The cleanliness requirements for many processing and manufacturing tasks are becoming ever stricter, resulting in a greater interest in the vacuum environment. Researchers discuss the importance of this special environment, and the development of robots which are physically and functionally suited to vacuum processing tasks. Work is in progress at the Center for robotic Systems in Microelectronics (CRSM) to provide a robot for the manufacture of a revolutionary new gyroscope in high vacuum. The need for vacuum in this and other processes is discussed as well as the requirements for a vacuum-compatible robot. Finally, researchers present details on work done at the CRSM to modify an existing clean-room compatible robot for use at high vacuum

Belinski, S.

Hackwood, S.

Imani-Shikhabadi, R.

Trento, W.

English

NASA Technical Reports Server

a 
Robot Design for a Vacuum Environment 
S. B e W ,  W. Trento, R. -, and s. H r l E w o o d  
University of Califonria, Santa Barbara 
SantaBarbara. CA 93116 
/.a ,I 
8 ,  --I 1. Abstract 
/- , i
' Thc clcanliiss requirements for many proctssing and manufacturing tasks - g  
ever smctcr, resulting in a greater intmst  in the vacuum environment Wediscuss the i importance of this mal environment, a d  the developanent of robots which are% y 
and functionally suited to vacuum processing tasks. Work is in progress at the Center for 
Robotic Systems in Microelectronics (CRSM? to provide a robot for the manufacture of a 
is discussed as well as the requirements for a vacuumumpatible robot. Finally, -nt 
details on work done at the CRSM to modify an existing clean-room compatible robot for use at 
revolutionary new gyroscope in high vacuum. The need for vacuum in this and other pmccses , .  - r  ,' 
I 
. - A . a c u U m .  
2. Introduction 
Among the many advantages of robots is their ability IO work in harsh environments. 
Robots are being developed for maintenance of nuclear facilities (for example, the ODEX 
wallring robots by odetics, Inc) and for high temperature and other harsh environments. The 
high vacuum environmeiu is now becoming more important in many high technology 
manufacturing tasks, and as i%wt the need for vacuum compatible robots is increasing. 
Most processes requiring high cleanliess standards are now performed in clean rooms. 
The principal users of clean rooms arc advanced industries making use of thin film technology. 
Materials manufactured in ultraclean environments include [ 1): VLSI semiconductors, compact 
discs. photographic films. magnetic and video tapes. precision mechanisms and sterile drugs 
and antibiotics. Today's r i g m s  cleanliness requirements can be illustrated dramatically with 
the example of the actual development going on in the VLSI semiconductor field. Table 1 
shows that the critical particle diameter, i.e. the maximum size of tolerable contaminant particles, 
is projected to be 0.05pm in the near future. 
'\ 
16 
64 
256 
4 x  Id 
1 x Id 
4.0 
2 5  
1.5 
0.9 
05 
0.4 1981 - 1984 
0.3 1984 - 1988 
0.17 1984 - 1988 
0.09 1988 - 1990+ 
0.05 1988 - 1% 
Table 1. Line spacing and critical particle diameters for high density 
integrated circuits (adapted from [I]). 
As of 1985, the most demanding air cleanliness level established in the U.S. Federal 
Standard 209b is a cleanliness class 100. This refers to a maximum concentration of l W f $  for 
Racrrch Assistrt in the m e a t  of Mechmiul Engineering. UCSB 
t F d t y  in the Deptmnent of Elaaicrl and Comprrn Engineering. UCSB 
tfThc CRSM is one of the Enginaing R a c u ~ f r  Cmtm atab1ishc.d by h e  N u i d  Science Foundation 
95 
https://ntrs.nasa.gov/search.jsp?R=19890017093 2020-03-20T02:10:08+00:00Z
particks of diameter greater than or equal to05 pm. It is proposed in (11 that thepresent 
scandardsbc extrapdatcd as listed in tabk2 
1 I d  3 x 1 0  . 
10 10 Id 3x1@ 
100 t 3 x  ld lo2 
lo00 t t ld 7 x 1 9  
lO.Oo0 t t lo' 7 x  10 
loOD00 t t ld 7 x 1 6  
*- mtmeaningfulfadlricrirvlreaow 
tlndication mcrelevantfortbeddinitionotdanlinessreqrrirrmern 
