(UNTITLED)

• Document Type: CREST
• Collection: NGA Records (Formerly NIMA)
• Document Number (FOIA) /ESDN (CREST): CIA-RDP78B04747A000500020005-7
• Release Decision: RIPPUB
• Original Classification: K
• Document Page Count: 9
• Document Creation Date: December 28, 2016
• Document Release Date: March 26, 2001
• Sequence Number: 5
• Content Type: REPORT

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Ground glass surfaces have long been used as screens upon which
optical images are displayed, particularly for back-projection devices.
The choice of grain size for the ground glass surface has always been the
result of a judicious compromise. The grain of the glass limits the
resolution of the image approximately to the dimensions of the grain.
As the grain of the screen is reduced in an attempt to improve image
resolution. the apparent brightness of the image decreases rapidly as the
viewing angle departs from the axis.
Introduction'
It has recently been demonstrated that the effect of grain size
on limits of resolution can be reduced by a substantial degree by impart-
ing a vibratory motion to the glass in the plane normal to the projection
axis. This, in effect, randomises the grain, and yields resolution
presumably determined by the statistics of screen brightness at any given
element of area over a period related to retinal image persistence. Grain
effect can be minimized further by using a double-layer screen, with the
ground surfaces in juxtaposition, and with the interface filled with a
suitable liquid of index of refraction similar to that of the glass.
Technical Reouirements
A device designed to exploit the phenomena discussed above must
provide: (1) a flexible mount that permits the screen to move freely in
the "Z,T" plane, but restricts motion along the "2" axis, (2) a drive
of adequate power to transmit the desired pattern of oscillation to the
flexibly mounted screen, and, (3) a method of retaining the mounting
liquid in place between the screens. The latter requirement may become
a serious problem for large, vertically mounted screens. Capillarity
can support a film only a few centimeters in height, and the small enclosed
volume in the thin film will result in a substantial change in film
height for small amounts of leakage= bag* of gasksting. Furthermore,
the hydrostatic fortes on. large, flat screen will result in a bowing
od &b. ggrgeD surface that may readily become significant if the clearance
between the stationary and oscillating surfaces is a matter for close
tolerances.
Declass Review by NIMA/DOD
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Proposed Design
1, Mount,
It is proposed to mount the vibrating screen upon 'hairpin"
springs that, with the screen, are mechanically resonant at the desired
oscillator frequencies. The spring mounts will be designed with two
preferred modes of oscillation and with the resonant frequencies related
to each other by a substantially incommensurate ratio that is approxi-
mately 3:4. This will result in a trace, for any point on the screen,
represented by a Lissajous figure of long period. The preferred modes
will be oriented at substantially right angles to each other, and
parallel to the vibratory motions of the drives described below. The
mounting hardware is schematically represented in Figure I.
.2. Drive
The drives will be solenoid motors actuated by variable-frequency
audio oscillators of power adequate to secure the desired amplitude.
Figura II illustrates the principles of the motor drive and linkages.
The oscillators will be tuned to the resonant frequencies of the mechanical
system to which they are coupled. The frequencies will be adjusted to
be well above the flicker fusion frequency of the retina but below those
at which auditory acuity is high. It is believed that frequencies between
30 and 60 cycles per second will be appropriate.
The power required to drive the screen may be considerable.
Despite the low amplitude and low frequency of the oscillatory motion,
the thinness of the fluid film results in high sheer gradients and sub-
stantial viscous drag. for a filling liquid comparable to a very light
lubricating oil, viscous losses in the oil will be about 40 watts ini-
tially, although the resultant heating of the oil will lead to lowered
viscosity and reduced drag during long-term operation.
The filling liquid may be chosen with lower viscosity, but the
lack of lubricity of the low-viscosity liquid may well result in glass-
to?glass friction losses as large as, or larger than, the fluid friction
losses in a light lubricating oil.
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3. Seal
It is proposed to seal the stationary screen to the projector
frame with a thick joint of room-temperature vulcanizing silicone rubber.
This will permit expansion and contraction of the screen or frame with-
out breaking the seal or crushing the glass. Such rubber is highly resis-
tant to many types of oils and to atmospheric checking and cracking.
The oscillating screen will be sealed along the two sides and
the bottom by a pneumatic gasket inflated to a pressure somewhat in excess
of the maximum hydrostatic pressure of the liquid between the screens.
Pressure will be maintained in the gasket by connection to a suitable
reservoir. A small liquid carbon dioxide cylinder, connected through a
diaphragm reducing valve set for the desired pressure, would provide a
reservoir with greatly reduced service demands. The gasket is made from
a length of laboratory tubing, and can be replaced readily when necessary.
As shown in Figure III (inset), a small reservoir is provided in a trough
at the upper margin of the screen. This provides for small amounts of
leakage, thermal expansion, or screen sag without the liquid level drop-
ping to leave a meniscus in the field of view.
On a screen 30 inches square,with a liquid fill having a specific
gravity of 0.8, the total hydrostatic force on each screen is over 300
pounds. This will result in some bowing of the screen, with an increase
in the front-to-back screen separation. This bowing may be controlled to
any required degree by a suitable combination of increased screen thick-
ness and pre-shaping the screen surfaces so that, in their stressed condi-
tion, they are closely enough planar. In the absence of data on the
permitted tolerance on screen separation, present design and cost estimates
are based on a maximum separation of the two ground glass surfaces of not
over 0.3 mm.
Optimization
No funding is provided in this estimate for "human engineering"
studies to determine the optimum design characteristics of the liquid-
filled, double-ground glass, viewing screen system. Neither is time
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included for adjustments or modifications of the instrument in connection
with human engineering studies of the sponsor. Should the sponsor desire
such services a proposal to conduct them will be submitted on request.
Time Schedules
The proposed design and modifications are estimated to required
sixty to seventy-five days for completion following authorization to
proceed. The power requirements for the solenoid motors (not less than
twenty-five watt each) will probably require custom design and manu-
facture of the motors. This will involve a delivery estimated to be
from four to six weeks, and the time estimate given is contingent upon
our ability to secure such delivery.
No difficulty is anticipated in obtaining promptly the other
components involved. Machine and assembly time are estimated to require
an additional week per unit as compared to the stationary screen model,
but this will overlap the delivery time on the solenoids.
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