Occupant sensor

• US 6,392,542 B1
• Filed: 07/11/2000
• Issued: 05/21/2002
• Est. Priority Date: 07/12/1999
• Status: Expired due to Term

• Current Assignee: Joyson Safety Systems Acquisition, LLC (Ningbo Junsheng Investment Group Co., Ltd.)
• Original Assignee: Automotive Systems Laboratory, Incorporated (Ningbo Junsheng Investment Group Co., Ltd.)
• Inventors: Stanley, James G.
• Primary Examiner(s): MULLEN, THOMAS J
• Application Number:
  US09/614,086
• Time in Patent Office: 679 Days
• Field of Search: 340/561, 340/562, 340/573.1, 701/45, 280/735, 180/271, 307/10.1, 600/547
• US Class Current: 340/561
• CPC Class Codes: B60N 2/002 Seats provided with an occupancy detection means mounted therein or thereon detection means responsive to presence or absence of children B60N2/266
• CPC Class Codes: B60N 2/0022 for sensing anthropometric parameters, e.g. heart rate or body temperature
• CPC Class Codes: B60N 2/0026 for distinguishing between humans, animals or objects
• CPC Class Codes: B60N 2/28 Seats readily mountable on, and dismountable from, existing seats or other parts of the vehicle
• CPC Class Codes: B60N 2/286 forward facing B60N2/2866 takes precedence
• CPC Class Codes: B60N 2/2863 backward facing
• CPC Class Codes: B60N 2/5685 Resistance
• CPC Class Codes: B60N 2210/12 Capacitive; Electric field
• CPC Class Codes: B60N 2220/20 using a deterministic algorithm
• CPC Class Codes: B60R 2021/0034 lying down
• CPC Class Codes: B60R 2021/0037 standing
• CPC Class Codes: B60R 21/01516 using force or pressure sensing means
• CPC Class Codes: B60R 21/01532 using electric or capacitive field sensors
• CPC Class Codes: B60R 21/01534 using electromagneticwaves, e.g. infrared
• CPC Class Codes: B60R 21/01536 using ultrasonic waves
• CPC Class Codes: B60R 21/01556 Child-seat detection systems
• CPC Class Codes: G01B 7/023 for measuring distance between sensor and object G01B7/082 and G01B7/102 take precedence
• CPC Class Codes: G01V 3/088 operating with electric fields G01V3/082 takes precedence
• CPC Class Codes: G08B 13/26 by proximity of an intruder causing variation in capacitance or inductance of a circuit
• CPC Class Codes: H03K 17/955 using a capacitive detector

Abstract

An electric field sensor (12) comprising at least one electrode (26) mountable within a seat (14) is operatively coupled to a sensing circuit (38), which applies an oscillating signal (28), comprising at least one frequency or at least one pulse, to at least one electrode (26) and generates a signal (32) responsive to at least one electric-field-influencing property of an object proximate to the electric field sensor (12). At least one frequency or pulse width of the applied signal (28) are adapted to be at most weakly responsive to a wetting condition of the seat (14). A method of sensing an occupant comprises placing at least one electrode (12) within a seat (14) of a motor vehicle (16), applying an oscillating signal (28) to at least one electrode, measuring (1112) the amplitude (1026) and phase (1038) of a signal (26) responsive to the at least one electrode (26), rotating (1116) the measured amplitude (1026) and phase (1038), compensating (1118) the rotated amplitude by a value responsive to the rotated phase, and comparing (1120) the compensated amplitude with a threshold.

Claims

1. An occupant sensor, comprising:

a. an electric field sensor comprising at least one first electrode mountable within a vehicle seat; and

b. a sensing circuit operatively coupled to at least one said first electrode, wherein said sensing circuit applies an applied signal to said at least one said first electrode, said applied signal comprises a first oscillating signal, said sensing circuit generates a first signal responsive to at least one electric-field-influencing property of an object proximate to said electric field sensor, said first oscillating signal comprises at least one frequency, said at least one frequency comprises a plurality of frequencies, and at least one of said at least one frequency is at most weakly responsive to a wetting condition of said vehicle seat by a liquid.

