An angular position transducer utilizing photocells and a light source is disclosed. The device uses a fully rotatable baffle which is connected via an actuator shaft to the body whose rotational displacement is to be measured. The baffle blocks the light path between the light source and the photocells so that a constant semicircular beam of light reaches the photocells. The current produced by the photocells is fed through a resistor, a differential amplifier measures the voltage drop across the resistor which indicates the angular position of the actuator shaft and hence of the object

Gray, D. L.

Sandford, M. C.

English

NASA Technical Reports Server

United States Patent [19] 
Sandford et al. 
[111 4,184,072 
[45] Jan. 15, 1980 
[54] SOLAR CELL ANGULAR POSITION 
[75] Inventors: Maynard C. Sandford, Hampton; 
TRANSDUCER 
David L. Gray, Newport News, both 
of Va. 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
[73] ,Assignee: The United States of America as 
[21] Appl. No.: 876,299 
[22] Filed: Feb. 9, 1978 
[51] Int. Cl.2 ............................................... GOlD 5/34 
[52] U.S. c1. .......................... 250/231 SE; 250/211 K 
[58] Field of Search ......... 250/211 K, 231 SE, 231 R 
[561 References Cited 
U.S. PATENT DOCUMENTS 
3,358,150 12/1967 Summer ........................... 250/211 K 
4,103,155 7/1978 Clark ........................... 250/211 K X 
Primary Examiner-David C. Nelms 
Assistant Examiner-Darwin R. Hostetter 
Attorney, Agent, or Firm-Howard J. Osborn; John R. 
Manning; John G. Mannix 
ABSTRACT 1571 
An angular position transducer utilizing photocells and 
a light source is disclosed. The device uses a fully rotat- 
able baffle which is connected via an actuator shaft to 
the body whose rotational displacement is to be mea- 
sured. The baffle blocks the light path between the light 
source and the photocells so that a constant semicircu- 
lar beam of light reaches the photocells. 
When the assembly is in the null position the illuminated 
area of each of the photocells is equal. As the actuator 
shaft rotates, the baffle also rotates which causes an 
increase in the area of illumination of one of the photo- 
cells together with an equal decrease in the area of 
illumination of the other photocell. 
The current produced by the photocells is fed through 
a resistor, a differential amplifier measures the voltage 
drop across the resistor which indicates the angular 
position of the actuator shaft and hence of the object. 
10 Claims, 11 Drawing Figures 
36 
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US. Patent ~ m .  15,1980 Sheet 1 of 4 
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U.S. Patent ~a. 15,1980 Sheet 2 of 4 4,184,072 
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FIG. 8 
'2 
PRE AMP OUTPUT, VOLTS 
I I I I 
5 10 15 20 25 
- 
25 20 IS IO 5 
MOTOR SHAFT ROTATION, DEGREES 
MOTOR POSITION PHOTOCELL CALIBRATION DATA 
FIG. 9 
4,184.072 
1 
SOLAR CELL ANGULAR POSITION 
TRANSDUCER 
ORIGIN OF THE INVENTION 
The invention described herein was made by employ- 
ees of the United States Government and may be manu- 
factured and used by or for the Government for govern- 
mental purposes without the payment of any royalties 
thereon or therefore. 
BACKGROUND OF THE INVENTION 
This invention relates to a device that can accurately 
ascertain the angular displacement of an object. And 
more particularly to a device that determines the con- 
trol surface angular displacement of wind tunnel scaled 
models of aircraft. 
DESCRIPTION OF THE PRIOR ART 
Wind tunnel tests are frequently made with model 
versions of airplane designs. It is important to know the 
angles of the control surfaces of the model throughout 
the test. 
Tho ..AA- ..*-A -&,.*:--&-- ^" ---.-I-- ---:A:-- 
5 
10 
15 
20 
housing block in such a way as to allow illumination of 
one-half of each photocell with a uniform light. The 
baffle is attached to a small shaft, lying on the longitudi- 
nal axis of the housing, which is fitted to the inner bore 
of two miniature precision ball bearings. 
The bearing arrangement allows only rotary motions 
of the baffle with respect to the stationary light source 
and photocells. 
As the control surface shaft is rotated from a zero null 
position, one photocell receives more illumination than 
the other, the current produced by the photocell is 
proportional to the shaft rotational angle. This current 
is fed through a resistor and the voltage drop thereof is 
measured by a high gain differential amplifier. The 
voltage is related, through a calibration procedure, to 
the control surface angular position. 
BRIEF DESCRIPTION OF THE DRAWINGS 
FIG. 1 is a side view of the assembled device; 
FIG. 2 is an exploded view of the invention which 
displays all the pieces and how they interact with each 
other: 
