Free Fall Detector Using Pre-calibrated Threshold
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Solution Overview
Problem
Existing free-fall detectors in portable electronic devices face challenges in precision and speed due to the need for extensive calculations and resource usage, leading to potential conflicts and false positives, especially when using microelectromechanical inertial sensors with three independent axes.
Innovation Solution
A free-fall detector device that employs a differential capacitive MEMS inertial sensor with a multiplexer and processing stage, utilizing a signal source and feedback circuit to generate detection signals by converting raw acceleration signals into quadratic values, allowing for rapid and precise detection of free-fall conditions without excessive resource usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If three acceleration signals are continuously converted into numeric signals and processed through squaring, summation, and square root extraction to determine total acceleration, then measurement precision is improved, but processing time increases and computation resources are markedly exploited
Solution Approach 1:
The patent pre-calculates and stores the square root of the sum of squares of the three sensitivity coefficients (Kx²+Ky²+Kz²) during a calibration phase. This pre-computed value is then used in the detection phase to directly calculate total acceleration magnitude from the squared acceleration components, eliminating the need for real-time square root extraction and reducing processing time while maintaining precision.
Solution Approach 2:
The patent extracts the computationally intensive square root operation from the real-time detection process and relocates it to the calibration phase. By separating the calibration function (pre-computation) from the detection function (real-time measurement), the system achieves both high precision and fast response during actual free-fall detection.
2Measurement precision
If three acceleration signals are continuously processed with extensive calculations to determine total acceleration, then measurement precision is improved, but device complexity increases due to requirement of independent processing unit
Solution Approach 1:
The patent performs the complex calibration calculations (determining sensitivity coefficients and their square root of sum of squares) during an initial setup phase using an independent processing unit. Once calibrated, the system stores these pre-computed values and uses them during normal operation with a simpler processing unit that only needs to perform multiplication and addition operations, thereby reducing the complexity requirement for the main processing unit while maintaining high measurement precision.
Solution Approach 2:
The patent extracts the complex computational tasks (squaring, summation, square root extraction) from the continuous detection process and consolidates them into an initial calibration routine. This separation allows the main processing unit to have reduced complexity while still achieving precise total acceleration measurement through the use of pre-computed calibration data.
3Speed
If acceleration signals are compared directly and separately with a threshold close to zero, then calculation speed is improved, but measurement precision deteriorates leading to false positives
Solution Approach 1:
The patent pre-calculates a single threshold value during calibration that accounts for the combined effect of all three acceleration axes. This pre-computed threshold incorporates the sensitivity coefficients and their relationships, allowing the system to perform a single comparison operation during detection that maintains both high speed and high accuracy, avoiding the false positives that would result from separate axis comparisons.
Solution Approach 2:
The patent merges the three separate acceleration component comparisons into a single total acceleration magnitude comparison. By combining the squared acceleration components (Ax²+By²+Cz²) and comparing their sum against a pre-computed threshold, the system achieves both fast calculation (single comparison) and high precision (accounts for all axes simultaneously), eliminating the false positive problem inherent in separate axis comparisons.
4Reliability
If a threshold close to zero is used for separate axis comparisons, then sensitivity is improved, but false positives increase due to anisotropic threshold in space
Solution Approach 1:
The patent merges the three anisotropic axis-specific thresholds into a single isotropic threshold that applies uniformly regardless of the direction of acceleration. By computing the total acceleration magnitude from all three axes and comparing against this unified threshold, the system maintains high sensitivity (equivalent to using low individual thresholds) while eliminating false positives caused by the directional bias of separate axis comparisons.
Solution Approach 2:
The patent changes the threshold parameter from three separate anisotropic values (one for each axis) to a single isotropic value that represents the combined effect of all axes. This parameter transformation, achieved through pre-computation during calibration, allows the system to maintain high detection sensitivity while achieving rotational invariance and eliminating false positives that arise from the directional dependence of separate axis thresholds.
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 precise and timely detection of free-fall conditions with reduced resource utilization, minimizing false positives and maintaining high precision by calculating the exact square value of total acceleration through a second reading iteration with feedback signals.
Implementation Method 1
inertial sensors of the types used in free-fall detectors can detect not only accelerations and decelerations of the device in which they are incorporated, but also the intensity of the action of the gravitational field with respect to one or more detection axes
Data Source
AI summary
A free-fall detector device includes an inertial sensor, a detection circuit associated to the inertial sensor, and a signal source for supplying a read signal to the inertial sensor. The device moreover includes: a storage element, selectively connectable to the detection circuit for storing a feedback signal generated by the detection circuit in response to the read signal supplied to the inertial sensor; and a feedback circuit coupled to the storage element for supplying the feedback signal to the inertial sensor so that the detection circuit generates at least one detection signal in response to the feedback signal supplied to the inertial sensor.