The design and test details of a high precision hinge and locking mechanism created principally in support of the Lockheed space deployable Flexrib Parabolic Antenna concept are presented. These developed improvements in the detail design of ultra-precise rib hinge and contour adjustment mechanisms will allow radio frequency antenna reflectors to expand into the 15-50 meter diameter size class and to support the .013 mm. deployment repeatability tolerance required to support the 12+ GHz frequency range

Ribble, J. W.

Wade, W. D.

English

NASA Technical Reports Server

ON THE DESIGN OF AN ADJUSTABLE HIGH 
PRECISION LATCHING HINGE 
John W .  R i b b l e  & W i l l i a m  D. Wade 
Cockheed M i s s i l e s  and Space Company 
A b s t r a c t  
The des ign and t e s t  d e t a i l s  o f  a h i g h  p r e c i s i o n  h inge and l o c k i n g  mech- 
anism c r e a t e d  p r i n c i p a l l y  i n  suppor t  o f  t h e  Lockheed space dep loyab le  F lex-  
r i b  P a r a b o l i c  Antenna concept a r e  presented. 
t h e  d e t a i l  des ign o f  u l t r a - p r e c i s e  r i b  h inge and contour  ad justment  mechanisms 
w i l l  a l l o w  r a d i o  f requency antenna r e f l e c t o r s  t o  expand i n t o  t h e  15-50 meter 
d iameter  s i z e  c l a s s  and t o  suppor t  t h e  .013 mm. deployment r e p e a t a b i l i t y  
t o l e r a n c e  r e q u i r e d  t o  suppor t  t h e  1 2 t  GHz f requency range. 
These developed improvements i n  
I n t r o d u c t i o n  
I n  t h e  s p r i n g  o f  1974 a 9.1 meter d iameter  P a r a b o l i c  Antenna designed 
f o r  use a t  f requenc ies  up t o  8 GHz was s u c c e s s f u l l y  p laced i n  o r b i t .  T h i s  
r e f l e c t o r ,  shown i n  F igure  1 i n  i t s  f i n a l  deployed s t a t e ,  has opera ted  s a t i s -  
f a c t o r i a l l y  ever  s ince .  The des ign i s  o f  t h e  f l e x i n g  wrap r i b  type ,  which 
c o n s i s t s  o f  a number ( v a r i a b l e )  o f  r a d i a l  r i b s  o r  beams which a r e  c a n t i l e -  
vered f rom a c e n t r a l  hub s t r u c t u r e .  Each o f  t h e  r i b s  i s  a t t a c h e d  t o  t h i s  hub 
through a hinge. T h i s  r a d i a l  spoke system prov ides  t h e  mount ing f o r  t h e  an- 
tenna s u r f a c e  s t r u c t u r e .  Arrays a r e  formed by mount ing a membrane w i t h  e l e -  
ments on t h e  f r o n t  edge o f  t h e  r i b s  and, i f  r e q u i r e d ,  a ground p lane on t h e  
r e a r  edge. For p a r a b o l i c  o r  o t h e r  curved r e f l e c t o r s ,  t h e  r i b s  a r e  formed i n  
t h e  r e q u i r e d  shape, and r e f l e c t i v e  pie-shaped gores a r e  a t t a c h e d  between t h e  
r i b s .  An overv iew o f  such a deployed system i s  presented i n  F i g u r e  2.  
The r i b  c ross  s e c t i o n  and m a t e r i a l  a r e  chosen t o  p e r m i t  e l a s t i c  b u c k l i n g  
Th is  i s  t o  a l l o w  t h e  r i b s  t o  be wrapped around t h e  hub s t r u c -  o f  t h e  r i b s .  
t u r e  i n  t h e  ascent  o r  stowed package c o n f i g u r a t i o n .  
I n  t h e  s towing process, t h e  r i b s  and a t tached s u r f a c e  a r e  r o t a t e d  about  
t h e  r i b  h inges u n t i l  t h e  r i b s  a r e  tangent  t o  t h e  hub. A f t e r  t h i s  r o t a t i o n ,  
t h e  r i b s  a r e  f l a t t e n e d  and wrapped c i r c u m f e r e n t i a l l y  around t h e  hub. 
e l a s t i c  b u c k l i n g  o f  each r i b  accommodates t h i s  a c t i o n .  
i s  a l l o w e d  t o  form a package between t h e  r i b s .  
t h e  wrapped r i b s  i s  s u f f i c i e n t  t o  accompl ish deployment o f  t h e  r e f l e c t o r .  
