Person:
Zhang, Fumin

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Dissipativity-Based Teleoperation with Time-Varying Communication Delays

2013-09 , Varnell, Paul , Zhang, Fumin

We analyze the effects of communication delays in teleoperation systems using dissipativity theory along with explicit models of the operator and robot. We utilize a simple model of the operator's behavior that describes human pointing motions, as generated by an interface such as a mouse pointer or tablet, and we use a robot model that is suitable for mobile robots or robotic manipulators. Using dissipativity conditions for stability, we show that the communication delays can be compensated for in the robot controller with a relatively simple extension to a controller designed for the situation without delays. We also show that the communication delays can lead to problems for human pointing in certain situations; specifically, if the operator overshoots their target, it may lead to instability unless corrective action is taken by the user interface. Simulation is shown to validate the result

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A Bio-inspired Plume Tracking Algorithm for Mobile Sensing Swarms in Turbulent Flow

2013-05 , Chang, Dongsik , Wu, Wencen , Webster, Donald R. , Weissburg, Marc J. , Zhang, Fumin

We develop a plume tracking algorithm for a swarm of mobile sensing agents in turbulent flow. Inspired by blue crabs, we propose a stochastic model for plume spikes based on the Poisson counting process, which captures the turbulent characteristic of plumes. We then propose an approach to estimate the parameters of the spike model, and transform the turbulent plume field detected by sensing agents into a smoother scalar field that shares the same source with the plume field. This transformation allows us to design path planning algorithms for mobile sensing agents in the smoother field instead of in the turbulent plume field. Inspired by the source seeking behaviors of fish schools, we design a velocity controller for each mobile agent by decomposing the velocities into two perpendicular parts: the forward velocity incorporates feedback from the estimated spike parameters, and the side velocity keeps the swarm together. The combined velocity is then used to plan the path for each agent in the swarm. Theoretical justifications are provided for convergence of the agent group to the plume source. The algorithms are also demonstrated through simulations.

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An Analytical Model of the CAN Bus for Online Schedulability Test

2012-12-04 , Shi, Zhenwu , Zhang, Fumin

Controller area network (CAN) is a prioritybased bus that supports real-time communication. Existing schedulability analysis for the CAN bus is peformed at the design stage, by assuming that all message information is known in advance. However, in pratice, the CAN bus may run in a dynamic environment, where complete specifications may not be available at the design stage and operational requirements may change at system run-time. In this paper, we develop an analytical model that describes the dynamics of message transmission on the CAN bus. Based on this analytical timing model, we then propose an online test that effectively checks the schedulability of the CAN bus, in the presence of online adjustments of message streams. Simulations show that the online test can accurately report the loss of scheduability on the CAN bus.

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Diagnosis and Prognosis of Scrubber Faults for Underwater Rebreathers based on Stochastic Event Models

2011-06 , Chang, Dongsik , Zhang, Fumin , West, Michael

Imperfect CO₂ removal mechanisms of CO₂ scrubbers often lead to the existence of CO₂ in gas inhaled by a diver from underwater rebreathers. This may cause CO₂ related rebreather faults and subsequently would increase the risk of human injuries. We introduce a stochastic model for three CO₂ related rebreather faults: CO₂ bypass, scrubber exhaustion, and scrubber breakthrough. We establish the concept of CO₂ channeling that describes the cause of the faults and present a CO₂ channeling model based on a stochastic process driven by a Poisson counter. This helps us to investigate how CO₂ flow inside the rebreather is affected by CO₂ related faults. Fault diagnosis/prognosis algorithms are developed based on the stochastic model and are tested in simulation.