2. An occupant sensor as recited in claim 1, wherein at least one of said at least one frequency is greater than 400 kilohertz.

3. An occupant sensor as recited in claim 1, wherein at least one of said at least one frequency is adapted so that a liquid proximate to said at least one first electrode reacts to a change in an electric field proximate to said at least one first electrode in a time period greater than a threshold.

4. An occupant sensor as recited in claim 3, wherein said threshold is 200 nanoseconds.

5. An occupant sensor as recited in claim 3, wherein said frequency is greater than 800 kilohertz.

6. An occupant sensor as recited in claim 1, wherein said plurality of frequencies comprises a first and second frequency, said first frequency is less than 100 kilohertz, and said second frequency is greater than 800 kilohertz.

7. An occupant sensor as recited in claim 1, wherein said sensing circuit is responsive to a capacitance of at least one said first electrode with respect to a circuit ground.

8. An occupant sensor, comprising:

a. an electric field sensor comprising at least one first electrode mountable within a vehicle seat; and

b. a sensing circuit operatively coupled to at least one said first electrode, wherein said sensing circuit applies an applied signal to said at least one said first electrode, said applied signal comprises a first oscillating signal, said sensing circuit generates a first signal responsive to at least one electric-field-influencing property of an object proximate to said electric field sensor, said first oscillating signal comprises at least one frequency, at least one of said at least one frequency is at most weakly responsive to a wetting condition of said vehicle seat by a liquid, said sensing circuit is responsive to a capacitance of at least one said first electrode with respect to a circuit ground, and said sensing circuit is responsive to a resistance of at least one said first electrode with respect to said circuit ground.

9. An occupant sensor as recited in claim 8, wherein said resistance is responsive to said wetting condition of said vehicle seat.

10. An occupant sensor, comprising:

a. an electric field sensor comprising at least one first electrode mountable within a vehicle seat; and

b. a sensing circuit operatively coupled to at least one said first electrode, wherein said sensing circuit applies an applied signal to said at least one said first electrode, said applied signal comprises a first oscillating signal, said sensing circuit generates a first signal responsive to at least one electric-field-influencing property of an object proximate to said electric field sensor, said applied signal and said sensing circuit are adapted so that said sensing circuit is responsive to a wetting condition of said vehicle seat, said first oscillating signal comprises at least one pulse, and at least one said pulse is adapted so that a liquid proximate to said at least one first electrode reacts to a change in an electric field proximate to said at least one first electrode in a time period greater than a threshold.

11. An occupant sensor as recited in claim 10, wherein said threshold is 200 nanoseconds.

12. An occupant sensor as recited in claim 10, wherein said at least one pulse has a pulse width less than 250 nanoseconds.

13. An occupant sensor as recited in claim 10, wherein said first oscillating signal comprises a plurality of pulses.

14. An occupant sensor as recited in claim 13, wherein each of said plurality of pulses has a pulse width, at least two of said plurality of pulses have different pulse widths, and at least one said pulse has a pulse width less than 250 nanoseconds.

15. An occupant sensor, comprising:

a. an electric field sensor comprising at least one first electrode mountable within a vehicle seat; and

b. a sensing circuit operatively coupled to at least one said first electrode, wherein said sensing circuit applies an applied signal to said at least one said first electrode, said applied signal comprises a first oscillating signal, said sensing circuit generates a first signal responsive to at least one electric-field-influencing property of an object proximate to said electric field sensor, said first oscillating signal comprises at least one frequency, and at least one of said at least one frequency is at most weakly responsive to a wetting condition of said vehicle seat by a liquid, wherein said sensing circuit comprises;

i) a source of an oscillatory signal;

ii) a voltage divider comprising;

(a) at least one capacitor, wherein said at least one capacitor is operatively coupled to said source of an oscillatory signal; and

(b) a resistor having a resistance, wherein said resistor is operatively coupled to said at least one capacitor at a first node and to a circuit ground, and at least one said first electrode is operatively coupled to said first node;

iii) a phase detector operatively coupled to said first node for detecting a phase difference comprising difference between a phase of said oscillatory signal and a phase of a signal at said first node, wherein said phase difference is substantially constant when said vehicle seat is substantially dry; and

iv) a discriminator operatively coupled to said phase detector, wherein said discriminator comprises a threshold responsive to said difference in phase and at least one of said threshold and said phase difference are adapted to compensate for a wetting of said vehicle seat.

