Planning the path of an autonomous, agile vehicle in a dynamic environment is a very complex problem, especially when the vehicle is required to use its full maneuvering capabilities. Recent efforts aimed at using randomized algorithms for planning the path of kinematic and dynamic vehicles have demonstrated considerable potential for implementation on future autonomous platforms. This paper builds upon these efforts by proposing a randomized path planning architecture for dynamical systems in the presence of fixed and moving obstacles. This architecture addresses the dynamic constraints on the vehicle's motion, and it provides at the same time a consistent decoupling between low-level control and motion planning. The path planning algorithm retains the convergence properties of its kinematic counterparts. System safety is also addressed in the face of finite computation times by analyzing the behavior of the algorithm when the available onboard computation resources are limited, and the planning must be performed in real time. The proposed algorithm can be applied to vehicles whose dynamics are described either by ordinary differential equations or by higher-level, hybrid representations. Simulation examples involving a ground robot and a small autonomous helicopter are presented and discussed.

/pdf/real-time-motion-planning-for-agile-autonomous-vehicles-4l6obiq3kn.pdf

Real-Time Motion Planning for Agile Autonomous Vehicles

Planning the path of an autonomous, agile vehicle in a dynamic environment is a very complex problem, especially when the vehicle is required to use its full maneuvering capabilities. Recent efforts aimed at using randomized algorithms for planning the path of kinematic and dynamic vehicles have demonstrated considerable potential for implementation on future autonomous platforms. This paper builds upon these efforts by proposing a randomized motion planning architecture for dynamical systems in the presence of fixed and moving obstacles. This architecture addresses the dynamic constraints on the vehicle's motion, and it provides at the same time a consistent decoupling between low-level control and motion planning. Simulation examples involving a ground robot and a small autonomous helicopter, are presented and discussed.

/pdf/real-time-motion-planning-for-agile-autonomous-vehicles-4eeud9gl71.pdf

Real-time motion planning for agile autonomous vehicles

Shape morphing of aircraft wing: Status and challenges

The operation of an autonomous vehicle in an unknown, dynamic environment is a very complex problem, especially when the vehicle is required to use its full maneuvering capabilities, and to react in real time to changes in the operational environment. A possible approach to reduce the computational complexity of the motion planning problem for a nonlinear, high dimensional system, is based on a quantization of the system dynamics, leading to a control architecture based on a hybrid automaton, the states of which represent feasible trajectory primitives for the vehicle. The paper focuses on the feasibility of this approach, in the presence of disturbances and uncertainties in the plant and/or in the environment: the structure of a robust hybrid automaton is defined and its properties are analyzed. In particular, we address the issues of well-posedness, consistency and reachability. For the case of autonomous vehicles, we provide sufficient conditions to guarantee reachability of the automaton.

/pdf/robust-hybrid-control-for-autonomous-vehicle-motion-planning-3jwg5yiuul.pdf

Robust hybrid control for autonomous vehicle motion planning

A review on static and dynamic shape control of structures by piezoelectric actuation

A game-matrix approach has been developed to generate intelligent maneuvering decisions for low-flying aircraft during one-on-one air combat over hilly terrain. The decisions are made by comparing scores based on the predicted orientation, range, velocity, and terrain clearance for various maneuver combinations of both aircraft. A computer program implements the decision process in real time and computes the state of the aircraft employing the selected maneuvers. Predicted states are obtained by numerically integrating the dynamic equations. The program has been installed and demonstrated at the NASA Ames vertical motion simulator to provide an automated adversary for manned helicopter combat simulations. A stand-alone version of the program, in which the decisions of both combatants are generated by the computer, has also been prepared for nonpiloted simulations. Sample trajectories show that this new automated maneuvering logic generates some of the tactics employed by experienced pilots in combat flight tests. Whereas the current application applies to helicopter combat, the program can be used for fixed-wing aircraft by replacing those subroutines that provide the aircraft capabilities.

Game theory for automated maneuvering during air-to-air combat

A theoretical method was developed, and experimentally validated, to control the static shape of flexible struc-tures by employing internal translational actuators. A finite element model of the structure, without the actuatorspresent, is employed to obtain the multiple-input, multiple-output control-system gain matrices for actuator-loadcontrol as well as actuator-displacement control. The method is applied to the quasistatic problem of maintainingan optimum-wing cross section during various transonic-cruise flight conditions to obtain significant reductionsin the shock-induced drag. Only small, potentially achievable, adaptive modifications to the profile are required.The adaptive-wing concept employs actuators as truss elements of active ribs to reshape the wing cross section bydeforming the structure. Finite element analyses of an adaptive-rib model verify the controlled-structure theory.Experiments on the model were conducted, and arbitrarily selected deformed shapes were accurately achieved.

/pdf/static-shape-control-for-adaptive-wings-14nln4uwsy.pdf

Static shape control for adaptive wings

A game-matrix approach is used to generate intelligent maneuvering decisions for nap-of-the-earth one-on-one helicopter air combat over hilly terrain. Decisions are made in real time using the AUTOMAN program by comparing scores based upon the predicted orientation, range, velocity, and terrain clearance for various maneuver combinations of both aircraft. The program has been demonstrated at the NASA Ames Vertical Motion Simulator, providing manned helicopter simulations. Sample trajectories from a stand-alone version of the program designed for nonpiloted simulations demonstrate that the present automated maneuvering logic generates some of the tactics employed by experienced pilots in flight tests. The program also has application to fixed-wing aircraft simulations.

Automated maneuvering decisions for air-to-air combat

An apparatus and method control the shape of a structure (6) with one or more surfaces (8, 9) and internal actuators (11). A plurality of translational actuators (11) are capable of extending and contracting. The structure (6) can have any number of controllable surfaces (8, 9) which are controlled by computing the actuator strokes or loads required for achieving specified surface deflections. There are two methods for accomplishing this control. In the actuator stroke-control method, the surface deflections, or deflection errors for closed-loop control, are multiplied by a stroke-control gain matrix which is a function of the properties of the structure with the actuators absent. In the actuator load-control method, the surface deflections, or deflection errors for closed-loop control, are multiplied by a load-control gain matrix which is a function of the properties of the structure with the actuators absent. In either of these methods, different control gain matrices can be developed depending on whether it is desired to minimize actuator loads or surface shape errors.

Apparatus and method for controlling the shape of structures

Exact solutions to the dynamic equations for a free-rotating, flexibly connected doublemass system, neglecting the central force field, have been investigated to ascertain the nonlinear effects on the system dynamics. The results are expressed in terms of the canonical forms of elliptic integrals. Numerical results illustrate the radial vibration waveform and the frequency variation with rotational speed. The nonlinear effects become pronounced in systems where the ratio of the rotational speed to nonrotating flexible-body frequency is high; however, for practical space-station applications, the character of the results can be closely predicted by the application of linearized solutions for oscillation amplitudes as large as 0.1 of the radius. It is also shown that the upper limit of the rotational velocity is equal to the nonrotating natural frequency of the system.

Fred Austin

Papers

Game theory for automated maneuvering during air-to-air combat

Static shape control for adaptive wings

Automated maneuvering decisions for air-to-air combat

Apparatus and method for controlling the shape of structures

Nonlinear dynamics of a free rotating flexibly connected double-massspace station.