In order to improve the tracking accuracy of the fine tracking system of free-space optical communications, a proposed active disturbance rejection control (ADRC) with iterative learning control (ILC) strategy is designed to regulate the fast steering mirror (FSM) system. First, based on the open-loop frequency response results of the system, we can approximately confirm the system transfer function and prepare for the design of the controller. Then, an improved ADRC that using sliding mode control instead of the traditional nonlinear state error feedback method is proposed to attenuate the influence of the unknown and unmolded parts. In addition, the ILC method is used to compensate the hysteresis of piezoelectric actuators and improve the overall system performance. The experimental results indicate that the tracking accuracy of the system is 1 μrad at 1k sampling frequency. In addition, the recommended method shows the better disturbance suppression performance than traditional ADRC in simulation and experimental investigations. This method has a very high application value in the field of visual axis stability, adaptive optics, and other fields.

Constructing a feasible solution, where the focus is on ‘hard’ constraints only, is an important part of solving timetabling problems. For the University Course Timetabling Problem, we propose a heuristic algorithm to schedule events to timeslots based on cliques, each representing a set of events that could be scheduled in the same timeslot, which the algorithm constructs. Our algorithm has been tested on a set of well-known instances, and the experimental results show that our algorithm is efficient and can compete with other effective algorithms.

Piezoelectric fast steering mirror (PZT FSM) is the core component of the fine tracking system for space laser communication, and its actuator is a piezoelectric ceramic. Consequently, there is a hysteretic nonlinear disturbance throughout the entire range of the FSM’s steering. To enhance the fine tracking system’s performance, this paper innovatively analyzes and verifies the effect of the PZT FSM hysteresis characteristics on the error suppression bandwidth of the fine tracking system. Firstly, the rate-dependent hysteresis model is established by serially connecting the Prandtl–Ishlinskii (P-I) model with the dynamic linear mode. The inverse model is designed as a feedforward controller, followed by the conduction of open-loop feedforward compensation experiments. Subsequently, we propose a compound control method based on the rate-dependent hysteresis mode and conduct a simulation analysis. Finally, the experimental platform for the fine tracking system is set up, and the optimization effect of compensating for hysteresis nonlinearity on the fine tracking system is verified. The experimental results show that the nonlinearity of the PZT FSM is improved by 30% in the middle- and high-frequency ranges, and the error suppression bandwidth of the fine tracking system is improved by 41.7%. This effectively enhances the fine tracking system’s error suppression capability.

In this study, Zernike polynomials and optical fiber field theory are applied to build a mathematical model of coupling efficiency (CE) and spatial mode of aberrations. The theory built in this paper can be used to quickly calculate the CE affected by a single aberration as well as the aberrations caused by atmospheric turbulence. The aberrations are classified based on Zernike polynomials and the effects of aberrations on CE of different types and different spatial frequencies are analyzed. The influence of the effects of AO system residual errors is also analyzed. Adaptive optics (AO) equipment is applied to build a system on which the proposed theory was tested; the experimental results validate the theoretical analysis.

The alignment accuracy and stability of shipborne electro-optical system are affected by external attitude disturbance and internal non-linear disturbance. Therefore, this study examined a new digital sliding mode control based on a novel reaching law with an n-order disturbance compensator to solve this problem. Specially, the proposed novel reaching law was a chatter-free method, in which, as the switching gain was replaced by an adaptive function, chattering on the sliding surface tended to zero. For perturbed systems, the new sliding mode controller was able to guarantee a narrow quasi-sliding-mode domain and the ultimate width was the order of O(T3), such that the narrower the quasi-sliding-mode domain width was, the more robust toward nonlinear disturbances. Both mathematical calculations and simulations verified the convergence and stability of the new controller. Finally, based on a compound control strategy that combined feedforward control with a sliding mode control position loop and proportional-integral velocity loop control structure, shipborne equivalent dynamic target tracking experiments were performed. The results, compared with existing controllers, showed that the robustness of the new controller to nonlinear disturbances was stronger and the tracking system accuracy clearly improved, while the influence of sliding mode chattering on the system was avoided.

In this study, a sliding mode control (SMC) algorithm was proposed based on a novel reaching law to solve the nonlinear disturbance problem of a ground-based laser communication turntable. This algorithm is a chatter-free method, in which the coefficient of sliding mode variable structure function is designed as an adaptive function, so the chattering of the sliding mode approaches zero. For any perturbed system, this algorithm can ensure a finite time for the system state to reach the sliding mode surface from any initial state. Additionally, the system will stabilize in the quasi-sliding mode domain (QSMD) with O(T³) width, where a narrower QSMD width corresponds to stronger robustness toward nonlinear disturbances. Both mathematical calculations and simulations verified the sliding mode and stability of this control algorithm. Experimental results of the velocity closed-loop of pitch axis show that the proposed algorithm effectively improved the anti-nonlinear disturbance ability of the control system compared with the effects of the traditional digital PID and the existing chatter-reduced SMC algorithms, for smooth system operation.