High-resolution laser linear encoder with numerical error compensation

Metrological feasibilities of the prototype of a high-resolution displaceme nt encoder with a laser diode light beam focused on the scale surface are i nvestigated. Resolution of 0.01 mu m has been obtained. The repeatability o f the system ranges from 0.02 to 0.03 mu m. A new simple reference point de tection method that uses a scale grating edge as a reference point has been proposed. We suggest two possible ways of implementation of this method: a nalog by de signal component extraction and digital by signal amplitude ext raction. The proposed reference point detection technique allows significan t reduction of nonlinearity errors of the measuring system. Nonlinearity of the prototype device does not exceed 0.1 mu m in the 48-mm measuring range . Due to the application of a focused laser beam, the proposed optical syst em is extremely insensitive to disturbing shifts and tilts of the scale. Th e acceptable tilts of the encoder detection head relative to the grating in the prototype device reach about 0.5 arcdeg in all directions. The toleran ce of the distance between detection head and the grating is approximately equal to 0.1 mm. (C) 1999 Society of Photo-Optical instrumentation Engineer s. [S0091-3286(99)02006-1].