A precise compensation method for lever arm of vehicle-mounted inertial navigation / odometer integrated navigation system

Abstract

The present invention relates to a method for accurately compensating a lever arm of a vehicle-mounted inertial navigation / odometer integrated navigation system, comprising the following steps: 1. determining the position of a drive wheel differential and the center position of the differential according to the vehicle driving mode; 2. measuring the longitudinal lever arm according to the relative position between the center of the inertial navigation unit (IMU) and the center of the differential, and measuring the lateral left-turn lever arm and the lateral right-turn lever arm according to the distance between the inertial navigation center and the left and right wheels of the vehicle; 3. substituting the lever arm measured in step 2 into a lever arm compensation formula to calculate the odometer lever arm compensation value, and compensating this amount into the inertial navigation dead reckoning algorithm to complete the odometer lever arm compensation process; and 4. verifying the odometer compensation method. The present invention truly reflects the process of changing the odometer output measurement point caused by the differential when the vehicle turns, improves the accuracy of the odometer lever arm compensation, and achieves the purpose of improving the initial alignment and dead reckoning accuracy of the vehicle-mounted inertial navigation / odometer integrated navigation system.

Description

Technical Field

[0001] The present invention belongs to the technical field of application of land-based vehicle-mounted inertial navigation / odometer combined positioning and orientation, and in particular relates to a precise compensation method for a lever arm of a vehicle-mounted inertial navigation / odometer combined navigation system. Background Art

[0002] In the vehicle-mounted inertial navigation / odometer combination, the odometer is generally used to measure the mileage increment of the carrier within a unit sampling time. The odometer is generally an electronic encoder connected to the drive shaft of the vehicle engine through a flexible shaft to measure the speed of the drive shaft. Therefore, the vehicle-mounted odometer does not directly measure the rotation rate of the vehicle wheels. Usually, the odometer input shaft is installed on the vehicle drive shaft, that is, the output shaft of the vehicle gearbox. For example, a front-engine rear-wheel drive vehicle is shown in the diagram of the vehicle drive shaft. Figure 1 shown.

[0003] Therefore, the speed measured by a vehicle's odometer does not directly reflect the speed of the vehicle's wheels, but rather the speed of the driveshaft. If the speed of the vehicle's driveshaft and tires were in a 1:1 relationship, the speed measured by the odometer would be equivalent to the speed of the vehicle's wheels. However, the vehicle's driveshaft transmits power to the vehicle's wheels through a special mechanical mechanism called a differential. Due to the presence of the differential, when the vehicle turns, the speed measured by the odometer, after scaling, does not represent the true speed of a single wheel, such as the left or right rear wheel. This can cause speed measurement errors in the inertial navigation / odometer integrated navigation system. In many references, the odometer measurement point is equivalent to a single wheel position, ignoring the mechanism of odometer lever arm generation. This leads to inaccurate lever arm compensation, affecting the positioning and initial alignment accuracy of the vehicle-mounted inertial navigation / odometer combination. Summary of the Invention

[0004] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a method for accurately compensating the arm of a vehicle-mounted inertial navigation / odometer combined navigation system.

[0005] The above-mentioned purpose of the present invention is achieved through the following technical solutions:

[0006] A method for accurately compensating a lever arm of a vehicle-mounted inertial navigation / odometer integrated navigation system comprises the following steps:

[0007] Step 1: Determine the position of the drive wheel differential according to the vehicle driving mode and determine the differential center position;

[0008] Step 2: Measure the longitudinal lever arm based on the relative position between the IMU center and the differential center, and measure the lateral left and right lever arms based on the distance between the IMU center and the left and right wheels of the vehicle.

[0009] Step 3: Substitute the lever arm measured in step 2 into the lever arm compensation formula to calculate the odometer lever arm compensation value, and then compensate this amount into the inertial navigation position calculation algorithm to complete the odometer lever arm compensation process;

[0010] Step 4: Verify the odometer compensation method.

