Robust Position Control Research Articles

Simulation and Analysis of Electro Mechanical Actuator with Position Control

In recent times, Electro-Mechanical Actuator (EMA) is widely employed in various aerospace applications
 because of its compactness, ease of maintenance, and cost efficiency. It attracts most of the researcher for simulation and performance analysis. It is very much important to study its control system behaviour. In general, EMA requires, three loop cascade control, but for aerospace application two loop cascade control is used for speed and position controls due to dynamic load changing requirement. Most research efforts on EMA system has used a transfer function model of all its subsystems. Nevertheless, this technique does not yield complete outcomes for analysing its performance. To analyse its performance and characteristics in dynamic condition, an experimental model is essential. In addition, this model needs to cater for analysing performance of different capacity EMA. The primary goal of this work is to simulate unique EMA model with position control using a practical data and analyse its performance. In this design, EMA is modelled by three-phase Brushless Direct Current (BLDC) motor, six-step commutation logic, a speed sensor (Tacho) and a position sensor using Linear Variable Differential Transformer (LVDT). Position and speed controls are handled by Proportional (P) and Proportional plus Integral (PI) controllers respectively. The process reaction curve method is used to tune the controllers. This tuning approach is adequate to enable accurate and robust speed and position control. This paper focus on the simulation and performance analysis of a practical EMA system with position and speed controls in matlab-simulink. The performance analysis results shows that simulated model characteristic is close to physical system and reliable.

Robust Attitude Controller Design for an Uncommon Quadrotor With Big and Small Tilt Rotors

AbstractIn this article, a robust attitude controller design for an uncommon quadrotor aerial vehicle is discussed. This aerial vehicle is designed to have two big rotors on the longitudinal axis to increase the lift capacity and flight endurance, and two small tilt rotors on the lateral axis to stabilize the attitude. Similar to other multirotors, linearization of the full nonlinear model and using an appropriate rotor mixing matrix give the approximate diagonal attitude model of this quadrotor around hover. However, this ideal model lacks sensor delays, uncertain parameters, flexible modes of a structure, and inexact decoupling dynamics. Therefore, using this model in the control design limits the achievable attitude control performance. Unlike most studies, a system identification method is applied to estimate a more accurate model and increase the resulting attitude control performance. The aim of this paper is to obtain a suitable nominal model with accompanying uncertainty using robust control criterion in the system identification. In this way, an uncertain model that gives high performance in the subsequent robust control design is obtained. The experimental results show that this combined identification and robust control procedure improves attitude control performance compared to existing classical controller design methods.

Robust Attitude Control of Helicopters with Three-Degree Freedom Based on Intermittent Event-Triggered Mechanism

In the field of the widely used helicopter, this paper studies whether the helicopters with three-degree freedom (3DOF helicopters) have a new control method of stable attitude. Therefore, two research methods are adopted. One is to use intermittent control, so as to achieve control stability in a short time without its inputting. The other is to find and update the time needed to meet the next control through the event-triggered mechanism. A theorem is given to prove the feasibility of these methods, and Lyapunov’s second law is also applied in this paper to analyze the stability of the model designed for robust attitude control. Besides, we use the linear matrix inequality solver to solve the feedback gain of the controller in the theorem. Finally, through MATLAB simulation, the system error state of helicopters tends to zero under intermittent control, which highlights the advantages of short communication time and few times of simulation, thus achieving the simulation goal.

Quaternion Attitude Control System of Highly Maneuverable Aircraft

In the era of rapid advancements in manned and unmanned aviation and robotics, there is a need for high-performance, robust attitude control of highly maneuverable fixed-wing aircraft, both manned and unmanned (UAVs). This paper presents an extension to research on spacecraft attitude control. The article extends existing concepts and applies them to the control problem of aircraft operating in Earth’s atmosphere. First, a general concept of quaternions is presented. Next, the attitude controller’s architecture is discussed. The controller synthesis is described using quaternion algebra. The quaternion-based attitude controller is then compared with a classical Euler-based attitude controller. The methodology for comparison and performance evaluation of both controllers is described. Lastly, the results of the simulations and a comparison of the two controllers are presented and discussed. The presented control scheme outperforms classical methods based on Euler angles, particularly at the aircraft’s high pitch and roll angles.