Table 2. Proposal for extrapolating the US Federal cleanliness 
standards (fmm [l]). 
In the near future, cleanliness class 1 and even stricter environments will be required The 
three main sources of particle contamination arc: the outside air ( lo7 - l@ particles > 0.5 pm 
m-3), equipment, and humans, who give off about 100,OOO dust particles > 0.3 p n  and mort 
than loo0 bacvria and spores pa minute An incrtasing number of specially designed robots 
arc bcing used in clean rooms not only beoruse oftheirpoctntial ef€icicncy and productivity, but 
also to replace one of the principal sources ofcontaminatian: human beings 
Eventually, a wide range of processing and analysis tasks will be performed in vacuum 
environments. The reasons for using this special environment arc many and inclucie the 
following (21: 
- To prevent physical or chemical reactions occurring between 
anmsphaic gases and a desired - To disturb an quilibrium condition that exists at room temperature so 
that absorbed gases orvolatileliquidscan be removedfran the bulk of 
the material (e.g.. degassing of oils and frceze drying), and adsorbed 
gases from the surfact; - To incnaSe the distance that gas and vapor particles must travel b c f m  
colliding with one another so that a process particle can rcach a solid 
surface without making a collision (e.g., vacuum coating and the 
production of high-energy particles); - To reduce both the number of molecular impacts per second and the 
contamination times of surfaces prepared in vacuo (e.g., clean surface 
studies and the preparation of thin films), and - To reduce the concentration of a component gas below a critical level 
(e.g., the removal of oxygen, water vapor and hydrocarbons in 
tungsten filamtnt valves). 
Presently, epitaxial growth of semiconductor films takes place in the low vacuum range. 
Sputtering, plasma etching, plasma deposition, and l o w - , u r c  chemical vapor deposition arc 
performed in the medium vacuum range. Rcssurrs in the high vacuum range arc required for 
most thin-film preparation, electron microscopy, mass spectroscopy, crystal growth. x-ray and 
electron beam lithography, molccular beam epitaxy, and the productioo of cathaie ray and other 
vacuum tubes. [3] These environments arc completely unsuitable for the presence of human 
beings. The special suits that are worn in cuter space, for example. would be much less 
96 
0 . .  
p;ppropriate m a spcciatitcdvacuumch?mbauscd for acritial proctssing ask. Tht pmount of 
time nttd#l to produce thcdesircd pressure kvcl once tbc suited worker had enbaed the 
principal advantage would be &e ability to manipulate objects within the chamber without 
opening the vessel and subsequently n l v a x a t i n g ,  thus avoiding a very time coasmning 
proctss. Tbc availability of ~cuum-compltible robotr will improve the efficiency of many 
proccssts now carried out in vacuum and should encourage the use of vacuum proassing in 
c h a m b a ~ p r w e t o b e q u i t c  long. ncnced farobo<ics and au- systems inside the 
Vacuum C h a n b a m y  thUSbt ma W t t h u r  h 8 d avifollllltnt a d e r n  r#1clb A 
newarcas. 
Thcrt arc a number of diffcrcnccs between the vacuum environment of space rad that 
produced artificially on earth. Rcssures can be achieved in vacuum chambers which uc 
comparable to those in standard space orbits. Pmsurc lcvtls reach lob .nd IC9 Tar at 20 
and 800 km above sea level, respectively. However. in vacuum chambers on ernh, the 
outgassing from components in the chamber works dirrctly against the pnnping equipment In 
space that is no problem maintaining the prrssurr, but it is known that the outgassing of the 
space vehicle causes an expanding gas cloud to surround it. The shape of this dcpends on the 
venting paths of the hardware. the outgassing of external surfaces and beclrscattaing by the 
local atmosphere. Thus, outgassing is also a major co~yxrn in space. In addition. spaacrpft arc 
exposed to the full solar spectrum as opposed to only a fraction of the spectrum on eanh. 
Possibly tht most imponant difference between vacuum processing facilities on earth aad those 
