No abstract

A simple and environmentally-friendly bio-oxidation approach to produce graphite oxide nanosheets is described.

This paper presents a novel robust fixed‐time fault‐tolerant control for global fixed‐time tracking of uncertain robot manipulators with actuator effectiveness faults. With the sufficient consideration of the effects on uncertain dynamics, external disturbances and actuator effectiveness faults to the trajectory tracking performance, a singularity‐free robust fault‐tolerant control with an auxiliary vector is constructed for the fixed‐time tracking control of uncertain robot manipulators. Lyapunov stability theory is employed to prove the global fixed‐time stability ensuring that both the position and velocity tracking errors converge globally to the origin within a fixed time. The appealing advantages of the proposed control are as follows: (i) it is easy to implement with the global robust fixed‐time fault‐tolerant tracking control for uncertain robot manipulators featuring with faster transient convergence rate and higher steady‐state tracking precision; (ii) the settling time is independent of the initial states of closed‐loop system and can be calculated in advance for robot manipulators with uncertain dynamics, external disturbances and actuator faults. Extensive simulations on a two‐DOFs robot are presented to demonstrate the effectiveness and improved performances of the proposed approach.

This paper addresses an adaptive fault-tolerant tracking control for robot manipulators. By fully considering the effects of uncertainties and actuator effectiveness faults (UAEFs), a robust fault-tolerant tracking control combining with an auxiliary function and an integral sliding manifold is first developed for uncertain robot manipulators. Then, an adaptive law for unknown parameters of the upper bounded uncertainties is constructed to obtain a robust fault-tolerant approach with the elimination of the reaching phase of sliding mode control (SMC). The stability of the proposed approaches is accomplished by Lyapunov stable theory. The key contributions of the proposed approach are as follows: i) the reaching phase of SMC is removed in the control design and then the sliding mode starts at very beginning; (ii) the nominal control term is eliminated in the design of integral sliding surface and then the algebraic loop problem is also avoided in the proposed approach for robot manipulators; (iii) the simple control structure with an adaptive law is obtained for improving chattering-restraining ability of the proposed approach and then the effects of time delay and computational burden are also restrained from the proposed approach. Simulation and experimental comparisons have been accomplished for verifying the effectiveness of the proposed approach.

Abstract-This paper presents an electrical tunable bandpass filter based on tunable LC resonators loaded with semiconductor varactors. Magnetic dominated mixed coupling between the tunable resonators is utilized to compensate the bandwidth of the tunable filter. Cross coupling is created by using magnetic dominated mixed coupling between the resonators and source to load electrical coupling, and two transmission zeros are generated beside the passband. The tunable mechanism of the proposed filter is studied. The tunable filter is analyzed, designed, fabricated and measured. The measurement shows that the filter can be tuned from 70 MHz to 270 MHz with a fractional bandwidth from 27% to 21%.