Chih-Fu Chang

Nonlinear control of a wheeled mobile robot with nonholonomic constraints

This paper proposed a novel way to design and analysis nonlinear controllers to deal with the tracking problem of a wheeled mobile robots (WMR) with nonholonomic constraints. One of the nonlinear controllers is adopted to control the system with position and torque tracking requirements simultaneously. Another one is chosen to follow the path considering with position, torque and actuator dynamics by backstepping control. Both of feedback systems are shown to be exponentially stable via Laypunov stability analysis. In order to guarantee the high performance operation of brushless DC motors (BLDCM) in such applications, the nonlinear model are accounted for increasing the precision actions through accuracy sketching nonlinear behaviours. The performances of controllers are verified through simulations.

A formation control framework based on Lyapunov approach

A general control framework for a formation system composed of a team of nonholonomic wheeled mobile robots (WMRs) considering the formation dynamics under static connection structure but subject to dynamic connection stability is proposed in this paper. Hence, a rigorous formation theory is obtained essentially based on the differential structure of the formation system. With this result, a case design using a Lyapunov based control complying with the proposed formation theory is provided to demonstrate the capability and feasibility of the proposed framework. Finally, the wander-mode simulation with three WMRs is conducted while the formation configuration may be changing on-line. It is believed that the present results can be further extended to many applications involving the nonlinear multi-agent system.

Human-centered robot navigation — Toward a harmoniously coexisting multi-human and multi-robot environment

This paper proposes a navigation algorithm that considers the states of humans and other robots in order to achieve harmonious coexistence between robots and humans. When navigating through humans and robots with different functions, a robot should not only pay attention to obstacle avoidance and goal seeking, it should also take care of whether it interferes with other people or robots. To deal with this problem, we propose several harmonious rules, which guarantee a safe and smooth navigation in multi-human and multi-robot (MHMR) environment. Based on those rules, a practical navigation method-human- centered sensitive navigation (HCSN)-is proposed. HCSN considers the fact that both humans and robots have sensitive zones depending on their security regions or on psychological feeling of people. We model these zones as various sensitive fields with priorities, whereby robots tend to yield socially acceptable movements.

Navigation of a wheeled mobile robot in indoor environment by potential field based-fuzzy logic method

In this paper, we address the navigation problem of a wheeled mobile robot (WMR) under behavior-based control, such as avoiding collision and approaching a target, with the proposed potential field based-fuzzy logic (PFBFL). Generally, how to design appropriate behavior-based control is rather challenging especially when control, sensor signal, and model constraints need to be considered all together. With this, a control infrastructure embedding a fuzzy-based fusion scheme and well posed interaction with the environment is derived here for solving the problem. The proposed approach in this paper requires neither building of a map of the environment nor prior investigation of the system configuration under different environments given various WMR tasks. Finally, feasibility and robustness of this approach are well evaluated in extensive experiments.

Dynamic state feedback control of robotic formation system

This paper proposes a constructive control approach, dynamic state feedback formation control, for achieving the realization of the Multi-Robot Formation System (MRFS) with respect to the problem of dilation of a formation shape and stabilization issue in nonholonomic system simultaneously. Combining with theoretical analysis, the proposed control approach has been successfully to deal with the following design issues: one is to elude the switch control of the nonholonomic MRFS for preventing the divergence of the MRFS; another one is to stabilize the MRFS which is allowed to change the interconnection structure dynamically.

bSLAM navigation of a Wheeled Mobile Robot in presence of uncertainty in indoor environment

In this paper, we propose a behavior-based Simultaneous Localization and Map building (bSLAM) approach to deal with the following navigation problem of a Wheeled Mobile Robot (WMR): the behavior fusion, the uncertainty from measurements and modeling and the WMR control. Considering the multiple control objects, i.e., goal approaching and navigation safety, the behavior-based fuzzy path planner is established to deal with the behavior fusion problem by means of different interpretation of the environment from sensing system. Typically, the uncertainty of measurements together with the incremental error of the WMR self-localization is classified as the SLAM problem. In this research, we further consider the modeling uncertainty comparing with the SLAM problem so that the reduced-order SLAM is theoretically obtained via the variation approach in cope with the slipping and sliding effects. Therefore, the uncertainties are able to be effectively reduced at any motion time instead the time that the WMR revisits the well-known landmark in the SLAM algorithm. The effectiveness and the performance of the proposed bSLAM are verified via experiment. Finally, the results compared with SLAM and bSLAM approach show the error covariance is averagely diminished 26.60% in the complex environment.

