Feedback Linearization Based Tracking Control of A Tilt-rotor with Cat-trot Gait Plan

TL;DR

This paper presents a feedback linearization based position and attitude tracking control method for tilt-rotors using a cat-trot gait plan, improving accuracy and reducing steady-state errors in trajectory tracking.

Contribution

It introduces a novel coupling analysis between position and attitude, and designs a gait-based control approach that avoids rapid tilting angle changes.

Findings

Significant reduction in steady-state error with the proposed controller.

The gait frequency impacts the steady-state error.

The method effectively tracks setpoint, linear, and circular references.

Abstract

With the introduction of the laterally bounded forces, the tilt-rotor gains more flexibility in the controller design. Typical feedback linearization methods utilize all the inputs in controlling this vehicle; the magnitudes as well as the directions of the thrusts are maneuvered simultaneously based on a unified control rule. Although several promising results indicate that these controllers may track the desired complicated trajectories, the tilting angles are required to change relatively fast or in large scale during the flight, which turns to be a challenge in application. The recent gait plan for a tilt-rotor may solve this problem; the tilting angles are fixed or vary in a predetermined pattern without being maneuvered by the control algorithm. Carefully avoiding the singular decoupling matrix, several attitudes can be tracked without changing the tilting angles frequently. While the position was not directly regulated in that research, which left the position-tracking still an open question. In this research, we elucidate the coupling relationship between the position and the attitude. Based on this, we design the position-tracking controller, adopting feedback linearization. A cat-trot gait is further designed for a tilt-rotor to track the reference; three types of references are designed for our tracking experiments: setpoint, uniform rectilinear motion, and uniform circular motion. The significant improvement with less steady state error is witnessed after equipping with our modified attitude-position decoupler. It is also found that the frequency of the cat-trot gait highly influenced the steady state error.