Design and Motion Planning of a Semi-Passive Mobile Platform for Locomotion on Slippery Surfaces

Slippery surfaces introduce various difficulties in motion planning and control. This paper presents a novel design and a motion planner for a mobile robot operating on slippery surfaces. The robot consists of an upper circular body and three identical semi-passive driving mechanisms. Each mechanism consists of a passive wheel that can roll, a rotation actuator along the normal axes and a linear actuator for motion along the radial direction of the upper body center. The wheels can easily be replaces by ice skating blades or skies for motion on icy or snowy surfaces. Each wheel is also equipped with a rotational encoder to measure roll. Using an odometric model, data from these encoders determines vehicle position. Kinematic analysis provides tools for designing a motion path that steers the robot to the desired location, and determines the singular configurations. Due to the passive roll, there is no longitudinal slippage, and lateral slippage is determined from the kinematic and odometric models. This enables accurate and reliable localization even with slippage. A gait pattern planer for up and down hills, as well as horizontal surfaces is presented. A prototype robot has been built and is currently being used in field tests. Experimental results verify the suggested models. Index Terms – Passive Motion planning, Skid steering, Slippage.