Photosensors maintain electrode-to-joint alignment in automatic precision arc welding. They detect the presence and relative position of a joint to be welded and actuate a servomechanism to guide the welding head accordingly thus permitting alignment for more than straight line or true circle joints

Bowen, J. B.

English

NASA Technical Reports Server

December 1965
	
Brief 65-10401 
NASA TECH BRIEF 
_& 
NASA Tech Briefs are issued by the Technology Utilization Division to summarize specific 
technical innovations derived from the space program. Copies are available to the public from 
the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia, 22151. 
Photosensors Used to Maintain Welding Electrode-to-Joint Alignment 
Right 
Transistorized 
I	 Lines of Photo-Sensors 
I	
Perception 
Amplifier 
The problem: Normally, in automatic precision 
arc welding, electrode-to-joint alignment is feasible 
only for straight line or true circle joints. Other pat-
terns require template control involving the problems 
of dimensional differences between hardware and tem-
plate in addition to mechanical linkage tolerances 
between template and welding head. 
The solution: A system that uses photosensors to 
detect the presence and relative position of a joint to 
be welded and actuates a servomechanism to guide the 
welding head accordingly.
How it's done: The device controls the direction of 
a welding setup that incorporates automatic electrode 
feed and travel. With the apparatus in place to begin 
the welding process, the system optics package is cen-
tered over the joint to be welded. The light source 
beam is transferred by the optics in a plane normal to 
the joint and reflected back to the optics so that the 
reflected light impinges on two photodiodes. Each 
photodiode is connected to a transistorized amplifier 
driving a servomotor that is connected to the system 
carriage. Output voltage to the motors controlled by 
(continued overleaf) 
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the sensors is originally equalized by tuning poten-
tiometers provided in the amplifier circuits so that the 
opposed servomotors are mutually stalled, maintain-
ing the welding head in position, centered above the 
joint. If the joint changes direction so that the joint 
moves beneath one of the sensors, light reflected-to 
that sensor drops off, output voltage to the servo-
motor associated with it is reduced, the opposed servo-
motor drives the welding head laterally in the direction 
that restores the joint between the sensors, restoring 
the original voltage to the affected sensor and restor-
ing equilibrium between the drive motors. The lead 
distance from sensors to welding head is adjusted to 
coincide with servomechanism response time related 
to welding speed. 
Notes: 
1. This method would be adyantageous in situations 
requiring precision welding with high reliability, 
especially where weld penetration must be closely 
controlled.
2. This innovation represents a considerable saving 
in setup time over previous methods involving the 
use of templates and mechanical linkages. 
3. Inquiries concerning this invention may be di-
rected to: 
Technology Utilization Officer 
Manned Spacecraft Center 
P.O. Box 1537 
Houston, Texas, 77001 
Reference: B65-10401 
Patent status: NASA encourages the immediate 
commercial use of this invention. Inquiries about 
obtaining rights for its commercial use may be made 
to NASA, Code AGP, Washington, D.C., .20546. 
Source: Joseph B. Bowen of 
North American Aviation, 
under contract to 
Manned Spacecraft Center 
(MSC-243) 
Brief 65-10401	 Category 05


Photosensors used to maintain welding electrode-to-joint alignment

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