Method for measuring the roundness of round profiles

A method for measuring the roundness or for measuring the shape deviation of round profiles moved forward in longitudinal direction inside of rolling mills, for which in a manner known per se and with the aid of a measuring instrument using two laser scanners, respectively provided with a light-sensitive sensor and a laser, at least three shadow edges that fit against the round profile to be measured and enclose the round profile so as to form a polygon are generated and measured and the corresponding tangents are computed from this,

• characterized in that
• a) prior to the measuring operation a center (Z0) is calibrated and determined in the measuring field, provided such a center (Z0) was not previously determined;
• b) perpendicular lines (r1, r2, r3, r4, r5, r6, r1′, r2′, r3′, r4′, r5′, r6′) are determined from the center (Z0) to the tangents (T1, T2, T3, T4, T5, T6, T1′, T2′, T3′, T4′, T5′, T6′) and the distance from the center (Z0) to the tangents (T1-T6′) is computed in this way;
• c) the corner points (A to K) of the polygon enclosing the round profile are computed, wherein a contour is determined;
• d) that a reference circle is positioned relative to the contour in such a way that
• i) the square shape deviation of the contour relative to this reference circle reaches a minimum;
• ii) the reference circle represents the smallest possible circle that can fit around the contour,
• iii) the reference circle represents the largest possible circle that can fit inside the contour;
• or
• iv) the reference circle together with a different circle, arranged concentric to the reference circle, encloses the contour with a minimum radial difference;
• e) the diameter (Dref) of the reference circle is computed and determined from the position in space of the reference center (Zp), which represents the center point of the reference circle, and
• f) at least two vectors extending from this reference center (Zp) to the contour are computed and that the out-of-roundness is determined from the obtained data.