Direct skew control and interlock of gantry

Details Direct skew control and interlock of gantry Direct skew control and interlock of gantry

1999-02-05

2001-06-12

Martin, David (Department: 2837)

Electricity: motive power systems

Positional servo systems

With particular 'error-detecting' means

C318S625000, C318S568220, C414S936000

Reexamination Certificate

active

06246203

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to the field of gantry positioning systems. More particularly, the invention relates to controlling and detecting skew in a gantry positioning system for semiconductor wafer transfer applications.
2. Discussion of the Related Art
Gantries in general face considerations resulting from dynamic or unbalanced loads that are transported across or along axes of the gantry. In applications related to silicon wafer fabrication processes, gantries are sometimes required to position robots that transport wafers between modules for performing fabrication steps on wafers. The robots serve to position wafers to a high degree of precision. For instance, robots are used to precisely position wafers within cassettes so as to place the wafers three pins or more pins. If the robot is even slightly misaligned, the robot may fail to transfer or place the wafer. However, the weight of the robot may also cause skew to develop on the gantry that affects alignment and ability to precisely position the wafers. In the worst case, skew may damage the robot or components on the gantry. Therefore, semiconductor wafer transfer gantries in particular face control problems arising in part from skew and misalignment.
As practiced in the known art, the control of gantry positioning systems is limited to using direct drive coupled systems that are unable to compensate for skew. For example, the known art provides for a gantry having gantry axes directly coupled together by a T gear box and/or miter gearbox. Such directly coupled gantries of the known art cannot compensate for deflections and misalignments due to dynamically driven loads. What is needed, therefore, is an approach to compensating for skew in a gantry.
SUMMARY OF THE INVENTION
An object of this invention is to detect and control skew on a gantry system having a variable load on a secondary (X) axis.
Another object of the invention is to provide a gantry having the ability to “hard interlock” differential motion with a mechanical assembly.
Another object of the invention is to provide a gantry with a mechanical fuse that powers off a controller to the gantry when excessive skew is detected.
In accordance with these goals, there is a particular need for providing a gantry with a trunnion engaged with a sensor adapted to detect skew. There is also a need to detect and compensate for skew appearing on a secondary axis of a gantry as the gantry is operated. And there is a need to provide a mechanical fuse that can shut down the system when skew is deemed excessive.
A first aspect of the invention is implemented in an embodiment that is based on an apparatus that comprises a gantry. The gantry includes a first member defining a gantry primary axis Z, a cross member defining a secondary axis X coupled to the first member and a second member defining a gantry primary axis Z′ coupled to the cross member via an elastic hinge. The cross member includes a trunnion that permits angular, radial, or lateral displacement of at least a portion of the cross member. An elastic hinge opposing the trunnion across the cross member may also allow for corresponding radial displacement.
A second aspect of the invention is implemented in an embodiment that is based on n apparatus that comprises a gantry. The gantry includes first member defining a gantry primary axis Z, a cross member defining a secondary axis X coupled to said first member, and a second member defining a gantry primary axis Z′ coupled to said cross member. The ross member includes a sensor adapted to measure a dimension representing skew of the cross member. The dimension can be controlled.
A third aspect of the invention is provided by an apparatus comprising a gantry which includes a first member defining a gantry primary axis Z, a cross member defining a secondary axis X coupled to the first member, and a second member defining a gantry primary axis Z′ coupled to the cross member. The gantry further includes a mechanical fuse adapted to detect excessive skew.
A fourth aspect of the invention is provided by a method for controlling skew on a cross member being moved by a first and second driver. The method comprises moving the first and second drivers to a first position, measuring a resulting skew value, and correcting the skew on the cross member by moving the first and/or the second driver.
A fifth aspect of the invention is provided by a method for controlling skew on a cross member of a gantry, the cross member being moved by a first and second driver, where the method comprises performing a homing sequence to determine a home position for the first driver, and aligning the second driver to be substantially parallel with the first driver. The method further comprises moving the first and second drivers to a first position, then measuring a resulting skew value, and then correcting the skew on the cross member by moving the first and/or the second driver, if necessary.
These, and other, goals and aspects of the invention will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following description, while indicating preferred embodiments of the invention and numerous specific details thereof, is given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the invention without departing from the spirit thereof, and the invention includes all such modifications.


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