Data processing: vehicles – navigation – and relative location – Navigation – Employing position determining equipment
Reexamination Certificate
2000-10-13
2002-08-27
Cuchlinski, Jr., William A. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Navigation
Employing position determining equipment
C701S300000
Reexamination Certificate
active
06442476
ABSTRACT:
TECHNICAL FIELD
The present invention relates to sensing and tracking the position of objects in an environment, particularly but not exclusively an environment where the features of the environment are not well controlled or predefined.
BACKGROUND ART
In order to undertake tasks in an environment that is known or unknown a priori, systems controlling machinery which must move in or through the environment, for example mining equipment, must have knowledge of the absolute or true position and orientation of the machinery in relation to the surroundings of the machinery. For some instances of controlled operation whereby elements of the control are exercised by a human operator and for autonomous operation, a control system must be equipped with a means to determine the absolute or true position and orientation of the machinery and the complete relationship of the machinery to the surroundings it is operating in.
The environment may be composed of natural or artificial features and may be complex thus possessing little or no regular structure. In addition, some features in the surroundings may be in motion relative to other features nearby.
Many methods have been disclosed, which enable a machine to navigate (determine its position and control its position) by using artificial features in a predetermined environment. For example, U.S. Pat. No. 4,831,539 to Hagenbuch discloses a system for identifying the location of a vehicle using distinctive signposts located at predefined positions. U.S. Pat. No. 4,811,228 to Hyyppa and U.S. Pat. No. 5,367,458 to Roberts utilise predefined target or signpost devices which are identified in some way by the vehicle to provide location information.
U.S. Pat. No. 5,051,906 to Evans, Jr., et al discloses an apparatus and method which provides for the determination of a vehicle's orientation and position in an environment, such as a hallway, from an image of a retroreflective ceiling feature.
These systems are inherently limited in their application by the requirement to determine the environment prior to operation of the machine and in many cases install artificial features which are used to determine the position of the machine within the defined environment. For example, it may be possible in a warehouse environment to provide a well controlled environment without unexpected features—however, this is much more difficult in a changing environment such as an open cut mine or underground mine, where the shape and location of objects are inherently in a state of change.
Other methods which enable a machine to navigate using inertial navigation systems have been disclosed. The operation of inertial navigation systems is usually based on assumptions about the reference frame—for example the rotation and revolution of the earth. Double integration of the acceleration determined by the navigation system often results in unacceptable drift in the calculated position determined by the inertial navigation system. Also, repeated changes in acceleration and repeated movement about a point tend to produce cumulative errors in inertial systems, as the next position assessment is based upon the previously determined value.
U.S. Pat. No. 4,626,995 to Lofgren et al discloses an arrangement in which a computer determines the Cartesian coordinates of a single light source through a camera attached to a vehicle. This arrangement requires that the height of the light source and the height of the sensor be predetermined. U.S. Pat. No. 4,858,132 to Holmquist discloses a system in which a computer determines the bearing of a composite light source through a camera attached to a vehicle, and from the apparent spacing between the elements of the lights determines bearing and range.
U.S. Pat. No. 5,483,455 discloses an arrangement in which targets located at predefined positions with respect to a base reference frame are detected and the position of a vehicle relative to the target determined. Location of the vehicle relative to the base reference frame is determined from the position of the vehicle relative to the known target.
It has been disclosed in the prior art that laser scanners may be used to determine position on a known path relative to a defined set of fixed reference points. In one embodiment, a laser or light transmitter scans a volume in which are located characteristic features consisting of reflectors intended to direct the emitted light back to a sensor located with the transmitter. The prior art also teaches the use of laser scanners to determine position relative to natural features and to memorise the position of such features in a two dimensional plane only in order to navigate between them.
It is also disclosed in the prior art to use scanning laser rangefinders to position equipment 2-dimensionally in a constrained environment such as a tunnel. Such techniques, known as wall following, are used for obstacle detection and the avoidance of collisions with fixed features such as walls and other obstacles. Such techniques may also be used to fuse data referenced to a known local environment with data from a dead reckoning system such as an inertial navigation system (INS) by periodically resetting the INS see “Experiments In Autonomous Underground Guidance”, Scheding S., Nebot E., Stevens M., Durrant-Whyte H., Roberts J., Corke P., Cunningham J., Cook B; in IEEE Conference on Robotics and Automation, Albuquerque 1997.
In “An Experiment in Guidance and Navigation of an Autonomous Robot Vehicle”, Bianche IEEE Transactions on Robotics and Automation, Vol 7 , No 2, April 1991, an experimental vehicle designed to operate autonomously within a structured office or factory environment is discussed. The disclosed device uses an odometry and steering angle based primary system, with a laser rangefinder used to correct this with respect to a predetermined 2-D map of the environment, and remotely generated path plans.
Methods have been disclosed also, which enable a machine to avoid collision with features in its environment, obstacle avoidance, that is, to determine its position and control its position relative to those features in such a manner as to avoid contact with the features. For example, U.S. Pat. No. 5,758,298 to Guldner discloses an autonomous navigation system for a mobile robot or manipulator. In the description of this patent all operations are performed on the local navigation level in the robot coordinate system. U.S. Pat. No. 4,954,962 to Evans, Jr., et al discloses a navigation control system of a robot which inputs data from a vision system and infers therefrom data relating to the configuration of the environment which lies in front of the robot so that the robot may navigate to a desired point without collision with obstacles or features in its environment.
Obstacle avoidance or collision avoidance systems are not required to determine and track the true position and orientation of the machine within the defined environment and therefore cannot be used for navigation and guidance except in the very local sense of avoiding collisions.
A plurality of methods have been disclosed involving the use of methods such as predetermined or installed reference points, stored maps of the local environment, infrastructure such as the Global Positioning System (GPS) or local radio navigation systems and systems such as inertial navigation systems. All of these methods use infrastructure which may be integral with the immediate environment or external to the immediate environment and must exist or be installed.
It is an object of the present invention to provide a location and navigation system which will enable a machine to operate over an extended area knowing its true location in that area which does not require the use of a predetermined reference frame or network of reference features, and is not reliant upon INS or GPS or similar sensing arrangements.
SUMMARY OF INVENTION
According to a first aspect, the present invention provides a method for determining the position of a movable object, including the steps of:
(a) initiating the process of de
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