Inertial navigation system and alignment precision optimization method thereof

Abstract

The invention discloses an inertial navigation system and an alignment precision optimization method thereof. The optimization method comprises the following steps: acquiring a set sampling frequency and a set multiplying power; when the inertial navigation system starts to align, the sampling frequency and the multiplying power of the I / F conversion circuit are respectively adjusted to the set sampling frequency and the set multiplying power, so that the amplitude of the low-frequency burr output by the I / F conversion circuit is the same as or similar to the amplitude of the inherent interference signal of the inertial navigation system. During self-alignment, the sampling frequency of the I / F conversion circuit is improved, the multiplying power of the I / F conversion circuit is reduced, the amplitude of low-frequency burrs in output pulses of the I / F conversion circuit is made to be the same as or similar to the amplitude of inherent interference signals of the inertial navigation system, and the low-frequency burrs caused by slow charging and discharging of a capacitor of an integrating circuit in the I / F conversion circuit are reduced; the problem of data distortion caused by low-frequency burrs during self-alignment is improved, and the alignment precision of the inertial navigation system is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of inertial navigation alignment, and in particular relates to an inertial navigation system and an alignment accuracy optimization method thereof. Background Art

[0002] Before the inertial navigation system starts working, it must be initially aligned to enable the inertial navigation system to establish a suitable navigation coordinate system. For the alignment technology of generalized digital signal processing implemented by recursive least squares, when the laser strapdown inertial group is self-aligned, the high-precision gyroscope points to the east or west, and the other horizontal accelerometer points to the south or north to complete the alignment of the two positions. The accuracy of the north acceleration channel will affect the self-alignment result. If there are large periodic glitches, it may cause data distortion, affect the accuracy of the north acceleration channel, and thus affect the alignment result.

[0003] The I / F (current / frequency) conversion circuit can realize the accurate measurement of the acceleration channel in the laser strapdown inertial unit. Among them, the integration circuit is the key circuit of the current / frequency conversion. When there is acceleration (current), the capacitor of the integration circuit is in the charging and discharging state. The I / F conversion circuit converts the output current of the accelerometer into a pulse output. The acceleration can be obtained according to the output pulse and scale factor of the I / F conversion circuit. The specific formula is:

[0004] It=CU k ;

[0005] a=P / S;

[0006] Where, I represents the output current of the accelerometer, t represents the sampling period of the I / F conversion circuit, C represents the capacitance value of the integration circuit, and U k represents the current integrated voltage, a represents acceleration, P represents the output pulse of the I / F conversion circuit, and S represents the set calibration factor.

[0007] During the initial alignment of inertial navigation, since the inertial group cannot maintain absolute levelness and the accelerometer has zero bias error, the glitches caused by the environment and parameter drift in the I / F conversion circuit are low-frequency glitches with a larger period. These low-frequency glitches affect the measurement accuracy of acceleration and thus affect the alignment results of the inertial navigation system. Summary of the invention

[0008] The object of the present invention is to provide an inertial navigation system and an alignment accuracy optimization method thereof, so as to solve the problem that the low-frequency burrs of the I / F conversion circuit affect the initial alignment accuracy when the inertial navigation system is aligned.

[0009] The present invention solves the above technical problems through the following technical solutions: a method for optimizing the alignment accuracy of an inertial navigation system, comprising:

[0010] Step S1: Get the set sampling frequency and set magnification;

[0011] Step S2: When the inertial navigation system starts to align, the sampling frequency and magnification of the I / F conversion circuit are adjusted to the set sampling frequency and the set magnification respectively, so that the amplitude of the low-frequency burr output by the I / F conversion circuit is the same as or similar to the amplitude of the inherent interference signal of the inertial navigation system.

