| 摘要 |
A positioning device has a shuttle slidably and rotatably supported above a base assembly. A first linear motor moves the shuttle linearly in a first direction while the second and third linear motors move the shuttle linearly in a second direction, normal to the first direction. The second and third linear motors are separated along an axis in the first direction. The linear motors have magnetic arrays including rows of magnets or a checkerboard array of magnets and provide continuously variable positioning. Rotary movement of the shuttle is achieved by operating the second and third linear motors in opposing directions or at differing rates. The positions of three points on the shuttle are determined by three optical encoders, or three interferometers, whose signals provide feedback to a controller which actuates the linear motors accordingly. The controller employs an algorithm for the translation of the three point positions into shuttle position and orientation information and for implementing a closed loop control system whereby the shuttle may be positioned with respect to a reference point, torque thereupon may be compensated for, and the shuttle may be rotated.
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