The stowed package i s  conta ined by a s e r i e s  o f  h inged doors which a r e  h e l d  
i n  p l a c e  by a r e s t r a i n i n g  cable.  
The 
The s u r f a c e  m a t e r i a l  
The e l a s t i c  energy s t o r e d  i n  
Deployment occurs when t h e  c a b l e  i s  severed. 
It was i n  t h e  d e t a i l  des ign o f  t h e  r i b  h inge and l a t c h i n g  mechanisms 
t h a t  need f o r  des ign improvement was no ted  f o r  l a r g e r ,  h i g h e r  f requency 
designs. 
j u s t i n g  t h e  r i b  t i p s  t o  t h e  r e q u i r e d  contour  p o s i t i o n  t o l e r a n c e  o f  - t.965 mm. 
Dur ing t h e  r e f l e c t o r  assembly, excess ive t i m e  was consumed i n  ad- 
127 
https://ntrs.nasa.gov/search.jsp?R=19790014379 2020-03-21T23:45:42+00:00Z
In addi t ion,  d u r i n g  testing larger-than-expected deviations from the  "as 
adjusted" contour were experienced. While these items caused no s ign i f i can t  
performance degredations on t ha t  r e f l e c t o r ,  i t  was recognized t h a t  unless 
improvements were made, additional capabi l i ty  i n  e i t h e r  operational frequency 
o r  ref1 ector  diameter would be 1 imi ted by these mechanism er rors .  
These concerns led t o  the i n i t i a t i o n  of  a development study aimed a t  
producing a mechanical r e f l ec to r  design showing improved se tab i l  i t y  and re-  
peatabi l i ty .  
Symbols 
r l =  
D =  
A =  
f =  
G =  
6 =  
l r =  
c =  
e f f i c i ency 
p i  = 3.141592654 
d i  ameter 
wavelength of the electromagnetic wave 
focal l e n g t h  of the antenna 
local speed of  l i g h t  
gain 
RMS d i s t o r t i o n  
Ref1 ec tor  Performance 
The need for  improved antenna surface tolerance control can be under- 
s t o o d  by a brief discussion of antenna performance. 
may be d i r ec t ly  re la ted  t o  the physical properties o f  the antenna surface.  
Consider the case of  a round aperture having a diameter D.  In this instance,  
the antenna gain i s  d i r ec t ly  re la ted  t o  the  diameter by the simple expression 
The gain of  an antenna 
G =  (+) 
The above formula indicates  t ha t  the  gain of an antenna i s  d i r e c t l y  propor- 
t ional t o  the square of  the diameter and the  square of increasing frequency. 
The eff ic iency fac tor  (qE)  accounts for  the normally encountered degrading 
factors  i n  any antenna system, including, among many other e f f e c t s ,  r e s i s t i v e  
losses ,  r e f l ec t ion  losses ,  aperture d is t r ibu t ion  lo s ses ,  and blockage losses .  
Highly e f f i c i e n t  systems have an eff ic iency of nearly 70 percent. 
w i d t h  systems have an eff ic iency o f  approximately 30 percent t o  40 percent; 
moderate bandwid th  systems o f  conventional performance generally have e f f i  - 
ciencies i n  t he  50 t o  55 percent region. By spec i f ic  exclusion, this e f f i -  
ciency fac tor  does n o t  include the impact of d i s to r t ions .  
Broad band- 
For estimation purposes d i s t o r t i o n s  o f  large s t ruc tures  can be consid- 
ered as  random er rors  i n  the  surface.  Exact treatment o f  t he  performance 
degradation caused by the actual d i s tor t ions  i s  a very complex i ssue ,  re la ted 
t o  the type of  antenna used, the d i s t r i b u t i o n  o f  e r r o r s ,  and many other fac- 
tors. However, a reasonably well accepted and accurate re la t ionship between 
gain i n  the  ideal case and t h a t  achieved i n  the  presence of small s t ruc tura l  
128 
d i s t o r t i o n s  i s  represented  by t h e  r e l a t i o n s h i p  
where h i s  t h e  wavelength and 6 i s  t h e  RMS s u r f a c e  e r r o r .  
w r i t t e n  i n  terms o f  r e f l e c t o r  e f f i c i e n c y  as 
T h i s  can be r e -  
- (v)2 ; mechanical e f f e c i e n c y  (3 )  Gd = 776 G where U6 = e 
I f  we a r e  d e a l i n g  w i t h  s t a t i s t i c a l l y  independent e r r o r  sources, then 6 i s  
t h e  RSS o f  t h e  i n d i v i d u a l  e r r o r  sources. The o v e r a l l  e f f i c i e n c y  equat ion  
can now be w r i t t e n  as 
where 6, i s  t h e  sur face  e r r o r  caused by manufactur ing e r r o r  and deployment 
n o n - r e p e a t a b i l i t y ,  hA i s  t h e  s u r f a c e  approx imat ion e r r o r ,  and 6~ i s  t h e  t h e r -  
ma l  d i s t o r t i o n  e r r o r .  