Iterative learning control of a pneumatically actuated lung tumour mimic model for an improvement of PET/CT-imaging

In this paper, a model-based tracking control is proposed for a mechanism dedicated to accurately reproduce the breathing-induced motion of a human lung tumour. In former work, a 3-dimensional mechanism equipped with three pneumatically driven axes has been developed and constructed for this purpose. The overall control structure consists of decentralised axis controller for each pneumatic cylinder with a cascaded structure: A fast inner control loop governs the pressure induced drive force using backstepping techniques, whereas the outer control loop is related to an optimal, robust position control of the cylinder. Additionally, discrete-time iterative learning controllers are utilised to compensate lumped disturbance forces and model uncertainties. The suggested overall control structure has been implemented on the innovative test rig and successfully validated in a clinical framework. The given work represents the basis for future improvements of algorithms regarding PET/CT-imaging as well as radiotherapy.

Towards the Mechatronic Development of a New Upper-Limb Exoskeleton (SAMA)

Modern neuromuscular rehabilitation engineering and assistive technology research have been constantly developing in the last 20 years. The upper body exoskeleton is an example of an assistive rehabilitation device. However, in order to solve its technological problems, interdisciplinary research is still necessary. This paper presents a new three-degrees of freedom (DOF) active upper-body exoskeleton for medical rehabilitation named “SAMA”. Its mechanical structure is inspired by the geometry and biomechanics of the human body, particularly the ranges of motion (ROM) and the needed torque. The SAMA exoskeleton was manufactured and assembled into an ergonomic custom-made wheelchair in a sitting posture in order to provide portability and subject comfort during experimental testing and rehabilitation exercises. Dynamic modeling using MATLAB–Simulink was used for calculating the inverse kinematics, dynamic analysis, trajectory generation and implementation of proportional–integral–derivative (PID) computed torque control (PID-CTC). A new framework has been developed for rapid prototyping (the dynamic modeling, control, and experimentation of SAMA) based on the integration between MATLAB–Simulink and the Robot Operating System (ROS) environment. This framework allows the robust position and torque control of the exoskeleton and real-time monitoring of SAMA and its subject. Two joints of the developed exoskeleton were successfully tested experimentally for the desired arm trajectory. The angular position and torque controller responses were recorded and the exoskeleton joints showed a maximum delay of 200° and a maximum steady state error of 0.25°. These successful results encourage further development and testing for different subjects and more control strategies.

Elliptical Encircling of Quadrotors for a Dynamic Target Subject to Aperiodic Signals Updating

This paper presents an elliptical target encircling control policy of quadrotors subject to uncertainties and aperiodic signals updating based on pure bearing measurements. At the translational level, by resorting to bearing-only data, rather than prior position and velocity information of target, a position estimator is constructed for locating the unknown target. Utilizing the localization result from position estimator, compared to the existing circular surrounding alternatives, a planar elliptical guidance law capable of adapting more sophisticated operational environment, and a longitudinal control law are synchronously established to generate the velocity reference. At the rotational level, an unknown system dynamics estimator (USDE) is introduced to online neutralize total adverse effect induced by exogenous disturbances and internal uncertainties, where high precision estimation and low computational complexity can be guaranteed with only one tuning argument, then an event-triggered robust attitude controller carrying a sampling deviation compensation item is synthesized accomplishing elliptical encircling for a dynamic target without involving Zeno behavior. Finally, stability of closed-loop system is analyzed via input-to-state stable principle, while simulations are given to verify the efficacy of suggested approach.

