Patent ID: 7808655

Claim:
A method for measuring physical characteristics of a shaft having a first end, a second end, and a shaft center axis extending from the first end to the second end, the method comprising: (a) securing the first end of the shaft to prevent movement thereof; (b) attaching a tip mass structure to the second end of the shaft, the tip mass structure having a reflective outer surface with a known curvature; (c) imparting oscillatory motion in the shaft, thereby causing the tip mass structure to oscillate in one or more directions substantially perpendicular to the shaft center axis; (d) illuminating the reflective outer surface of the tip mass structure with at least two spaced apart laser beams as the tip mass structure oscillates; (e) detecting laser energy reflected from the reflective outer surface of the tip mass structure as the tip mass structure oscillates; (f) generating shaft distance signals based upon the laser energy detected in step (e); and (g) based on the shaft distance signals and the known curvature of the reflective outer surface of the tip mass structure, determining information about the oscillatory motion of the second end of the shaft.