Projectile Inertial Navigation with Kalman Roll Error Correction
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Solution Overview
Problem
Inertial navigation systems for projectiles face challenges in maintaining roll angle accuracy due to high roll rates and scale factor errors in low-cost MEMS gyroscopes, leading to significant navigation errors, especially during the initial phase of flight.
Innovation Solution
An inertial measurement system that includes a roll gyro and two other gyros to define a 3D coordinate system, a controller to compute attitude and calculate roll angle error, and a Kalman filter to provide roll angle and scale factor corrections, which models roll angle error as a function of roll rate and wind variables, allowing for real-time correction without the need for attitude reset or additional aiding sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If low-cost MEMS gyroscopes are used, then device cost is reduced, but measurement precision deteriorates due to scale factor errors of several thousand ppm
Solution Approach 1:
The patent implements a feedback mechanism where the calculated roll angle error is fed back into the Kalman filter to continuously estimate and correct the roll gyro scale factor. The system computes roll angle from gyro outputs, calculates the error between computed and expected roll angles, and uses this error to update the scale factor estimate, creating a closed-loop correction system that compensates for the inherent inaccuracies of low-cost MEMS gyroscopes
Solution Approach 2:
The system performs self-calibration by using its own operational data (pitch and yaw angles from the gyro outputs) to detect and correct its own errors. The Kalman filter autonomously estimates the scale factor error based on the discrepancy between computed roll angle and expected roll angle, eliminating the need for external calibration equipment or high-precision reference sensors
2Reliability
If high roll rates are used for projectile stabilization, then navigation reliability is improved, but measurement precision deteriorates due to error accumulation of several degrees per second
Solution Approach 1:
The system continuously monitors the computed roll angle and compares it with the expected roll angle, feeding the error back to the Kalman filter for real-time scale factor correction. This feedback loop prevents error accumulation by dynamically adjusting the scale factor based on actual performance, allowing the system to maintain accuracy even at high roll rates where error accumulation would normally be problematic
Solution Approach 2:
The system pre-computes the expected pitch and yaw angles based on the known projectile trajectory and dynamics model. These pre-calculated reference values are then used to detect roll angle errors, enabling the system to identify and correct scale factor deviations before they lead to significant navigation inaccuracies
3Measurement precision
If Kalman filtering is used for integrated navigation, then navigation precision is improved, but device complexity increases due to the need to maintain error constraints
Solution Approach 1:
The patent extracts and isolates the specific problem of roll gyro scale factor error from the overall navigation system. Instead of implementing a full-scale error correction system for all navigation parameters, the invention focuses specifically on detecting and correcting roll angle errors using only the available pitch and yaw angle data, simplifying the Kalman filter implementation while maintaining navigation precision
Solution Approach 2:
The system uses the existing pitch and yaw angle computations (which are already being calculated for navigation purposes) to simultaneously detect roll angle errors. This multi-functional approach allows the same computational resources to serve dual purposes: maintaining navigation accuracy and correcting gyro scale factor errors, thereby reducing overall system complexity
Data Source
AI summary
An inertial measurement system for a spinning projectile includes: a first, roll gyro to be oriented substantially parallel to the spin axis of the projectile; a second gyro and a third gyro with axes arranged with respect to the roll gyro; 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; calculate a roll angle error; provide the roll angle error as an input to a Kalman filter that outputs a roll angle correction and a roll rate scale factor correction; and apply the calculated roll angle correction and roll rate scale factor correction to the output of the roll gyro.