Method of strapdown inertial navigation using micromechanical sensor elements

Abstract

The invention relates to navigational technology, and more particularly to methods for strapdown inertial navigation of small-sized moving objects. According to the proposed method, N micromechanical sensor elements are installed in triads on a mechanical base which is in the form of a cube placed on an object, each sensor element comprising n physical-quantity sensors (for acceleration, angular velocity and the like). Groups consisting of six sensor elements are disposed on the faces of the cube, according to the Z-axis of the triad which is perpendicular to a cube face with the X-axis of the triad being set on the basis of the angle α relative to the edges of the cube. The physical quantities are defined in terms of an orthogonal coordinate system, wherein the Zo axis exits the top face of the cube at the point of intersection of the top-face diagonals, which diagonals themselves constitute the Xo and Yo axes, and the 18 individual signals measured by the triads on the basis of the defined angle α, which can be 30-45°, are converted according to the given formulas into 42 signal projections along the Xo, Yo and Zo axes. Increasing the amount of measured data significantly reduces the number of random and systematic measurement errors, as well as errors when manufacturing the shape of the cube and errors when installing the sensor elements at angle α. The obtained measurement results are subsequently processed and the navigational parameters of the moving object are defined. The technical result of applying the proposed method is that of improving the navigational accuracy for small-sized objects.

Description

[0001] A METHOD OF PLATFORM-LESS INERTIAL NAVIGATION BASED ON MICROMECHANICAL SENSORS

[0002] The invention relates to navigation technology, namely to methods of strapdown inertial navigation of small-sized moving objects using micromechanical sensitive elements (accelerometers, gyroscopes, magnetometers).

[0003] A known method of strapdown navigation [1] involves installing n tetrads of micromechanical gyroscopes and n tetrads of micromechanical accelerometers on board a moving object. These tetrads have their sensitivity axes positioned along the diagonals of a single mechanical base cube, the faces of which are oriented parallel to the orthogonal axes of the object. The tetrads' output signals are converted into projections of signals acting on the object's orthogonal coordinate system. The resulting signals are filtered, and navigational orientation parameters are calculated. A disadvantage of this method is the difficulty of installing the sensing elements within the mechanical base cube along its diagonals. Inaccuracies in the installation of the sensing elements limit the accuracy of navigation.

[0004] A micromechanical electronic inertial navigation device and a navigation method adopted as a prototype are also known [2]. According to the method, implemented in a device on a mechanical base in

[0005] SUBSTITUTE SHEET (RULE 26) n sensitive elements are installed in the form of a cube, each of which contains n sensors of physical quantities, while the sensitive elements are installed on the faces of the cube and the sensitivity axes of the sensors are oriented at an angle of a = 35.26° to the surface of the lower face of the cube, the output signals of the sensors are converted into projections of the signals on the axes of the orthogonal coordinate system Хо, Yo, Zo with a scaling factor КО = Cos(90-a) = 0.578, while the axes Хо and Yo are oriented along the diagonals of the upper face of the cube, and the Zo axis is oriented perpendicular to the center of the upper face of the cube at the intersection of its diagonals, then the received signals are summed along each of the axes Хо, Yo, Zo and subtracted, the navigation parameters of the object on which the cube is installed are calculated.

[0006] A disadvantage of this method is the use of only one scaling factor, KO, which determines the projection of the sensor signal onto one of the axes (Хо, Yo, Zo). This means that only the projections of signals from those sensors whose sensitivity axes are at an angle of α = 35.26° to the Хо, Yo, Zo axes are taken into account. However, projections of sensor signals onto the Хо, Yo, Zo axes at other angles, unequal to α, are possible, and are not taken into account.

[0007] The claimed invention solves the problem of ensuring that all possible projections of measured sensor signals onto the orthogonal axes of the object Xo, Yo, Zo are taken into account.

[0008] The technical result of the claimed invention is an increase in the accuracy of determining the navigation parameters of an object due to a significant increase in the amount of summarized data on the physical quantities acting on the object.