[0011] Further: Step 1 is:

[0012] Vehicle drive modes include front-engine rear-wheel drive and front-engine front-wheel drive; the position of the vehicle's drive wheels is determined according to the determined drive mode; for front-engine rear-wheel drive, the engine is located in the engine box at the front of the vehicle, and the engine output power is output to the rear wheel position through the power transmission shaft, and then the power is distributed to the two rear wheels through the rear axle differential. The differential center corresponding to the drive wheel is located near the drive wheel, and the protruding position of the rear axle is the position where the differential is located;

[0013] For front-engine, front-wheel drive, the engine is located in the engine box at the front of the vehicle. The engine output power is output to the front wheels through the power transmission shaft, and then distributed to the two front drive wheels through the front axle differential. The differential center corresponding to the drive wheel is the position close to the drive wheel, and the protruding position of the front axle is the position where the differential is located.

[0014] Further: In step 2, the arm size is measured, specifically:

[0015] The odometer arm needs to measure three values, namely the longitudinal arm dy and the transverse arm, where the transverse arm includes the left turn arm dx L and right lever arm dx R , which represents the projection of the vector between the center point O of the inertial navigation IMU and the center point C of the rear axle or front axle differential on the vehicle coordinate system OXY, that is, dy measures the distance between the center point C of the rear axle or front axle differential and the center point O of the inertial navigation IMU on the OY axis, the left turn arm dx L Represents the lever arm in the positive direction of the inertial navigation IMU output angular rate. The measurement method is to measure the distance between the center point of the left rear wheel or left front wheel and the center point O of the IMU in the OX axis direction; the right turn lever arm dx R Represents the lever arm in the negative direction of the IMU output angular rate. The measurement method is to measure the distance between the center point of the right rear wheel or right front wheel and the IMU center point O in the OX axis direction.

[0016] Further: Step 3 is: obtain the three odometer arm compensation values ​​respectively through step 2, and then compensate the odometer arm according to the positive and negative angular rates measured by the inertial navigation, specifically:

[0017] The odometer arm is compensated to the speed, and the speed is then compensated to the dead reckoning position through dead reckoning. The specific compensation formula is:

[0018]

[0019]

[0020] in, is the speed output by the odometer after compensation, The equivalent speed in the navigation coordinate system is obtained by the position increment output by the odometer, is the attitude matrix output by the inertial navigation, is the calibrated installation angle matrix between the odometer and the inertial navigation; dy is the longitudinal arm of the odometer, dx is the transverse arm of the odometer, and the value of dx is:

[0021]

[0022] Among them, dx L and dx R They represent the size of the left and right turn lever arms respectively, and are determined based on the angular rate ω measured by the inertial navigation.

[0023] The odometer dead reckoning calculation after lever arm compensation is obtained by integrating the equivalent velocity after compensation:

[0024]

[0025] in L is latitude, R is E , R N It is the principal curvature radius of the earth's meridian circle and the principal curvature radius of the meridian circle (east-west circle or main vertical line).

[0026] Further: Step 4 is to verify the effectiveness of the compensation arm algorithm by comparing the initial alignment and positioning accuracy of the vehicle inertial navigation / odometer before and after the arm compensation.

[0027] The present invention has the following advantages and positive effects:

[0028] When compensating for the odometer arm error, the present invention first determines the center position of the differential output shaft as the odometer longitudinal arm measurement point, and then divides the odometer transverse arm into a left-turn arm and a right-turn arm according to the vehicle turning situation. In this way, under different turning situations, the odometer measurement point will change according to the turning direction, truly reflecting the change process of the odometer output measurement point caused by the differential when the vehicle turns, improving the accuracy of the odometer arm compensation, and achieving the purpose of improving the initial alignment and dead reckoning accuracy of the vehicle-mounted inertial navigation / odometer integrated navigation system. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of the vehicle odometer installation location

[0030] Figure 2 This is a flow chart of the precise compensation method for the lever arm of the vehicle-mounted inertial navigation / odometer integrated navigation system of the present invention;

[0031] Figure 3a Schematic diagram of the center point of the front-mounted rear-drive differential of the present invention;

[0032] Figure 3b It is a schematic diagram of the center point of the front-mounted, front-wheel drive differential of the present invention;

[0033] Figure 4a This is a schematic diagram of the front-engine, rear-wheel drive lever arm measurement of the present invention;

[0034] Figure 4b This is a schematic diagram of the measurement of the front-mounted, front-drive lever arm of the present invention;

[0035] Specific implementation methods

[0036] The structure of the present invention will be further described below with reference to the accompanying drawings and through examples. It should be noted that the present examples are descriptive rather than restrictive.

