Fluidic gap gauge

A split-ring hermetically sealed pressure enclosure is positioned around a ap formed between a shell body and base plate of a projectile for the purpose of measuring an unknown gap volume and comparing it to a standard acceptable volume. The system utilizes a gauging system which pressurizes both the known volume of the standard volume and unknown volume of the test body simultaneously and then measures the rate at which each volume is depleted. Fluidic sensing, amplifying, and gating systems are utilized for generating an output signal responsive to comparative pressure rate changes of both standard and test volumes. The output signal is used to operate a visual, biased, no-go, go pneumatic indicator.

BACKGROUND OF THE INVENTION 
Various means have been used in the past to determine whether the gap 
between the shell body and the base plate of a projectile is excessive. It 
has been determined that under certain firing conditions assembly pins 
holding parts together are sheared and the base plate driven forward 
against the shell body. This movement, in turn, drives the fuze mechanisms 
and charges in the shell body forward, and on occasion has caused 
premature, in-bore detonation of the shell, with resultant catastrophic 
effect on the launch weapon and the gun firing crew. 
In order to accurately measure the gap between the shell body and the base 
plate, the prior art utilized inspection techniques consisting of manually 
checking the periphery of the body-base joint with a feeler type hand held 
gauge. This method has been found to be unacceptable due to an inability 
to measure all types of out of tolerance conditions. This difficulty in 
determining out of tolerance gap distances is particularly prevalent in 
the instance where the rim of the base plate is thicker than the inner 
portion. In such circumstances a "no-go" feeler gauge used to measure the 
gap would indicate a "good" assembly, while in fact the assembly would be 
out of tolerance and probably hazardous to fire. In addition, the feeler 
gauge method has been found to be unreliable as a means for accurately 
measuring a gap in a projectile assembly because it was always dependent 
upon a subjective human response which could vary from person to person 
and from one time to another. 
SUMMARY OF THE INVENTION 
The present invention relates to a gauging system which utilizes a volume 
measuring technique to determine an average gap size upon which the gap 
size of a body-base interface geometry of a projectile assembly is either 
accepted or rejected. The present device comprises a split ring inclosing 
and sealing means for creating a volume around the body-base interface of 
a test projectile which is simultaneously pressurized along with a 
standard volume. The residual pressure of both volumes is compared by a 
fluidic amplifying, gating and indicating circuit to give a visual "go" 
signal for a test assembly which is less than a predetermined average gap 
size and a "no-go" signal for a test assembly which is greater than the 
predetermined average gap size. 
An object of the present invention is to provide a fluidic gap sensor for 
testing the acceptability of a body-base gap interface of a projectile. 
Another object of the present invention is to provide a fluidic gap sensor 
for accurately measuring the gap between the shell body and the base plate 
of a base dispensing type of projectile. 
Another object of the present invention is to provide a fluidic gap sensor 
for reliably checking the size of the gap around the periphery of a 
body-base joint of a projectile without being dependent upon the manual 
use of a feeler gauge. 
A further object of the present invention is to provide a fluidic gap 
sensor which is independent of the shell body-base interface geometry and 
utilizes a volume measuring system which indicates whether the test 
specimen meets a predetermined average gap size. 
For a better understanding of the present invention, together with other 
and further objects thereof, reference is made to the following 
descriptions taken in connection with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to FIGS. 1-3, these drawings illustrate a shell body 10 
separated from a shell base plate 12 by an unwanted gap .alpha.. FIG. 2 
shows the condition where the rim 14 of the shoulder 16 of the base plate 
12 is thinner than the inside section of the shoulder. In this case, a 
"no-go" feeler gauge could enter gap .alpha. and if the gap is within 
allowable tolerance the projectile could be properly assembled using these 
parts. In the aforementioned case, the inspector would have to determine 
if the gauge passed completely across shell body wall 10, indicating a 
"bad" assembly or stopped at some point radially outward, indicating a 
"good" assembly. The feeler gauge inserted in the gap would be marked for 
maximum permissible penetration and a judgement made as to the 
acceptability of the assembly. FIG. 3 shows an out of tolerance condition 
that cannot be adequately measured by a prior art feeler type gauge. In 
this latter case, the outer rim 18 of the base plate shoulder 20 is 
thicker than the inner section of the shoulder, resulting in a gap as 
illustrated. Under this latter gap condition a "no-go" feeler gauge used 
to measure the gap .alpha. would indicate a "good" assembly, while in fact 
the assembly would be out of tolerance and the projectile hazardous to 
fire. 