The r e p e a t a b i l i t y  e r r o r  te rm may now be i n v e s t i g a t e d  p a r a m e t r i c a l l y  by 
p l o t t i n g  i t s  e f f i c i e n c y  a g a i n s t  RMS d i s t o r t i o n  e r r o r  d i v i d e d  by wavelength i n  
o rder  t o  normal ize  t h e  r e s u l t s  w i t h  r e s p e c t  t o  f requency.  
shown i n  F i g u r e  3. Based on p r e v i o u s  exper ience i n  e r r o r  a l l o c a t i o n  budgets 
f o r  antenna systems, a reasonable e f f i c i e n c y  c o n t r i b u t i o n  f o r  r e p e a t a b i l i t y  
i s  95%. Thus i t  can be seen t h a t  i n  o r d e r  t o  o b t a i n  a h i g h  o v e r a l l  r e f l e c t o r  
e f f i c i e n c y ,  t h e  r e f l e c t o r  mechanisms d i s t o r t i o n s  must be kept  smal l  ( i  ..e. 2 1/ 
50) compared t o  t h e  wavelength o f  t h e  r a d i a t e d  energy.  
Th is  r e s u l t  i s  
Mechanical Development 
I n  response t o  t h e  recognized need f o r  reduced s u r f a c e  d i s t o r t i o n s  and 
improved s u r f a c e  r e p e a t a b i l i t y  f o r  e v o l v i n g  antenna needs, a development p ro-  
gram was i n i t i a t e d  i n  1975 t o  i s o l a t e  t h e  sources o f  t h e  e r r o r s  encountered 
w i t h  t h e  9.1 meter d iameter  r e f l e c t o r  and t o  reduce them w i t h  d e t a i l  des ign 
improvements. As p r e v i o u s l y  discussed, one e r r o r  i n  t h e  des ign was t r a c e d  t o  
t h e  r i b  l a t c h  mechanism, shown p i c t o r i a l l y  i n  F i g u r e  4 .  
The l a t c h  c o n s i s t e d  o f  a taper-ended p lunger  s i t u a t e d  p a r a l l e l  t o  t h e  
r i b  h inge 1 i n e  and pre loaded by a 22 newton s p r i n g .  
a quadrant l o c a t e d  on t h e  r i b .  
t i o n ,  t h e  p lunger  would t r a v e l  beyond t h e  end o f  t h e  quadrant and snap i n t o  
t h e  l a t c h e d  p o s i t i o n .  A l o a d i n g  diagram o f  t h e  h inge p o r t i o n  o f  t h i s  l a t c h  
mechanism i s  shown i n  F i g u r e  5 .  This  l a t c h  o r i e n t a t i o n  induced t o r q u e  mo- 
ments T about  t h e  l o n g  a x i s  o f  t h e  r i b  which caused i t  t o  d e f l e c t  f rom t h e  
d e s i r e d  c o n t o u r  p o s i t i o n .  
The p lunger  rode a g a i n s t  
When t h e  r i b  reached t h e  f u l l y - d e p l o y e d  p o s i -  
I n  a d d i t i o n ,  t h i s  t o r q u e  v a r i e d  accord ing  t o  t h e  
129 
exact f ina l  position of the plunger each time the  r ib  was deployed, g i v i n g  
r i s e  t o  var ia t ions i n  the  r i b  position each time i t  was operated. 
A second area o f  concern i n  t he  r e f l ec to r  was the method used t o  ad jus t  
the r i b  posit ions t o  es tab l i sh  the required contour. 
ments were required t o  be nade simultaneously. 
ca l ly  a t  the h u b ,  rotated w i t h  respect t o  the hinge ax is  i n  order t o  provide 
ver t ical  adjustment a t  the  t i p ,  and the  f u l l y  deployed position was adjusted 
t o  insure t h a t  the r i b  extended i n  an exact ly  radial  d i rec t ion .  
position s t o p  was a screw adjustable  s top,  which operated qui te  s a t i s f ac to r -  
i a l l y .  The other  adjustments, however, i n  pract ice  required the expenditure 
o f  large amounts o f  time t o  achieve the  required accuracy. 
the r i b  was adjusted ve r t i ca l ly  by exchanging matched pairs  of graduated 
shims. While the  shims functioned well , changing and checking these matched 
pairs  was extremely time consuming. The angular adjustment a t  the hinge re-  
quired t o  achieve ver t ica l  adjustment a t  the r i b  t i p  was accomplished by tap- 
p i n g  a s l id ing  block hous ing  for the  hinge bearing w i t h  a su i tab le  hammer. 
