Abstract-The problem of path following and formation control for underactuated 3-degrees-of-freedom surface vessels in the presence of unknown ocean currents is considered. The proposed controllers make the vessels asymptotically constitute a desired formation that follows a given straight-line path with a desired speed profile. This control goal is achieved in the presence of currents of unknown direction and magnitude. The proposed controller consists of an adaptive yaw controller, which makes every vessel converge to its desired path, and a surge controller, which guarantees formation assembly along the path with the desired forward speed. The results are illustrated by simulations.
For tracking control of nanopositioning stages using piezoelectric actuators, controllers with integral action can be employed to robustly track a reference in the presence of hysteresis, creep, and plant parametric uncertainties. In any practical configuration of instrumentation for this application, saturations will be present. Thus, a controller with integral action is prone to windup, which typically cause large transients and long settling times, and will in general degrade performance and potentially damage equipment. In this paper it is demonstrated that conditional integrators provides a very accessible and convenient framework for introducing anti-windup for any order integral controller, and the effectiveness is verified experimentally. Also, the influence reconstruction and anti-aliasing filters have on the stability limits for PI and PI 2 controllers is investigated, and a novel tuning procedure is proposed in order to obtain the best performance for the overall system. It is demonstrated experimentally that optimal tuning can damp resonances and increase bandwidth.
Following curved trajectories with a formation of vehicles can be accomplished by defining the formation positions relative to the trajectory. Using a Serret-Frenet frame results in problems along straight lines and at inflection points; we suggest to use a geodesic reference frame instead. Conditional integrators are used to obtain robustness against constant external disturbances. Simulation results are provided to illustrate the effectiveness of the proposed method.
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