Sleepiness level detection device

• US 20040243013A1
• Filed: 05/25/2004
• Published: 12/02/2004
• Est. Priority Date: 05/27/2003
• Status: Active Grant

• Current Assignee: DENSO Corporation
• Original Assignee: DENSO Corporation
• Inventors: Ito, Akiko, Kawachi, Taiji, Nakagawa, Tsuyoshi, Yoshinori, Takeshi
• Granted Patent: US 7,206,631 B2
• Time in Patent Office: Days
• US Class Current: 600/509
• CPC Class Codes: A61B 5/024 Detecting, measuring or recording pulse rate or heart rate A61B5/0205, A61B5/021 take precedence
• CPC Class Codes: A61B 5/18 for vehicle drivers or machine operators
• CPC Class Codes: A61B 5/417 the bone marrow
• CPC Class Codes: A61B 5/7253 characterised by using transforms
• CPC Class Codes: A61B 5/7257 using Fourier transforms

Abstract

A sleepiness level detection device detects a heartbeat signal when a time equal to or longer than T1 and equal to or shorter than T2 has elapsed since the start of driving. The heartbeat signal is subjected to FFT processing to obtain a spectrum signal. By use of a peak frequency of the spectrum signal, a driver conscious-state peak frequency is estimated. A consciousness level index band α is set with respect to the conscious-state peak frequency. A sleepiness level index band β is set with respect to a frequency, which is calculated by multiplying the conscious-state peak frequency by a predetermined ratio (65 to 90%). A sleepiness level evaluation parameter Sp (=βp/(αp+βp)) for indicating the sleepiness level of the driver is calculated with the use of the strength αp and βp of spectrum signals.

Claims

1. A sleepiness level detection device comprising:

means for detecting a heartbeat signal of a test subject;

calculation means for performing frequency analysis on the heartbeat signal and calculating a spectrum signal that indicates the distribution of frequency components included in the heartbeat signal; and

evaluation means for setting a band having a lower frequency than a conscious-state peak frequency as a sleepiness level index band for indicating a sleepiness level, in the spectrum signal, with respect to the conscious-state peak frequency in a conscious state of the test subject, and evaluating the sleepiness level of the test subject, on basis of strength of the spectrum signal in the sleepiness level index band.

2. The sleepiness level detection device according to claim 1, wherein

the calculation means converts the heartbeat signal into a signal that has peaks only at largest peak positions of the heartbeat signal, and performs frequency analysis on the converted signal.

3. The sleepiness level detection device according to claim 1, wherein

the evaluation means evaluates the sleepiness level of the test subject when the test subject operates predetermined equipment, and the peak frequency of the spectrum signal, at a time after a predetermined time has elapsed since the test subject began operating the predetermined equipment, is set as the conscious-state peak frequency.

4. The sleepiness level detection device according to claim 3, wherein

the conscious-state peak frequency is calculated by averaging peak frequencies of a plurality of spectrum signals that are calculated for a predetermined detection time, from a point in time after a predetermined time has elapsed since the test subject began operating the predetermined equipment.

5. The sleepiness level detection device according to claim 3, wherein

the predetermined time is selected in a range from 100 seconds to 500 seconds.

6. The sleepiness level detection device according to claim 1, wherein

the evaluation means sets a band including the conscious-state peak frequency as a consciousness level index band, and evaluates the sleepiness level of the test subject by using strength of the spectrum signals in the consciousness level index band and the sleepiness level index band.

7. The sleepiness level detection device according to claim 6, wherein

the evaluation means calculates a sleepiness level evaluation parameter, a denominator of which is a sum of the strength of the spectrum signals in the consciousness and sleepiness level index bands, and a numerator of which is a the strength of the spectrum signal in the sleepiness level index band.

8. The sleepiness level detection device according to claim 6, wherein

the consciousness level index band is set to have a bandwidth of ±

0.05 Hz with respect to the conscious-state peak frequency as a center.

9. The sleepiness level detection device according to claim 6, wherein

the sleepiness level index band is set to include any frequency of 65 to 90% of the conscious-state peak frequency.

10. The sleepiness level detection device according to claim 1, wherein

the evaluation means evaluates the sleepiness level of the test subject, when the test subject operates the predetermined equipment, and the evaluation means repeatedly calculates a peak frequency of the spectrum signal after the test subject starts operating the predetermined equipment, and when the difference between maximum peak frequency and minimum peak frequency in a predetermined time period is equal to or less than a predetermined value, an average value of the peak frequencies in the time period is set as the conscious-state peak frequency.

11. The sleepiness level detection device according to claim 3, wherein

the evaluation means calculates the conscious-state peak frequency every time the test subject starts operating the equipment, and the evaluation means determines a final conscious-state peak frequency based on a latest conscious-state peak frequency and a past conscious-state peak frequency.