[0009] In order to solve the stated problem, in the navigation method, according to which N sensitive elements are installed on a mechanical base in the form of a cube, located on a moving object, each of which contains n sensors of physical quantities, on the face of the cube and the sensitivity axes of the sensors located on the lateral faces of the cube are oriented at an angle of a = 35.26° to the surface of the lower face of the cube, the output signals of the sensors are converted into projections of the signals on the axes of the orthogonal coordinate system Хо, Yo, Zo with a scale factor КО = Cos(90-a), while the axes Хо and Yo are oriented along the diagonal of the upper face of the cube, and the Zo axis is oriented perpendicular to the center of the upper face of the cube, after which the received signals are summed up along each of the axes Хо, Yo, Zo and the navigation parameters of the object are calculated, operations have been introduced according to which three-axis sensors of physical quantities are used, the sensitivity axes of which are located relative to the body of the sensitive element along the orthogonal coordinate system X, Y,Z, where N pieces of sensitive elements consist of m groups of six sensitive elements. Sensitive,

[0010] SUBSTITUTE SHEET (RULE 26) the elements of one group are placed on six faces of the cube and their Z axes are oriented perpendicular to the planes of the face of the cube, four of the group of sensitive elements 1, 2, 3, 4 are placed on the side faces of the cube, the X5 axis of the sensor of the fifth sensitive element, located on the upper face of the cube, is oriented at an angle of 45°-a relative to the axis Хо and at an angle of 45°+a relative to the axis Yo, and the sixth sensitive element is placed on the lower face of the cube with an inclination of the sensitivity axis X6 of the sensor relative to the axis Хо at an angle of 135°+a, and relative to the axis Yo at an angle of 135°-a, while the scale factors are introduced

[0011] K1 = Cos a; K2 = Sin a • Cos 45°; K3 = Cos a • Cos 45°; K4 = Cos 45°;

[0012] K5 = Sin(45-a); K6 = Cos(45-a) after which the signal levels reduced to the axes Хо, Yo, Zo are calculated by summing the signals of all six sensitive elements along their three axes Uxi, Uyi, Uzi, taking into account the scale factors and signs of their projections onto the axes Хо, Yo, Zo

[0013] UxO = short circuit (Ux1 - Ux2 - Ux3 + Ux4) + K6 (Ux5 - Ux6) + K2 (-Uy1 + Uy2 + Uy3 - Uy4) + K5 (Uy5 - Uy6) + K4 (Uz1 + Uz2 - Uz3 - Uz4);

[0014] UyO = short circuit (Ux1 + Ux2 - Ux3 - Ux4) + K5 (Ux5 - Ux6) + K2 (-Uy1 - Uy2 + Uy3 + Uy4) + K6 (Uy5 + Uy6) + K4 (-Uz1 + Uz2 + Uz3 - Uz4);

[0015] UzO = (Uz5 - Uz6) + KO (11x1 + Ux2 + Ux3 + Ux4) + K1 (Uy1 + Uy2 + Uy3 + Uy4).

[0016] The essence of the proposed invention is explained in Drawing 1, which shows a development onto one plane of the cube faces 1, 2, 3, 4, 5, 6 with an indication of the placement at an angle a of the housings of the sensitive elements in relation to the edges of the cube, the axes Xo, Yo, Zo are the axes of the orthogonal coordinates of the cube, and the axes Xi, Yi, Zi are the orthogonal axes of the sensitivity of the sensitive element.

[0017] Figure 2 shows a three-dimensional representation of a cube with the directions of the sensitivity axes of the six sensing elements indicated. The axes Xo' and Yo' are auxiliary axes located on the bottom face of the cube, parallel to the axes Xo and Yo.

[0018] As shown in Drawing 2, the sensor signals, excluding those with the Z5 and Z6 axes, have projections onto all 3 axes Хо, Yo, Zo. The relative magnitude of the projections is taken into account by the introduced scale factors K5 + K6, and the projection sign is determined according to Drawing 2 by the projection direction relative to the Хо, Yo, Zo axes. For example, the projection of the X-axis signal onto the Хо axis is determined first by the projection of the signal onto the "ab" edge lying in the XoUYo plane Х1аб = X1 Cos а, and then by the projection of the Х1 ab signal onto the Хо axis Х1 хО = Х1 аб • Cos45° = Cos a Cos45°X1 = K3X1. In this case, the found projection coincides in direction with the Хо axis, therefore it has a positive sign.

[0019] SUBSTITUTE SHEET (RULE 26) The remaining projections of the measured signals onto the Xo, Yo, and Zo axes are found in a similar manner. It should be noted that the scaling factors KO-5-Kb are generally expressed through the angle α. Therefore, when implementing this method, angle α need not necessarily be set equal to 35.26°, which is difficult to achieve in practice. Angle α can be set to 30°; 35°; 40°; or 45°, which is physically much easier to implement, while still obtaining a reliable measurement result according to the formulas UxO, UyO, and UzO.

