Adaptive saturated control for spacecraft rendezvous and docking under motion constraints

Adaptive safe control for tethered aircrafts with input and output constraints

“…Remark Compared with the existing control strategies in References 18, 20, and 32, the developed adaptive safe control strategy is applied to the tethered aircraft, which solves the problem that the initial output exceeds the constraint boundary by using the shifting function, guarantees system safety by tackling the conflict between input saturations and ATVOCs, and improves system performance by taking into account the system's tolerance for output constraints.…”

“…[15][16][17] In addition, some scholars have proposed some control methods for systems with input saturation and output/state constraints by assuming that these constraints do not affect each other. 18,19 However, the assumption is not suitable for the tethered aircraft. From the perspective of achieving the balance between input saturations and output constraints, the auxiliary system-based control approach may be more effective because the auxiliary system can be easily established to describe their connections.…”

“…Recently, many control methods have been studied to cope with input saturation 15‐17 . In addition, some scholars have proposed some control methods for systems with input saturation and output/state constraints by assuming that these constraints do not affect each other 18,19 . However, the assumption is not suitable for the tethered aircraft.…”

“…Compared with the traditional constraint control method, 32,33 where the initial output is confined to a constraint, the shifting function‐based asymmetric BLF is introduced to deal with the deferred ATVOC, which ensures the output within an ATVOC after a pre‐specified finite time and removes the initial output constraint condition simultaneously. A novel auxiliary system is established to solve the conflict between input saturations and ATVOCs, which can actively adjust the constraint boundaries according to input saturation errors and the system's tolerance for output constraints. Different from References 15 and 18, the conflict between input saturations and ATVOCs is considered to guarantee system safety. More importantly, compared with References 3 and 20, the system's own adjustment capability is introduced to further improve system performance. By synthesizing the disturbance observer, shifting function, asymmetric BLF and auxiliary system within the dynamic surface control (DSC) framework, an adaptive safe control scheme is presented to ensure that the tethered aircraft tracks safely the desired trajectory and satisfies the deferred ATVOC in the presence of unknown disturbances, input saturations and any bounded initial condition. …”

Collision response and obstacle avoidance of the tethered-space net robot system with non-target objects

“…However, this method has a defect of an over-bending segment of the trajectory, which will increase the burden to the maneuver of TSNRS and also the risk of collision. Moreover, in available studies (Chen et al , 2020; Islam et al , 2019; Zhao and Zhang, 2021), the envelope of the spacecraft is usually constant, while the envelope of the TSNRS is changing, it seems conservative to set TSNRS’s envelope as a constant larger than TSNRS’s real size; otherwise, if the constant envelope is equal to the size of TSNRS, the risk of collision will increase. It needs to improve the APF method to avoid the over bending segment of the trajectory, then couple the improved APF method with the changing envelop of the TSNRS to address the obstacle avoidance.…”