[0037] The present invention accurately compensates for the change in speed measurement point caused by turning motion in the odometer output based on the working principle of the vehicle odometer measurement and the working characteristics of the vehicle differential, combined with the attitude angular rate output by the vehicle-mounted inertial navigation.

[0038] The differential's primary function during vehicle motion is to enable the left and right, and front and rear drive wheels, to rotate at different speeds when the vehicle turns. In other words, the differential is a device designed to adjust the speed difference between the left and right wheels and is a required device on any vehicle. Its principle is to use the rotation and revolution of planetary gears to distribute vehicle power to the side with less resistance when the two drive wheels have different torques. Therefore, when the vehicle turns left, the differential distributes the speed of the power shaft to the right wheel, while when turning right, it distributes the speed to the left wheel. The odometer is typically mounted at the front of the differential, and the presence of the differential causes the odometer's position increment to change during left and right turns.

[0039] When compensating for the odometer arm error, the present invention first determines the center position of the differential output shaft as the odometer longitudinal arm measurement point, and then divides the odometer transverse arm into a left-turn arm and a right-turn arm according to the vehicle turning situation. In this way, under different turning situations, the odometer measurement point will change according to the turning direction, truly reflecting the change process of the odometer output measurement point caused by the differential when the vehicle turns, improving the accuracy of the odometer arm compensation, and achieving the purpose of improving the initial alignment and dead reckoning accuracy of the vehicle-mounted inertial navigation / odometer integrated navigation system.

[0040] The algorithm flow of the compensation method of the present invention is as follows: Figure 2As shown, the algorithm calculation is completed in the following steps:

[0041] Step 1: Determine the position of the drive wheel differential according to the vehicle driving mode and determine the differential center position.

[0042] Step 2: Measure the longitudinal lever arm based on the relative position of the center of the inertial measurement unit (IMU) of the inertial navigation system and the center of the differential, and measure the lateral left and right turn lever arms based on the distance between the inertial navigation center and the left and right wheels of the vehicle;

[0043] Step 3: Based on the lever arm measured in step 2, substitute it into the lever arm compensation formula to calculate the odometer lever arm compensation amount, and compensate this amount into the inertial navigation position calculation algorithm to complete the odometer lever arm compensation process.

[0044] Step 4: Verify the odometer compensation algorithm.

[0045] 2. Specific implementation process

[0046] Step 1: Determine the vehicle differential position based on the vehicle drive type.

[0047] The main vehicle drive modes are front-engine rear-wheel drive and front-engine front-wheel drive. The position of the vehicle drive wheels is determined according to the determined drive mode. For example, the drive shaft is for the rear wheels in front-engine rear-wheel drive and for the front wheels in front-engine front-wheel drive. For example, the engine is located in the engine box of the front compartment of the vehicle. Figure 3a As shown, the engine output power is output to the rear wheel position through the power transmission shaft, and then distributed to the two rear wheels through the rear axle differential. The differential center corresponding to the drive wheel is near the protruding position of the rear axle near the drive wheel and the center of the differential is where the differential is located.

[0048] For front-wheel drive, the drive shaft is the front wheel, and the engine is located in the engine box in the front compartment of the vehicle. Figure 3b As shown, the engine output power is output to the front wheel position through the power transmission shaft, and then the power is distributed to the two front wheels through the front axle differential. The differential center corresponding to the drive wheel is near the drive wheel, and the protruding position of the front axle is the center of the differential.

[0049] Step 2: Measure the arm size:

[0050] like Figure 4a As shown, the odometer arm needs to measure three values, namely the longitudinal arm dy and the transverse arm, where the transverse arm includes the left turn arm dx L and right lever arm dx R, which represents the projection of the vector between the center point O of the inertial navigation IMU and the center point C of the rear axle differential on the vehicle coordinate system OXY, that is, dy measures the distance between the center point C of the rear axle differential and the center point O of the inertial navigation IMU on the OY axis, the left turn arm dx L Represents the lever arm in the positive direction of the inertial navigation IMU output angular rate, and the measurement method is to measure the distance between the center point of the left rear wheel and the center point O of the IMU in the OX axis direction; the right turn lever arm dx R Represents the lever arm in the negative direction of the IMU output angular rate. The measurement method is to measure the distance between the center point of the right rear wheel and the IMU center point O in the OX axis direction.

