A spacecraft-oriented non-physical connection high-precision impact calibration method

Abstract

The present application relates to spacecraft health monitoring technical field, provide a kind of non-physical connection high-precision impact calibration method for spacecraft, it includes as follows: S1: for spacecraft to be measured structure installation with detector, rotatable cantilever;S2: calibration direction is θ;S3: launch metal ball and carry out impact on the fixed position on the structure to be measured;S4: after monitoring impact occurs, impact wave propagation reaches the time of laser measuring point;S5: the accurate speed value of impact wave in the direction of angle θ is obtained by fitting algorithm;S6: obtain the propagation speed of impact wave in different angle direction on the material to be measured.In the non-physical connection high-precision impact calibration method for spacecraft of the present application, speed calibration is in-situ calibration under the actual working environment of spacecraft, instead of simply bringing into laboratory pre-calibration speed value, overcome the drawbacks that conventional method cannot realize in-situ calibration, positioning is more accurate.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of spacecraft health monitoring, and particularly relates to a non-physical connection high-precision impact calibration method for spacecraft. BACKGROUND

[0002] Impact damage of a structure has a great influence on the health condition of the structure, and especially for a spacecraft, accurate positioning of the impact is of great significance. Common methods for impact positioning include acoustic emission, acceleration, thermal imaging, calorimetry, fiber Bragg grating, microwave emission, resistance film, and surface optical shooting, etc. Among them, the positioning method based on acoustic emission, especially the acoustic emission positioning algorithm based on arrival time, is one of the most commonly used methods at present, but this method has some drawbacks in actual engineering application, mainly showing that:

[0003] Firstly, this method needs to complete the velocity calibration of the impact wave in the laboratory in advance, and cannot be calibrated on site in the actual working environment, that is, the velocity used is the calibration value in the laboratory environment, rather than the actual value in the actual working environment, and the specificity of the real working environment (such as temperature, stress, pressure, etc.) can cause a large difference between the current impact wave propagation velocity and the previous laboratory calibration velocity value, causing inaccurate subsequent impact positioning.

[0004] Secondly, for velocity calibration, one method is to simply use a constant to represent the velocity in all directions, and when the physical and chemical properties of the structure to be measured in all or part of the directions are different with the direction, the velocities in each direction are often different. Another method is to consider the different velocities of the impact wave in each direction, and paste sensors on the surface of the structure to be measured to complete the calibration of different velocities. Here, the problem is exposed: in order to obtain different velocities in different directions, a large number of sensors need to be pasted on the structure to be measured, which not only has a large amount of work, but also has great difficulty in consistency.

[0005] Thirdly, pasting sensors on the surface of the structure to be measured is equivalent to changing the structural characteristics of the original object (adding an accessory), which indirectly affects the accuracy of velocity calibration.

[0006] Fourthly, after completing the velocity calibration by pasting the sensors, the sensors need to be removed, otherwise it is equivalent to introducing redundant objects, and the removal process is easy to cause irreversible damage to the original structure, especially flexible components.

[0007] Therefore, it is of great significance to provide a flexible high-precision impact calibration method that can face different configurations and does not need physical connection. SUMMARY

[0008] To address the problems existing in the background art, the present invention provides a high-precision impact calibration method for spacecraft without physical connection, which includes the following steps:

[0009] S1: Install a rotatable cantilever with detectors on the spacecraft structure to be tested, the number of detectors being n; mark the initial angle of the cantilever as 0°; during the calibration process, the rotation angle of the cantilever represents the calibration direction, denoted as θ;

[0010] S2: When the calibration direction is θ, the lasers emitted from the n signal detectors on the cantilever strike the structure under test, and the laser measurement points are marked as P. θi (i = 0...n-1);

[0011] S3: Launch a metal ball to impact a fixed position on the structure under test, and record the impact point as o;

[0012] S4: Monitor the propagation of the impact wave to different laser measurement points P after the impact occurs. θi The time is denoted as t. θi (i = 0...n-1);

[0013] S5: The accurate velocity value of the impact wave in the direction of angle θ is obtained through a fitting algorithm;

[0014] S6: By rotating the arm, the calibration direction starts from 0° and increases in increments of unit step angle ω within the range of 0°-360°. Repeat steps S3-S5 every time the arm rotates by ω, thereby obtaining the propagation speed of the impact wave in different angular directions on the material under test.

[0015] In the preferred embodiment, the number of detectors is n = 8.

[0016] In a preferred embodiment, the cantilever is a straight arm or a curved arm, matching the shape of the structure to be tested.