T h i s  proved t o  be a t rying process. Therefore, design e f f o r t s  i n  the  develop- 
ment program were directed a t  eliminating these causes for concern. 
Three rib hinge adjust-  
The r ib  was adjusted ve r t i -  
The radial  
The hub end o f  
Design requirements for  a new re f l ec to r  were based on typical known 
large r e f l ec to r  needs. 
these requirements, recognizing future  needs t o  extend both  the  s i ze  and 
operating frequency of parabolic antennas. 
ments for the study. 
In t h a t  design the plunger was relocated t o  the r i b  and positioned t o  move i n  
a direct ion perpendicular t o  the hinge 1 ine ha1 fway between the hinge bearings. 
Thus ,  no torque i s  transmitted t o  the  r i b  from var ia t ions i n  l a tch  loads,  e l i -  
minating one source of contour non-repeatabil i ty.  
An attempt was made where economics allowed, t o  be t te r  
Table I l i s t s  the assumed require- 
The hinge design which evolved i s  shown i n  Figure 6 .  
The elimination of induced torque due t o  la tching loads also allowed the  
la tch  mechanism t o  be u t i l i zed  t o  eliminate bearing freeplay. 
rib hinge always creates  hinge bearing clearance problems which manifest them- 
selves as  contour inaccuracies. In the  case of the new design the bearing 
freeplay magnification r a t i o  ( i  .e.  , length of rib/bearing separation) i s  50:l. 
Therefore i n  order t o  produce a r e f l ec to r  contour which i s  repeatable,  the  
bearing freeplay was eliminated a t  the completion of  deployment by u t i l i z i n g  
a very h i g h  force s p r i n g  t o  drive the la tching plunger. A fur ther  complica- 
t i o n  i s  the one-9 environment under which the contour must be s e t  and measur- 
ed. 
able  posit ion whether the r e f l ec to r  i s  deployed w i t h  the  concave s ide  up or  
down, thus eliminating the  one-g deadband i n  the bearings. 
The use o f  a 
The l a t ch  s p r i n g  was a l so  designed t o  drive the r i b  bearings t o  a repeat- 
The other major change incorporated i n t o  the new design i s  the method 
of achieving ver t ica l  adjustments a t  the r i b  root and t i p .  
vernier r i b  adjustment mechanism which was developed i s  shown in Figure 7 .  
The design goals which led t o  this  adjustment device were: 
(1) 
The resu l t ing  
Adjustment Fineness - The a b i l i t y  o f  the mechanic t o  "feel"  - +.25 mm 
t i p  motion. 
130 
( 2 )  R e p e a t a b i l i t y  - Once the  adjustment was made, i t  cou ld  be expected t o  
remain i n  t h a t  p o s i t i o n .  
(3)  R e a d j u s t a b i l i t y  - I f  f o r  some reason i t  was found necessary t o  change t h e  
s e t t i n g ,  d i  sassembly woul d no t  be requ i red .  
The bottom (s ide  away from contoured s ide  o f  r i b )  h inge bear ing i s  he ld  by a 
housing which i s  ad jus ted  r a d i a l l y  by a d i f f e r e n t i a l  screw device.  
the  a d j u s t i n g  c o l l a r  18O r e s u l t s  i n  a .25RN v e r t i c a l  r i b  mot ion a t  t he  r i b  
r o o t  v e r t i c a l  adjustments can be made by changing one shim, thus  e l i m i n a t i n g  
the  need f o r  matched shim p a i r s .  
Turn ing 
Design V e r i f i c a t i o n  
The hinge model shown i n  F igure  6 was subjected t o  r e p e a t a b i l i t y  t e s t s  
du r ing  t h e  s p r i n g  o f  1978. Resul ts  o f  those t e s t s  a re  summarized i n  Table 11. 
