A two axis mirror positioning system with quadrature encoder output

Abstract

This project was conducted in support of a solar concentrating technology that required the design and construction of a low cost, two axis rotational drive system with a resolution of one degree or better. The scope of this project was to design and build a two axis drive system capable of supporting a 20" square acrylic mirror. Cost, reliability, and the ability to be built by students using student resources were of primary concern. The primary design concern was the development of a low cost feedback system. Several different feedback sensors were considered, and a quadrature encoder was chosen. To reduce cost, the encoder disk was made from an overhead transparency with a slotted image printed on it. The required encoder accuracy was 1.0 degree, and a measured accuracy of 0.85 degrees was achieved. The encoder was designed with an optimum accuracy of 0.55 degrees per transition and the observed discrepancy in resolution is primarily due to high tolerances that could not be met with hand assembly.