[0017] In the preferred embodiment, the unit step angle ω is 3°.

[0018] In step S5, the specific process of the fitting algorithm includes:

[0019] y = oP θi ×cosα+t θi ×sinα, α∈(0,360°), i=(0,…,n-1);

[0020] Among them, oP θi This represents the distance from the i-th measuring point to the impact point o when the calibration direction is θ, and y represents the distance from the impact point to (oP). θi , t θi The distance between the fitted lines, α is (oP) θi , t θiThe inclination angle of the fitted line;

[0021] From the above equation, it can be seen that when i is fixed, y and α can uniquely determine a curve; conversely, when y and α are fixed, a straight line can be uniquely determined in a rectangular coordinate system. Based on the above theory, the process of determining the fitting equation is as follows:

[0022] First, obtain 8 measured values ​​ti (i = 0, ..., 7) at a certain angle, substitute them into the above formula to obtain the relationship between y and α, and then discretize them, 0 ≤ α < 360°, 0 ≤ y < a (a can be taken as the upper limit according to the fineness of discretization). The discretization accuracy depends on the value interval of α and the value interval of y.

[0023] If each measuring point takes h discrete points, then the n measuring points on the cantilever correspond to nh discrete points. By statistically analyzing these values, we can find the value of y that appears most frequently. By fitting the numerical points corresponding to this value, we can automatically eliminate bad points or abnormal points in the measurement process and further obtain the accurate velocity value in this direction after removing bad points.

[0024] The beneficial effects achieved by this invention are as follows:

[0025] First, in the non-physical connection high-precision impact calibration method for spacecraft of the present invention, the velocity calibration is the on-site calibration under the actual working environment of the spacecraft, rather than simply bringing in the pre-calibrated velocity value in the laboratory. This overcomes the drawback of conventional methods being unable to achieve on-site calibration, and the positioning is more accurate.

[0026] Second, when calibrating speed in actual environments, considering the damage to monitoring points or other abnormal emergencies, a fitting method that automatically removes bad points is adopted, which is more accurate than the conventional method of directly fitting data that cannot automatically filter all data.

[0027] Third, the velocity calibration system has no physical connection with the structure under test and will not change the inherent properties of the structure under test. When calibrating velocities in different directions, it is not necessary to attach a large number of sensors to the surface of the structure under test. Only a few non-physically connected signal detectors arranged on the cantilever are needed, which is more convenient. After calibration, there is no risk of damage to the original structure caused by disassembling the calibration sensors.

[0028] Fourth, this invention is applicable to typical structures commonly used on spacecraft, such as planar and spherical surfaces. For different structures, only the cantilever of the signal-carrying detector needs to be adjusted, which is highly flexible. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the structure of Embodiment 1 of the present invention;

[0030] Figure 2 This is a schematic diagram of the structure of Embodiment 2 of the present invention;

[0031] Figure 3 is an implementation flowchart of the present application.

[0032] Figure 4 is a time signal processing flowchart for monitoring the arrival of the shock wave propagation at different laser measuring points. DETAILED DESCRIPTION

[0033] The technical solutions in the present application will be described clearly and completely below in combination with the drawings in the present application. In addition, the forms of each structure described in the following embodiments are only examples, and the present application is not limited to each structure described in the following embodiments. All other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the scope of protection of the present application.

[0034] The present application aims to overcome the shortcoming of pre-calibration of shock wave propagation speed in the laboratory. There are great differences in temperature, stress, pressure and many other factors between the on-orbit flight environment of a spacecraft and the calibration environment in the laboratory. In particular, the structure may change suddenly, which will cause a large error in the speed directly brought into the laboratory pre-calibration. The actual calibration in the on-orbit environment is the most accurate calibration method. Conventional measurement of speed at different angles requires pasting a large number of sensors. For example, 8 measuring points are measured in each direction at every 3°, and 960 sensors need to be pasted in the 0°-360° direction, which is a huge workload. There are great difficulties in consistent installation between sensors, and there is a risk of falling off or damage. Considering abnormal data or data points, the conventional fitting method does not have a bad point elimination function. The present application can automatically eliminate bad points and complete fitting. There is no installation and disassembly process before and after calibration, so it will not cause irreversible damage to the original structure, especially the flexible member. The specific implementation process of the present application includes the following steps:

[0035] S1: A rotatable cantilever with a detector is installed on the spacecraft structure to be measured, and the number of detectors is n; mark the initial angle of the cantilever as 0°. During the calibration process, the rotation angle of the cantilever represents the calibration direction, denoted as θ.

