Velocity Estimation Using Non-Linear Gravity Separation

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Solution Overview

Problem

Current fall detection systems face challenges in accurately measuring velocity and height changes due to sensitivity to gravity orientation, calibration errors, and environmental barometric fluctuations, which affect the reliability of fall detection and height estimation.

Innovation Solution

A method using non-linear filters to estimate acceleration due to gravity and separate it from motion-related acceleration, followed by integration to calculate velocity and position, with a second filter to remove offset and drift, enhancing the accuracy of velocity and height estimation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If air pressure sensors are used to detect height changes, then height measurement capability is provided, but the device complexity increases due to requirements for fast-responding channels and shielding against moisture, light, and pollution

Engineering Contradiction:

Improveheight measurement capabilityVSAvoidmechanical construction complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent extracts and removes the air pressure sensor from the device, eliminating the need for complex mechanical construction while retaining height measurement capability through alternative means (accelerometer-based integration). This directly resolves the contradiction by taking out the problematic component that caused increased device complexity.

Inventive Principle:

Principle #2Taking out (Extraction)

2Measurement precision

If accelerometer signals are integrated to estimate velocity and position, then height change detection is enabled, but errors accumulate due to residual gravity components and orientation estimation inaccuracies

Engineering Contradiction:

Improveheight change detection accuracyVSAvoidmeasurement reliability

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent applies feedback by using a median filter to continuously monitor and correct the gravity estimate based on the accelerometer signal characteristics. This feedback mechanism identifies and removes residual gravity components that would otherwise accumulate as errors during integration, thereby improving measurement reliability while maintaining height change detection accuracy.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent changes the parameter estimation approach by using non-linear median filtering to dynamically estimate and separate the gravity component from the motion-induced acceleration. This parameter change in the filtering method reduces sensitivity to orientation estimation errors and prevents error accumulation during double integration, resolving the reliability issue.

Inventive Principle:

Principle #35Parameter changes

3Ease of manufacture

If linear filters are used to process accelerometer signals, then simple implementation is achieved, but accuracy deteriorates due to inability to properly separate gravity from motion acceleration during orientation changes

Engineering Contradiction:

Improvefilter implementation simplicityVSAvoidgravity separation accuracy

Core Design Contradiction:

Ease of manufactureVSMeasurement precision

Solution Approach 1:

The patent changes the filter type from linear to non-linear (median filter), which fundamentally alters the signal processing characteristics. This parameter change enables proper separation of gravity from motion acceleration even during orientation changes, significantly improving gravity separation accuracy while maintaining reasonable implementation complexity.

Inventive Principle:

Principle #35Parameter changes

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 improves the accuracy of velocity and height estimation, reducing errors caused by orientation changes and calibration issues, leading to more reliable fall detection and height measurement.

Implementation Method 1

Commonly, fall detectors are based on an accelerometer (usually a 3D accelerometer that measures acceleration in three dimensions)

Methodology Applied

Scientific EffectAcceleration measurement: Accelerometer

Implementation Method 2

By integrating the vertical acceleration signal, a measure for vertical velocity can be obtained, and by integrating the vertical velocity signal, a measure for position/height can be obtained

Methodology Applied

Scientific EffectIntegration:

Implementation Method 3

Currently available air pressure sensors provide a resolution in the relative altitude of the order of 10 cm

Methodology Applied

Scientific EffectBarometric measurement: Pressure Gradient

Data Source

PatentUS9835644B2Estimating velocity in a horizontal or vertical direction from acceleration measurements

Publication Date: 2017.12.05 KONINKLIJKE PHILIPS NV

AI summary

There is provided a method of determining an estimate of the velocity of a device in a horizontal or vertical direction, the method comprising obtaining measurements of the acceleration acting on the device in three dimensions; using a first filter and the obtained measurements to estimate acceleration due to gravity; estimating the acceleration acting in a horizontal or vertical direction due to motion of the device using the estimated acceleration due to gravity; integrating the estimate of the acceleration acting in said direction due to motion of the device to give an estimate of velocity in said direction; and using a second filter to remove offset and/or drift from the velocity to give a filtered velocity; wherein at least one of the first filter and second filter is a non-linear filter. An apparatus configured to operate according to the above method is also provided.