Closed-loop Attitude Control System Research Articles

Design and Implementation of a Linear Active Disturbance Rejection Control-Based Position Servo Control System of an Electromotive Valve for Exhaust Gas Recirculation.

An exhaust gas recirculation (EGR) valve is used to quickly and dynamically adjust the amount of recirculated exhaust gas, which is critical for improving engine fuel economy and reducing emissions. To address problems relating to the precise positioning of an electromotive (EM) valve under slowly varying plant dynamics and uncertain disturbances, we propose a servo control system design based on linear active disturbance rejection control (LADRC) for the EGR EM valve driven by a limited angle torque motor (LATM). By analyzing the structure of the LATM and the transmission, the dynamic model of the system is derived. In addition, to solve the problems caused by slowly varying plant dynamics and uncertain disturbances, we combine the effects of uncertain model parameters and external disturbances as the total disturbance, which is estimated in real time by an extended state observer (ESO) and then compensated. In addition, accurate angular information is obtained using a non-contact magnetic angle measurement method, and a high-speed digital communication channel is established to help implement a closed-loop position control system with improved responsiveness and accuracy. Simulation and experimental results show that the proposed servo system design can effectively ensure the precision and real-time performance of the EM valve under slowly changing plant dynamics and uncertain disturbances. The proposed servo system design achieves a full-stroke valve control accuracy of better than 0.05 mm and a full-stroke response time of less than 100 ms. The controlled valve also has good robustness under shock-type external disturbances and excellent airflow control capability. The repeatability of the airflow control is generally within 5%, and the standard deviation is less than 0.2 m3/h.

Efficient on board storage and retrieval of fast maneuver profiles for space applications

Attitude guidance is a concept for implementing performance enhancing rotational maneuvers that uses a conventional closed-loop attitude control system to track an optimized maneuver trajectory. Minimum-time attitude guidance is presently being used for executing fast occultation avoidance maneuvers on NASA’s Lunar Reconnaissance Orbiter (LRO). A challenge in operationalizing the idea is related to the limited size of the spacecraft’s command buffer, which was not designed with maneuver tracking in mind. In this paper, we propose an interpolating pre-filter built on B-splines that can be used on board to process downsampled maneuver commands (to save buffer space) and provide attitude control inputs at the servo-rate. The approach is validated using a high-fidelity simulation of the LRO developed at NASA’s Goddard Space Flight Center.

Non-fragile negative imaginary output feedback control for attitude stabilization of flexible spacecraft

The robust non-fragile attitude stabilization controller for flexible spacecraft with model parameters uncertainty is difficult to be synthesized with negative imaginary system which is widely applicable for the vibration control of flexible structures. To address this issue, this paper proposes a negative imaginary output feedback H∞ synthesis strategy, in which the model parameters uncertainty, controller gain perturbations, unknown inertia and actuator faults are considered simultaneously. This strategy can guarantee that the closed-loop attitude control system has asymptotical stability with H∞ performance and approximates to negative imaginary. The iterative algorithm under linear matrix inequality constraints gives the conditions for the existence of such controller. In addition, external disturbance and input saturation are also taken into account. Compared with the general non-fragile H∞ controller, the numerical simulations demonstrate the superiority of the proposed controller in attitude stabilization and vibration suppression of flexible spacecraft.

NI-based static output feedback control for attitude stabilization of post-capture flexible spacecraft

This paper investigates the attitude stabilization problem of post-capture flexible spacecraft with non-cooperative target in the presence of input fault and saturation. In modeling, these non-cooperative characteristics are often manifested in uncertain and unknown inertia, model parameter uncertainty, input faults, etc. In this paper, aiming at the attitude stabilization problem of such post-capture flexible spacecraft, the attitude dynamics modeling is completed by introducing the nominal inertia to construct the comprehensive disturbance term including external disturbance, inertia uncertainty and actuator failure. Then, a static output feedback controller is applied to convert the closed-loop attitude control system to a stable negative imaginary system with H∞ performance constraints according to negative imaginary theory. As long as the optimization variables approach zero, the iterative algorithm can find such a static output feedback controller to achieve attitude stabilization of post-capture flexible spacecraft. It is worth mentioning that an event-triggered mechanism is introduced into the control scheme to reduce the communication pressure. Finally, the numerical simulation is performed in the presence of model parameter uncertainty and controller gain perturbations. Simulation results demonstrate the effectiveness, robustness and non-fragility of the control method.

