IMU Error Compensation via Periodic Vehicle Maneuvers
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Solution Overview
Problem
Inertial measurement units (IMUs) used in high-speed vehicles, such as the Exo-atmospheric Kill Vehicle, accumulate errors over time, leading to inaccuracies in position, velocity, and attitude, which are costly to mitigate with low bias IMUs or additional weight from stellar sensors.
Innovation Solution
A guidance system that detects and mitigates IMU errors through a series of preprogrammed maneuvers, including rotations about orthogonal axes, to periodically cancel biases and other errors, thereby improving accuracy without increasing cost or weight.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional IMUs are used in exo-atmospheric vehicles, then the system cost and weight are kept low, but measurement precision degrades over time due to error accumulation
Solution Approach 1:
The patent applies periodic maneuvers (such as 180-degree rotations about orthogonal axes) to the exo-atmospheric vehicle at specific intervals during flight. These periodic actions cause the IMU errors to accumulate in predictable patterns that can be mathematically modeled and subtracted from the measurements, thereby maintaining measurement precision over the extended time of flight without requiring expensive low-bias IMUs.
2Measurement precision
If low bias IMUs are used to minimize errors, then measurement precision improves, but device complexity and cost increase substantially
Solution Approach 1:
The patent makes the exo-atmospheric vehicle itself serve the dual purpose of both mission execution and IMU error characterization. By performing periodic maneuvers that generate measurable error patterns, the vehicle's own motion serves to characterize its IMU's errors, eliminating the need for separate calibration equipment or expensive low-bias IMUs. This self-service approach maintains measurement precision while avoiding increased device complexity.
3Measurement precision
If stellar sensors are added to compensate for gyro errors, then measurement precision improves, but weight increases and system performance decreases
Solution Approach 1:
The patent replaces the need for mechanical stellar sensors with a mathematical/software-based solution. By performing periodic maneuvers and using algorithms to model and subtract IMU errors from the measurements, the system achieves attitude accuracy comparable to stellar sensor compensation without adding any physical sensor mass. This substitution of mechanical systems with computational methods maintains measurement precision while avoiding weight increase.
Data Source
AI summary
The effects of IMU gyro and accelerometer bias errors are significantly reduced in accordance with the present teachings by a system or method for commanding an IMU or vehicle through a series of preprogrammed maneuvers. The maneuvers can be designed to minimize the effects of other gyro errors including scale factor errors, nonlinearities, cross coupling/misalignment, and scale factor asymmetries. A sample maneuver is provided which demonstrates performance based on a sequence of roll and yaw maneuvers resulting in zero build up of error at the end of a maneuver cycle period as a result of these errors. Modification of the system involves the addition of control logic to determine the maneuver period, maneuver rate, and vehicle orientation. No additional hardware beyond possible fuel required to perform the maneuver is required.