Rotating shuttle payload platform

[0002] Not Applicable

[0003] Not Applicable

[0004] The present invention relates generally to manufacturing operations, and more specifically to a system and apparatus for transport of semiconductor wafers in a semiconductor wafer fabrication facility.

[0005] Shuttle platforms are known which transport a payload, such as a semiconductor wafer pod, about a manufacturing facility. The payload is manipulated by various fabrication processes at different locations. The use of a shuttle platform expedites transport, provides precise placement, and minimizes the potential for operator error, such as a dropped payload. In manufacturing of delicate products, such as semiconductor wafers, operator error can result in substantial losses.

[0006] It is often advantageous to rotate a payload on a shuttle platform. Rotation serves to dispose the payload for optimal access by the various fabrication processes which manipulate the payload. A payload may be rotated to orient the payload for storage, to position the payload for access to a sealed environment, to allow for pickup by a robotic arm, and for other fabrication operations.

[0007] Rotation may be provided by direct activation from a drive source, such as a servo motor, or selectively provided through a rotary indexing mechanism. A separate drive source, however, must then be provided and powered, thereby increasing complexity and cost. Further, such a drive source must be calibrated to provide the precise positioning required. Finally, as a payload such as semiconductor wafers must not be subjected to bumping or jarring, rotation must not accelerate or decelerate too abruptly to avoid damaging the payload.

[0008] It would be beneficial, therefore, to provide a rotating payload platform which does not require a separate drive source, which provides a smooth motion profile through rotary acceleration and deceleration, and which minimizes calibration maintenance without sacrificing precision of rotation.

[0009] A semiconductor wafer pod payload platform is operable for rotation in response to linear movement of the platform by a cam assembly having rollers adapted to engage a cam surface. The payload platform is rotatably attached to a shuttle platform adapted for movement along linear rails. The shuttle platform is supported by shuttle glides adapted to move along the linear rails. A cam follower assembly is connected to the payload platform through a shaft extending through the shuttle platform and operable to rotate the payload platform. A cam surface substantially parallel to the linear rails is adapted to engage rollers on the cam follower assembly. Linear movement of the shuttle platform causes the rollers on the cam follower assembly to engage the cam surface and dispose the cam follower assembly so as to rotate the payload platform via the shaft.

[0010] A shuttle drive motor attached to the shuttle platform drives the platform along the linear rails by engaging a gear or roller along a drive track surface. As the shuttle platform moves, the rollers on the cam follower assembly follow the contour of the cam surface. The cam follower assembly has a plurality of rollers which follow different cam tracks on the cam surface. The cam follower assembly is therefore rotated as the rollers are disposed along the cam surface. The payload platform is thus rotated by the cam follower assembly through the shaft. Since rotary motion is derived from the linear movement through the cam assembly, no additional rotational drive sources are required. The cam surfaces do not require adjustment, and are shaped so as to provide a smooth cycloidal rotational momentum from a constant linear velocity.

[0011] The invention will be more fully understood with reference to the following detailed description and drawings, of which:

[0012] FIG. 1 is a perspective view of the shuttle platform apparatus as defined herein;

[0013] FIG. 2ais an exploded view of the underside of the shuttle platform of FIG. 1;

[0014] FIG. 2bis a view of the underside of the shuttle platform of FIG. 1;

[0015] FIG. 2cis a perspective view of the shuttle platform and linear shuttle drive motor of FIG. 1;

[0016] FIG. 3 is a perspective view of the cam surface of FIG. 1;

[0017] FIGS. 4a-4eare top views of the cam follower assembly on the underside of the shuttle platform of FIGS. 2a-2c;

[0018] FIG. 5 is an alternate embodiment which rotates the cam follower assembly 180 degrees; and

[0019] FIG. 6 is an alternate embodiment which rotates the cam follower assembly a predetermined amount.

[0020] Referring to FIG. 1, the shuttle platform apparatus 10 includes a payload platform 12 rotatably mounted on a shuttle platform 14 by a shaft 22. The platform 14 is operable for movement along a pair of linear rails 16 by shuttle glides 18 attached to the underside of the platform 14. A shuttle drive motor 20 is adapted to move the shuttle platform along the rails 16. The shaft 22 attached to the payload platform extends through the shuttle platform. A cam follower assembly 24 is connected to the end of the shaft 22 beneath the shuttle platform 14. The cam follower assembly is operable to rotate the payload platform about the shaft 22. As the shuttle platform 14 is moved along the rails 16, rollers on the cam follower assembly 24, described further below, engage a cam surface 26 to rotate the payload platform 12.

[0021] FIGS. 2a-2cshow the shuttle platform in more detail. FIG. 2ais an exploded view of the underside of the shuttle platform which shows the cam follower assembly 24. The cam follower assembly includes three rollers 38, 40 and 42 adapted to engage the cam surface 26. The shaft 22 disposed through the shuttle platform 14 is secured by payload platform bearings 28 and shaft housing 30. The payload platform 12 is fixed to shaft 22 and rotates with the cam follower assembly 24 which is also fixed to the shaft. FIG. 2cshows the assembled shuttle platform with the payload platform cut away to show the connection to the shaft 22.

