Abstract:
A work piece transfer mechanism for use in a chamber has at least one port through which a work piece may be passed along a linear work piece transfer path between a retracted location inside the chamber and an extended location outside the chamber. The chamber has a predetermined internal dimension of given axial extent in the direction of the transfer path, and the transfer mechanism includes a work piece support movable with a linear stroke. The work piece support is driven along the linear stroke by a drive lever pivotally attached to the work piece support by a pivot, and the drive lever is drivable such that the pivot is driven along a linear path to move the work piece support along the linear work piece transfer path. The linear work piece transfer path includes a portion beyond the port of axial extent greater than predetermined internal dimension.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to an improved transfer mechanism in particular, but not exclusively for transferring articles into and out of a confined area such as a vacuum treatment chamber, and to equipment incorporating such mechanisms. 
     2.Description of the Related Art 
     Known vacuum chambers might typically employ a rack and pinion type mechanism within the chamber which extends through a port in the chamber and includes a table which can be loaded with work pieces. The table is then retracted using the rack and pinion mechanism into the chamber. The rack and pinion type mechanisms employed in known mechanisms typically achieve a maximum reach out of the chamber of less than 70% of the chamber width or diameter. However it is very desirable to reach further out of the vacuum chamber with a simple transfer mechanism, to improve the layout of the processing area surrounding the chamber. Thus the ratio of the reach of a transfer mechanism compared to the area that it occupies in its closed state is an important benchmark. Where a transfer mechanism is used in a vacuum chamber, for example an ultra high vacuum (UHV) chamber, purely mechanical devices are preferred. 
     In some instances, it is preferred that a work piece in a confined space such as a vacuum chamber is loaded into the chamber through one port and unloaded through another port. Therefore, it is desirable also that the transfer mechanism employed is rotatable to achieve the different transfer directions. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is, in embodiments, directed to addressing the problems mentioned above. 
     According to one aspect, this invention provides a work piece transfer mechanism for use in a chamber having at least one port through which a work piece may be passed along a linear work piece transfer path between a retracted location inside the chamber and an extended location outside the chamber, the chamber having a predetermined internal dimension of given axial extent in the direction of said work piece transfer path, the work piece transfer mechanism including a work piece support movable with a linear stroke, the work piece support being driven along said linear stroke by means of a drive lever pivotally attached to the work piece support by means of a pivot, said drive lever being drivable such that the pivot is driven along a linear path to move said work piece support along said linear work piece transfer path, wherein said linear work piece transfer path comprises a portion beyond said port of axial extent greater than predetermined internal dimension. 
     According to another aspect, a work piece transfer mechanism for use in a chamber having at least one port through which a work piece may be passed along a linear work piece transfer path between a retracted location inside the chamber and an extended location outside the chamber, the chamber having a predetermined internal dimension of given axial extent in the direction of said work piece transfer path, the work piece transfer mechanism including a work piece support movable with a linear stroke, the work piece support being driven along said linear stroke by means of a drive lever pivotally attached to the work piece support by means of a pivot, said drive lever being drivable such that the pivot is driven along a linear path to move said work piece support along said linear work piece transfer path, wherein the midpoint of the linear path of the pivot is offset from the midpoint of the predetermined internal dimension of the chamber, in a direction towards said port. 
     According to a yet another aspect, the invention provides a work piece transfer mechanism, including a work piece support moveable with a linear stroke, the work piece support being drivable in said linear stroke by means of a drive lever pivotally attached to the work piece support by means of a pivot, said drive lever being drivable such that the pivot is driven along a linear path parallel with said substantially linear stroke. 
     Where the mechanism is used in a confined space such as for example a vacuum chamber, the mechanism is conveniently such as to provide a linear stroke of length greater than the chamber dimensions. 
     In an embodiment the drive lever is driven by a plurality of rotary elements which describe the linear path of the pivot. 
     Conveniently the plurality of rotary elements forms an epicycloid straight line linkage, which could be for example a Cardan mechanism. 
