Method for measuring the roundness of round profiles

1. 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 (Z 0 ) is calibrated and determined in the measuring field, provided such a center (Z 0 ) was not previously determined;

b) perpendiculat lines (r 1 , r 2 , r 3 , r 4 , r 5 , r 6 , r 1′ , r 2′ , r 3′ , r 4′ , r 5′ , r 6′ ) are determined from the center (Z 0 ) to the tangents (T 1 , T 2 , T 3 , T 4 , T 5 , T 6 , T 1′ , T 2′ , T 3′ , T 4′ , T 5′ , T 6′ ) and the distance from the center (Z 0 ) to the tangents (T 1 -T 6′ ) 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 (D ref ) of the reference circle is computed and determined from the position in space of the reference center (Z p ), which represents the center point of the reference circle, and

f) at least two vectors extending from this reference center (Z p ) to the contour are computed and that the out-of-roundness is determined from the obtained data.

2. The method according to claim 1 ,

characterized in that

a step c1) follows the step c) prior to the step d) in which the polygon obtained in step c) is expressed as a numerical approximation with polygons as continuous function in accordance with the Weierstrass Approximation Theorem, wherein a smoothed simulated contour is obtained and the steps d) to f) are realized by using the simulated contour.

3. The method according to claim 2 ,

characterized in that

the smoothing is carried out with the aid of an adapted spline interpolation.

4. The method according to claim 1 ,

characterized in that

in step f) the vectors are computed and determined such that they represent the minimum distance (R min ) as well as the maximum distance (R max ), extending from the reference center (Z p ) to the contour/simulated contour.

5. The method according to claim 1 ,

characterized in that

one set or several sets of 2, 3 or more vectors (V GT1 , V GT2 and V GT3 and/or V DT1 , V DT2 and V DT3 ) are determined, which extend from the reference center (Z p ) to the contour and/or the simulated contour and that the vectors of a set in particular enclose the same angle between themselves.

6. The method according to claim 5 ,

characterized in that

if several sets of vectors exist, the angle enclosed by all vector sets is the same, but that the vectors of one set are rotated relative to the vectors of the other sets.

7. The method according to claim 5 ,

characterized in that

the vectors of one set point from the reference center (Z p ) in the direction of the roll gap of the last roll stand while the vectors of another set point from the reference center (Z p ) in the direction of the roll center of the last roll stand.

8. The method according to claim 5 ,

characterized in that

two sets of respectively three vectors are computed and that the vectors of the first set and the vectors of the second set are rotated relative to each other by a fixed angle of 60° and that typical GT and DT values for the 3-roll stands are determined from this.

9. The method according to claim 1 ,

characterized in that

the measuring instrument is rotated around the round profile and, in particular, carries out an oscillating rotary movement over an angle of 60°.

10. The method according to claim l,

characterized in that

the measuring instrument is not rotated around the round profile.