The flexibility of the free-floating flexible space manipulator system’s link and joint may affect the control accuracy and cause vibrations. We studied the dynamics modeling, joint trajectory tracking control, and vibration suppressing problem of free-floating flexible-link and flexible-joints space manipulator system with external interference and uncertain parameter. The system’s dynamic equations are established using linear momentum conservation, angular momentum conservation, assumed mode method, and Lagrange equation. Then, the system’s singular perturbation model is established, and a hybrid control is presented. For the slow subsystem, a robust fuzzy sliding mode control is proposed to realize the joint desired trajectory tracking. For the fast subsystem, a speed difference feedback control and a linear-quadratic optimal control are designed to suppress the vibration caused by the flexible joints and the flexible link separately. The simulation comparison experiments under different conditions are taken. The simulate results demonstrate the proposed hybrid control’s validity.

Actuator failure and joint flexibility will dramatically impact space robot system control. In this paper, free-floating flexible-joint space-manipulator dynamic-modeling is studied and a state-observer-based robust backstepping fault-tolerant control is proposed for the system joint actuator failure. Based on the flexible-joint simplified model, the system’s rigid-flexible coupled-dynamic equations are established according to momentum conservation, angular momentum conservation, and the Lagrange equation. Then the system is decoupled based on the singular perturbation method. For the slow subsystem, a robust backstepping fault-tolerant controller base on a state observer is designed to eliminate the angle error, compensate for the uncertain parameter and the external disturbance, and achieve the joint-trajectory asymptotic-tracking. The use of a speed filter makes it inappropriate to measure and provide feedback about the system’s velocity signals, so the controller is simpler and more precise. For the fast subsystem, a velocity differential-feedback control is adopted to suppress the system vibration caused by the flexible joint, to ensure the stability of the system. Finally, the feasibility and effectiveness of the model and control method are proved by some simulations. The simulation results indicate that the proposed fault-tolerant control method can make the free-floating flexible-joint space manipulator system track the desired trajectory accurately and steadily, regardless of whether the actuator fails or not.

空间机器人在实际运作中往往会遇到控制系统输入受限的情况，这将严重影响系统的控制品质。考虑输入受限的情况，对漂浮基多柔性空间机器人系统进行研究。通过对系统进行运动学和动力学分析，构建系统的动力学方程。采用奇异摄动方法，将刚柔耦合系统分为慢变子系统和快变子系统，并为各个子系统设计控制方法。最终提出由改进的鲁棒滑模模糊控制方法、速度差值反馈控制法和线性二次最优控制方法组成的混合控制方法。该控制方法能够主动减小空间机器人完成期望运动所需的力矩，使系统适应输入受限的工作条件；同时能够补偿系统的不确定参数和外部干扰，最终实现系统运动的精确控制和振动的主动抑制。仿真对比实验证明了在输入受限的情况下，所提出的混合控制方法的有效性和强适应性。

At present, piezoelectric actuators featuring both multi-directional output capability and autonomous backward motion suppression are scarce, which limits the application of piezoelectric actuation technology. To address this issue, inspired by the rapid opening-closing switching of crab claws during movement, a novel bionic crab-claw stick-slip piezoelectric actuator is designed based on the stick-slip actuation principle. The actuator adopts a symmetric structure and exhibits bi-directional motion characteristics and is equipped with a flexible hinge amplification mechanism for autonomous backward motion suppression. In this paper, the structural reliability is first verified through mechanical theoretical analysis and the finite element method. Then, an experimental platform is built, and a prototype is fabricated for experimental testing. The results show that the proposed actuator not only has high symmetry in bi-directional output performance but also demonstrates the effectiveness of the backward motion suppression mechanism in the designed comparative experiments. The mechanism can achieve high-speed motion at low frequencies, with a maximum speed of 4.58 mm/s, which exhibits a high speed under comparable dimensions and a lower driving frequency, and the maximum load capacity reaches 0.9 N.

Accurate characterization of the measured surface profile is crucial for the calculation and analysis of real surface contact. This study introduces a model that approximates the original profile using a quadratic function, referred to as the deterministic method. Based on the height ratio criterion of asperity peaks to valleys, a moving reference line strategy is further proposed to enhance the accuracy of profile simplification and to determine the corresponding contact characteristic parameters. Characteristic parameters calculated via deterministic and spectral moment methods are integrated into typical micro-contact models to examine the rough surface contact performance, with particular focus on the real contact area and the contact load. The results demonstrate that the proposed improved method enhances the accuracy of rough surface topography characterization. Greater stability under low sampling intervals is observed in the deterministic method relative to the spectral moment method, indicating reduced sensitivity to sampling interval variation.

Most existing stick-slip piezoelectric actuators cannot actively suppress backward motion during operation, which degrades output performance and positioning accuracy. This study proposes a bidirectional stick-slip piezoelectric actuator inspired by the gait of starfish tube feet. The actuator combines a symmetric flexure-hinge structure with four PZT stacks and a tube-foot attach-pull-switch (TF-APS) control sequence. During each sequence, the driving side first establishes effective contact with the slider through its normal PZT stack and then advances the slider tangentially. The opposite side subsequently locks the slider and takes over load support before the driving side disengages and resets. This sequence maintains effective contact on at least one side, thereby reducing return-stage backward motion and enabling stable bidirectional stepping. An equivalent mechanical model of the flexure-hinge mechanism was established, and a direct FEM parameter scan was used to evaluate key geometric parameters and determine the structural dimensions. A prototype was then fabricated and tested to characterize its output, bidirectional motion, and return-stage backward-motion suppression. Its performance was also compared with that under a conventional stick-slip sequence. The actuator achieved a maximum speed of 4.31 mm s ⁻¹ . The TF-APS sequence markedly reduced return-stage backward displacement and enabled stable bidirectional motion. At 150 V and 100 Hz, the actuator maintained stable motion at approximately 1.7 mm s ⁻¹ under a carrying load of 10 N.