Attitude Tracking Research Articles

Underactuated attitude tracking control of tethered spacecraft for deployment and spin-up

This paper investigates the underactuated attitude tracking control problem of tethered spacecraft during tether deploying and spinning. The attitudes are controlled by the torque inputs along two body axes and perturbed by the tether tension torque. The coupling effect between spacecraft attitudes and flexible tethers can be alleviated by simplifying control inputs. The main contribution is the development of an underactuated tracking controller with an adaptive barrier function that inhibits unknown disturbance. To avoid singularity problems with tether and spacecraft during simulation, the dynamic model of a tethered system is derived using quaternion transformations. The underactuated attitude control strategy is designed by kinematic state coupling relations and dynamic backstepping technique, which is given extensive stability demonstration using Lyapunov’s theory. An adaptive controller gain with barrier function is employed to inhibit the bounded unknown disturbance with no need for the online estimation signal. Finally, numerical simulations demonstrate the effectiveness and robustness of the proposed underactuated strategy in the case of tether deployment and spin-up, respectively.

Robust Dynamic Geofencing Attitude Control for Quadrotor Systems

In this article, a robust disturbance rejection controller is designed for quadrotor attitude tracking within dynamic safety operational envelopes. A scalable constraint technique based on the unified barrier function is developed to transform the attitude restricted within the dynamic safety envelope into a new unconstrained state variables. The closed-form state stabilization control input based on the operational safety rules derived from backstepping method with dynamic surface control can simultaneously guarantee the safety and asymptotic stability of underlying system. A sliding mode disturbance observer is used to estimate and compensate for unknown time-varying perturbations with minor chattering and rapid convergence. Finally, numerical simulations and platform experiments are conducted to verify the effectiveness of the proposed dynamic geofencing attitude control.

Cascade-modified uncertainty and disturbance estimator–based control of quadrotors for accurate attitude tracking under exogenous disturbance

This paper presents a cascade-modified uncertainty and disturbance estimator (CMUDE)–based controller. The attitude-tracking performance of a quadrotor would be greatly degraded due to two factors: (1) a nonideal actuator and (2) an exogenous disturbance. Based on these factors, an actuator model is accurately identified using a thrust test platform. Then, a cascade-structured CMUDE controller is designed through the backstepping method, so the disturbances from different channels can be separately dealt with. The idea of the uncertainty and disturbance estimator (UDE) is then applied to dynamically compensate for not only the exogenous disturbance but also the time delay in the actuator dynamics. Benefitting from that, the problem of mismatched disturbances is solved by defining virtual control inputs; furthermore, the nonlinear term in the attitude kinematics is included in the model uncertainty to be canceled instead of being ignored. When tracking attitude commands, the exogenous disturbance and model uncertainty along with the time delay of the actuator are estimated and compensated for by the proposed controller, so the performance of the disturbance rejection is significantly improved while maintaining a quick response to the rapidly changing commands. To verify that, the proposed controller is implemented on a quadrotor platform to carry out exhaustive experiments and compared with the mainstream cascade PID (CPID) controller, the classic UDE-based controller, and the latest modified-UDE (MUDE)–based controller. The results show that our control strategy achieves a better disturbance rejection and more accurate tracking performance than other controllers.

Inducing Performance of Commercial Surgical Robots in Space.

Pre-existing surgical robotic systems are sold with electronics (sensors and controllers) that can prove difficult to retroactively improve when newly developed methods are proposed. Improvements must be somehow "imposed" upon the original robotic systems. What options are available for imposing performance from pre-existing, common systems and how do the options compare? Optimization often assumes idealized systems leading to open-loop results (lacking feedback from sensors), and this manuscript investigates utility of prefiltering, such other modern methods applied to non-idealized systems, including fusion of noisy sensors and so-called "fictional forces" associated with measurement of displacements in rotating reference frames. A dozen modern approaches are compared as the main contribution of this work. Four methods are idealized cases establishing a valid theoretical comparative benchmark. Subsequently, eight modern methods are compared against the theoretical benchmark and against the pre-existing robotic systems. The two best performing methods included one modern application of a classical approach (velocity control) and one modern approach derived using Pontryagin's methods of systems theory, including Hamiltonian minimization, adjoint equations, and terminal transversality of the endpoint Lagrangian. The key novelty presented is the best performing method called prefiltered open-loop optimal + transport decoupling, achieving 1-3 percent attitude tracking performance of the robotic instrument with a two percent reduced computational burden and without increased costs (effort).