in space is thc difference in the gravitational force. S o m  processing tasks may be ktta suited 
to the weightless envinwuncnt of space. 
3. APPLICATION: Gyroscope Assembly in High Vacuum 
Delco Systems Operations in Santa Babara, CA has developed a rtvolutionary new 
gyroscope, which is now entering the production stage. For reasons described later. the 
assembly must take place in a high vacuum environmnt of 10-8 Torr. 'Ihe CRSM is modifying 
an existing robot so that it can operate at high vacuum. It will be used by Delco for pduction 
of the new gyroscope. 
Gyroscope Description 
The gyroscope to be assembled is thc hemispherical resonator gyro (HRG) which D e b  has 
been developing since 1975. The HRG is not a laser based gyro. yet does not have thc romting 
parts usually found in mechanical Edward Loperand David Lynch of Deblist the 
following attractive characteristics of tftls gyroscope[41: 
Exnemely low power dissipation, and hence * 
Passive mechanical integration of angular 
rate, but with whole angle readout, making it 
immune to electrical power intaruption, and 
thus giving it high tolerance to nuclear 
radiation effcca 
Ability to operate at very high angular rates 
without pcrfomancc degmdatioa 
Capability to operate over the military 
temperature range without temperature 
coaml. 
The HRG consists of three principal parts 
constructed of fused quartz as shown in figure 1. 
negtigiblt warm-up transitnt 
Figure 1. Principal Cmpoacnts 
of the HRG (from [4)). 
97 
. ,  a 
Cyrosaopc Prudkcdon 
In orda to achieve adatively high prcxiuctioa ratc forthe gyro, Dclcohas pmposai the use 
of a large vacuum chamber as shown in Figure 3. Thcn will be a large central chamber 
surrounded by 12 smaller compamncnts. each of which may be opened to either the outside or 
the ant ra l  chamber. The central chamber will be constantly maintained at high vacuum 
Ideally, then. the raw gyro paru would be placed into compamncnt #I and be m v d  
sometime later as a completed gyro, with the intervening assembly tasks pa-formd 
automatically. Om alternative to this is a unal la  vacuum chamber in which all steps of thc 
continual and rimconsuming actions of venting and reevacuating the chamber. In d e r  to 
assembly would be paformd This would ltsult in an extrrmcly slow assunbly task due tu the 
figure& V r c m n n ~ c o n c c p f o r H R G A s s c m M y  
~lrdvlultapofthcina#scd nrrnufrcapingefficiarcythclpgaustmMydrambawould 
bing. a muns  of transferring gym putt btrantn vrsious strg# of assembly isrtquired A 
robapositiondatthcanmddrtdychrmbaisthcidalampontnt 
The availability of -e roboa is presently limited. although lhis is Wdy 10 
change in the near future. A procotypt vrcuumcompStiMc robot hu btca dcvelapcd by 
Yaskawa OfJapan. but thc 9131u sioc ofthis Idmtcdimhes it frrwncawidaraoa - fixustinrbt 
Dda,systtm Asrrscarchpogrtsscsoatbcdmbpnclltofncurnrrawpotibicrobas,Dtlco 
has jccided to have the CRSM modify m existingrobor foruse in theirassunbly ask. 'zbt 
motivaring fictas in thisdaiskm mere cost md ttn. Altbougb it is &sinble toohain rroba 
which was designed and built SpaCiFicrly fa& vrc~uncnvirrmnCnt. he fintrotpis mokrin 
a n c u M K m n p a t b l c W  ThiswilloawmaenpkUybydcingrmodificra<a - manexising 
robot. When a 'ground-up' vmumcompatiblc robot becomes available it can thcn be 
~ t o t h e m o d i f i e d r o b a .  
4. Description of the CMF E-310 Clan-Room Robot 
The robot undergoing modifiatim U E& CRSM is I GMF (-4 M O C O ~  - F ~ u c )  
RlDdel E - 3 1 0 ~ M  - d o t ,  aiginrllydcsigd f a =  in C ~ U I I  r04113 toclrrt 10. 
This robot was chosen for its size and configuration as well as its good accuracy and 
repeatability for a robot of its size. Tests at the CRSM have shown the rrpcrtability 10 be 
Figm 4) consisting of two linear axes and two rotational axes. The robot has three unio 
housings which art joined by the shafts of two liatsr axes The base bousiag contains the 
