Abstract: A method and apparatus for straightening longitudinal curvature of a workpiece by a bending action involves supporting the workpiece between two supporting members, rotating the workpiece, engaging a plurality of sensors with the peripheral surface of the workpiece at longitudinally spaced-apart locations and generating with the sensors first periodic electric signals proportional to the apparent radius at the location of the sensors, whereby the signals are an indication of longitudinal curvature and of any deviation of the cross-sectional shape of the workpiece from a true circle, transforming the first signals into second electric signals the magnitude of which varies with the law of variation corresponding to the first harmonic of the development in Fourier's series of the first signals and the frequency of which equals the frequency of rotation of the workpiece, and applying bending forces to the workpiece in the sense of deforming the workpiece to minimize the amplitude of the second signals.

Abstract: An apparatus and method for straightening an elongated workpiece such as a crank shaft is disclosed. At least four measuring devices are disposed along the workpiece for measuring the position of four points on the workpiece relative to an axis extending between the ends of the workpiece. Signals from the measuring devices are converted to curvature signals representing the curvature of each section of the workpiece spanned by a sequence of three of the points, and straightening blows are applied as needed to sections of the workpiece to reduce or remove the curvatures. Subsequently the measuring devices may be employed to measure eccentricity at the four points and further straightening blows can be applied to reduce or remove eccentricity.