This paper presents a novel quasi-zero-stiffness (QZS) isolator designed by combining a tension spring with a vertical linear spring. In order to improve the performance of low-frequency vibration isolation, geometric nonlinear damping is proposed and applied to a quasi-zero-stiffness (QZS) vibration isolator. Through the study of static characteristics first, the relationship between force displacement and stiffness displacement of the vibration isolation mechanism is established; it is concluded that the parameters of the mechanism have the characteristics of quasi-zero stiffness at the equilibrium position. The solutions of the QZS system are obtained based on the harmonic balance method (HBM). Then, the force transmissibility of the QZS vibration isolator is analyzed. And the results indicate that increasing the nonlinear damping can effectively suppress the transmissibility compared with the nonlinear damping system. Finally, this system is innovative for low-frequency vibration isolation of rehabilitation robots and other applications.

The optimal placement and active vibration control for piezoelectric smart single flexible manipulator are investigated in this study. Based on the assumed mode method and Hamilton’s principle, the dynamic equation of the piezoelectric smart single flexible manipulator is established. Then, the singular perturbation method is adopted and the coupled dynamic equation is decomposed into slow (rigid) and fast (flexible) subsystems. After that, the couple optimal placement criterion of piezoelectric actuators is proposed on the base of modal H₂ norm of the fast subsystem and the change rate of natural frequencies. Using an improved particle swarm optimization algorithm, the optimal placement of piezoelectric actuators is realized. Subsequently, in order to verify the validity and feasibility of the presented optimal placement criterion, the composite controller is designed for the active vibration control of the piezoelectric smart single flexible manipulator. Finally, numerical simulations and experiments are presented. The results demonstrate that the piezoelectric smart single flexible manipulator system has a better single modal controllability and observability and has a good result on the vibration suppression using the optimization results of actuators. The proposed optimal placement criterion and method are feasible and effective.

The fourth-generation synchrotron light source has higher requirements for small-size beam precision than the previous three generations, making beam stability one of the most important factors constraining the experiments of the fourth-generation light source. In order to improve the control accuracy of the beam stabilisation system, we propose an improved adaptive control method based on the Least Mean Squares(LMS) algorithm and reference voltage, based on a piezoelectric drive platform. Firstly, a Hammerstein model is built by connecting the improved Prandtl-Ishlinskii(PI) model and Auto-Regressive with Extra Inputs(ARX) model in series to describe the hysteresis and rate dependence of the piezoelectric platform. Then its inverse model is used as a feedforward controller and Proportion Integration Differentiation(PID) feedback algorithm to form a feedforward PID control scheme. Finally, the reference voltage model is fitted on this basis and an improved adaptive control method is proposed to adaptively regulate the inverse model parameters. The experimental results show that the relative displacement error of the piezoelectric platform is reduced to less than 1.6% under the improved adaptive control method, which effectively compensates the tracking error caused by the hysteresis and rate dependence of the platform.

The four-blade slit is an important part in the neutron beamlines, which can help to regulate the flow of neutron beams through the slit. The current phase II of the China Spallation Neutron Source has higher requirements for the precision of neutron beamline control. Piezoelectric platform facilitates precise control of slit position and can be used in environments with strong magnetic fields. In order to improve the tracking accuracy of the piezoelectric platform, a Hammerstein model composed of improved P–I model and ARX model was established to characterize the hysteresis of the piezoelectric actuator. The third-order transfer function obtained from the identification of the electromechanical coupling model of the system characterized the dynamic characteristics of the system. Then, a dynamic model of piezoelectric positioning platform with hysteretic nonlinear input is obtained. At the same time, the Hammerstein inverse model is established to design the feedforward controller and feedforward PID compound controller. The experimental results show that, under feedforward PID compound control, the root mean square error of the tracking signal displacement is lower than that under feedforward control, and the tracking precision is better. This study provides a dynamic control model and theoretical support for the design of piezoelectric-driven neutron slits, which can be extended to other applications of high-precision control under strong magnetic fields.