Nurul Dayana Salim

Robust attitude control design for a low-cost hexarotor micro aerial vehicle

This article proposes a new practical robust attitude state feedback controller of a low-cost hexarotor micro aerial vehicle under the effects of noise in angular velocity measurements and multiple uncertainties (called the equivalent disturbance), which consist of external time-varying wind disturbance, nonlinear dynamics, coupling and parametric uncertainties. The proposed method is designed in two simple steps. Firstly, a nominal cascade controller is designed to reduce noise in angular velocity measurements and to achieve good attitude tracking performance in nominal conditions. Then, a second-order robust compensator is integrated into the closed-loop system to reduce the effects of the equivalent disturbance. The proposed control design is a linear time-invariant controller which is easily implemented in practical applications. Compared to other advanced attitude controllers, the proposed controller incurs lower computational costs and can easily be implemented in a low-cost embedded microcontroller system. In addition, a practical computational design procedure and an intuitive online tuning method for the proposed controller are presented in this article in order to provide a complete reference to micro aerial vehicle developers. The simulation and experimental results are presented to demonstrate the robustness of the proposed controller in operation in outdoor environments, to show good steady-state and dynamic tracking performance of the closed-loop system and to prove that the tracking errors are ultimately bounded within desired limits.

PID plus LQR attitude control for hexarotor MAV in indoor environments

The aim of this paper is to propose an optimum linear control algorithm that is able to stabilize the attitude of a hexarotor micro aerial vehicle (MAV) in indoor environment. The work will then compare it with the classical control PID (proportional-integral-derivative) and optimal control LQR (linear quadratic regulator) techniques. The proposed attitude controller is based on an outer-inner loop structure PID plus LQR (PID+LQR) control method where the controller combines the positive features of each sub-controller (PID and LQR). The key contribution of this work is the proposed attitude controller can improve robustness and transient response thus leads to faster response in indoor flying environment. The attitude tracking errors are proven to be ultimately bounded with specified boundaries. Simulation results on the hexarotor demonstrate the effectives of the proposed attitude controller.

Robust Optimal Attitude Controller for MIMO Uncertain Hexarotor MAVs: Disturbance Observer-Based

This paper proposes a robust optimal attitude control design for multiple-input, multiple-output (MIMO) uncertain hexarotor micro aerial vehicles (MAVs) in the presence of parametric uncertainties, external time-varying disturbances, nonlinear dynamics, and coupling. The parametric uncertainties, external time-varying disturbances, nonlinear dynamics, and coupling are treated as the total disturbance in the proposed design. The proposed controller is achieved in two simple steps. First, an optimal linear-quadratic regulator (LQR) controller is designed to guarantee that the nominal closed-loop system is asymptotically stable without considering the total disturbance. After that, a disturbance observer is integrated into the closed-loop system to estimate the total disturbance acting on the system. The total disturbance is compensated by a compensation input based on the estimated total disturbance. Robust properties analysis is given to prove that the state is ultimately bounded in specified boundaries. Simulation results illustrate the robustness of the disturbance observer-based optimal attitude control design for hovering and aggressive flight missions in the presence of the total disturbance.

Robust position hold control of hexarotor UAVs

This paper presents a practical robust position hold control design for hexarotor unmanned aerial vehicles (UAVs) under the effects of uncertainties (equivalent disturbance) which contain external disturbances, nonlinear dynamics, coupling, and parametric uncertainties. The proposed controller has three main loops which are position-xy, altitude, and attitude loop. Thenominal linear time-invariant controller is designed for each loop based on cascade proportional-integral-derivative (PID) method while a robust compensator based on second order robust filter is added on attitude loop in order to improve the attitude tracking performance when the hexarotor leaves the nominal conditions due to presence of uncertainties. The experimental results prove the effectiveness of proposed controller to reduce and bind the attitude tracking errors at certain boundaries and demonstrate the ability of controller to hold the vehicle position in the outdoor flight environment.

Modeling, attitude estimation, and control of Hexarotor micro aerial vehicle (MAV)

This paper describes modeling, attitude estimation, attitude control, and altitude control for Hexarotor micro aerial vehicle (MAV). Hexarotor has high potential to carry more payload and high maneuverability compared to quadrotor. This paper proposes a new approach for attitude estimation in realtime system by using a nonlinear complementary observer based on special orthogonal group of rotation matrices SO(3), rather than conventional extended Kalman filter (EKF), to exploit the near-global convergence property of the observer and reduced computational complexity. The proposed attitude controller is based on an inner-outer loop structure PI+PID (proportional-integral plus proportional-integral-derivative) control method to reduce the overshoot effects, leads to faster response, improve robustness and transient response, whilst the proposed altitude controller is based on classical closed loop PID control system. Simulation results will be presented showing the proposed controller achieves excellent dynamical performance and finally, the experimental results, both in indoor and outdoor flying environment demonstrate the effectiveness of the proposed attitude observer and controller in real flight condition.