FIG. 3 is a front elevational view of the LED's posi- 
3 
4,184,072 
4 
ing housing 18 contains two miniature ball bearings sured. The axis of rotation of the object must align with 
which enable actuator shaft 20 to rotate therein. Actua- the axis of rotation of shaft 20. The object is then angu- 
tor shaft 20 contains a groove 22, displayed in FIG. 4, larly displaced which rotates shaft 20 (FIG. 2) which 
for a spring clip 24 to hold the shaft in the bearings. rotates bame 28. This results in one photocell receiving 
Shaft 20 is of a smaller diameter 26 after exiting from 5 more light (the top photocell in FIG. 66) and the other 
bearings housing 18 to enable it to slip through a center photocell receiving less light (the bottom photocell in 
hole 27 in LED board 14. Returning to FIG. 2, it can be FIG. 66). The current emitted by the other photocell is 
seen that the end of actuator shaft 26 is connectable to correspondingly decreased. These currents are fed into 
light baffle 28 enabling it to rotate with shaft 26. BaffIe potentiometer 45 (FIG. 1) and the differential amplifier 
28 is painted or masked such that only a semicircular 10 measures the voltage across the potentiometer 45. The 
beam of light is transmitted therethrough, as can be seen voltage is indicative of the difference between the two 
in FIGS. 5a and 5b. Referring again to FIG. 2, inner currents. The circuit is shown more clearly in FIG. 8. 
sleeve 30 slips over baffle 28 and engages LED board 14 
Photocell mount 32 holds photocell 34 (FIG. 2) which 15 
has been prepared to behave as two photocells. This 
was accomplished by masking the back of the photocell 
exposing only two narrow strips along the side edges of 
the cell. A solution of hydrochloric and nitric acid was 
applied to etch the gold and nickle coating from the 20 
on one side and photocell mount 32 on its other side. il=current emitted by 1 photocell 
iZ=current emitted by the other photocell 
R =  R1+ R2 
strip along the back of the photocell. FIG. 7 displays v = VL - VR 
the back of a photocell prepared in such a way. The = ilRi - izR2 
illuminated area is on the side not shown in the figure. 
The solar cell consists of a layer of p type material 60 on 
a base of n type material 61. The back is coated with a 25 
layer of gold and nickle 62. The gold and nickle coating 
is etched away along the center of the back of the cell 
63. Contact 64 on the front of the cell provides a com- 
mon contact. The other contacts 65 and 66 are on the 
back of the cell. 30 and the voltage is thus directly proportional to the dif- 
The advantage of this procedure over the use of two faence in C ~ ~ e n t s -  
distinct photocells is that the sensitivity differs slightly The c ~ ~ e n t  Output of a Photocell is directly Propor- 
from one photocell to another. By adopting proce- tional to the illuminated area thereof. Therefore the 
dure, two identical photocells are obtained avoiding the voltage as n~asured by the differential amplifier is di- 
necessity of compensating for a slightly less sensitive 35 rectly ProPortional to the angle of rotation of the Ob- 
photocell. ject. 
The electrical circuit is displayed in FIG. 8. The and 
photocells are represented by current sources. The cur- corresponding voltage output obtained in testing the 
rent produced by a photocell is directly proport,ional to invention. 
the area of illumination of the photocell. The current 40 It is understood that the foregoing description is of a 
produced by the photocells runs through a low reis- particular embodiment of the invention and is therefore 
tan- resistor R. Differential amplifier 47 measures the merely representative. Obviously there are variations 
voltage drop across the resistor. This voltage is &E- and modifications of the present invention in the light of 
played on meter 51. the above teachings. It is, therefore, understood that 
Solder terminal board 36 (FIG. 2) allows easy con- 45 within the scope of the appended claims the invention 
nections to be made with the LED wires 39 and the may be practical otherwise than as specifically de- 
photocell wires 40. The entire assembly is pressed into scribed. 
housing block 42. Solder terminal board 36, photocell What is claimed as new and desired to be served by 
mount 32, photocells 34, inner sleeve 30, LED board 14, Letters Patent of the United States is: 
LEDs 12, LED spacer 16, and bearing housing 18 50 1. A device for measuring the angular displacement 
remain stationary relative to the housing block 42. Ac- of an object comprising: 
tuator shaft 20, the bearings within bearing housing 118, (a) radiation means for producing a constant radia- 
and baffle 28 are the onlv moving nieces. 
the wiper is positioned SO that R I =R2= 4R 
thus 
V=&R(il-iZ) 
FIG- 9 displays a &raPh ofthe shaft rotation 
tion, 
Y 1  
(b) radiation sensing means comprised of two radia- 
