The purpose of this thesis is to develop a generic control law for unmanned-trail vehicles as they follow a manned lead vehicle. The development of this semi-robotic convoy control law begins with a model of an individual vehicle. Two methods are then explored of coupling these into a model of the column. A relationship between these two methods is derived. The model is then expanded to n vehicles. Utilizing a digital simulation, a three-vehicle convoy is controlled in one degree-of-freedom (DOF) using pole-placement, state-feedback control theory. The analysis shows this to be an unacceptable method of control due to the steady-state error. The 1 DOF model is then controlled with series compensation. Simulations verify that the steady-state error is eliminated. The system is then expanded into a 2 DOF system. Using the same series compensator, a 2 DOF simulation is developed. It is shown that the only additional requirement of the 2 DOF system is that the trail vehicles need to determine their orientation. This is accomplished by first saving the position and velocity profile of the lead vehicle and then developing a search algorithm to find the appropriate information. The simulation verifies that the convoy is controlled within the specifications of the system. / Master of Science

A method for coordinating a homogeneous swarm of autonomous mobile robots is presented. The broadcast-based coordination scheme was developed for the Army Ant swarm—a system of small, relatively inexpensive mobile robots that can accomplish complex tasks by cooperating as a team. The primary drawback of the Army Ant system is that the absence of a central supervisor poses difficulty in the coordination and control of the agents. Our coordination scheme provides a global "group dynamic" that controls the actions of each robot using only local interactions. Coordination of the swarm is achieved with signals we call "heartbeats". Each agent broadcasts a unique heartbeat and responds to the collective behavior of all other heartbeats. We generate heartbeats with van der Pol oscillators, which are nonlinear oscillators that modify their output when coupled to other oscillators. Van der Pol oscillators have long been utilized in simulations, particularly to model rhythmic behavior in biological systems. In this application, we use the known properties of coupled van der Pol oscillators to create predictable group behavior. We emphasize the use of this controller to allow agents to simultaneously perform an action such as lifting, steering, or changing speed. For this research we synthesize a three oscillator network to show that we can achieve multi-agent coordination. An inexpensive FM communication link is used to broadcast and receive oscillator signals. We show that the network may be configured to entrain to a leader or to a common frequency. Additionally, we use our coordination scheme to provide global speed control to our three agent system. / Master of Science

A novel material transport system is presented that uses 'swarms' of small autonomous mobile robots to collectively lift and move palletized loads. The robots are relatively unsophisticated in design and have no advanced sensory or communications capability. There is no central or supervisory controller directing the robots. Each robot must be able react to its environment autonomously, yet cooperate within a team of similarly designed robots. Reactive and behavior-based principles are the basis of the system design. Although the entire material transport scenario is presented in this thesis in the context of a reactive behavior-based control architecture, emphasis is placed on developing a single behavior that allows the robots to move a loaded pallet once it has been lifted by a team of robots. Toward this goal, a centralized control scheme is derived that directs the actions of the robots while underneath a loaded pallet. It is shown that this approach produces an 'optimal' distribution of work among the robots. Alternatively, a distributed control scheme is derived that allows each robot to autonomously assist in moving a palletized load. This approach assumes a team of robots is capable of electing a leader and uses the dynamics of a caster as the basis for the development of a control law. Both the central and distributed control schemes are verified via computer simulation. / Master of Science

We design and analyze algorithms for the following two robot navigation problems: 1. TARGET SEARCH. Given a robot located at a point s in the plane, how will a robot navigate to a goal t in the presence of unknown obstacles ? 2. LOCALIZATION. A robot is "lost" in an environment with a map of its surroundings. How will it find its true location by traveling the minimum distance ? Since efficient algorithms for these two problems will make a robot completely autonomous, they have held the interest of both robotics and computer science communities. Previous work has focussed mainly on designing competitive algorithms where the robot's performance is compared to that of an omniscient adversary. For example, a competitive algorithm for target search will compare the distance traveled by the robot with the shortest path from s to t. We analyze these problems from the worst-case perspective, which, in our view, is a more appropriate measure. Our results are : 1. For target search, we analyze an algorithm called Dynamic A*. The robot continuously moves to the goal on the shortest path which it recomputes on the discovery of obstacles. A variant of this algorithm has been employed in Mars Rover prototypes. We show that D* takes O(n log n) time on planar graphs and also show a comparable bound on arbitrary graphs. Thus, our results show that D* combines the optimistic possibility of reaching the goal very soon while competing with depth-first search within a logarithmic factor. 2. For the localization problem, worst-case analysis compares the performance of the robot with the optimal decision tree over the set of possible locations. No approximation algorithm has been known. We give a polylogarithmic approximation algorithm and also show a near-tight lower bound for the grid graphs commonly used in practice. The key idea is to plan travel on a "majority-rule map" which eliminates uncertainty and permits a link to the half-Group Steiner problem. We also extend the problem to polygonal maps by discretizing the domain using novel geometric techniques.

This thesis is concerned with the applicability of model reference adaptive control to the control of robot manipulators under a wide range of configuration and payload changes, and a comparison of the performance of this technique with that of the non-adaptive schemes. The dynamic equations of robot manipulators are highly nonlinear and are difficult to determine precisely. For these reasons there is an interest in applying adaptive control techniques to robot manipulators. In this work, the detailed performance of three adaptive controllers are studied and compared with that of a non-adaptive controller, namely, the computed torque control scheme. Computer simulation results show that the use of adaptive control improves the performance of the manipulator despite changes in the payload or in the manipulator configuration. Making use of these results, a rule-based controller is developed by dividing a given manipulation task into portions where a particular adaptive control scheme, based on a specific linearized subsystem model, performs best. This strategy of selecting the proper controller during each portion of the overall task yields a performance having the least deviation from the desired trajectory during the entire length of the task.

published_or_final_version / Industrial and Manufacturing Systems Engineering / Doctoral / Doctor of Philosophy

In the design of autonomous mobile robots, databases have been used mainly to store information on the environment in which the device is to operate. For most of the models and ready systems, the database when used, is not a stand alone component in the system, rather it is only intended to keep static information on the disposition and properties of objects on the map.

Abstract not available

University of Macau / Faculty of Science and Technology / Department of Electromechanical Engineering

In conventional bilateral teleoperation, transmission delay over the Internet can potentially cause instability. The wave variable algorithm guarantees stability under varying transmission delay at the cost of poor transient performance. Adding a predictor on the master side can reduce this undesirable side-effect, but that would require a slave model. An inaccurate slave model used in the predictor as well as variations in transmission delay, both of which are likely under realistic situations, can result in steady state errors. A direct drift control algorithm is used to drive this error to zero regardless of the source of error. A semi-adaptive predictor that can distinguish between free space and rigid contact environment is used to provide more accurate force feedback on the master side. A full adaptive predictor is also used that estimates the slave environment parameters using recursive least squares with a forgetting factor. This research presents the experimental results and evaluations of the wave variable based methods under a realistic operation environment using a real master and slave. The effectiveness of this algorithm is fully evaluated using human subjects with no previous experience in haptics. Three algorithms are tested using PHANTOM brand haptic devices as master and slave: conventional bilateral teleoperation with no transmission delay as control, wave variable teleoperation with approximately 200 ms transmission delay one way, and wave variables with adaptive predictor and direct drift control with approximately 200 ms transmission delay one way. For each algorithm the human subjects are asked to perform three simple tasks: use the master to force the slave to track a reference trajectory in free space with the least amount of error, identify a contour surface on the slave side as accurately as possible using only haptic information from the master, and navigate a simple maze on the slave side in the least amount of time using haptic information from the master.