Optical encoder based on the Lau effect

Daniel CrespoJose´AlonsoDepartamento de O´pticaUniversidad Complutense de MadridFacultad de Ciencias Fi ´sicasCiudad Universitaria, s/nMadrid 28040, SpainToma´s MorlanesDepartamento de I1DFagor Automation S. CoopBarrio de San Andre´s s/nP.O. Box 194Mondrago´n 20500, Guipuzcoa, SpainEusebio BernabeuDepartamento de O´pticaUniversidad Complutense de MadridFacultad de Ciencias Fi´sicasCiudad Universitaria, s/nMadrid 28040, SpainAbstract. An optical encoder based on the Lau effect is presented. It isshown that this system has several advantages over standard opticalencoders based on the moire´effect, such as smaller sensitivity to varia-tions in the gap between gratings and higher design simplicity. Problemsdue to the quality of the collimated beam, which are present in moire-effect-based encoders, are also avoided. Two different optimized de-signs for different resolutions are presented. Experimental measure-ments, in good agreement with the model developed by us, arepresented.