Guidance & Navigation System for an Autonomous Lawnmower: CWRU Cutter

B. Hughes, J. Beno, A. Schepelmann, D. Bennett, H. Snow, K. Daltorio, J. Green, R.D. Quinn

Abstract:	"CWRU Cutter" pronounced "crew cutter," is an autonomous lawnmower developed at Case Western Reserve University (CWRU) in collaboration with MTD Products, Inc. for the annual Institute of Navigation (ION) Autonomous Lawnmower Competition. Unlike commercially available autonomous mowers, CWRU Cutter is able to accurately navigate a series of global waypoints via several predefined path primitive types. A series of connected path primitives are automatically generated according to user defined parameters such as desired cutting pattern, deck overlap, and globally registered mowing boundaries. To achieve navigation superior to competitors, CWRU Cutter employs an Extended Kalman Filter (EKF) to estimate the robot´s position, velocity, and orientation. A commercial off the shelf differential global positioning system (GPS) receiver is used to obtain a globally registered state observation. L1/L2 dual frequency antennae are used in conjunction with a wide-area differential GPS system to mitigate ionospheric and atmospheric effects on GPS pseudo ranges for both the rover and the base station. An inexpensive COTS inertial measurement unit (IMU) provides acceleration and angular rate measurements. Motor shaft encoders provide wheel displacement observations. To achieve low level obstacle avoidance, outputs from a light detection and ranging (LIDAR) unit and a FireWire camera are combined and passed to a reactive control algorithm. Color and texture processing of monocular vision is used to determine the location of obstacles as well as the location of the globally registered field boundary lines. More recent positioning work includes the evaluation of a Scale Invariant Feature Transform (SIFT) key point based visual odometry estimation algorithm for use in GPS occluded areas. Future work includes the integration of SIFT-based simultaneous localization and mapping (SLAM.) The basic guidance and navigation system was successfully implemented for the 2009 ION Autonomous Lawnmower Dynamic Competition where CWRU Cutter won 1st place.
Published in:	Proceedings of the 22nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2009) September 22 - 25, 2009 Savannah International Convention Center Savannah, GA
Pages:	3611 - 3618
Cite this article:	Hughes, B., Beno, J., Schepelmann, A., Bennett, D., Snow, H., Daltorio, K., Green, J., Quinn, R.D., "Guidance & Navigation System for an Autonomous Lawnmower: CWRU Cutter," Proceedings of the 22nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2009), Savannah, GA, September 2009, pp. 3611-3618.
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