Switch mechanism limits the stroke of the piston by stopping the piston motor drive. This allows retention of a fluid sample in an automated wet-chemical analysis system

Davis, R. R.

English

NASA Technical Reports Server

Rotating Lead
Screw 
r	
Coil Spring 
Belicrank Lever 
(Motor Stopped)
Spr 
Switch 
Actuatin 
Lever 
Adjusta_ - -
Bellcrank Lever 
(Motor Stopped 
at Last One cc) 
tch Plunger 
an Position) 
Pawl
A
July 1970	 Brief 70-10279 
.	
NASA TECH BRIEF 
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 Clearinghouse for Federal Scientific and Technical 
Information, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Division, NASA, Code UT, Washington, D.C. 20546. 
A Long-Lived Precision Switch Actuator for Controlling 
Pump-Piston Action - 
Last One cc 
of Fluid  
Piston	 '1
Purge Port 
Motor	
Helical Cam 
U Helical Position of Helical Cam	 Cam when Motoris Running
Switci i Actuator 
The problem:	 straints imposed by the pump precluded the use of 
During the development of an automated wet- 	 available switch actuating mechanisms. 
chemical analysis system, it was found desirable to	 The solution: 
retain a sample of the' collected fluid for a subsequent 	 A switch mechanism, shown in the illustration, was 
step in the analysis sequence. A switching mechanism, 	 designed which limited the stroke of the piston by 
compatible with the existing pump mechanism, was 	 stopping the piston motor drive. A cam and lead-
required to control the pump piston action in order	 screw mechanism actuated a "micro" snap switch at 
to acquire the fluid sample. The mechanical con- 	 the proper travel. The fluid sample remaining in the 
(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. 
Motor Switch 
View A-A
https://ntrs.nasa.gov/search.jsp?R=19700000268 2020-03-17T00:18:44+00:00Z
reservoir was then pumped into the sample chamber 
of the analysis system. 
How it's done: 
The operation of an electrical switch to open the 
motor circuit for precise limiting of the pump piston 
is effected by a rotating lead-screw mechanism which 
produces a translatory movement of the pump piston, 
and a cam which rotates with the screw mechanism 
but which also moves along the screw axis for a limited 
portion of the piston translation. Rotation of the 
screw mechanism imparts limited translatory move-
ment to the pawl which engages the cam at a pre-
selected point of the piston translation. The pawl 
shifts the cam into a position so that further rotation 
of the cam causes a bellcrank lever to actuate the 
switch. The switch actuating arm of the bellcrank 
lever is long enough to depress the switch plunger in 
a straight-line action which minimizes plunger wear. 
The plunger is normally held depressed by action of 
an external spring bearing on the actuating arm to 
effect closure of the normally open switch contacts. 
Movement of the actuating arm to depress the switch 
plunger is restricted by an adjustable stop which pre-
vents excessive overtravel of the plunger; this could 
damage the internal operating mechanism of the 
switch. Cam engagement with the other bellcrank arm
offsets the pressure exerted by the external spring and 
allows the switch plunger to be raised by action of the 
internal spring arrangement of the switch to open the 
switch contacts. 
Note: 
Requests for further information may be directed to: 
Technology Utilization Officer 
NASA Pasadena Office 
4800 Oak Grove Drive 
Pasadena, California 91103 
Reference: B70-10279 
Patent status: 
This invention is owned by NASA, and a patent 
application has been filed. Royalty-free, nonexclusive 
licenses for its commercial use will be granted by 
NASA. Inquiries concerning license rights should 
be made to NASA, Code GP, Washington, D.C. 
20546.
Source: Robert R. Davis of
Caltech /J PL
-under contract to

NASA Pasadena Office
(NPO-10757) 
Brief 70-10279	 Category 07


A long-lived precision switch actuator for controlling pump-piston action

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server