In this paper, after complete modelling of a flexible satellite equipped with a control moment gyroscope (CMG) actuator, it is shown that a PD-like controller can globally asymptotically stabilize this satellite by using Lyapunov’s direct method. Despite the simplicity, simulations show that the controller can stabilize the flexible satellite in a three-axis manoeuvre even in the presence of external disturbances. Then, using a non-linear variable gains PD controller, which only uses angular velocity of the rigid body and the attitude parameters as the inputs, the performance of the control system is improved in some important aspects such as reducing maximum control torque, reducing maximum peak of deflection of the appendages and increasing robustness of the controller against the orbital disturbances. In addition, locally asymptotically stability of the non-linear variable gain PD controller is guaranteed using a novel Lyapunov candidate function. Considering the difficulty in measuring the appendages’ deflection and the primarily existence of parameter uncertainties, and as this controller is independent of changes in these parameters, such a control system is very useful and applicable. In order to validate the system’s mathematical model and the control system performance, an exact model of the satellite is constructed in the ADAMS/View software that is linked to the MATLAB software. The efficacy of the proposed approach is demonstrated by several numerical examples.
This study investigated associations of attitude tracking control of an underactuated spacecraft with consideration of saturation and perturbations. A nonsingular attitude tracking control was proposed which did not need limiting initial conditions of the quaternions. The controller was analyzed based on Lyapunov criteria and LaSalle’s invariance theorem in the large-angle maneuver. In order to control, the complete kinematic and dynamic model of the underactuated spacecraft was reconstructed. According to simulation results, our controller has excellent robustness against the hard saturation, external disturbances, time-varying inertia uncertainties, and internal disturbances of actuators. As result, we found that the attitude controller was asymptotically stable under the soft saturation and the perturbations so that quaternions and angular velocity converged to the desired path within the 80 s. Also, it was still asymptotic stable under the hard saturation whose level is equal to 0.035 Nm, 3.5% of the soft saturation level. In this case, errors of quaternions and angular velocity were converged to the origin within the 150 s. Finally, the closed-loop system was verified by Adams-MATLAB co-simulation. The maximum verification errors for quaternions were less than 19%, while the maximum verification errors for angular velocity were less than 13.5%.
The three-axis attitude tracking manoeuvre and vibration suppression of a flexible spacecraft in the presence of external disturbances are investigated in this paper. The spacecraft consists of a rigid hub and two flexible appendages. The Euler–Bernoulli beam theory is used to model the flexible parts. The attitude dynamic equations of motion are derived using the law of conservation of angular momentum, and the flexural equations are derived. The attitude of the spacecraft is represented using the quaternion parameters. The controller is designed based on the super-twisting sliding mode control. The sliding surfaces are introduced and the global asymptotic stability of the flexible spacecraft on the sliding surfaces is assured via Lyapunov method. The control law is designed such that the sliding condition is satisfied and the system reaches the sliding surfaces in finite time. The simulation results verify the performance of the controller in the presence of bounded disturbances, sensor noises and abrupt changes in parameters.
Recently, the increasing need for performing intricate operations in small dimensions has motivated many researchers and industrialists to focus on minirobots. Different types of minirobots with diverse locomotive mechanisms have been designed for various applications. Modular design is a new method which is employed to fabricate small robots with more flexibility and capability. In many works, each module of modular minirobots has rotational displacement. In this article, a flexible minirobot module is developed and manufactured which can produce controlled rotational displacement. Shape memory alloy springs are applied as the actuators to provide impressively large strokes. The final fabricated flexible minirobot module is verified by the open-loop experimental tests. In order to achieve the desired maneuvers and have a perfect tracking of reference input, a nonlinear fuzzy controller is developed and implemented to control the maneuvers of flexible minirobot module. Finally, the results are discussed which show good agreement between the simulations and experimental tests.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.