SPEED LETTER

• Document Type: CREST
• Collection: NGA Records (Formerly NIMA)
• Document Number (FOIA) /ESDN (CREST): CIA-RDP78B04747A003000040012-2
• Release Decision: RIPPUB
• Original Classification: S
• Document Page Count: 11
• Document Creation Date: December 28, 2016
• Document Release Date: January 16, 2003
• Sequence Number: 12
• Publication Date: February 7, 1967
• Content Type: FORM

Approved For Release 2003/01/28: CIA-RDP78B04747A_0
SECRET
(When Filled In)
SPEED LETTER
/-4, c--o
FROM:
J/7/
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DATE
10 Feb. 67
The subject matter of this patent application is not classified.
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FORM
5-61 1831
SECRET
Declass Review by NIMA / DoD.
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Pte. N, cc
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 Approved For&ease 2003/01/28: CIA-RDP78BO474 03000040012-2
MEANS TO nETECT AMOUNT AND nIRECTION OF
SHAFT ROTATION
This invention relates to means to detect amount
and direction of shaft rotation using polarized light.
There are many instances were it is desirable to
detect and provide an electrical output proportional
to.the relative rotation of two shafts or the
rotation of one shaft with relation to a fixed index.
The devices of the prior art of the synchro type
or of the type generating a series of pulses to be
counted, both of which are expensive and bulky.
The present invention provides means to detect
the amount and direction of shaft rotation with a
minimum of apparats which may be extremely light
weight.
In the present invention, the first polarization
means is mounted on one shaft. The polarization means
has a first area for instance, a center area of one
polarization and an outer ring of a polarization
displaced 900, the two portions baing'fixed together.
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 Approved For=ease 2003101/28: CIA-RDP78B04747AQ0300004001'2 2;
Light is passed through both areas and then through
a second polarizing plate of a single, polarization.
Behind the second polarizing plate are moun.,two
photocell pickups, one to receive light from the first
area and the second to receive light from the second
area. The elements of the first polarizing means are
adjusted so that equal light is passed through said
areas, then if the first shaft is rotated in one
direction, one photoelectric pickup will receive more
light and the second photoelectric pickup will receive
less light and vice versa.
The amount of light difference is directly
proportional to the amount of angular rotation.
Another embodiment of the invention is also
shown wherein the first polarization plate is on
a single polarization and the separate polarization
is provided by 4-separate half wave plate.
Accordingly, a principal object of.the inven'ti'on'l
is to provide new and improved means to detect direction
and amount of angular rotation.
Another object of the invention is to provide new
and improved means to detect direction and amount of
angular rotation using polarization light means.
Another object of the invention is to provido new
and improved light means for detecting angular rotation
comprising means on a rotatable shaft providing two
areas of different polarization and polarization sensitive
means to detect the light received from these two areas.
Another object of the invention is to provide now
and improved polarizing ss#ght means for detecting relative
rotation of two rotatable shafts.
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 Approved ForUlease 2003/01/28 CIA-RDP78BO474 p03000040012-2
Another object of the invention is to provide now
and improved means to detect direction and amount of
shaft rotation comprising, first polarization means
mounted on a rotatable shaft, said polarization means
having a first area of a first polarization and a
second area of a second polarization at 90? to said
first polarization, a source of light mounted on one
side of said polarizer and adapted to transmit light
through said first and second areas, a stationary
polarizer adapted to receive said light from said
first polarizer, said stationary polarizer having a
fixed polarization, a pair of photoelectric pickups
mounted on the other side of said stationary polarizer,
-the first of said pickups being adapted to receive
light passed through said first area and the second
of said pickups being adapted to receive. light passed
through said second area, whereby if said shaft is
rotated in one direction, said first pickup will
receive more light and if said shaft is rotated in
the other direction, said pickup will receive
more light.
These and othor objects of the invention will become
apparent from the following specification and drawings of
which:
Figure 1 is an exploded perspective view of an
embodiment of the invention.
Figures 2, 3, 4 are diagrams illustrating the operation
of the invention.
Figure 5 is a perspective view of a modification of
the invention.
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 Approved Fore. ease 2003/01/28: CIA-RDP78B0474Z 03000040Q12-2 ?
Referring to the Figures, the invention generally
comprises a first polarization plate means 1 which is
mounted on a rotatable shaft 2. The polarizing means 1
has a first center area 3 which has a first polarization
and a second outer ring area 4 having a second
polarization P2.and which is 90? displaced from said
first polarization. A source of, light 5 is fixedly
mounted and positioned to pass light through both
areas 3 and 4.
The light then passes through a second
polarization means 7 which has a single polarization. P3,
The second polarization means 7 may be mounted on the
shaft 8 which may be rotatably mounted or locked in
one position. Fixedly mounted beyond the other side
of the plate 7 areas pair of photocells. The photocell 9
is adapted to receive light which is passed through
the ring portion 4.and a second photocell 10 is
adapted to receive light passed through the center
portion 3.
