Distorted laser interferometric angle measurements of a disk drive pivot

A laser interferometric measurement sensor is used for angle measurements o f rotating ultralight structures in order to avoid the mechanical interacti on between the system and the sensor, Nevertheless, the laser interferomete r detects a linear displacement which is a distorted image of the angle dis placement. The distortion depends strongly on the amplitude and the laser m isalignment angle. In this paper, a measurement procedure is presented base d on an analytical expression that describes the nonlinear relationship bet ween the measured displacement and the actual angle displacement. Furthermo re, a distortion map is presented to quantify the nonlinear effects and to indicate the necessity for compensation of these effects. Finally, a calibr ation procedure for identifying the geometrical parameters, i.e., the arm l ength and laser misalignment angle, is included, The method is applied to t he pivot of a Kitty Hawk, a miniature hard disk drive.