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Robust Geometric Formation Control of Multiple Autonomous

2013-06 , Yang, Huizhen , Wang, Chuanfeng , Zhang, Fumin

This paper develops a robust controller for autonomous underwater vehicles with bounded time delays, so that the AUVs form and keep a desired formation shape and track a desired trajectory. We use a six-degree-of-freedom dynamic model for each AUV to describe its motions in the three-dimensional space. We design an orientation controller based on feedback linearization, so that the orientation of each AUV converges to its desired value. We derive formation dynamics of AUVs and decouple the dynamics into a formation shape and a formation center, using the Jacobi transform. We treat couplings in the formation dynamics as perturbations and design a robust formation-keeping controller to tolerate both the perturbations and the time delays. We demonstrate the effectiveness of our controller in simulations.

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Controlled Lagrangian Particle Tracking Error Under Biased Flow Prediction

2013 , Szwaykowska, Klementyna , Zhang, Fumin

In this paper we model the controlled Lagrangian particle tracking (CLPT) error for marine vehicles moving in an ocean flow field, with guidance from ocean models. We linearize the error about the nominal modeled trajectory of the system and derive an exact expression for the linearized error in the case of constant modeled ocean flow. We show that this simple error model can be used to estimate error in predicted positions of autonomous vehicles, using data from a field deployment of autonomous underwater gliders in Long Bay, SC, in winter 2012.

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Bio-inspired Source Seeking with no Explicit Gradient Estimation

2012-09 , Wu, Wencen , Couzin, Iain D. , Zhang, Fumin

Inspired by behaviors of fish groups seeking darker (shaded) regions in environments with complex lighting variations, we develop distributed source-seeking algorithms for a group of sensing agents with no explicit gradient estimation. We choose a baseline for agent groups and decompose the velocity of each agent into two parts. The first part, which is perpendicular to the baseline, is chosen to be proportional to the measurements, agreeing with observations from fish groups. The second part, which is parallel to the baseline, can be designed to control the relative distances among the agents. This decomposition is leveraged to implement formation- maintaining strategies and source seeking behaviors for the entire group. We prove that the moving direction of a group will converge towards the gradient direction while the formation is maintained.

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Robustness of a Class of Three-Dimensional Curve Tracking Control Laws Under Time Delays and Polygonal State Constraints

2013-06 , Malisoff, Michael , Zhang, Fumin

We analyze the robustness of a class of controllers that enable three-dimensional curve tracking of free moving particles. By building a strict Lyapunov function and robustly forwardly invariant sets, we show input-to-state stability under predictable tolerance and safety bounds that guarantee robust- ness under control uncertainty, input delays, and a class of polygonal state constraints. Such understanding may provide certified performance when the control laws are applied to real life systems. We demonstrate our findings in simulations

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Trend and Bounds for Error Growth in Controlled Lagrangian Particle Tracking

2012-12-18 , Szwaykowska, Klementyna , Zhang, Fumin

This paper establishes the method of controlled Lagrangian particle tracking (CLPT) to analyse the offsets between physical positions of marine robots in the ocean and simulated positions of controlled particles in an ocean model. The offset, which we term the CLPT error, demonstrates distinguished characteristics not previously seen in drifters and floats that cannot be actively controlled. The CLPT error growth over time is exponential until it reaches a turning point that only depends on the resolution of the ocean model. After this turning point, the error growth slows down significantly to polynomial functions of time. In the ideal case, a theoretical upper threshold on exponential growth of CLPT error can be derived. These characteristics are proved theoretically, verified via simulation, and justified with ocean experimental data. The method of CLPT may be applied to improve the accuracy of ocean circulation models and the performance of navigation algorithms for marine robots.

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Intruder Capturing Game on a Topological Map Assisted by Information Networks

2011-12 , Kim, Jonghoek , Maxon, Sean , Egerstedt, Magnus B. , Zhang, Fumin

Intruder capturing games on a topological map of a workspace with obstacles are investigated. Assuming that a searcher can access the position of any intruder utilizing information networks, we provide theoretical upper bounds for the minimum number of searchers required to capture all intruders on a Voronoi graph. Intruder capturing algorithms are proposed and demonstrated through an online computer game.

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