The present invention relates to autonomous navigation apparatus for a mobile vehicle, such as a robot, truck, automobile, boat, airplane or space ship, which vehicle is arranged to move in a forward (or rearward) direction within an environment that is delimited, at least in part, by a boundary, such as a wall, curb, ocean buoys or the like.
For example, in the case of a robot, which may be designed to deliver mail within an office building, move boxes in a warehouse or perform other tasks, the robot moves in a forward and rearward direction within the boundaries set by walls, fixtures, furniture and the like.
In the case of a truck, this vehicle may be required to move either forward or backward on a ramp, delimited on one side by a loading platform, and then to back toward the loading platform and to stop just prior to contact.
A truck, or an automobile, is also required to drive on a road which is delimited on the left side by a painted center line or barrier strip and on the right side by a painted line, curb, wall or the like.
In the case of a boat, this mobile vehicle is required to stay within water traffic lanes and, upon approach to a harbor, its movement is delimited by the harbor shore line defined by docks, cement abutments and the like.
In the case of an airplane, this "vehicle" is required to move about or taxi on the ground within an area delimited by the edges of runways, taxiways and ramps, and is even limited in its movements while in the air.
While most applications of the present invention concern three degrees of freedom--that is, movement in a horizontal plane defined by orthogonal coordinates such as Cartesian (X Y) coordinates and yaw (angle of rotation about a third (e.g., Z) orthogonal coordinate)--the invention is also applicable to an airplane or a space ship which operates with six degrees of freedom--that is, three dimensional space coordinates plus three motion coordinates (roll, pitch and yaw). For example, the invention may be applied to a small, cylindrical robot arranged to move in a gravity-free environment within an enclosed space defined by the walls of a large space ship. This robot must be controlled to move from one desired position to another within the three dimensional space and to orient itself at each position.
The invention will be described herein with reference to a robot designed to move in two dimensions along hallways within a building and to rotate about its vertical axis; however, it will be readily apparent that the invention is applicable also to other types of mobile vehicles as noted above.
Mobile robots used in the delivery of mail, for example, have relied for navigation on devices external to the robot, such as active beacons and/or bar code targets, for determining the instantaneous location of the robot and maintaining calibration. In addition to using these external devices, the wheels of some mobile robots have been equipped with high precision wheel odometers to keep track of movement from one position to another.
The disadvantages associated with these navigation systems may be categorized as both qualitative and quantitative. Systems which use external bar code targets require a large number of these targets in the enclosed environment, each of which must be precisely aligned in height, etc. for interrogation by the target readers located on the robot. Position accuracy provided by systems based on active beacons is inadequate for some applications. High precision wheel odometry systems are expensive to design, manufacture and maintain.