Wenxiang Deng

Bio: Wenxiang Deng is an academic researcher from Nanjing University of Science and Technology. The author has contributed to research in topics: Parametric statistics & Full state feedback. The author has an hindex of 1, co-authored 3 publications receiving 1 citations.

Active Disturbance Rejection Adaptive Control of Tank Turret-gun Control Systems

Abstract: Aiming at parametric uncertainties and unmodeled disturbances of tank turret-gun control systems, this paper presents an adaptive control scheme via full state feedback. The basic idea of this control scheme is to combine adaptive control with extended state observer through back stepping method. The control scheme can effectively improve the stabilization accuracy of the marching tank. Based on the interaxial coupling nonlinear dynamic model of the tank turret-gun systems, an extended state observer is constructed to observe the unmodeled disturbance of the systems in real time to suppress its adverse effects and a parameter adaptive law is designed to learn and compensate the parametric uncertainties of the tank turret-gun control systems. The proposed active disturbance rejection adaptive control algorithm can simultaneously deal with the parametric uncertainties and unmodeled disturbances of the tank gun control systems. As a result, it can avoid the problem of high-gain feedback and improve the servo performance of the tank turret-gun control system. The controller theoretically has asymptotic tracking performance in the presence of parametric uncertainties and constant disturbances. In addition, prescribed transient tracking performance and final tracking accuracy can also be guaranteed when existing time-variant uncertain nonlinearities. A large number of comparative simulation results are obtained to verify the high performance nature of the proposed control strategy.

Asymptotic Adaptive Motion Control of Hydraulic Systems

Abstract: Considering parametric uncertainties and unmodeled disturbances in hydraulic systems, this paper presents an asymptotic adaptive motion control scheme by adopting full state feedback. To accomplish this study, a novel parameter adaptive law based on both parametric estimation errors and tracking errors is developed to deal with parametric uncertainties of hydraulic systems, which can attenuate the major of parametric uncertainties and enhance the tracking performance. Then a composite robust integral of the sign of the error (RISE) feedback controller is employed to restrain the rest of parametric uncertainties and unmodeled disturbances. The developed continuous RISE-based controller is free of chattering, which is beneficial to practical implementation. Stability analysis indicates that the proposed method guarantees an excellent asymptotic tracking performance even in facing with time-variant disturbances and parametric uncertainties. Comparative simulation results are obtained to verify the high-performance nature of the proposed control strategy as well.

Asymmetric molten pool morphology in wire-arc directed energy deposition: Evolution mechanism and suppression strategy

Abstract: Symmetric molten pool morphology is essential and fundamental in manufacturing three-dimensional (3D) components by wire-arc directed energy deposition (DED) method. However, when the molten metal droplets are deposited on non-level surfaces, various inclined substrates lead to undesirable molten pool behaviors, asymmetrical weld bead morphologies, or even formation of defects, which are mainly triggered by the gravity. Therefore, the evolution mechanism and suppression strategy of the asymmetric molten pool morphology on the inclined surface are necessary for the fabrication of 3D components. Herein, experimental and simulation analysis was carried out to reveal the evolutionary mechanism of molten pool and forming characteristics of wire-arc DED on various inclined surfaces, and a printing strategy was proposed to suppress the asymmetric molten pool morphology. First, a series of deposition experiments based on variable tilted substrates was conducted to evaluate the influence mechanism of weld bead morphology, and a characteristic parameter was introduced to quantitatively analyze the influence of inclination angle on the forming morphologies of weld beads. Second, in order to better comprehend the evolution of the asymmetric molten pool morphology, 3D numerical simulation and high-speed photography test were conducted to investigate the evolution of temperature field, velocity field, and fluid dynamics during the deposition on variable substrates. Finally, based on the theory of equilibrium of forces, a strategy was proposed to suppress the undesirable fluid flow pattern and eliminate the asymmetric morphology of single bead. Besides, for the multi-bead deposition process, this paper proposed an alternate printing strategy to alleviate asymmetric molten morphology and improve the forming quality. The feasibility of the proposed methods were verified via comparative quantitative evaluation. • Evolution mechanism of molten pool in wire-arc DED is systematically investigated. • Adverse effect of gravity on the mass transfer behavior of molten pool is revealed. • The influencing mechanisms of asymmetric morphology of molten pool are explored. • Printing strategies are proposed to eliminate the asymmetric weld bead morphology.

A Review on Distortion and Residual Stress in Additive Manufacturing

Abstract: Additive manufacturing (AM) has gained extensive attention and tremendous research due to its advantages of fabricating complex-shaped parts without the need of casting mold. However, distortion is a known issue for many AM technologies, which decreases the precision of as-built parts. Like fusion welding, the local high-energy input generates residual stresses, which can adversely affect the fatigue performance of AM parts. To the best of the authors’ knowledge, a comprehensive review does not exist regarding the distortion and residual stresses dedicated for AM, despite some work has explored the interrelationship between the two. The present review is aimed to fill in the identified knowledge gap, by first describing the evolution of distortion and residual stresses for a range of AM processes, and second assessing their influencing factors. This allows us to elucidate their formation mechanisms from both the micro- and macro-scales. Moreover, approaches which have been successfully adopted to mitigate both the distortion and residual stresses are reviewed. It is anticipated that this review paper opens many opportunities to increase the success rate of AM parts by improving the dimension precision and fatigue life.

Nonlinear Adaptive Robust Precision Pointing Control of Tank Servo Systems

Abstract: This paper focuses on the high performance pointing control of tank servo systems with parametric uncertainties and uncertain nonlinearities including nonlinear friction, backlash and structural flexibility. A comprehensive dynamic nonlinear mathematical model of the two-DOF tank servo system is established. Specifically, to accurately describe the nonlinear friction characteristics in actual systems, a continuous friction model is employed. Moreover, a hybrid nonlinear model combining structural flexibility and transmission backlash is constructed to characterize the nonlinear characteristics of the backlash and flexible coupling between the input and output shafts of the drive end for the tank servo system. By using the backstepping method, a nonlinear adaptive robust controller is presented. In the controller, the adaptive law is compounded to dispose of parametric uncertainties and a well-designed continuous nonlinear robust control law is developed for the purpose of coping with unmodeled disturbances. The closed-loop system stability analysis indicates that the presented controller achieves an asymptotic tracking performance with parametric uncertainties and ensures the robustness against unmodeled disturbances theoretically. The effectiveness of the proposed control strategy is verified by a large number of comparative simulation results.