I n i t i a l  t e s t s  showed excessive d e f l e c t i o n s  i n  the  h inge.  The d i f f i c u l t y  was 
t raced t o  d e f l e c t i o n  i n  t h e  lower  hinge p i n  (see F igure  8 ) .  The d e f l e c t i o n  
i n  t h i s  p i n  caused by t h e  l a t c h i n g  loads from t h e  p lunger  s p r i n g  were i n  the  
order  o f  0.2 mm, which cou ld  r e s u l t  i n  a mechanical e f f i c i e n c y  c o n t r i b u t i o n  
i n  t h e  p r o j e c t e d  design o f  36%. The p i n  was t h e r e f o r e  redesigned and s t i f -  
fened as shown i n  F igure  8. 
Table I1 obta ined,  r e s u l t i n g  i n  a p ro jec ted  mechanical e f f i c i e n c y  c o n t r i b u -  
t i o n  o f  98% fo r  t h e  design which was w e l l  above t h e  95% goal .  
The new p i n  was i n s t a l l e d  and the  r e s u l t s  o f  
The r e s u l t s  o f  these t e s t s  enabled a go-ahead t o  manufacture and assemble 
Th is  model a 4 - r i b ,  3-gore sec t i on  o f  a complete 15  meter diameter r e f l e c t o r .  
(F igure  9)  has been completed and i s  c u r r e n t l y  scheduled t o  undergo engineer-  
i n g  development t e s t i n g  t o  v e r i f y  deployment dynamics and contour  repeat -  
a b i l i t y .  
Concl usions 
The des ign o f  a l a t c h i n g  hinge capable o f  suppor t ing  antenna r e f l e c t o r s  
This  h inge design achieves deployment r e p e a t a b i l i t y  o f  w i t h i n  +.010 mm 
i n  the  15-50 meter diameter range and 12+ GHz frequency range has been achiev-  
ed. 
across t h e  bear ings and a l lows p o s i t i v e  v e r t i c a l  r i b  adjustments of-.05 mm 
a t  t h e  r o o t  and .25 mm a t  the  t i p .  
131 
TABLE I 
Re q u i rem en t 
Diameter Depl oyed 
Diameter Stowed 
Ref1 e c t o r  Weight 
Operati  ng Frequency 
Surface Approx Loss 
Thermal Dist. Loss 
Torque Transmit ted t o  S/C 
Launch Environment 
f/D Rat io  
Mfa. & Reoeatab i l i tv /Loss  
Val ue 
15 M 
<200  M 
< 138 Kg 
9 GHz 
c . 5  dB 
.1 dB 
< 46.6 Newton-M 
- + 20 G I s *  
.44 
c .07  dB 
Comol i a nce 
15.24 M 
1.90 M 
122 Kg 
8.5 GHz 
.5 dB 
.045 dB 
34 Newton-M 
.08 M.S. 
.44 
.02 dB 
* Applied i n  3 orthogonal d i r e c t i o n s  s imul taneous ly  - equivalent s t a t i c  
i n e r t i a l  l oad  
TABLE I1 
Load Condition 
Ver t ica l  Shear 
Horizontal  Shear 
(Toward Deployment S top)  
Horizontal  Shear 
(Away from Deployment Stop)  
. Deflec t ion  After I Load Removal Def lec t ion  a t  l q  load  
.015 
.012 
.011 
.OlO 
,008 
.0075 
132 
R R  
133 
SOLAR ARRAYS 
8. ANTENNAS 
DEPLOYED - OPERATIONAL 
SEPARATION 
FIGURE 2 MISSION PROFILE-SATELLITE DELIVERY (OPTIONAL DELTA LAUNCH) 
1 .o 
.a 
rl 
EFFICIENO 
.4 
.4 
.2 
0 1 1 I 1 .a? .w .06 .08 
RIB TIP DEFLECllON 6 1  -
WAVELENGTH 
FIGURE 3 REFLECTOR EFFICIENCY EFFECT OF SURFACE DISTORTION 
134 
FIGURE 4 
RIB HINGE & LATCH ASSEMBLY FOR 9.1 METER DIAMETER REFLECTOR 
FIGURE 5 HINGE LOADING DIAGRAM 
FIGURE 6 
REDESIGNED RIB HINGE & LATCH ASSEMBLY FOR 15 METER DIAMETER REFLECTOR 
135 
ADJUSTING 
JAM 
LOWER HINGE 
EARING PIN 
ADJUSTING SHIM 
L32 PITCH THREAD 
FIGURE 7 
I I 
ORIGINAL DESIGN STIFFENED DESIGN I 
FIGURE 8 
FIGURE 9 
136 


On the design of an adjustable high precision latching hinge

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