Estimating Initial Condition Inertial Reference Frame
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Solution Overview
Problem
Current weapons systems, such as those using dual axis spinning mass gyros like the Paveway III, face challenges in accurately determining the orientation and attitude of a weapon during the initial 100 ms after release due to the rapid onset of mechanical and aerodynamic variables, which are not adequately accounted for by existing inertial measurement technologies like Humphrey gyroscope, and the increasing difficulty in finding replacement spinning mass gyros.
Innovation Solution
An inertial device comprising one or more inertial measurement units (IMUs), processing devices, and memory devices is used to estimate the initial condition inertial reference frame of a body by combining rotation information with pre-programmed model spin-up characteristics to account for the rotation experienced during the startup time, allowing for accurate estimation of the weapon's orientation from the beginning of its motion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If spinning mass gyros like Humphrey gyroscope are used to establish inertial coordinate frame, then rapid start time (100 ms) is achieved, but mechanical complexity and difficulty in finding replacement technologies increase
Solution Approach 1:
The patent replaces spinning mass gyros (mechanical system) with an inertial measurement unit (electronic system) that uses accelerometers and gyroscopes integrated on a chip. This substitution eliminates the mechanical complexity of spinning mass gyros while achieving comparable or superior performance in establishing the inertial coordinate frame
2Device complexity
If IMU is used instead of spinning mass gyro, then device complexity is reduced, but start time increases from 100 ms to 300-600 ms
Solution Approach 1:
The patent applies preliminary action by estimating the weapon's orientation during the IMU startup period (300-600 ms) using a mathematical model that predicts rotation based on initial conditions and expected spin-up characteristics. This allows the system to provide orientation estimates before the IMU is fully initialized, effectively compensating for the longer startup time
Solution Approach 2:
The patent introduces a mathematical model as an intermediary between the IMU and the final orientation output. This model fills the gap during startup by estimating orientation based on predicted spin-up characteristics, allowing smooth transition from model-based estimates to IMU-based measurements
3Device complexity
If rotation during startup period is not accounted for, then device complexity is reduced, but measurement precision of weapon orientation deteriorates
Solution Approach 1:
The patent performs preliminary action by calculating and storing the expected rotation during the IMU startup period using a mathematical model. This pre-calculated rotation information is then applied to correct the orientation estimates, ensuring high measurement precision without adding complex hardware
Data Source
AI summary
An inertial device for determining an initial condition reference frame for a body is provided. The inertial device includes at least one inertial measurement unit, one or more processing devices, and one or more memory devices. The inertial measurement unit provides rotation information along at least one axis to the one or more processing devices. The one or more processing devices use the rotation information to estimate the current attitude of the body, based on estimates of a total rotation angle experienced by the body from the beginning of body motion to when the inertial measurement unit initialized.