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

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 2ⁿ² compared with that of the traditional 1-D codes (2ⁿ). 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.

I. Introduction

Absolute optical encoders are non-contacted electromechanical sensors which employ unique coded patterns to find real-time absolute positions. They are considered as an integral part of any automation and precision controlling system. Due to their high accuracy, high resolution, long lifetime, high reliability and wide measurement range, they can be used in high-performance servo applications, precise position controlling of robotic arms, radar systems and various astronomical and avionic apparatus etc [1]–[7].