Appointed Fixed Time Observer-Based Sliding Mode Control for a Quadrotor UAV Under External Disturbances

In this article, a study of the appointed fixed time control problem is presented for the quadrotor unmanned aerial vehicle attitude control system subject to external disturbances. Based on the appointed fixed time sliding mode variable and the adaptive technique, a novel sliding mode observer is first established to estimate the external disturbances within the appointed settling time. Subsequently, an appointed fixed time controller is proposed to track the desired attitude regardless of the initial states. To circumvent the singularity problem of the above controller, a novel improved adaptive sliding mode control law is designed by employing a nonlinear function and a modified sliding mode observer. Moreover, the chattering phenomenon is attenuated by replacing the sign function with hyperbolic tangent function. The appointed practical fixed time stability of the closed-loop attitude control system is proved and analyzed rigorously utilizing the Lyapunov theory. Finally, the effectiveness and fine performance of the proposed schemes are illustrated by numerical simulation results.

Attitude estimation and control based on modified unscented Kalman filter for gyro-less satellite with faulty sensors

A modified unscented Kalman filter is presented to estimate the quaternion parameters as well as the angular velocities of a rigid gyro-less satellite under faulty sensor conditions. The task is carried out using the Sun sensor and magnetometers as attitude sensors with bounded noise and unknown fault(s). Following the presentation of the satellite attitude dynamics and filtering formulations, a new fault detection and isolation algorithm is proposed. The latter is based on a modified unscented Kalman filter structure for improved fault detection, sensor isolation, and attitude control (AC). A Backtracking Search Algorithm (BSA) is also used to design and optimize the PID controller gains, as well as to optimize sensor installation orientation for residual signal decoupling. In this regard, the paper presents and proves a theory that describes how the proposed optimization process for sensor installation can analytically decouple the faulty orientation signal from the healthy ones. A comparison of attitude and angular velocity estimation approaches using the standard Kalman, extended Kalman, and a proposed modified unscented Kalman filter is also provided. The results show that the proposed filter performs significantly better in closed-loop AC systems and copes adequately with sensor faults.

An active force controlled of small CMG-based satellite

Purpose This paper aims to investigate the attitude control pointing improvement for a small satellite with control moment gyroscopes (CMGs) using the active force control (AFC) method. Design/methodology/approach The AFC method is developed with its governing equations and integrated into the conventional proportional-derivative (PD) controller of a closed-loop satellite attitude control system. Two numerical simulations of an identical attitude control mission namely the PD controller and the PD+AFC controller were carried out using the MATLAB®-SimulinkTM software and their attitude control performances were demonstrated accordingly. Findings Having the PD+AFC controller, the attitude maneuver can be completed within the desired slew rate, which is about 2.14 degree/s and the attitude pointing accuracies for the roll, pitch and yaw angles have improved significantly by more than 85% in comparison with the PD controller alone. Moreover, the implementation of the AFC into the conventional PD controller does not cause significant difference on the physical structure of the four single gimbal CMGs (4-SGCMGs). Practical implications To achieve a precise attitude pointing mission, the AFC method can be applied directly to the existing conventional PD attitude control system of a CMG-based satellite. In this case, the AFC is indeed the backbone for the satellite attitude performance improvement. Originality/value The present study demonstrates that the attitude pointing of a small satellite with CMGs is improved through the implementation of the AFC scheme into the PD controller.

Output constrained adaptive neural control for generic hypersonic vehicles suffering from non-affine aerodynamic characteristics and stochastic disturbances

This paper proposes a novel output constrained non-affine control structure by combining backstepping adaptive control with coordinate transformation technique for Generic Hypersonic Vehicles (GHVs) attitude tracking problem suffering from stochastic uncertainties. Firstly, by introducing several specific nonlinear functions, the output constrained control problem is transformed into a stabilization problem of several new variables. Then a novel adaptive control scheme that employee the boundary estimation technique and Nussbaum-type functions to counteract the effect of non-affine aerodynamic characteristics is integrated to address the attitude tracking problem. Meanwhile, two Neural Networks (NNs) are introduced to approximate and compensate the unknown nonlinearities. With the aid of a four-order Lyapunov function, the closed-loop attitude control system is proved to be stochastically stable. As a result, the output tracking errors can be guaranteed to stay in the predefined constraints during the whole control process and finally converge to an acceptable small value. Comparative simulation results are presented to demonstrate the effectiveness and advantages of the proposed control strategy.

