At the heart of the scanner is a range-finder that uses a laser beam to measure distance. The range-finder emits continuous laser energy concentrated in a narrow beam which reflects off the mirror and travels into the world much like the beam from a lighthouse. Two motors orient the mirror; one motor continuously rotates the mirror, while the other is used to make it "nod". The result is a spherical scan pattern that offers a horizontal field of view of nearly 360 degrees and a vertical field of view of over 70 degrees. When the beam hits an object, some of the energy is reflected back to the range-finder. The scanner is based on the principle of phase-based distance measurement: The range to the object is computed by comparing the phase of the emitted signal and the returned signal. Phase difference is then used to derive range.
The spherical laser scanner is used in Carnegie Mellon's Dante Explorer, an eight-legged walking robot, to generate terrain information surrounding the robot. This terrain information is used for two purposes. First, the data is used in a 3-D graphical user interface to provide information about terrain geometry under and around Dante for teleoperation and monitoring purposes. Second, the terrain data is used to autonomously determine leg lift height, body clearance height, and body attitude for traversing uneven and boulder strewn terrain. The figures below show data acquired from the scanner during Dante's mission to Mount Erebus, Antarctica.
Figure 2. This depth image (39x360 degree field of view) is an unfolded ring of points cast by the laser around the robot. Brighter points are farther away from the sensor. Scanner data taken with Dante standing on the rim of Mount Erebus
Figure 3: Elevation map generated from depth image.
Other applications can benefit from the use of this sensor. Omni-directional robots, in particular, benefit from the terrain information provided by the scanner. Their mobility is no longer constrained by the limited knowledge of the environment provided by traditional narrow field of view sensors. In addition to terrain mapping, the spherical laser scanner can be used for safeguarding a mobile robot. Traditional safeguarding sensors suffer from blind spots, or are only able to detect objects at a certain height. In contrast, this sensor creates a complete shroud around the robot while sensing terrain. The scannerŐs large field of view also permits better navigation and position estimation. More navigational features can be tracked, and for longer periods of time, providing more information from which position can be determined.
Point of Contact:
Jay West,
John Bares
Robotics Institute
Carnegie Mellon University
Pittsburgh, PA 15213
412-268-7091
bares@frc2.frc.ri.cmu.edu
Telerobotics Program
page
Please email the site webmaster
with any comments, criticisms or corrections
for this page.
Maintained by: Dave Lavery
Last updated: May 10, 1996