MEMS Accelerometer Activity Detection Using Stored Baseline
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Solution Overview
Problem
MEMS accelerometers face challenges in detecting activity and inactivity, especially in the presence of a constant 1 g field from the Earth's gravitational force, and struggle to detect slow movements or changes in orientation, leading to inefficient monitoring of user interactions with electronic devices.
Innovation Solution
A method that captures and stores acceleration values, calculates changes, and compares them to thresholds to detect activity or inactivity, using a sensor management system with digital logic and state machines to differentiate between dynamic and static acceleration components, allowing for efficient detection even in the presence of a constant acceleration field.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a 1 g threshold is set to eliminate gravitational field contribution, then acceleration detection accuracy is improved, but the device cannot detect slow movements or interactions below 1 g threshold
Solution Approach 1:
The system performs preliminary action by capturing and storing an acceleration value before the comparison operation. This stored value serves as a reference baseline that allows the system to detect changes in acceleration without being constrained by the 1 g gravitational threshold, enabling detection of both high and low acceleration events.
Solution Approach 2:
The patent applies partial action by comparing only the change in acceleration (difference between current and stored values) rather than the absolute acceleration value. This partial comparison approach allows the system to filter out constant gravitational effects while remaining sensitive to subtle movements below the 1 g threshold.
2Adaptability or versatility
If high pass filters are used to compensate for 1 g field limitation, then detection capability is improved, but extremely slow interactions cannot be detected
Solution Approach 1:
The system captures and stores an acceleration value as a preliminary reference point. This stored value enables the detection of extremely slow interactions by comparing subsequent acceleration measurements against this baseline, allowing the system to detect even minimal changes without requiring high pass filter processing that would eliminate slow movement detection.
3Measurement precision
If the microprocessor remains active for continuous monitoring, then activity detection accuracy is improved, but power consumption increases
Solution Approach 1:
The system implements periodic action by having the microprocessor enter a dormant state after capturing the initial acceleration value, then waking only to perform comparison operations when needed. This periodic activation pattern maintains accurate activity detection capability while significantly reducing overall power consumption compared to continuous microprocessor operation.
Solution Approach 2:
The accelerometer operates in a self-service manner by autonomously capturing acceleration values and comparing them against stored references without requiring continuous microprocessor intervention. This self-contained operation maintains detection accuracy while minimizing the power-consuming microprocessor activity.
Data Source
AI summary
A method of detecting activity with a MEMS accelerometer stores a value of acceleration, then measures acceleration at a later time, calculates a change in acceleration using the measured acceleration and the stored acceleration, and compares the change in acceleration to an activity threshold to detect activity. A method of detecting inactivity uses a similar technique along with a timer. The method of detecting inactivity with a MEMS accelerometer stores an acceleration value, then measures acceleration at a later time, calculates a change in acceleration using the measured acceleration and the stored acceleration, and compares the change in acceleration to an inactivity threshold. If the change in acceleration is less than the inactivity threshold and, if a predetermined period of time has elapsed, then inactivity is detected.