[0012] Furthermore, in step S1, the acquisition process of setting the sampling frequency and setting the magnification includes:

[0013] Step S1.1: When debugging the inertial navigation system as a whole, filter out the low-frequency burrs in the output pulse of the I / F conversion circuit to obtain the inherent interference signal, and then obtain the amplitude of the inherent interference signal;

[0014] Step S1.2: Under the condition that the output pulse of the I / F conversion circuit remains unchanged, the sampling frequency and magnification of the I / F conversion circuit are adjusted, and the output pulse of the I / F conversion circuit is measured;

[0015] Step S1.3: When the amplitude of the low-frequency burr in the output pulse measured in the step S1.2 is the same as or similar to the amplitude of the inherent interference signal obtained in the step S1.1, the sampling frequency corresponding to the output pulse is used as the set sampling frequency, and the magnification corresponding to the output pulse is used as the set magnification.

[0016] Furthermore, in the step S1.1, filtering out low-frequency glitches in the output pulse of the I / F conversion circuit includes:

[0017] Determine the commutation frequency of the I / F conversion circuit according to the excitation signal;

[0018] Determine the frequency range of low-frequency glitches in the output pulse of the I / F conversion circuit according to the commutation frequency;

[0019] Designing a filter according to the frequency range of the low-frequency burr;

[0020] The designed filter is used to filter out the low-frequency glitches in the output pulse of the I / F conversion circuit.

[0021] Furthermore, in step 1.2, the calculation formula of the output pulse of the I / F conversion circuit is:

[0022]

[0023] Wherein, P represents the output pulse of the I / F conversion circuit, B represents the magnification, f represents the sampling frequency, ΔU represents the difference between the current integrated voltage and the previous integrated voltage of the I / F conversion circuit, and K represents the discharge voltage reference parameter.

[0024] Furthermore, the process of obtaining the discharge voltage reference parameter K includes:

[0025] When debugging the I / F conversion circuit, the discharge voltage reference parameter K is adjusted based on the original sampling frequency and original magnification of the I / F conversion circuit;

[0026] The discharge voltage reference parameter when the output pulse of the I / F conversion circuit is stable is used as the final discharge voltage reference parameter K.

[0027] Based on the same concept, the present invention further provides an inertial navigation system, which optimizes alignment accuracy by using the above-mentioned inertial navigation system alignment accuracy optimization method.

[0028] Beneficial Effects

[0029] Compared with the prior art, the advantages of the present invention are:

[0030] The present invention improves the sampling frequency of an I / F conversion circuit and reduces the magnification of the I / F conversion circuit during self-alignment of an inertial navigation system, so that the amplitude of a low-frequency burr in an output pulse of the I / F conversion circuit is the same as or similar to the amplitude of an inherent interference signal of the inertial navigation system, reduces the low-frequency burr caused by slow charging and discharging of a capacitor of an integration circuit in the I / F conversion circuit, improves the data distortion problem caused by the low-frequency burr during self-alignment, and improves the alignment accuracy of the inertial navigation system. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solution of the present invention, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only one embodiment of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0032] Figure 1 is a flow chart of a method for optimizing alignment accuracy of an inertial navigation system in an embodiment of the present invention;

[0033] Figure 2 is the output pulse of the I / F conversion circuit in the embodiment of the present invention at the original sampling frequency and the original magnification;

[0034] Figure 3 It is the output pulse of the I / F conversion circuit in the embodiment of the present invention when the sampling frequency is increased and the magnification is reduced. DETAILED DESCRIPTION

[0035] The following is a clear and complete description of the technical solutions in the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] The technical solution of the present application is described in detail with specific embodiments below. The following specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described in detail in some embodiments.

