US 6,445,294 B1Granted

Proximity sensor

AssigneeAutomotive Systems Laboratory, Inc.

InventorsJudson G. McDonnell, James G. Stanley

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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).

Claims29

Dependent claims

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.

7 more elements

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.

5 more elements

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.

3 more elements

Dependencies are inferred from the claim text.

Facts

Application: 09/616,406Filed 14 Jul 2000 · us provisional application
Priority: 15 Jul 1999
Granted: 3 Sep 2002
Term ends: Not estimatedThe source records don’t support an estimate.

Classification18 codes

B60R 21/015
Electrical circuits for triggering passive safety arrangements, e.g. airbags, safety belt tighteners, in case of vehicle accidents or impending…:…
B60N 2/0021
Seats provided with an occupancy detection means mounted therein or thereon: characterised by the type of sensor or measurement
B60N 2/28
For children: seats readily mountable on, and dismountable from, existing seats or other parts of the vehicle
B60N 2/286
Characterised by the peculiar orientation of the child: forward facing