Apparatus for process for measuring the thickness and out-of-roundness of elongate workpieces

A process for measuring the diameter and out-of-roundness of elongate workpieces advanced in their longitudinal direction in rolling mill trains, with a measuring device comprised of three or more laser scanners each of which having a light-sensitive sensor and a laser which is directed for illuminating a sensor, comprising the process steps below:

• illuminating the workpiece such that each of the lasers casts one or two shadow edges onto each of the sensors,
• calculating a straight line, bearing on the outer edge of the workpiece for each laser scanner, which extends in parallel with the laser beam, from the shadow edge (38,44) which the workpiece casts onto the sensor of the laser scanner,
• calculating, with an evaluation device, a circle on which three of the straight lines bear as tangent lines,
• repeating several times the measurement made for the calculation of a circle using the three straight line calculation, and
• the out-of-roundness of the workpiece is determined from the circle diameters measured as the difference between largest and smallest diameter.