Measurement of the sleeping state is useful for monitoring the health of a person being nursed. The sleeping state can be estimated from biological information such as respiration rate, heart rate, body motion, and lying posture. A heart rate measurement method that considers the harmonics of a respiratory signal is described herein. The harmonics of respiratory signals for heart rate measurement has not been considered hitherto. An unconstrained method is proposed for measuring respiration, heart rate, and lying posture using a Smart Rubber sensor, which is a rubber-based flexible planar tactile sensor developed for this study. Respiration and heart rates are measured by applying frequency analysis to time-series data of body pressure. The harmonics of a respiratory signal serves as noise in heart rate measurement. Therefore, the heart rate measurement is improved by eliminating the effects of harmonics. The average frequency error of the heart rate measurement by our proposed method is 0.144 Hz. Experimental results show that our proposed method enhances the precision of heart rate measurement. Hence, this method enables the accurate measurement of the sleeping state.

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