Patent ID: 6275770
Filing Date: 2001-08-14
Classification: G01B,G01N

Abstract:
A method of measuring the surface profile of an object to develop a surface profile map for the object's surface without station-induced errors, the method comprising the steps of:1) providing an object having a surface whose profile is to be measured;2) providing a measurement device having an object holder, a first distance sensor and a second distance sensor spaced apart from the first distance sensor by a known distance;3) holding the object with the object holder in a first orientation with respect to the object holder;4) disposing the object in the first orientation with respect to the object holder between the first and second distance sensors so that the object's surface is facing the first distance sensor;5) measuring the distance between the first distance sensor and the object's surface in the first orientation with respect to the object holder for a plurality of points over the object's surface in a first coordinate pattern of known orientation with respect to the object holder to obtain a first matrix of measurement points;6) rotating the object about a first axis which is substantially normal to the object's surface so as to hold the object with the object holder in a second orientation with respect to the object holder, wherein said rotation is represented by a rotation matrix;7) disposing the object in the second orientation with respect to the object holder between the first and second distance so that the object's surface is facing the first distance sensor;8) measuring the distance between the first distance sensor and the object's surface in the second orientation with respect to the object holder for a plurality of points over the object's surface in second coordinate pattern of known orientation with respect to the object holder to obtain a second matrix of measurement points;9) obtaining a difference matrix by subtracting the first matrix from the second matrix;10) removing the rotation matrix by applying an inverse matrix to the difference matrix, wherein the inverse matrix is the inverse of the difference between the rotation matrix and an identity matrix;11) flipping the object about a second axis which is substantially perpendicular to the first axis so as to hold the object with the object holder in a third orientation with respect to the object holder;12) disposing the object in the third orientation with respect to the object holder between the first and second distance so that object's surface is facing the second distance sensor;13) measuring the distance between the second distance sensor and the object's surface in the third orientation with respect to the object holder for a plurality of points over the object's surface in third coordinate pattern of known orientation with respect to the object holder to obtain a third matrix of measurement points; and14) obtaining the surface map of the object's surface by applying the selected measurement points of the third matrix to the difference matrix as processed in step 10.