On the Comparison of Type 1 and Interval Type 2 Fuzzy Logic Controllers Used in a Laser Tracking System

Abstract

This study is an extension of our previous researches for a type-1 fuzzy logic controller used in a Laser Tracking System (LTS). In a LTS the control objective is for a laser beam to track a retro-reflecting moving target through adjustment of joint angles and velocities of a two Degrees-Of-Freedom (DOF) tracking gimbals on which tracking mirrors are mounted. This is done based on two types of feedback signals: Distance reading, obtained by a laser interferometer and off-center distance error of the returning laser beam, as measured by a four-quadrant photo-detector. The LTS control system should effectively provide a high-speed and smooth tracking on the target with lowest steady state errors. A complete LTS consists of laser interferometer transducer subsystem, opto-electronic beam steering subsystem, gimbals driving subsystem and the digital control subsystem. As high tracking accuracy and high tracking speed are both vital for LTS operation, a design of a high performance controller is critical. This paper shows that an interval type 2 fuzzy logic controller (IT2FLC) can outperform a type 1 fuzzy logic controller (T1FLC) in such applications. Complete and extensive simulation studies are discussed and analyzed with a performance comparison between a type 1 and an interval type 2 FLC. The advantages of utilizing an IT2FLC over T1FLC to improve the control and tracking performance for a LTS with random noises are confirmed by simulation results.