Capacitive occupant detection system

• US 20080186034A1
• Filed: 02/06/2007
• Published: 08/07/2008
• Est. Priority Date: 02/06/2007
• Status: Active Grant

• Current Assignee: IEE International Electronics & Engineering SA (Aerospace Hi-Tech Holding Group Company Limited)
• Original Assignee: IEE International Electronics & Engineering SA (Aerospace Hi-Tech Holding Group Company Limited)
• Inventors: Scheckenbach, Ingrid, Fuks, Stephen, Krautheim, Thomas, Wendt, Christoph, Althaus, Frank
• Granted Patent: US 7,656,169 B2
• Time in Patent Office: Days
• US Class Current: 324/679
• 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: B60R 21/01532 using electric or capacitive field sensors

Abstract

A capacitive occupant detection system has an oscillator and an electrode operatively coupled to the oscillator, to which the oscillator applies an oscillating voltage signal. In response to the oscillating voltage being applied, an electric current is caused to flow in the electrode, the current being responsive to an electric-field-influencing property of an object or occupant proximate to the electrode. The current caused to flow in the electrode has a first current component in phase with the oscillating voltage signal and a second current component 90°-phase-offset with respect to the oscillating voltage signal. A sensing circuit is operatively coupled to the electrode and to the oscillator so as to generate a first signal indicative of the first current component and a second signal indicative of the second current component. The first signal indicative of the first current component and the second signal indicative of the second current component are provided to a processor, which is operatively coupled to the sensing circuit and which determines an occupancy state based upon the first and second signals indicative of the first and second current components, respectively, and outputs an output signal indicative of the occupancy state.

Claims

1. A capacitive occupant detection system, comprising:

an oscillator;

an electrode operatively coupled to said oscillator, wherein said oscillator applies an oscillating voltage signal to said electrode, wherein a current is caused to flow in said electrode, said current being responsive to an electric-field-influencing property of an object or occupant proximate to said electrode, said current having a first current component in phase with said oscillating voltage signal and a second current component 90-degrees-phase-offset with respect to said oscillating voltage signal;

a sensing circuit, operatively coupled to said electrode and to said oscillator, said sensing circuit generating a first signal indicative of said first current component and a second signal indicative of said second current component; and

a processor, operatively coupled to said sensing circuit, determining an occupancy state based upon said first and second signals indicative of said first and second current components, respectively, and outputting an output signal indicative of said occupancy state.

2. The capacitive occupant detection system as claimed in claim 1, wherein said applied oscillating voltage signal is a sinusoidal voltage signal having a number of oscillation periods, said oscillating voltage signal being positive during first time intervals, negative during second time intervals, of positive slope during third time intervals and of negative slope during fourth time intervals, each one of said first, second, third and fourth time intervals having a duration of half said oscillation period, said first time intervals being in alternate succession with said second time intervals, said third time intervals being in alternate succession with said fourth time intervals, each of said first intervals overlapping with one of said third intervals and one of said fourth intervals, and each of said second intervals overlapping with one of said third intervals and one of said fourth intervals,

wherein said sensing circuit comprises

a current-to-voltage converter operatively coupled to said electrode so as to output a converter voltage signal proportional to the current flowing in said electrode,

a clocked rectifier, said clocked rectifier being operatively coupled to said oscillator and to said current-to-voltage converter, wherein said clocked rectifier provides

(a) a first intermediate voltage signal comprising, during said first time intervals, one of a non-inverse copy and an inverse copy of said converter voltage signal and, during said second time intervals, the other of said non-inverse copy and said inverse copy, and

(b) a second intermediate voltage signal comprising, during said third time intervals, one of a non-inverse copy and an inverse copy of said converter voltage signal and during said fourth time intervals the other of said non-inverse copy and said inverse copy,

and wherein said clocked rectifier generates said first signal indicative of said first current component as a time average or time integral of said first intermediate voltage signal and said second signal indicative of said second current component as a time average or time integral of said second intermediate voltage signal.

