| 摘要 |
<p>Rotation of one machine part relative to another is measured by determining the amount by which the plane of polarisation of a linearly polarised light beam is changed by the rotation. Two methods are disclosed along with apparatus for carrying out the methods. In a first method a polariser (3) attached to a linearly moving machine part (11) produces from an input laser beam (2) a linearly polarised output beam (4) of known polarisation angle. The output beam is passed to a polarising beam splitter (5) to produce orthogonally polarised light beams which are directed onto detectors (8, 9). Any change in the intensity of the light beams at the two detectors can be used as a measure of the roll of the moving machine part during its linear movement. Changes of intensity of the input laser beam are determined from the changes in the total intensity of the two beams reaching the detectors. In an alternative method a linearly polarised light beam is passed through a half-wave plate carried by the moving member.</p> |
