Neuromotor control experiments have shown that humans are able to adapt limb impedance to stably and properly interact with various environmental forces with dexterous skills. Inspired by these observations, in this paper, we develop a control approach in which the robot automatic control is combined with impedance control using stiffness transferred from human operator. Under the assumption of linear mapping between muscle surface electromyography signal amplitude and human arm stiffness, we employ the incremental stiffness extraction method in operational space with an improved performance by compensation of the nonlinear residual error in the mapping. The teleoperated robotic exoskeleton is able to replicate the impedance of human operator's arm, and simultaneously, compensate for external disturbances by the technique of disturbance observer. Experimental studies have been carried out to test the antidisturbance ability of the proposed approach for the pose maintenance task in the presence of both stable and unstable interactive forces. The effectiveness of the proposed approach has been demonstrated by the experimental results.
Summary Offshore cranes are complicated underactuated systems, which work in harsh sea conditions. Due to the various severe disturbances, the control of offshore cranes has always been a great challenge, which is made even more complicated when considering some practical issues such as actuator saturation and coordination. Until now, few results have been published in the literature on this topic. To address this problem, an efficient nonlinear control method is proposed for offshore boom cranes suffering from both ship roll and heave motion in this paper, which takes full consideration of actuator saturation, as well as the coordination problem between actuators. Furthermore, regarding the various extra nonvanishing disturbances, such as winds, frictions, and unmodeled dynamics, a disturbance observer is designed to estimate and eliminate these uncertainties. The asymptotic stability of the desired equilibrium point is rigorously guaranteed by Lyapunov techniques and LaSalle's invariance theorem. Finally, extensive hardware experimental tests are carried out to demonstrate the feasibility and efficiency of the proposed method. To the best of our knowledge, this paper proposes the first method that considers the saturation and coordination problem for offshore cranes while guaranteeing the asymptotic stability of the desired equilibrium point.
In the hybrid ac-dc microgrid, the ac and dc subgrids are connected by bidirectional power converters (BPCs) that play an important role in the load power sharing and power interaction between the ac and dc subgrids. The coordination control and circulating current suppression for the parallel BPC system are very challenging. In this paper, a decentralized coordination control method is proposed for parallel three-phase BPCs, which can suppress the circulating currents, realize proper power interaction, and achieve overall load power sharing in both the grid-connected mode and the islanded mode. The performance of the proposed control methods is verified by the real-time hardware-in-loop tests.
Size control of multicellular organisms poses a longstanding biological question that has always fascinated scientists. Currently the question is far from being resolved because of the complexity of and interconnection between cell division and cell expansion, two different events necessary to form a mature organ. Because of the importance of plants for food and renewable energy sources, dissecting the genetic networks underlying plant growth and organ size is becoming a high priority in plant science worldwide. Here, we review the current understanding of the cellular and molecular mechanisms that govern leaf organ size and discuss future prospects on research aiming at understanding organ size regulation.
Mode transitions are significant events in the operation of series-parallel hybrid electric vehicles (SPHEVs) with a clutch serving as the key enabling actuator element. Due to the friction-induced discontinuity of the clutch torque, seamless transition is difficult to achieve. In this paper, a model reference control (MRC) law is proposed to coordinate the motor torque, engine torque, and clutch torque to manage transitions. The control system is overactuated in the sense that three inputs (i.e., three torques) can be manipulated to control the two outputs (angular speeds of the two sides of the clutch). The effects of using different input combinations are analyzed to exploit the overactuation feature of the system, and performance sensitivities to various design factors are studied. The simulation and experimental results from an SPHEV bus demonstrate that the MRC achieves reduced torque interruption, less vehicle jerk, and smaller frictional losses, compared to the conventional operation method.
