Se-Hung Kwak

An experimental comparison of hierarchical and subsumption software architectures for control of an autonomous underwater vehicle

A three-level hybrid architecture is used to model both a hierarchical and a subsumption controller for an autonomous underwater vehicle (AUV). The hierarchical model uses a backward chaining language (PROLOG) while the subsumption model uses a forward chaining language (CLIPS). The details of the backward chaining hierarchical implementation of the strategic level of mission control are first presented. This is followed by a similar description of the functionally equivalent subsumption controller. Experimental results and the advantages and disadvantages of each approach are discussed. CLIPS and PROLOG ran virtually even in terms of execution time. Also, the total run time of the experiment was dominated by the graphical simulator. A repeat of the experiment in which the controllers were decoupled from the simulator resulted in execution times between three and four seconds. This reinforces the view of PROLOG and CLIPS as viable language alternatives for the mission control of complex systems. However, PROLOG is the more concise of the two languages and is easier to read.<<ETX>>

Three-dimensional visualization of mission planning and control for the NPS autonomous underwater vehicle

The Naval Postgraduate School (NPS) is constructing a small autonomous underwater vehicle (AUV) with an onboard mission control computer. The mission controller software for this vehicle is a knowledge-based artificial intelligence (AI) system requiring thorough analysis and testing before the AUV is operational. The manner in which rapid prototyping of this software has been demonstrated by developing a controller code on a LISP machine and using an Ethernet link with a graphics workstation to simulate the controllers environment is discussed. The development of a testing simulator using a knowledge engineering environment (KEE) expert system shell that examines AUV controller subsystems and vehicle models before integrating them with the full AUV for its test environment missions is discussed. This AUV simulator utilizes an interactive mission planning control console and is fully autonomous once initial parameters are selected. >

Tactical/execution level coordination for hover control of the NPS AUV II using onboard sonar servoing

This paper describes work with the NPS AUV II vehicle in the further development of the execution level software to incorporate hover control behavior in the NPS hover tank. Of particular interest is the use of the ST 1000 and ST 725 high frequency sonars to provide data about the environment. Thus positioning can be accomplished without the use of beacons. Motion behaviors may be instituted that include diving and pitch control under thruster power; heading control at zero speed; lateral and longitudinal positioning, as well as the automatic initiation of filters as needed when a new target is found. A simple task level language that will be used to direct tactical level output to a port in communication with the execution level software is given.

Rule-based motion coordination for a hexapod walking machine

This paper is concerned with rule-based coordination of motion for rough-terrain locomotion by a hexapod walking machine. The logic for generating leg commands is written in Prolog while the simulation of the terrain and of the vehicle kinematics, as well as low-level on-board computer functions, are written in extended Common Lisp. It is found that this approach results in code that is much easier to understand and modify than previous motion coordination programs written in Pascal. We believe that the motion coordination rule set included in this paper results in better adaptation of walking machine leg sequencing to terrain constraints than any previously published means.

Incorporation of global positioning system into autonomous underwater vehicle navigation

The authors provide a brief introduction to the global positioning system (GPS). In addition, the issues of incorporating GPS into autonomous underwater vehicles (AUVs) navigation are explored. Test results conducted on a stationary GPS receiver are analyzed for suitability in AUV navigation. These results meet the minimum criteria of AUV employment as established. It was demonstrated that small, low-cost, low-power GPS receivers, in general, are suitable for AUV applications. In addition, a system design that the Naval Postgraduate School is now pursuing to incorporate GPS into AUV navigation is presented.<<ETX>>