Nonlinear Robust Control on Yaw Motion of a Variable-Speed Unmanned Aerial Helicopter under Multi-Source Disturbances

This paper studies the multi-source disturbances attenuation problem on the yaw motion of unmanned aerial helicopter with a variable-speed rotor. The yaw motion subsystem dominated by an electrically-driven tail rotor is firstly introduced, and its trajectory accuracy requires particularly close attention. To this end, we establish a fourth-order yaw error dynamic equation; subsequently, a nonlinear robust control scheme based on optimal H∞ principle is developed, consisting of laws of virtual functions, parameter estimation and a compensation signal. The novelty of this scheme lies in unifying the techniques to deal with the uncertain parameters, noise perturbations, actuator output fault and external airflow turbulence into a simple framework. Stability analysis guarantees that the yaw closed-loop system has the predefined performance of disturbance suppression in the sense of a finite L2-gain. Comparison results with the extended state observer based backstepping controller verify the effectiveness and superior performance of proposed scheme in an aircraft prototype.

Event-driven NN adaptive fixed-time control for nonlinear systems with guaranteed performance

This article investigates the adaptive neural network fixed-time tracking control for a class of strict-feedback nonlinear systems with prescribed performance demands, in which radial basis function neural network (RBFNN) is utilized to approximate the unknown items. First, an improved fractionalorder dynamic surface control (FODSC) technique is incorporated to address the issue of the iterative derivation, where a fractional-order filter is adopted to improve the filter performance. What's more, the error compensation signal is established to remove the impact of filter error. Furthermore, a fixed-time adaptive event-triggered controller is constructed to reduce the communication burden, where the Zeno-behavior can also be excluded. Stability results prove that the designed controller not only guarantees all the signals of the closedloop systems (CLS) are practically fixed-time bounded, but also the tracking error can be regulated to a predefined boundary. Finally, the feasibility and superiority of the designed control algorithm are verified by two simulation examples.

Shape Deviation of Surface Structures Produced by WaveShape (Structuring by Laser Remelting) on Ti6Al4V and a Method for Deviation Reduction

Laser structuring by remelting (WaveShape) is a manufacturing process for metal surfaces in which structures are generated without material removal. The structuring principle is based on the controlled motion of the three-phase line in the area of the solidification front. The contour of the solidification front is imprinted into the remelting track during the continuous solidification process. Typically, harmonic surface structures in the form of sinusoidal oscillations are generated by means of WaveShape with virtually no material loss. However, a significant shape deviation is often observed over a wide range of process parameters. In this study, it was found that much of the shape deviation is concentrated at a spatial wavelength equal to half the spatial wavelength used for structuring. Therefore, an approach to reduce the shape deviations was specifically investigated by superimposing a compensation signal on the harmonic structuring signal. In this approach, a compensation signal with half the spatial wavelength was varied in phase and amplitude and superimposed on the structuring signal. Amplitude and phase shift of the compensation signal were further investigated for selected laser beam diameters and spatial wavelengths. This demonstrated that a shape deviation of harmonic surface structures on titanium alloy Ti6Al4V could be reduced by up to 91% by means of an adapted compensation signal.

Tracking control via sliding mode for heavy-haul trains with input saturation

To address the tracking control problem of heavy-haul trains (HHTs) with input saturation during operation, an anti-saturation sliding mode (SMES) control method based on dynamic auxiliary compensator (DAC) is presented. Firstly, an HHT model with nonlinear coupling and uncertain disturbances is built. Secondly, a new type of DAC is introduced to overcome the difficulty of traditional dynamic auxiliary compensator (TDAC) with a large upper bound on the compensation signal. Finally, an anti-saturation SMES control algorithm is designed to reduce the influence of input saturation on the tracking accuracy of each carriage. Simulation results verify the effectiveness of the algorithm in terms of tracking accuracy, anti-interference, and anti-saturation.

Adaptive fuzzy practical tracking control for flexible-joint robots via command filter design

This paper investigates the issue of finite-time tracking control for flexible-joint robots. In the design scheme, the unknown continuous function is identified by a fuzzy system. By introducing the command filter technique, “explosion of complexity” problem which arises from repeated differentiation of virtual controllers is avoided. Meanwhile, errors resulting from the first-order filters can be reduced with the introduced compensation signal. Besides, the proposed method ensures that the tracking performance could be achieved within a limited time. Eventually, the simulation is given to demonstrate the effectiveness of the proposed scheme.

Digital Fuzzy Current Mode Controlled Integrated PFC Converter with External Ramp Compensation

This paper propounded a novel method of design and realization of a digital fuzzy controlled buck integrated power factor correction (PFC) converter. It derives its advantages through the low buck capacitor voltage and single control switch (SW1), which leads to reduced complex control and price. Sub-harmonic oscillations generated in the peak current mode technique can be nullified by using the ramp signal, thereby improving the overall performance of the converter. The fuzzy logic controller (FLC) is robust and effective than the conventional linear controllers like P, PI, PID. In this paper, the digital fuzzy current mode controlled integrated PFC converter with external ramp compensation signal for 100 W load operating in the universal range of voltage (90[Formula: see text]V–265[Formula: see text]V), 50[Formula: see text]Hz has been designed and implemented using MATLAB/Simulink, verified in hardware using the TMS320F2812 digital processor board, and the results are found to be complying with international regulatory standards (IEC 6100-3-2 and IEEE 519-1992).