy of execution, a significant part of which is typical for modern microelectronics as a whole. Production is carried out on automatic lines, the most critical operations are carried out in a vacuum. However, the rejection rate is usually more than half, and this is considered normal. Although at present the MMG escape rate is at the level of 10 7 h, it is expected that it can be increased by an order of magnitude. This opens up the possibility of mass use of MMG in a wide variety of fields. For many technical applications where accuracy is of little concern, the exceptionally low cost of MMG is critical. It is no coincidence that in the MMG passport data produced by leading companies, information on the rate of departures is not given at all. In relation to the features of MMG mass production technologies, the most important thing is that due to the elastic mobility of the inertial body, assembly operations are completely excluded during the manufacture of the sensitive element, which are necessary only when connecting the electrodes and casing. (Special technologies for the manufacture of precision units and elements of gyroscopic instruments. St. Petersburg ITMO University, 2017)

Thus, the introduction of eight gyroscopes-accelerometers 8 into the system allows not only to implement a full-fledged inertial system, in which, with the correct operation of all eight gyroscopes-accelerometers 8, an increase in the accuracy of calculations of the coordinate system is provided, and if one of the eight gyroscopes-accelerometers 8 fails, the remaining ones provide necessary information sufficient for accurate calculation and maintenance of the inertial system.

This design allows you to install a larger number of measuring devices and reduce navigation errors significantly below the errors of individual sensing elements due to the use of a conditional cube 10 and conditional tetrahedra 11 to improve the accuracy of determining the installation locations of eight gyroscopes-accelerometers 8 on spherical belts 4 and 5. parameters and orientation parameters is increased by reducing the random and systematic components and increasing the probability of detection and identification of failures while improving the accuracy of measurements.

The proposed solution automatically and continuously compensates for the low-frequency components of the systematic errors of the angular velocity sensors, which leads to an increase in the accuracy of the orientation of a moving object, an increase in battery life and useful application, as well as a reduction in power consumption.

The use of spherical belts provides, when designing in the actual use of the claimed devices, the practical possibility of reliable fastening of blocks of measuring sensors with ensuring their positional adjustment.

Literature

1. Patent RU No. 2432548.

2. Patent RU No. 2162203, IPC G01C 21/00 (2006.01).

Claims (1)

A strapdown inertial measuring unit containing gyroscopes-accelerometers with electrodes for excitation of oscillations and retrieval of information from sensitive elements and a temperature sensor placed on a base fixed on a substrate on which service electronics microassemblies are installed, characterized in that the base for installing gyroscopes-accelerometers is made in in the form of spherical belts rigidly fastened together perpendicular to each other at two points of their contact, on the outer surface of which there are substrates for attaching eight gyroscopes-accelerometers installed at the points of conjugation of spherical belts with the vertices of the internal corners of a conditional cube and conditional tetrahedra.

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