mo(0n f0rthcZaxisa.d the Theta-axis. The Zuirmooa. duough abclt.&ivcs akad saew - lincar bearing - linear guide rssembly which cltls~ the Z-axis shaft to move Vmically. An 
dropping when puwa is not availabk. ?he Thar-rris motoris tided to tht robot base h g h  
an RV gearrcduca and a pair ofspn gears A cross rdkr baring is used 1O supporr the robot 
~ ~ Q L I I I .  Tht E-3 10 uscd fOr the d y  asL h S  fW dcgrcts Ot frtcdom (sct 
elecmnnagnctic brake is installed on the topend ofthe lead ftrcw to p e n t  the robot fran 
99 
" .  
- R - m k  maintain Soomm stroke if possible; if reduced, 
- T b m - o t b : * f l K P ~  - Aipb&*flSOOlffatioa 
DesigItfnSlOOOCapauingcmrirormrnt 
caaQlc+h rryrdifirarirmwithinoQtycar. 
ItspltingsadrcrIlmtbelrufLlint&:vacumnchsmba 
Limit ncgtivce&caonIbevaarmnemrirolrmcnt (outgassingeoc) 
5 .  for 8 Vlcoum-Compmtlbk Robot 
Tbc design droboa favacuum beings togctbamany disciplines, inclpdiag tht shdy of 
kincnmtics, dptmics, control, sensors, mechanics, mataials, and tribology. Tribology, the 
uudy of friction, wear lad the application of lubricants, is critical when applied to 
v r c u v t i b l c  robon Txaditional lubricants have vaporprtssuns which art much too 
high for vacuum appliitiom, resulting in rapid evllporatioll and unpro&ctcd surfaces. Dry 
lubriants, espcci.lly MOS,. have been used in many high vacuum applicationS, howeva they 
mdto~nmedcbrisandnudrrplenishing~oftenthanwtt lubriwnts  Advanctsin 
both dry and wet lubricants arc being made rapidly, helping to make this important part ofthe 
The f m  decision in the modification of the GMF E-310 was between two basic 
phibsophi# Tberobotcould either be totally cxposcd to thcvaEaumenvironmnt or it could 
k salaj in atypcof"suit" which wouldallow theinsidecompoacnts toopcratcatatmosphcric 
pnturr. as they were originally designed to do. In order to exposc the entire robot to a 
pcssum of 1~ Torr, a number of key changes would have to be made. Thc majaroaes would 
drir ctroicc, itwasamcludcd that it wouldentail a substantial amount ofrcdesign work, and that 
a toQI exposure robot would be better designed from scratch. The goal then became one of 
&signing a new housing forthe robot which would seal it from the vacuum en- whilc 
as thc walls of a highquality vacuum chamba, yet rrmst also allow the $cshd movemtIlt by 
robot design less complex. 
k in the l u m  systaI& the surf= fiaish and mamials, and the mo<ors After examining 
-lishillg the design goalsassaforthin scctioa4. The scaling "suit" has mbe as leaklight 
d i n g  two lilxar (R and z) and two IMary (ncta and Alpha) lnotiom 
Rota?Y* 
A differentially pumped 360" rotatable plalfarm from Thermionics was chosen as the 
rotational sealing mechanism. As shown in the cross &on of figwe 5(a). the pladomr 
mains thra spring loaded seals which art 80% tcflon and 20% graphite. Twochambas art 
famed which axe pumped to different levels ofvacuom. For this application, the chamber 
closest to the armosphaic prcssurt d e  is roughed to a ximately lo' Tar, while the 
chmbcrclodesttothevacuumsideismaintainedbelowl osp" Tonusinganianpump. Figun6 
indicates the placcmntof thcromabk platfbrms m thedesign. 
(4 0 
Figun 5. (a) Diffennti&y pumped rotatable platform fa sealing Theta 
tad Alpha rotatioas. (b) Stainless stet1 M o w  for sealing R and 2 Linear 
mddons. 
101 
. .  . ,. . . . . . . . . - _ . . ~ . .  
3 .  
F i 6 .  ModifidE-31ORobot 
102 
. 
[2] J. kp. "What do we mean by prcssmt?", Vacuam, V d  20, No. 10, pp. 443444, 
1970. 
[3] John H. 0"anlon. "A Usds  Guide to Vacrmm Tcchndogy", John Wilty & Soas, 
Inc., 1980. 
- -  
16"-Joint Servicts Data Exchange for Inatial Systems, LOJ Angela N O ~ .  16, 
1982. 
[5l EJ. Lopa and D.D. Lynch, Tkjectcd Systan Performance Based 011 Rtctnt HRG 
Tat  Results", AvionicS S Y  confacace, Oa. 31 - Nclv. 3,1983, p ~ .  181.1 - 
18.1.6. 
[q EJ. Lopa and D.D. Lynch, "Hensisphaical Resoaator Gyro: Status Reports and Tcst 
Results", National Technical Meeting of the Institute of Navigation, Jan. 17-19, 
1984, san Diego, C A  
103 


Robot design for a vacuum environment

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