[0022] The shuttle platform 14 is supported by shuttle glides 18, which are attached by any suitable means to the underside of the shuttle platform. The shuttle glides 18 are formed of a rigid plastic adapted to slide along the rails. Alternatively, the glides include a bearing or other member which minimizes friction against the rails. The shuttle drive motor 20 rotates a drive roller 32 (FIG. 2b), in frictional contact with a side of the rail 16, to move the shuttle platform along the rails. Other suitable drive means, such as a drive gear engaging a gear track, can also be employed to move the shuttle platform.

[0023] The shuttle platform apparatus 10 is shown with the shuttle platform removed in FIG. 3. The cam surface 26 includes an upper cam track 36 and a lower cam track 34. Referring again to FIG. 2a, the cam follower assembly includes an upper roller 38, and leading and lagging lower rollers 42 and 40, respectively. The upper roller 38 is disposed so as to engage the upper cam track 36, and the leading and lagging lower rollers 42, 40 are disposed so as to engage the lower cam track 34.

[0024] FIGS. 4a-4eshow the rotation of the cam follower assembly 24 as the shuttle platform is moved along the rails 16. As shown in FIG. 4a,at the start of the movement, upper roller 38 and lagging lower roller 40 are both engaged with the cam surface 26 on the side of a rail 16. The leading lower roller 42 is not engaged with the cam surface. In FIG. 4b,the upper roller 38 engages the upper cam track 36, and the lagging lower roller 40 engages the lower cam track 34. The lagging lower roller 40 moves the cam follower assembly 24 in the direction shown by arrow 44. The upper roller 38 prevents excessive rotation of the cam follower assembly 24, thereby providing precise rotation of the cam follower assembly based on the distance of linear movement.

[0025] In FIG. 4c,the lagging lower roller 40 has caused the cam follower assembly to be rotated 45 degrees, disposing the leading roller 42 towards the lower cam track 34. As the lagging roller 40 disengages from the cam track 34, the leading roller 42 engages the track 34. As linear movement continues, shown in FIG. 4d,the upper roller 38 continues the rotation of the cam assembly in the direction of arrow 44. The leading roller 42 prevents excessive rotation. FIG. 4eshows the completion of the 90 degree rotation. At this point, the leading roller 42 and the upper roller 38 are engaging the cam surface 26, and the lagging roller 40 is not engaged.

[0026] Since there are always at least two rollers engaging the cam tracks 34 and 36, the rotation of the cam follower assembly 24, and therefore the rotation of the payload platform 12, is precisely determined by the amount of linear movement of the shuttle platform. The contour of the upper and lower cam tracks 34, 36 provides a cycloidal motion profile by smoothing rotary acceleration and deceleration, and avoids sudden movement which can dislodge wafers on the payload platform.

[0027] In another embodiment, shown in FIG. 5, a 180-degree rotational movement is shown. In this embodiment, the cam follower assembly 50 includes an extra upper roller, and the cam surface includes a second segment of upper and lower tracks. A leading and a lagging upper roller 54, 52 respectively, are provided. As the cam follower assembly 50 moves, the leading upper roller 54 engages a first upper cam track segment 62, and a lagging lower roller 58 engages a first lower cam track segment 60, similar to FIG. 4b.The leading lower roller 56 and lagging upper roller 52 remain disengaged. As the cam follower assembly rotates in the direction shown by arrow 68, the lagging lower roller 58 disengages the track 60 as the leading lower roller engages the track 60, similar to FIG. 4c.After passing the first upper and lower cam tracks 62, 60, the cam assembly 50 has rotated 90 degrees. A second upper and lower cam track segment 66, 64 are provided. The second segments 66, 64 reverse the contour of the upper and lower segments. Therefore, the second upper segment 64 has a contour similar to the first lower segment 60, and the second lower segment 66 has a contour similar to the first upper segment 62. The leading upper roller 54 engages the second upper segment 64, and the leading lower roller 56 engages the second lower segment 66. As rotation continues in the direction of arrow 68, lagging upper roller 52 engages the second upper segment 64 as the leading upper roller 54 disengages the segment 64. After the cam follower assembly has passed the second segments 64, 66, a full 180 degree rotation has been completed.

[0028] In a further embodiment, shown in FIG. 6, a selected degree of rotation can be achieved. Since the degree of rotation is determined by the distance that the rollers on the cam follower assembly are disposed from the contour of upper and lower cam tracks 70, 72, rotation can be varied by altering the contour of the cam tracks 70, 72. Lower cam track 70 does not return to a colinear orientation with respect to the upper cam track. In this manner, a predetermined rotation less than 90 degrees is achieved.

[0029] Those of ordinary skill in the art should further appreciate that variations to and modification of the above-described methods and apparatus, particularly with respect to inverting the positions of the upper and lower tracks, may be made without departing from the inventive concepts disclosed herein. Accordingly, the invention should be viewed as limited solely by the scope and spirit of the appended claims.