Vacuum interlock

The invention provides a two part vacuum interlock for a vacuum chamber wh utilizes the chamber itself as an interconnecting member.

BACKGROUND OF THE INVENTION 
In Patent Application Ser. No. 930264 (EPA No. 1876) filed on even date 
herewith by E. Vincent Patrick et al for a "Method and Apparatus to 
Fabricate Image Intensifier Tubes," there is disclosed a unique vacuum 
chamber system. This system employs a special transport mechanism 
described in Patent Application Ser. No. 930437 (EPA No. 1877) also filed 
on even date herewith by E. Vincent Patrick et al for a "Vacuum Sealed 
Manipulator." The chambers in the vacuum system are generally cylindrical 
in shape and the manipulator in each chamber is generally a cantilever arm 
which moves tube parts around a large circle of process stations within 
the chamber. While the rotation of the arm about the axis of the chamber 
can be unrestricted, radial movement is limited to 25 mm and axial 
(vertical) movement to 40 mm. One function of the arm is to move parts 
into and out of a vacuum lock. With conventional designs, this is very 
difficult and in general requires extensive additional vacuum hardware and 
motion feedthroughs. 
The conventional interlock uses an external vestibule which is added to a 
larger vacuum chamber by bolting onto the flange of an access port. The 
interlock chamber including the part entering or leaving the chamber 
remains outside the chamber. In the system described above, the 
manipulator cannot reach outside the chamber to position these parts as 
required. Additional mechanical devices must be added to the chamber. For 
example, part cradles that are magnetically propelled through glass walled 
tubing have been used for this function, but these complicate the task of 
keeping the chamber clean and can function improperly, on occasion 
damaging parts or delaying the vacuum processing underway, and by their 
configuration add a volume that is difficult to evacuate. 
BRIEF DESCRIPTION OF THE INVENTION 
It is an object of the present invention to provide a simple interlock 
structure which extends into and utilizes the wall structure of the main 
vacuum chamber in its operation. It is a further object to provide such an 
interlock wherein the part entering and leaving the vacuum is placed 
directly in the main chamber and is easily accessable once the interlock 
is open on the vacuum side. And further, an object is to provide a fully 
demountable interlock assembly such that any or all parts can be removed 
from the chamber for repair or replacement and such that the interlock can 
be installed in any suitably prepared opposed openings in the vacuum 
chamber. The interlock is to be bakeable to 400.degree. C. and to this end 
incorporates a metal-to-metal sealing system in the vacuum valve portion 
of the interlock.