Anti‐unwinding adaptive attitude tracking control for spacecraft with quantized torques

SummaryThe adaptive attitude tracking control with limited communication to actuators is addressed in this paper. To avoid unwinding, a rotation matrix rather than a quaternion is used to describe the attitude, for which the stability is proved by Morse‐Lyapunov function. To meet the need of restricted communication, two different quantizers, logarithmic quantizer and hysteres quantizer, are used to quantize the control torque signal. Two robust adaptive control techniques, indirect and direct, are proposed to deal with the impacts of quantization error and external disturbances. The proposed control schemes, in conjunction with quantizers, guarantee the global boundedness of all signals in the closed‐loop system, allowing the attitude tracking error to converge toward an ultimately bounded region. Finally, numerical simulations are conducted to illustrate the performance of the proposed controllers.

Attitude and vibration control of a solar sail

The solar sail, a new type of spacecraft that uses only the Solar Radiation Pressure (SRP) for its propulsion, has great application prospect in the pole-sitter mission and deep space exploration. However, because of the large surface-to-mass ratio and the coupling effect of attitude and structure vibration, the study of dynamics and control of solar sail is challenging. This paper investigates the attitude control of a class of solar sails through control boom, and proposes a new vibration control strategy of the solar sail using self-contained cable actuators on the sail surface. Firstly, a rigid-flexible coupling dynamic model of the solar sail system is established by using the velocity variational principle considering the membrane tensioning stress. Then, an attitude tracking controller is designed utilizing the backstepping method, and by using the tensioning cables as actuators controller is designed to suppress the vibration of the sail surface. Finally, numerical simulations are conducted to verify the effectiveness of the methods presented in this paper. Research results show that the dynamic model developed in this paper can describe the dynamic behavior of the solar sail system precisely, and the designed controllers can have the solar sail following the desired attitude trajectory accurately and suppress the vibration of the sail surface significantly.

On adaptive attitude tracking control of spacecraft: A reinforcement learning based gain tuning way with guaranteed performance

This paper investigates the attitude tracking control problem of a rigid spacecraft subject to inertial uncertainties, uncertain space perturbations and actuator saturation. Firstly, a static inertial-matrix free attitude controller is designed to guarantee the appointed-time convergence and tracking accuracy indicators of the spacecraft. Then, two-layer critic-action NNs are used to tune and optimize the control gains adaptively to improve the robustness and tracking performance of the devised static attitude controller via exploring the reinforcement learning (RL) technique. Compared with the existing attitude control methods, the prominent advantage of our work is that the devised controller is inertial-matrix free with a simple RL-based adaptive parameter tuning scheme, which reduces the conservativeness of the traditional attitude controllers with fixed control gains and is also easy to be achieved. Finally, two groups of illustrative examples are organized to validate the effectiveness of the proposed attitude control method.

Practical predefined-time barrier function-based adaptive sliding mode control for reusable launch vehicle

This paper proposes a novel barrier function-based adaptive sliding mode control scheme with practical predefined-time convergence for reusable launch vehicles subject to parametric uncertainties and external disturbances. Distinguished from existing similar works, the proposed control scheme ensures that the attitude tracking errors converge to a pre-assigned region in a prescribed time without any prior information on the lumped disturbance, and the control gain is not overestimated. Firstly, a novel performance function with quantitatively predefined convergence time and steady-state error is designed to constrain the attitude tracking errors, and the equivalent unconstrained transformation is carried out for the constrained model. Subsequently, a novel adaptive sliding mode controller is devised for the transformed system by synthesizing the integral sliding mode paradigm and the barrier function-based adaptive gain technique. The stability of the controller is analyzed by the Lyapunov method. Finally, comparative numerical simulation results are presented to demonstrate the effectiveness and improved performances of the proposed control scheme.

Spacecraft attitude estimation under attitude tracking maneuver during close-proximity operations

This paper presents a real-time relative three-axis attitude estimation using a camera and two gyros under momentum changes during close-proximity operations. The camera sensor provides quaternion measurements that relate the body frame of the deputy spacecraft with respect to the body frame of the chief spacecraft. The quaternion measurements are coupled with gyro measurements and attitude dynamics model in a multiplicative extended Kalman filter to determine relative attitude and gyro biases under momentum changes. The relative quaternion kinematics is augmented with spacecraft relative motion dynamics to represent the filter process dynamics. The quaternion measurements from a camera sensor and inertial measurement units (IMU) are utilized to the filter measurement model. The fault-tolerant attitude controller actuated by four reaction wheels, which has no unwinding problem is used for attitude tracking maneuvers during close-proximity operations in the presence of external disturbances, uncertain inertia parameter and actuator faults. This controller is combined with the extended Kalman filter to filter noisy measurements and to estimate gyro biases, which leads to a full-state feedback control system. Numerical simulations are performed to verify the effectiveness of the attitude estimation and control systems of the spacecraft with four reaction wheels during close-proximity operations of spacecraft in low-Earth orbit.

