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Summary: This article looks into the dynamic event‐triggered fixed‐time adaptive attitude control problem for nonlinear six‐rotor unmanned aerial vehicle (UAV) with external disturbances. The multiple six‐rotor UAVs considered are regarded as nonlinear multi‐agent systems (MASs), and each subsystem has multiple inputs. Under the framework of backstepping recursive design, an effective adaptive fixed‐time control method is proposed by combining neural networks (NNs) technology and fixed‐time theory. NNs are utilized to handle unknown nonlinearity and unmodeled parts in attitude systems. The hyperbolic tangent function is ushered to address the singularity problem that may occur in the derivative of the controller, thereby averting the phenomenon of chattering. For the sake of alleviating the correspondence burden of multiple UAVs attitude systems, a modified dynamic event‐triggered mechanism (DETM) is ushered. The developed controller swears for that all signals of the six‐rotor UAV attitude systems are bounded and the tracking errors converge to a small neighborhood of the origin within a fixed‐time interval. Eventually, with the help of simulation results, the effectiveness of the proposed control scheme was verified. [ABSTRACT FROM AUTHOR]

Summary: The problem of adaptive fuzzy fixed‐time tracking control based on a category of nonlinear systems with unmodeled dynamics and dynamic disturbances is investigated in this article. By introducing the novel fixed‐time dynamic signal, the unmodeled dynamics can be disposed of. On the basis of the fuzzy logic systems (FLSs) and adaptive backstepping technology, the disposing difficulty of the unknown nonlinear portions is reduced. Then, all signals in the closed‐loop system are ensured to be bounded under the fixed‐time Lyapunov stability theory. Simultaneously, the tracking error converges to a small neighborhood of the origin. Eventually, simulation consequences reveal the validity of the presented control method. [ABSTRACT FROM AUTHOR]

Summary: This paper presents an analog tracking bandpass filter that is intended to be applied in ac signal acquisition circuits to reduce measurement noise. A fast and accurate frequency tuning technique is developed based on the phase control loop. A complete derivation process is provided to build the mathematical model describing the control loop for the tracking filter. Accordingly, a zero‐crossing detector is designed to accurately extract signal phases in the proposed loop. As a closed‐loop control system, the loop dynamics such as stability, transient response, and steady‐state error are analyzed using the derived model. From both the simulations and measurements, the developed filter is found to provide excellent performance in frequency tracking, noise reduction, and linearity compared to existing work. The maximum and minimum Q value reaches 42.2 and 14, respectively, in the frequency tuning range of 34 to 107 kHz, while the frequency tracking error is less than 1.18% at 100 kHz. [ABSTRACT FROM AUTHOR]

Summary: A servo channel loading card (SCLC) with high precision data acquisition and output is developed for static and fatigue testing of aircraft wings. A high‐performance processor field programmable gate array (FPGA) is at the core to control the excitation source (ES) output circuit to provide excitation for the force and displacement sensor. To improve the precision of the ES output circuit, a 3DA‐based ES auto‐calibration circuit is designed. Simulation results show that the 3DA improves the precision of the automatic calibration of the ES circuit. The sensor signals are collected through high precision analog channels, and the signals are automatically zero calibrated and numerical control gain processed. Ultimately, a voltage or current signal is generated through the drive circuit to control the electro‐hydraulic servo loading system to complete a high precision force loading test on the aircraft wings. The experimental results show that the board designed has high reliability in both acquisition and output. The ES output achieved a precision of 0.1375 mV/V, the precision of signal acquisition achieves a precision of −0.175 mV/V, and the servo drive output achieves a precision of −0.06 mV/V, meeting the expected design precision of 1 mV/V. [ABSTRACT FROM AUTHOR]

This paper establishes a novel fractional‐order model for n‐links flexible‐joint (FJ) robots and proposes an adaptive dynamic surface control (DSC) scheme to address the tracking control problem. The fractional‐order FJ model is built by fractional‐order viscoelastic dynamics model to have a more concise form. An adaptive DSC strategy is proposed to address the tracking control problem based on backstepping method. By selecting the appropriate orders for fractional filters, the controller could solve the "explosion of complexity" problem. The unknown nonlinearities of FJ robot systems are approximated by Radial basis function (RBF) neural networks (NNs). Based on the Lyapunov stability theory, the bounds of all signals in the closed‐loop system are achieved. The simulation results confirm the effectiveness of the presented control scheme. [ABSTRACT FROM AUTHOR]

Summary: In this paper, an observer‐based adaptive neural output‐feedback control scheme is developed for a class of nonlinear stochastic nonstrict‐feedback systems with input saturation in finite‐time interval. The mean value theorem and the property of the smooth function are applied to cope with the difficulties caused by the existence of input saturation. According to the universal approximation capability of the radial basis function neural network, it will be utilized to compensate the unknown nonlinear functions. Based on the state observer, the finite‐time Lyapunov stability theorem, we propose an adaptive neural output‐feedback control scheme for nonlinear stochastic systems in nonstrict‐feedback form. The developed controller guarantees that the system output signal can track the given reference signal trajectory, and all closed‐loop signals are semi‐globally finite‐time stability in probability. The observer errors and the tracking error can converge to a small neighborhood of the origin. Finally, simulation results demonstrate the effectiveness of the developed control scheme. [ABSTRACT FROM AUTHOR]

The key circuits of servo channel loading card with high‐precision data acquisition and output functions for wing fatigue testing are studied and improved in this paper. To solve the problem of large offset voltage in some op‐amps, non‐inverting combined amplifier circuit (NCAC) and inverting combination amplifier circuit (ICAC) are proposed by utilizing precision op‐amps combined with wide voltage and high‐power output op‐amps. In the force signal acquisition section, a non‐inverting combined zeroing filter circuit (NCZFC) is proposed to improve the precision of signal acquisition. In the excitation source output section, a non‐inverting combined excitation output circuit (NCEOC) is proposed to improve the precision of the positive excitation output; an inverting combined excitation output circuit (ICEOC) is also proposed, which improves the precision of the negative excitation output and also realizes the inversion of the input and output signals. In the servo drive output section, a non‐inverting combined voltage and current conversion circuit is proposed to improve the precision of voltage and current outputs, which has two modes of non‐inverting combined voltage output (NCVO) and non‐inverting combined current output (NCIO) modes. Simulation experiments in Multisim and actual tests have been carried out on the above improved circuits to verify the stability and precision. [ABSTRACT FROM AUTHOR]