Swing Suppression and Accurate Positioning Control for Underactuated Offshore Crane Systems Suffering From Disturbances

Offshore cranes are widely applied to transfer largescale cargoes and it is challenging to develop effective control for them with sea wave disturbances. However, most existing controllers can only yield ultimate uniform boundedness or asymptotical stability results for the system's equilibrium point, and the state variables' convergence time cannot be theoretically guaranteed. To address these problems, a nonlinear sliding mode-based controller is suggested to accurately drive the boom/rope to their desired positions. Simultaneously, payload swing can be eliminated rapidly with sea waves. As we know, this paper firstly presents a controller by introducing error-related bounded functions into a sliding surface, which can realize boom/rope positioning within a finite time, and both controller design and analysis based on the nonlinear dynamics are implemented without any linearization manipulations. Moreover, the stability analysis is theoretically ensured with the Lyapunov method. Finally, we employ some experiments to validate the effectiveness of the proposed controller.

Enhanced Autonomous Exploration and Mapping of an Unknown Environment with the Fusion of Dual RGB-D Sensors

The autonomous exploration and mapping of an unknown environment is useful in a wide range of applications and thus holds great significance. Existing methods mostly use range sensors to generate twodimensional (2D) grid maps. Red/green/blue-depth (RGB-D) sensors provide both color and depth information on the environment, thereby enabling the generation of a three-dimensional (3D) point cloud map that is intuitive for human perception. In this paper, we present a systematic approach with dual RGB-D sensors to achieve the autonomous exploration and mapping of an unknown indoor environment. With the synchronized and processed RGB-D data, location points were generated and a 3D point cloud map and 2D grid map were incrementally built. Next, the exploration was modeled as a partially observable Markov decision process. Partial map simulation and global frontier search methods were combined for autonomous exploration, and dynamic action constraints were utilized in motion control. In this way, the local optimum can be avoided and the exploration efficacy can be ensured. Experiments with single connected and multi-branched regions demonstrated the high robustness, efficiency, and superiority of the developed system and methods.

Augmented Virtual Stiffness Rendering of a Cable-driven SEA for Human-Robot Interaction

Human-robot interaction(HRI) is fundamental for human-centered robotics, and has been attracting intensive research for more than a decade. The series elastic actuator(SEA) provides inherent compliance, safety and further benefits for HRI, but the introduced elastic element also brings control difficulties. In this paper, we address the stiffness rendering problem for a cable-driven SEA system, to achieve either low stiffness for good transparency or high stiffness bigger than the physical spring constant, and to assess the rendering accuracy with quantified metrics. By taking a velocity-sourced model of the motor, a cascaded velocity-torque-impedance control structure is established. To achieve high fidelity torque control, the 2-DOF(degree of freedom) stabilizing control method together with a compensator has been used to handle the competing requirements on tracking performance, noise and disturbance rejection,and energy optimization in the cable-driven SEA system. The conventional passivity requirement for HRI usually leads to a conservative design of the impedance controller, and the rendered stiffness cannot go higher than the physical spring constant. By adding a phase-lead compensator into the impedance controller,the stiffness rendering capability was augmented with guaranteed relaxed passivity. Extensive simulations and experiments have been performed, and the virtual stiffness has been rendered in the extended range of 0.1 to 2.0 times of the physical spring constant with guaranteed relaxed passivity for physical humanrobot interaction below 5 Hz. Quantified metrics also verified good rendering accuracy.

Rongchang and Xifeng capsules suppress pentylenetetrazole-induced seizures and change rest/wake behavior in zebrafish larvae

OBJECTIVE:To evaluate the effects of Rongchang capsule and Xifeng capsule on pentylenetetrazoleinduced epilepsy in zebrafish larvae and to explore the possible mechanisms behind their actions.METHODS:We utilized a trajectory tracking system to monitor seizures in zebrafish larva to confirm that certain concentrations of Rongchang capsule and Xifeng capsule produce antiepileptic effects.c-fos expression was assessed by quantitative reverse transcription-polymerase chain reaction to validate the efficacy of the capsules.Rest/wake behavior and correlation analysis predicted the targets of Rongchang capsule and Xifeng capsule.RESULTS:Larval movement times and total distances traveled by zebrafish larvae experiencing pentylenetetrazole(PTZ)-induced seizures were decreasedbyvalproatetreatment.Rongchang(500μg/m L)and Xifeng(200μg/m L)rescued the epileptic behaviors and down-regulated c-fos expression in the brains of larvae,which indicated antiepileptic effects.The rest/wake behavioral profiles showed that Rongchang and Xifeng differentially decreased rest time at night and increased larval locomotor activities during the day.Based on correlation between the actions of the two capsules and known compounds,we predicted that they might change rest/wake behaviors by affecting serotonin,GABAergic and histamine signaling pathways.CONCLUSION:The efficacy of Rongchang capsule and Xifeng capsule in alleviating epilepsy-like behaviors and molecular responses was confirmed.Our study provides insight into the capsules'effect on epilepsy.

Drug screening： zebrafish as a tool for studying epileptic-related chemical compounds

Dear Editor, Here we report findings of zebrafish behavior and develop- ment during drug screening. In developing zebrafish embryos, epileptic seizure-like locomotor defects can be induced by brief treatment with GABAA receptor antagonist pentylenetetrazole （PTZ）. Using a trajectory video tracking system, we recorded zebrafish movements and constituted convulsant-like locomotor behaviors after treatment with PTZ. This led to the development of the first 3-D trace map of zebrafish locomotor behaviors in response to drug treat- ment. In addition, we examined the dose-dependent rescues of the locomotor defects in PTZ-treated animals after treat- ment with anti-epileptic drugs, such as valproate （VPA）. We also examined the effects of drug treatment on animal development, such as hatching and mortality. Together, this research sheds new light for the development of new strategies for high-throughput drug screens using zebrafish models.