746 research outputs found
Fault tolerant control of a quadrotor using L-1 adaptive control
Purpose β The growing use of small unmanned rotorcraft in civilian applications means that safe operation is increasingly important. The purpose of this paper is to investigate the fault tolerant properties to faults in the actuators of an L1 adaptive controller for a quadrotor vehicle.
Design/methodology/approach β L1 adaptive control provides fast adaptation along with decoupling between adaptation and robustness. This makes the approach a suitable candidate for fault tolerant control of quadrotor and other multirotor vehicles. In the paper, the design of an L1 adaptive controller is presented. The controller is compared to a fixed-gain LQR controller.
Findings β The L1 adaptive controller is shown to have improved performance when subject to actuator faults, and a higher range of actuator fault tolerance.
Research limitations/implications β The control scheme is tested in simulation of a simple model that ignores aerodynamic and gyroscopic effects. Hence for further work, testing with a more complete model is recommended followed by implementation on an actual platform and flight test. The effect of sensor noise should also be considered along with investigation into the influence of wind disturbances and tolerance to sensor failures. Furthermore, quadrotors cannot tolerate total failure of a rotor without loss of control of one of the degrees of freedom, this aspect requires further investigation.
Practical implications β Applying the L1 adaptive controller to a hexrotor or octorotor would increase the reliability of such vehicles without recourse to methods that require fault detection schemes and control reallocation as well as providing tolerance to a total loss of a rotor.
Social implications β In order for quadrotors and other similar unmanned air vehicles to undertake many proposed roles, a high level of safety is required. Hence the controllers should be fault tolerant.
Originality/value β Fault tolerance to partial actuator/effector faults is demonstrated using an L1 adaptive controller
CONTROL STRATEGY OF MULTIROTOR PLATFORM UNDER NOMINAL AND FAULT CONDITIONS USING A DUAL-LOOP CONTROL SCHEME USED FOR EARTH-BASED SPACECRAFT CONTROL TESTING
Over the last decade, autonomous Unmanned Aerial Vehicles (UAVs) have seen increased usage in industrial, defense, research, and academic applications. Specific attention is given to multirotor platforms due to their high maneuverability, utility, and accessibility. As such, multirotors are often utilized in a variety of operating conditions such as populated areas, hazardous environments, inclement weather, etc. In this study, the effectiveness of multirotor platforms, specifically quadrotors, to behave as Earth-based satellite test platforms is discussed. Additionally, due to concerns over system operations under such circumstances, it becomes critical that multirotors are capable of operation despite experiencing undesired conditions and collisions which make the platform susceptible to on-board hardware faults. Without countermeasures to account for such faults, specifically actuator faults, a multirotors will experience catastrophic failure.
In this thesis, a control strategy for a quadrotor under nominal and fault conditions is proposed. The process of defining the quadrotor dynamic model is discussed in detail. A dual-loop SMC/PID control scheme is proposed to control the attitude and position states of the nominal system. Actuator faults on-board the quadrotor are interpreted as motor performance losses, specifically loss in rotor speeds. To control a faulty system, an additive control scheme is implemented in conjunction with the nominal scheme.
The quadrotor platform is developed via analysis of the various subcomponents. In addition, various physical parameters of the quadrotor are determined experimentally. Simulated and experimental testing showed promising results, and provide encouragement for further refinement in the future
Nonlinear MPC for Quadrotor Fault-Tolerant Control
The mechanical simplicity, hover capabilities, and high agility of quadrotors
lead to a fast adaption in the industry for inspection, exploration, and urban
aerial mobility. On the other hand, the unstable and underactuated dynamics of
quadrotors render them highly susceptible to system faults, especially rotor
failures. In this work, we propose a fault-tolerant controller using nonlinear
model predictive control (NMPC) to stabilize and control a quadrotor subjected
to the complete failure of a single rotor. Differently from existing works,
which either rely on linear assumptions or resort to cascaded structures
neglecting input constraints in the outer-loop, our method leverages full
nonlinear dynamics of the damaged quadrotor and considers the thrust constraint
of each rotor. Hence, this method could effectively perform upset recovery from
extreme initial conditions. Extensive simulations and real-world experiments
are conducted for validation, which demonstrates that the proposed NMPC method
can effectively recover the damaged quadrotor even if the failure occurs during
aggressive maneuvers, such as flipping and tracking agile trajectories.Comment: 9 pages, 13 figure
Upset Recovery Control for Quadrotors Subjected to a Complete Rotor Failure from Large Initial Disturbances
This study has developed a fault-tolerant controller that is able to recover
a quadrotor from arbitrary initial orientations and angular velocities, despite
the complete failure of a rotor. This cascaded control method includes a
position/altitude controller, an almost-global convergence attitude controller,
and a control allocation method based on quadratic programming. As a major
novelty, a constraint of undesirable angular velocity is derived and fused into
the control allocator, which significantly improves the recovery performance.
For validation, we have conducted a set of Monte-Carlo simulation to test the
reliability of the proposed method of recovering the quadrotor from arbitrary
initial attitude/rate conditions. In addition, real-life flight tests have been
performed. The results demonstrate that the post-failure quadrotor can recover
after being casually tossed into the air.Comment: 7 pages, 9 figures, accepted by International Conference of Robotics
and Automation (ICRA) 202
Accurate Tracking of Aggressive Quadrotor Trajectories using Incremental Nonlinear Dynamic Inversion and Differential Flatness
Autonomous unmanned aerial vehicles (UAVs) that can execute aggressive (i.e.,
high-speed and high-acceleration) maneuvers have attracted significant
attention in the past few years. This paper focuses on accurate tracking of
aggressive quadcopter trajectories. We propose a novel control law for tracking
of position and yaw angle and their derivatives of up to fourth order,
specifically, velocity, acceleration, jerk, and snap along with yaw rate and
yaw acceleration. Jerk and snap are tracked using feedforward inputs for
angular rate and angular acceleration based on the differential flatness of the
quadcopter dynamics. Snap tracking requires direct control of body torque,
which we achieve using closed-loop motor speed control based on measurements
from optical encoders attached to the motors. The controller utilizes
incremental nonlinear dynamic inversion (INDI) for robust tracking of linear
and angular accelerations despite external disturbances, such as aerodynamic
drag forces. Hence, prior modeling of aerodynamic effects is not required. We
rigorously analyze the proposed control law through response analysis, and we
demonstrate it in experiments. The controller enables a quadcopter UAV to track
complex 3D trajectories, reaching speeds up to 12.9 m/s and accelerations up to
2.1g, while keeping the root-mean-square tracking error down to 6.6 cm, in a
flight volume that is roughly 18 m by 7 m and 3 m tall. We also demonstrate the
robustness of the controller by attaching a drag plate to the UAV in flight
tests and by pulling on the UAV with a rope during hover.Comment: To be published in IEEE Transactions on Control Systems Technology.
Revision: new set of experiments at increased speed (up to 12.9 m/s), updated
controller design using quaternion representation, new video available at
https://youtu.be/K15lNBAKDC
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