16. An occupant sensor as recited in claim 15, wherein said resistance is substantially higher than an impedance of said at least one electrode with respect to a circuit ground at a frequency of said oscillatory signal.

17. An occupant sensor as recited in claim 15, wherein a first signal at said first node is responsive to said oscillatory signal, to said voltage divider, and to an impedance of at least one said first electrode with respect to said circuit ground, said impedance is substantially capacitive when said vehicle seat is substantially dry, and said impedance is also resistive when said vehicle seat is wetted by a liquid.

18. An occupant sensor as recited in claim 15, further comprising a voltage follower having an input and an output, wherein said input is operatively coupled to said first node, and said phase detector is operatively coupled to said first node through said voltage follower.

19. An occupant sensor as recited in claim 15, wherein said phase detector further comprises a filter.

20. An occupant sensor, comprising:

a. an electric field sensor comprising at least one first electrode mountable within a vehicle seat; and

b. a sensing circuit operatively coupled to at least one said first electrode, wherein said sensing circuit applies an applied signal to said at least one said first electrode, said applied signal comprises a first oscillating signal, said sensing circuit generates a first signal responsive to at least one electric-field-influencing property of an object proximate to said electric field sensor, said first oscillating signal comprises at least one frequency, and at least one of said at least one frequency is at most weakly responsive to a wetting condition of said vehicle seat by a liquid, wherein said sensing circuit comprises.

i) a source of an oscillatory signal;

ii) a voltage divider comprising;

(c) at least one capacitor, wherein said at least one capacitor is operatively coupled to said source of an oscillatory signal; and

(d) a resistor having a resistance, wherein said resistor is operatively coupled to said at least one capacitor at a first node and to a circuit ground, and at least one said first electrode is operatively coupled to said first node;

iii) an amplitude detector operatively coupled to said first node for detecting for detecting an amplitude of said signal at said first node, wherein said amplitude of said first signal is responsive to a wetting condition of said vehicle seat, whereby said amplitude is decreased responsive to said liquid; and

iv) a discriminator operatively coupled to said amplitude detector, wherein said discriminator comprises a threshold responsive to said amplitude and at least one of said threshold and said amplitude are adapted to compensate for a wetting of said vehicle seat.

21. An occupant sensor as recited in claim 20, wherein said resistance is substantially higher than an impedance of said at least one electrode with respect to a circuit ground at a frequency of said oscillatory signal.

22. An occupant sensor as recited in claim 20, wherein a first signal at said first node is responsive to said oscillatory signal, to said voltage divider, and to an impedance of at least one said first electrode with respect to said circuit ground, said impedance is substantially capacitive when said vehicle seat is substantially dry, and said impedance is capacitvie reactive when said vehicle seat is wetted by a liquid.

23. An occupant sensor as recited in claim 20, further comprising a voltage follower having an input and an output, wherein said input is operatively coupled to said first node, and said phase detector is operatively coupled to said first node through said voltage follower.

24. An occupant sensor as recited in claim 20, wherein said amplitude detector further comprises a filter.

25. An occupant sensor as recited in claim 20, wherein said sensing circuit further comprises:

a. a phase detector operatively coupled to said first node for detecting a phase difference comprising difference between a phase of said oscillatory signal and a phase of a signal at said first node, wherein said discriminator is operatively coupled to said phase detector, and said threshold is responsive to said difference in phase; and

b. a processor operatively coupled to said phase detector and to said amplitude detector, wherein said processor generates a first measure for said first frequency having at least one component selected from an output of said phase detector, an output of said amplitude detector, and a capacitance of at least one said first electrode with respect to said circuit ground.

