A Robust Quadrature Decoding Logic and its FPGA Implementation for Measurement of Angular Motion using a Ring Laser Gyroscope

Abstract

A ring laser gyroscope outputs an interference pattern that rotates at a rate proportional to the rotation rate of the body on which the gyroscope is strapped. The standard measurement setup for similar such systems consists of a pair of photo-detectors followed by wave shapers that convert the'rotating interference pattern into a pair of pulse trains in quadrature. The phase relation between the two pulse trains indicates the direction of rotation, and counting anyone of the pulse trains over a period of time gives a measure of the incremental motion. Commercially available optical encoder assemblies using similar quadrature-output sensors implement a sequence of noise filtering, quadrature phase detection and counting to measure incremental motion. Such designs have certain limitations in so far as their applicability is concerned. This paper documents these limitations briefly and proposes a novel design and its FPGA implementation of an improved digital noise filter and a high-resolution quadrature phase decoder for measurement of incremental motion based on the processing of the output of a ring laser gyroscope.