Driven shielding capacitive proximity sensor

• US RE36,772 E
• Filed: 11/06/1996
• Issued: 07/11/2000
• Est. Priority Date: 06/06/1991
• Status: Expired due to Term

• Current Assignee: United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration
• Original Assignee: United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration
• Inventors: McConnell, Robert L., Vranish, John M.
• Primary Examiner(s): Horabik, Michael
• Assistant Examiner(s): Edwards, Jr., Timothy
• Application Number:
  US08/999,976
• Time in Patent Office: 1,343 Days
• US Class Current: 340/870.37
• CPC Class Codes: B25J 13/087 for sensing other physical parameters, e.g. electrical or chemical properties
• CPC Class Codes: B25J 19/06 Safety devices

Abstract

A capacitive proximity sensing element, backed by a reflector driven at the same voltage as and in phase with the sensor, is used to reflect the field lines away from a grounded robot arm towards an intruding object, thus dramatically increasing the sensor'"'"'s range and sensitivity.

Claims

1. A capacitive type proximity sensor having improved range and sensitivity between a machine and an intruding object in the immediate vicinity of the machine, comprising:

an outer electrical conductor on said machine forming one electrode of a sensor capacitor, .[.the.]. .Iadd.an .Iaddend.other electrode comprising said .Iadd.intruding .Iaddend.object, said outer .Iadd.electrical .Iaddend.conductor comprising a first thin sheet of conductive material;

an intermediate electrical conductor located between said outer .Iadd.electrical .Iaddend.conductor and said machine and being of a size substantially larger than said outer .Iadd.electrical .Iaddend.conductor to act as a shield for reducing the parasitic capacitance between said outer .Iadd.electrical .Iaddend.conductor and said machine, said intermediate .Iadd.electrical .Iaddend.conductor comprising a second thin sheet of conductive material substantially wider than said .[.first.]. .Iadd.outer electrical .Iaddend.conductor;

said outer and intermediate conductors attached to a surface on said machine .[.with no gap between the conductors.]. .Iadd.wherein said conductors are spaced apart in substantially overlapping parallel fashion, .Iaddend.and no gap between said surface and said intermediate conductor and .[.said outer and intermediate conductors coplanar with each other.]. and said surface of said machine, said surface of said machine acting as a ground plane.Iadd., with said intermediate electrical conductor and said surface of said machine spaced apart in substantially overlapping parallel fashion.Iaddend.;

first circuit means for coupling in phase the instantaneous voltage at said outer electrical conductor to said intermediate electrical conductor;

second circuit means coupled to said outer .Iadd.electrical .Iaddend.conductor and being responsive to the capacitance of said sensor capacitor for generating a control signal to said machine.

2. The sensor of claim 1 wherein said first circuit means comprises a voltage follower circuit comprised of an operational amplifier.

3. The sensor of claim 2 wherein said second circuit means comprises a signal generator having an output signal indicative of the capacitance of said sensor capacitor.

4. The sensor of claim 3 wherein said signal generator comprises a variable frequency oscillator.

5. The sensor of claim 1 wherein said machine comprises a robotic apparatus.

6. The sensor of claim 5 wherein said robotic apparatus comprises a movable member of said robotic apparatus.

7. The sensor of claim 6 wherein said movable member comprises an articulated member.

8. The sensor of claim 7 wherein said articulated member comprises a robotic arm.