Proximity sensor

• US 6,445,294 B1
• Filed: 07/14/2000
• Issued: 09/03/2002
• Est. Priority Date: 07/15/1999
• 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., McDonnell, Judson G.
• Primary Examiner(s): MULLEN, THOMAS J
• Application Number:
  US09/616,406
• Time in Patent Office: 781 Days
• Field of Search: 340/562, 340/561, 340/573.1, 340/686.6, 180/272, 280/735, 307/10.1, 701/45, 324/688
• US Class Current: 340/562
• 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 2/0021 characterised by the type of sensor or measurement
• 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 2210/12 Capacitive; Electric field
• CPC Class Codes: B60R 21/015 including means for detecting the presence or position of passengers, passenger seats or child seats , and the related safety parameters therefor, e.g. speed or timing of airbag inflation in relation to occupant position or seat belt use
• CPC Class Codes: B60R 21/01532 using electric or capacitive field sensors
• 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

A sense electrode (12) is driven by a first oscillatory signal (26) and at least one control electrode (14) is driven by a second oscillatory signal (30). In first (38) and second (40) states (36), the second oscillatory signal (30) respectively has a first and second phase with respect to the first oscillatory signal (26). The proximity of an electric-field-influencing media (20) to the proximity sensor (10) is responsive to the difference of third (50) and fourth (52) signals that are respectively measured when the second oscillatory signal (30) is in respective first (38) and second (40) states. The proximity sensor (10) is calibrated with a known capacitance operatively coupled to the sense electrode (12) with a plurality of switches (S1, S2) adapted so that the switches (S1, S2) have a relatively small effect on the capacitance of the sense electrode (12).

Claims

1. A proximity sensor for sensing an electric-field-influencing media within a region of space, comprising:

a. a first electrode, wherein said first electrode is conductive;

b. a first oscillatory signal operatively coupled to said first electrode;

c. at least one second electrode, wherein said at least one second electrode is conductive and said at least one second electrode is separated from said first electrode;

d. a second oscillatory signal operatively coupled to said at least one second electrode, wherein said second oscillatory signal comprises a state, said state is selected from a first state and a second state, when in a first state said second oscillatory signal has a first phase relative to said first oscillatory signal, when in a second state said second oscillatory signal has a second phase relative to said first oscillatory signal;

e. a means for controlling said state of said second oscillatory signal;

f. a means for measuring a third signal from said first electrode when said second oscillatory signal is in said first state;

g. a means for measuring a fourth signal from said first electrode when said second oscillatory signal is in said second state;

h. a means for forming a difference of said third and fourth signals; and

i. a means for generating a measure of proximity of an object to said proximity sensor responsive to said difference.

2. A proximity sensor for sensing an electric-field-influencing media within a region of space as recited in claim 1, wherein said first phase is substantially out-of-phase with respect to said first oscillatory signal, and said second phase is substantially in-phase with said first oscillatory signal.

3. A proximity sensor for sensing an electric-field-influencing media within a region of space as recited in claim 1, wherein said at least one second electrode is located proximate to said first electrode so that an electric field between said first electrode and said at least one second electrode occupies said region of space, wherein said electric field is responsive to said first and second oscillatory signals.

4. A proximity sensor for sensing an electric-field-influencing media within a region of space as recited in claim 1, wherein said at least one second electrode is located outside a periphery of said first electrode.

5. A proximity sensor for sensing an electric-field-influencing media within a region of space as recited in claim 1, wherein said at least one second electrode comprises a plurality of second electrodes at least partially surrounding said first electrode, wherein said plurality of second electrodes are separated from one another.

6. A proximity sensor for sensing an electric-field-influencing media within a region of space as recited in claim 1, wherein said first oscillatory signal comprises an oscillatory voltage, further comprising a voltage divider comprising a capacitor and a terminal of said first electrode wherein one terminal of said capacitor is operatively coupled to said first electrode at a first node, another terminal of said capacitor is operatively coupled to said first oscillatory signal, said third signal is responsive to a voltage at said first node, and said fourth signal is responsive to a voltage at said first node.

7. A proximity sensor for sensing an electric-field-influencing media within a region of space as recited in claim 1, further comprising a means for calibrating said difference.

8. A proximity sensor for sensing an electric-field-influencing media within a region of space as recited in claim 1, further comprising:

a. at least one third electrode at least partially between said first electrode and said at least one second electrode; and

b. a fifth oscillatory signal operatively coupled to said at least one third electrode, wherein said fifth oscillatory signal is substantially in-phase with said first oscillatory signal.

9. A method of sensing the proximity of an electric-field-influencing media within a region of space, comprising:

a. applying a first oscillatory signal to a first electrode;

b. applying a second oscillatory signal to at least one second electrode, wherein said first and second oscillatory signals have a substantially common frequency of oscillation and said second oscillatory signal has a first phase relative to said first oscillatory signal;

c. measuring a third signal from said first electrode, wherein said third signal is responsive to a capacitance of said first electrode;

d. modifying a phase of said second oscillatory signal so that said second oscillatory signal has a second phase relative to said first oscillatory signal;

e. measuring a fourth signal from said first electrode, wherein said fourth signal is responsive to a capacitance of said first electrode;

f. generating a first difference of said third and fourth signals; and

g. generating a measure of proximity of an object to said first electrode responsive to said first difference.

10. A method of sensing the proximity of an electric-field-influencing media within a region of space as recited in claim 9, wherein said first phase is substantially out-of- phase with said first oscillatory signal and said second phase is substantially in-phase with said first oscillatory signal.