26. An occupant sensor as recited in claim 25, wherein said resistance is substantially higher than an impedance of at least one said first electrode with respect to circuit ground at a frequency of said oscillatory signal.

27. An occupant sensor as recited in claim 25, wherein a first signal at said first node is responsive to said oscillatory signal, to said voltage divider, and to an impedance of at least one said first electrode with respect to said circuit ground, said impedance is substantially capacitive when said vehicle seat is substantially dry, and said impedance is also resistive when said vehicle seat is wetted by a liquid.

28. An occupant sensor as recited in claim 25, further comprising a voltage follower having an input and an output, wherein said input is operatively coupled to said first node, and said phase detector is operatively coupled to said first node through said voltage follower.

29. An occupant sensor as recited in claim 25, wherein said phase detector further comprises a first filter, and said amplitude detector further comprises a second filter.

30. An occupant sensor as recited in claim 25, wherein said processor generates a second measure for said second frequency having components selected from an output of said phase detector, an output of said amplitude detector, and a capacitance of at least one said first electrode with respect to said circuit ground, and said processor compares said first measure with said second measure so as to discriminate a type of object on said vehicle seat and a condition of said vehicle seat.

31. An occupant sensor as recited in claim 30, wherein said processor is operatively coupled to a safety restraint system and said safety restraint system is enabled when at least one of said first and second measures exceeds a threshold.

32. An occupant sensor as recited in claim 30, wherein said first and second measures are measures of a capacitance of at least one said first electrode, and said sensing circuit adapts at least one of said threshold, said first measure, and said second measure responsive to a detected wetness of said vehicle seat, whereby said first measure is greater than said second measure when said vehicle seat is wetted by a liquid.

33. An occupant sensor as recited in claim 32, wherein said threshold is compared with a capacitance of at least one said first electrode.

34. An occupant sensor as recited in claim 33, wherein said threshold is increased responsive to a detected wetness of said vehicle seat.

35. A method of sensing an occupant, comprising:

a. placing at least one electrode within a seat of a motor vehicle;

b. applying an oscillating signal to said at least one electrode;

c. generating a second signal responsive to said at least one electrode;

d. measuring an amplitude of said second signal;

e. measuring a phase of said second signal relative to said oscillating signal;

f. rotating said amplitude and phase in amplitude-phase space by an angle, so as to create a rotated amplitude and a rotated phase;

g. compensating said rotated amplitude by a value responsive to said rotated phase so as to create a compensated rotated amplitude; and

h. comparing said compensated rotated amplitude with a threshold.

36. A method of sensing an occupant as recited in claim 35, further comprising:

a. applying said oscillating signal to a first capacitance;

b. generating a third signal responsive to said first capacitance;

c. measuring an amplitude of said third signal;

d. measuring a phase of said third signal relative to said oscillating signal;

e. applying said oscillating signal to a second capacitance;

f. generating a fourth signal responsive to said first capacitance;

g. measuring an amplitude of said fourth signal;

h. measuring a phase of said fourth signal relative to said oscillating signal;

i. adjusting said amplitude of said second signal responsive to said amplitude of said third signal and to said amplitude of said fourth signal;

j. adjusting said phase of said second signal responsive to said phase of said third signal and to said phase of said fourth signal.

37. A method of sensing an occupant as recited in claim 35, wherein said angle is calculated from a plurality of measurements of amplitude and phase from at least one electrode in a seat for a plurality of seat occupancy scenarios for a dry said seat.

38. A method of sensing an occupant as recited in claim 35, wherein said step of compensating said rotated angle is responsive to a compensation function, and said compensation function is calculated from a plurality of measurements of amplitude and phase from at least one electrode in a seat for a plurality of seat occupancy scenarios and for a plurality of degrees of wetness of said seat.

39. A method of sensing an occupant as recited in claim 35, further comprising the operation of enabling a safety restraint system if said compensated rotated amplitude exceeds said threshold.

40. A method of sensing an occupant as recited in claim 35, further comprising the operation of disabling a safety restraint system if said compensated rotated amplitude is less than said threshold.