Angular Velocity Constraints Research Articles

A Flexible Topology Control Strategy for Mega-Constellations via Inter-Satellite Links Based on Dynamic Link Optimization

In large-scale satellite constellations, the efficiency of inter-satellite communication is paramount. Traditional topology control strategies, such as the Manhattan configuration, provide stable links but can result in indirect communication paths, affecting the efficiency of information transfer. This paper addresses this issue by proposing an innovative “3 + 1” dynamic topology control scheme. The scheme retains three static links determined by the relative angular velocity and acceleration while introducing a dynamic link based on distance and angular velocity constraints to optimize the link duration and overall network communication efficiency. To address the complexity of matching dynamic links, this paper introduces an elite strategy-based maximum weighted matching algorithm for general graphs. Compared to traditional greedy algorithms, our proposed algorithm significantly improves the link duration and topological stability. Through simulation experiments comparing communication delays between Xiamen and Los Angeles, our results show that the proposed dynamic link scheme substantially reduces the average delay, enhancing the efficiency and flexibility of inter-satellite communication. This research not only extends the duration of inter-satellite links but also provides new perspectives and methodologies for further studies on inter-satellite topology control strategies.

Finite-Time Attitude Maneuver Control for Liquid-Filled Spacecraft with Attitude and Angular Velocity Constraints Based on Barrier Lyapunov Function

Finite-Time Attitude Maneuver Control for Liquid-Filled Spacecraft with Attitude and Angular Velocity Constraints Based on Barrier Lyapunov Function

A Fast Self-Calibration Method for Dual-Axis Rotational Inertial Navigation Systems Based on Invariant Errors.

In order to ensure that dual-axis rotational inertial navigation systems (RINSs) maintain a high level of accuracy over the long term, there is a demand for periodic calibration during their service life. Traditional calibration methods for inertial measurement units (IMUs) involve removing the IMU from the equipment, which is a laborious and time-consuming process. Reinstalling the IMU after calibration may introduce new installation errors. This paper focuses on dual-axis rotational inertial navigation systems and presents a system-level self-calibration method based on invariant errors, enabling high-precision automated calibration without the need for equipment disassembly. First, navigation parameter errors in the inertial frame are expressed as invariant errors. This allows the corresponding error models to estimate initial attitude even more rapidly and accurately in cases of extreme misalignment, eliminating the need for coarse alignment. Next, by utilizing the output of a gimbal mechanism, angular velocity constraint equations are established, and the backtracking navigation is introduced to reuse sensor data, thereby reducing the calibration time. Finally, a rotation scheme for the IMU is designed to ensure that all errors are observable. The observability of the system is analyzed based on a piecewise constant system method and singular value decomposition (SVD) observability analysis. The simulation and experimental results demonstrate that this method can effectively estimate IMU errors and installation errors related to the rotation axis within 12 min, and the estimated error is less than 4%. After using this method to compensate for the calibration error, the velocity and position accuracies of a RINS are significantly improved.

Optimal Fully Actuated System Approach-Based Trajectory Tracking Control for Robot Manipulators.

In this article, a trajectory tracking control strategy is proposed for robot manipulators via a fully actuated system (FAS) approach, which has shown its simplicity and flexibility for most of the nonlinear controller design. However, the motion control for robot manipulators is more complicated since unknown dynamical model, external disturbances, friction forces, and various physical constraints are required to be considered. Therefore, the FAS approach cannot be straightforwardly applied. To address these challenges, the dynamic model of robot manipulators is established via model identification methods. Furthermore, based on the identified model, an FAS composite control strategy with simple structure is designed, which is achieved by integrating a high-order disturbance observer (HODO) in the inner loop, with an FAS trajectory tracking controller in the outer loop. Specifically, the HODO is utilized for handling the uncertain dynamics and external disturbances. Moreover, the controller gains are optimized using a gradient-based optimal parameter tuning method (OPTM). By imposing joint angle constraints, joint angular velocity constraints, and input torque limits into the formulation, the OPTM also ensures the satisfaction of these physical constraints. Numerical simulations and experiments are provided to validate the performance of the proposed controller.

Adaptive global prescribed performance control for rigid spacecraft subject to angular velocity constraints and input saturation

Adaptive global prescribed performance control for rigid spacecraft subject to angular velocity constraints and input saturation

Flatness-Based Quadcopter Trajectory Planning and Tracking With Continuous-Time Safety Guarantees

This work proposes a convex optimization-based framework for the trajectory planning and tracking of quadcopters that ensures continuous-time safety guarantees. Using the convexity property of B-spline curves and the differential flatness property of quadcopters, a second-order cone program is formulated to generate an optimal nominal trajectory that respects state and input constraints, including position, linear velocity, angle, angular velocity, thrust, waypoints, and obstacle avoidance constraints, rigorously in the continuous-time sense. To ensure safe trajectory tracking, a convex quadratic program is proposed based on control barrier functions, which guarantees that the actual trajectory of the quadcopter remains within a prescribed safe tube of the nominal trajectory in continuous time. Furthermore, conditions that ensure the safe tracking controller respects thrust, roll, and pitch constraints are also presented. Both the planning and control approaches are suitable for online implementation, and the effectiveness of the proposed framework is demonstrated through simulations and experiments with a Crazyflie2.1 nano quadcopter.

