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Highlights • Model of dual planar cranes carrying a distributed-mass beam is derived. • A new method is developed for estimating the natural frequency of dual planar cranes. • MEI input shaper is presented for limiting oscillations of dual cranes. • Experiments validate dynamic behaviour and the effectiveness of MEI shaper. Abstract Unwanted oscillations caused by the operator-commanded motions lower the capable operating speeds and degrade the safety of dual cranes moving distributed-mass payloads. Mounting numbers of works have been devoted to the dynamics and control of dual cranes. However, few studies have been dedicated to the accurate estimation of natural frequency, which is a critical factor for controlling the dual cranes. This paper develops a new method to predict the natural frequency of dual planar cranes with different cable lengths. Furthermore, a modified extra-insensitive (MEI) input shaper is proposed to suppress the oscillations of the payload swing and pitch in the dual cranes. The MEI shaper has good robustness to large changes in the frequency, and has good performance in the jerk limitation. Simulated and experimental investigations are performed on small-scale dual cranes transporting a slender beam to validate the system dynamic behavior and the effectiveness of the MEI shaper. [ABSTRACT FROM AUTHOR]

Highlights • A new dynamic model is developed for a flexible single-link manipulator. • The model includes an infinite number of uncoupled Duffing oscillators. • Two methods are presented for controlling the vibrations of Duffing oscillators. • Experiments validate Duffing model and the effectiveness of control methods. Abstract Unwanted vibrations caused by the commanded motions lower the positioning accuracy and degrade the control performance of flexible link manipulators. Much work has been devoted to the dynamics and control of flexible link manipulators. However, there are few studies dedicated to the flexible link manipulators having Duffing oscillator dynamics. This paper develops a new model for a flexible single-link manipulator by assuming large mechanical impedance in the drives or large inertia of the motor hub and by considering the flexibility of the single-link manipulator. The derived model includes an infinite number of uncoupled Duffing oscillators by ignoring the modal coupling effects. Two new methods are presented for controlling the vibrations of the flexible manipulator governed by Duffing oscillators. One is designed for the single-mode Duffing oscillator, and the other is for the multi-mode Duffing oscillators. A comparison of these two methods is made using the results of numerical simulations and experimental measurements. Experimental investigations are also performed on a flexible single-link manipulator to validate the dynamic behavior of Duffing oscillators and the effectiveness of the new control methods. [ABSTRACT FROM AUTHOR]

Multivariate signal processing methods are becoming more prevalent as sensors and modern science and technology improve. However, most existing multivariate signal decomposition methods suffer from the following challenges: (i) requiring prior knowledge of multivariate signal modes; (ii) limiting to narrowband signal analysis; (iii) presenting mode mixing. To overcome the challenges mentioned above, this study proposes a novel method, named adaptive multivariate chirp mode decomposition (AMCMD). The method captures time-varying joint modes one-by-one in a recursive framework without knowing the precise number of modes. Specifically, a multivariate chirp mode (MCM) is modeled first based on AM–FM signals, with the constraint that there is a joint frequency component between all signal channels. Furthermore, demodulation techniques are used to entail the wideband multivariate signal mode exhibit narrowband characteristics. Finally, the objective function is established and the modes of each channel signal are estimated one by one. The efficacy and superiority of the method are verified by a series of numerical examples. In addition, the analysis of real-world time-varying vibration signals also confirms the practicality of the method. The findings demonstrate that the proposed method can converge faster to the same satisfactory results as existing state-of-the-art methods at a faster rate, even without knowing the precise number of modes. [ABSTRACT FROM AUTHOR]

• Planar dynamic model of an underwater soft-link manipulator is derived. • Equations for estimating frequency and mode shape are proposed. • A control method is presented to control coupled vibrations. • Experiments validate effectiveness of dynamic model and control method. Underwater soft-link manipulators can be applied in offshore and marine industries. However, the soft-body link may interact with the fluid flow in this type of coupled liquid-link system. Both frequencies and mode shapes of the coupled system differ from those of uncoupled link vibrations and water flow due to the liquid-link interaction. Therefore, the dynamic model of underwater soft-body manipulators that account for liquid-link interaction is required to comprehend and control. Although significant work has been focused on the underwater manipulator and the soft manipulator, no significant dynamic modeling, control study, and experimental validation have been directed at the liquid-link interaction in underwater soft-body manipulators. A dynamic model of underwater soft-link manipulators undergoing planar motions is presented in this article. The analyses of frequencies and mode shapes for the liquid-link interaction are also described. Meanwhile, a control method is designed to mitigate coupled vibrations in underwater soft-link manipulators. Simulated and experimental results validate the utility of the dynamic model and control method. [ABSTRACT FROM AUTHOR]

