Trajectory Determination Using Accelerometer and Magnetometer
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Solution Overview
Problem
Existing navigation systems face challenges in accuracy and cost due to signal obstructions and the complexity of using multiple sensors, particularly in determining trajectories of mobile elements like the human foot, which affects applications in motion capture and geolocation.
Innovation Solution
A device using a triaxial accelerometer and a triaxial additional sensor, such as a magnetometer, to determine the trajectory by calculating orthogonal projections and subtracting terrestrial gravity and drifts, allowing for accurate and cost-effective trajectory determination in a fixed global reference frame.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If satellite-based navigation or radiolocation systems are used for motion capture and geolocation, then navigation and trajectory determination can be achieved, but signal obstructions in numerous geographical zones heavily degrade accuracy and sometimes render the service unavailable
Solution Approach 1:
The patent introduces an intermediary inertial measurement system (accelerometer, magnetometer, gyrometer) that operates independently of satellite signals. This intermediary system provides continuous trajectory determination through inertial navigation, bridging the gap when satellite-based systems fail due to signal obstructions in urban canyons, indoor environments, or areas with poor satellite visibility.
Solution Approach 2:
The patent changes the measurement parameters from satellite-based pseudo-range measurements to inertial measurements (acceleration, magnetic field, rotation). By integrating accelerometer data to obtain velocity and position, and using magnetometer data for heading determination, the system maintains operation under conditions where satellite signals are unavailable, thus improving both accuracy and reliability.
2Measurement precision
If inertial sensors (accelerometer, magnetometer, gyrometer) are used to compute trajectory, then navigation can be undertaken, but the systems exhibit high cost and complexity
Solution Approach 1:
The patent extracts and eliminates the gyrometer from the sensor system, relying instead on the combination of accelerometer and magnetometer data processing. By removing this expensive and complex sensor while implementing sophisticated algorithms to determine orientation from the remaining sensors, the system achieves comparable trajectory determination accuracy with reduced device complexity and cost.
Solution Approach 2:
The patent replaces the mechanical/physical gyroscope mechanism with a computational approach using accelerometer and magnetometer data. Instead of relying on a physical rotating mass to measure angular velocity, the system uses algorithmic processing of linear acceleration and magnetic field vectors to derive orientation and trajectory, thereby reducing mechanical complexity.
3Ease of manufacture
If other inertial sensor systems with reduced cost are used, then cost is reduced, but they assume perfect sensor placement in the sagittal plane which is almost impossible to achieve, causing estimation errors
Solution Approach 1:
The patent implements a dynamic sensor placement approach that does not require fixed orientation of the sensor assembly. The system adapts to any initial orientation of the accelerometer and magnetometer by using the accelerometer to detect gravity direction and the magnetometer to detect magnetic north, then computationally determining the correct coordinate transformations. This dynamic adaptation eliminates the need for precise mechanical alignment during manufacturing.
Solution Approach 2:
The patent performs preliminary calibration and orientation determination actions using the accelerometer and magnetometer data before trajectory computation begins. By establishing the sensor orientation relative to the global reference frame through initial measurements and computational processing, the system prepares the correct transformation matrices in advance, ensuring accurate trajectory estimation regardless of initial sensor placement.
4Measurement precision
If gyrometers are used to estimate rotation speed, then rotation can be measured, but the cost increases due to the need for expensive gyrometer components
Solution Approach 1:
The patent creates a computational copy of the gyrometer function using cheaper sensors. By processing accelerometer data to detect changes in orientation and combining it with magnetometer data for heading reference, the system replicates the rotation measurement capability of a gyrometer through software algorithms rather than expensive hardware, achieving similar accuracy at lower cost.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables accurate and cost-effective determination of trajectories of mobile elements, such as a foot or robot, without the need for expensive gyroscopes, improving navigation and motion capture applications.
Implementation Method 1
a triaxial accelerometer rigidly tied to a mobile element... delivering inertial measurements
Implementation Method 2
a triaxial additional sensor for measuring a vector of a substantially constant vector field... in a fixed global reference frame tied to the terrestrial reference frame
Implementation Method 3
first calculation means for calculating, at said successive instants, first orthogonal projections onto said plane of the vectors delivered by the triaxial accelerometer and of the vectors delivered by the additional sensor
Implementation Method 4
third calculation means for subtracting from each second orthogonal projection in said fixed global reference frame the mean vector over said successive instants, so as to obtain the accelerations centered in said plane, devoid of the influence of terrestrial gravity and of drifts
Data Source
AI summary
Device for determining a characteristic of a trajectory formed of successive positions of a triaxial accelerometer (3A) rigidly tied to a mobile element (EM), between a first instant of immobility (t0) and a second instant of immobility (tn) of the triaxial accelerometer (3A), subsequent to said first instant of immobility (t0), said device comprising, furthermore, a triaxial additional sensor for measuring a vector of a substantially constant vector field between said first and second instants of immobility (t0,tn), in a fixed global reference frame (GE) tied to the terrestrial reference frame, said additional sensor being rigidly tied to said mobile element (EM) and fixed in the reference frame of the accelerometer (3A), and control means (CMD).