A decentralized controller that uses event-triggered communication scheduling is developed for the leader-follower consensus problem under fixed and switching communication topologies. To eliminate ...continuous interagent communication, state estimates of neighboring agents are designed for control feedback and are updated via communication to reset growing estimate errors. The communication times are based on an event-triggered approach and are adapted based on the trade-off between the control system performance and the desire to minimize the amount of communication. An important aspect of the developed event trigger strategy is that communication is not required to determine when a state update is needed. Since the control strategy produces switched dynamics, analysis is provided to show that Zeno behavior is avoided by developing a positive constant lower bound on the minimum inter-event interval. A Lyapunov-based convergence analysis is also provided to indicate bounded convergence of the developed control methodology.
In this article, a leader-follower system is developed for cooperative transportation. To the best of our knowledge, this is the first work in which interunmanned aerial vehicle communication is not ...required and the reference trajectory of the payload can be modified in real time, so that it can be applied to a dynamically changing environment. To track the modified reference trajectory in real time under the communication-free condition, the leader-follower system is considered as a nonholonomic system in which a controller is developed for the leader to achieve an asymptotic tracking of the payload. To eliminate the need to install force sensors, unscented Kalman filters (UKFs) are developed to estimate the forces applied by the leader and the follower. Stability analysis is conducted to prove that the tracking error of the closed-loop system is asymptotically stable; however, the dynamics of the UKF estimators is not considered in the closed-loop system, which is assumed to be a deterministic system for the controller. The experiments show that the controllers of the leader and the follower can work in the real world, but the tracking errors are affected by the disturbance of airflow in a restricted space.
A leader-follower system is developed to cooperatively swing a payload up to a desired angle without interagent communication. The main advantages of this system are that no force sensor is required ...to measure the swing angle, and the states of the leader and the follower are not communicated to achieve synchronous swinging. The leader actively swings up the payload using an energy-based controller. The follower controller can compensate the angle difference and mimic the leader swing simultaneously by estimating the difference in swing angle and the energy rate, which avoid any need for interagent communication of their states for achieving the appropriate interaction. Force sensors are also not needed since unscented Kalman filters are developed to estimate the external forces applied to the agents. The results from a stability analysis prove that the system is stable. Simulation was conducted to verify the performance of the developed controllers and estimator.
This study investigated how creative personality, psychological empowerment, and job stress affect creative self‐efficacy and innovative behavior in hospitality employees. A hypothesized moderating ...role of knowledge‐sharing role in the relationship between creative self‐efficacy and innovative behavior was also tested. Three hundred and thirty‐nine employees and 89 supervisors employed by International Tourist Hotels in Taiwan participated in the study. A structural equation modeling analysis indicated that creative self‐efficacy significantly mediates the effects of creative personality and psychological empowerment on innovative behavior in the hospitality industry. The positive effect of creative self‐efficacy on innovative behavior was larger in high knowledge‐sharing work environments than in low knowledge‐sharing work environments. Theoretical and practical implications are further discussed.
A cooperative transportation system (CTS) composed of two multirotors has been developed to facilitate the cooperative transportation of a payload, even in the presence of defective motors. The ...reduced thrust generated by the faulty motors may cause greater tracking errors, making it challenging to control and estimate the system. Moreover, the reduced thrust can also act as a disturbance to the other UAV, further exacerbating the problem. To address these issues, the motor thrust is reconfigured using an efficiency estimator based on an unscented Kalman filter (UKF). This estimator increases the thrust of the defective motors, thus improving the system's performance. The CTS achieves trajectory tracking despite the defective motors by using a geometric controller that incorporates the motor-efficiency estimator. A stability analysis has been conducted to prove the stability of the tracking errors. The estimation and control performances have been verified through simulations.
A heterogeneous sensing multiunmanned aerial vehicle (UAV) system is developed to track a moving target undergoing unknown motion. Using heterogeneous sensors for tracking can increase robustness and ...reduce costs. However, the formation configuration of the multi-UAV system needs to be designed to ensure the best estimation performance. A metric based on the Fisher information matrix is used to determine the best formation configuration since the state covariance matrix was proven to be lower bounded by the Cramer-Rao lower bound. In other words, the determinant value of the Fisher information matrix is designed to be the cost function, and limitation of the field of view (FOV), limitation of the tracking distance, and avoiding inter-UAV collisions are considered as constraints. Finally, the generated optimal formation configuration is converted to the relative position for the distributed controller of the UAVs to achieve tracking. Controllers for UAVs are designed to ensure that tracking of the target is achieved in the optimal configuration with the constraints satisfied. In addition to performing the theoretical analysis, experiments and simulations were conducted to verify the efficacy of the developed heterogeneous sensing system.