Full spectrum and holospectrum are homogeneous information fusion technology developed for the fault diagnosis of rotating machinery, which is extensively exploited in the analysis of the orbits of rotor-bearing systems. However, they are not adapted for non-stationary signals, nor can they be used for fusion analysis of vibrations of multiple bearing sections. By drawing inspiration from the multivariate variational mode decomposition (MVMD) and the complex-valued signal decomposition, we propose a method called multivariate complex variational mode decomposition (MCVMD). It can simultaneously extract the forward and backward components of multiple bearing sections and realize non-stationary complex signal decomposition of multiple bearing sections of the rotor. To achieve the visualization goal of condition monitoring, we propose the three-dimensional instantaneous orbit map (3D-IOM). It enables more features of shaft vibration of a rotor system to be displayed and offers a new way for the fusion analysis of vibration signals of multiple bearing sections of rotating machinery. Furthermore, making the most of the joint information, we also provide a high-resolution time-full spectrum (Time-FS) to display the forward and backward frequency components of multiple bearing sections. The effectiveness of the proposed method through both the simulated experiment and the real-life complex-valued signals is demonstrated in this paper. • A new multivariate complex variational mode decomposition method (MCVMD) is proposed. • 3D instantaneous orbit map is raised to visualize the instantaneous vibration state. • Time-FS, to integrate the frequency components into a TF plane, is devised. • The effectiveness is verified by the simulation test and real-world data. [ABSTRACT FROM AUTHOR]

Operating cranes is challenging because payloads experience large and dangerous oscillations, especially when the system is suffering from wind disturbances and the large-size payload is modeled as a distributed-mass model. The payload oscillations induced by both intentional motions commanded by the human operator and by the external wind disturbances make the dynamics more complicated. This paper presents a novel combined control architecture to limit oscillations of the distributed-mass payload caused by both human-operator commands and wind disturbances. While a smoothed command suppressed operator-induced oscillations, a wind-rejection command eliminated the payload swing resulting from the wind gusts. Through simulations, a large range of system parameters and motions are analyzed to investigate the dynamic behavior of bridge cranes with distributed-mass beams and wind disturbances by using the new control scheme. Experimental results obtained from a small-scale bridge crane validate the simulated dynamic behavior and the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Motion-induced oscillations of crane payloads seriously degrade their effectiveness and safety. Significant progress has been achieved with reducing payload oscillations on a single-pendulum crane with a point-mass payload attached to the end of the cable. However, large payloads and the actual configuration of the hoisting mechanism may transform the crane to a double-pendulum system with a distributed-mass payload. The manipulation task can be more challenging because of the complicated dynamics. The dynamics of bridge cranes transporting distributed-mass beams are derived. A command-smoothing scheme is presented to suppress the complex payload oscillations. Simulations of a large range of motions are used to analyze the dynamic behavior of the cranes and the robustness of the method. Experimental results obtained from a small-scale double-pendulum bridge crane transporting a distributed-mass beam validate the simulated dynamic behavior and the effectiveness of the method. [ABSTRACT FROM AUTHOR]

Abstract: A method is presented for limiting vibration in flexible systems by smoothing the original command. The original command is smoothed to drive the flexible systems without inducing vibration. The proposed smoother is designed as a function of system natural frequency and damping ratio. The comparison between the new method and the zero vibration and triple derivative (ZVDDD) shaper for modeling error is explored and quantified. The theoretic analysis shows that the new method is more insensitive at higher frequencies, while the ZVDDD shaper has more insensitivity at lower frequencies. Moreover, the designed smoother benefits vibration reduction for multi-mode systems. Experimental results for single-mode and multi-mode systems validate the simulated dynamic behavior and the effectiveness of the new method. [Copyright &y& Elsevier]

• Model of tower cranes carrying slender payloads is derived. • Equation for estimating the twisting frequency is presented. • A discontinuous piecewise smoother is proposed for controlling swing and twisting. • Experiments validate dynamic behaviour and the control effectiveness. Tower cranes suspending slender payloads are widely used in the construction site. Both the payload swing and twisting degrade the efficient and safe operation. However, the twisting dynamics is more complicated than the swing dynamics. Although numerical analysis of the twisting dynamics has been reported, little attention has been directed at the analytical analysis of the twisting dynamics. A new dynamic model including swing and twisting has been derived in this article. The analytical analysis of the twisting dynamics from the new model has been described. The closed-form solution for estimating frequencies of the payload twisting have been presented. In addition, a new control method is proposed for suppressing swing and twisting in tower cranes transporting slender payloads. The control method has good robustness to variation in working conditions and system parameters, and good performance in rise time. Numerous simulations and experiments demonstrated the key dynamic behavior of the payload twisting and effectiveness of the control method. [ABSTRACT FROM AUTHOR]