Driven Shielding Capacitive Proximity Sensor - the "Capaciflector"
Robotic manufacturing and security applications on Earth can get a boost
in precision and sensitivity from the "Capaciflector," a capacitive
proximity sensor originally developed to prevent space robots from colliding
with humans and spaceborne structures. Simple, versatile, and inexpensive
to manufacture, the sensor offers unmatched accuracy and the ability to
detect objects more than 12 inches away.
The invention is a robotic arm proximity sensing skin made of a capacitive
sensing element and backed by a reflector driven at the same voltage as,
and in phase with, the sensing element. Its exceptional range and sensitivity
stem from an ability to reflect electric field lines of the sensor capacitor
away from the grounded robot arm toward an oncoming object. Several sensors
can be packed in immediate proximity to each other without crosstalk, which
takes them to new dimensions in capabilities.
In addition to the devices' utility for collision avoidance, circuitry modifications
now allow them to be used for precision assembly. Sensors have been embedded
in robot grippers and power tools as well as screw tips that can be driven
into holes at clearances of three thousandths of an inch without contact.
Such an ultra-soft touch is immensely valuable in space assembly, where
the slightest contact by the robot may send an object careening away.
By virtue of this new precision, Johnson Space Center engineers have begun
Capaciflectors for future use in space station assembly and maintenance.
The sensors also were installed in Goddard's Robot-Operated Materials Processing
System (ROMPS) robot, and validated in flight during 1994.
Several commercial uses, including automotive safety, heavy machinery safety
and closed-loop control and robotic obstacle detection, are being considered.
Space application of the sensor has been validated, with custom electronics
and sensors developed for the ROMPS flight experiment
It is envisioned that a wide range of other spinoffs for the Capaciflector,
such as automated maintenance and welding, mechatronic control of magnetically-powered
devices, and semiconductor inspection. They could be attached to paintings
in art galleries to detect tampering or theft; incorporated into safes and
cash boxes or doors and windows of private homes for burglary prevention;
embedded into machinery to issue warning or shut down if people get dangerously
close; or used to open and close elevator doors.
Point of contact:
John Vranish
Goddard Space Flight Center
Greenbelt, M D20771
301-286-2431
John.Vranish@ccmime.gsfc.nasa.gov
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Maintained by: Dave Lavery
Last updated: May 10, 1996