Neural adaptive with impedance learning control for uncertain cooperative multiple robot manipulators

In this paper, an adaptive radial basis function neural network (RBFNN) control scheme is studied for the desired tracking of multiple robot manipulators with carrying a common object in joint-space. First, a non-zero time-varying parameter is introduced into the RBFNN, as well as a novel universal approximation of RBFNN with this non-zero parameter is introduced. Second, a switching control scheme based on this approximation property is designed. When the states of uncertainties terms leave the universal approximation domains, the suggested adaptive laws established by a sliding surface would pull them back, then the uncertain nonlinear functions are approximated by the RBFNNs in the domains. With this new structure of control technique, the limitation of a finite universal approximation can be broken. Third, the cooperative multiple manipulators can track the desired trajectory determined through impedance learning, which is used to modulate the control input in order to optimize the environment robot interaction. Finally, simulation results are shown to demonstrate the effectiveness in terms of expected tracking performance and position tracking errors constraints.

Attitude tracking control design of fixed-wing UAVs having uncertain dynamics and corrupted gyro sensor outputs

Flight performance of unmanned aerial vehicles (UAVs) strongly depends on implemented attitude tracking control. For designing better controllers, nonlinear control design techniques are often opted instead of control design based on linearized models. Uncertainty in nonlinear dynamics estimation may arise due to inaccuracies in aerodynamic derivatives and simplifications/assumptions made during the derivation of nonlinear models. This paper considers attitude tracking control of fixed-wing UAVs having uncertain dynamics and corrupted gyro sensor outputs. An integral chain differentiator (ICD) is used to provide the analytical redundancy to the gyros used to measure the angular rates. Two control design schemes are proposed, a neuro-fuzzy adaptive sliding mode control (NFASMC) and an ICD approximation-based fuzzy adaptive sliding mode control (ICD-FASMC). In NFASMC, the uncertain part of the dynamics is estimated using an adaptive radial basis function neural network. Gyro sensor output errors are estimated in real-time, using ICD based error estimation scheme and used in the control law along with the sensor’s corrupted outputs. In ICD-FASMC, the uncertain dynamics and angular rates of UAV are estimated using the ICD such that the requirement of the gyro sensor outputs for control design is bypassed. The switching gain of the designed controllers is made adaptive using fuzzy logic to mitigate the chattering effect. The stability of the proposed controllers is proved using the Lyapunov approach. The proposed schemes are implemented using a nonlinear simulation of a fixed-wing UAV. Simulation results are presented to show the effectiveness of the proposed techniques.

Nonsingular fixed‐time fault‐tolerant attitude control for tailless flying wing aircraft with time‐varying flight envelope constraints

AbstractThis article investigates the fault‐tolerant attitude control problem for the tailless flying wing aircraft subject to time‐varying flight envelope constraints in the presence of the matched/mismatched disturbance, uncertain parameters, and time‐varying actuator failures. To handle these problems and improve the convergence rate of the attitude control system, a nonsingular fixed‐time convergent robust fault‐tolerant control methodology is proposed. First, the time‐varying barrier Lyapunov functions is introduced to confine the flight envelope within the predefined time‐varying compact set while ensuring the transient performance of the attitude tracking error. Subsequently, the fixed‐time sliding mode observer is designed to compensate for the matched/mismatched disturbance, uncertainties, and time‐varying actuator failures, meanwhile, by introducing an intermediate control law in the attitude controller, the singularity problem is avoided without utilizing any filters or continuous and differentiable piecewise functions. Further, it has been analytically proved that all signals of the closed‐loop system are bounded and converge to the residual set around the origin in a fixed time. Finally, simulations are conducted to illustrate the superiorities of the proposed scheme.

