Cluster unmanned aerial vehicles (UAVs) are widely demanded. To achieve high rate and large capacity communication with cluster UAVs, one of the key but still challenge task is to perform multi-target acquisition, pointing and tracking (APT) under complex airborne environment. To solve this problem, this paper gives one composite axis APT system for multi-target laser communication with cluster UAVs. The APT system consists of a gimbal mirror and piezoelectric fast steering mirrors (FSMs), which can achieve independent and synchronous control of multiple optical axes. The cascade control scheme is designed for the gimbal mirror and the H-infinite controller is designed for the FSM. To further improve the control accuracy, the hysteresis compensator based on least square support vector machines (LS-SVM) is proposed. The pruning error minimization method of LS-SVM is applied to reduce the computational cost. The simulation studies validate the control performance of the multi-target APT system. Finally, the experimental prototype is developed. The experimental results further validate the effectiveness of the proposed multi-target APT system.

Accurate modeling and identification of the piezoelectric actuators (PAs) are increasingly demanded for intelligent micro-nano manufacturing to improve the accuracy of positioning and scanning. In this paper, one coupled fractional-order creep and hysteresis model is established only using 5 parameters. Then, the properties of the coupled fractional-order creep and hysteresis are investigated under sinusoidal and step inputs. The identification approaches are thus proposed by leveraging the special characteristics of the proposed fractional-order model. Simulation and experimental studies are carried out to validate the effectiveness of the proposed fractional-order creep and Bouc-Wen hysteresis model. Additionally, model-based inversion feedforward is implemented to validate the parameter identification. The experimental results demonstrate the effectiveness of the modeling and parameter identification approaches.

High-performance instruments are very sensitive to vibrations and jitters. In this article, a new approach towards multi-degree-of-freedom (DOF) active vibration isolation and its application in spacecraft jitter suppression are presented. Model reference adaptive control (MRAC) with acceleration feedback is used to isolate random disturbances. However, a side effect of this algorithm is that displacements at low frequencies are amplified. Thus, the MRAC is augmented with proportional–integral–differential (PID) displacement feedback to suppress vibration displacements. The MRAC-PID composite control is applied to a 4-leg platform to isolate vibrations and suppress tip/tilt jitters. The scheme is also used to isolate 6-DOF vibrations and steer the payload of a flexible spacecraft. Satisfactory performance of vibration isolation and jitter attenuation has been observed.

The measurement and control strategy of a piezo-based platform by using strain gauge sensors (SGS) and a robust composite controller is investigated in this paper. First, the experimental setup is constructed by using a piezo-based platform, SGS sensors, an AD5435 platform and two voltage amplifiers. Then, the measurement strategy to measure the tip/tilt angles accurately in the order of sub-μrad is presented. A comprehensive composite control strategy design to enhance the tracking accuracy with a novel driving principle is also proposed. Finally, an experiment is presented to validate the measurement and control strategy. The experimental results demonstrate that the proposed measurement and control strategy provides accurate angle motion with a root mean square (RMS) error of 0.21 μrad, which is approximately equal to the noise level.