At the end of the manufacturing process of rods and tubes of metal, these have to be examined regarding straightness. Rods which are not straight could, for example, during further processing in automatic lathes cause damage to the machine due to their unbalanced mass. Methods known up to now which determine the straightness are based, for example, on measuring rolling-off times on a sloped plane or on optical measuring with the aid of laser scanners or CCD cameras.
Thus a method for sorting of bent rods, tubes or the like is known from the Reference DE 35 01 725 C1, where it is suggested to place the respective articles on a sloped plane with a specified angle of inclination and to detect the rolling-off operation via a time interval. If a bent tube rolls off too slowly within the specified time interval, a rocking bar provided at the outlet end of the sloped plane is operated and the tube is sorted out into a further container for waste. The rods which, due to their straightness, roll sufficiently quickly down the plane, are collected in a separate storage container.
Also a method for measuring the curvature of cylindrical bodies is known from the Reference U.S. Pat. No. 3,710,935, where contact elements are arranged below a rolling plane, which contact elements detect a curvature. If the body to be examined has a curvature which is too great, it contacts the contact elements while rolling down the sloped plane, whereby said body is then sorted out. The parts to be examined in this manner must, of course, have a high flexural resistance since otherwise no reproducible measuring results can be achieved. Thus such a method is of limited use in the examination of long and in particular thin rods.