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Graceful Navigation for Balancing Mobile Robots

Traditionally, motion planning and control for mobile robots have been decoupled. Robot motion planning procedures, generally, account for obstacles in the environment and workspace constraints but do not account for the system dynamics and the constraints on them. They also do not have any knowledge of the details of the controller that is used to achieve these motion plans. On the other hand, the controller does not have any knowledge of the workspace constraints and obstacles in the environment. These decoupled approaches work well for kinematic systems. Though it is possible to make highly dynamic balancing mobile robots like the ballbot navigate environments using these decoupled procedures, they are often sub-optimal and result in jerky motions, where the controller is fighting with the dynamics of the system to move it around. Moreover, when disturbed, these procedures often either result in collision with the obstacles or drive the system unstable. In order to achieve robust, graceful and collision-free motions, an integrated planning and control procedure is necessary, where both the planner and the controller understand the system dynamics and also understand each other's details.

In this work, motions are planned in shape space that enable the balancing robots to achieve fast, graceful motions in position space, taking into account the dynamic constraint equations. Controllers called motion policies are designed to achieve fast, graceful motions in small domains of the position space that are collision-free. A hybrid control architecture is used for motion planning, where the planner chooses a sequence of motion policies to achieve the overall navigation task. The sequence of motion policies are chosen such that they are gracefully composable, i.e., they result in overall graceful motion when composed. This ensures that the high-level motion planner has knowledge of the low-level controller it uses. Each motion policy is designed such that when sequentially composed they result in overall graceful motion. This ensures that the low-level controllers understand what the high-level motion planner is trying to achieve thereby forming a truly integrated planning and control procedure.

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Related Publications

Integrated Motion Planning and Control for Graceful Balancing Mobile Robots
Umashankar Nagarajan, George Kantor and Ralph Hollis
International Journal of Robotics Research (IJRR), Special Issue: Motion Planning for Physical Robots, Volume 32, Issue 9 – 10, pp. 1005 – 1029, August/September 2013
IJRR | PDF

Integrated Planning and Control for Graceful Navigation of Shape-Accelerated Underactuated Balancing Mobile Robots
Umashankar Nagarajan, George Kantor and Ralph Hollis
IEEE International Conference on Robotics & Automation (ICRA), pp. 136 - 141, May 2012
IEEEXplore | PDF

Hybrid Control for Navigation of Shape-Accelerated Underactuated Balancing Systems
Umashankar Nagarajan, George Kantor and Ralph Hollis
IEEE Conference on Decision and Control (CDC), pp. 3566 - 3571, December 2010
IEEEXplore | PDF

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