Impedance control of VToL UAVs with a momentum-based external generalized forces estimator

Abstract

An estimator of external generalized forces (force plus moments) acting on aerial platforms, and based on the momentum of the mechanical system, is proposed for the control of VToL UAVs together with a hierarchical architecture separating the translational and rotational dynamics of the vehicle. The closed-loop system equations are shaped as mechanical impedances, programmable through the controller gains, and forced by the residuals given by the estimation error. This arrangement allows the VToL UAVs to perform hovering and tracking tasks without a precise knowledge of the vehicle dynamics and in presence of external disturbances and unmodeled aerodynamic effects. Experiments are presented to evaluate the performance of the proposed control design.

Characterization of the Aerodynamic Ground Effect and Its Influence in Multirotor Control

“…As a conclusion, although the ground effect in multirotors (multiple coplanar rotors) has been assumed by most researchers to be the same as for helicopters (a single rotor) [18][19][20][21][22][23][24][25][26][27][28][29] and be significant up to distances to the ground of 2 rotor radii, the results presented in this section show clearly that this is not the case; the ground effect for multirotors is much larger, being significant for distances to the ground of up to 5 rotor radii. Although the PFI can be expanded to include the contributions of all the rotors of a quadrotor (see (3)), the addition of a body lift term with an empirical coefficient (see (4)) reproduces the experimental behavior and can be used in simulations and controller development.…”

“…This control alternative includes a torque disturbance observer that is used to estimate the torque induced by the partial ground effect, caused by the different aerodynamic thrust generated by the rotors when the multirotor is in partial ground effect. Several approaches have been used to estimate external force and torque disturbances in multirotors [22][23][24]38]. In this paper, a nonlinear torque disturbance observer has been implemented [24].…”

“…Disturbance observers have become popular in the last years for estimating external wrench in multirotors [21,22]. In most cases, it is assumed that the external disturbance source is unique, mainly contact forces [23,24] or wind. In [25], the simultaneous online estimation of aerodynamic and contact forces is studied to discriminate between them and compute the wind velocity by means of model inversion.…”

Aerial robotic contact-based inspection: planning and control

“…This may be done by feeding the attitude tracking error as input to a linear observer with relatively slow dynamics and then using its output to accordingly adjust the reference attitude signal. The contributions in , Ruggiero et al (2014) have presented elaborated methodologies on the topic of external force observation. As long as the collisiondynamics are considered then any of the typically available controllers will naturally not be able to respond timely.…”

Battery-aware dynamical modeling and identification for the total thrust in multi-rotor UAVs using only an onboard accelerometer

“…A more accurate, yet static, mapping of the force produced by a typical brushless motor for aerial vehicle has been proposed by [8], based on discretized force measurements for desired commands. In [9] a momentum based external generalized force observer is presented, which requires to measure the whole dynamical system state, the control torques and the thrust to produce an estimate of the external forces and torques. The methods has been proven to work indoor by using a precise off-board motion capture tracking.…”