This paper discusses the importance and realizability of the "high-level programmability" concept for wheeled mobile robots. A new high-level mobile robot language, called motion description language (MDL), is proposed. This language has a strong and stable theoretical foundation. The Java-based object-oriented MDL implements the structured robot geometry into its class hierarchy perfectly. The language MDL is not only "a" mobile robot language, but is a strong candidate for "the standard" mobile robot language. This innovation will thrust the mobile robotics field forward to meet the challenges of the new century head on.

This paper proposes a new "heterogeneous" two-dimensional (2D) transformation groupto solve motion analysis/planning problems in robotics. In this theory, we use a 3/spl times/1 matrix to represent a transformation as opposed to a 3/spl times/3 matrix in the homogeneous formulation. First, this theory is as capable as the homogeneous theory, Because of the minimal size, its implementation requires less memory space and less computation time, and it does not have the rotational matrix inconsistency problem. Furthermore, the raw rotation angle /spl theta/ is more useful than the trigonometric values, cos /spl theta/ and sin /spl theta/, in the homogeneous transformations. This paper also discusses how to apply the groupto solve problems related to motion analysis/planning, trajectory generation, and others. This heterogeneous formulation has been successfully implemented in the MML software system for the autonomous mobile robot Yamabico-11 developed at the Naval Postgraduate School.

We investigate the problem of finding an algorithm for the movement of a vehicle under the nonholonomic constraint to track a given directed straight line without allowing any spinning motion. We propose a new principle of computing the derivative of path curvature as a linear combination of the current vehicle path curvature, vehicle orientation error, and positional error. We call this function the steering function. By linearization we find an optimal selection of parameters for critically damped motions and obtain a single parameter, /spl sigma/, for tracking, which we call smoothness. The uniform asymptotic stability of the feedback rule is proved through a Lyapunov function. Numerous simulation results as well as experimental results obtained on the autonomous robot Yamabico at the Naval Postgraduate School are included to show the effectiveness of this method.

Most existing real-time control systems use ad hoc static priority scheduling methods, in spite of the fact that the rate monotonic scheduling algorithm was proved to be the optimal static priority scheduling algorithm over 20 years ago. In this paper, we discuss a task library we are using for the real-time control of autonomous robots. The task library comprises a preemptive rate-monotonic scheduler which provides guaranteed optimal scheduling when certain conditions of processor utilization are met. The task library has been implemented as a collection of lightweight threads, which operate entirely in user-space for maximum efficiency. We show the performance advantages resulting from the reduced overhead of this approach, compared with commercial operating systems. The task system is robust, extensible, and portable, and has been successfully used to control the autonomous mobile robot Yamabico-11 developed at the Naval Postgraduate School.

This paper develops a fundamental theory of two dimensional wheeled vehicle kinematics. The author first analyzes rigid body robot 2D motions so that a mixture of translational and rotational motions is considered to be a purely rotational motion with its center. Next the author defines the class of tangential motions. Motions in this class are relatively easy to execute by vehicles normally available. A curve with discontinuous curvature is not appropriate for tangential motions for any vehicle architecture. The most important finding in this paper is that any general motion is embodied by an SS type vehicle which does not use any special tires or special complex mechanisms.>

This paper describes a solution to the problem of planning a leg motion for a six legged robot when smooth versatile motion commands of its body are given. The well-known wave gait for a longitudinally symmetric robot is generalized to solve the omnidirectional gait planning problem for a radially symmetric six legged robot. The algorithm can handle any combination of translational and rotational motions for a variable crab angle condition as long as the rates of speed and crab angle are moderate. Guaranteeing the maximum duty factor for any given commanded motion, this solution optimizes the stability margin of the robot. The foot trajectory planning algorithm dynamically generates a smooth foot trajectory as a function of the instantaneous body motions.>

