Pseudo-inverse Control Allocation Research Articles

Quaternion-Based Non-Singular Terminal Sliding Mode Control of Quadrotor with a Two-Degree-of-Freedom Deformable Arm for Narrow Environments

Conventional multi-rotors with limited deformation capability are unable to meet the traversal capability of complex and narrow environments. In order to solve the above problems, a novel type of deformable quadrotor with a two-degree-of-freedom arm, named QTDA, is proposed. Firstly, the overall structural design of the QTDA is introduced, and its movement strategy is analyzed. Secondly, the Newton–Euler equations based on a quaternion are utilized to model the omnidirectional dynamics and kinematics of the system. Next, to tackle the multi-actuator control problem, a pseudo-inverse control allocation method is developed, along with an analysis of control allocation singularities. Furthermore, non-singular terminal sliding mode position control law and non-singular terminal sliding mode attitude control law based on a quaternion are designed. Finally, simulations are conducted to verify the effectiveness of the proposed control methods. The results demonstrate the QTDA’s ability to traverse both narrow horizontal and vertical environments, thereby validating the effectiveness of the approach presented in this paper.

Fixed-time regulation of spacecraft orbit and attitude coordination with optimal actuation allocation using dual quaternion.

On-orbit service spacecraft with redundant actuators need to overcome orbital and attitude coupling when performing proximity maneuvers. In addition, transient/steady-state performance is required to fulfill the user-defined requirements. To these ends, this paper introduces a fixed-time tracking regulation and actuation allocation scheme for redundantly actuated spacecraft. The coupling effect of translational and rotational motions is described by dual quaternion. Based on this, we propose a non-singular fast terminal sliding mode controller to guarantee fixed-time tracking performance in the presence of external disturbances and system uncertainties, where the settling time is only dependent on user-defined control parameters rather than initial values. The unwinding problem caused by the redundancy of dual quaternion is handled by a novel attitude error function. Moreover, optimal quadratic programming is incorporated into null space pseudo-inverse control allocation that ensures the actuation smoothness and never violates the maximum output capability of each actuator. Numerical simulations on a spacecraft platform with symmetric thruster configuration demonstrate the validity of the proposed approach.

Fuzzy adaptive sliding mode fault estimation and fixed-time fault-tolerant control for coupled spacecraft based on SE(3)

The goal of this study is to develop fault estimation (FE) and fault tolerant control (FTC) techniques for rigidly coupled spacecraft. A fuzzy adaptive sliding mode fault estimation approach is proposed to address fault tolerance against a large scale of disturbances, including inertia parametric uncertainties, space disturbances, actuator faults and saturation constraints. Firstly, a six-degrees of freedom (6-DOF) fault tolerant control architecture is established on the Lie group SE(3), which combined rotation and translation coupling kinematics and dynamics together. Then, a nonlinear fault estimator is used to deal with controllability loss of the fault actuator and the fuzzy logic system (FLS) is presented to solve the lumped disturbance. Next, in order to reduce the number of control parameters, the exponential parameters of the fast double-power sliding mode surface and the reaching law are set to be the same, which are nested with the estimated value of actuator effectiveness and combined with the pseudo inverse control allocation method to form the control algorithm in this paper. Finally, the stability and fixed-time convergence of the proposed method are proved theoretically by Lyapunov function, and the effectiveness of the scheme is verified by numerical simulation.

Control Allocation Reconfiguration for Actuator Failure on a Coaxial-Pusher Helicopter

An elastic blade flight dynamics model for a coaxial helicopter platform based on the Sikorsky X2 Technology™ Demonstrator is presented and validated with steady trim and frequency response flight-test data. A full authority explicit model following control architecture along with pseudoinverse control allocation is implemented for the model in hover and cruise at 180 kt using CONDUIT® in order to stabilize the vehicle and meet a set of stability, handling qualities, and performance requirements. Different fault scenarios are considered including failure of rotor swashplate actuators and tail surface actuators in hover and forward flight, which are compensated for by recalculating the pseudoinverse control mixing accordingly. The approach is shown to maintain aircraft stability through the fault transient and into a new steady trim state for the vehicle. Though the implemented controller is successful in maintaining the aircraft state, different fault cases lead to violations in rotor tip clearance limits, which will require additional effort to account for in flight.