Experimental Validation of Constrained Spacecraft Attitude Planning via Invariant Sets

This paper experimentally validates the invariant-set motion planner (ISMP) for the spacecraft attitude motion planning problem. Three novel results are presented that enable the experimental implementation: i) a method for gridding quaternions from the keep-in cone, ii) a method for scaling the invariant sets to enforce angular velocity constraints, and iii) a method for scaling the sets used by the ISMP to ensure their positive invariance despite this torque constraint. The ISMP is experimentally validated through three experimental scenarios. In the first scenario, the spacecraft must perform a re-orientation maneuver that caused it to move toward a keep-out cone. The ISMP manages the momentum of the spacecraft to prevent it from overshooting into the keep-out cone. In the second scenario, the spacecraft performs a slalom maneuver to avoid a pair of keep-out cones. The ISMP must reverse the momentum of the spacecraft to transition from avoiding the first keep-out cone to the second. The final scenario is an unrealistically difficult scenario designed to stress-test the capabilities of the ISMP where the spacecraft must escape from a maze of keep-out cones. These results demonstrate the ability of the ISMP to control the spacecraft attitude while enforcing state and input constraints.

Rudder/fin joint anti-rolling control system based on interference model predictive control and sliding mode observer

To overcome the difficulties of time-varying disturbance, model mismatch, and frequent operation in the rudder/fin joint control system, an interference model predictive control (I-MPC) rudder/fin joint control system with sliding mode observer is proposed. Considering that the model mismatch problem occurs when the ship is sailing, the model mismatch and external disturbance are regarded as the total disturbance. A discrete 3-degree-of-freedom ship disturbance mathematical model is established. The rudder angle and fin angle are selected as the system inputs, then a sliding mode observer is designed to observe the time-varying disturbance and system output in real time. Different from traditional MPC and feedforward compensation, I-MPC will predict the output based on the disturbance observation value, and the control law is solved under rudder/fin angle and angular velocity constraints. Simulation results show that the proposed method improves the tracking performance and anti-disturbance performance of the rudder/fin system. The observer has high observation accuracy for constant, sinusoidal, and time-varying disturbances. Mechanism wear and energy loss caused by frequent operation are avoided.

Finite element dynamic modeling and attitude control for a slender flexible spacecraft

This paper aims to study the dynamic modeling and attitude control of a kind of slender flexible spacecraft. The basic structure of this kind of spacecraft is different from the traditional structure of a center rigid body with flexible appendages, but rigid bodies at both ends, which are connected by a flexible truss structure. Firstly, the finite element modeling method is adopted to establish the dynamic model of this kind of spacecraft, and the vibration frequency and damping of the flexible structure are obtained. The unconstrained modes of the flexible spacecraft are obtained through mathematical analysis, finite element analysis and frequency domain analysis. In addition, a nonlinear sliding surface with angular velocity constraint is designed. On this basis, an adaptive sliding mode (ASM) controller is proposed, stability of the close-loop system under the controller is proved, and the dynamic model is verified through mathematical simulation.

Multi-UAV Formation Control in Complex Conditions Based on Improved Consistency Algorithm

Formation control is a prerequisite for the formation to complete specified tasks safely and efficiently. Considering non-symmetrical communication interference and network congestion, this article aims to design a control protocol by studying the formation model with communication delay and switching topology. Based on the requirements during the flight and the features of the motion model, the three-degrees-of-freedom kinematics equation of the UAV is given by using the autopilot model of longitudinal and lateral decoupling. Acceleration, velocity, and angular velocity constraints in all directions are defined according to the requirements of flight performance and maneuverability. The control protocol is adjusted according to the constraints. The results show that the improved control protocol can quickly converge the UAV formation state to the specified value and maintain the specified formation with communication delay and switching topology.

Koopman-Operator-Based Safe Learning Control for Spacecraft Attitude Reorientation With Angular Velocity Constraints

This paper presents the design of a safe learning attitude controller, based on the Koopman operator (KO), for rest-to-rest spacecraft attitude reorientation under angular velocity constraints. Specifically, a higher-dimensional linear error attitude model is established based on the KO theory and then discretized. An explicit safe learning control strategy with safety-stabilization guarantee is then developed based on the transformed KO model. By performing a loop transformation and convexifying the safety-stabilization conditions, the safe learning controller design is further transformed into a constrained optimization problem, which is independent of the attitude states and thus can be solved offline. Finally, the trained higher-dimensional safe learning controller is mapped to the three-dimensional attitude controller of the original nonlinear system via the least-squares method for online implementation. In addition, the inner-approximation of the region of attraction (ROA) is provided. Comparison simulations are carried out to validate the effectiveness of the presented strategy.