Referring now to diagramatic view of the system in FIG. 4, the present 
invention utilizes a volume measuring system to determine the average gap 
size upon which the assembly will be accepted or rejected. A split-ring 
pressure enclosure 22 hermetically seals a volume circumferentially around 
the shell body-base plate interface gap .alpha., as shown in FIGS. 1-3, of 
the projectile 24. A pneumatic input line 26 is connected from the 
split-ring enclosure 22 to a pneumatic supply source 28 through a four-way 
six-ported manually controlled valve 30 and through a first unidirectional 
valve check 32. A pneumatic output line 34 from the split-ring enclosure 
22 is connected to and utilized as an input to a first control port 35 of 
a first proportional pneumatic amplifier 36. A first variable restriction 
38 is pneumatically connected to pneumatic line 34 at junction point 40 
and is used to vent gases to the atmosphere and for balancing the system 
pneumatically during initial set-up. A reference volume 42 is similarly 
pneumatically connected via pneumatic input line 44 to the pneumatic power 
supply 28 through the manual control valve 30 and through a series 
connected second unidirectional check valve 46. Check valves 32 and 46 
each guarantee gas supply flow in one direction only. Output line 48 
pneumatically connects the reference volume 42 to a second control port 37 
of the first fluidic proportional amplifier 36. A second variable 
restriction 50 is pneumatically connected to pneumatic line 48 at junction 
point 52 and is included in pneumatic line 48 for the purpose of 
pneumatically balancing the system during initial set-up conditions. The 
dual outputs of the first proportional amplifier 36 are connected to first 
and second control ports 54 and 56 respectively of the second proportional 
amplifier 58 via pneumatic lines 60 and 62 respectively. The output signal 
from signal output side 55 of the second fluidic proportional amplifier 58 
is pneumatically connected to the control input port 64 of the fluidic 
Schmitt Trigger network 66 via pneumatic line 68. The output of Schmitt 
Trigger 66 is pneumatically connected to the control port 70 of a 
geometrically biased fluidic bi-stable gate 72 via pneumatic line 74. The 
output of the biased bi-stable pneumatic gate 72 is pneumatically 
connected to a pneumatic indicator 76 via pneumatic line 78. Fluidic power 
is supplied from the pneumatic supply source 28 to the first and second 
proportional amplifiers 36 and 58 respectively, the Schmitt trigger 
network 66, and to the bi-stable pneumatic gate 72 by a pneumatic line 80 
through series connected fluidic variable restrictions 82, 84, 86 and 88 
respectively. Third, fourth, fifth and sixth variable restrictions 82, 84, 
86 and 88 respectively are utilized to adjust the supply pressure to the 
input supply lines 83, 85, 87 and 89 of the first and second proportional 
amplifiers, Schmitt Trigger, and bi-stable gate 36, 58, 66 and 72 
respectively. 
In operation, once the pneumatic power supply is initiated, the first and 
second fluidic proportional amplifiers 36 and 58 respectively, the Schmitt 
Trigger network 66, and the bi-stable gate 72 are brought up to operating 
power. The bi-stable gate 72 is geometrically normally biased so that when 
fluidic power is applied through restriction 88, its initial output is 
always in a given "off" state indicated by a + sign and the pneumatic 
indicator 76 in an "off" position visually indicating a "good" assembly. 
