Cascaded VFO Control for Non-Standard N-Trailer Robots

Articulated mobile robots consisting of a tractor and passively off-hooked trailers belong to a class of highly nonlinear, nonholonomic, structurally unstable, differentially nonflat, and underactuated dynamic systems. Due to the mentioned properties of their kinematics, motion control problems related to N-trailer robots (N-trailers) are non-trivial and challenging. Cascaded control strategy presented in this paper provides unified solution to the set-point and trajectory tracking control tasks for articulated robots equipped with arbitrary number of passively off-axle hitched trailers. Practically useful features of the proposed controller come from its high scalability and from application of the VectorField-Orientation (VFO) controller in the outer loop, which ensures fast errors convergence and simplicity of control implementation and tuning. Control input limitations of the robot are directly taken into account by utilization of a simple velocity scaling procedure which preserves an instantaneous motion curvature of a tractor. Description This work was supported by the Polish scientific fund in years 2010-2012 as the research project No. N N514 087038. M. M. Michałek (B) · M. Kiełczewski · T. Jedwabny Chair of Control and Systems Engineering, Poznan University of Technology (PUT), Piotrowo 3A, 60-965 Poznan, Poland e-mail: [email protected] and theoretical substantiation of the concept are followed by the results of experimental validation tests conducted with usage of a 3-trailer semiautonomous vehicle.