Capaciflector-guided mechanisms

• US 5,539,292 A
• Filed: 11/28/1994
• Issued: 07/23/1996
• Est. Priority Date: 11/28/1994
• Status: Expired due to Term

• Current Assignee: The United States of America As Represented By The Secretary of Agriculture
• Original Assignee: United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration
• Inventors: Vranish, John M.
• Primary Examiner(s): Wysocki, Jonathan
• Application Number:
  US08/346,593
• Time in Patent Office: 603 Days
• Field of Search: 318/568.1, 318/562.11, 318/568.16, 318/568.21, 318/570, 340/870.37, 340/562, 901/23, 901/31, 901/35, 901/36, 901/38, 901/46, 324/686, 324/687, 324/690, 324/600, 324/601, 361/179, 361/101, 364/424.37, 364/482
• US Class Current: 318/568.21
• CPC Class Codes: B25J 13/086 Proximity sensors
• CPC Class Codes: B25J 9/1612 characterised by the hand, wrist, grip control
• CPC Class Codes: G05B 2219/37284 Capacitive 3-D proximity sensor
• CPC Class Codes: G05B 2219/40082 Docking, align object on end effector with target
• CPC Class Codes: G05B 2219/40087 Align hand on workpiece to pick up workpiece, peg and hole

Abstract

A plurality of capaciflector proximity sensors, one or more of which may be overlaid on each other, and at least one shield are mounted on a device guided by a robot so as to "see" a designated surface, hole or raised portion of an object, for example, in three dimensions. Individual current-measuring voltage follower circuits interface the sensors and shield to a common AC signal source. As the device approaches the object, the sensors respond by a change in the currents therethrough. The currents are detected by the respective current-measuring voltage follower circuits with the outputs thereof being fed to a robot controller. The device is caused to move under robot control in a predetermined pattern over the object while directly referencing each other without any offsets, whereupon by a process of minimization of the sensed currents, the device is dithered or "wiggled" into position for a soft touchdown or contact without any prior contact with the object.

Claims

1. A system for guiding a piece of apparatus into relationship with another piece of apparatus, comprising:

robotic means for guiding a device into position relative to an object;

means for controlling said robotic means;

a device attached to said robotic means and including at least one capaciflector type proximity sensor affixed thereto for sensing an object coming into relatively close proximity therewith;

said capaciflector type proximity sensor including,

at least one outer electrical conductor on a surface of said device and forming one electrode of a sensor capacitor, the other electrode of said sensor capacitor comprising said object,

an intermediate electrical conductor located between said at least one outer conductor and said surface and being of a size larger than said at least one outer conductor to act as a shield for reducing the parasitic capacitance between said outer conductor and said surface,

said intermediate conductor and said outer conductor mutually overlaying each other,

said at least one outer conductor and said intermediate conductor further being located on said surface with no air gap therebetween and no air gap between said intermediate conductor and said surface, and wherein said surface acts as a surface of reference potential or a ground plane;

an AC voltage source; and

circuit means coupled between said AC voltage source and said at least one outer and intermediate conductors for coupling a same voltage from said voltage source to said outer electrical conductor and said intermediate electrical conductor, said circuit means being responsive to the change in capacitance of said sensor for generating an output signal, said output signal being coupled to said means for controlling said robotic means, and

wherein said means for controlling generates control signals for controlling said robotic means to move said device in an operational mode whereby said robotic means guides said device to a predetermined location on said object and moves said device in a predetermined scan pattern over said location, whereby since electrical charge slides along the surface of a conductor the charge thereat induces an equal but opposite charge on an opposing member these charges collect at the point nearest each other, thereby referencing each other without any offset, and by a process of signal minimization of said output signals which are generated in response to a capacitance verses distance characteristic of said sensor, said device is moved in ever decreasing translational increments by said robotic means into position for making contact with said object without any prior undesired contact or collision therewith.

2. A system according to claim 1 wherein said at least one outer conductor and said intermediate conductor are comprised of relatively thin strips of conductor material.

3. A system according to claim 1 wherein said at least one outer conductor comprises at least two overlaid and mutually insulated outer conductors of different sizes.

4. A system according to claim 3 wherein said at least two outer conductors and said intermediate conductors are comprised of relatively thin strips of conductive material.

5. A system according to claim 1 wherein said at least one outer conductor comprises a plurality of outer conductors, each being located on a mutually different surface of said device.

6. A system according to claim 5 wherein said plurality of outer conductors comprises at least two outer conductors respectively located on two separate mutually orthogonal surfaces of said device.

7. A system according to claim 5 wherein said plurality of outer conductors comprises at least three outer conductors respectively located on three mutually intersecting surfaces of said device.

8. A system according to claim 1 wherein said circuit means includes means for sensing a current in said at least one outer conductor.

9. A system according to claim 8 wherein said means for sensing current comprises a current-measuring voltage follower circuit means.

10. A system according to claim 9 wherein said current-measuring voltage follower circuit means includes a current sensing resistor and wherein the voltage across said resistor comprises said output voltage.

11. A system according to claim 1 wherein said circuit means comprises respective current sensing voltage follower circuit coupled between said AC voltage source and at least one outer conductor and said intermediate conductor.

12. A system according to claim 1 wherein said device comprises a gripper mechanism.

13. A system according to claim 12 wherein said gripper mechanism includes a pair of opposing gripper members having a plurality of capaciflector type proximity sensors mounted thereon for sensing said object in three dimensions for generating a 3-D image.

14. A system according to claim 1 wherein said device comprises a tool for engaging said object, said object comprising a piece of hardware.

15. A system according to claim 14 wherein said tool comprises a screw driving tool having a plurality of capaciflector type proximity sensors mounted thereon for sensing said piece of hardware and any surfaces and objects in relatively close proximity thereto.

16. A system according to claim 1 wherein said device comprises an alignment pin having at least one capaciflector type proximity sensor mounted thereon for sensing and mating with a hole in said object.