A hybrid system design of a mobile manipulator

In this paper, a novel design and implementation of a hybrid system of the multi-agent is proposed. First of all, a hybrid system is established to characterize different behaviours of an agent. From the well designed feedback linearization control law, the autonomous agent which is composed by wheeled mobile manipulator (WMM) switches well-depicted behaviours such as obstacle avoid, target approach, cruise, grasp etc. from the feedback signals. Next, a two-level control architecture is devised for the WMM system, where the first level mainly handles sensor feedback subject to sensor fusion, whereas the second level is responsible for providing a well performed supervisory control that can manipulate all available surrounding resources to successfully accomplish the aforementioned mission. An actual WMM is developed, named The Treasure Hunter (TTH), which is able to hunt treasures in an unknown environment whereby the effectiveness of the proposed approach is satisfactorily demonstrated

Modeling and Stability Analysis of the Nonholonomic Multi-Agent Formation Problem

This paper addresses the problem of distributed motion control of highly structured formations of nonholonomic multi-agent robotic systems. For concentrating on the multi-agent formation problem, a local stable feedback control laws based on relative distance and angular and bearing measurements are used. There are topological obstructions to globally stable system operation for such laws, but by appropriately switching among them, it is possible to stably control a rich class of formation motions. In this paper, the modeling and stability analysis is obtained to the proposed nonholonomic multi-agent formation systems. Beyond the modeling, a leaders control configuration is obtained from the cost function of the MFCS with local control of followers. Hence, we start with the fundamental definitions of a noholonomic WMR for looking for the system properties. After extending to the problem of multi-agent formation, an innovative analysis of the platform is provided for the further study on multi-agent cooperation/coordination problem.

Analysis of a Behavior Based Nonholonomic Wheeled Mobile Robot Control With Hybrid System Approach

In this paper, a novel design and analysis of a hybrid multiagent system (HMAS) with switching behaviors, random walk, formation, and obstacle avoidance is proposed. Under the well designed Lyapunov based controller, each autonomous agent which is composed of a wheeled mobile manipulator (WMM) with switching behaviors subjected to the flow over a hybrid model can manipulate the surrounding objects together with other agents so as to successfully accomplish the cooperative mission. Not only the stability of different behaviors on an agent is analyzed under the well-designed controller but also that of the entire hybrid system is established so that different behaviors of an agent can be alternated successfully. The contributions of this paper can be split into three parts: first, behaviors are designed subjected to the Lyapunov based control and their stability issues are proved; second, the dynamic hybrid system is analyzed with dynamic properties of behaviors; third, the innate characteristics of task switching are analyzed for multiagent hybrid system. Finally, a design example and simulation of a hybrid system is obtained in this paper to show the advantages of this framework

A behavior based nonlinear multi-agent framework using a hybrid approach

Abstract In this paper, a novel design and implementation of a multi‐agent system via a hybrid approach is proposed. First of all, an autonomous agent is insured to be stable by employing the proposed local feedback control besides appropriate switching among well‐posed behaviors including obstacle avoidance, target approaching, wandering, manipulator grasping, etc. Next, a hybrid framework of the multi‐agent system (HMAS) is established for dealing with multi‐agent cooperative problems. The architecture of the inherent hierarchical control is designed consisting of two levels, where the first (lower) level mainly handles the continuous state describing the data acquired from various sensors, whereas the second (higher) level is responsible for providing a well performed supervisory control that can manipulate all available resources to successfully accomplish the underlying mission. In the Advanced Control Laboratory of the Department of Electrical Engineering at National Taiwan University, an actual wheeled mobile robot (WMR) has been developed, named The Treasure Hunter (TTH), which is able to hunt treasures in an unknown environment whereby the effectiveness of the proposed approach can be satisfactorily demonstrated.