Abstract: A dynamic balance testing machine is provided with mechanical arrangements for canceling out a free moment of an asymmetrical crank shaft and capable of accurately measuring a rotating unbalance of the asymmetrical crank shaft. A compensation rotational shaft 10 having a compensation weights 11 for canceling out a free moment of a crank shaft 5 as a test piece is provided on a vibration cradle 1. The compensation rotational shaft 10 is rotated by a synchronous motor 9 other than a synchronous motor 8 for rotating the crank shaft 5. The synchronous motor 9 is rotated based on a reference signal detected by an optical sensor 18 (13, 14) in such a manner that the synchronous motor 9 is synchronously rotated with the rotation of the crank shaft.

Abstract: A control device is associated with a dynamic balancing machine for indexing a rotor being examined for unbalance. The control device determines the angular position of unbalance of the rotor during an unbalance measurement run and stops the rotation of the rotor while bringing it to a stop at an angular position related to the determined angular position of unbalance.