A Novel High-Resolution Optical Encoder With Axially Stacked Coded Disk for Modular Joints: Physical Modeling and Experimental Validation

Abstract

A novel approach to realize a high-resolution absolute encoder with compact disk size for the application in a light weight robotic arm modular joint is proposed in the present research. First, the high resolution coded disk of the absolute encoder is designed using graph theory-based Hamiltonian cycle. Unlike the traditional 1-D binary coded tracks, the proposed generated code is a 2-D n × n matrix code with 0s and 1s as the matrix elements and n numbers of uniquely coded tracks. The 2-D matrix code improves the code density of the encoder system by 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n2</sup> compared with that of the traditional 1-D codes (2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</sup> ). Second, the coded tracks are arranged axially along Z-axis to stack the tracks within a constant disk diameter and to avoid the radially divergent track patterns. These combined operations result in a high-resolution absolute encoder with a compact constant disk diameter which is essential to comply with the size constraint of the modular joint. With the proposed designed framework, a prototype with n = 2 is manufactured using 3-D printing technology. The designed encoder with two tracks is tested on a rotary system and the absolute angle values are obtained using the unique codes generated by the photosensors installed in the prototype.