Vehicle Heading Determination Using GNSS and IMU Offset Correction
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Solution Overview
Problem
Existing methods for determining a vehicle's forward/reverse state are unreliable, especially at low speeds and in noisy conditions, leading to inaccurate heading alignment errors and potential safety issues in automatic steering systems.
Innovation Solution
A method that adjusts the heading alignment error by 180 degrees if it exceeds a predetermined range, allowing for the calculation of an unambiguous heading direction by offsetting the unresolved IMU heading, and compares this direction with the GNSS direction of motion to determine if the vehicle is traveling forward or reverse, using a system comprising a GNSS unit, IMU, and a processing module to ensure accurate forward/reverse state detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the heading alignment error is calculated directly using the difference between GNSS direction of motion and unresolved IMU heading, then the calculation is simple, but large jumps of 180° occur when the vehicle changes from forward to reverse state, degrading measurement precision
Solution Approach 1:
The system dynamically adjusts the GNSS direction of motion by 180° when reverse state is detected, making the heading alignment error calculation adaptive to the vehicle's operational state. This dynamic adjustment prevents the 180° jumps that would otherwise occur during forward-reverse transitions, maintaining measurement precision without requiring complex alternative calculation methods
Solution Approach 2:
The system uses feedback from the forward/reverse state detection to modify the GNSS direction of motion before calculating the heading alignment error. This feedback mechanism ensures that the error calculation always uses appropriately adjusted values, preventing large errors while maintaining a relatively simple calculation process
2Reliability
If the vehicle transmission sensor is used to determine forward/reverse state, then the gear state can be detected, but the vehicle may still be travelling momentarily forwards when reverse gear is already engaged, leading to unreliable detection
Solution Approach 1:
The system introduces an intermediary calculation method that combines multiple data sources (unresolved IMU heading, adjusted GNSS direction of motion, and transmission state) to determine the true forward/reverse state. This intermediary approach resolves the timing mismatch between gear engagement and actual vehicle motion, providing more reliable and timely detection than transmission sensor alone
Solution Approach 2:
The system changes the parameters used for state detection by incorporating heading direction analysis alongside transmission state. By monitoring whether the calculated heading aligns with or opposes the GNSS direction of motion, the system can accurately determine true vehicle state even during transient conditions when transmission state lags behind actual motion
3Ease of manufacture
If coarse alignment is performed using the first GPS direction of motion at startup, then the alignment process is simple, but the IMU heading may be approximately 180° offset from the true heading if the vehicle reverses out of storage, degrading measurement precision
Solution Approach 1:
The system performs preliminary forward/rereverse state detection and GNSS direction adjustment before calculating the heading alignment error during coarse alignment. This preliminary action ensures that even if the vehicle is in reverse during startup, the adjusted GNSS direction will be properly aligned with the IMU heading, preventing the 180° offset problem while maintaining simple alignment procedures
Solution Approach 2:
The system uses feedback from the forward/reverse state detection mechanism to adjust the GNSS direction of motion during the coarse alignment phase. This feedback ensures that the initial heading calculation is based on properly adjusted directional data, eliminating the 180° offset issue that would otherwise occur during reverse startup conditions
Data Source
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AI summary
An unambiguous heading direction is calculated to determine the forward/reverse state of a vehicle. A heading alignment error is determined at step 100, being the difference between a GNSS direction of motion and the unresolved IMU heading of the vehicle. The heading alignment error is adjusted by 180° to be within a predetermined range at step 200. The unresolved IMU heading of the vehicle 10 is adjusted using the heading alignment error to determine an ambiguous error corrected IMU heading at step 300. Step 400 determines whether the ambiguous error corrected IMU heading is substantially in the true direction of the nose of the vehicle. The unambiguous heading direction is calculated at step 500 by offsetting the ambiguous error corrected IMU heading by 180 degrees if the ambiguous error corrected IMU heading is substantially opposite the true direction of the nose of the vehicle. The forward/reverse state is determined by comparing the unambiguous heading direction with the GNSS direction of motion of the vehicle.