[0037] According to the two-position alignment principle of the laser strapdown inertial system, the two-position self-alignment method estimates the eastward angular velocity error of the two static positions to obtain the azimuth error for compensation. The specific compensation formula is:

[0038]

[0039] in, Indicates the azimuth error that needs to be compensated in each iteration. The accuracy of the azimuth error directly affects the convergence accuracy and convergence speed; ω ie represents the angular velocity of the Earth; represents the local geographical latitude, ω zg The eastward gyro angular velocity measurement error of the static position is represented by (1) and (2), and the superscripts (1) and (2) both represent the serial number of the static position. The two-position alignment error uses the horizontal position error as the observation quantity to establish the two-position self-alignment error model. The specific formula is:

[0040]

[0041] Among them, r yg (t),r zg (t) represents the position measurement error of the two positions, V yg ,V zg represents the speed of two positions, β m , γ m represents the pitch angle (i.e. horizontal attitude) of the two positions, ω yg ,ω zg Indicates the horizontal gyro zero position at two locations, R y θ z (t),R z θ y (t) represents the dynamic error.

[0042] In the self-alignment calculation, the position measurement error r yg (t),r zg(t) is the observed value. The least squares fitting is performed on the velocity, horizontal attitude, horizontal gyro zero position and dynamic error of the two positions. According to formula (1), the factor affecting the azimuth error is the east gyro angular velocity measurement error ω zg , and the east gyro angular velocity measurement error ω zg is the cubic coefficient in the two-position self-alignment error model. Therefore, the east gyro angular velocity measurement error ω zg The calculation of is obtained by fitting the cubic term of the north channel position error. The change of the north accelerometer output error per unit time affects the north position error accuracy (as shown in formula (2)) by affecting the north velocity channel error, thereby affecting the azimuth error accuracy (as shown in formula (1)).

[0043] The calculation formula of the output pulse of the I / F conversion circuit is:

[0044]

[0045] Wherein, P represents the output pulse of the I / F conversion circuit, B represents the magnification, f represents the sampling frequency, ΔU represents the difference between the current integrated voltage and the previous integrated voltage of the I / F conversion circuit, and K represents the discharge voltage reference parameter.

[0046] In the case of unchanged hardware parameters, according to formula (3), if the sampling frequency of the I / F conversion circuit is increased, the number of sampling times will increase. To ensure that the output remains unchanged, the magnification needs to be reduced accordingly. Since the amplitude of the burr caused by the I / F conversion circuit is proportional to the magnification B, the reduction of the magnification B will directly reduce the amplitude of the burr; and the burr is generated when the I / F conversion circuit is commutated, the increase in the sampling frequency will lead to an increase in the frequency of the burr. If the sampling frequency of the I / F conversion circuit is adjusted to a suitable value, so that the burr amplitude is reduced to the same or similar to the amplitude of the inherent interference signal of the inertial navigation system, the data distortion problem caused by the I / F conversion circuit can be avoided, thereby improving the accuracy of the initial alignment of the inertial navigation.

[0047] like Figure 1 As shown, a method for optimizing the alignment accuracy of an inertial navigation system provided by an embodiment of the present invention comprises the following steps:

[0048] Step S1: Get the set sampling frequency and set magnification;

[0049] Step S2: When the inertial navigation system starts to align, the sampling frequency and magnification of the I / F conversion circuit are adjusted to the set sampling frequency and the set magnification respectively, so that the amplitude of the low-frequency burr output by the I / F conversion circuit is the same as or similar to the amplitude of the inherent interference signal of the inertial navigation system.

[0050] When the inertial navigation system is aligning, the acceleration is measured by using the I / F conversion circuit based on the set sampling frequency and the set magnification, and the amplitude of the low-frequency burr output by the I / F conversion circuit is reduced to the same or similar amplitude as the inherent interference signal of the inertial navigation system, thereby improving the data distortion problem caused by the low-frequency burr during self-alignment and improving the alignment accuracy of the inertial navigation system.

