Pushing motion control of n passive off-hooked trailers by a car-like mobile robot

There are two different motions of a trailer system that consists of a car and n passive off-hooked trailers. When a car “pulls” n passive trailers, a trailer system moves forward. A trailer system moves backward when a car “pushes” n passive trailers. Backing up a trailer system is difficult because it is an open loop unstable problem. In this paper, we investigate the backward motion control problem of a car with n passive trailers. We have shown that n passive trailers can be successfully controlled by an omni-directional mobile robot in our prior works. Unlike an omni-directional robot, a car-like mobile robot has nonholonomic constraints and limitations of the steering angle. For these reasons, the backward motion control problem of a car-like mobile robot with n passive trailers is not trivial. In spite of difficulties, backing up a trailer system is useful for parking control. In this study, we proposed a mechanical alteration which is connecting n passive trailers to the front bumper of a car to improve the backward motion control performance. By adopting the new design, a car pushes n passive trailers by its forward motion. A practical trailer-pushing control algorithm was also proposed. Stability analysis of the controller under kinematic modeling error was presented. Theoretical verification and experimental results proved that the control strategy of pushing n passive trailers by forward motion of a car can be successfully implemented.