Attitude Tracking Control of Uncertain Flexible Spacecraft Systems Subject to External Disturbances*

In this paper, we consider the attitude tracking and disturbance rejection problem of uncertain flexible spacecrafts. Compared with existing works, we consider two types of uncertainties of flexible spacecrafts, that is, the uncertain parameters of the inertial matrix, and the unknown external disturbance with unbounded energy. Inspired by the internal model principle, we design a class of dynamic compensators and some auxiliary dynamic systems to compensate the external disturbance. Then, by introducing a series of coordinate transformations, we convert the attitude tracking and disturbance rejection problem into an adaptive regulation problem of an augmented system. Finally, we design the adaptive control law and show that attitude tracking of uncertain flexible spacecrafts can be achieved in the presence of unknown disturbances. The effectiveness and robustness of the controller are illustrated by some numerical simulations.

Estimation and Correction of Azimuth and Attitude Errors of Attitude Tracking for Vehicular Spacecraft

Shortening the ground preparation time of vehicular spacecraft is an important topic in the aerospace field. The time is hard to be significantly shortened using the traditional methods, because initial alignment and spacecraft erection must be fulfilled in order. To solve the problem, an estimation and correction method for azimuth and attitude errors of attitude tracking is proposed in this article. We propose a real-time error estimation model to reveal the effect of the initial azimuth, attitude errors and the gyro biases of the spacecraft inertial measurement unit (SIMU) on the current azimuth and attitude errors during attitude tracking, making it possible to post-compensate the initial coarse azimuth error and the gyro biases of the SIMU at the end of attitude tracking. This model is the key and the theoretical basis of our proposed method. Detailed estimation and correction steps are designed, to achieve the purpose of fulfilling the spacecraft erection and the fine-alignment of the vehicular inertial measurement unit in parallel. The results of the simulations and experiments show that the preparation time is remarkably shortened using the proposed method, without decreasing the final azimuth and attitude accuracy of the SIMU. This proposed method detaches the inherent viewpoint that fine-alignment must be completed before attitude tracking and spacecraft erection in the traditional horizontal collimation scheme. It provides a completely new way to shorten the ground preparation time of vehicular spacecraft.

Saturated Attitude Control of Multi-Spacecraft Systems on SO(3) Subject to Mixed Attitude Constraints With Arbitrary Initial Attitude

In this paper, for multi-spacecraft systems (MSSs) with a directed complete communication topology and a time-varying virtual leader, an adaptive saturated attitude controller is proposed to achieve attitude consensus and attitude tracking under arbitrary initial attitude, mixed attitude constraints, input saturation and external disturbances. Firstly, considering the time-varying desired attitude provided by the virtual leader in a directed complete topology, an MSS attitude error function and an MSS attitude error dynamics based on SO(3) are developed. Next, an effective mixed potential function for the MSS on SO(3) is proposed for the static attitude-forbidden zones, the relative dynamic attitude-forbidden zones and the attitude-mandatory zones. In particular, different from the existing potential functions, the proposed mixed potential function is suitable for arbitrary initial attitude of the spacecraft in MSS, relaxing the restriction on the initial attitude associated with each static and dynamic attitude constraint zones. Then, an adaptive saturated attitude controller is designed to realize attitude consensus and tracking for the MSSs on SO(3) under arbitrary initial attitude, mixed attitude constraints, saturation constraints and external disturbances. Finally, simulation results of an MSS with a time-varying virtual leader are demonstrated to illustrate the efficiency of the proposed attitude controller.

Singularity-Avoidance Prescribed Performance Control for Spacecraft Attitude Tracking

The attitude tracking control problem with preassigned performance requirements has earned tremendous interest in recent years, and the Prescribed Performance Control (PPC) scheme is often adopted to tackle this problem. Nevertheless, traditional PPC schemes may suffer singularity problems when the expected state constraint is violated. This may cause a decrease in the control effect or even the unstable of the system. Motivated by this issue, this paper proposes a Singularity-Avoidance Prescribed Performance Control scheme (SAPPC) to deal with these problems, of which the core is a shear mapping-based error transformation procedure that globally transforms the original error state without singularity. Based on the presented non-singular error transformation, this paper presents a perspective to guarantee the satisfaction of given transient performance requirements by leading the state trajectory converging along a preassigned smooth trajectory called Reference Performance Function (RPF). Based on the concept of the RPF, this paper naturally adopts an error-defined-type state constraint, providing a time-varying constraint boundary and alleviating the potential over-control problem at the steady state. Further, in order to validate the proposed SAPPC scheme, a simple backstepping controller is developed by employing the predefined-time stability technique and the dynamic surface control technique. Finally, theoretical analysis and numerical simulation results are presented to validate the proposed control scheme's effectiveness and robustness.

