Orientation Estimation Using Rotation Matrix and Gravity Extraction
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Solution Overview
Problem
Existing methods for estimating the orientation and motion of a moving solid using accelerometers and magnetometers face challenges in distinguishing gravitational field components from proper acceleration under dynamic conditions, leading to inaccurate Euler angle calculations due to uncertainties and time drift in sensor measurements.
Innovation Solution
A method that involves measuring acceleration and magnetic field vectors at successive instants, estimating a rotation matrix U(n,n0) to rotate the solid's orientation from a reference time n0 to a later time n, using a first rotation angle based on magnetic field vector changes and a second rotation angle estimated from extrapolated gravitational field vectors, allowing for precise orientation and acceleration calculations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If additional sensors such as gyrometers are associated with the accelerometer to distinguish gravitational field component from proper acceleration under dynamic conditions, then measurement precision is improved, but device complexity increases and signal processing becomes particularly complex
Solution Approach 1:
The patent extracts and isolates the gravitational field component from the total acceleration vector by identifying periods of zero proper acceleration (reference instants) where the accelerometer measurement equals the gravitational field. This extracted gravitational information is then used to correct orientation estimates at subsequent dynamic instants, avoiding the need for additional gyrometer sensors while maintaining measurement precision.
Solution Approach 2:
The patent performs preliminary measurement and storage of the gravitational field vector at reference instants when proper acceleration is zero. These pre-acquired gravitational references are then applied later to correct orientation estimates during dynamic periods, enabling accurate orientation determination without requiring continuous complex multi-sensor fusion.
2Device complexity
If gravitational field component is estimated by extrapolation of acceleration vectors from preceding instants, then device complexity is reduced, but measurement precision deteriorates due to significant uncertainty in the extrapolated vector
Solution Approach 1:
The patent performs preliminary measurements of the gravitational field vector at reference instants when proper acceleration is known to be zero. These pre-acquired gravitational references are stored and then applied later to correct orientation estimates during dynamic periods, replacing the inaccurate extrapolation method with empirically measured gravitational data.
Solution Approach 2:
The patent uses feedback by continuously monitoring acceleration vectors to identify when proper acceleration returns to zero, thereby detecting new reference instants. At these detected reference instants, updated gravitational field measurements are taken and used to correct subsequent orientation estimates, creating a closed-loop system that maintains precision without complex devices.
3Ease of operation
If Euler angles are determined from the passage matrix of gravitational field and magnetic field vectors, then orientation estimation is achieved, but reliability deteriorates due to significant inaccuracy from extrapolated gravitational field vector
Solution Approach 1:
The patent extracts accurate gravitational field vector values at reference instants where proper acceleration is zero, separating this reliable gravitational information from the noisy total acceleration measurements. This extracted gravitational data is then used to construct the passage matrix for Euler angle calculation, eliminating the reliability issues caused by extrapolation while maintaining the simplicity of the Euler angle approach.
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
This approach reduces uncertainty in orientation and acceleration calculations by minimizing the degrees of freedom in extrapolated gravitational field components, resulting in more accurate Euler angle determinations and proper acceleration measurements.
Implementation Method 1
The acceleration vector comprises a component of gravitational field and a component of proper acceleration of the solid
Implementation Method 2
The sensor measures, at each instant, an acceleration vector and a magnetic field vector in a moving frame of the sensor
Data Source
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AI summary
The invention relates to a method for estimating the direction in an inertial frame of reference of a moving solid provided with an accelerometer and a magnetometer mounted on said solid. According to said method, a direction of the solid is measured at a reference time, defined by a rotation matrix of the mobile frame of reference of the solid at the reference time in the inertial frame of reference. Next, a rotation matrix is estimated between the direction of the solid at a later time n and said direction of the solid at the reference time. Next, the direction of the solid is determined at the time n according to the previously estimated rotation matrix and the known direction of the solid at the reference time.