2.3 Mathematical analysis for straightness error
At the measurement of straightness, misalignment causes a slope to be measured, since the straightedge, for example, is not directing its reference bisector along a path parallel to the axis of the guideway, Fig. 4. This misalignment must be removed from the dates before calculating the true straightness (Hewlett-Packard, 1988). There are some methods used to remove the slope value from dates such as “End Point Fit ” and “Least Squares Fit”.
Figure 4. Misalignment between machine travels and reference line.
End point fit method
To remove slope from the measurements data, using the “End Point Fit”, is need to find the line which contains the first and the last date of measurement.
Figure 5: “End Point Fit” Method
By this way, the equation of the line r is identified, Eq. (1).