Planar oscillatory stirring apparatus

Apparatus (11) for applying planar oscillations to a container (13). Pressurized air (99) is supplied to a moveable slide plate (27) which employs arms (19) having an air bearing vent structure (29, 31) which allows the slide plate to float and to translate. The container (13) to be oscillated is secured to the upper surface of the slide plate (27). A motor (39) driven rotating eccentric shaft (59) loosely extends into a center hole bearing (37) of the slide plate (27) to cause the oscillations.

TECHNICAL FIELD 
This invention relates to an apparatus for applying planar oscillations, 
and more particularly to an apparatus for applying horizontal 
perpendicular oscillations to a sealed container such as a Bridgman 
crystal growth crucible. 
BACKGROUND ART 
In crystal growth from solution, stirring has been a vital part of the 
crystallization process. The major benefit is that the solution is 
homogenized, so that regions of locally high solute concentration where 
new crystals might nucleate (even in the presence of seed crystals or of 
crystals grown in the initial stages) can be avoided. In addition, the 
stirring action reduces the inhomogeneity in supersaturation between the 
face centers and edges, and so favors the growth of well facetted crystals 
rather than a tendency towards dendritic growth. 
Efficient stirring is easily accomplished in many simple open systems like 
those used for aqueous solution growth, by the insertion of a rod fitted 
with a paddle and rotated about a vertical axis. Glass rods are widely 
used for this purpose in commercial crystallizers. There are, however, 
several systems for which this simple technique is not possible. These 
include open systems in which finding a stirrer which is not attacked by 
the liquid is difficult and closed systems in which volatile reactive 
materials are held in sealed containers. 
An effective method for stirring liquids in sealed containers is the 
accelerated crucible rotation technique in which the container is 
periodically accelerated and decelerated, and the sense of the accelerated 
rotation may be reversed. The technique has been recognized as a valuable 
tool in crystal growth, particularly for the growth of magnetic garnet 
crystals from lead salt solvents in sealed platinum containers. 
STATEMENT OF THE INVENTION 
It has been discovered that low frequency, orthogonal oscillations applied 
horizontally to a Bridgman crucible provides a very rigorous stirring 
action, comparable with and often more effective by an order of magnitude 
than the accelerated crucible rotation technique. The stirring is 
particularly effective when coupled low frequency oscillations are applied 
at right angles so that there is simultaneous movement of the crucible in 
both horizontal directions. 
To accomplish the discovery, a unique planar motion air bearing support for 
a sealed container has been made. The air bearing support has a moveable 
slide plate sandwiched between two fixed parallel support plates. 
Pressurized air is supplied to the moveable slide plate which employs a 
tri-arm air bearing vent structure which allows the slide plate to float 
and to translate between the parallel support plates. The container to be 
orthogonal oscillated is secured to the upper surface of the slide plate 
through an aperture in the upper support plate. The slide plate is 
provided with a center bearing hole which receives an eccentric cam shaft 
fixed to a motor shaft that extends through a small aperture in the lower 
support plate. The eccentric shaft does not interfere with the vertical 
float of the side plate. 
Accordingly, it is an object of the present invention to provide an 
apparatus for stirring using planar orthogonal axes oscillations. 
Another object is to provide an apparatus that given relatively 
harmonic-and-noise-free planar orthogonal axes oscillations. 
Yet another object is to provide a apparatus that applies controlled 
perpendicular oscillations to a sealed container that is free from 
microphonic and other unwanted oscillations. 
A further object is to provide a planar motion air bearing support that is 
capable of supporting a large mass at the end of a long moment arm.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to the drawings, particularly FIG. 1, there is shown the planar 
motion air bearing support 11 of the present invention with an elongated 
sealed container or crucible 13 fixed thereto. The sealed container 13 is 
adapted to have therein a liquid 15 utilized in crystal growth 17. A 
particular stirring action is applied to the liquid 15 by the motion of 
the air bearing support 11 to obtain improved crystal quality. 
The air bearing support 11 has a three arm structure slide plate 19 that is 
sandwiched between two fixed parallel support plates 21, 23. The 
separation by block dividers 25 of the parallel support plates 21, 23 is 
such as to provide standard air bearing tolerances from each side of the 
slide plate of approximately 0.001 inch. Midway of the length of each arm 
27 of the slide plate 19 is an upper and lower circular air bearing recess 
29, 31 (see FIG. 5) each of which has a center air outlet hole 33 which 
communicates with an internal arm passageway 35 that extends from the arm 
end back to the center area of the slide plate 19 and communicates with a 
distinct air inlet hole 71 in the upper central portion 36. 