A few fundamental concepts useful for building a high-level mobile robot language are discussed. The method of describing a vehicle path by a sequence of configurations, the use of coordination transformation (or composition of configurations), and the concept of symmetric configurations are examined, with programming examples and the resultant paths. These concepts are robot independent and can be applied to the kernel of any high-level mobile robot language in the future. These functions have already been successfully implemented in the Model-based Mobile Robot Language (MML).>

Proposes a stable control rule to find a reasonable target linear and rotational velocities ( nu , omega )/sup t/. The stability of the rule is proved through the use of a Lyapunov function. The rule contains three parameters, K/sub x/, K/sub y/ and K/sub theta /. Although any set of positive parameters makes the system stable, a condition on the parameters for the system being critically damped for a small disturbance is obtained through linearizing the system's differential equation. This method was successfully implemented on the autonomous mobile robot Yamabico-11. Experimental results obtained turn out to be close to the results with the velocity/acceleration limiter.>

A stable tracking control rule is proposed for nonholonomic vehicles. The stability of the rule is proved through the use of a Liapunov function. Inputs to the vehicle are a reference posture (x/sub r/, y/sub r/, theta /sub r/)/sup t/ and reference velocities ( nu /sub r/, omega /sub r/)/sup t/. The major objective of this study is to propose a control rule to find reasonable target linear and rotational velocities ( nu , omega )/sup t/. Linearizing the system's differential equation is useful for deciding parameters for critical dumping for a small disturbance. In order to avoid slippage, a velocity/acceleration limitation scheme is introduced. Several simulation results are presented with or without the velocity/acceleration limiter. The control rule and limiting method proposed are robot independent and hence can be applied to various kinds of mobile robots with a dead reckoning ability. This method was implemented on the autonomous mobile robot Yamabico-11. Experimental results obtained are close to the results with the velocity/acceleration limiter.>

Two cost functions of paths for smoothness are defined: path curvature and the derivative of path curvature. Through these definitions, two classes of simple paths are obtained, namely the set of circular arcs and the set of cubic spirals. A cubic spiral is a curve whose tangent direction is described by a cubic function of path distance s. These sets of simple paths are used for solving path planning problems of symmetric posture (position and orientation) pairs. For a nonsymmetric posture pair, two simple paths are used as a solution, based on the fact that the locus of split postures is a circle or a straight line. A posture q is said to be a split posture of a pair (p/sub 1/,p/sub 2/) of postures, if p/sub 1/ and q are symmetric and so are q and p/sub 2/. The resultant solutions are smoother than those obtained using clothoid curves. This algorithm has been successfully implemented on the autonomous mobile robot Yamabico-11.>

An idea of planning safer paths for robot motion is outlined. Use is made of algebraic cost functions of clearance to obstacles. A parameter k, safety factor, controls the balance between safety and length of the resultant paths. Analytical solutions are given for a polygon world by using calculus of variations. Results are reported about simple regions only. Another fundamental idea of the 'equivalence classes' of paths is introduced.>

The authors present a locomotion control method for autonomous vehicles. The main difficulties in controlling an autonomous vehicle lie in the fact that vehicles usually have three degrees of freedom in position and orientation in spite of having only two degrees of freedom for motion control. To use any find of path for vehicle navigation, the authors control a vehicle in a tracking mode. Decomposition of error between the reference posture and the current posture makes control of speed and steering possible. The locomotion control system works as a flexible interface between the path planner and the motor-wheel system.>

A path-description method that uses a sequence of straight lines with coordinate transformations is presented. This concept is hardware-independent and may be applied to any kind of vehicle. A local vehicle-trajectory-control algorithm is used both for determining the transient portions of each vehicle trajectory and for keeping the vehicle moving along a given directed straight line. A vehicle-control command-system, MITCHI, is one realization of the idea and is introduced. The MITCHI command-system has been implemented on self-contained Yamabico mobile robots. Several design features, such as status transition, fast/slow command execution, and velocity control, as well as simulation results, are described.>