Design, tuning and evaluation of a stand-alone nitinol based thermomechanical actuator driver with a closed-loop position control system

Nitinol based actuators can be used in many applications. Many of them are simple logic-type applications where intermediate positions or contractions are not required. For such applications, a simple current limiting circuit with enable function can be used. The biggest problem is when we want to use the actuator for positioning applications. In this case, by simply adjusting the current flowing through the nitinol wire is not going to solve the problem. On one hand, the range where we can adjust the current is very small. On the other hand, the hysteresis and thermal inertia are involved in the process. The last and the worst thing is the ambient temperature that will vary in a random way. As a conclusion, the author’s original research for a dedicated driver with position feedback did the job done, eliminating all the related problems. Finally, the driver was implemented, tuned for the mechanical test jig and evaluated under rough conditions in order to prove that the driver can reject the external disturbances. Furthermore, unlike a traditional on/off driver, the designed driver can prolong the lifetime of the actuator by keeping the actuator current at a safe level even in saturation conditions and, by limiting the maximum rate of change of the temperature, thermal shocks can be avoided.

Fixed-time observer based fault tolerant attitude control for reusable launch vehicle with actuator faults

This paper focuses on the fault tolerant attitude control problem for the reusable launch vehicle (RLV) with model uncertainties, external disturbances and actuator failures/faults during the reentry phase. First, the kinematics and dynamics of the RLV are presented, and the control-oriented mode subject to actuator malfunction is established. Next, a novel fixed-time observer is designed to estimate the compound disturbances, including failure information and uncertainties. Specifically, the proposed observer can guarantee the estimation errors converging to zero within a settling time, which is independent with the system initial conditions. Based on the proposed observer, a finite-time fault tolerant attitude control scheme is developed based on the nonsingular terminal sliding mode technology, which would improve the reentry attitude tracking performance and ensure the finite-time stability of the closed-loop attitude control system even in presence of the actuator faults. Finally, the effectiveness of the proposed method is demonstrated by numerical simulations.

Attitude Determination and Control System Design of Sub-Arcsecond Pointing Spacecraft

Spacecraft pointing accuracies with sub-arcsec to milli-arcsec levels are becoming a norm for the future space missions, which is mainly achieved by employing mission-specific fine guidance sensor (FGS). European Space Agency’s Herschel is the only spacecraft to date that has achieved an accuracy between 0.8 and 0.9 arcsec without employing FGS and by using only precise commercial-off-the-shelf (COTS) sensors. This paper improves upon Herschel’s pointing accuracy by at least [314, 925, 925]% for German Aerospace Center’s future mission named “Infrared Astronomy Satellite Swarm Interferometer (IRASSI).” IRASSI’s closed-loop attitude determination and control system (ADCS) is carefully developed by selecting high-precision COTS sensors and actuators, implementing two optimal attitude estimation algorithms for the sensor data fusion, three robust control algorithms for the attitude control, and a pseudoinverse distribution algorithm for spacecraft momenta allocation among the redundant reaction wheels in three different configurations. Monte Carlo simulations of IRASSI’s ADCS demonstrate that an unprecedented three-axis absolute pointing error of [0.193, 0.078, 0.078] arcsec is achieved. Furthermore, performance comparison between the rate-integrating and rate-gyroscope-based multiplicative extended Kalman filter for this mission is demonstrated. Finally, performance comparison of three attitude controllers establishes their feasibility for this mission.

