Oscillatory electromagnetic mirror drive system for horizon scanner

Groom, N. J.

Hatcher, N. M.

Newcomb, A. L., Jr.

English

NASA Technical Reports Server

OR 3,437,394 
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April 8, 1969 N. M. HATCHER ETAL 3,437,394 
ELECTROMAGNETIC MIRROR DRIVE SYSTEU 
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ARTHUR L. NEWCOMB, JR. 
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3,437,394 United States Patent Office Patented Apr. 8, 1S69 
1 
3,437,394 
ELECTROMAGNETIC MIRROR DRIVE SYSTEM 
Norman M. Hatcher, Gloucester, and Nelson J. Groom 
and Arthur L. Newcomb, Jr., Newport News, Va., as- 
signors to the United States of America as represented 
by the Administrator of the National Aeronautics and 
Space Administration 
Filed July 26. 1966, Ser. No. 568,071 
Int. CI. G02b 17/00 
U.S. C1. 350-6 4 Claims 
ABSTRACT OF THE DISCLOSURE 
A device for scanning a horizon with a pair of mirrors. 
The two mirrors scan in the same plane but in different 
directions. Each of the mirrors has a gear attached to 
its back and the two gears are meshed together. Electro- 
magnetic means are provided for imparting an oscillatory 
rotation to one of the mirrors. Hence, this oscillatory 
rotation is imparted to the orher mirror through the two 
gears. 
The invention described herein was made by employees 
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 therefor. 
The invention relates generally to a mirror scanning 
drive system and more specifically concerns an oscillatory 
e!ectromagnetic mirror drive system for spacecraft ho- 
rizon scanners. 
The general purpose of the invention is to provide an 
improved mirror drive system for horizon scanners of 
the type disclosed and described in US.  Patent No. 
3,038,077 and US. patent application Ser. No. 369,334. 
This type of horizon scanner includes two pairs of mirrors 
that are coupled together and mounted for rotation in a 
frame that is fixed relative to the spacecraft on which 
the horizon scanner is used. The mirrors of each pair 
of mirrors scan the horizon in different directions and the 
two pairs of mirrors scan the horizon in two mutually 
perpendicular planes. 
The horizon scanner disclosed in US. Patent No. 
3,038,077 uses a conventional electric motor to continu- 
ously rotate the four scanning mirrors. Movement of the 
scanning mirrors is necessary to rotate the fields of view 
of irfrared radiation sensitive detectors from space across 
the horizon of the desired planetary body in order for 
the attitude of the spacecraft to be computed within 
the scanner. The disadvantages of this mirror drive 
system relative to the present invention are its larger 
weight, volume, and power consumption rate; and its 
lower probable lifetime due to its relatively high speed 
bearings, 
The horizon scanner described in US.  patent applica- 
tion Serial No. 369,334 oscillates four scanning mirrors 
by means of a leaf spring and solenoid mechanism which 
transmits the forces it generates to the mirrors through 
linkages. The disadvantages of Yhis mirror drive system 
result from its requirement ofginkages and connecting 
joints between the motor and the mirrors. Since the joints 
are subject to wear, reliability and accuracy of the scan- 
ner are seriously compromised. 
It is therefore an object of this invention to provide 
an improved mirror drive system for a horizon scanner 
which eliminates most of the linkages between the motor 
and the mirrors. 
Another object of this invention is to provide an 
improved mirror drive system for a horizon scanner 
which is lighter in weight, smaller in volume and uses 
less power than previous mirror drive systems. 
2 
A further object of this invention is to provide an 
improved mirror drive system for a horizon scanner that 
has a longer probable lifetime and is more reliable than 
previous mirror drive systems. 
Other objects and advantages of this invention will 
5 further become apparent hereinafter and in the drawings, 
in which: 
FIG. 1 is a schematic drawing of the mechanical com- 
ponents of this invention; and 
FIG. 2 is a block diagram of the electrical components 
In describing the preferred embodiment of the inven- 
tion illustrated in the drawings, specific terminology will 
be resorted to for the sake of clarity. However, it is not 
intended to be limited to the specific terms so selected, 
and it is to be understocd that each specific term includes 
all technical equivalents which operate in a similar man- 
ner to accomplish a similar purpose. 
Turning now to the preferred embodiment of the in- 
vention selected for illustration in the drawing, the num- 
2o bers 11, 12 and 13 in FIG. 1 designate the mirrors 
that scan the horizon. Even though only three mirrors are 
shown, it is to be understood that there are four mirrors. 
Another mirror appears opposite mirror 12. Mirrors 11 
and 13 scan in one plane, and mirror 12 and the mirror ’’ not shown scan in a plane perpendicular to the plane 
scanned by mirrors 11 and 13. Mirrors 11, 12 and 13 are 
mounted on shafts 14, 15 and 16, respectively, for rota- 
tion relative to a frame 17 by means not shown. Frame 
17 is only partially shown and is fixed relative to the 
30 spacecraft. Attached to mirrors 11, 12 and 13 are gears 
18, 19 and 20, respectively, which mesh at the primary 
axis of the scanner. Three permanent magnets 21, 22 
and 23 are used to determine the rest position of the 
scanner. Magnet 22 is attached to gear 20 and magnets 
3S 21 and 23 are attached to frame 17 by any suitable means. 
The field of magnet 22 opposes the fields of magnets 
21 and 23, and thus tends to position the mirrors at 
some point between their scan arc limits. A solenoid coil 
24 having terminals 25 and 26 is attached to frame 17 
of the scanner by any suitable means 27. A solenoid 
armature 28 is attached to mirror 13 so that it is free 
to move in and out of solenoid coil 24. In the rest position 
