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Mobile Robot Navigation

Mobile robot navigation using range measuring scanning lasers allow an indoor vehicle to keep track of its position and avoid collisions using the same sensor. As the laser continouosly scans the environment the vehicle can adjust its plans to avoid temporary obstacles.

The image above shows a range scan taken with a scanning laser on a vehicle. This particular laser makes a 270 degree scan with 450 measurements in 125ms. Each dot in the image represents one measurement with the laser at position 0,0. The scale is in meters and the gray space shows the "free space" verified by the laser.

Mobile Robotics does not sell a complete mobile robot, rather we seek to cooperate with manufacturers (or users) of existing or new vehicles. Our part in such a cooperation would mainly be the navigation and control system, although we can also participate in the electrical and mechanical design if needed.

Navigation

Navigation using a range measuring laser can be done in either of two ways:

• Using a predefined map. A drawing of the building is used to teach the robot of its environment.
• Exploration. The robot is allowed to explore the environment and build its own map. Usually by having a human operator driving it around the relevant areas while the robot builds the map. Changes in the environment can optionally be incorporated in the map automatically by the robot.

Combinations of the two methods are of course also possible.

Destinations and allowed paths can then be added to the map. The exact design of the system depending upon the intended tasks.

Collision Avoidance and Dynamic Planning

The scanning range measuring laser can also be used for collision avoidance. Depending on the requirements it can be used for:

• A simple emergency stop.
• Temporary stop until the obstacle moves away.
• The vehicle can attempt to move around an obstacle.
• If it is not possible to move around the obstacle, the vehicle can replan its route and take another path, maybe through another room.

The competition

The main competing technologies usually mentioned are GPS and laser-scanner/reflector-beacon systems.

• GPS is a very useful system for outdoors use, and using dGPS with local reference stations give rather good precision today. However GPS is not useful indoors, and can be problematic in forests and other areas where the sky is obscured. Also high precision GPS is dependent on the good will of the US government.
• Laser-scanner/reflector-beacon systems uses a scanning laser (usually not a range measuring laser) to measure angles to retroreflective beacons mounted in the workspace. This gives a simple and reliable system. However it relies on the beacons being placed in advance and their positions calibrated with high accuracy.

Our approach using a rangemeasuring scanning laser does not require any preparation of the environment before operation. It has the added benefit that the laser can also be used for collision avoidance at the same time as it is used for navigation. This allows more flexible pathplanning.