Linear parameter-varying gain-scheduled preview-based robust attitude control design for a staring-mode satellite

It is challenging to precisely control the attitude of a satellite when performing a fast and large-angle maneuver, for instance, in the staring mode. To solve this issue, this paper investigates a gain-scheduled preview-based robust attitude control method in the framework of linear parameter-varying control theory. Firstly, the linear parameter-varying model of an observation satellite with large-angle rotations is developed by choosing the attitude angles as scheduling parameters to take the dynamics variation into consideration. In order to ease the implementation in practical engineering applications, the structure of the linear parameter-varying controller is in the form of modified proportional-integral-derivative control. To simultaneously satisfy the requirements of fast rotational speed and high dynamic tracking performance, a gain-scheduled proportional-integral-derivative controller is designed with the future information of desired attitude signals included in the feedforward path. The proposed controller is synthesized within the framework of H∞ robust control to enhance the robustness against inaccurate previewed information and external disturbances. The corresponding control synthesis condition is derived as an optimization problem with linear matrix inequality constraints. Monte Carlo simulation results demonstrate that the dynamic tracking accuracy of the proposed control algorithm can be guaranteed to be less than 0.01 deg in the face of fast large-angle commands, inaccurate previewed information and external disturbances.

Fixed-time convergence attitude control for a tilt trirotor unmanned aerial vehicle based on reinforcement learning

This paper presents a new nonlinear robust attitude control strategy for the tilt trirotor unmanned aerial vehicle (UAV). Fixed-time convergence control of the UAV’s attitude tracking errors under the effects of model uncertainties and unknown external disturbances is achieved by utilizing the proposed control design. Actor–critic (AC) structure based neural networks are trained only with the information of the UAV’s inputs and outputs data, to handle the UAV’s modeling uncertainties with bounded estimation error. Then a sliding-mode based fixed-time controller is designed to compensate the approximation error of the neural networks and the unknown external disturbances. Based on the Lyapunov stability theory, the stability analysis of the closed-loop system is presented. The performance of the presented nonlinear robust control strategy is validated through the real-time flight experiments.

Data driven adaptive robust attitude control for a small size unmanned helicopter

In this paper, the data driven based control design problem for a small size unmanned helicopter is investigated. The helicopter is subjected to the effects associated with modeling uncertainties and unknown external disturbances. A new model free robust adaptive attitude control law is proposed with the combination of the model-free-adaptive-control (MFAC) design, the immersion and invariance (I&I) approach, and the super-twisting technique. Different from the most existing linear or nonlinear model-dependent control designs for unmanned helicopters, the proposed control strategy requires very less model knowledge. The controller depends mainly on the input and output data of the helicopter, and no boundedness knowledge of the unknown disturbances is required. Stability of the closed-loop system has been proved. Real-time flight experiments have been performed on the self-developed helicopter testbed only with the available feedback data of the helicopter. The experimental results have validated the good robustness of the proposed control methodology.

Transportation of Payload Using Multiple Quadrotors via Rigid Connection

Due to the limited payload capability of an aerial robot, multiple quadrotors can be used to manipulate payloads in aerial transportation, construction, and assembly tasks. This paper focuses on the cooperative transportation of a payload rigidly attached to multiple quadrotor bodies. These quadrotors may have different orientations. The dynamics equation of a rigid body in 3-D space is derived to describe the motion of such a transportation system. Robust position and attitude controllers are designed to drive the system to the desired pose. To assign control signals for each quadrotor, the control command allocation method compatible with the case that partial or all quadrotors are in parallel planes is developed. Finally, experimental results are presented to validate the effectiveness of the proposed controllers and control command allocation methods. Different from classical works in this field, this paper can solve the dynamics modeling, controller design, and control command allocation problems for the transportation of a rigidly connected payload using a team of quadrotors with different orientations.

Robust Attitude Control Scheme for Constantly Spinning Small-Sized Quadrotor in the Presence of Imbalance Characteristics

Unlike normal yaw motion, a constantly spinning quadrotor experiences severe instability while rotating at high angular speeds owing to its imbalancecharacteristics originating from the off-center parts. To resolve this issue, this study proposes a novel composite robust control scheme for a constantly spinning quadrotor, with the aim to achieving omnidirectional sensing by scanning its surroundings with a single field of view limited sensor. The proposed scheme makes use of both offline calibration and online disturbance observation to compensate for the variation in the center of mass and misalignment between the body-fixed frame and principal axis of rotation, respectively. Additionally, the reference inputs are reshaped, or leading in time, to achieve the desired flying direction. It is demonstrated through an experiment that the proposed control scheme compensates well for the effect of the imbalance characteristics of the quadrotor, thus achieving good omnidirectional sensing with more stable rotation.