tion sensitive Darts that sense the relative amount of OPERATION OF THE INVENTION 55 ~~ 
Output wires 40, as shown in FIG. 1 are connected to 
a low resistant potentiometer 45 which in turn is con- 
nected to a differential amplifier 47. Shaft 20 is rotated 
until baffle 28 is in a position that the light impinging on 
the cells 34 is such that the straight edge 49 (FIG. 6u) of 60 
the illuminated area 48 is perpendicular to the gap 50 
between the cells. The point of intersection of the 
straight edge 49 of illuminated area 48 and the gap 50 
between the cells is aligned precisely with the shaft 20 
axis of rotation. This is easily accomplished by observ- 65 
ing the output voltage and rotating shaft 20 (FIG. 1) 
until a null output appears. Shaft 20 is then connected to 
the object whose angular displacement is to be mea- 
the radiation impinging thereon to determine the 
angular displacement of said object, and 
(c) radiation obstruction means that rotates in unison 
with the object being angularly displaced in order 
to obstruct said radiation such that said radiation 
impinges upon varying areas of one of said radia- 
tion sensitive parts with respect to the other of said 
radiation sensitive parts, said radiation sensitive 
parts producing an output that is directly propor- 
tional to the rotation of said object. 
2. A device as in claim 1 including a housing; 
said radiation means being supported within said 
housing; 
5 
4,184,072 
6 - 
said radiation means being a light source; 9. A device as in claim 8 in which wires are con- 
said radiation sensing means being photocells sup- nected to said photocells, said photocells and said wires 
ported within said housing and facing said light being rigidly fixed in said housing to prevent their rota- 
source; and said radiation obstruction means being tion therein and to prevent said wires from entangle- 
a rotatable baffle supported within said housing 5 ment. 
and spaced between said light source and said pho- 10. A device for measuring the angular displacement 
tocells to optically obstruct part of the light path of an object comprising: 
between said light source and said photocells. (a) a housing; 
3. A device as in claim 2 including a rotatable shaft (b) a light source supported within sald housing for 
that is fixed to said baffle, said shaft being attached to 10 producing a constant radiation; 
said rotating object to enable said baffle to rotate in (c) two photocells supported within said housing and 
unison therewith. facing said light source; 
4. A device as in claim 2 wherein said baffle obstructs (d) a rotatable baMe supported within said housing 
the optical path between said light source and said pho- and spaced between said light source and said pho- 
tocells such that a semi-circular beam of light impinges 15 tocells that obstructs the optical path between said 
upon said photocells. light source and said photocells such that a semicir- 
5. A device as in claim 4 wherein said semi-circular cular beam of light impinges upon said photocells; 
beam of light rotates upon said cells, illuminating vary- (e) a rotatable shaft that is fixed to said baffle, said 
ing areas of one of said photocells with respect to the shaft being attached to said rotating object to en- 
other of said photocells, each of said photocells creating 20 able said baffle to rotate in unison therewith caus- 
an electrical current directly proportional to their re- ing said semicircular beam of light to rotate upon 
spective illuminated areas. said cells, illuminating varying areas of one of said 
6. A device as in claim 5 including a potentiometer photocells with respect to the other of said photo- 
and a differential amplifier, said electrical currents cells, each of said photocells creating an electrical 
being fed through said potentiometer and said differen- 25 current directly proportional to their respective 
tial amplifier measuring the voltage drop across said illuminated areas; 
potentiometer which is directly proportional to the (0 a potentiometer connected to said photocells such 
rotation angle of said shaft. that said electrical currents from said photocells 
7. A device as in claim 2 in which said housing iso. are fed therethrough; and 
lates said photocells from external light sources. (g) a differential amplifier connected to said potenti- 
8. A device as in claim 2 in which wires are con- ometer so as to measure the voltage drop across 
nected to said light source, said light source being rig- said potentiometer which is directly proportional 
idly fixed in said housing to prevent their rotation to the rotational angle of said shaft. 
3 0  
, 
therein and to prevent said wires from entanglement. + I * * *  
35 
40 
45 
5 0  
55 
60 
65 


Solar cell angular position transducer

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