Stage Metrology Concepts: Application Specific ... - Owens Design

Measurement Techniques
Straightedge Reversal Technique
• Place straightedge on the carriage, parallel to the axis that is being tested
• Mount gage on a stationary part of the tool, with the sensitive contact
positioned against the straightedge and scan axis of interest
• Repeat scan with the straightedge flipped 180 degrees around its long axis,
and the gage head repositioned on the opposite side of the machine scanning
the same surface.
• The gage head's direction of motion is reversed, so that a "bump" on the
straightedge should read as a positive number on both trials.
• The results of one trace are subtracted from the other. Because the gage head
was reversed, carriage errors cancel each other out, so any remaining
deviation from zero reflects error in the straightedge. (assumes that carriage
errors are repeatable.)
• The results can be used as correction factors for all future uses of the
straightedge.