of the scanner armature 28 is located outside coil 24. 
When a pulse is applied to terminals 2.5 and 26 of coil 
q5 24, armature 28 is pulled intm coil 24 and the center 
mirror mounted magnet 22 is moved closer to the upper 
fixed magnet 23. Equilibrium of the forces exerted by 
the magnet fields is now overbalanced and a net force is 
exerted on the mirror mounted magnet 22, opposing the 
60 force exerted on armature 28 by coil 24. When the 
pulse applied to terminals 25 and 26 is terminated, mirror 
13 is forced by the opposing magnetic fields of magnets 
23 and 22 through its rest position. Then the opposing 
fields of magnets 22 and 21 forces mirror 13 back into 
55 its rest position. Armature 28 is now in a position that 
when another pulse is applied to coil 24 armature 28 
will again be pulled into the coil. By varying the strength 
of the magnets and the widths and frequency of fne 
pulses to coil 24, the mirrors can be made to oscillate at 
80 different frequencies and amplitudes. 
Attached to mirror 11 is a permanent magnet 29, and 
attached to frame 17 by suitable means, not shown, is a 
coil 30 having terminals 31 and 32. When mirror 13 is 
in its rest position, mirror 11 is also in its rest position 
66 and magnet 29 is located outside of coil 30. When a pulse 
is applied to coil 24 and mirror 13 is pulled out of its 
rest position, magnet 29 is pushed into coil 30 thereby 
generating a voltage across terminals 31 and 32 that is 
proportional to the angular velocity of the mirrors. This 
70 voltage is used to make the angular velocity of the mu- 
rors more constant. 
10 of this invention. 
, 
3,437,394 
3 
The block diagram of the electrical system which is 
suitable for use with the horizon scanner drive system dis- 
closed in FIG. 1 is shown in FIG. 2. An astable mul- 
tivibrator 36 produces pulses which are applied to an 
adder 33. The angular velocity signals generated across 
solenoid coil 30 are applied through a voltage amplifier 
34 to adder 33. The output of adder 33 is applied through 
a power amplifier 35 to coil 24 to produce the move- 
ments of the mirrors. 
This invention has numerous advantages over similar 
scanning devices. It is smaller in volume, it is lighter in 
weight, it requires less electrical power and it does not 
have rotor bearings or moving joints. The elimination of 
these bearings and joints increase the scanner’s reliability, 
life expectancy, and accuracy. 
It is to be understood that the form of the invention 
herewith shown and described is to be taken as a preferred 
embodiment. Various changes may be made in the shape, 
size and arrangement of parts. For example, equivalent 
elments may be substituted for those illustrated and de- 
scribed herein. Parts may be reversed and certain features 
of the invention may be utilized independently of the use 
of othre features, all without departing from the spirit or 
scope of the invention as defined in the subjoined claims. 
Torsion bars could be used instead of permanent magnets 
21, 22 and 23 to determine the rest position of the mir- 
rors. If torsion bars were used, the bars would pass 
through the mirrors along their rotational axes. One end 
of each bar would be attached to one side of a mirror and 
the opposite end would be attached to frame 17. 
What is claimed is: 
1. An oscillatory electromagnetic mirror drive system 
for spacecraft horizon scanners of the type in which a 
pair of mirror assemblies are coupled together and mount- 
ed in a frame that is fixed relative to the spacecraft for 
scanning a horizon in different directions and in the same 
plane comprising: a solenoid consisting of a coil and an 
armature with the coil fixed to said frame and with the 
armature attached to either of said mirror assemblies such 
that it moves in and out of said coil when the mirror 
assemblies move; first and second permanent magnets at- 
tached to said frame; a third permanent magnet attached 
to one of said mirror assemblies such that it is located 
5 
10 
1 5 
20 
25 
30 
35 
40 
4 
between said first and second permanent magnets and 
such that its field opposes the fields of the first and second 
permanent magnets whereby a rest position for the mirror 
assemblies is determined; and means for periodically ap- 
plying a voltage to said coil whereby said armature is 
pulled into said coil while said voltage is applied to said 
coil and said opposing fields produced by said first and 
second permanent magnets pull the mirror assemblies 
into their rest position while a voltage is not applied to said 
coil thereby producing an oscillatory moLion of said mirror 
assemblies. 
2. An oscillatory electromagnetic mirror drive system 
as defined in claim 1 wherein there are two pairs of mirror 
assemblies that are coupled together to scan the horizon 
in two mutually perpendicular planes. 
3. An oscillatory electromagnetic mirror drive system 
as defined in claim 1 wherein said means for periodically 
applying a voltage to said coil inciudes an astable multi- 
vibrator. 
4. An oscillatory electromagnetic mirror drive system 
as defined in claim 3 wherein means are provided for 
generating an electrical signal proportional to the angular 
velocity of the mirror assemblies and means are provided 
for adding this electrical signal to the output from said 
astable multivibrator before it is applied to said coil. 
References Cited 
UNITED STATES PATENTS 
3,215,033 1111965 VanGelder et al. _ _ _ _ _  350-301 
3,262,364 7/1966 Kollmorgen _ _ _ _ _ _ _ _  3.50-301 
2,922,894 1/1960 Kerr et ai. _ _ _ _ _ _ _ _  250-235 X 
3,038,077 6/1962 Gillespie, et al. 
3,225,206 12/1965 Strong et al. _ _ _ _ _ _ _  250-235 X 
FOREIGN PATENTS 
252,387 12/1926 Great Britain. 
DAVID SCHONBERG, Primary Examiner. , 
PAUL R. GILLIAM, Assistant Examiner. 
U.S. C1. X.R. 
178-7.6; 350-7 


Electromagnetic mirror drive system

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