Velocity Sensor for Real-Time Backstepping Control of a Multirotor Considering Actuator Dynamics.

Walter Alejandro Mayorga-Macías,Luis Enrique González-Jiménez,Luis Fernando Luque-Vega,Marco Antonio Meza-Aguilar

doi:10.3390/s20154229

Abstract

A real-time implementation of a control scheme for a multirotor, based on angular velocity sensors for the actuators, is presented. The control scheme is composed of two loops: an inner loop for the actuators and an outer loop for the unmanned aerial vehicle (UAV). The UAV control algorithm is designed by means of the backstepping technique and a robust sliding mode differentiator, and the actuator control strategy is based on a standard proportional-integral-derivative (PID) controller. A robust exact differentiator, based on high order sliding modes, is used to estimate the complex derivatives present in the proposed control law. As the measurements of the propeller’s angular velocities are required for the control law, velocity sensors are mounted in the axles of the rotors to retrieve them and a signal conditioning stage is implemented. In addition, dynamical models for the actuators of the aircraft were calculated by means of transfer functions obtained via experimental measurements in a test bench developed for this purpose. This test bench permits to characterize the parameters of the transfer functions by comparing the forces computed using the nominal parameter to the measured forces. To this end, it is assumed that the loads in the actuators of the vehicle are insignificant during flight. The effectiveness of the proposed sensor, its signal conditioning, and the overall control scheme are validated by means of simulation results and real-time experiments.

Highlights

An unmanned aerial vehicle (UAV) is an aircraft with no aircrew, which is replaced by a control computer system and radio-link for remote controllability or autonomous flight
In order to avoid the cumbersome characterization of these parameters, we propose to obtain their approximated transfer functions in an experimental manner, defining the duty cycle of the pulse-width modulation (PWM) signal and the rotor’s angular velocity as its input and output, respectively
The control proposal was implemented in simulation and real-time experiments considering the same control and system parameters aiming to analyse the results, which are presented

Summary

Introduction

An unmanned aerial vehicle (UAV) is an aircraft with no aircrew, which is replaced by a control computer system and radio-link for remote controllability or autonomous flight. The applications of UAVs cover diverse technology areas from monitoring and surveillance to transportation, which influence research fields as computer vision, mechanical design and automatic control. In order to implement a UAV flight controller in real-time, it is important to first validate the designed control scheme using simulation results and, implement it in an electronic embedded system. Multirotors are a type of UAV characterized by easy construction and control. A great diversity of research works oriented to the control for multirotors can be found in the literature, as shown in [1,2].

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