[0051] like Figure 4b As shown, the odometer arm needs to measure three values, namely the longitudinal arm dy and the transverse arm, where the transverse arm includes the left turn arm dx L and right lever arm dx R , which represents the projection of the vector between the center point O of the inertial navigation IMU and the center point C of the front axle differential on the vehicle coordinate system OXY, that is, dy measures the distance between the center point C of the front axle differential and the center point O of the inertial navigation IMU on the OY axis, the left turn arm dx L Represents the lever arm in the positive direction of the inertial navigation IMU output angular rate, and the measurement method is to measure the distance between the center point of the left front wheel and the center point O of the IMU in the OX axis direction; the right turn lever arm dx R Represents the lever arm in the negative direction of the IMU output angular rate. The measurement method is to measure the distance between the center point of the right front wheel and the center point O of the IMU in the OX axis direction.

[0052] Step 3: Substitute the speed lever arm compensation formula to perform compensation and calculate the compensated odometer dead reckoning position.

[0053] The three odometer arm compensation values ​​are obtained through step 2, and then the odometer arm is compensated according to the positive and negative angular rates measured by the inertial navigation.

[0054] Considering the cumulative nature of the lever arm error, the traditional approach of treating the odometer measurement point as a single measurement point and applying position increment compensation is clearly unrealistic. The present invention compensates the odometer lever arm to the velocity, which is then compensated to the dead-reckoned position through dead reckoning. This conforms to the fundamental principle that the odometer position lever arm is essentially the integral of the velocity lever arm. The specific compensation formula is:

[0055]

[0056]

[0057] in, is the speed output by the odometer after compensation, The equivalent speed in the navigation coordinate system is obtained by the position increment output by the odometer, is the attitude matrix output by the inertial navigation, is the calibrated installation angle matrix between the odometer and the inertial navigation. dy is the longitudinal arm of the odometer, dx is the transverse arm of the odometer, and the value of dx is:

[0058]

[0059] where dx L and dx R They represent the size of the left and right turn lever arms respectively, and are determined based on the angular rate ω measured by the inertial navigation.

[0060] The odometer dead reckoning calculation after lever arm compensation is obtained by integrating the equivalent velocity after compensation:

[0061]

[0062] in L is latitude, R is E , R N is the principal curvature radius of the earth's meridian circle and the principal curvature radius of the meridian circle (east-west circle or main vertical line), which can be obtained through the general calculation formula in the field of inertial navigation and will not be described in detail here.

[0063] Step 4: Verify the effectiveness of the compensation lever arm algorithm proposed in this invention by comparing the initial alignment and positioning accuracy of the vehicle inertial navigation / odometer before and after lever arm compensation.

[0064] A sports car test was conducted using a fiber-optic strapdown inertial navigation system. The odometer was calibrated beforehand to determine the odometer installation error and scale factor error. Semi-physical simulations were then conducted to compare the on-the-go initial alignment and navigation positioning results with lever arm error compensation with those without lever arm compensation. To ensure a clearer comparison, the sports car employed large maneuvers to fully stimulate the odometer lever arm error. The simulation results are shown in Tables 1 and 2.

[0065] Table 1. Comparison of initial alignment errors before and after arm compensation (unit: mil)

[0066]

[0067]

[0068] Table 2. Comparison of positioning errors before and after arm compensation (unit: ‰D)

[0069] Voyage Before compensation After compensation 1 1.4 1.0 2 1.1 1.1 3 0.66 0.67 4 1.6 0.9 5 1.2 0.64 6 1.4 0.75

[0070] According to the initial alignment accuracy of the sports car in Table 1 and Table 2, it can be seen that there is no obvious improvement in the initial alignment error of the system before and after the odometer arm compensation under the trajectory condition of straight driving. This is because the error of the arm itself will not be stimulated during straight driving and thus affect the system error. However, under violent maneuvering conditions such as turning or U-turning, the odometer arm compensation effect is obvious. From the positioning accuracy, it can also be seen that the odometer arm error also improves the positioning accuracy of the positioning and orientation system. Therefore, the present invention can improve the initial alignment and positioning and orientation accuracy of the inertial navigation / odometer combined navigation system.