Flight quality characteristics and observer-based anti-windup finite-time terminal sliding mode attitude control of aileron-free full-wing configuration UAV

This paper evaluates the flight quality of an aileron-free full-wing configuration UAV and proposes a highly robust attitude controller considering the typical control problems (i.e., manipulation saturation, coupling, susceptibility to the disturbance, nonlinearity, and uncertainty) of the aileron-free full-wing configuration UAV. First, the flight quality characteristics are analyzed through the change of the flight modes at different trim state points in the flight envelope. Then, the back-stepping method is introduced for decoupling and systematic control law design. Based on the Lagrange multiplier approach, the pseudoinverse control allocation is adopted to realize command decoupling and acquire the minimal 2-norm control output. In order to improve the robustness and control accuracy of the controller, a novel continuous finite-time terminal sliding mode control scheme with adaptive law is designed, which has the virtue of suppressing the chattering and avoiding singularity. In addition, an anti-windup compensator (AWC) is developed to ensure the stability of the flight state under manipulation saturation and make the manipulation output exit the saturation region quickly. To further solve the problem that the aileron-free full-wing configuration UAV is susceptible to disturbances, an adaptive super-twisting disturbance observer (ASTDO) is designed to estimate and compensate the uncertain compound disturbance including the uncertain time-varying disturbance and nonlinear dynamic term to improve control performance. The proposed observer can suppress chattering, adjust gain parameters adaptively and have high observation accuracy. Based on the Lyapunov stability theorem, the anti-windup compensation variable in the AWC and the disturbance estimation error in the ASTDO can gradually converge to neighborhoods of the equilibrium points in finite time. Moreover, the practical finite-time stability of the closed-loop control system is proved. According to the flight quality evaluation, the aileron-free full-wing configuration UAV has poor flight quality at the boundary of the flight envelope and exhibits inherent longitudinal high-frequency oscillation characteristics. The simulation results demonstrate that the designed ASTDO-AWFTTSMC guarantees strong robustness, high accuracy, and fast convergence speed for attitude tracking, solves the saturation problem and realizes state decoupling and manipulation decoupling. Moreover, the designed controller overcomes the adverse effects of disturbance, nonlinearity, and uncertainty, greatly suppresses the longitudinal high-frequency oscillation and still exhibits excellent control performance at the flight state points on the flight envelope boundary.

Active versus passive fault-tolerant control of a redundant multirotor UAV

ABSTRACTThis paper considers actuator redundancy management for a redundant multirotor Unmanned Aerial Vehicle (UAV) under actuators failures. Different approaches are proposed: using robust control (passive fault tolerance), and reconfigurable control (active fault tolerance). The robust controller is designed using high-order super-twisting sliding mode techniques, and handles the failures without requiring information from a Fault Detection scheme. The Active Fault-Tolerant Control (AFTC) is achieved through redistributing the control signals among the healthy actuators using reconfigurable multiplexing and pseudo-inverse control allocation. The Fault Detection and Isolation problem is also considered by proposing model-based and model-free modules. The proposed techniques are all implemented on a coaxial octorotor UAV. Different experiments with different scenarios were conducted for the validation of the proposed strategies. Finally, advantages, disadvantages, application considerations and limitations of each method are examined through quantitative and qualitative studies.

Selection of Actuator Combination in Integrated Chassis Control Using Taguchi Method

This paper presents a method to select the actuator combination in integrated chassis control using Taguchi method. Electronic stability control (ESC), active front and rear steering (AFS/ARS) are used as an actuator, which is needed to generate a control tire force. After computing the control yaw moment in the upper-level controller, it is distributed into the control tire forces, generated by ESC, AFS and ARS in the lower-level controller. In this paper, the weighted pseudo-inverse control allocation (WPCA) with variable weights is used to determine the control tire forces of each actuator. Taguchi method is adopted for sensitivity analysis on variable weights of WPCA in terms of the control performances such as the maneuverability and the lateral stability. For sensitivity analysis, simulation is performed on a vehicle simulation package, CarSim. From sensitivity analysis, the most effective actuator combination is selected.

Robust adaptive FTC allocation for over‐actuated systems with uncertainties and unknown actuator non‐linearity

In this study, a robust adaptive fault-tolerant control (FTC) allocation method is proposed to address the FTC problem of over-actuated systems in the presence of matched disturbance, unmodelled dynamics and unknown actuator non-linearity simultaneously. The main idea is to design the virtual control law via robust adaptive control and then distribute the virtual control among individual actuators by weighted pseudo-inverse control allocation whether the actuators are faulty or not. The virtual control consists of three terms: a linear term is designed through adaptive control to maintain stability, a non-linear term constructed by radial basis function neural network (RBFNN) is used to approximate the unmodelled dynamics, and a robust term is added to eliminate the approximation error introduced by RBFNN as well as matched disturbance and unknown actuator non-linearity. With the aid of the Lyapunov stability theorem, the convergence of the closed-loop system is proven. The simulation results demonstrate the effectiveness, fault-tolerant capability and robustness of the proposed method.

Fault Diagnosis and Fault-Tolerant Control of an Octorotor UAV using motors speeds measurements

Abstract This paper presents an active fault-tolerant control strategy (AFTCS) for an octorotor unmanned aerial vehicle (UAV) regarding several motors failures or rotors damages. A complete AFTC architecture including error detection, fault isolation and system recovery is presented. The diagnosis system is based on the motors speeds and currents measurements. Once the motor failure or the rotor loss is diagnosed, a recovery algorithm is applied. It uses the pseudo-inverse control allocation approach to redistribute the control efforts among the healthy actuators. This architecture is validated in real flights.