DESCRIPTION OF INVENTION 
In the above mentioned figure a portion of the main vacuum chamber 10 is 
defined by an upper generally circular wall 11, a similar lower wall 12 
and a toroidal wall 13. These walls are welded together and have an upper 
portal flange member 14 and a lower portal flange member 15 welded 
thereto. The walls and flanges have mating openings for communication 
through the walls 11 and 12. One part 16 of the interlock, usually denoted 
as a vestibule, consists of a preferably straight upper tubing member 17 
having a length preferably several times its diameter. This tube is 
supported by an auxiliary flange portion 18 welded thereto and coupled to 
flange 14 by bolts or machine screws 19. A vacuum seal between these two 
flanges is provided by a copper gasket 20 which fits into grooves in the 
flanges, the grooves containing standard knife edge ridges which bite into 
the gasket. Outside the chamber the tube 17 terminates in a flange 21. A 
cover 22, which may include a hermitically sealed window 23, is bolted to 
flange 21 by means of additional bolts 24 and the same type of sealing 
gasket 23 as found between flanges 14 and 18 is employed. A tee arm tube 
26 of smaller diameter is welded into an aperture in tube 17 outside the 
chamber. This tube is also provided with a flange 27 and copper gasket 
assembly 28 as previously described to mate with the line to a standard 
sputter ion and roughing pump. This pump can reduce pressure in the 
smaller vestibule to approximately that of the main chamber in a fraction 
of time required to evacuate the main chamber and further includes a hand 
operated valve to flood the chamber, when desired, back to ambient 
atmospheric pressure. 
The vacuum sealing function of the interlock is performed by a special 
configuration of the conventional poppet valve. To this end, the tube 17 
inside the main chamber 10 terminates in a hardened stainless steel knife 
edge 29. This knife edge may be integral with tube 17 or be a separate 
coupling which is vacuum welded to the tube. The latter configuration 
facilitates construction and maintenance. A toroidal alignment collar 30 
is added to the knife edge 29. The interior diameter of the alignment 
collar is tapered, decreasing in dimension in the direction of the knife 
edge. 
A second part 31 of the interlock contains the poppet valve driver assembly 
31 and the vacuum valve sealing disc 41. It is attached to portal flange 
15 by means of a lower auxiliary flange 32, screws 33, and a copper gasket 
34 and knife edges on the flange (not shown) as described previously. The 
driver assembly includes a preferably straight lower tubing member 35 
welded to flange 32 which extends both inside and outside the chamber, its 
axis being coaxial with the upper tubing member 17. A stationary threaded 
driver member 36 fits within tubing member 35 and seats in an inner 
stepped portion of the end of the latter where it is vacuum welded in 
place. A rotatable driver member 37 is threaded through the stationary 
member and into a socket for rotation in a gate member 38. The outer end 
of the rotatable member 37 has a drive socket so that torsion can be 
applied. A bellows 40 completes the vacuum seal between the stationary 
member 40 and the gate member 38. The upper end of the gate member 
includes the usual metal (typically copper) vacuum sealing disc 41. The 
outer dimension of the gate member is either relieved or tapered to engage 
into the alignment collar 30. The mating of the tapered gate member and 
the tapered alignment collar is such that as the gate member moves into 
the alignment collar the sealing disc is aligned to the exact same 
location relative to the knife edge 29 so that the same cut is made in the 
sealing disc at each sealing cycle. The rotatable driver 37 is used to 
raise and lower the gate member and to apply the necessary force to obtain 
a leak tight vacuum seal between the sealing disc and the knife edge. 
The two sections of the interlock are demountable from the main chamber by 
means of flange couplings 18 and 14 or 32 and 14. With the following 
configuration, standard, commercially available, vacuum flanges may be 
used for the coupling. Because of the high forces normally required to 
obtain a vacuum seal with metal-to-metal valve seals, typically 600 lbs 
per inch of knife edge circumference, all vacuum flanges must have 
auxiliary exterior welds, such as welds 44 and 45 on flanges 18 and 14, to 
reduce the stress on the vacuum welds 46 and 47. The flange gasket sealing 
system 20 must be one in which the flanges 18 and 14 can be bolted in 
contact and prestressed so that the force of sealing the disc 41 to knife 
edge 29 is absorbed by the bolt 19 preload without the reduction of the 
gasket 20 sealing pressure. 
To assure sealing of the valve, care must be taken in construction so that 
the knife edge 29 is parallel to the mating face of flange 18 and 
similarly gate member 38 is parallel to flange 32. Minor deviations in 
concentricity due to mounting of the two separate interlock parts is 
corrected by alignment collar 30. Any portal to which the interlock is to 
be mounted must be suitably prepared in that the portal flanges 15 and 14 
shall be parallel and have the reinforcing weldments discussed above. To 
this end, portal preparation is readily satisfied by counterbores such as 
48. Chamber structure, such as walls 11 and 12 must be sufficiently rigid 
to accommodate the above sealing forces with minimum reflection. 
With the above construction, the interlock is bakeable to 400.degree. C. 
without loss of vacuum integrity. The minor variations in alignment due to 
the use of separate interlock members have resulted in no more than a 25% 
reduction in service range of sealing force for standard metal sealing 
discs. Thus the sealing disc is capable of hundreds of sealing cycles. 
With the poppet valve closed (driver 37 fully up) parts to be transferred 
into the main chamber are entered into the vestibule 16 by removing the 
flange cover 22. By means of suitable part carriers, the part, or series 
of parts, are placed in cradle 43. This cradle is attached to the sealing 
disc 41 by means of a suitable protrusion 42 on the disc or blind topped 
holes into the disc. After resealing flange cover 22 and evacuating the 
vestibule 16, the driver is lowered and the cradle with parts moved into 
the main chamber. The parts are unstacked from the cradle by manipulator 
49, of a type previously discussed, and distributed to appropriate 
locations in the chamber. With the poppet valve open, the manipulator arm 
is obviously freer to engage and remove the pabts. Finished assemblies or 
reject parts are removed from the chamber by the reverse of the above 
operation. The use of a vacuum window 50 facilitates the operation of part 
transfer from the cradle to the manipulator and permits sealing disc 
replacement without demounting the interlock. There is no limitation on 
the size of either the diameter of the vestibule or the open clearance 
between sealing disc 41 and alignment collar 30. Both dimensions can be 
designed to meet part size and numbers per load requirements. The only 
consideration is the increased force needed to obtain a vacuum seal for 
larger diameter valves and hence mechanical requirements for the strength 
of the chamber shell. For high vacuum compatibility, all members, except 
the sealing disc, are conveniently fabricated of stainless steel. 
Sealing or locking tube 17 with the gate member automatically inserts the 
cradle 43 and its contents from the main chamber into the tube and 
unsealing or delocking performs the reverse function. Removing the cradle 
or its contents from the tube externally can be a more tedious operation, 
but being an external operation this is not critical. Generally the length 
of tube 17 will be about equal to the height of the chamber. The internal 
length in this embodiment was chosen to place the tube near the middle of 
the chamber and obviate the need for a long bellows 40 and long threaded 
driver members 36 and 37, since the sample height in this instance is only 
a small fraction of the chamber height. A tall sample would, of course, 
necessitate a short internal intrusion of tube 17 and a long external tube 
portion, as well as a long bellows and jack arrangement. The latter 
arrangement would also have the advantage of handling both short and tall 
samples. It might also be advantageous to stack a number of short samples 
into one tall load. The cradle could be designated to maintain each of 
these short samples at a fixed spacing from the non-rotatable gate member 
38 and height of the latter varied to bring any desired sample within 
range of the arm 44. 
Many variations of the above structures will be obvious to those skilled in 
the art, but the invention is not to be limited except as defined in the 
claims which follow.