Integrated Fixed Time Sliding Mode Control for Motion and Vibration of Space Robot with Fully Flexible Base–Link–Joint

The dynamic modeling, motion control and flexible vibration active suppression of space robot under the influence of flexible base, flexible link and flexible joint are explored, and motion and vibration integrated fixed-time sliding mode control of fully flexible system is designed. The flexibility of the base and joints are equivalent to the vibration effect of linear springs and torsion springs. The flexible links are regarded as Euler–Bernoulli simply supported beams, which are analyzed by the hypothetical mode method, and the dynamic model of the fully flexible space robot is established by using the Lagrange equation. Then, the singular perturbation theory is used to decompose the model into slow subsystem including rigid motion and the link flexible vibrations, and fast subsystems including the base and the joint flexible vibrations. A fixed time sliding mode control based on hybrid trajectory is designed for the slow subsystem to ensure that the base and joints track the desired trajectory in a limited time while achieving vibration suppression on the flexible links. For the fast subsystem, linear quadratic optimal control is used to suppress the flexible vibration of the base and joints. The simulation results show that the controller proposed in the paper can make the system state converge within a fixed time, is robust to model uncertainty and external interference, and can effectively suppress the flexible vibration of the base, links, and joints.

Hybrid-Trajectory Based Terminal Sliding Mode Control of a Flexible Space Manipulator with an Elastic Base

SummaryA hybrid-trajectory based terminal sliding mode controller (TSMC) is addressed for a free-flying two-flexible-link space manipulator with an elastic base. In this system, there are unknown but bounded external disturbances and parameters. First, the Lagrange dynamic model of the manipulator was established by the momentum conservation. Second, a TSMC based on desired trajectory was proposed, by which the terminal trajectories were asymptotically tracked and periodic flexible vibrations were excited. Then based on virtual control force, hybrid trajectories were generated, in which the flexible variables, the joint angular displacement errors and the base’s attitude error were considered. Finally, a hybrid-trajectory TSMC was presented, by which the terminal trajectories were asymptotically tracked and the flexible vibrations were suppressed.

Carbody vibrations of high-speed train caused by dynamic unbalance of underframe suspended equipment

The effect of dynamic unbalance of the underframe suspended rotational equipment on the flexible vibrations of the carbody has become a major concern for high-speed trains. It is known from the field tests that the dynamic unbalance has a significant influence on carbody vibrations, especially the local flexible vibration, which leads to a decrease in the passenger ride comfort and may even cause structural damage to the carbody. A vertical mathematic model considering the carbody flexibility and the underframe suspended equipment is first set up, and then a three-dimensional dynamic model for a rigid–flexible coupled vehicle system is established. The effect mechanism of the dynamic unbalance on carbody flexible vibration is extensively studied, and the efficient measures to reduce the carbody flexible vibrations are proposed. The theoretical and simulation models are verified by comparing with a field test conducted on a newly designed high-speed railway. The results show that decreasing the unbalanced mass of the rotational equipment can reduce the carbody vibrations. Moreover, the use of elastic suspension for the underframe equipment can isolate the vibration transmission to the carbody. Both the theory of dynamic vibration absorber and dynamic unbalance should be considered to optimize reasonable suspension parameters, especially the suspension location and the suspension frequency.

Simple model-free attitude control design for flexible spacecraft with prescribed performance

In this paper, a model-free attitude control approach is proposed for the spacecraft in the presence of external disturbances and flexible vibrations with both complexity and performance concerns. By utilizing prescribed performance and backstepping techniques, the controller is constructed in a simple form without requiring any relevant information of the attitude control system dynamics. Moreover, fuzzy/neural network approximations, observers, or adaptive laws are not adopted into the control design, so that the related problems introduced by these estimation structures can be avoided. Numerical simulations in different cases show that the control system can obtain quick and smooth dynamic process and expected tracking accuracy despite the influence of disturbances and flexible vibrations, which demonstrates the effectiveness of the proposed scheme. Owing to the above good features, it is suitable for practical engineering.

High Precision Roll/Yaw Attitude Stabilization for Flexible communication satellite

The aim of this paper is to realize high-precision attitude stabilization for roll/yaw axes of flexible communication satellite while attenuate the effects of the elastic vibrations and multiple disturbances such as solar radiation and model uncertainties. a composite control has been designed which is comprise two part an anti-disturbance proportional-derivative (PD) controller is designed to stabilize the attitude while rejecting the effects of flexible vibrations, environmental disturbances, and unmodelled dynamics, whose are assumed as an extended state. This controller comprises two parts, i.e. an extended state observer and a PD controller with feedforward. First, flexible vibrations, environmental disturbances and unmodelled dynamics are regarded as an extended state, which can be estimated by the proposed observer. The estimated extended state can be compensated by feedforward where the attitude can be stabilized by the PD controller. Numerical simulation results are presented to demonstrate the effectiveness of the control scheme.