     In an embodiment the plurality of rotary elements, or the Cardan mechanism includes a fixed gear and a carriage rotatably mounted about the effective centre of the fixed gear, said carriage supporting a first idler gear including first idler gear teeth in intermeshing engagement with teeth of the fixed gear, the carriage rotatably supporting a second drive gear including teeth in intermeshing engagement with the teeth of the first idler gear, the second drive gear being non-rotatably connected to the drive lever, the arrangement being such that rotational driving of the carriage causes rotation of the first idler gear with respect to the fixed gear, which in turn produces rotation of the second drive gear and the drive lever, the ratios of the effective diameters of the respective gears being such that the said pivot is caused to move along said linear path. 
     Depending on the size of the passage through a port the drive arm may be arcuate to allow the effective length thereof to be increased without engaging the walls defining the port. 
     Preferably the mechanism includes an anti-backlash provision. This may comprise a spring biasing the drive lever. Conveniently the spring is a spiral or clock spring adapted to provide a bias force throughout the stroke of movement in both directions of movement. 
     Preferably, said carriage is caused to rotate about the centre of the fixed gear by means of a further drive gear, driven by a driving pinion. 
     In an embodiment the work piece support is mounted for movement on or in a telescoping support arm. 
     The fixed gear may be part-circular, e.g. segment-shaped or sector-shaped with teeth around the circular part only of the periphery. In an embodiment said carriage is rotated by the further drive gear and pinion through approximately 180 degrees from a starting position, to effect said linear stroke of the work support to its maximum extent and is rotatable in the opposite sense back through the 180 degrees to move the work support in the opposite linear direction to the starting position of the work support. 
     In an embodiment the transfer mechanism further includes a drive for rotatably driving said drive pinion to cause said linear stroke. 
     Conveniently the drive further includes a lift for lifting and lowering said transfer mechanism in a direction substantially transverse to the linear stroke. 
     Preferably, the drive provides for rotating the transfer mechanism about an axis generally transverse to the linear stroke. 
     More preferably, said axis is coincident with a driving axis of the drive pinion. 
     Conveniently, said axis is offset relative to the centre of the fixed gear. 
     In addition, said axis may be parallel or coincident with the direction of lifting and lowering. 
     According to a second aspect there is provided a vacuum chamber including a transfer mechanism as described above. 
     In an embodiment, the chamber includes a chamber body and said drive is external to said body. 
     In an embodiment said chamber body includes more than one radial port and the rotation of the mechanism about the axis allows the work piece support to be passed through each of said more than one radial port along the path of said linear stroke. 
     In an embodiment, the chamber is generally cylindrical in plan and the stroke of the transfer mechanism exceeds the diameter of the chamber. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention can be put into effect in numerous ways, one embodiment only being described below by way of example only, with reference to the drawings wherein: 
         FIG. 1  shows a pictorial view of a transfer mechanism according to the invention, housed within a vacuum chamber; 
         FIG. 2  shows the vertical section through the transfer mechanism within the chamber and an external drive; 
         FIGS. 3 ,  4  and  5  show a plan view of the mechanism in three states of operation, and 
         FIG. 6  illustrates an anti-backlash arrangement for the mechanism. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a transfer mechanism  10  housed generally within an ultra high vacuum (UHV) chamber  20 . The chamber  20  will, generally, be what is know as a pancake chamber of flat cylindrical form, serving as the hub of a plurality chambers connected to the pancake by a number of radial ports,  22   a  to  22   e  for example. The chamber has two axial ports  49  and  50 , to the upper one  49  of which is connected the drive mechanism  40  as described below, the lower one  50  being available for pumping for example. The transfer mechanism  10  includes a telescopic arm  12 , described in more detail below, which supports a work piece support  11  which can be passed with linear motion into and out of the chamber  20  via the radial access ports  22   a  to  22   e . The telescopic arm  20  is driven with a reciprocal linear stroke by means of an epicycloid linear mechanism, which here is in the form of a Cardan gear and lever mechanism shown generally by the reference  30 . The Cardan mechanism includes a drive pinion  31 , a further drive gear  32 , a fixed gear segment  33 , a driven carriage  34  non-rotatably secured to the further drive gear  32 , an idler gear  35  in intermeshing engagement with the fixed gear segment  33 , and a second drive gear  36  having rigidly connected thereto a drive lever  37 . The drive lever  37  is connected to a pivot pin  38  which is secured to the end of a member of the telescopic arm  12 . 
