Inertial Navigation Roll Error Correction
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Solution Overview
Problem
Inertial navigation systems for projectiles face challenges in maintaining accurate roll angle calculations due to high roll rates and low accuracy of inexpensive MEMS gyroscopes, leading to significant errors in navigation, especially when scale factor errors are not corrected in real-time.
Innovation Solution
An inertial measurement system that includes a roll gyro and orthogonal pitch and yaw gyros, a controller computes and corrects roll angle and scale factor errors by comparing computed pitch and yaw angles with expected values, allowing for accurate navigation without additional attitude sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If inexpensive MEMS gyroscopes are used, then system cost is reduced, but roll angle measurement precision deteriorates due to high scale factor errors
Solution Approach 1:
The system uses pitch and yaw angle measurements from low-cost MEMS gyroscopes to detect deviations from expected trajectory, then feeds this information back to calculate and apply corrections for roll gyro scale factor errors. This closed-loop feedback mechanism enables inexpensive sensors to achieve accurate roll angle measurements by continuously compensating for their inherent errors during flight.
Solution Approach 2:
The navigation system performs self-correction by using its own pitch and yaw measurements to identify and compensate for roll gyro errors. The system serves itself by detecting trajectory deviations caused by roll errors and automatically calculating correction factors, eliminating the need for expensive high-precision roll gyroscopes or additional attitude sensors.
2Reliability
If roll rate increases to stabilize projectile, then navigation accuracy improves, but roll gyro error accumulation worsens due to rate-dependent scale factor errors
Solution Approach 1:
The system continuously monitors pitch and yaw angles during high-roll-rate flight and uses deviations from expected values to detect roll gyro errors. The feedback loop calculates correction factors based on actual flight performance, enabling accurate roll angle measurement even at high roll rates where scale factor errors would normally accumulate rapidly.
Solution Approach 2:
The system changes the operational parameters of the roll gyro by applying dynamic scale factor corrections during flight. Instead of relying on the gyro to maintain constant accuracy across varying roll rates, the system adjusts the gyro's output parameters in real-time based on trajectory feedback, compensating for rate-dependent errors and maintaining navigation accuracy throughout the flight envelope.
3Measurement precision
If additional attitude sensors are added to correct roll errors, then measurement precision improves, but device complexity increases
Solution Approach 1:
The system makes the existing pitch and yaw gyroscopes multi-functional by using them not only for their primary navigation functions but also for detecting roll gyro errors. This universal utilization of available sensors eliminates the need for additional dedicated attitude sensors, maintaining measurement precision while avoiding increased system complexity.
Solution Approach 2:
The navigation system performs self-diagnosis and self-correction using only its existing sensors. The pitch and yaw gyroscopes serve themselves by providing data that reveals roll errors, which the system then corrects through calculated scale factor adjustments. This self-service capability achieves accurate roll angle measurement without requiring additional hardware.
Data Source
Figure 1a~2
Figure 3~4
AI summary
An inertial measurement system for a longitudinal projectile comprising :a first, roll gyro to be oriented substantially parallel to the longitudinal axis of the projectile;a second gyro and a third gyro with axes arranged with respect to the roll gyro such that they define a three dimensional coordinate system; a controller, arranged to: compute a current projectile attitude from the outputs of the first, second and third gyros, the computed attitude comprising a roll angle, a pitch angle and a yaw angle; compare the computed pitch and yaw angles with expected values for the pitch and yaw angles;calculate a roll angle error and a roll scale factor error based on the difference between the computed pitch and yaw angles and the expected pitch and yaw angles; and apply the calculated roll angle error and roll scale factor error to the output of the roll gyro. Calculating both roll angle error and roll scale factor error as corrections in the inertial measurement system allows much better control and correction of the calculated roll angle from the roll gyroscope even at high roll rates (e.g. 10-20 rotations per second). This correction system compensates for the large errors that can arise in inexpensive gyroscopes and therefore allows an accurate navigational system to be built with inexpensive components. No additional attitude sensors such as magnetometers are required, again reducing the cost and complexity of the system.