# Stage Validation Result

The purpose of stage validation is to verify that the stage moves to its commanded poses (X, Y, Theta), and to characterize certain types of systematic errors in the observed motion.

Like the hand-eye calibration usage model, this tool uses correspondence data extracted from all views (images) from all cameras, along with the UncorrectedHome2DFromStage2D pose associated with each view. The tool validates the motion stage for all sets of UncorrectedHome2DFromStage2D poses that contain motion corresponding to the metric requested for in the input parameters. The following metrics are available:

- XScale
- YScale
- ThetaScale
- Skew between the X and Y motion axes

During stage validation AlignPlus requires that subsets of UncorrectedHome2DFromStage2D poses contain elements where all degrees of freedom except for one are constant. For example, a subset of commanded poses should contain constant Y and Theta values. This would allow validation of the X degree of freedom.

On AlignPlus applications where the vision system controls the motion device, the stage validation is performed as a part of the hand-eye calibration process. AlignPlus moves the stage in a fashion that makes stage validation feasible. For application where the PLC controls the motion device it is recommended that the stage is moved in a fashion recommended in this document

1. XScale

   Stage’s x scale based on three movements along x axis, where the scale is the ratio of translations in the x direction for UnCorrectedHome2DFromStage2D and CorrectedHome2DFromStage2D. The closer it is to 1, the better.

2. YScale

   Stage's y scale based on three movements along y axis, where the scale is the ratio of translations in the y direction for UnCorrectedHome2DFromStage2D and CorrectedHome2DFromStage2D. The closer it is to 1, the better.

3. Theta Scale

   Stage's theta scale based on rotation movement, where the scale is the ratio of rotation for UnCorrectedHome2DFromStage2D and CorrectedHome2DFromStage2D. The closer it is to 1, the better.

4. Skew

   Skew between the X and Y motion axes based on all movements along x and y axes.

   X axis and Y axis are perpendicular if skew is 0.