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Proceedings Paper

Two-dimensional laser servoing for precision motion control of an ODV robotic license plate recognition system
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Paper Abstract

As an outgrowth of series of projects focused on mobility of unmanned ground vehicles (UGV), an omni-directional (ODV), multi-robot, autonomous mobile parking security system has been developed. The system has two types of robots: the low-profile Omni-Directional Inspection System (ODIS), which can be used for under-vehicle inspections, and the mid-sized T4 robot, which serves as a ``marsupial mothership'' for the ODIS vehicles and performs coarse resolution inspection. A key task for the T4 robot is license plate recognition (LPR). For a successful LPR task without compromising the recognition rate, the robot must be able to identify the bumper locations of vehicles in the parking area and then precisely position the LPR camera relative to the bumper. This paper describes a 2D-laser scanner based approach to bumper identification and laser servoing for the T4 robot. The system uses a gimbal-mounted scanning laser. As the T4 robot travels down a row of parking stalls, data is collected from the laser every 100ms. For each parking stall in the range of the laser during the scan, the data is matched to a ``bumper box'' corresponding to where a car bumper is expected, resulting in a point cloud of data corresponding to a vehicle bumper for each stall. Next, recursive line-fitting algorithms are used to determine a line for the data in each stall's ``bumper box.'' The fitting technique uses Hough based transforms, which are robust against segmentation problems and fast enough for real-time line fitting. Once a bumper line is fitted with an acceptable confidence, the bumper location is passed to the T4 motion controller, which moves to position the LPR camera properly relative to the bumper. The paper includes examples and results that show the effectiveness of the technique, including its ability to work in real-time.

Paper Details

Date Published: 30 September 2003
PDF: 12 pages
Proc. SPIE 5083, Unmanned Ground Vehicle Technology V, (30 September 2003); doi: 10.1117/12.485692
Show Author Affiliations
Zhen Song, Utah State Univ. (United States)
Kevin L. Moore, Utah State Univ. (United States)
YangQuan Chen, Utah State Univ. (United States)
Vikas Bahl, Utah State Univ. (United States)

Published in SPIE Proceedings Vol. 5083:
Unmanned Ground Vehicle Technology V
Grant R. Gerhart; Charles M. Shoemaker; Douglas W. Gage, Editor(s)

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