Where am I? Sensors and Methods for Mobile Robot Positioning

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164 Part II Systems and Methods for Mobile Robot Positioning Y Figure 6.16: The TRC Beacon Navigation System calculates position and heading based on ranges and bearings to two of four passive beacons defining a quadrilateral operating area. (Courtesy of TRC.) of all four beacons is required for initial acquisition and setup, after which only two beacons must remain in view as the robot moves about. At this time there is no provision to periodically acquire new beacons along a continuous route, so operation is currently constrained to a single zone roughly the size of a small building (i.e., 24.4×24.4 m or 80×80 ft). System resolution is 120 millimeters (4¾ in) in range and 0.125 degrees in bearing for full 360-degree coverage in the horizontal plane. The scan unit (less processing electronics) is a cube approximately 100 millimeters (4 in) on a side, with a maximum 1-Hz update rate dictated by the 60-rpm scan speed. A dedicated 68HC11 microprocessor continuously outputs navigational parameters (x,y,) to the vehicle’s onboard controller via an RS-232 serial port. Power requirements are 0.5 A at 12 VDC and 0.1 A at 5 VDC. The system costs $11,000. θ X 6.3.6 Siman Sensors and Intelligent Machines Ltd., ROBOSENSE The ROBOSENSE is an eye-safe, scanning laser rangefinder developed by Siman Sensors & Intelligent Machines Ltd., Misgav, Israel (see Figure 6.17). The scanner illuminates retroreflective targets mounted on walls in the environment. It sweeps 360-degree segments in continuous rotation o but supplies navigation data even while observing targets in narrower segments (e.g., 180 ). The system's output are x- and y-coordinates in a global coordinate system, as well as heading and a confidence level. According to the manufacturer [Siman, 1995], the system is designed to operate under severe or adverse conditions, such as the partial occlusion of the reflectors. A rugged case houses the electro-optical sensor, the navigation computer, the communication module, and the power supply. ROBOSENSE incorporates a unique self-mapping feature that does away with the need for precise measurement of the targets, which is needed with other systems. The measurement range of the ROBOSENSE system is 0.3 to 30 meters (1 to 100 ft). The position accuracy is 20 millimeters (3/4 in) and the accuracy in determining the orientation is better than 0.17 degrees. The system can communicate with an onboard computer via serial link, and it updates the position and heading information at a rate of 10 to 40 Hz. ROBOSENSE navigates through areas that can be much larger than the system's range. This is done by dividing the whole site map into partial frames, and positioning the system within each frame in the global coordinate system. This method, called Rolling Frames, enables ROBOSENSE to cover practically unlimited area. The power consumption of the ROBOSENSE system is less than 20 W at 24 VDC. The price for a single unit is $12,800 and $7,630 each for an order of three units.
Chapter 6: Active Beacon Navigation Systems 165 x x 1 rcos y y 1 rsin Figure 6.17: The ROBOSENSE scanning laser rangefinder was developed by Siman Sensors & Intelligent Machines Ltd., Misgav, Israel. The system determines o its own heading and absolute position with an accuracy of 0.17 and 20 millimeters (3/4 in), respectively. (Courtesy of Siman Sensors & Intelligent Machines.) 6.3.7 Imperial College Beacon Navigation System Premi and Besant [1983] of the Imperial College of Science and Technology, London, England, describe an AGV guidance system that incorporates a vehicle-mounted laser beam rotating in a horizontal plane that intersects three fixed-location reference sensors as shown in Figure 6.18. The photoelectric sensors are arranged in collinear fashion with equal separation and are individually wired to a common FM transmitter via appropriate electronics so that the time of arrival of laser energy is relayed to a companion receiver on board the vehicle. A digitally coded identifier in the data stream identifies the activated sensor that triggered the transmission, thus allowing the onboard computer to measure the separation angles 1 and 2. AGV position P(x,y) is given by the equations [Premi and Besant, 1983] (6.3) Y T 3 where r asin( 1 ) sin 1 (6.4) a T2 a β T1 (X 1 ,Y 1 ) θ r Low Power Laser Beam α 2 α 1 P(x,y) AGV arctan 2tan 1 tan 2 tan 2 tan 1 1 (6.5) φ X 1 . (6.6) Figure 6.18: Three equidistant collinear photosensors are employed in lieu of retroreflective beacons in the Imperial College laser triangulation system for AGV guidance. (Adapted from [Premi and Besant, 1983].)
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INTRODUCTION Leonard and Durrant-Wh
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Part I Sensors for Mobile Robot Pos
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218 Appendices, References, Indexes
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220 Appendices, References, Indexes
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Systems-at-a-Glance Tables Odometry
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Systems-at-a-Glance Tables Landmark
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REFERENCES 1. Abidi, M. and Chandra
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238 References 31. Boltinghouse, S.
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240 References MOBOT-IV.” Proceed
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242 References 90. Dahlin, T. and K
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244 References 120. Fisher, D., Hol
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246 References 156. Janet, J., Luo,
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248 References 187. Larsson, U., Ze
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252 References 249. Sanders, G.A.,
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254 References 278. Turpin, D.R., 1
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256 References 309. EATON - Eaton-K
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258 References 349. SPSi - Spatial
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260 References 380. MacKenzie, P. a
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262 Index AC ..............47, 59,
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