Anti-Disturbance Tracking Control for a Class of PMSM Driven-Based Flexible Manipulator Systems With Input Saturation and Angular Velocity Constraint

Anti-Disturbance Tracking Control for a Class of PMSM Driven-Based Flexible Manipulator Systems With Input Saturation and Angular Velocity Constraint

DOPH∞-based path-following control for underactuated marine vehicles with multiple disturbances and constraints

This paper presents a new robust path-following (PF) control method for underactuated marine vehicles with multiple disturbances and constraints. To improve the control performance and reduce the conservativeness of many PF control strategies described in the previous literature, which treated the multiple disturbances of the underactuated marine vehicle as a single equivalent disturbance, the multiple disturbances are categorized into two types according to their characteristics in this paper, i.e., the slowly varying disturbance and the H2-norm bounded disturbance. Then, a composite controller combining Disturbance-Observer-based control with H∞ control, which can be abbreviated as DOPH∞-based controller, is constructed for the control model. A disturbance observer is designed for estimating and eliminating the slowly varying disturbance, and the H∞ theory is used to attenuate the H2-norm bounded disturbance. Moreover, to improve the practicability of the control method in engineering applications, the virtual yaw angular velocity constraint and the actuator constraints are considered, and the auxiliary dynamic compensators are used to compensate for them. Finally, the closed-loop stability of the whole system is guaranteed. Simulations and comparative analyses are presented to demonstrate the effectiveness and robustness of the presented strategy.

Prescribed Performance Attitude Stabilization of a Rigid Body Under Physical Limitations

This article investigates the prescribed performance control problem associated with attitude stabilization of a rigid body, considering angular velocity constraint, actuator faults, and input saturation. The desired performance specifications in transient and steady-state phases including convergence speed, overshoot, and steady-state value for attitude variable are also provided. To this end, the prescribed performance control methodology is combined with backstepping-based barrier Lyapunov function so as to develop a controller with simple structure compared to the existing constrained controls. The main idea behind the control design is to remove partial differential and complex function terms to considerably decrease complexity of the proposed controller. Moreover, a hyperbolic tangent function and an auxiliary system are employed to develop the constrained virtual rotation velocity control and to consider input saturation. The simulation results carried out on a rigid spacecraft confirm efficiency and success of the proposed constrained attitude control method.

Finite-Time Distributed Attitude Synchronization for Multiple Spacecraft With Angular Velocity and Input Constraints

The attitude synchronization problem for multiple spacecraft with angular velocity and input constraints is investigated in this article, under the mild assumptions that the leader’s states can reach each follower through a path and the communications between followers are bidirectional. An adaptive finite-time distributed observer is designed to estimate the leader’s states for each follower spacecraft, which has the superiority in the fully distributed that the communication topology or some other global information is not required, and the finite-time convergence can be guaranteed. Furthermore, the novel auxiliary systems are first proposed to avoid the angular velocity and input constraints being violated, while the finite-time command filtered backstepping controller is designed to track the leader’s attitude motion. The remarkable features of the developed algorithm are the global finite-time attitude consensus of multiple spacecraft, with the constraints satisfied. Moreover, the efficiency of the proposed method is illustrated by numerical simulations and real-time platform verification.

A time optimal trajectory planning method for offshore cranes with ship roll motions

With the fast development of the economy, marine activities are increasing. Due to the advantages of offshore cranes, they are widely used in marine production as effective transportation tools. As a matter of fact, the offshore crane works on the ship known as a typical noninnertial system, which is affected by the ship movement. To tackle this problem, we propose a time optimal trajectory planning method for the considered offshore crane. Specifically, to tackle the couplings between state variables, we show that the offshore crane system is differentially flat with the payload coordinates as the flat outputs. Based on this fact, the planning problems for the jib motion and the rope length are further converted into the planning problems for flat outputs. Then, in order to ensure the trackability of the planned trajectory and improve the safety, we consider a series of physical constraints including the jib luffing motion velocity and acceleration constraints, the rope length varying velocity and acceleration constraints, and the payload swing angle and angular velocity constraints, and then a time optimization problem is further formulated. By utilizing a bisection-based method, the optimal payload transportation time is obtained as well as the corresponding time optimal trajectories. As far as we know, it is the first time optimal trajectory planning method designed for offshore cranes to achieve the fast and accurate payload transportation as well as the payload swing elimination in earth-fixed frame. At last, the effectiveness of the proposed method is verified by simulation tests.

