Patent Number: 042726824
Section: description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, there is shown an ion milling machine, generally designated by the reference numeral 10, having a main working chamber 12, a specimen positioning cylinder 14 and a small upper chamber 16. A piston 18 is disposed for vertical movement in cylinder 14 and extends into working chamber 12. Positioning cylinder 14, having a neck portion 15, is secured to the bottom of working chamber 12. An O-ring seal 20 is provided around neck 15 which extends from cylinder 14 into the lower portion of working chamber 12. A vacuum tight seal is thus provided between neck 15 and work chamber 12. Elongated piston 18 extends through the neck 15 of positioning cylinder 14 and into working chamber 12. An O-ring seal 22 provides a seal between piston 18 and the neck 15 of positioning cylinder 14. A sealing plate 24 is slidably disposed within cylinder 14 around piston 18. Sealing plate 24 includes an O-ring seal 26 which provides a pressure seal between sealing plate 24 and the inner wall of cylinder 14. Another O-ring seal 28 provides a seal between sealing plate 24 and piston 18. Bearing 38 is provided between sealing plate 24 and piston 18 to facilitate rotation of piston 18 during ion milling operations. A port 30 is provided for communicating with the inside of cylinder 14. Piston 12 is held in its lowered operating position as shown in FIG. 1 by admitting pressurized gas into cylinder 14 through port 30. The pressurized gas entering cylinder 14 through port 30 forces sealing plate 24 downwardly and this in turn moves piston 18 toward its lowered position. A stop plate 40 is provided on the bottom of cylinder 14. As sealing plate 24 is forced downwardly, it engages and is stopped by stop plate 40. Atmospheric pressure tends to bias piston 18 upwardly because working chamber 12 is evacuated. However, the pressurized gas admitted through port 30 and acting upon sealing price 24 overcomes this upward bias and moves piston 18 to its lowered position. In its lowered position, piston 18 is rotated about its vertical axis by a drive motor 32 acting through meshed nylon bevel gears 34 and 36, the latter being secured to the bottom of piston 18. Stop plate 40 has an opening 42 formed therethrough which is larger in diameter than bevel gear 36. Bevel gear 36 can thus pass through opening 42 and move into cylinder 14 when piston 18 moves upwardly. A specimen 50 to be thinned by ion milling machine 10 is mounted on the horizontal top surface of specimen holder 52 which is screwed onto the top of piston 18. Ion guns 54 are movably mounted within work chamber 12. Ion guns 54 direct beams of ions along paths 56 and 56' to the upper and lower surfaces, respectively, of specimen 50 as it slowly rotates with the rotation of piston 18. To raise the specimen 50 for easy viewing, the pressurized gas in positioning cylinder 14 is released and atmospheric pressure acting on piston 18 forces piston 18 to rise until it is stopped by the sealing plate 24 engaging the top of cylinder 14. A limit switch (not shown) senses the upward movement of piston 18 and stops drive motor 32; this facilitates re-engagement of bevel gears 34 and 36 when piston 18 is lowered to resume ion milling operations. A sealing O-ring 58 is disposed in the top opening of working chamber 12 to provide an air tight seal between working chamber 12 and piston 18 as piston 18 raises specimen holder 52 into smaller chamber 16. When piston 18 is in the raised position, a vacuum tight seal is thereby provided between small upper chamber 16 and working chamber 12. A phantom view of specimen holder 52 in its fully raised position within upper chamber 16 is shown in FIG. 1. In this position, specimen 50 can be inspected at close quarters through transparent viewing window 60. If desired, small upper chamber 16 can be removed from the work chamber 12 by admitting air into the inside of the upper chamber by depressing valve 62. When the pressure inside of upper chamber 16 is raised to atmospheric, chamber 16 can be lifted away, thereby exposing specimen 50. Specimen holder 52 can then be unscrewed from the top of piston 18 to remove the specimen. The specimen 50 on holder 52 is returned to working chamber 12 by first screwing holder 52 onto the top of piston 18. The small upper chamber 16 is then repositioned over specimen holder 52 and the air inside of upper chamber 16 is evacuated by depressing vacuum valve 64 which provides communication between upper chamber 16 and a vacuum source line 66. When chamber 16 is evacuated, pressurized gas is admitted to cylinder 14 to force sealing plate 24 downwardly and move the specimen into its normal working position in the evacuated working chamber 12. As piston 18 reaches its lowered position, the limit switch described above is actuated as bevel gears 34 and 36 engage. Motor 32 is thereby re-started to rotate piston 18 at a relatively slow speed, such as 1 rpm, to resume ion milling operations. Electrical isolation of piston 18 during ion milling operations is provided by nylon gears 34 and 36, the various rubber O-rings described above, plastic screws and washings which attach stop plate 40 to cylinder 14, and a plastic bushing within neck 15. A micro-ammeter (not shown) connected between stop plate 40 and work chamber 12 gives a continual indicaton of the ion and electron currents flowing between the ion guns 54 and the specimen 50 and specimen holder 52.