uRad accumulated angle error FOG

Abstract

Closed Loop Fiber Optic (FOG) gyroscopes are known for their high performance in terms of noise and accuracy. They are also the accurate gyro of choice for long and accurate missions. One of the demands in such missions is a very low error in accumulated angle at every step of the mission. The simple PI loop that is commonly implemented as part of a closed loop IFOG can yield errors under certain conditions. Particularly of concern are rate integration errors that appear during angular accelerations. These errors accumulate during longer period of acceleration. To meet the specifications of a precise application in which accurate angle is required at all times, an improved PI loop is suggested. Theoretical analysis for stability and responses for step and ramp changes in rates is shown for both configurations. The proposed solution was implemented and tested using hardware-in-the-loop simulation that allows different mission profiles to be compared. Further, experimental measurements were performed. We show an a 10 to 100 fold improvement in accumulated angle error for a single gyro resulting with less than 10 uRad error at any given time.