Adaptive feedforward control of closed orbit distortion caused by fast helicity-switching undulators

A new correction algorithm for closed orbit distortion based on an adaptive feedforward control (AFC) has been developed. At SPring-8, two helicity-switching twin-helical undulators (THUs) had been implemented with conventional feedforward corrections. However, the validity of these corrections turned out to be expiring due to unforeseen variation in the error magnetic fields with time. The developed AFC system has been applied to the THUs dynamically updating the feedforward table without stopping the helicity switching amid user experiments. The error sources in the two THUs are successfully resolved and corrected even while the two THUs are switching simultaneously with the same repetition period. The actual operation of the new AFC system enables us to keep the orbit variations suppressed with an accuracy at the sub-micrometre level in a transparent way for light source users.

Active vibration control for GyroWheel based on sliding mode observer and adaptive feedforward compensator

This article proposes an active vibration control method for the GyroWheel to ensure the attitude stability precision of the spacecraft. The method includes sliding mode disturbance observer and adaptive feedforward compensator. First, considering the disturbance torque caused by rotor imbalance, the dynamic equation adopting complex coefficients is derived with synchronous disturbances. To reduce the influence of model parameter perturbation, a finite time sliding mode observer is designed to estimate the rotor imbalance owing to its robustness. An integrator for the switching term is introduced in the sliding manifold, which attenuates the chattering phenomenon. Then, the observed unbalanced torque is utilized to generate the reference compensation tilting angle, which is fedforward to the command value to offset the synchronous frequency current. A variable step size seeking algorithm is adopted to tune the feedforward compensator gain adaptively. Finally, both numerical simulations and experiments have verified the effectiveness of the active vibration control scheme, achieving clean vibration torque.

Summarisation, Simulation and Comparison of Nine Control Algorithms for an Active Control Mount with an Oscillating Coil Actuator

With the further development of the automotive industry, the traditional vibration isolation method is difficult to meet the requirements for wide frequency bands under multiple operating conditions, the active control mount (ACM) is gradually paid attentions, and the control algorithm plays a decisive role. In this paper, the ACM with oscillating coil actuator (OCA) is taken as the object, and the comparative study of the control algorithms is performed to select the optimal one for ACM. Through the modelling of ACM, the design of controller and the system simulations, the force transmission rate is used to compare the vibration isolation performance of the nine control algorithms, which are least mean square (LMS) adaptive feedforward control, recursive least square (RLS) adaptive feedforward control, filtered reference signal LMS (FxLMS) adaptive control, linear quadratic regulator (LQR) optimal control, H2 control, H∞ control, proportional integral derivative (PID) feedback control, fuzzy control and fuzzy PID control. In summary, the FxLMS adaptive control algorithm has the better performance and the advantage of easier hardware implementation, and it can apply in ACMs.

An Adaptive Assistance Controller to Optimize the Exoskeleton Contribution in Rehabilitation

In this paper, we present a novel adaptation rule to optimize the exoskeleton assistance in rehabilitation tasks. The proposed method adapts the exoskeleton contribution to user impairment severity without any prior knowledge about the user motor capacity. The proposed controller is a combination of an adaptive feedforward controller and a low gain adaptive PD controller. The PD controller guarantees the stability of the human-exoskeleton system during feedforward torque adaptation by utilizing only the human-exoskeleton joint positions as the sensory feedback for assistive torque optimization. In addition to providing a convergence proof, in order to study the performance of our method we applied it to a simplified 2-DOF model of human-arm and a generic 9-DOF model of lower limb to perform walking. In each simulated task, we implemented the impaired human torque to be insufficient for the task completion. Moreover, the scenarios that violate our convergence proof assumptions are considered. The simulation results show a converging behavior for the proposed controller; the maximum convergence time of 20 s is observed. In addition, a stable control performance that optimally supplements the remaining user motor contribution is observed; the joint angle tracking error in steady condition and its improvement compared to the start of adaptation are as follows: shoulder 0.96±2.53° (76%); elbow −0.35±0.81° (33%); hip 0.10±0.86° (38%); knee −0.19±0.67° (25%); and ankle −0.05±0.20° (60%). The presented simulation results verify the robustness of proposed adaptive method in cases that differ from our mathematical assumptions and indicate its potentials to be used in practice.

A novel ship path following method in inland waterways based on adaptive feedforward PID control

Given the complex and time-varying external disturbances of inland waterways, designing an accurate path following controller is challenging. Based on the traditional PID controller, combined with the servo system model and the lead compensator, an adaptive feedforward PID controller for path following of ships in inland waterways is designed considering ship maneuverability and external disturbances. Simulations of a ship in a curved channel in different scenarios are carried out to illustrate the effectiveness of the proposed path following method. Compared with the traditional path following controller, the proposed one based on adaptive feedforward PID control has favorable relative stability, anti-interference ability and high steady-state precision in inland waterways.