11. A method of sensing the proximity of an electric-field-influencing media within a region of space as recited in claim 9, further comprising:

a. operatively connecting a first capacitance to said first electrode;

b. measuring a fifth signal from said first electrode, wherein said fifth signal is responsive to a combination of a capacitance of said first electrode and said first capacitance;

c. operatively disconnecting said first capacitance from said first electrode; and

d. generating a first factor responsive to a second difference of said fifth and third signals and to said first capacitance, wherein said measure of proximity is further responsive to said first factor.

12. A method of sensing the proximity of an electric-field-influencing media within a region of space as recited in claim 11, wherein said first phase is substantially out-of-phase with said first oscillatory signal and said second phase is substantially in-phase with said first oscillatory signal.

13. A method of sensing the proximity of an electric-field-influencing media within a region of space as recited in claim 12, wherein said fifth signal is measured when said second oscillatory signal has said first phase relative to said first oscillatory signal.

14. A method of sensing the proximity of an electric-field-influencing media within a region of space as recited in claim 13, further comprising operatively connecting a second capacitance to said first electrode when said second oscillatory signal has said second phase relative to said first oscillatory signal, wherein said fourth signal is further responsive to said second capacitance and said measure of proximity is further responsive to said second capacitance.

15. A method of sensing the proximity of an electric-field-influencing media within a region of space as recited in claim 12, further comprising operatively connecting a second capacitance to said first electrode when said second oscillatory signal has said second phase relative to said first oscillatory signal, wherein said fourth signal is further responsive to said second capacitance and said measure of proximity is further responsive to said second capacitance.

16. A method of sensing the proximity of an electric-field-influencing media within a region of space as recited in claim 11, wherein said third signal is a third voltage, said fourth signal is a fourth voltage, said fifth signal is a fifth voltage, said first factor comprises a sensitivity factor in units of volts/capacitance, and said measure of proximity comprises said first difference divided by said first factor.

17. A method of sensing the proximity of an electric-field-influencing media within a region of space as recited in claim 11, further comprising operatively connecting a second capacitance to said first electrode when said second oscillatory signal has said second phase relative to said first oscillatory signal, wherein said fourth signal is further responsive to said second capacitance and said measure of proximity is further responsive to said second capacitance.

18. A method of sensing the proximity of an electric-field-influencing media within a region of space as recited in claim 9, further comprising operatively connecting a second capacitance to said first electrode when said second oscillatory signal has said second phase relative to said first oscillatory signal, wherein said fourth signal is further responsive to said second capacitance and said measure of proximity is further responsive to said second capacitance.

19. A method of sensing the proximity of an electric-field-influencing media within a region of space as recited in claim 9, further comprising comparing said measure of proximity with a first threshold and disabling a restraint actuator if said measure of proximity is less than a threshold.

20. A method of sensing the proximity of an electric-field-influencing media within a region of space as recited in claim 9, further comprising calculating an offset as an average of said measure of proximity.

21. A method of sensing the proximity of an electric-field-influencing media within a region of space as recited in claim 20, wherein said average incorporates only those measures of proximity that are both greater than said first threshold and less than a second threshold.

22. A method of sensing the proximity of an electric-field-influencing media within a region of space as recited in claim 20, further comprising:

a. generating a third difference of said offset and said measure of proximity;

b. comparing said third difference with a third threshold; and

c. disabling a restraint actuator if said third difference is greater than said third threshold.

23. A method of sensing the proximity of an electric-field-influencing media within a region of space as recited in claim 20, further comprising comparing said measure of proximity with a fourth threshold, and if said measure exceeds said fourth threshold, updating said offset if a measure responsive to a change in said third signal exceeds a measure responsive to a change in said fourth signal.

24. A method of sensing the proximity of an electric-field-influencing media within a region of space as recited in claim 9, further comprising locating at least one third electrode at least partially between said first electrode and said at least one second electrode and applying a fifth oscillatory signal to at least one third electrode, wherein said at least one fifth oscillatory signal is substantially in-phase with said at least one first oscillatory signal.

25. A method of sensing the proximity of an electric-field-influencing media within a region of space as recited in claim 9, further comprising comparing said measure of proximity with a fourth threshold and if said measure exceeds said fourth threshold, disabling a restraint actuator if a measure responsive to a change in said fourth signal over time exceeds a fifth threshold.

26. A method of operatively coupling adding capacitance to an input of an operational amplifier, comprising:

a. operatively coupling a first terminal of a first switch to a first terminal of a second switch at a second node;

b. operatively coupling a first terminal of a capacitor to said second node;

c. operatively coupling a second terminal of said second switch to a first input of an operational amplifier;

d. operatively coupling one of a second terminal of said capacitor and a second terminal of said first switch to a second input of said operational amplifier;

whereby said operational amplifier acts to substantially null a potential difference between said first and second inputs, and

e. operatively coupling the other of said second terminal of said capacitor and said second terminal of said first switch to a circuit ground, wherein said capacitor has a capacitance between said first and second terminals of said capacitor, wherein when said first switch is closed and said second switch is open, said capacitance is added to said second input of said operational amplifier, and when said first switch is open and said second switch is closed, said capacitance is not added to said second input of said operational amplifier.

27. A method of operatively coupling adding capacitance to an input of an operational amplifier as recited in claim 26, wherein said first and second switches comprise field effect transistors.

28. A method of operatively coupling adding capacitance to an input of an operational amplifier as recited in claim 26, wherein said second terminal of said capacitor is operatively coupled to said second input of said operational amplifier and said second terminal of said first switch is operatively coupled to said circuit ground.

29. A method of operatively coupling adding capacitance to an input of an operational amplifier as recited in claim 26, wherein said second terminal of said first switch is operatively coupled to said second input of said operational amplifier and said second terminal of said capacitor is operatively coupled to said circuit ground.