Robust attitude control of a quadrotor unmanned aerial vehicles using optimized disturbance observer

AbstractThis article proposes a method of realizing robust attitude stabilization control of a quadrotor UAV using the disturbance observer (DOB), where Q–filter is optimally designed considering performances of attenuating disturbance and estimation noise, and robust stability against parameter variations and sampling duration delay due to discrete time control in microcontroller. Disturbance rejection performance mainly depends on the bandwidth determined by cut‐off frequency of DOB's Q–filter. However, extension of the Q–filter's bandwidth must be restricted due to the requirement of robust stability against parameter uncertainty and sampling duration delay in onboard microcontroller for flight control of quadrotor. In order to optimize the disturbance rejection performance under the restriction of bandwidth, an norm minimization problem is defined considering the frequency bands of disturbance and noise. The optimization problem is transformed into standard control design problem by pseudo loop factorization method so as to resolve the structural constraint of Q–filter. Then, stability of the discrete time system configured by digital controller is tested in relation with the time constant of the designed DOB's Q–filter under different inertia moment values. The comparisons between simulation results by different control methods validate that the robust control method using proposed DOB provides a better performance of disturbance attenuation than that using conventional DOB.

Uncertainty and disturbance-observer based robust attitude control for satellites

The manoeuvre of a small satellite in a defined orbit at an accurate position with payload complexity and mass constraint is very challenging. Small satellites are highly prone to circumferential disturbances in space. Mathematical modelling of satellite dynamics is studied in detail. Stability regions are analysed with phase portrait. Feedback linearisation implemented with Uncertainty and Disturbance Estimation (UDE) based controller-observer is designed. The novelty of the research is to robustify the satellite by estimating the overall uncertainties and disturbances. The resultant controller requires the angular positions and angular rates of the spacecraft. The observer provides the angular rate. The closed-loop stability of the overall system has been established. The efficacy of the proposed design is demonstrated on a three-axis nanosatellite. Comparison of proposed strategy is made with other control methods through simulation in Matlab platform.

Magnetorquers-based satellite attitude control using interval type-II fuzzy terminal sliding mode control with time delay estimation

This paper presents a novel robust attitude controller for satellite applications with magnetic actuation. First, at the kinematical level, a terminal sliding mode (TSM)-based sliding surface is proposed to achieve attitude tracking. Next, at the dynamical level, a controller is designed for robust stabilization of the sliding surface. Time delay estimation (TDE) is used to estimate the uncertainty caused by parametric uncertainty and external disturbances in the satellite dynamics. The TDE output is then combined with an interval type-2 fuzzy logic (IT2FL)-based robust TSM controller. The main merits of this control strategy are fast convergence of the tracking errors and strong robustness against disturbances/parametric uncertainty. The closed-loop stability and convergence of the tracking errors are proved by Lyapunov analysis. Software simulations confirm the effectiveness of the proposed control method.

Adaptive Robust Position Control of Electro-Hydraulic Servo Systems with Large Uncertainties and Disturbances

In this paper, a novel adaptive robust control (ARC) scheme is proposed for electro-hydraulic servo systems (EHSSs) with uncertainties and disturbances. All dynamic functions in system dynamics are effectively approximated by multi-layer radial basis function neural network (RBF NN)-based approximators with online adaptive mechanisms. Moreover, neural network-based disturbance observers (NN-DOBs) are established to actively estimate and efficiently compensate for the effects of not only the matched/mismatched but also the imperfections of RBF NN-based approximators on the control system. Based on that, the nonlinear robust control law which integrates RBF NNs and NN-DOBs is synthesized via the sliding mode control (SMC) approach to guarantee the high-accuracy position tracking performance of the overall control system. Furthermore, the problem of the combination between DOBs and RBF NNs is first introduced in this paper to treat both disturbances and uncertainties in the EHSS. The stability of the recommended control mechanism is proven by using Lyapunov theory. Finally, numerical simulations with several distinct frequency levels of reference trajectory are conducted to convincingly demonstrate the effectiveness of the proposed approach.

