Method and system for contactless evaluation of fatigue of an operator

• US 20050148894A1
• Filed: 12/22/2004
• Published: 07/07/2005
• Est. Priority Date: 01/06/2004
• Status: Active Grant

• Current Assignee: Dale Julian Misczynski, Vladislav Bukhman
• Original Assignee: Dale Julian Misczynski, Vladislav Bukhman
• Inventors: Bukhman, Vladislav, Misczynski, Dale Julian
• Granted Patent: US 7,254,439 B2
• Time in Patent Office: Days
• US Class Current: 600/513
• CPC Class Codes: A61B 5/02405 Determining heart rate variability
• CPC Class Codes: A61B 5/05 Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves impedance plethysmography A61B5/0295; measuring movement of the entire body or parts thereof A61B5/11; detecting, measuring or recording bioelectric or biomagnetic signals of the body or parts thereof A61B5/24
• CPC Class Codes: A61B 5/7257 using Fourier transforms

Abstract

The invention relates to a method and device for contactless assessment of fatigue of a user, in particular a vehicle operator. The invention is comprised of a seamless continuous evaluation of cardiac activity variability and uses this data as an input for evaluation and quantitative assessment of sympathetic and parasympathetic activity of the autonomic nervous system, which are reliable markers of the physiological condition of a user. The small device is fixed to a driver'"'"'s safety belt or embedded in the back of driver'"'"'s seat without direct contacts to a user'"'"'s body. The device continuously monitors the fatigue level of a user and alerts the user if he/she unexpectedly drifts from wakefulness to drowsiness. The invention significantly improves the safety of a vehicle operator.

Claims

1. A method and system of assessing fatigue of an operator comprising:

a) Electromagnetic inductance device fixed to vehicle'"'"'s safety belt and positioned against driver'"'"'s chest;

b) Another version of said device embedded in the back of driver'"'"'s seat;

c) Said electromagnetic inductance device is connected to the vehicles'"'"'s computer via cable;

d) Passing an alternating current through the excitation coil;

e) Measuring at least one induced current waveform derived from a receiver coil;

f) Processing said at least one induced current waveform associated with changes in the amplitude caused by eddy current losses in the heart region;

g) Determining fatigue level based on the said changes in said eddy current.

2. The method of claim 1, wherein the act of processing said at least one induced current waveform comprises of evaluation of heart rate (HR), stroke volume (SV), and cumulative index of cardiac activity (CA) as function of said heart rate and said stroke volume in normalized units.

3. The method of claim 2, wherein CA is calculated by:

CA _i =k*Q _i n.u.

Where;

k is a normalizing factor for converting calculated value of Q_i in the meaningful value;

Q_i=area of wave W_i;

n.u. stands for normalized unit.

4. The method of claim 3, wherein Q1 is calculated by:

$Q_i=\underset{j=1}{\overset{n}{\sum <br><br>}}<br><br>\text{\hspace{1em}<br><br>}<br><br>A_j$

Where;

Q_i=area of CA wave related to cardiac cycle i,

A_j=amplitude of sample j of CA wave of cardiac cycle i,

n=number of samples within cardiac cycle i.

5. The method of claim 1, wherein fatigue level (F) is determined by:

$\begin{array}{cc}F=\frac{\mathrm{LP}}{\mathrm{HP}}& \left(4\right)\end{array}$

Where;

F=fatigue value,

LP=sympathetic activity power,

HP=parasympathetic activity power.

6. The method of claim 5, wherein sympathetic activity power (LP) and parasympathetic activity power (LP) is determined using Fast Fourier Transform (FFT) algorithm.

7. The method of claim 5, wherein the baseline fatigue level (pattern) is determined during the first 30 minutes using a 5 minutes moving window with 30 second increment.

8. The method of claim 7, wherein the said pattern is updated every 5 minutes thus providing adaptation to changing driving environment.

9. The method of claim 1, wherein the transition from wakefulness to drowsing is characterized by the rapid shift of predominance of sympathetic activity to predominance of parasympathetic activity.

10. The method of claim 9, wherein said sympathetic power, LP drops up to 10%, while said parasympathetic power, HP increases up to 50% during time interval from 1 to 5 minutes.