A tracking controller for unmanned aerial vehicles (UAVs) is developed to track moving targets in the presence of occlusion. The controller can track moving targets based on a bounding box of the ...target detected by a deep neural network using the you-only-look-once (YOLO) method. The features generated from the YOLO approach relaxes the assumption of continuous availability of the feature points for applications, which facilitates estimation using an unscented Kalman filter (UKF) and the design of image-based tracking controller in this work. The challenge is that when occlusion is present, the bounding box of the moving target becomes unobtainable and makes the estimation diverge. To solve this, a motion model derived by quadratic programming is employed as a process model in the UKF, wherein the estimated velocity is implemented as a feedforward term in the developed tracking controller in order to enhance the tracking performance. Since no motion constraint is assumed for the target, the developed controller can be applied to track various moving targets. Simulations are used to demonstrate the performance of the developed estimator and controller in the presence of occlusion. Experiments are also conducted to verify the efficacy of the developed estimator and controller.
Image sensors have widespread use in many robotics applications and, in particular, in target tracking. While existing methods assume continuous image feedback, the novelty of this brief stems from ...the development of dwell time conditions to guarantee convergence of state estimates to an ultimate bound for a class of image-based observers in the presence of intermittent measurements. A Lyapunov analysis for the switched system is performed to develop convergence conditions based on the minimum amount of time the object must be visible and on the maximum amount of time the object may remain outside the camera view. Experimental results are included to verify the theoretical results and elucidate real-world performance.
Functional electrical stimulation (FES) can be used to activate the dysfunctional lower limb muscles of individuals with neurological disorders to produce cycling as a means of rehabilitation. ...However, previous literature suggests that poor muscle control and nonphysiological muscle fiber recruitment during FES-cycling causes lower efficiency and power output at the cycle crank than able-bodied cycling, thus motivating the investigation of improved control methods for FES-cycling. In this paper, a stimulation pattern is designed based on the kinematic effectiveness of the rider's hip and knee joints to produce a forward torque about the cycle crank. A robust controller is designed for the uncertain, nonlinear cycle-rider system with autonomous, state-dependent switching. Provided sufficient conditions are satisfied, the switched controller yields ultimately bounded tracking of a desired cadence. Experimental results on four able-bodied subjects demonstrate cadence tracking errors of 0.05 ±1.59 and 5.27 ±2.14 revolutions per minute during volitional and FES-induced cycling, respectively. To establish feasibility of FES-assisted cycling in subjects with Parkinson's disease, experimental results with one subject demonstrate tracking errors of 0.43 ±4.06 and 0.17 ±3.11 revolutions per minute during volitional and FES-induced cycling, respectively.
In Geosynchronous SAR (GEO SAR), because of the increase of orbit height, the signal propagation delay time reaches up to hundreds of milliseconds, and the synthetic aperture time also reaches up to ...hundreds of seconds which will result in a curved synthetic aperture trajectory, thus the "Stop-and-Go" assumption and conventional imaging methods of low earth orbit SAR (LEO SAR) will lose effect in GEO SAR. In addition, because the angular velocity of earth rotation is approximately equal to that of satellite rotation, the Doppler parameter and resolution analysis in LEO SAR cannot be directly used too in GEO SAR either. In this paper, firstly, the accurate slant range model in GEO SAR is created based on the consideration of the error of "Stop-and-Go" assumption, and then the improved imaging method is proposed to compensate for the error of "Stop-and-Go" assumption and the effect of the curved synthetic aperture trajectory. Finally, based on the generalized ambiguity function (GAF) and projection theory, the accurate Doppler gradient vector is analytically obtained based on the consideration of earth rotation in GEO SAR, and the accurate resolution calculation in arbitrary direction is also derived in detail. All the simulation results verify the correctness and effectiveness of the proposed imaging method and resolution analysis method.
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