Absolute Stability Condition Derivation for Position Closed-Loop System in Hydraulic Automatic Gauge Control

In the metallurgical industry, hydraulic automatic gauge control (HAGC) is a core mechanism for thickness control of plates used in the rolling process. The stability of the HAGC system’s kernel position closed-loop is key to ensuring a process with high precision, speed and reliability. However, the closed-loop position control system is typically nonlinear, and its stability is affected by several factors, making it difficult to analyze instability in the system. This paper describes in detail the functioning of the position closed-loop system. A mathematical model of each component was established using theoretical analysis. An incremental transfer model of the position closed-loop system was also derived by studying the connections between each component. In addition, based on the derived information transfer relationship, a transfer block diagram of disturbance quantity of the system was established. Furthermore, the Popov frequency criterion method was introduced to ascertain its absolute stability. The results indicate that the absolute stability conditions of the position closed-loop system are derived in two situations: when spool displacement is positive or negative. This study lays a theoretical foundation for research on the instability mechanism of an HAGC system.

Fault-Tolerant Attitude Stabilization Incorporating Closed-Loop Control Allocation Under Actuator Failure

This paper addresses the difficult problem of fault-tolerant control and closed-loop control allocation for spacecraft attitude control system with actuator failures, actuator saturation, and external disturbances. As a fundamental step, a modified fault diagnosis observer is proposed utilizing the iterative learning methodology to reconstruct the actuator failures in real time. On the basis of the previously reconstructed failure information, a fault-tolerant control scheme incorporating with a parameter adjusting law is presented to enforce the spacecraft attitude control system to reach the real sliding mode surface in finite time. Meanwhile, the singularity of control command will be avoided using the saturation function, and the chattering problem restrained by the adjusting law. Furthermore, with the concept of control allocation, a novel on-line closed-loop constrained optimal fault-tolerant control allocation scheme is employed to distribute the signals synthesized by the baseline controller over the redundant actuators with failures and constraints. The stability of the closed-loop fault-tolerant control allocation process is guaranteed by the theory of the closed-loop discrete-time feedback control system. The key achievement of the proposed systematic strategy is that the whole closed-loop attitude control system can theoretically be guaranteed to be stable. Numerical simulations are carried out to verify the effectiveness and superiority of the developed approach.

Development of a piezoelectric high speed on/off valve and its application to pneumatic closed-loop position control system

The use of smart materials-based high speed on/off valve has exhibited the potential to replace traditional servo and proportional valves in fluid power systems. In this paper, a novel pneumatic high speed on/off valve driven by a piezoelectric stack actuator is developed and its dynamics are studied. For an upstream gauge pressure of 0.5 MPa, the valve exhibited a large flow rate of up to 86 L/min. Furthermore, to study the ability of this novel high speed on/off valve to be applied in closed-loop control systems, a real-time position control system is realized using a PID controller. In order to prove its feasibility and effectiveness, a number of closed-loop trajectory tracking experiments are conducted on a pneumatic cylinder. The system is proved feasible and the results demonstrate good tracking performance.

Finite-time Extended State Observer based fault tolerant output feedback control for attitude stabilization

This work addresses the challenging problem of finite-time fault tolerant attitude stabilization control for the rigid spacecraft attitude control system without the angular velocity measurements, in the presence of external disturbances and actuator failures. Consider the severe circumstances with above failures and uncertainties, a novel continuous finite-time Extended State Observer is first established to observe the attitude angular velocity and the synthetic failure simultaneously. Unlike the existing observers, the finite-time methodology and Extended State Observer are utilized, to achieve the finite-time uniformly ultimately bounded stability of the attitude angular velocity and extended state observation errors. Furthermore, a novel continuous finite-time attitude controller is developed by using the nonsingular terminal sliding mode control and super-twisting method. The main feature of this work stems from our use of multiply advanced techniques or methodologies that enables the finite-time stability of the closed-loop attitude control system and the designed control scheme is continuous with the property of chattering restraining. Finally, numerical simulation results are presented to illustrate the effectiveness and fine performances of the finite-time observer and controller for the attitude control system.

Finite‐time disturbance observer based integral sliding mode control for attitude stabilisation under actuator failure

This work develops a novel disturbance observer and integral sliding mode technique based fault tolerant attitude control scheme for spacecraft, which is subject to external disturbance torques and actuator failures. More specifically, a simple and novel finite-time disturbance observer is first designed to reconstruct the synthetic uncertainty deriving from actuator failures and disturbances, by which the synthetic uncertainty is also compensated or restricted. Then, an integral sliding mode based finite-time fault tolerant attitude stabilisation controller incorporating with an adjusting law is investigated to ensure the closed-loop attitude control system converge to the stable region in finite time. And also the finite-time stability of the closed-loop attitude control system driven by the proposed attitude control scheme is analysed and proved utilising Lyapunov methodology. Finally, a simulation example for a rigid spacecraft model is carried out to verify the effectiveness and superiority of the proposed attitude control approach.