•Present the overall design idea of the multi-agent energy-coordination control system.•Designed the agent model according to the output characteristics of different power-generation equipment.•Identify reasonable and efficient energy-coordination mechanisms.•Achieve the maximum economic benefit on the basis of stable operations. A multi-agent-based energy-coordination control system (MA-ECCS) is designed for grid-connected large-scale wind–photovoltaic energy storage power-generation units (WPS-PGUs) to address the challenges of low operation efficiency, poor stability, and complex decision making. The proposed system adopts the negotiation model of the contract net protocol with the non-fixed client–server cooperative mechanism among agents. When the power supply and demand are imbalanced, the system selects the state-changeable agent as the task initiator according to the load balance principle. In the energy-coordination process, the proposed system solves the global optimal-energy distribution plan of the system by considering the self-constraint and control objective of each agent and by using the improved particle swarm algorithm to achieve the maximum economic benefit on the basis of stable operations. The paper presents the overall design idea of the system, the agent models of different equipment, and the global energy-coordination optimization algorithm. An example is given to discuss the behavior characteristics of the agent and communication negotiation process and to verify that the system designed in this paper can realize the energy-coordination dispatching flexibly and efficiently. The method adopted by the system can improve the overall operation efficiency and economic benefits of WPS-PGUs.
Proteolytic processing of cell-surface-bound ligands, called shedding, is a fundamental system to control cell-cell signaling. Yet, our understanding of how shedding is regulated is still incomplete. One way to increase the processing of dual-lipidated membrane-associated Sonic hedgehog (Shh) is to increase the density of substrate and sheddase. This releases and also activates Shh by the removal of lipidated inhibitory N-terminal peptides from Shh receptor binding sites. Shh release and activation is enhanced by Scube2 [signal sequence, cubulin (CUB) domain, epidermal growth factor (EGF)-like protein 2], raising the question of how this is achieved. Here, we show that Scube2 EGF domains are responsible for specific proteolysis of the inhibitory Shh N-terminus, and that CUB domains complete the process by reversing steric masking of this peptide. Steric masking, in turn, depends on Ca2+ occupancy of Shh ectodomains, unveiling a new mode of shedding regulation at the substrate level. Importantly, Scube2 uncouples processing of Shh peptides from their lipid-mediated juxtamembrane positioning, and thereby explains the long-standing conundrum that N-terminally unlipidated Shh shows patterning activity in Scube2-expressing vertebrates, but not in invertebrates that lack Scube orthologs.
•A switch mode control and a dc–dc coordination control for dc–dc converters’ coordinated operation is proposed.•Real-time coordinated control enabling automatic dispatch of the dc–dc converters.•The unbalanced power from one dc grid could be optimally distributed with proposed control.•The serious power fluctuation events could be prevented with proposed control. Dc–dc converters are emerging as a key device for future dc transmission networks. This paper develops a switch mode control and a dc–dc coordination control for dc–dc converters’ coordinated operation in the multi-voltage-level dc grid. The switch mode control is a local controller on the dc–dc converter to enable the automatic switch of the dc–dc operation mode. The dc–dc coordination control is an advanced control based on the switch mode control. With the dc–dc coordination control, unbalanced power from one dc grid could be optimally distributed to other grids, in order to avoid serious power fluctuation events. Simulation results are provided to demonstrate the performance of the switch mode control and dc–dc coordination control.
In this article, the authors discuss the evolution of trust, distrust, and formal coordination and control in interorganizational relationships. They suggest that the degrees to which managers trust and distrust their partners during initial stages of cooperation leave strong imprints on the development of these relationships in later stages of collaboration. This derives from the impact of trust and distrust on (a) formal coordination and control, (b) interorganizational performance, and (c) the interpretations that managers attribute to the behavior of their partners. Collectively, the authors' arguments give rise to a conceptual framework that indicates that there is a high propensity for interorganizational relationships to develop along vicious or virtuous cycles. By integrating and reconciling previous work on the trust-control nexus and by emphasizing the dynamics associated with it, the article contributes to a more comprehensive and refined understanding of the evolution of interorganizational cooperation.