     The operation of the Cardan mechanism is described in more detail below, but the drive lever  37  moves the pivot pin in a linear path without side loads. The transfer mechanism  10 , in use, can rotate wholly about a Z axis generally central to the chamber  20 . Thus, the linear stroke of the telescopic arm  12  can be in any radial direction in a plane transverse to the Z axis. In addition, the transfer mechanism  10  can be traversed along the Z axis (in the Z direction). Thus, the transfer mechanism can be used to pick up work pieces W from outside the chamber  20 , by means of lifting them in the Z direction prior to bringing them into the chamber  20 . Once in the chamber  20  the work piece can be rotated about the Z axis, for transfer via a further port if required, or for unloading from the chamber  20 . 
       FIG. 2  is a vertical section through the Z axis, showing additionally a drive  40  for driving the transfer mechanism  10 . The drive  40  includes a drive shaft  41  which, in use rotates the drive pinion  31  of the Cardan mechanism in clockwise and anticlockwise directions to extend and retract the telescopic arm  12 . The drive shaft  41  is disposed concentrically within a drive tube  48  which itself is rigidly connected to the transfer mechanism  10  via a mounting bracket  43 . Rotation of the drive tube  48  revolves the whole transfer mechanism  10  about the Z axis in the direction of arrows R to angularly move the telescopic arm to align with different ports  22   a  to  22   e . The drive  40  is rigidly connected to the vacuum chamber  20  at a mounting flange of axial port  49 . The drive  40  further includes a drive motor  15  for driving the drive shaft  41 , via a concentric magnetic coupling  42 . A further drive motor  45  in use rotates the drive tube  48  via a further concentric magnetic coupling  44 . The magnetic couplings  42 ,  44  each comprise an external drive element magnetically coupled to an internal drive element. The drive  40  further includes a Z shift mechanism  46  which provides translational movement of the drive tube  48  along the Z axis, to shift the transfer mechanism  10  in the Z direction. The motor  15  and external drive element of magnetic coupling  42  for turning the drive pinion  31  via drive shaft  41 , are mounted on the external drive element of the magnetic coupling  44 , so that the external drive element of coupling  42  rotates with the external drive element of coupling  44  as it is rotated. In practice this ensures that the drive tube  48  and the drive pinion  31  will rotate together, unless the motor  15  is activated. This avoids complicated synchronisation of the rotation of the whole transfer mechanism and the rotation of the drive pinion  31 . 
     Shown in  FIG. 2  also are sections through the drive pinion  31 , the driven gear  32  and the static gear segment  33 . The static gear  33  is mounted to the telescopic arm  12  by means of a mounting frame  39 . 
       FIG. 3  shows a section through the vacuum chamber  20 , showing a plan view of the transfer mechanism  10 . The chamber  20  shown includes 5 access ports,  22   a, b, c, d  and  e . Otherwise the chamber  20  is identical to the chamber shown in the previous Figures. The mechanism  10  can be rotated about the Z axis, which in this embodiment coincides with the axis of the drive pinion  31 . In that case, the work piece support  11  will rotate in the direction of arrows R. The work piece support  11  is also moveable with linear movement in the direction of arrow A. The linear movement is provided by a telescopic sliding arm  12 , driven by the Cardan mechanism  30 . 
