Cycab bi-steerable cars: a new family of differentially flat systems

摘要

The Cycab robots are a family of new mobile platforms already used in several research laboratories and meant for different applications such as public transportation in airport terminals or self-service cars in pedestrian zones. From a kinematic point of view, the Cycab specificity is the turning of its rear wheels as a function of the steering angle of the front wheels which makes it a bi-steerable non-holonomic vehicle. This feature enhances the maneuverability of the Cycab in cluttered environments. However, the associated kinematic model is new and different from those commonly treated in the robotics literature (such as the car-like robot, tractor-trailer, etc). To our knowledge such a system has not yet been studied and, in particular, there is no existing motion planner for it. In this paper, we tackle the study of this non-holonomic system, by establishing its kinematic model and analyzing its differential flatness property. We give a necessary and sufficient condition on the front/rear steering angle relation to guarantee the flatness of the system. This opens the way to the application of many motion planning and control methods. From this study we deduce a first motion planner for the system.