[0051] In a specific embodiment of the present invention, the acquisition process of setting the sampling frequency and setting the magnification includes:

[0052] Step S1.1: When debugging the inertial navigation system as a whole, filter out the low-frequency burrs in the output pulse of the I / F conversion circuit to obtain the inherent interference signal, and then obtain the amplitude of the inherent interference signal;

[0053] Step S1.2: Under the condition that the output pulse of the I / F conversion circuit remains unchanged, the sampling frequency and magnification of the I / F conversion circuit are adjusted, and the output pulse of the I / F conversion circuit is measured;

[0054] Step S1.3: When the amplitude of the low-frequency burr in the output pulse measured in step S1.2 is the same as or similar to the amplitude of the inherent interference signal obtained in step S1.1, the sampling frequency corresponding to the output pulse is used as the set sampling frequency, and the magnification corresponding to the output pulse is used as the set magnification.

[0055] The commutation frequency of the I / F conversion circuit is related to its sampling frequency. When designing the I / F conversion circuit, first determine the commutation frequency and sampling frequency of the I / F conversion circuit, and then select the components. Usually, the sampling frequency determined when designing the I / F conversion circuit is low, so adjusting the sampling frequency and magnification of the I / F conversion circuit usually increases the sampling frequency of the I / F conversion circuit and reduces the magnification of the I / F conversion circuit.

[0056] For different application scenarios and inertial navigation systems, the frequency and amplitude of the inherent interference signal of the inertial navigation system are different. Therefore, the inherent interference signal of the inertial navigation system is first determined, and then the amplitude of the inherent interference signal is used as a reference. By increasing the sampling frequency of the I / F conversion circuit and reducing the magnification of the I / F conversion circuit, the sampling frequency and magnification of the I / F conversion circuit are determined when the burr amplitude in the output pulse of the I / F conversion circuit is equivalent to the amplitude of the inherent interference signal, thereby determining the set sampling frequency and set magnification. Under the set sampling frequency and set magnification, the burr amplitude in the output pulse of the I / F conversion circuit is reduced to the same as the amplitude of the inherent interference signal. On the basis of ensuring the authenticity of the output pulse of the I / F conversion circuit, the influence of the low-frequency burr of the I / F conversion circuit on the initial alignment accuracy of the inertial navigation system is avoided.

[0057] In a specific embodiment of the present invention, in step S1.1, filtering out low-frequency glitches in the output pulse of the I / F conversion circuit includes:

[0058] Determine the commutation frequency of the I / F conversion circuit according to the excitation signal; determine the frequency range of the low-frequency glitches in the output pulse of the I / F conversion circuit according to the commutation frequency; design a filter according to the frequency range of the low-frequency glitches; and use the designed filter to filter out the low-frequency glitches in the output pulse of the I / F conversion circuit.

[0059] The commutation frequency of the I / F conversion circuit is different due to different excitation signals, so the commutation frequency of the I / F conversion circuit can be determined according to the excitation signal. Low-frequency glitches usually appear during commutation, so the frequency range of the low-frequency glitches in the output pulse of the I / F conversion circuit can be determined according to the commutation frequency. The designed filter is used to filter out the signals within the frequency range of the low-frequency glitches, that is, to filter out the low-frequency glitches in the output pulse of the I / F conversion circuit. The integration circuit is the core part of the I / F conversion circuit. The external excitation directly leads to the capacitor in the integration circuit. When the capacitor reaches the threshold voltage, the capacitor is discharged through FPGA control. One charge and discharge of the capacitor is one commutation.

[0060] In a specific embodiment of the present invention, the process of obtaining the discharge voltage reference parameter K includes:

[0061] When debugging the I / F conversion circuit, adjust the discharge voltage reference parameter K based on the original sampling frequency and original magnification of the I / F conversion circuit (i.e., the sampling frequency and magnification determined when the I / F conversion circuit is designed) until the output pulse of the I / F conversion circuit is stable. The discharge voltage reference parameter at this time is used as the final discharge voltage reference parameter K.

[0062] In order to verify the effectiveness of the method of the present invention, a mathematical model of the I / F conversion circuit is constructed to simulate the drift of key parameters. The output stability and burr amplitude before and after adjusting the sampling frequency and magnification are shown in Table 1. The output pulse is as follows: Figure 2 and Figure 3 shown.

