Optical grating system for displacement measurement - has cursor assembly sliding along fixed rule and uses electronic circuit to switch detector heads when grating junction detected

摘要

The displacement of a carriage is determined from the displacement of optical gratings through which a luminous beam passes. The grating formed from elements which are mounted end-to-end, and the interruption to the Moire fringes is overcome using a second detector head. A cursor assembly (2) slides along a fixed rule (1) comprising a series of gratings (1a, 1b, 1c) placed end-to- end. The cursor contains two measuring heads, each containing a counter grating (5, 6). A light source (8) directs a luminous beam (100) through a prism (8) so that the light passes through both gratings to detectors (9) behind the parts of the counter gratings. As the cursor moves, a junction (10) between two grating elements on the rule interrupts the signals from the measuring heads. A processing circuit uses the signal from the first head (3) before the unction interrupts it and then the second head isused.