[0071] Although the embodiments and drawings of the present invention are disclosed for illustrative purposes, those skilled in the art will understand that various replacements, changes and modifications are possible without departing from the spirit of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the contents disclosed in the embodiments and drawings.

Claims

1. A method for accurately compensating the lever arm of a vehicle-mounted inertial navigation / odometer integrated navigation system, comprising the following steps: Step 1: Determine the position of the drive wheel differential according to the vehicle driving mode and determine the differential center position; Step 2: Measure the longitudinal lever arm based on the relative position between the IMU center and the differential center, and measure the lateral left and right lever arms based on the distance between the IMU center and the left and right wheels of the vehicle. Step 3: Substitute the lever arm measured in step 2 into the lever arm compensation formula to calculate the odometer lever arm compensation value, and then compensate this amount into the inertial navigation position calculation algorithm to complete the odometer lever arm compensation process; Step 4: Verify the odometer compensation method; In step 1, the vehicle driving mode includes front-engine rear-wheel drive and front-engine front-wheel drive; the position of the vehicle driving wheel is determined according to the determined driving mode; For front-engine, rear-wheel drive, the engine is located in the engine box at the front of the vehicle. The engine output power is output to the rear wheels through the power transmission shaft, and then distributed to the two rear wheels through the rear axle differential. The differential center corresponding to the drive wheel is the position close to the drive wheel, and the protruding position of the rear axle is the position where the differential is located. For front-engine, front-wheel drive, the engine is located in the engine box at the front of the vehicle. The engine output power is output to the front wheels through the power transmission shaft, and then the power is distributed to the two front wheels through the front axle differential. The differential center corresponding to the drive wheel is near the protruding position of the front axle near the drive wheel, and the center of the differential is where the differential is located.

2. The method for precise arm compensation of a vehicle-mounted inertial navigation / odometer integrated navigation system according to claim 1, characterized in that: Measure the arm size in step 2, specifically: The odometer arm needs to measure three values, namely the longitudinal arm dy and the transverse arm, where the transverse arm includes the left turn arm dx L and right lever arm dx R , which represents the projection of the vector between the center point O of the inertial navigation IMU and the center point C of the rear axle or front axle differential on the vehicle coordinate system OXY, that is, dy measures the distance between the center point C of the rear axle or front axle differential and the center point O of the inertial navigation IMU on the OY axis, the left turn arm dx L Represents the lever arm in the positive direction of the inertial navigation IMU output angular rate. The measurement method is to measure the distance between the center point of the left rear wheel or left front wheel and the center point O of the IMU in the OX axis direction; the right turn lever arm dx R Represents the lever arm in the negative direction of the IMU output angular rate. The measurement method is to measure the distance between the center point of the right rear wheel or right front wheel and the IMU center point O in the OX axis direction.

3. The precise compensation method for the lever arm of the vehicle-mounted inertial navigation / odometer integrated navigation system according to claim 2 is characterized in that: Step 3 is: obtain the three odometer arm compensation values ​​through step 2, and then compensate the odometer arm according to the positive and negative angular rates measured by the inertial navigation. Specifically: The odometer arm is compensated to the speed, and the speed is then compensated to the dead reckoning position through dead reckoning. The specific compensation formula is: in, is the speed output by the odometer after compensation, The equivalent speed in the navigation coordinate system is obtained by the position increment output by the odometer, is the attitude matrix output by the inertial navigation, is the calibrated installation angle matrix between the odometer and the inertial navigation; dy is the longitudinal arm of the odometer, dx is the transverse arm of the odometer, and the value of dx is: Among them, dx L and dx R Represent the size of the left and right turn lever arms, respectively, and are determined based on the angular rate ω measured by the inertial navigation system; The odometer dead reckoning calculation after lever arm compensation is obtained by integrating the equivalent velocity after compensation: in L is latitude, R is E , R N It is the principal curvature radius of the earth's meridian and the principal curvature radius of the earth's meridian.

4. The method for precise arm compensation of a vehicle-mounted inertial navigation / odometer integrated navigation system according to claim 3, characterized in that: Step 4 is to verify the effectiveness of the compensation arm algorithm by comparing the initial alignment and positioning accuracy of the vehicle inertial navigation / odometer before and after the arm compensation.

Images