[0036] S2: When the calibration direction is θ, the n signal detectors on the cantilever emit laser light to the structure to be measured, and the laser measuring point is marked as P θi (i=0……n-1).

[0037] S3: A metal ball is launched to hit a fixed position on the structure to be measured, and the impact point is marked as o.

[0038] S4: Monitor the time when the shock wave propagates to different laser measuring points P θi after the impact occurs, denoted as t θi (i=0……n-1).

[0039] S5: obtaining the accurate velocity value of the impact wave in the direction of angle θ by a fitting algorithm;

[0040] S6: calibrating the direction with 0° as the starting point, and increasing by a unit step angle ω in the range of 0°-360°, repeating steps S3-S5 every ω angle, to obtain the propagation velocity of the impact wave in different angle directions on the material to be measured.

[0041] Example 1,

[0042] The application will be described below in conjunction with specific example 1, referring to Figure 1 , Figure 1 For the case of a flat structure of the spacecraft structure to be measured, the propagation velocities of the impact wave of the spacecraft structure plate in different directions may be different. In order to accurately locate the impact position in the space environment, we need to calibrate the propagation velocities of the impact wave in different directions on site. For this purpose, the application designs a system including an impact device, a cantilever, a signal detector and a rear-end signal processing system. The impact device mainly consists of a base, a spring and a metal ball; eight signal detectors are fixed on the cantilever; the application can use a sturdy thin line, one end of which is tied to the metal ball, and the metal ball has a small beam for tying beforehand; the other end is fixed to a force-controllable gripper, which has a function similar to a mechanical arm, and the gripper is connected to the base tail end through the spring inside the thin line. In the initial state, the gripper gives a constant pulling force, so that the spring is in a compressed state, and at this time the metal ball is at the top end of the spring; when the impact occurs, the force of the gripper disappears instantaneously, and the metal ball flies out with the thin line under the action of the spring force, and the impact occurs. After the impact occurs, the gripper gives a constant pulling force to the thin line, so that the metal ball returns to the initial state, at which time the spring is again in a compressed state, and the metal ball is at the top end of the spring, as shown in the figure, waiting for the next impact. In this way, the impact point o of each impact can be ensured to be the same position. Figure 1 Figure 1

[0043] Example 2, which is different from example 1, is that the spacecraft structure to be measured in this embodiment is a spherical structure.

[0044] Example 3, which introduces the specific content of step S4, includes the accurate acquisition of the impact wave time signal by the rear-end signal processing system, and the working process is as follows Figure 4 , which is the time signal processing process of the high-precision impact positioning system. The light source uses a 1550 single-frequency laser, which is divided into two beams by a 1:2 beam splitter, and enters the 8-channel detection light path and the 8-channel reference light path respectively. The 8-channel detection light path is detected by a non-physical connection method, and the returned light and the reference light enter 8 double-channel photodetectors to complete the photoelectric conversion. The signal enters an 8-channel high-speed oscilloscope, and the accurate acquisition of the time signal is completed.​​

[0045] Example 4: This example describes the fitting algorithm in S5, the specific process of which includes:

[0046] y = oP θi ×cosα+t θi ×sinα, α∈(0,360°), i=(0,…,n-1);

[0047] Among them, oP θi This represents the distance from the i-th measuring point to the impact point o when the calibration direction is θ, and y represents the distance from the impact point to (oP). θi , t θi The distance between the fitted lines, α is (oP) θi , t θi The inclination angle of the fitted line;

[0048] From the above equation, it can be seen that when i is fixed, y and α can uniquely determine a curve; conversely, when y and α are fixed, a straight line can be uniquely determined in a rectangular coordinate system. Based on the above theory, the process of determining the fitting equation is as follows:

[0049] First, obtain 8 measured values ​​t at a certain angle. i (i = 0, ..., 7), substitute them into the above formula to obtain the relationship between y and α, and then discretize them, 0 ≤ α < 360°, 0 ≤ y < a (a can be taken as the upper limit of the discretization precision), the discretization precision depends on the value interval of α and the value interval of y.

[0050] Here, we assume that each measuring point has 1000 discrete points. Then, the 8 measuring points on the cantilever correspond to 8000 discrete values. By statistically analyzing these values, we can find the value that y appears most frequently. By fitting the numerical points corresponding to this value, we can automatically eliminate bad points or abnormal points in the measurement process and further obtain the accurate velocity value in this direction after removing bad points.

[0051] Example 5 describes the process of locating the actual impact point after calibration is completed.