3. The capacitive occupant detection system as claimed in claim 2, wherein said clocked rectifier provides said first intermediate voltage signal and said first signal indicative of said first current component in alternation with said second intermediate voltage signal and said second signal indicative of said second current component.

4. The capacitive occupant detection system as claimed in claim 2, wherein said clocked rectifier provides said first intermediate voltage signal and said first signal indicative of said first current component in parallel with said second intermediate voltage signal and said second signal indicative of said second current component.

5. The capacitive occupant detection system as claimed in claim 2, wherein said clocked rectifier comprises

at least one amplifier circuit operatively connected to said current-to-voltage converter, said at least one amplifier circuit being capable of alternately inverting and non-inverting said converter voltage signal so as to provide the inverted and non-inverted copies of said first and/or second intermediate voltage signals,

and a switch operatively connected to said at least one amplifier circuit for switching said at least one amplifier circuit between inverting and non-inverting said converter voltage signal.

6. The capacitive occupant detection system as claimed in claim 5, wherein said clocked rectifier comprises a low-pass filter or integrator, wherein said at least one amplifier circuit includes an inverting amplifier and a non-inverting amplifier arranged in parallel, and wherein said switch alternately switches said said inverting amplifier and said non-inverting amplifier to said low-pass filter or integrator.

7. The capacitive occupant detection system as claimed in claim 2, wherein said clocked rectifier comprises

at least one first amplifier circuit operatively connected to said current-to-voltage converter and a first switch switching said at least one first amplifier circuit between inverting and non-inverting said converter voltage signal so as to provide the inverted and non-inverted copies of said first intermediate voltage signal,

and at least one second amplifier circuit operatively connected to said current-to-voltage converter and a second switch switching said at least one second amplifier circuit between inverting and non-inverting said converter voltage signal so as to provide the inverted and non-inverted copies of said second intermediate voltage signal.

8. The capacitive occupant detection system as claimed in claim 7, wherein said clocked rectifier comprises a first low-pass filter or integrator and a second low-pass filter or integrator, wherein said at least one first amplifier circuit includes an inverting first amplifier and a non-inverting first amplifier arranged in parallel, said first switch alternately switching said inverting first amplifier and said non-inverting first amplifier to said first low-pass filter or integrator, and wherein said at least one second amplifier circuit includes an inverting second amplifier and a non-inverting second amplifier, said second switch alternately switching said inverting second amplifier and said non-inverting second amplifier to said second low-pass filter or integrator.

9. The capacitive occupant detection system as claimed in claim 2, wherein said clocked rectifier comprises at least one low-pass filter providing said first signal indicative of said first current component as a time average of said first intermediate voltage signal and/or said second signal indicative of said second current component as a time average of said second intermediate voltage signal.

10. The capacitive occupant detection system as claimed in claim 2, wherein said clocked rectifier comprises at least one integrator providing said first signal indicative of said first current component as a time integral of said first intermediate voltage signal and/or said second signal indicative of said second current component as a time integral of said second intermediate voltage signal.

11. The capacitive occupant detection system as claimed in claim 1, wherein said processor determines said occupancy state based upon a comparison of said second signal indicative of said second current component with a threshold, said threshold being dependent upon said first signal indicative of said first current component.

12. The capacitive occupant detection system as claimed in claim 11, wherein said threshold is a growing function of said first signal indicative of said first current component.

13. The capacitive occupant detection system as claimed in claim 1, wherein said processor modifies said second signal indicative of said second current component based upon said first signal indicative of said first current component and determines said occupancy state based upon a comparison of said modified second signal with a threshold.