Robust Control Design for Accurate Trajectory Tracking of Multi-Degree-of-Freedom Robot Manipulator in Virtual Simulator

Robot manipulators have complex dynamics and are affected by significant uncertainties and external disturbances (perturbations). Consequently, determining the exact mathematical model of a robot manipulator is a tedious task. Accordingly, accurate trajectory tracking is a dominant feature in the design of position control for robot manipulators. The main objective of this research is to design a robust and accurate position control for a robot manipulator despite the absence of an exact model. For this purpose, an extended state observer (ESO)-based sliding mode control (SMC) is proposed. The main concept in the ESO is to define and estimate the assumed perturbation, which includes known and unknown system dynamics, uncertainties, and external disturbances. Additionally, the ESO estimates the system states. This estimated perturbation information, which is combined with the SMC input, is utilized as a feedback term to compensate for the effect of the actual perturbation. The perturbation compensation improves the controller performance, resulting in a slight position error, less sensitivity to perturbation, and a small switching gain required for the SMC. The advantage of the proposed algorithm is that it only requires partial state information and position feedback. Thus, identifying the system parameters for the nominal model before designing the controller is unnecessary. The proposed algorithm is implemented and compared with the conventional SMC and the SMC with a sliding perturbation observer (SMCSPO) in a virtual environment based on MATLAB SimMechanics. The comparison results validate the robustness of the proposed technique in the presence of perturbation and show that the technique has a significantly reduced trajectory tracking error than the conventional SMC and SMCSPO.

Force/Torque-Based Impedance Control With Perturbation Observer—Toward High Payload System Robust Trajectory Tracking

This paper presents a robust force/torque-based impedance control that reacts to deviated motion by generating forces to achieve the desired impedance, particularly for high payload systems. One of the special cases of such systems is an assistive robot for paraplegics (ARP) with a sit-stand mechanism (STSM) and, therefore, its control is investigated. Recently, a nonlinear robust position control known as sliding mode control with sliding perturbation observer (SMCSPO) was implemented on STSM and proven its effectiveness. However, with increasing subject body mass, high switching control gains are required which consequently either result in increased tracking error or chattering in control performance. In this regard, a new framework of integrated control was proposed which combines the feature of impedance control with estimated information from SMCSPO resulting in an enhanced control algorithm. The advantage of this impedance control is that because of SMCSPO, it utilizes the linear system information with position feedback only to estimate the states and perturbation (nonlinearities, uncertainties, and disturbance). This estimated perturbation then helps in compensating the actual perturbation effect from the system response. Moreover, the impedance control excludes the saturation function which helps prevent the chattering with low control gains. The comparison simulation and experiment results of the proposed impedance control with SMCSPO validated the proposed algorithm which enhances the transient response with minimized estimation error and better perturbation estimation.

측정 민감도 및 외란 하에서 쿼드로터의 강인 자세 제어

A robust attitude control scheme for quadrotor is proposed under measurement sensitivity and external disturbance. In order to treat measurement sensitivity, a new determination process of a compact with allowed measurement sensitivity is presented by utilizing Lyapunov equation. With our control scheme, all controlled system states are shown to be bounded. Moreover, the ultimate bounds of all states can be made arbitrarily small by adjusting the gain-scaling factor in the presence of external disturbance. The validity of our control method is first checked via simulation, and then is also experimentally shown in the attitude control of quadrotor system.

L2‐gain robust trajectory tracking control for quadrotor UAV with unknown disturbance

AbstractIn this paper, the trajectory tracking problem of the position and yaw angle of an underactuated quadrotor UAV is studied. Considering that the quadrotor UAV often encounters unknown disturbance resulted by model parameter perturbations and environmental changes, a new L2‐gain robust control method is presented based on dissipation theory. First, the dynamic model of the quadrotor UAV with disturbances is transformed by introducing three virtual control variables. In this way, the trajectory tracking control can be implemented by the dual loop control, that is, the position control loop and the attitude control loop. Then, based on dissipation inequality, the robust position controller and attitude controller are developed to guarantee the L2‐gain of the system to the unknown disturbance. It is proved that all the tracking errors are uniformly ultimate boundedness. In addition, the controller is further reconstructed by introducing a new class K functions to improve the transient and steady‐state performances of the quadrotor UAV system. In the end, two simulation examples are provided to check the validity of the control method proposed and the convergence of the quadrotor UAV trajectory tracking error.