The split-ring enclosure 22 is then assembled around the projectile 24 and 
clamped in place. To initiate the test an operator depresses push button 
90 of valve 30 causing the supply pressure to charge up the body-base gap 
volume as well as the reference volume 42 to the same pressure. The 
pneumatic lines 34 and 48 under this initial charging condition are at the 
same pressure, and the pressures in the output pneumatic lines 60 and 62 
of the first proportional amplifier are therefore also equal. This makes 
the pressure in the output line 68 from the second fluidic proportional 
amplifier 58 less than that necessary to switch the Schmitt Trigger 
network 66. As a result, the pressure in the pneumatic line 74, to the 
bi-stable gate 72, is zero and the bi-stable gate 72 remains in its 
initial state. When the opeator releases push button 90 on valve 30, the 
supply pressure gas source 28 is removed from the body-base gap volume 
contained within split-ring enclosure 22 and from the reference volume 42. 
These two volumes than start to bleed down, from their higher than ambient 
pressure, to atmospheric pressure through the first and second control 
ports 35 and 37 respectively of the first fluidic proportional amplifier 
36. Since both the volume contained within the split-ring enclosure 22 and 
the volume in the reference volume 42 are charged to the same pressure, 
the volume that is greater will bleed down to atmospheric pressure more 
slowly than the smaller volume. This results in a pressure differential 
between pneumatic lines 34 and 48. If the body-base gap volume is larger 
than the preselected reference volume 42 the pressure in line 34 will be 
greater than that in line 48. This difference in pressure is reflected in 
the signal outputs from the first fluidic proportional amplifier 36, such 
that the pressure in pneumatic line 62 will be greater than the pressure 
in pneumatic line 60. This differential in pressure than causes the second 
fluidic proportional amplifier 58 to switch and in turn provide a higher 
than normal pressure to the Schmitt Trigger network 66 via pneumatic line 
68. This higher than normal pressure in pneumatic line 68, which is 
connected to the control input of the Schmitt Trigger 66, switches the 
Schmitt Trigger network 66 from an off position to an on position 
generating a pneumatic signal over pneumatic line 74 which causes 
bi-stable gate 72 to move from its initial "off" condition to the opposite 
output leg driving the fluidic indicator 76 via pneumatic line 78 to show 
a visual signal which indicates a "bad" assembly. 
In the event that the shell body-base plate gap volume is less than that of 
the reference volume 42 the pressure in line 48 will be greater than that 
in line 34. This volume difference will cause the pressure in pneumatic 
line 60 to be greater than that in pneumatic line 62. This differential 
pressure presented to the control ports of the first fluidic proportional 
amplifier 36 drives the output from the second fluidic proportional 
amplifier 58 toward the vented output side 92. Under these conditions, 
since no signal is given to the Schmitt Trigger network 66, via pneumatic 
line 68, the fluidic indicator 76 remains in the initial state or "off" 
position indicating a "good" projectile assembly. 
All fluidic components of the system can be separate as shown in FIG. 4, or 
can be mounted directly to the split-ring enclosure 22 for compactness in 
order to reduce line losses. In addition, since the two fluidic 
proportional amplifiers 36 and 58 only perform an amplification function, 
they could be replaced by a single multi-stage fluidic proportional gain 
block. A further modification of the circuit shown in FIG. 4 may have 
balancing restrictions 38 and 50 included in series with pneumatic lines 
34 and 48 respectively leading into the first and second control ports 35 
and 37 respectively of the first fluidic proportional amplifier 36, to 
eliminate the two vents to the atmosphere. Finally, the circuit may be 
modified to include a manual reset control to reset the bi-stable gating 
device 72 to its initial "off" state after experiencing a "bad" assembly. 
While there has been described and illustrated specific embodiments of the 
invention, it will be obvious that various changes, modifications and 
additions can be made herein without departing from the field of the 
invention which should be limited only by the scope of the appended 
claims.