Real-Time Nonlinear Complementary Filter on SO(3) for Attitude Estimation of Small-Scale Aerial Robot

This paper presents the real-time implementation of a powerful nonlinear complementary filter on special orthogonal group of rotation matrices, called as NCF SO(3) for attitude estimation. It fuses the raw data from accelerometers, magnetometer, and gyroscopes sensors to get reliable real-time attitude estimation. Gyroscopes is used as the main sensor for attitude estimation and another two sensors are used to correct drift error of gyroscopes. In this paper, the performance of NCF SO(3) is explored on performance in highly dynamic manoeuvres in real-time. Real-time experiments were conducted to compare its performance with conventional Extended Kalman Filter (EKF) to exploit the positive features of NCF SO(3) for small-scale aerial robot with limited on-board processor memory cases. The experimental results show the proposed real-time filter has excellent estimated attitude data and can reduce the computational cost, compared to EKF. Thus, it is suitable for small-scale aerial robot which has memory limitation of on-board processor.

Robust optimal control for attitude tracking of hexarotor UAVs: Switching robust compensator approach

This paper proposes a robust optimal control design for attitude tracking of hexarotor unmanned aerial vehicles (UAVs) in varying operating conditions subject to external disturbances under the presence of parametric uncertainties, nonlinear dynamics, and coupling. All these uncertainties are considered as equivalent disturbance in this paper. The proposed attitude controller is designed for pitch, roll, and yaw subsystems and it consists of a nominal optimal controller and switching robust compensator. The nominal optimal controller is based on linear quadratic regulator (LQR) control approach to achieve good tracking performance in nominal condition. The switching robust compensator is added in order to improve the attitude tracking performance due to the presence of equivalent disturbance where the amount of equivalent disturbance is changing dynamically. The simulation results prove that the switching robust compensator has ability to maintain the robustness in small and large amount of equivalent disturbance. It also prove that the attitude tracking errors are bounded in specified boundaries.

Image feature extraction algorithm for robotic applications: Region features case

This paper presents an image feature extraction algorithm for robotic applications. The proposed method robust against scene illumination change, viewpoint change, specularity, colour saturation, imperfect focus of image, and shadows. The proposed algorithm is a bottom up approach which consists of three phases: colour classification, correction, and description. In colour classification phase, chrominance (CIE Lab colour space) is used to segment coloured images in order to detect potential coloured region. Thresholding and several morphological operations are applied in correction phase in order to eliminate the noise pixels. Finally, moment method is used to identify the desired image features (area, position and orientation) of targets. The results are presented to illustrate each operations involved and demonstrate the performance of proposed image feature extraction algorithm. Overall, the proposed method is suitable for known operating environment cases where a robot operates in predefined workspace with prior knowledge of target.

Robust attitude tracking control of hexarotor MAVs using plug-in gain scheduling robust compensator technique

This paper proposes a robust attitude tracking control scheme for hexarotor micro aerial vehicles (MAVs) under the effects of uncertainties (equivalent disturbances) which consist of external disturbances, nonlinear dynamics, coupling, and parametric uncertainties. The proposed scheme is easy to be implemented compared to other robust controller techniques since it consists of a nominal controller and a plug-in gain scheduling robust compensator only for pitch, roll, and yaw subsystems. The nominal controller is based on cascade PID (P, I, D denote for proportional, integral, and derivative term, respectively) control approach. A plug-in gain scheduling robust compensator is added in order to improve the attitude tracking performance due to the presence of uncertainties. The simulation results prove the attitude tracking errors are bounded in specified boundaries and demonstrate the robustness of the proposed controller and thus suitable for outdoor flight condition.

Robust attitude controller for uncertain hexarotor micro aerial vehicles (MAVs)

This paper proposes a practical robust attitude controller for uncertain hexarotor micro aerial vehicles (MAVs). The proposed robust controller consists of a nominal linear time-invariant controller and a robust compensator for pitch, roll, and yaw subsystems. The nominal controller is an inner-outer loop structure of PI+PID (proportional-integral plus proportional-integral-derivative) control method to achieve the desired tracking of the nominal system, whilst the robust compensator is added to restrain the influence of the uncertainties (equivalent disturbances) which contain parametric uncertainties, coupling, nonlinear dynamics, and external disturbances. The real-time experimental results on the hexarotor demonstrate the effectiveness of the proposed controller in real flight condition and finally, the attitude tracking errors are proven to be ultimately bounded with specified boundaries.