[0052] In this embodiment, four sensors are fixed on the spacecraft structural plate, denoted as A1, A2, A3, A4, and A5. k (k=1……

[0053] 4) The coordinates are (X) k Y k When an impact event occurs, the time 'a' when each sensor receives the impact signal is recorded. k According to a kThe sizes are arranged in size, assuming that a4 >= a3 >= a2 >= a1, if not meet this order, can change the label of 1, 2, 3, 4, so that it satisfies a4 >= a3 >= a2 >= a1.

[0054] Let:

[0055] X1+m·V(β)·cos(β)

[0056] =X2+(m+a2-a1)·V(γ)·cos(γ)

[0057] =X3+(m+a3-a1)·V(δ)·cos(δ)

[0058] =X4+(m+a4-a1)·V(ε)·cos(ε)

[0059] Wherein, X1, X2, X3, X4, a1, a2, a3, a4 are known quantities;0° <= beta, gamma, delta, epsilon <= 360°, represent the impact wave velocity propagation direction;V(beta), V(gamma), V(delta), V(epsilon) are the accurate calibration speed of each direction introduced in the foregoing calibration work, the impact wave propagation speed in any direction is a known quantity;M is a mathematical variable, m > 0, m continuously increases from 0, when m increases to a certain specific value, the above equation is established.

[0060] Similarly

[0061] Y1+m·V(β)·sin(β)

[0062] =Y2+(m+a2-a1)·V(γ)·sin(γ)

[0063] =Y3+(m+a3-a1)·V(δ)·sin(δ)

[0064] =Y4+(m+a4-a1)·V(ε)·sin(ε)

[0065] By solving, the impact point coordinates (X1+m·V(beta)·cos(beta), Y1+m·V(beta)·sin(beta)) can be obtained.

[0066] The above only for the preferred embodiments of the present application, and not for limiting the present application, any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application, should be included in the protection scope of the present application.

Claims

1. A spacecraft-oriented non-physical connection high-precision impact calibration method, characterized in that, It comprises the following steps: S1: install a rotatable cantilever with n detectors on the spacecraft structure to be measured; mark the initial angle of the cantilever as 0°, and during the calibration process, use the rotation angle of the cantilever to represent the calibration direction, denoted as θ; S2: When the calibration direction is θ, the n signal detectors on the cantilever emit laser light to the structure to be measured, and the laser measurement points are marked as P θi (i = 0...n-1); S3: shoot a metal ball at a fixed position on the structure to be measured, and mark the impact point as o; S4: Monitor the propagation of the impact wave to different laser measurement points P after the impact occurs. θi The time is denoted as t. θi (i = 0...n-1); S5: obtain the accurate speed value of the impact wave in the direction of θ through a fitting algorithm; S6: rotate the arm, take 0° as the starting point, and increase the unit step angle ω in the range of 0°-360°. Repeat steps S3-S5 every ω angle to obtain the propagation speed of the impact wave in different angle directions on the material to be measured.

2. The non-physical connection high-precision impact calibration method for spacecrafts according to claim 1, characterized in that: The number of detectors is n=8.

3. The non-physical connection high-precision impact calibration method for spacecrafts according to claim 1, characterized in that: The cantilever is a straight or curved arm that matches the shape of the structure to be measured.

4. The non-physical connection high-precision impact calibration method for spacecrafts according to claim 1, characterized in that: The unit step angle ω is 3°.

5. The non-physical connection high-precision impact calibration method for spacecrafts according to claim 1, characterized in that: In step S5, the specific process of the fitting algorithm includes: y = oP θi x cos a + t θi x sin a, a e (0, 360°), i = (0,..., n - 1); wherein oP θi represents the distance from the i-th measuring point to the impact point o when the calibrated direction is θ, y is the distance from the impact point to the (oP θi , t θi ) fitting line, and α is the inclination angle of the (oP θi , t θi ) fitting line; As can be seen from the above formula, when i is fixed, y and α can uniquely determine a curve; conversely, when y and α are fixed, a straight line can be uniquely determined in the rectangular coordinate system; according to the above theory, the process of determining the fitting equation is as follows: First, obtain 8 measurement values ti(i=0,…,7) at a certain angle, substitute them into the above formula to obtain the relationship between y and α, then discretize them, 0≤α<360°, 0≤y<a, a is a threshold value, and the discretization accuracy depends on the interval of α and the interval of y; Suppose each measurement point takes h discrete points, then n measurement points on the cantilever correspond to nh discrete points, and the values are counted to find the value of y that appears most frequently. Fitting the value point corresponding to the value can automatically exclude bad points or abnormal points in the measurement process, and further obtain the accurate speed value in that direction after removing bad points.

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