Adaptive coordinated leader–follower control of autonomous over-actuated electric vehicles

In this paper, the leader–follower formation control problem of autonomous over-actuated electric vehicles on a highway is studied. As the autonomous over-actuated electric vehicles have the characteristics of non-linearities, external disturbances and strong coupling, a novel coordinated three-level control system is constructed to supervise the longitudinal and lateral motions of autonomous electric vehicles. Firstly, an adaptive terminal sliding high-level control algorithm is designed to compute a vector of total forces and torque of vehicles, and the stability of the high-level control system is proven via Lyapunov analysis where uniform ultimate boundedness of the closed-loop signals is guaranteed. Then, a pseudo-inverse control allocation algorithm, which can achieve fault tolerance and reconfiguration of the redundant tyre actuation system, is presented to generate the desired longitudinal and lateral tyre forces. Then, a separate low-level controller consisting of an inverse tyre model and two inner loops for each wheel is designed to achieve its desired forces. Finally, simulation results demonstrate that the proposed control system not only enhance the tracking performance, but also improve the stability and riding comfort of autonomous over-actuated electric vehicles in a platoon.

전륜 횡력의 포화를 고려한 ESC와 AFS의 통합 섀시 제어

This article presents an integrated chassis control with electronic stability control (ESC) and active front steering (AFS) under saturation of front lateral tire force. Regardless of the use of AFS, the front lateral tire forces can be easily saturated. Under the saturated front lateral tire force, AFS cannot be effective to generate a control yaw moment needed for the integrated chassis control. In this paper, new integrated chassis control is proposed in order to limit the use of AFS in case the front lateral tire force is saturated. Weighed pseudo-inverse control allocation (WPCA) with variable weight is adopted to adaptively use the AFS. To check the effectiveness of the proposed scheme, simulation is performed on a vehicle simulation package, CarSim. From simulation, the proposed integrated chassis control is effective for vehicle stability control under saturated front lateral tire force.

Adaptive Energy-Efficient Control Allocation for Planar Motion Control of Over-Actuated Electric Ground Vehicles

A hierarchical control structure, consisting of a high-level dynamic sliding mode control (SMC) and a low-level adaptive energy-efficient control allocation (A-EECA) scheme, is presented to track the planar motions of an electric ground vehicle with four in-wheel motors while achieving the optimal energy consumption. By explicitly incorporating the efficiency functions and input constraints of in-wheel motors in the low-level A-EECA design, virtual control signals from the high-level dynamic SMC are distributed to four actuators with an adaptive convergence to the energy-optimal operating points. Taking allocation errors between the virtual control efforts and the real actuation realizations as inputs, the input-to-state stability of the overall feedback system is proved. Both simulation and experimental results in different maneuvers are demonstrated to validate the control design. The high-level vehicle tracking performance, low-level torque distributions, and total energy consumptions in the test maneuvers are compared between the proposed A-EECA and a standard pseudoinverse control allocation without considering the power optimization.

Fault-tolerant Sliding Mode Control for Uncertain Over-actuated Systems

This paper presents the sliding mode control design based on nonlinear sliding surface that ensures high performance step response of uncertain over-actuated system. High performance sliding mode control is designed for the system with predefined virtual control inputs having order less than the order of the system. Total control effort is then distributed among the actuators using pseudo-inverse control allocation technique. To make the system fault-tolerant (actuator saturation tolerant), the control allocation is updated online in a predefined way.

Rolling flight control using pseudo inverse control allocation for UAVs with multiple seamless warping control surfaces

In this paper, investigation has been made into the rolling control system design for an unmanned aerial vehicle of flexible warping wing. The research is focus on the design of control laws and control allocator for the aircraft rolling by actively operating several pairs of unconventional seamless flexible leading and trailing edge control surfaces. The first step is to design the control laws, which provide the total control command; the second step is to design a control allocator that distribute the total control command for each individual control surface. The main challenge is how to specify the rolling rate of the aerial vehicle with the control effectiveness of each control surface varying non-linearly with the flight speed and angle of attack. An iteration method of pseudo inverse allocation is investigated to map the control command varying with the flight speed to achieve the rolling control target.

Disturbance Rejection and Robust Least-Squares Control Allocation in Flight Control System

The problem of disturbance rejection and control allocation with an uncertain control effectiveness matrix is investigated in this paper for a flight control system. AnH2=H1 feedback controller is designed to produce the three axismoments and simultaneously suppress disturbance noise. A feedforward controller is used to track the reference signals.Under the condition of uncertainty included in the control effectivenessmatrix, a robust least-squares scheme is employed to deal with the problem of distributing the three axis moments to the corresponding control surfaces. The proposed robust least-squares control allocation is studied for both unstructured and structured uncertainties. To illustrate the effectiveness of the proposed scheme, a simulation for an experimental satellite launch vehiclemodel is conducted. Comparisons of robust least-squares control allocation and pseudoinverse control allocation are presented. Results show that a disturbance is rejected and robust least-squares control allocation is effectively robust to uncertain control effectiveness matrix.