Data processing: vehicles – navigation – and relative location – Relative location – Collision avoidance
Reexamination Certificate
2002-06-20
2004-08-31
Nguyen, Tan Q. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Relative location
Collision avoidance
C701S120000, C340S961000
Reexamination Certificate
active
06785610
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a guidance method and system suitable for use with autonomously guided and man-in-the-loop guided vehicles where the presence of obstacles and/or threats must be considered in guiding the vehicle to a destination.
BACKGROUND OF THE INVENTION
During the travel of an autonomously guided or man-in-the-loop guided vehicle towards a destination, there may be obstacles, impediments and/or threats present in the path of travel which must be avoided which otherwise would prevent the vehicle from reaching its destination or would cause damage to the vehicle. Various guidance augmentation concepts have been suggested for avoiding obstacles, operational boundaries, and/or threats. Generally, these concepts have been developed with the approach such that if no impediments are present, then the travel of the guided vehicle is not changed. However, if impediments are present, these concepts provide the guidance system with directions diverting the vehicle around the impediment to allow the vehicle to proceed to the desired destination.
These avoidance methods have been used, for instance, in the field of tactical missiles. There, during the launch, flight, and intercept phases of flight, there are numerous constraints on the guidance system that result from obstacles or operational limitations that must be accommodated in addition to the requirement that the missile be guided so as to hit the target. Some of these constraints include maneuverability constraints based on dynamic, kinematic, and/or mechanical constraints of the vehicle; operational envelope constraints such as maximum altitude or minimum altitude limitations on the vehicle; obstacle constraints, such as friendly airborne assets; and, threat constraints such as enemy assets which may target the vehicle in an attempt to destroy the vehicle. All of these factors are significant considerations in shaping the trajectory of the missile during its flight. Various textbook guidance methods that have been proposed will be briefly discussed below. These methods, however, do not take into account all of those constraints and therefore would benefit from augmentation in some form prior to implementation in a real world application.
A first known method for accommodating guidance constraints is known as a waypoint method. This guidance method uses waypoints or intermediate points along a trajectory. One such concept is described in the article “Obstacle-Avoidance Automatic Guidance: A Concept Development Study” by Victor H. L. Cheng, published in
AIAA Journal
, Paper Number 88-4189-CP, 1988. The basic idea behind the waypoint concept is that if an obstacle, operational boundary, or threat is perceived, a set of waypoints is constructed such that an avoidance path can be achieved. This concept is illustrated in FIG.
1
. As shown in
FIG. 1
, a vehicle
10
can be navigated from a starting point
110
to a destination
140
via waypoints
120
and
130
. To generate an efficient trajectory, the waypoints must be selected carefully. The waypoint method is suitable for applications where the impediments are stationary and are not dynamic.
Another known avoidance method is to use optimal guidance strategies to steer a vehicle around obstacles or boundaries. One such approach is described in the article “Control Theoretic Approach to Air Traffic Conflict Resolution”,
AIAA Journal
, Paper Number 93-3832-CP, 1993. This method involves the definition of a cost function that measures the quality or goodness of a particular trajectory and which optimizes the cost function over a set of possible trajectories. The construction of the cost function is generally based on the dynamics or relative motion of the obstacles, operational boundaries, and/or threats to the missile. Generally, this method must be solved numerically and can require large amounts of real time processing to solve. Also, the addition of multiple obstacles, operational boundaries, and/or dynamic threats in the operation or flight significantly increases the complexity of the cost function and thus further increases processing requirements.
Another avoidance method relies upon mathematical representations of potential fields. In this approach, sources, which are potential field elements that provide a mathematically repelling force, can be used individually or as a surface to provide a range dependent force in order to push the missile guidance away from the obstacle. Sources have a unique quality in that the amount of repelling force is inversely proportional to the distance from the source. For example, a missile that is close to a source will be pushed away with greater force than a missile that is far from the source. Because of this range dependent characteristic, and because sources are computationally efficient to use, sources can be used in a large number of avoidance applications. However, source methods have a drawback that, if they are not modified, they will affect the guidance commands by directing the vehicle away from the obstacle throughout the trajectory of the vehicle because the source has an infinite range of influence.
A modification to the source approach adds a range boundary beyond which the source will not affect the vehicle. One such approach is described in “Generation of Conflict Resolution Maneuvers for Air Traffic Management”, by Claire, et al.,
IEEE Journal
, Paper No. 0/7803-4119-8, 1997. In this approach, the method will push the guidance command away from the obstacle only when the missile is inside the range boundary and will not affect the vehicle when it is outside the boundary. One drawback to this method is that the guidance command is mathematically discontinuous across the boundary. Discontinuous commands are undesirable because they can cause instabilities in the guidance solution in the circumstance when multiple obstacles, boundaries, or threats are encountered. Another drawback to this method is in regard to threat avoidance. Specifically, this method will tend to direct a vehicle along the direction of the velocity of the threat in order to avoid the threat. However, if the threat has sufficient velocity to overtake the vehicle and the source potential is located on the vehicle, the threat can nevertheless have a successful intercept. The Claire, et al. article also mentions the use of vortex potential field elements in the construction of an avoidance solution. Vortex elements are essentially planar rotation elements that push the field in a rotational direction about a point. Vortex elements are not easily adapted to multi-dimensional spaces above two dimensions, because they are two-dimensional elements. To apply a vortex element in a three-dimensional space would require knowledge of the direction which the vortex would act about. In a dynamic situation, the addition of a vortex element would limit the number of evasive solutions and would hinder the performance of an avoidance algorithm. Nevertheless, two-dimensional applications of vortex elements can be appropriate in circumstances such as traffic management applications where the flow of vehicles conforms to pre-established guidelines.
Another known avoidance method employs specific geometric boundary shapes to describe how an avoidance maneuver is to be performed. These geometric methods use the surface tangents from the geometric boundary to provide a direction of avoidance for the avoidance maneuver. One such avoidance approach is described in “A Self-Organizational Approach for Resolving Air Traffic Conflicts”, pages 239-254, by Martin S. Eby, published in
The Lincoln Laboratory Journal
, Volume 7, No. 2, 1994. Such an approach is illustrated in
FIG. 2
, where a vehicle
10
is traveling in direction of arrow D and must avoid obstacle plane
200
. A geometric boundary shape
210
is defined around obstacle plane
200
at a radius r
D
which is the desired miss distance. In the case where the path of the subject plane
10
to its destination
220
intersects the geometric boundary shape
210
, an avoidance maneuver i
Baker Brian C.
Paynter Scott J.
Lockheed Martin Corporation
Nguyen Tan Q.
Sadacca Stephen S.
Sidley Austin Brown & Wood LLP
Tran Dalena
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