Three-cutter machining system for foam-covered tanks incorporates eddy-current sensor. Sensor feeds signal to numerical controller which programs rotational and vertical axes of sensor travel, enabling cutterhead to profile around tank protrusions

Copper, W. P.

English

NASA Technical Reports Server

Note: All Dimensions in
1.30 I
T 
1.75 
0.250
Foam Machining-Tool Cutter Blade, Top and Side Views
December 1975	 B75-10309 
NASA TECH BRIEF S Marshall Space Flight Center 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 2251. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Foam-Machining Tool With Eddy-Current Transducer 
The problem: 
Previous methods of machining large-diameter 
foam-covered tanks depended on a microwave 
transducer to direct machine-tool activity. A micro-
wave transducer, however, is complicated and 
cumbersome to mount on the machine-tool head and 
requires extensive support equipment. Prior foam-
maching tools also require a specially designed 
cutterhead.
The solution: 
A three-cutter machining system incorporates an 
eddy-current sensor. This type of sensor is smaller and 
enables more accurate cuts to be made than 
microwave-based sensors. The eddy-current trans-
ducer feeds a signal to a numerical controller which 
programs the rotational and vertical axes of sensor 
travel, thus enabling the cutterhead to profile around 
tank protrusions. The chips produced are evacuated 
through a hollow spindle. 
(continued overleaf) 
This document was prepared under the sponsorship of the National
	
Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States
	
information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States
	
will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19750000309 2020-03-19T20:15:42+00:00Z
How it's done: 
The multicutters slice a 24-inch (61-cm) bandwidth 
per pass and operate at a maximum of 12 surface feet 
(3.5 m) per minute around a tank measuring 33 feet 
(10 m) in diameter. The sensor is installed in the 
center of the cutter and spindle. A set-vocontroller 
directs the movements of a servomotor which drives a 
ball-screw-and-nut advance/retract mechanism. 
The servosystem is activated by electrohydraulic 
components. A 12-inch (30-cm) double-acting pri-
mary positioning cylinder is controlled by a four-way 
solenoid-actuated valve. A 4-inch (10-cm) double-
acting secondary positioning cylinder moves the 
machining unit into or away from the foam. This 
cylinder is directed via a two-stage flow-control 
servovalve which, in turn, receives its signal from the 
eddy-current sensor. 
The machining head has three hollow spindles. 
Each consists of an aluminum spindle body and a 
hollow steel shaft with ball bearings pressed into the 
spindle bodies. The spindles are alined vertically in 
the cutter mechanism. 
The sensor operates via eddy-current loss. A bridge 
circuit is activated by a 1-MHz carrier signal. Two 
arms of the bridge (two coils) comprise the 
transducer. Magnetic-flux lines emanating from the
transducer pass into the conductive surface being 
sensed and produce eddy currents. As the conductive 
surface moves closer (or further away) the transducer 
eddy-current loss increases or decreases accordingly. 
Sensed impedance variations are converted to a dc 
voltage proportional to the distance being sensed. 
Note: 
Requests for further information may be made in 
writing to: 
Technology Utilization Officer 
Marshall Space Flight Center 
Code ATO1 
Marshall Space Flight Center, Alabama 35812 
Reference: B75-10309 
Patent status: 
Inquiries concerning rights for the commercial use 
of this invention should be addressed to: 
Patent Counsel 
Marshall Space Flight Center 
Code CCO1 
Marshall Space Flight Center, Alabama 35812 
Source: W. P. Coppferof
Martin Marietta Corp.

(MFS-23298)
. 
. 
Categories: 08 (Fabrication Technology) 
B75-10309	 02 (Electronics Systems)


Foam-machining tool with eddy-current transducer

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