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Abstract The vibration isolation system is crucial to high-precision space systems. This paper studies dynamics and control of a six-axis vibration isolator via a flexible Stewart platform. The parasitic stiffness induced by flexible joints is considered in dynamics modeling and compensated in control for the first time. The explicit dynamic equations are established based on the pseudo-rigid-body model and the principle of virtual power. After validation by ADAMS/Flex and the finite element method, the dynamic equations are used for designing a decoupled controller. The control force is synthesized based on the leg's force and position feedback. The impact of bending and torsional stiffness of flexible joints is compensated and the MIMO system is consequently decoupled in modal space, making parameter design and performance implementation more convenient and effective. The identical sub-controller for every SISO system makes the six-DOF isolator achieve the capability of vibration isolation simultaneously for the six modes. With a proportional plus integral compensator as the sub-controller, the vibration isolation bandwidth and active damping can be regulated separately. [ABSTRACT FROM AUTHOR]

Parallel piezostages have been prevalently applied in the micro-/nano-positioning field, but, unluckily, suffer from the undesired effects, like creep, hysteresis, vibration, cross coupling, and input saturation. To eliminate these nonlinearities, a new discrete-time sliding mode predictive control (DSMPC) with decoupling and damping properties (DSMPC-DDP) is proposed for a parallel six-axis piezostage devoted to cell micromanipulation. Firstly, a state-space-based decoupler is applied to make the MIMO system decoupled into six SISO subsystems, and then a damping compensator via the notch filter principle is selected to suppress the high-frequency vibration dynamics of six subsystems. After that, a feedback DSMPC law is designed for each decoupled and damped subsystem. Unlike the traditional linear model predictive control (MPC), the feedback DSMPC is developed based on a nonlinear discrete-time terminal sliding mode prediction model, leading to stronger robustness and faster convergence speed. Through the utilization of the receding horizon optimization, the sliding mode states are optimized to explicitly deal with the input constraints. The stability of the closed-loop subsystems is analyzed based on the terminal constraint theory. Finally, the effectiveness and superiority of the proposed controller is validated by a series of experimental tests. Results show that the proposed DSMPC-DDP scheme can achieve higher tracking accuracy and control bandwidth than the existing proportional–integral (PI) and MPC methods in the context of abovementioned nonlinearities. • A new DSMPC-DDP is proposed for a parallel six-axis piezostage. • Attenuating the creep, hysteresis, cross coupling, vibration, and input saturation simultaneously. • Providing rigorous stability analysis for the closed-loop control system. • Comprehensive comparative experiments are conducted for validating the superiority. [ABSTRACT FROM AUTHOR]

Parallel micropositioning piezostages are widely used in the micro-/nano-manipulation applications, but also subject to the nonlinear disturbances, like hysteresis, creep and cross-coupling effects. In this paper, a new fractional robust adaptive decoupled control (FRADC) is synthesized for a six-axis parallel micropositioning piezostage to improve the positioning accuracy. The proposed FRADC contains three intuitional terms: (1) a decoupling term that alleviates the coupled motions among different axes, making the controller implementation more convenient and efficient; (2) a feedforward compensation term based on a fractional normalized Bouc-Wen (FONBW) model, compensating for the rate-dependent hysteresis effect induced by the piezoelectric actuators; (3) a feedback model reference adaptive control (MRAC) term with fractional proportional-plus-integral-type updating rules that suppresses the creep effect, parameters uncertainty and external disturbances, further enhancing the robustness and positioning accuracy. The stability of the closed-loop system is analyzed in theory. The effectiveness of the proposed FRADC is experimentally validated by comparing with the standalone inverse-FONBW-based feedforward control, the standalone feedback fractional MRAC, and the traditional integer-order control methods. Results demonstrate that the proposed FRADC can guarantee higher positioning accuracy for the piezostage system in wider control bandwidth. [ABSTRACT FROM AUTHOR]

• The transmission models of single TSS with arbitrary route configurations are developed. • A tendon-sheath-based bending sensor is proposed for online parameter identification. • Two compensation strategies are developed to enhance the control accuracy of TSS without distal feedback. • The effectiveness is validated by trajectory tracking and frequency response experiments. Tendon sheath system (TSS) has been widely used in many applications with strict spatial limitations due to its flexibility, dexterity, and remote transmission ability. However, the inherent configuration-dependent nonlinearities between tendon and sheath seriously degrade the transmission performance and result in inaccurate force and position control. In this paper, the force and position transmission models of single TSS with arbitrary route configurations and terminal loads are developed based on the analysis of system friction and deformation. A tendon-sheath-based bending sensor is proposed for the online identification of accumulated bending angle. To enhance the accuracies of force control and position control with time-varying configuration, two control strategies are developed for the friction and deformation compensation without sensory feedback from distal end. An experimental setup of tendon sheath actuation is established to gain insights into the force and position transmission processes and evaluate the effectiveness of the developed transmission models and compensation controllers. The results of model validation experiments with sinusoidal force input show that the modeling errors of force and position transmission are less than 5% and 2.5%, respectively. Moreover, the trajectory tracking experiments and frequency response experiments are carried out, and the results demonstrate the feasibility of the proposed identification strategy and compensation controllers in improving control accuracy and ensuring control bandwidth of single TSS with time-varying bending angle. [ABSTRACT FROM AUTHOR]

A novel functional biochar (BC) was prepared from industrial waste red mud (RM) and low-cost walnut shell by one facile-step pyrolysis method to adsorb phosphorus (P) in wastewater. The preparation conditions for RM-BC were optimized using Response Surface Methodology. The adsorption characteristics of P were investigated in batch mode experiments, while a variety of techniques were used to characterize RM-BC composites. The impact of key minerals (hematite, quartz, and calcite) in RM on the P removal efficiency of the RM-BC composite was studied. The results showed that RM-BC composite produced at 320 °C for 58 min, with a 1:1 mass ratio of walnut shell and RM, had a maximum P sorption capacity of 15.48 mg g−1, which was more than double that of the raw BC. The removal of P from water was found to be facilitated significantly by hematite, which forms Fe–O–P bonds, undergoes surface precipitation, and exchanges ligands. This research provides evidence for the effectiveness of RM-BC in treating P in water, laying the foundation for future scaling-up trials. [Display omitted] • Preparation conditions for biochar composite from red mud and walnut shell were optimized. • Batch adsorption experiments were conducted on the adsorption characteristics of P. • The maximum P adsorption capacity of biochar composite reached 15.48 mg g−1. • Fe from hematite in red mud of the biochar composite play an important role in removing P. • Adsorption mechanism includes creation of Fe–O–P bonds, surface precipitation and ligand exchange. [ABSTRACT FROM AUTHOR]