Contactless Pulse Rate Detection With SNR and Disturbance Screening
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Solution Overview
Problem
Existing non-contact pulse rate detection technologies face reliability issues due to disturbances such as subject movement and environmental light changes, leading to uncertain accuracy and reduced detection periods when stringent reliability evaluation is applied.
Innovation Solution
A pulse rate detection device and program that evaluates reliability based on Signal-to-Noise Ratio (SNR) and considers movement and light disturbances, setting criteria for reliable pulse rate output, and reducing reliability if disturbances are within predetermined thresholds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If pulse rate is detected by analyzing acceleration data from a motion sensor, then pulse rate information can be obtained without direct contact with blood vessels, but the detected pulse rate may be inaccurate when the user is moving
Solution Approach 1:
The patent uses acceleration data as an intermediary to detect motion states and heartbeat sounds separately, then combines both pieces of information to calculate pulse rate. This mediator approach allows the system to distinguish between motion-induced vibrations and actual heartbeat signals, resolving the contradiction between contactless detection and measurement accuracy during motion
Solution Approach 2:
The system changes the parameter being measured from purely acceleration-based pulse detection to a hybrid approach using both acceleration data and microphone audio data. By switching between different detection modes (acceleration-only, audio-only, or combined) based on motion state, the system maintains accuracy across different activity levels while preserving contactless operation
2Device complexity
If pulse rate is detected using only acceleration data from the motion sensor, then the device structure can be simplified, but detection accuracy deteriorates when the user is in motion
Solution Approach 1:
The patent makes the detection system universal by enabling it to function effectively in multiple scenarios (rest, light motion, intense exercise) using different detection strategies. The system can switch between acceleration-based detection, audio-based detection, or combined detection modes, making it adaptable to various activity levels without requiring separate dedicated systems for each scenario
Solution Approach 2:
Acceleration data serves as an intermediary that informs the system about the user's motion state, which then determines the appropriate detection strategy to employ. The acceleration sensor doesn't directly measure pulse rate in all cases but rather provides contextual information that guides the selection of the most accurate detection method for the current situation
3Measurement precision
If the device switches between different detection methods based on motion state, then pulse rate accuracy can be maintained during exercise, but the control logic becomes more complex
Solution Approach 1:
The system uses parameter changes in the acceleration data (specifically, the ratio of heartbeat-related acceleration components to total acceleration) to automatically determine when to switch detection modes. When this ratio falls below a threshold indicating intense motion, the system switches to audio-based detection; otherwise, it uses acceleration-based detection. This parameter-threshold approach simplifies the control logic compared to more complex decision-making systems
Data Source
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Figure 2
Figure 3(a)~3(d)
AI summary
The object of the present invention is to output a pulse rate that is highly reliable. A pulse rate detection device 1 evaluates the reliability of a detected pulse rate on the basis of the SN ratio of a pulse signal while taking into account disturbance factors. The pulse rate detection device 1 has a pulse rate display criteria 1 and a pulse rate display criteria 2 for displaying the pulse rate, wherein when the SN ratio is equal to or greater than the former, the pulse rate is displayed, and when the SN ratio is equal to or greater than the latter and less than the former, the pulse rate is displayed on the condition that the difference from the immediate past pulse rate is smaller than a predetermined reference. When the SN ratio is less than the pulse rate display criteria 2, the reliability is considered low and the pulse rate is not displayed. Additionally, the pulse rate detection device 1 takes into account a movement disturbance caused by movement of the face of a subject 11 and a light disturbance caused by changes in the light illuminating the face of the subject 11, and when the peak frequency in the frequency domain of the movement disturbance or light disturbance is close to the pulse rate at a value equal to or greater than the predetermined reference, the pulse rate detection device 1 determines that the reliability of the detected pulse rate is low due to these disturbances and does not display the pulse rate.