14. A capacitive occupant detection system for a vehicle seat, comprising:

an oscillator;

a sensing electrode for being arranged underneath a surface of said vehicle seat,

a shielding electrode, for being placed adjacent said sensing electrode so that said sensing electrode is situated between said surface and said shielding electrode, wherein said sensing and shielding electrodes are operatively coupled to said oscillator, wherein said oscillator is configured for driving said sensing and shielding electrodes with an oscillating voltage signal, said oscillating voltage signal being substantially the same in amplitude and phase for said sensing and shielding electrodes, a current being caused to flow in said sensing electrode in response to said oscillator driving said sensing and shielding electrodes, said current being responsive to an electric-field-influencing property of an object or occupant proximate to said electrode, said current occurring with a first current component in phase with said oscillating voltage signal and a second current component 90-degrees-phase-offset with respect to said oscillating voltage signal;

a sensing circuit, operatively coupled to said sensing electrode and to said oscillator and configured for generating a first signal indicative of said first current component and a second signal indicative of said second current component; and

a processor, operatively coupled to said sensing circuit, configured for determining an occupancy state based upon said first and second signals indicative of said first and second current components, respectively, and for outputting an output signal indicative of said occupancy state.

15. The capacitive occupant detection system as claimed in claim 14, wherein said applied oscillating voltage signal is a sinusoidal voltage signal having a number of oscillation periods, said oscillating voltage signal being positive during first time intervals, negative during second time intervals, of positive slope during third time intervals and of negative slope during fourth time intervals, each one of said first, second, third and fourth time intervals having a duration of half said oscillation period, said first time intervals being in alternate succession with said second time intervals, said third time intervals being in alternate succession with said fourth time intervals, each of said first intervals overlapping with one of said third intervals and one of said fourth intervals, and each of said second intervals overlapping with one of said third intervals and one of said fourth intervals,

wherein said sensing circuit comprises

a current-to-voltage converter operatively coupled to said sensing electrode and configured for outputting a converter voltage signal proportional to the current flowing in said sensing electrode,

a clocked rectifier, said clocked rectifier being operatively coupled to said oscillator and to said current-to-voltage converter, wherein said clocked rectifier is configured for providing

(a) a first intermediate voltage signal comprising, during said first time intervals, one of a non-inverse copy and an inverse copy of said converter voltage signal and, during said second time intervals, the other of said non-inverse copy and said inverse copy, and

(b) a second intermediate voltage signal comprising, during said third time intervals, one of a non-inverse copy and an inverse copy of said converter voltage signal and during said fourth time intervals the other of said non-inverse copy and said inverse copy,

and wherein said clocked rectifier generates said first signal indicative of said first current component as a time average or time integral of said first intermediate voltage signal and said second signal indicative of said second current component as a time average or time integral of said second intermediate voltage signal.

16. The capacitive occupant detection system as claimed in claim 15, wherein said clocked rectifier comprises

at least one amplifier circuit operatively connected to said current-to-voltage converter, said at least one amplifier circuit being configured for alternately inverting and non-inverting said converter voltage signal so as to provide the inverted and non-inverted copies of said first and/or second intermediate voltage signals,

and a switch operatively connected to said at least one amplifier circuit for switching said at least one amplifier circuit between inverting and non-inverting said converter voltage signal.

17. The capacitive occupant detection system as claimed in claim 15, wherein said clocked rectifier comprises at least one low-pass filter for providing said first signal indicative of said first current component as a time average of said first intermediate voltage signal and/or said second signal indicative of said second current component as a time average of said second intermediate voltage signal.

18. The capacitive occupant detection system as claimed in claim 15, wherein said clocked rectifier comprises at least one integrator for providing said first signal indicative of said first current component as a time integral of said first intermediate voltage signal and/or said second signal indicative of said second current component as a time integral of said second intermediate voltage signal.

19. The capacitive occupant detection system as claimed in claim 14, wherein said processor is configured for determining said occupancy state based upon a comparison of said second signal indicative of said second current component with a threshold, said threshold being dependent upon said first signal indicative of said first current component.

20. The capacitive occupant detection system as claimed in claim 19, wherein said threshold is a growing function of said first signal indicative of said first current component.

21. The capacitive occupant detection system as claimed in claim 14, wherein said processor is configured for modifying said second signal indicative of said second current component based upon said first signal indicative of said first current component and for determining said occupancy state based upon a comparison of said modified second signal with a threshold.