In FIG. 1 is shown the small electric motor 39 (Electrocraft Model 586B) 
that is fastened by bolts 41 to an adapter spool member 43 that has upper 
and lower flanges 45, 47 and a central passageway 49. The motor 39 is 
fastened by bolts 47 to the lower flange 47. The upper flange 45 is 
secured by bolts 51 to the lower support plate 23. The motor shaft 53 is 
secured by set screws to an extension shaft 55 which rotates within the 
central passageway 49 of the spool member 43. The extension shaft 55 
extends through a hole 57 in the lower support plate 23. The upper end of 
the extension shaft 55 has an off-center axis dowel/cam 59 which extends 
loosely within the center axis hole bearing of the slide plate 19 (See 
FIG. 5) as not to interfere with its vertical float. Therefore, as the 
extension shaft 55 is rotated by the motor 39 the slide plate 19 is acted 
upon by the eccentric dowel 59 causing the floating plate 19 to oscillate 
along planar orthogonal axes. The air bearings 31 assures very low 
frictional movement of the slide plate 19 with good stiffness so as to 
adequately support the elongated sealed container 13. 
The fixed parallel support plates 21, 23 are supported by posts 60 from a 
base member 61. Four posts one at each corner of the support plates 21, 23 
are provided. The posts 60 are secured to the base plate 61 and the lower 
support plate 23 by bolts 63 or other equivalent devices. 
Referring again to FIG. 1, there is shown the upper adapter support member 
65 for securing the seal container 13 to the upper, central area 67 of the 
slide plate 19. The support member 65 has a separate lower air plenum 
chamber 69 which communicates with the three air inlet holes 71 of the 
slide plate 19. A standard hose fitting (Swageloc) 73 extending through 
the side wall of the member 65 permits air to be forced into the plenum 
chamber 69. The upper support plate 21 has a large central hole 75 which 
permits the orthogonal oscillation of the slide member 19 within the range 
caused by the rotation of the off-axis dowel 59. To cause the slide to 
vibrate 1/8 inches in the X and Y planes with a phase relationship of 90 
degrees have been found to be satisfactory in providing the needed 
stirring action. 
The upper support member 65 has a lower circular flange which is bolted to 
the upper surface of the slide plate 19. An O-ring 79 fits within a groove 
81 in the face of the slide plate 19 beneath the flange 77 when assembled 
so as to seal against air leaks from the plenum chamber 69. 
The upper portion of the support member is tubular and pipe-like and is 
adapted to receive the lower end of the elongated sealed glass container 
13. The sealed container 13 is cylindrical and has an outer diameter 
smaller than the inner diameter of the upper opening 83 of the support 
member 65 so as to permit the use of a clamping means which includes a cap 
85 which is screwed onto the upper threaded portion 87 of the support 65. 
The cap 85 has a central opening through which the sealed container 13 
extends. The clamping means shown in FIG. 1 includes an upper cylindrical 
tubular member 89 with a flange 91 that the cap member 85 acts against, 
and another lower tubular cylindrical member 93 that encircles the lower 
portion of the seal container 13. Two O-rings 95, 97 are used, one 97 
between the lower cylindrical member 93 and the bottom of the end of the 
container 13, and another 95 between the lower and upper tubular 
cylindrical members 89, 93. The upper and lower tubular cylindrical 
members 89, 93 act as compressors when assembled. As the cap 85 is screwed 
down on the threaded portion 87, the O-rings 95, 97 are trapped and 
compressed causing a capturing action against the elongated seal container 
13. 
In operation, the sealed elongated container 13 containing the crystal 
growth material 15 is clamped to the upper support member 65. Pressurized 
air 99 is supplied through the fitting 73 to the lower separate air 
chamber 69 within the support 65 which air flows in the direction of the 
arrows 99 shown in FIG. 1 to provide adequate support for the slide plate 
19. Then, the motor 39 is turned on which causes the floating slide plate 
19 to slide and to vibrate in a planar manner with a phase relationship of 
90.degree. describing a circle. 
It is evident that the floating slide plate 19 may easily be modified for 
rotation movement by not using an off-set dowel 59 and simply securing the 
center axis of the slide plate 19 to the shaft extension 55. 
It has been found that the invention described is capable of supporting a 
large mass at the end of a long moment arm, and to be free from 
microphonic and other unwanted oscillations. Mixing time of the crystal 
growth liquid using the invention exceeds the other techniques herebefore 
used. 
While the invention has been described relative to a specific embodiment, 
it is evident that modifications and changes may be made with regard 
thereto without departing from the scope of the invention.