Inertial Sensor Initialization Using Soft Constraints
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Solution Overview
Problem
Existing methods for initializing inertial sensors require the sensor to be at rest or rely on additional sensor hardware, which are not applicable in all situations and can be impractical due to cost and complexity.
Innovation Solution
A method that estimates initial conditions of an inertial sensor using soft constraints and penalty metrics based on expected patterns of motion during an initialization time interval, allowing for initialization without the need for additional sensor hardware or a static position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the sensor is placed at rest in a known position and orientation for initialization, then the initialization process is simple and reliable, but the method is not applicable when initial position/orientation is unknown or when continuous use is required
Solution Approach 1:
The patent transforms the initialization problem from a static parameter determination (position and orientation at rest) to a dynamic parameter estimation problem. By using motion data during an initialization interval and applying soft constraints with penalty functions, the system can estimate initial conditions without requiring the sensor to be stationary, thus adapting to continuous use scenarios while maintaining reliability
Solution Approach 2:
The system performs preliminary motion capture during an initialization time interval before formal motion tracking begins. This preliminary action collects data that is then processed using soft constraints to establish initial conditions, allowing the system to prepare for continuous operation without requiring a separate static initialization phase
2Measurement precision
If additional sensor hardware such as GPS or magnet sensors is used for initialization, then absolute position and orientation can be determined, but the cost and complexity of the system increases
Solution Approach 1:
The inertial sensor system performs its own initialization using only its existing accelerometers and gyroscopes. By analyzing its own motion data during an initialization interval and applying soft constraints based on expected motion patterns, the system determines its initial conditions without requiring external sensor inputs, thus maintaining measurement precision while reducing device complexity
Solution Approach 2:
The patent makes the inertial sensor system universally applicable by enabling it to perform both motion tracking and initialization functions using the same hardware. The soft constraint approach allows the existing sensors to serve multiple purposes, eliminating the need for dedicated initialization sensors like GPS or magnetometers while maintaining functionality across different application scenarios
Data Source
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AI summary
An initialization method for an inertial sensor that estimates starting orientation and velocity without requiring the sensor to start at rest or in a well-known location or orientation. Initialization uses patterns of motion encoded as a set of soft constraints that are expected to hold approximately during an initialization period. Penalty metrics are defined to measure the deviation of calculated motion trajectories from the soft constraints. Differential equations of motion for an inertial sensor are solved with the initial conditions as variables; the initial conditions that minimize the penalty metrics are used as estimates for the actual initial conditions of the sensor. Soft constraints and penalty metrics for a specific application are chosen based on the types of motion patterns expected for this application. Illustrative cases include applications with relatively little movement during initialization, and applications with approximately periodic motion during initialization.