22. A capacitive occupant detection system, comprising:

an oscillator;

a transmitting electrode, operatively coupled to said oscillator, said oscillator being configured for applying an oscillating voltage signal to said transmitting electrode,

a sensing electrode for being arranged in proximity of said transmitting electrode in such a way that a current may be caused to flow in said sensing electrode by capacitive coupling between said transmitting electrode and said sensing electrode, said current being responsive to an electric-field-influencing property of an object or occupant in a region between said transmitting and sensing electrodes, said current occurring with a first current component in phase with said applied oscillating voltage signal and a second current component 90-degrees-phase-offset with respect to said oscillating voltage signal;

a sensing circuit, operatively coupled to said sensing electrode and to said oscillator and configured for generating a first signal indicative of said first current component and a second signal indicative of said second current component; and

a processor, operatively coupled to said sensing circuit, configured for determining an occupancy state based upon said first and second signals indicative of said first and second current components, respectively, and for outputting an output signal indicative of said occupancy state.

23. The capacitive occupant detection system as claimed in claim 22, wherein said applied oscillating voltage signal is a sinusoidal voltage signal having a number of oscillation periods, said oscillating voltage signal being positive during first time intervals, negative during second time intervals, of positive slope during third time intervals and of negative slope during fourth time intervals, each one of said first, second, third and fourth time intervals having a duration of half said oscillation period, said first time intervals being in alternate succession with said second time intervals, said third time intervals being in alternate succession with said fourth time intervals, each of said first intervals overlapping with one of said third intervals and one of said fourth intervals, and each of said second intervals overlapping with one of said third intervals and one of said fourth intervals,

wherein said sensing circuit comprises

a current-to-voltage converter operatively coupled to said sensing electrode and configured for outputting a converter voltage signal proportional to the current flowing in said sensing electrode,

a clocked rectifier, said clocked rectifier being operatively coupled to said oscillator and to said current-to-voltage converter, wherein said clocked rectifier is configured for providing

(a) a first intermediate voltage signal comprising, during said first time intervals, one of a non-inverse copy and an inverse copy of said converter voltage signal and, during said second time intervals, the other of said non-inverse copy and said inverse copy, and

(b) a second intermediate voltage signal comprising, during said third time intervals, one of a non-inverse copy and an inverse copy of said converter voltage signal and during said fourth time intervals the other of said non-inverse copy and said inverse copy,

and wherein said clocked rectifier generates said first signal indicative of said first current component as a time average or time integral of said first intermediate voltage signal and said second signal indicative of said second current component as a time average or time integral of said second intermediate voltage signal.

24. The capacitive occupant detection system as claimed in claim 23, wherein said clocked rectifier comprises

at least one amplifier circuit operatively connected to said current-to-voltage converter, said at least one amplifier circuit being configured for alternately inverting and non-inverting said converter voltage signal so as to provide the inverted and non-inverted copies of said first and/or second intermediate voltage signals,

and a switch operatively connected to said at least one amplifier circuit for switching said at least one amplifier circuit between inverting and non-inverting said converter voltage signal.

25. The capacitive occupant detection system as claimed in claim 23, wherein said clocked rectifier comprises at least one low-pass filter providing said first signal indicative of said first current component as a time average of said first intermediate voltage signal and/or said second signal indicative of said second current component as a time average of said second intermediate voltage signal.

26. The capacitive occupant detection system as claimed in claim 23, wherein said clocked rectifier comprises at least one integrator providing said first signal indicative of said first current component as a time integral of said first intermediate voltage signal and/or said second signal indicative of said second current component as a time integral of said second intermediate voltage signal.

27. The capacitive occupant detection system as claimed in claim 22, wherein said processor is configured for determining said occupancy state based upon a comparison of said second signal indicative of said second current component with a threshold, said threshold being dependent upon said first signal indicative of said first current component.

28. The capacitive occupant detection system as claimed in claim 27, wherein said threshold is a growing function of said first signal indicative of said first current component.

29. The capacitive occupant detection system as claimed in claim 22, wherein said processor is configured for modifying said second signal indicative of said second current component based upon said first signal indicative of said first current component and for determining said occupancy state based upon a comparison of said modified second signal with a threshold.