Methods of Rotor-Unbalance Determination

Abstract

Abstract Rotor-unbalance determinations both in balancing machines and from vibration readings taken on the rotor during normal operation have in some cases been rather complicated and often subject to considerable error. This paper suggests methods intended to improve balancing methods in these cases. In part I a more or less conventional method of calculating unbalance corrections from vibration readings is reviewed and the limitations and errors pointed out. Next, an extension of the method is developed which is in some cases simpler and inherently more accurate. In part II a mathematical method is developed for determining unbalance corrections in cases where the locations of the corrections are completely prescribed in contradistinction to the ordinary case in which the axial position of the correction is prescribed but the angular position is to be determined. Also, a balancing machine is described which reads directly the unbalance corrections required at four preselected locations in a rigid rotor. This balancing machine is especially suited for the quick determination of unbalance corrections required in an internal-combustion-engine crankshaft. In part III center-of-percussion balancing is described which is a method of taking vibration readings which can be interpreted directly in terms of unbalance. This method is applicable only under certain conditions which are noted.