     In use, the drive pinion  31  is rotated in the direction of arrow B. This in turn causes the driven gear  32  to rotate in the opposite direction. Carriage  34  is rigidly connected to the driven gear  32  and rotates in the same direction as that gear. This motion causes the idler gear  35  to orbit around the fixed gear segment  33 . The idler gear  35  is rotatably supported on the arm  34 . The orbiting and rotating motion of the idler gear  35  in turn causes rotation of a further gear  36 . A drive lever  37  is rigidly connected to the further gear  36  and rotates therewith. The distal end of the guide lever  37  is connected to a pivot pin  38 , in turn attached to the telescopic arm  12 . 
     The arrangement of the Cardan gears is such that the pivot pin  38  is driven in the direction of arrow A with linear motion. In turn, this forces the work piece support  11  in the direction of arrow A to exit the chamber to transfer a work piece supported thereon. This linear movement is a function of the gearing and linkages of the Cardan mechanism, and is not necessarily dependent on the constraint of the telescopic arm or other constraint. 
       FIG. 4  shows the Cardan mechanism approximately half way through its stroke and showing the telescopic arm  12  partially extended. 
       FIG. 5  shows the Cardan mechanism at full stroke with the telescopic arm  12  fully extended. In this view the construction of the telescopic arm  12  is more clearly shown. The arm  12  includes an outer section  12   d  and inner sections  12   a ,  12   b  and  12   c . In this construction, the inner section  12   c  extends from the work piece support  11  to the pivot pin  38  and is supported in its extended condition by the sections  12   d ,  12   a  and  12   b . In this embodiment, ball bearings are employed between the sections to provide rolling support. When extended, the mechanism  10  can be used to pick up work pieces, for example semiconductor material which is to be treated, or which has already been treated, by means of chemical vapour deposition. Rotation of the drive pinion  31  in the direction opposite to direction B, moves the mechanism back to its starting position as shown in  FIG. 3 . 
     Referring to  FIGS. 3 ,  4  and  5  it will be noted that the drive pinion  31  and further driven gear  32  allow the Cardan mechanism to have a carriage  34  which rotates about the drive Z axis, which is offset in the direction A from the axes of the chamber and the drive shaft  41 . This results in a greater throw of the lever arm  37  in the direction of arrow A and consequently a greater reach of the mechanism outside the chamber  20 . In this embodiment, the drive pinion  31  and further drive gear  32  form additional gears to a standard Cardan mechanism and offset the centre C of the Cardan mechanism, at the centre of the fixed gear  32 , from the generally central Z axis of the chamber. 
     One embodiment only has been described above and illustrated, however, it will be apparent to the skilled addressee that modifications, variants, omissions and additions are possible within the scope of the invention. The Cardan mechanism described uses a gear segment  33  and is driven in both clockwise and anti clockwise directions for transfer of the work piece support  11 . However, the Cardan mechanism  30  will operate in a satisfactory reciprocal manner if it is driven only in one sense and if the static gear  33  is made whole. Although the transfer mechanism provides angular movement about a Z axis and radial movement in the X-Y plane, it will be appreciated that this mechanism could be used in applications where there was no angular movement. 
     The invention has been described as employed with a UHV chamber  20 . However, other applications for the transfer mechanism are envisaged. For example, the mechanism  10  could be employed externally to apparatus that needs to be loaded and unloaded with linear motion, for example a long narrow furnace or other work treatment area. The transfer device  10  provides a stroke for the work piece support  11  which is greater than the dimensions of the chamber  20 , and thus the stroke is greater than that achievable by means of other transfer mechanisms. 
     Referring now to  FIG. 6 , in this modification the mechanism is provided with two anti-backlash features. Firstly, a flexure feature  60  within arm  34  is provided which urges the idler gear  35  in a radial direction towards a notional line connecting the centres of the fixed gear  33  and the second drive gear  36 , to maintain tight meshing engagement between the three gears and to reduce backlash. Secondly, a spiral clock spring  62  provides a continuous bias torque on the second drive gear  36  to bias the entire drive train back to the motor in one direction throughout the range of angular movement of the second drive gear. The inner end of the spring is attached to a shaft  64  which rotates with the second gear, and the outer end is fixed to an anchorage  66  provided on the lever  34 .