Figures 2, 3, 4 illustrate the operation of the
embodiment of Figure 1. The polarization means;j
should be zero set so that there is equal intensity
to the two photocells as shown in Figure 2.
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 Approved Fo, elease 2003/01/28: CIA-RDP78B04T4 A003000040012-2
Referring to Figure 3, the polarization plate 1
.has been rotated clockwise so that the polarization P2
lines up with the polarization P3 of the element 7.
At the same time, the polarization ?l is at 900 to
the polarization P3.. Therefore, the amount of light
passing through the ring area 4 will be greater than
that passing through the center area 3 and the output
of the. photocell 9 will be greater than that of the
photocell 10.
Figure 4 shows the reverse operation wherein
the member 1 is rotated counterclockwise. In this
position the ring polarization k'2 is at 900 to the
polarization P3, and the center polarization P1 lines
up with the polarization P3. Therefore, the center
area will pass more light and the ring area will pass
less light so that the photocell 10 will have a
greater output than that of photocell 9.
The amount, of light difference is a function of
the amount of rotation.
Figure S shows a modification of the invention in
which a separate half wave plate 11 is used to provide
the center polarization. In this embodiment a first
polarization 'means 1' which is fixedly mounted to the,
shaft 2', has a single polarization e4 and half wave
plate 11 is also fixedly mounted to the shaft 2' and
has the property of rotating the polarization-of the
light 900. Therefore, the operation of the second
polarization means 7' and the photocells 9' and 10'
will be exactly the same as previously described.
Alternatively, the half wave, plate may be the ring portion.
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 Approved Forplease 2003/01/28 : CIA-RDP78B0474, 003000040012-2
The system may be used to detect the relative
displacement between a hand turned command shaft
and a shaft connected to a load. The displacement or
error signal is then. used to drive a servo motor to
keep the load shaft position synchronized with the
handwheel without requiring the operator to supply any
of the driving torques.
The advantages of this invention are as followss
1) The light source and light sensitive
detectors need not be a part of the rotating assembly.
These items may be mounted solidly on the base of the.
instrument, there is no physical or electrical
connection between these parts and the rotating members.
2) The two shafts do not require any mechanical
connectors or electrical connections. An optical path
between the two polarizers is the only requirement.
The shafts may be displaced axially, radially, or
skewed. For large displacements, an optical link
may be used to transmit the information.
3) System is insensitive to displacements, linear or
angular, of the shafts except, of course, for angular
rotation of the shafts about th eir axes. This eliminates
the need for high accuracy machining tolerances and
precision bearings.
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 Approved For Iease 2003/01/28 : CIA;RDP78B0474Z003000040012-2
4) Use of a single light source results in a
constant zero or null position with bulb voltage
variation.
5) System sensitivity is adjustable by changing
the relative position of the 1/2 wave plate or third
polarizing ring.
6) Since the system does not depend on small
slits or holes, large surface area sensors may be
employed. This increases the possible power gain
available and minimizes the effect of small imperfections
on the polarizing surfaces.
Many modifications of the invention may be made
by those who desire to practice the invention without
departing from the scope thereof which is defined by
the following claimsi
! j~ ril
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 Approved For (ease 2003/01/28 : CIA-RDP78B04747}03000040012-2
I claims
1. Means to detect direction and amount of shaft.
rotation comprising,
first polarization means mounted on a rotatable
shaft, said polarization moans having a first area of
a first polarization and a second area of a second
polarization at 900 to said first polarization,
a source. of light mounted on one side of said
polarizer and adapted to transmit light through said
first and second areas,
a second polarizer adapted to receive said
light from said first polarizer, said second
polarizer having a fixed polarization,
a pair of photoelectric pickups mounted on the
other side of said second polarizer, the first
of said pickups being adapted to receive light passed-
through said first area and the second of said pickups
being adapted to receive light passed through said
second area, whereby if said shaft is rotated in one
direction, said first pickup will receive more light
and if said shaft is rotated in the other direction,
said second pickup will receive mote light.
2. Apparatus as in Claim 1 wherein one of said
-areas has' a ring shape.
3. Apparatus as in Claim 1 wherein said first polarization
means has only one polarization and a portion of the
light is then passed through a separate half wave plate.
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 Approved FoWelease 2003/01/28: CIA-RDP78B0474A003000040012-2
4. Apparatus as in Claim 1 wherein said second
polarization means is mounted on a.second rotatable
shaft.
5. Apparatus as in Claim 1 wherein said second
polarization means is mounted on a stationary support.
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 FIG I
FIG 2
.FI G 3
FIG 4
FIG 5
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