Motion planning implemented in ROS for Omni-directional Wheeled Mobile Robot

Omni-directional Wheeled Mobile Robots (Omni-WMR) are holonomic system able to move sideways. They have locomotive advantage and are widely deployed in a larger range of application fields, especially in narrowly constrained service-styled manufacturing industries. To ensure smooth motion and full development of locomotive advantages, motion planning draws great attention. Thanks to the mechanism of powered caster wheel (PCW), the motion of Omni-WMR can be decoupled. The collective motion can be decomposed into dimensions of x, y and θ, then planned independently and superposed. In this way trajectory can be planned in the Cartesian space, and later on transformed to the joint space through inverse instantaneous kinematics model for actuation of the motor at each joint. Quintic-polynomial interpolation is used for the case of start to goal with only initial and final configurations known, and piecewise-cubic-spline interpolation is applied for the case of a sequence of intermediate way-points known in the configuration space as input. Here the geometric points for the robot to go through are assumed to be known as a priori without loss of generality. The approaches are implemented in python on ROS (Robot Operating System), and these modular ROS packages are tested on a physical Omni-WMR developed at our lab. Meanwhile, these ROS packages are also tested equivalently in a virtual simulation environment modelled using ROS stage simulator. The experimental results have proved that the motion planning algorithms are able to generate smooth velocity profile for the robot to achieve the goal, which have validated the effectiveness of these algorithms.