[0020] Six triads of sensing elements generate a total of 18 signals describing the effect of a physical quantity. However, when using the claimed method, a total of 42 signal projections are formed along the Xo, Yo, and Zo axes. This allows for a measurement system with high redundancy and a high utilization rate of the measuring axes of the micromechanical sensing elements. Summing a large number of measurement data leads to increased accuracy, since random measurement error is inversely proportional to the square root of the number of measurements, and systematic error is also reduced by the presence of measurement projections acting oppositely along the Xo, Yo, and Zo axes.

[0021] The proposed method, using the formulas provided, effectively converts signals from sensing elements with increased accuracy into projections of the vector of the measured physical quantity onto the orthogonal axes of the moving object. The angle of inclination of the sensing element housing on the cube face relative to its face can be selected arbitrarily, within a range of 30-45°, as convenient for the manufacturer.

[0022] Bibliography:

[0023] 1. Russian Federation Patent 2577567.

[0024] Authors: Mumin O.L. et al. A method for strapdown inertial navigation using micromechanical sensing elements.

[0025] 2. PRC patent dated 2020-09-03 EPO patent: CN202078615

[0026] Authors: S.ZIochevskiy and others. Micromechanical electronic inertial navigation apparatus and navigation method thereof.

[0027] Publication of WO2020143846A3

[0028] SUBSTITUTE SHEET (RULE 26)

Claims

CLAUSES OF THE INVENTION A method of strapdown inertial navigation using micromechanical sensing elements, according to which N sensing elements are installed on a mechanical base in the form of a cube, each of which contains n sensors of a physical quantity, on the face of the cube and the sensitivity axes of the sensors located on the lateral faces of the cube are oriented at an angle a to the surface of the lower face of the cube, the output signals of the sensors are converted into projections of the signals onto the axes of the orthogonal coordinate system Хо, Yo, Zo with a scaling factor Ko = Cos(90-a) = Sin a, while the axes Хо and Yo are oriented along the diagonals of the upper face of the cube, and the Zo axis is oriented perpendicular to the center of the upper face of the cube, after which the received signals are summed and the navigation parameters of the object's movement are calculated, characterized in that operations have been introduced according to which three-axis sensors of physical quantities having sensitivity axes are used,located relative to the body of the sensitive element along the orthogonal coordinate system X, Y, Z, wherein N pieces of sensitive elements consist of m groups of six sensitive elements, the sensitive elements of one group are located on six faces of the cube and their Z axes are oriented perpendicularly to the planes of the faces of the cube, four from the group of sensitive elements 1, 2, 3, 4 are placed on the side faces of the cube, and their axes XI, X2, X3, X4 are set equally at an angle a to the lower face of the cube, the X5 axis of the sensor of the fifth sensitive element, located on the upper face of the cube, is oriented at an angle of 45°-a relative to the axis Хо and at an angle of 45°+a relative to the axis Yo, and the sixth sensitive element is located on the lower face of the cube with an inclination of the sensitivity axis X6 of the sensor relative to the axis Хо at an angle of 135°+a, and relative to the axis Yo at an angle of 135°-a, while scaling factors are introduced, KI = Cos a; K2 = Sin a • Cos 45°; SC = Cos a • Cos 45°; K4 = Cos 45°; SUBSTITUTE SHEET (RULE 26) K5 = Sin(45-a); Kb = Cos(45-a) after which the signal levels reduced to the axes Хо, Yo, Zo are calculated by summing the signals of all 6 sensitive elements along their three axes Uxi, Uyi, Yzi, taking into account the scale factors and signs of their projection onto the axes Хо, Yo, Zo UxO = short circuit (Uxl - Ux2 - Ux3 + Ux4) + K6 (Ux5 - Ux6) + K2 (-Uyl + Uy2 + Uy3 - Uy4) + K5 (Uy5 - Uy6) + K4 (Uzl + Uz2 - Uz3 - Uz4); UyO = short circuit (Uxl + Ux2 - Ux3 - Ux4) + K5 (Ux5 - Ux6) + K2 (-Uyl - Uy2 + Uy3 + Uy4) + K6 (Uy5 + Uy6) + K4 (-Uzl + Uz2 + Uz3 - Uz4); UzO = (Uz5 - Uz6) + KO (Uxl + Ux2 + Ux3 + Ux4) + KI (Uyl + Uy2 + Uy3 -+ Uy4). SUBSTITUTE SHEET (RULE 26)

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