Continuous finite-time extended state observer based fault tolerant control for attitude stabilization

This work investigates the challenging problem of fast robust fault tolerant attitude control for spacecraft to handle external disturbances, actuator failures and misalignments. More specially, a novel nonsingular terminal sliding mode based finite-time extended state observer is first designed to estimate and compensate for the lumped system faults or uncertainties. And the proposed extended state observer is analysed and proved to be stable in the sense of fast finite-time uniformly ultimately bounded stability. Then, utilizing the techniques of super-twisting and terminal sliding mode control synthetically, a novel continuous attitude control algorithm is developed. The finite-time stability of the closed-loop attitude control system is proved by using a continuously-differentiable, homogeneous and strict Lyapunov function. And also the proposed control scheme is continuous with the property of chattering restraining. Finally, some numerical simulation results are shown to verify the effectiveness and superior performances of the spacecraft attitude stabilization control system driven by the proposed fast robust fault tolerant attitude control scheme.

Observer-Based Fault-Tolerant Attitude Control for Rigid Spacecraft

This paper addresses the problem of robust fault-tolerant control of spacecraft attitude stabilization in the presence of model uncertainties, actuator failures, and external disturbances simultaneously. Utilizing the fast nonsingular terminal sliding mode control technique, a novel finite-time extended state observer is first proposed to estimate and compensate for the specified synthetic uncertainties derived from actuator failures and/or model deviations. And also the detailed derivations of the observer are provided, along with a thorough analysis for the associated ultimately bounded stability and estimation error convergence property in the sense of finite-time control. Then, with the reconstructed information achieving from the finite-time observer, an adaptive robust sliding mode based fault-tolerant control approach is developed to ensure that the closed-loop attitude control system reach the real sliding mode surface in finite time. Meanwhile, the chattering problem has been restrained via the modified gain adjusting law. The key feature of the proposed strategies is that the whole closed-loop fault-tolerant control system can be guaranteed theoretically to be finite-time stable by the development of Lyapunov methodology. Finally, numerical simulation results are presented to illustrate and highlight the fine performance benefits obtained using the proposed schemes.

Dynamic surface active fault tolerant control design for the attitude control systems of UAV with actuator fault

In this paper, an active fault tolerant control (FTC) approach based on transient performance index is proposed for the attitude control systems of unmanned aerial vehicle (UAV) with actuator fault. The nonlinear attitude control system model for UAV with actuator faults is given, which represents the dynamic characteristics of UAV. A fault diagnosis component is used for fault detection and estimation. According to the fault estimation information obtained during the fault diagnosis, the fault tolerant control scheme is developed by adopting the adaptive dynamic surface control technique, which guarantees the asymptotic output tracking and ultimate uniform boundedness of the closed-loop attitude control systems of UAV in actuator faulty case. Further, a prescribed transient performance of the FTC attitude control systems is considered which characterizes the convergence rate and maximum overshoot of the attitude tracking error. Finally, simulation results are shown that the attitude control system states remain bounded and the output tracking errors converge to a neighborhood of zero.

Dynamic Surface Fault Tolerant Tracking Control Design for UAV with Transient Performance

In this paper, a novel fault tolerant control (FTC) approach is proposed for the attitude control systems of unmanned aerial vehicle (UAV) using dynamic surface control technique. Firstly, the nonlinear attitude dynamic models of UAV with actuator faults are given, which represent the dynamic characteristics of UAV. Then, a fault tolerant control scheme is proposed, which guarantees the asymptotic tracking and ultimate uniform boundedness of the closed-loop attitude control systems of UAV in the presence of an actuator fault. Further, a transient performance is considered in the designing of FTC, which characterizes the convergence rate and maximum overshoot of the attitude tracking error. Finally, simulation results are given to illustrate the effectiveness of the developed FTC algorithm.