[0063] In Table 1, δ represents the standard deviation. From the data in Table 1 and Figure 2 , Figure 3 It can be seen that after increasing the sampling frequency of the I / F conversion circuit and reducing the magnification, although the number of glitches increases, the amplitude of the glitches is greatly reduced, and the output stability of the I / F conversion circuit is correspondingly improved, thereby improving the initial alignment accuracy of the inertial navigation.

[0064] Table 1 Output comparison of I / F conversion circuit before and after adjustment

[0065] Stability (3δ) Glitch Amplitude Before adjusting the sampling frequency and magnification <![CDATA[2.694910354e -05 ]]> 0.6644529 After adjusting the sampling frequency and magnification <![CDATA[3.896410529e -06 ]]> 0.0634045

[0066] What is disclosed above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of changes or modifications within the technical scope disclosed in the present invention, which should be covered within the protection scope of the present invention.

Claims

1. A method for optimizing the alignment accuracy of an inertial navigation system, characterized in that: The optimization method comprises: Step S1: Get the set sampling frequency and set magnification; Step S2: When the inertial navigation system starts to align, the sampling frequency and magnification of the I / F conversion circuit are adjusted to the set sampling frequency and the set magnification respectively, so that the amplitude of the low-frequency burr output by the I / F conversion circuit is the same as or similar to the amplitude of the inherent interference signal of the inertial navigation system.

2. The method for optimizing the alignment accuracy of an inertial navigation system according to claim 1, characterized in that: In step S1, the acquisition process of setting the sampling frequency and setting the magnification includes: Step S1.1: When debugging the inertial navigation system as a whole, filter out the low-frequency burrs in the output pulse of the I / F conversion circuit to obtain the inherent interference signal, and then obtain the amplitude of the inherent interference signal; Step S1.2: Under the condition that the output pulse of the I / F conversion circuit remains unchanged, the sampling frequency and magnification of the I / F conversion circuit are adjusted, and the output pulse of the I / F conversion circuit is measured; Step S1.3: When the amplitude of the low-frequency burr in the output pulse measured in the step S1.2 is the same as or similar to the amplitude of the inherent interference signal obtained in the step S1.1, the sampling frequency corresponding to the output pulse is used as the set sampling frequency, and the magnification corresponding to the output pulse is used as the set magnification.

3. The method for optimizing the alignment accuracy of an inertial navigation system according to claim 2, characterized in that: In the step S1.1, filtering out low-frequency glitches in the output pulse of the I / F conversion circuit includes: Determine the commutation frequency of the I / F conversion circuit according to the excitation signal; Determine the frequency range of low-frequency glitches in the output pulse of the I / F conversion circuit according to the commutation frequency; Designing a filter according to the frequency range of the low-frequency burr; The designed filter is used to filter out the low-frequency glitches in the output pulse of the I / F conversion circuit.

4. The method for optimizing the alignment accuracy of an inertial navigation system according to claim 2, characterized in that: In step 1.2, the calculation formula of the output pulse of the I / F conversion circuit is: Wherein, P represents the output pulse of the I / F conversion circuit, B represents the magnification, f represents the sampling frequency, ΔU represents the difference between the current integrated voltage and the previous integrated voltage of the I / F conversion circuit, and K represents the discharge voltage reference parameter.

5. The method for optimizing the alignment accuracy of an inertial navigation system according to claim 4, characterized in that: The process of obtaining the discharge voltage reference parameter K includes: When debugging the I / F conversion circuit, the discharge voltage reference parameter K is adjusted based on the original sampling frequency and original magnification of the I / F conversion circuit; The discharge voltage reference parameter when the output pulse of the I / F conversion circuit is stable is used as the final discharge voltage reference parameter K.

6. An inertial navigation system, characterized in that: The inertial navigation system optimizes alignment accuracy by using the inertial navigation system alignment accuracy optimization method according to any one of claims 1 to 5.

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