Parity Logic for IMU Fault Detection and Isolation
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Solution Overview
Problem
Inertial measurement units used in vehicles like aircraft and missiles are prone to failures, which can cause vehicles to deviate from their intended path, and fault-tolerant units are expensive, making them costly for single-use vehicles.
Innovation Solution
Implementing a fault-tolerant avionic architecture using parity logic to monitor non-fault-tolerant inertial measurement units, identifying failures based on calculated thresholds, and utilizing backup units to maintain system functionality even after one or two failures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If fault-tolerant inertial measurement units are used, then system reliability is improved, but system cost increases significantly
Solution Approach 1:
The system segments the fault tolerance function into two parts: (1) use multiple inexpensive non-fault-tolerant IMUs, and (2) implement software-based parity logic to detect and isolate failures. This separates the hardware from the fault detection function, allowing cheap sensors to achieve system-level reliability through intelligent processing.
Solution Approach 2:
Parity logic acts as an intermediary between the IMUs and the navigation system. It continuously monitors sensor outputs, compares expected vs. actual measurements, and isolates failed sensors before they can compromise navigation accuracy, enabling cheap sensors to perform reliably.
2Ease of manufacture
If multiple non-fault-tolerant inertial measurement units are used with parity logic, then cost is reduced, but device complexity increases
Solution Approach 1:
The parity logic processor performs multiple functions: it monitors all IMUs simultaneously, detects failures through parity checks, identifies which specific sensor failed, and isolates the fault. This single multi-functional block replaces what would otherwise require complex hardware redundancy in each individual IMU.
Solution Approach 2:
The patent replaces mechanical/hardware fault tolerance mechanisms (redundant components within each IMU) with software-based parity logic. Instead of building physical fault tolerance into expensive hardware, the system uses computational algorithms to achieve the same reliability outcome.
3Reliability
If fault detection and isolation systems are implemented, then mission success probability is improved, but system complexity increases
Solution Approach 1:
The parity logic continuously performs preliminary fault detection and isolation before failures can impact navigation. By detecting and isolating failed sensors in advance, the system prevents potential mission-critical errors from occurring, ensuring mission success without requiring complex real-time reaction systems.
Solution Approach 2:
The system implements continuous feedback through parity checks that monitor IMU outputs in real-time. When discrepancies indicate a failure, the feedback loop immediately triggers fault isolation, allowing the navigation system to adapt and continue operating accurately despite sensor failures.
Data Source
AI summary
A method of implementing a fault-tolerant-avionic architecture in a vehicle includes using parity logic to monitor the functionality of at least three non-fault-tolerant inertial measurement units during a parity check and calculating a threshold from expected inertial measurement unit performance during a parity check. If a failure of an inertial measurement unit is detected based on the calculated threshold, then the method further includes identifying the failed inertial measurement units based on a direction of a parity vector in parity space. Each inertial measurement unit comprises at least one triad of sensors.