Strap-down Ship Gyro Compass Autonomous Latitude Determination
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Solution Overview
Problem
Conventional strap-down ship's gyro compasses require specification of the ship's position and velocity for operation, making them unavailable immediately after a system failure and susceptible to GPS interference for geographic latitude determination.
Innovation Solution
A method using three rotational rate sensors and two orthogonal acceleration sensors to calculate position and course without external information, employing dynamic equations and measured data equations to determine geographic latitude and ship speed, with error corrections via an optimum filter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If GPS single-frequency receiver is used to obtain geographic latitude, then position information is available, but the system becomes susceptible to intentional and unintentional interference (jamming) and deception signals (spoofing)
Solution Approach 1:
The system determines geographic latitude autonomously using only onboard sensors (rotational rate sensors and acceleration sensors) without external GPS signals. The latitude is calculated from the vertical component of Earth's rotation rate measured by the rotational rate sensors, making the system self-sufficient and immune to external interference or deception signals.
2Measurement precision
If conventional strap-down ship's gyro compass requires specification of ship's position and velocity, then the system can operate with external information, but the compass will not be immediately available again after a system failure
Solution Approach 1:
The system performs preliminary autonomous determination of geographic latitude and ship velocity using onboard sensors before compass operation is needed. This preliminary action stores necessary parameters (latitude and velocity) that enable immediate compass availability after system failure without requiring external information input, while maintaining high measurement precision through sensor-based calibration.
3Reliability
If external position information and velocity information are used, then North direction is found and retained, but the rotational rate sensors are not calibrated for increased course accuracy
Solution Approach 1:
The system uses external position and velocity information as feedback to calibrate the rotational rate sensors. By comparing sensor measurements with externally determined values, the system calculates calibration parameters that compensate for sensor errors, thereby increasing course accuracy while maintaining North direction retention through continuous feedback adjustment.
Data Source
AI summary
Method for operation of a strap-down ship's gyro compass for optimal calculation of position and course angle on a ship, with three rotational rate sensors each mutually aligned to each other at a right angle, and two nominally horizontally aligned orthogonal acceleration sensors, without required specification of the geographic latitude and/or of the speed of the ship, characterized by the steps: a. Preparation of a set of dynamic equations based on the angular velocity components detected by the rotational rate sensor, b. Preparation of a measured data equation based on the force components detected by the acceleration sensors, c. Determination of the properties of the lever arm between the strap-down ship's gyro compass and the point of rotation of the ship, and d. Determination of the properties of the earth's rotation and of the ship's angular velocity, wherein their properties are determined on the basis of the set of dynamic equations and the measured data equation, and are used in each case as parameters for calculation of the geographic latitude and/or speed of the ship.