11. The method of claim 9, wherein the mean ratio, F_c of said sympathetic and said parasympathetic activity, LP/LH for the last 5 minutes using data stored in the FIFO buffer and compares F_c with 30 minutes meant value F_m (driving pattern).

12. The method of claim 11, wherein if said F_c≦

0.75*F_m, (i.e. ratio of sympathetic activity to parasympathetic activity drops by equal or more then 25% during the last 5 minutes), then the system alarms the user.

13. The method of claim 1, wherein the system also warns the driver if the driver is drifting from wakefulness to drowsing.

14. The method of claim 13, wherein the intensity of said warning signal depends on the calculated length of the expected transition time from wakefulness to drowsing.

15. The method of claim 14, wherein the said intensity gradually increases from lowest to highest level reflecting the expected transition time from equal or less than 60 s to less then 5 s.

16. The method of claim 13, wherein the projected values of the said fatigue level, F is determined within next 60 seconds of driving.

17. The method of claim 16, wherein 10 last stored values of fatigue level are smoothed using 9-points triangular smooth method:

$F_j=\frac{Y_{j-4}+2<br><br>Y_{j-3}+3<br><br>Y_{j-2}+4<br><br>Y_{j-1}+5<br><br>Y_j+4<br><br>Y_{j+1}+3<br><br>Y_{j+2}+2<br><br>Y_{j+3}+Y_{j+4}}{25}$

Where;

Y_j=value of measurement j;

j=5 to n-4;

n=10.

18. The method of claim 17, wherein the said smooth method comprises two iterations and transforms the fatigue level waveform in a vector representing the tendency of CAV of a current driving pattern of the driver.

19. The method of claim 18, wherein the said iterations j=5, determines the first pair of coordinates of the vector:

$\begin{array}{c}{F}_5=\frac{Y_1+2<br><br>Y_2+3<br><br>Y_3+4<br><br>Y_4+5<br><br>Y_5+4<br><br>Y_6+3<br><br>Y_7+2<br><br>Y_8+Y_9}{25}\\ t=5,\end{array}$

while the said iterations j=6, determines the second pair of coordinates of the vector;

$\begin{array}{c}{F}_5=\frac{Y_2+2<br><br>Y_3+3<br><br>Y_4+4<br><br>Y_5+5<br><br>Y_6+4<br><br>Y_7+3<br><br>Y_8+2<br><br>Y_9+Y_{10}}{25}\\ t=6.\end{array}$

20. The method of claim 18, wherein the said vector is determined by:

F=A*t 

 

(6)

Where;

F=fatigue level;

A=liner coefficient;

t=measurement number.

21. The method of claim 13, wherein the driver is drifting from wakefulness to drowsiness if the said vector crosses a threshold line during 60 seconds after the last measurement.

22. The method of claim 21, wherein the said threshold line is determined by:

Y=F _d

Where;

F_d=0.75*F_m.

23. The system comprises of 2 sensing coils for supplying an induced current from the subject without contacting the body;

excitation coil for induction magnetic field into the subject;

power amplifier providing AC current to the excitation coil;

amplifier which serves for reducing an effect of residue voltage;

lock-in amplifier for driving the excitation coil;

a digital processor for controlling the lock-in amplifier and analyzing of the digital data of CA waveforms and evaluation the condition of the user;

sound alarm unit for audio alerting the user; and

memory for storing intermediate data during calculation provided by the processor.

24. The system of claim 23, wherein said sensing coils are shielded in order to avoid capacitive effect.

25. The system of claim 23, wherein said power amplifier uses the oscillator signal from lock-in amplifier to drive excitation coil.

26. The system of claim 23, wherein said an additional amplifier is used providing the signal to the lock-in amplifier for phase detection.

27. The system of claim 26, wherein the reference signal for phase detection is fed from the resistor.

28. The system of claim 23, wherein said lock-in amplifier provides oscillator output, phase detection and measurement of the output signal.

29. The system of claim 23, wherein said processor, controls operation of the lock-in amplifier, hosts and run application FFT routine and provides evaluation of measured parameters and sends the signal to alert the driver if the parameters fall outside threshold values.