Feedback-controlled workpiece positioning system
AssigneeEaton-Optimetrix, Inc.
InventorsEdward H. Phillips, Lawrence A. Wise
Life of this patent
Estimating the term…
Abstract
X-Y position measurement apparatus is employed with feedback controlled X-Y positioning apparatus for positioning a workpiece stage at a desired X-Y coordinate position in response to signals indicative of the actual position and the desired position of the workpiece stage. A normalization circuit is employed for gain correction of the signals indicative of the actual position of the workpiece stage.
Claims30
Apparatus for positioning a workpiece at a predetermined coodinate location relative to a datum, said apparatus comprising:
- a stage, movable along coordinate axes, for holding the workpiece, said stage being positioned at a desired coodinate stage position when the workpiece is positioned at a predetermined location;
- measurment means for determining the coordinate position of the stage relative to the datum, said measurement means including an array of uniformly spaced coordinate indicia affixed to the stage for movement therewith, a sensor means for generating at least three spatially periodic sensor signals for each axis of movement of the state with the signals generated for each axis of movement having periods corresponding to the spacing of the coordinate indicia and being spatially out of phase by a uniform offset, and signal processing means for processing the sensor signals to produce a stage position signal determinative of the coordinate position of the stage relative to the datum;
- and
- positioning means for moving the stage to position the workpiece at the predetermined location, said positioning means including comparison means for comparing the stage position signal with input address information specifying the desired coordinate stage position to provide a positional error, and servo drive means for moving the stage in response to the positional error so as to minimize the positional error.
A method for positioning a workpiece at a preselected coordinate location, said method comprising the steps of:
- supporting the workpiece on a stage moveable along coordinate axes and having an array of coordinate indicia attached thereto for movement therewith;
- projecting an image of the array of coordinate indicia onto a sensor;
- sensing the projected image of the array of coordinate indicia to generate at least three spatially periodic position signals for each axis of movement of the stage, the position signals generated for each axis of movement being proportional to the relative position of the projected image of the array of coordinate indicia and being uniformly spatially offset with respect to each other, the position signals generated for the coordinate axes of movement being determinative of an actual workpiece position;
- comparing the actual workpiece position to the preselected coordinate location and generating an error signal in proportion to the difference between the actual workpiece position and the preselected coordinate location;
- and
- moving the stage in response to the error signal to a position corresponding to the preselected coordinate location.
A method of normalizing a feedback signal comprising two or more oscillatory signals out of phase by a uniform shift, said method comprising the steps of:
- summing two adjacent ones of those oscillatory signals, one leading and one trailing, to produce a numerator;
- substracting the two adjacent oscillatory signals to produce a denominator;
- and
- dividing the numerator by the denominator to yield a dimensionless normalized linear signal of reduced error content;
- and
- selecting a portion of the dimensionless normalized signal for utilization as a feedback signal.
Dependencies are inferred from the claim text.