Attitude control of on-orbit capture spacecraft with angular velocity constraint

Aiming at the attitude control problem of spacecraft in the capturing non-cooperative target process, a dual tracking robust adaptive attitude controller is designed. Firstly, a bounded virtual angular velocity is designed for the kinematics equations to guarantee that the attitude converges to zero quickly. Secondly, a new attitude controller is constructed based on the barrier Lyapunov function to ensure that the tracking error between virtual angular velocity and real angular velocity is bounded. The physical constraint of the angular velocity is satisfied. Applying Lyapunov's stability theory, the global asymptotic stability of the closed-loop system is analyzed. To overcome the nonlinear parameter perturbation with unknown upper bound in the process of capturing non-cooperative target, an adaptive updating law based on linear regression operator is constructed to estimate the rotational inertia on-line. Finally, the process of capturing the trajectory tracking of non-cooperative targets through numerical simulation. The simulation results demonstrate that the algorithm designed is effective and robust under the constraint of the bounded angular velocity or internal parameter perturbation with unknown upper bound.

Control Algorithm for Trajectory Tracking of an Underactuated USV under Multiple Constraints

A trajectory tracking control method based on the cascade of optimal guidance and adaptive control laws was proposed for trajectory tracking of an unmanned surface vehicle under multiple motion constraints including an ocean current disturbance environment. Considering the velocity and acceleration constraints, angular velocity, and angular acceleration constraints in guidance law design, motion planning was conducted with three degrees of freedom using a motion model and predictive control, while optimal guidance law was designed through a rolling optimization strategy to stabilize the position error under multiple constraints. Moreover, the stability of the guidance law was proven. In control law design, an adaptive observer was introduced to estimate and compensate for ocean current disturbance, which affected the precision of control. The course and velocity control laws were designed with the adaptive sliding mode control technology to stabilize the course angle and longitudinal velocity errors; the stability of these control laws was further proven. Based on the system design, the stability of the entire closed-loop control system was proven with the cascade system and Lyapunov theory. Theoretical analysis and simulation experiments demonstrated the effectiveness and advancement of the proposed algorithm.

Fault-Tolerant Reduced-Attitude Control for Spacecraft Constrained Boresight Reorientation

This paper is devoted to investigating the fault-tolerant reduced-attitude control problem for boresight reorientation of an uncertain spacecraft subject to pointing and angular velocity constraints. First, the stereographic projection is used to transform this problem to an obstacle avoidance problem on a two-dimensional Euclidean sphere world with circular obstacles. Then, an adaptive fault-tolerant control strategy is proposed to solve the transformed problem, by designing two potential functions for constraint handling in conjunction with a sliding vector containing hyperbolic tangent functions. Stability analysis shows that the derived controller can achieve asymptotic convergence of the gradient of the obstacle avoidance potential and angular velocities, while ensuring the satisfaction of both pointing and angular velocity constraints, despite the presence of unknown time-varying inertia parameters, disturbances, and actuator faults. In particular, benefiting from incorporating the spacecraft principal moments of inertia into the potential field design, the risk of the system losing strong controllability under multiplicative actuator faults is greatly reduced. To accommodate actuator faults under input saturation, the adaptive fault-tolerant controller is further extended to a saturated counterpart, which is capable of making full use of the remaining actuation power to react to actuator faults. Finally, simulation results are presented to demonstrate our theoretical findings.

Event-triggered attitude maneuver control of spacecraft under angular velocity constraints

Considering the spacecraft attitude system subject to angular velocity constraints, limited communication resources, the inaccurate moment of inertia, and external interference, a neural network-based adaptive event-triggered attitude maneuver control scheme is proposed. Specifically, the angular velocity constraint is first transformed into the performance boundary constraint based on the prescribed performance method, and then the equivalent error model of the attitude system is established using error transformation, which tactfully transforms the attitude maneuver control problem with angular velocity constraints into the state-bounded stability control problem of the unconstrained error system. Subsequently, by applying the radial basis function neural network, an adaptive online updating law is designed to approximate the uncertainty term caused by the unknown moment of inertia online. Meanwhile, considering the limited communication resources, a unified time-varying event-triggered mechanism is developed by establishing the explicit relationship between the trigger control signal and the real-time control one. The control command and the adaptive law are synchronously updated once the trigger condition is satisfied. By doing so, the frequent network signal transmissions between the controller and the actuator are reduced significantly. In addition, the time-varying term in the event-triggered mechanism strictly guarantees that no Zeno phenomenon occurs. The simulation results show that the proposed attitude control algorithm can achieve the specified attitude maneuver task with higher accuracy, stability, and robustness and reduce frequent control signal updates by about 97.50%, significantly reducing the on-board communication burden.