Control of Quadrotor Based on RBF Neural Network Adaptive Fast Terminal Sliding-Mode Strategy

I The purpose of this paper is to propose a fast adaptive terminal sliding mode control method for quadrotor unmanned aerial vehicles (UAVs) under dynamic uncertainties and external interference. Firstly, a complete mathematical dynamics model of a quadrotor UAV is presented. Secondly, a robust dual-loop nonlinear control law for the quadrotor velocity and attitude tracking is designed. Through the introduction of equivalent control inputs, the attitude control channels can be decoupled and attitude stabilized controllers can be designed separately. For velocity tracking and altitude tracking control, coupled controllers are designed to ensure velocity tracking based on the stability of altitude tracking control. The attitude loop adopts RBF neural network sliding mode control, to compensate for model disturbance uncertainty, adjust its gain in real time, and suppress chattering problems. Finally, the experimental results show that the designed controller can not only suppress external interference, but also achieve accurate tracking of the desired flight command.

An Adaptive Control Methodology for Spacecraft Attitude Tracking Under Model and Environmental Uncertainties

This study investigates the attitude tracking problem for rigid spacecraft under model and environmental uncertainties. Two different control laws are separately developed and combined. First, based on a nominal attitude dynamic model assuming no uncertainty, the first controller is developed that exactly tracks a prespecified attitude reference trajectory with minimized control cost. The designer can generate this reference to prescribe desired performance specifications such as the maximum convergence time and overshoot. Next, an uncertain attitude dynamic system is considered, and the second controller is designed and added so that the controlled system can successfully track the predesigned reference trajectory with a user-specified tolerance even subject to uncertainty whose bounds are unknown. Compared to existing adaptive control schemes, the proposed approach possesses a very simple structure with a small number of control parameters and is not computationally intensive, making it more attractive for practical implementation. The proposed control laws generate smooth control signals and any information about the uncertainty bound is not needed in its design. Simulation results are provided to demonstrate the practical feasibility of the proposed approach, where reorientation/slew maneuvers of a large spacecraft are considered. The effects of limitations on the control torques are also investigated to show the effectiveness of the control methodology developed herein.

Dynamics and FNTSM Control of Spacecraft with a Film Capture Pocket System

To solve the problem of space debris, a film capture pocket system is designed in this paper. The film capture pocket is more flexible and reliable, compared with the space rope net. The film capture pocket system contains many flexible structures that are prone to large deformation and vibration during movement. The deformation causes large disturbances to the service spacecraft. It is necessary to establish an accurate rigid-flexible coupling dynamic model for quantitative analysis of disturbances. First, a film dynamic model is developed using high-order absolute nodal coordinate formulation. Second, an attitude tracking control law is designed by using the fast nonsingular terminal sliding mode controller and fixed time dilation observer (FxESO). Finally, combining dynamics and control principles, a virtual prototype of spacecraft with film capture pocket system is established. The simulation results show that higher-order absolute nodal coordinate formulation elements have better convergence, compared to ABAQUS finite element analysis. Meanwhile, the dynamic model simulates the deformation and vibration states of large flexible structures, during the spacecraft maneuver. The FxESO can estimate and compensate the complex disturbance. The error under fast nonsingular terminal sliding mode + FxESO control law converge more rapidly than the nonsingular terminal sliding mode + expansion observer control law. The final spacecraft attitude tracking error is about 10 −4 , indicating the effectiveness of the controller.

Research on transfer case clutch accurate position control of on-demand four-wheel drive systems

<p indent="0mm">The on-demand four-wheel-drive system has been widely used because of its simple structure and low cost. The core component of the on-demand four-wheel-drive system in this study is a transfer case based on an electronically controlled multi-plate wet clutch. Its actuator consists of a worm gear driven by a permanent magnet synchronous motor and a helical booster mechanism. The actuator can control the position of the clutch pressure plate to change the drive torque transmitted to the front axle, and adjusting the front axle torque significantly affects the handling stability and dynamics. Therefore, the precise position control of the transfer clutch is of great significance. In this paper, a model of the PMSM actuator system and load is first established, which provides the basis for the design of the controller. Then, explicit model predictive controllers for current tracking control and position tracking control are designed based on the model. Finally, typical working condition position tracking simulations and experiments are carried out. The results show that the proposed position control algorithm can achieve relative accuracy of 1%, which can meet the requirements of the real-time online high-precision position control of an on-demand four-wheel-drive system.